2013

TECHNO-COMMERCIAL ANALYSIS OF INTEGRATING VAM WITH SMALLER BIOMASS POWER PLANT

PROJECT REPORT

UJJAWAL KISHORE

MBA IN POWER

NATIONAL POWER TRAINING

INSTITUTE , FARIDABAD

2

SUMMER INTERNSHIP REPORT

On

TECHNO-COMMERCIAL ANALYSIS OF INTEGRATING

VAM WITH SMALLER BIOMASS POWER PLANT

UNDER THE GUIDANCE OF

Ms. Sreelata Nilesh, Senior Fellow, CAMPS, NPTI

&

Mr. Rahul Pruthi, Lead-Business Development (DDG), Tata Power

At

TATA POWER

Submitted By

UJJAWAL KISHORE

ROLL NO – 93

MBA ( POWER MANAGEMENT )

( Under the Ministry of Power, Govt. of India )

Affiliated to

MAHARSHI DAYANAND UNIVERSITY, ROTHAK

AUGUST 2013

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DECLARATION

I, UJJAWAL KISHORE, Roll No.-93, student of MBA (Power Management) at National Power

Training Institute, Faridabad, hereby declare that the summer training report entitled

“Techno-commercial analysis of integrating VAM with smaller biomass power plant”

is an original work and the same has not been submitted to any other Institute for the award of

any other degree.

A Seminar presentation of the Training Report was made on 30th

Aug, 2013 and the suggestions

as approved by the faculty were duly incorporated.

Presentation In charge Signature of the Candidate

Amit Mishra Ujjawal Kishore

Asst. Director

CAMPS, NPTI

Countersigned

Director/Principal of the Institute

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CERTIFICATE

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ACKNOWLEDGEMENTS

Words can never be enough to express my true regards to all those who have helped me in

completing this project. I can’t in full measure, reciprocate the kindness shown and contributions

made by various persons on this endeavour of mine. I shall always remember them with gratitude

and sincerity. I take this opportunity to thank all those who have been instrumental in successful

completion of my training.

I wish to express my sincere gratitude to my mentor, Mr Rahul Pruthi , Lead- Business

Development (DDG- Biomass & Micro Generation), who not only extended his precious

guidance and suggestions but his incredible help coupled with relentless efforts, constructive

criticism and timely disapprobation’s resulted in ultimate efficacy. I thank Mr Pramod Singh,

(Head-Business Development (DDG)) for his advice and inputs towards taking the project

forward. Thanks to Mr Varinder Singh (Lead Associate - L&D) for enlightening me on the work

culture of the organization. I thank Mr Chandra Tiwari (Group Head- CT&DS ) for his valuable

inputs.

I also thank Mr. S.K. Choudhary (Principal Director), Mrs. Manju Mam (Director), Mrs. Indu

Maheshwari (Dy. Director), Mrs. Farida Khan (Sr. Fellow) for providing me such a nice

opportunity to work with an esteemed organization. My internal guide Mrs. Sreelata Nilesh

(senior fellow) helped me in structuring this project report and also on various other aspects of

the study.

Special thanks to all other staff members of Tata Power, and my entire faculty, who helped me

directly or indirectly in completion of the project.

I place on record my deep sense of gratitude to the management of Tata Power for giving me an

opportunity to pursue my summer training in their organization and for their valuable support.

I am grateful to my friends who gave me the moral support in my times of difficulties. Last but

not the least I would like to express my special thanks to my family for their continuous

motivation and support.

Ujjawal Kishore

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EXECUTIVE SUMMARY

With growing economy, increasing population, the energy demand is increasing all over the

World. The spiraling increase in global warming has added to sustainability concerns. With all

these issues of power supply deficits, growing power consumption, sustainability and climatic

change, the world is now looking for cleaner sources of energy with the improved efficiency.

Depleting ‘stock’ of conventional fuel source has made the move towards renewable sources

more vigorous.

India, one of the largest developing nations faces acute power supply deficit (8-10%) with rising

cost of the power. The high dependence of the country on coal only adds to the problems it faces

like the rest of the world. With all these concerns in mind, one alternate energy source that is

booming these days is the Biomass. It is a form of energy that’s found in every corner of the

world and can be used easily with the DDG ( decentralized distributed generation ), however

most of the energy of biomass remains unutilized and wasted to the environment in the form of

discharged flue gases from the biomass power plant. Hence better technology is required for the

effective use of the biomass energy available with rice husk, woody mass etc. so as to provide

power at an affordable rate. More energy efficient & technological gasifier is required to convert

the biomass into useful gases such as producer gas, biogas etc.

Biomass is a source of renewable clean energy which is available in the country like India and

has huge potential of 18000 MW but the efficiency of the power generation by biomass is less as

compared to the other fuel source such as coal, oil & gas. Hence to improve the efficiency by

tapping the exhaust heat energy of the waste flue gases, implementation of VAM as CHP

(combined heat and Power) is the need of an hour & required in the present days. Hence a focus

is needed towards the combined heat and power using VAM in the biomass power plant.

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LIST OF TABLES

TABLE 1 BIOMASS PROCESSING TECHNOLOGIES IN COMPARISON WITH OTHER LOW CARBON ENERGY TECHNOLOGIES ............................ 21

TABLE 2 PRIMARY PROCESSING TECHNOLOGIES AND THE ABILITY TO PROCESS DIFFERENT BIO MOLECULES ........................................... 22

TABLE 3 OVERVIEW OF BIOMASS TECHNOLOGY ....................................................................................................................... 30

TABLE 4 DIRECT COMBUSTION TECHNOLOGY .......................................................................................................................... 31

TABLE 5 ANAEROBIC DIGESTION TECHNOLOGY SUMMARY......................................................................................................... 33

TABLE 6 FERMENTATION TECHNOLOGY SUMMARY .................................................................................................................. 34

TABLE 7 OIL EXTRACTION SUMMARY .................................................................................................................................... 36

TABLE 8 PYROLYSIS TECHNOLOGY SUMMARY .......................................................................................................................... 37

TABLE 9 GASIFICATION TECHNOLOGY SUMMARY ..................................................................................................................... 40

TABLE 10 SUSTAINABILITY CONSIDERATIONS OF BIOMASS PROCESSING TECHNOLOGIES ................................................................. 41

TABLE 11 ADVANTAGE AND DISADVANTAGE OF VARIOUS GASIFIER ............................................................................................. 45

TABLE 12 COMPARISON OF BIOMASS GASIFIER ....................................................................................................................... 46

TABLE 13 COMPOSITION OF PRODUCER GAS FROM VARIOUS FUELS ............................................................................................ 50

TABLE 14 COMPARISON OF PRODUCER GAS WITH BIOGAS & NATURAL GAS .................................................................................. 51

LIST OF FIGURES

FIGURE 1 SIMPLE SCHEMATIC OF COMBINED HEAT AND POWER ................................................................................................. 14

FIGURE 2 CHP SHARE OF TOTAL NATIONAL POWER PRODUCTION ............................................................................................. 15

FIGURE 3: CURRENT & PROJECTED CHP CAPACITIES UNDER ACS, 2015 & 2030 ........................................................................ 16

FIGURE 4 BIOMASS CONVERSION & ITS APPLICATION ............................................................................................................... 19

FIGURE 5 SCHEMATIC OF BALANCED CARBON CYCLE ................................................................................................................. 22

FIGURE 6 ONE OF THE LARGEST HEAT AND POWER PLANTS IS THE ALHOLMENS KRAFT FACILITY IN FINLAND, WHICH GENERATES 560

MEGAWATTS THERMAL (MWTH) AND 240 MEGAWATTS ELECTRICAL (MWE) FROM WOODY BIOMASS .................................... 32

FIGURE 7 ANAEROBIC DIGESTION AT THE CARRUM SEWAGE TREATMENT PLANT OF MELBOURNE WATER ........................................... 33

FIGURE 8 THE WORLD’S LARGEST FUEL ETHANOL PLANT, JILIN, CHINA, PROCESSES CLOSE TO 2 M TONNES OF CORN PER YEAR TO PRODUCE

SOME 2.3 ML PER DAY ETHANOL ................................................................................................................................ 35

FIGURE 9 DYNAMOTIVE FLASH PYROLYSIS PLANT IN WEST LORNE CANADA .................................................................................. 38

FIGURE 10 SOIL REGENERATION THROUGH ‘TERRA PRETA’ ........................................................................................................ 38

FIGURE 11 STRATEGIC PLATFORM FOR MAXIMUM VALUE CAPTURE FROM BIO ENERGY RESOURCES ................................................... 42

FIGURE 12 BIOMASS ENERGY CONVERSION OVERVIEW ............................................................................................................ 43

FIGURE 13 PRODUCTS OF GASIFICATION ................................................................................................................................ 44

FIGURE 14 VARIOUS TYPES OF GASIFIER ................................................................................................................................ 45

FIGURE 15VARIOUS ZONES IN UPDRAFT GASIFIER & GASIFICATION PROCESS IN DOWNDRAFT GASIFIER ............................................... 47

FIGURE 16 GASIFICATION PROCESS IN CROSS-DRAFT GASIFIER& SINGLE & DOUBLE THROAT GASIFIER ................................................. 47

FIGURE 17 MASS AND ENERGY BALANCE ................................................................................................................................ 53

FIGURE 18 PROCESS FLOW CHART ....................................................................................................................................... 55

FIGURE 19 VAPOUR COMPRESSION CYCLE ............................................................................................................................. 56

FIGURE 20 VAPOR ABSORPTION CYCLE ................................................................................................................................. 57

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FIGURE 21VAPOR ABSORPTION SYSTEM WITH SILICA GEL ABSORBENT ....................................................................................... 61

FIGURE 22 VAPOR ABSORPTION SYSTEM WITH AQUEOUS ABSORBENT ....................................................................................... 62

FIGURE 23 VAPOUR ABSORPTION CYCLE ................................................................................................................................ 63

FIGURE 24 BASIC CYCLE OF SINGLE EFFECT CHILLER ................................................................................................................ 65

FIGURE 25 SINGLE EFFECT STEAM FIRED VAPOR ABSORPTION CHILLER MACHINE ......................................................................... 66

FIGURE 26 BASIC CYCLE OF DOUBLE EFFECT TYPE CHILLERS ...................................................................................................... 67

FIGURE 27 TWO STAGE VAPOR ABSORPTION CHILLER MACHINE ............................................................................................... 68

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LIST OF ABBREVIATIONS

1. VAM Vapour absorption machine

2. CHP Combined heat and power

3. DDG Decentralized distributed generation

4. TERI The energy and research institute

5. LIBR Lithium bromide

6. CW Circulating water

7. H.E. Heat exchanger

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Table of Contents

DECLARATION ........................................................................................................................................................ 3

BACKGROUND & INTRODUCTION ........................................................................................................................ 12

ABOUT DECENTRALIZED DISTRIBUTED GENERATION ( DDG ) ................................................................................................. 12

COMBINED HEAT AND POWER (CHP) ................................................................................................................... 13

BENEFITS OF CHP ........................................................................................................................................................ 13

GLOBAL SCENARIO ....................................................................................................................................................... 14

INDIAN CONTEXT ......................................................................................................................................................... 16

CHP POLICIES-INDIA .................................................................................................................................................... 17

BIOMASS ................................................................................................................................................................. 18

Advantage with Biomass System ....................................................................................................................... 19

Application of Biomass ....................................................................................................................................... 20

Sustainability Consideration ............................................................................................................................... 21

RESEARCH OBJECTIVE & METHODOLOGY ............................................................................................................ 23

BACKGROUND: ............................................................................................................................................................ 23

BUSINESS OBJECTIVES: .................................................................................................................................................. 23

RESEARCH OBJECTIVES: ................................................................................................................................................. 23

RESEARCH METHODOLOGY: ........................................................................................................................................... 23

INFORMATION REQUIRED: .............................................................................................................................................. 24

PROCESS: ................................................................................................................................................................... 24

LIMITATIONS: .............................................................................................................................................................. 24

COMPANY PROFILE .............................................................................................................................................. 25

BUSINESS ................................................................................................................................................................... 27

BIOMASS TECHNOLOGIES FOR ENERGY AND MATERIALS .................................................................................... 30

DIRECT COMBUSTION ................................................................................................................................................... 31

ANAEROBIC DIGESTION ................................................................................................................................................. 32

FERMENTATION ........................................................................................................................................................... 34

OIL EXTRACTION .......................................................................................................................................................... 35

PYROLYSIS .................................................................................................................................................................. 36

GASIFICATION ............................................................................................................................................................. 39

Integration of Technology Aspects ..................................................................................................................... 40

Integration of Sustainability Aspects .................................................................................................................. 41

BIOMASS GASIFICATION ...................................................................................................................................... 44

TYPES OF GASIFIERS ..................................................................................................................................................... 44

PROCESS ZONES .......................................................................................................................................................... 46

REACTION CHEMISTRY .................................................................................................................................................. 48

PROPERTIES OF PRODUCER GAS ...................................................................................................................................... 49

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HEAT AND MASS TRANSFER ................................................................................................................................. 52

VAPOUR ABSORPTION MACHINE ......................................................................................................................... 56

WHAT IS ABSORPTION? ................................................................................................................................................ 56

APPLICATIONS OF ABSORPTION SYSTEMS .......................................................................................................................... 59

THE BASIC PRINCIPLE OF ABSORPTION COOLING ................................................................................................................ 60

HOW ABSORPTION MACHINE WORKS ............................................................................................................................. 62

FUNCTION OF COMPONENTS .......................................................................................................................................... 63

Generator: .......................................................................................................................................................... 63

Condenser: ......................................................................................................................................................... 64

Expansion Device: ............................................................................................................................................... 64

Evaporator: ........................................................................................................................................................ 64

Absorber: ............................................................................................................................................................ 64

TYPES OF VAM ......................................................................................................................................................... 65

Single Effect Absorption Chillers ......................................................................................................................... 65

Double Effect (2-Stage) Absorption Systems ...................................................................................................... 66

EFFICIENCY OF VAPOR ABSORPTION MACHINE (VAM) ....................................................................................................... 69

WHAT DO YOU NEED TO RUN A VAM? ............................................................................................................................ 69

Heat Source ........................................................................................................................................................ 69

Lithium Bromide (LiBr) – Water Absorption System ........................................................................................... 70

Cooling Water .................................................................................................................................................... 71

PRACTICAL PROBLEM .................................................................................................................................................... 72

CHALLENGES IN THE BIOMASS POWER PLANT ..................................................................................................... 73

INTEGRATION OF SMALLER BIOMASS PLANT & VAM........................................................................................... 74

TECHNO-COMMERCIAL ANALYSIS & CALCULATIONS ........................................................................................... 75

FINDINGS & CONCLUSION.................................................................................................................................... 76

FUTURE SCOPE ..................................................................................................................................................... 76

BIBLIOGRAPHY ..................................................................................................................................................... 76

ANNEXURE ........................................................................................................................................................... 76

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BACKGROUND & INTRODUCTION

About decentralized distributed generation ( DDG )

Decentralized Distributed Generation is a form of power generation that can be from

conventional or renewable sources such as Biomass, Biofuels, Biogas, Mini Hydro, Solar etc. for

villages where grid connectivity is either not feasible or not cost effective.

1. Decentralized Distributed Generation (DDG) under Rajiv Gandhi Grameen Vidyutikaran

Yojana has the goal of providing access to electricity to all households, electrification of

about 1.15 lakh1 un-electrified villages and electricity connections to 2.34 crore BPL

households by 2009. The Ministry of Power, Government of India had accorded permission

for capital subsidy of Rs.540 crore2 for DDG scheme out of total capital subsidy of Rs. 28000

crore available for RGGVY in XI Plan period.

2. Rural Electrification Corporation (REC) is the Nodal Agency for the scheme. The capital

subsidy for eligible projects under the scheme would be given through REC. In the event, the

projects are not implemented satisfactorily in accordance with the conditionality of this

order; the capital subsidy would be converted into interest bearing loans.

3. The DDG projects would be owned by State Government. Implementing agencies of the

projects shall be either the State Renewable Energy Development Agencies (SREDAs) /

departments promoting renewable energy or State Utilities or the identified CPSUs. The

State Governments will decide the implementing agency for their respective states.

4. The projects under the scheme will be subject to Quality Monitoring Mechanism.

1 Guidelines for Decentralized Distributed Generation (DDG), No.44/1/2007-RE, Ministry of Power, GOI Dated 12th Jan, 2009

2 Distributed generation” by Dugan, R.C.; McDermott, T.E. (Mar/Apr 2002

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Combined heat and power (CHP)

Combined heat and Power also known as Cogeneration is simultaneous generation of useful heat

and power using a heat engine or in a power station. Cogeneration can be defined as the

sequential generation of two different forms of useful energy namely electrical energy and

thermal energy from a single primary energy source. All thermal power plants or heat engines

produce large amount of heat during generation of electricity which is wasted/ released into the

atmosphere in the form of flue gases. In a combined heat and power some or all the waste heat is

captured and changed into useful heat which can be used either for direct process applications or

for indirectly producing steam, hot water, hot air for dryer or chilled water for process cooling.

Conventional thermal power plants and heat engines do not convert all their thermal energy into

electricity and are only about 30%-35% efficient. By capturing the waste heat a CHP uses the

heat that would be otherwise wasted in a conventional power plant increasing it efficiency up to

80%-85% consequently reducing fuel needs.

Benefits of CHP

CHP has wide array of advantages ranging from economic to environmental benefits; first and

foremost it is a proven energy efficient technology. CHP can achieve significant cost savings,

environment benefits by reducing carbon emissions, enhanced energy security and overall

efficiency in excess of 80%.

A summary of benefits are listed below:

1. High overall efficiency in excess of 80%

2. Cost savings of between 15% and 40% over electricity sourced from the grid and heat

generated by on-site boilers

3. Flexibility to use bio-mass and other environmental friendly fuels

4. Enhanced security of supply, making energy go further, through more efficient use of fuel –

regardless of whether the fuel is renewable or fossil

5. Flexible and responsive heat supplies – the thermal energy (heat or cooling) produced by CHP

can be easily stored and later delivered to meet demand

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6. More towards decentralized form of electricity generation thus avoiding high transmission

losses, increased flexibility, high reliability and less dependency on grid

Figure 1 Simple schematic of combined heat and power

Global Scenario

The global average share of CHP share of total national power production is 9% with countries

like Finland and Denmark being the most intensive cogeneration economies. Europe has actively

incorporated cogeneration in its energy policy as CHP has been identified a proven energy

efficient technology.

European Union generates 11% of its electricity using cogeneration, saving Europe an

estimated 35 MTOE per annum a day.

CHP potential identified by different countries using different assumption is as below:

1. European Union has CHP directive as part of their policy and requires member states to

undertake comprehensive national studies of the potential for CHP.

2. Studies present more than 150 - 250 GW CHP potential up to 2025

3. Current CHP share in Canada is 6% and plan to take it to 12 % of project national

capacity by 2015 under a “CHP Promotion” scenario.

4. The UK CHP economic potential study undertaken by the UK government identified an

economic potential for CHP of 17% of total national power generation by 2010 (currently

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7.5%), with a potential for an additional 10.6 GWe of CHP on top of the current level of

5.4 GWe by 2015

5. The German CHP target was in 2007 raised to 25% (a doubling of the current share) in

2020, based on a National Potential Study conducted by the government under the

European Union’s CHP Directive. This study also cites economic CHP potential to be up

to 50% of electricity capacity

6. CHP potential in Japan for 2030 has been identified as up to 29.4 GW, around 11% of

projected total capacity for that year

7. In India, the additional potential for industrial CHP alone has been identified as exceeding

7,500 (MWe).3

Figure below gives global estimates by IEA on CHP potential by 2015 and 2030 based on the

rates of CHP development that approach the rates seen over the last three decades in countries

like Denmark, the Netherlands and Finland under the Accelerated CHP Scenario (ACS).

Figure 2 CHP Share of Total National Power Production

3 Source: IEA, DEFRA, Germany Ministry for Environment, BMU, METI

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4

Figure 3: Current & Projected CHP Capacities under ACS, 2015 & 2030

Indian Context

Estimates of CHP in India have been lacking and those that exist have been based on differing

definitions of CHP. The GOI estimate is restricted to bagasse-based cogeneration, where the

current capacity is estimated to be over 700 MW, predominantly in the states of Andhra Pradesh,

Karnataka, Maharashtra, Tamil Nadu and Uttar Pradesh.

However, this is likely to strongly underestimate the total use of cogeneration in India. Using the

best available data, the IEA estimates that in 2005, CHP capacity in India was over 10 GW from

over 700 units, with a heat-generating capacity of 170MW.

This is about 5%of the total electricity generated. This demonstrates that a good first step would

be to commission further work in India to improve cogeneration/CHP definitions and improve

data quality.

4 (Source: IEA, CHP: Evaluating the Benefits of Great Global Investment)

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CHP Policies-India

1. 1993 Policy for Cogeneration

• Set methodology for fixing tariffs for sale of CHP power to State Electricity Boards

2. Energy Conservation Act 2001 enacted to provide for energy efficiency and conservation

• Bureau of Energy Efficiency (BEE) created with mandate to promote energy efficiency,

including CHP and demand-side management

3. Electricity Act 2003

• A number of market liberalisation provisions

• Creates district level committees to promote EE

• Includes non-fossil fuel obligation

4. National Electricity Policy 2005

• Enacted to promote non-conventional energy source and cogeneration

5. Tariff Policy 2006

• State can mandate % of power from non-fossil resource (including CHP); also feed-in

tariff

6. Central Electricity Regulatory Commission (CERC) Discussion Paper

• Proposes preferential treatment (exemption from inter-state open access charges for

transmission, wheeling, standby power, grid connection, and scheduling) to renewable

energy sources for arranging inter-state transmission when open access is used

• Allows reactive energy charges to be applied by the host utility under the Indian

Electricity Grid Code

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Research Challenges

Improve efficiency of the smaller biomass based power plant with the use of VAM

Lower heat emission to the environment

Improve integration with existing generation system

Reduction of green house effect

Improvement in bio-diversity

BIOMASS

Biomass is natural product of solar energy and therefore, a renewable source of carbon

and hydrogen which are the basic constituents of energy and chemical products. Renewable

organic materials, such as wood, agricultural crops or wastes, and municipal wastes, especially

when used as a source of fuel or energy. Following is an attempt to define Biomass

1. Total amount of animal and plant life

2. Biomass is an organic matter i.e. photochemical approach to harness solar energy can

be converted into other forms of energy like heat, electricity etc. using available

conversion processes

3. Biomass energy in the context of the present day industrialized world means the use of

natural organic resources to manufacture fuel

4. Biomass is the organic matter derived from plants as a result of photosynthesis.

Photosynthesis is the process by which solar energy is converted into chemical

energy by the plants with the help of the pigment called chlorophyll

6co2 + 6H2O + sunlight + chlorophyll – C6H12O6 + 6CO2 + chlorophyll

This process uses carbon dioxide and water in the presence of sunlight to produce

glucose

The term biomass includes all plant-trees, agriculture plant, bush, grass and algae, and

their residue after processing. Biomass may be obtained from forest, woods and

agricultural lands. It may be obtained in a planned manner. The term is also generally

understood to include animal and human waste.

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Figure 4 Biomass conversion & its application

Advantage with Biomass System

Stored energy for use at will

Renewable

Dependent on technology already, with minimum capital input

Can be developed with present manpower and material sources

Reasonably priced

When we burn the biomass, the oxygen from the atmosphere combines with the carbon in

the plant to produce co2 and water. This co2 and water are again available for the plant

growth and hence the cyclic process continues making the biomass, a renewable source

of energy

Biomass energy is unique because

It is available in majority of the geographical locations

It effectively stores solar energy and

It is renewable source of energy in the form of carbon which can be processed

into solid, liquid and gaseous fuels

The vast majority of the rural population of the world is totally dependent on biomass as

fuel. Some sources of biomass are

Agricultural waste

Crop residue

Wood & woody waste

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Organic waste etc.

Biomass does not contribute to global warming. Low levels of sulphur and ash in biomass

prevent acid rain formation. Biomass energy brings in numerous benefits. To name a few,

Reduction in usage of conventional fuels

Reduction in environmental pollution

Improving the nations economy

Meets the basic needs of the rural poor

Land use competition and land tenure

The environment benefits include reduction in air and water pollution reducing co2

emission, green house gases like so2

Availability of biomass in almost all geographical locations

Electrical energy can be produced in large scale at low cost

Low gestation period

Rural employment generations

Results in less ash production minimizing ash disposal cost

Application of Biomass

Direct thermal applications

Boiler

Institutional cooking and other thermal applications

Production of producer gas used as fuel in

IC engines, vehicles

Irrigation water pumping/ village water supply

Bio fuels applications

Ethanol for transport applications

Generation of electricity

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Table 1 Biomass processing technologies in comparison with other low carbon energy technologies5

Sustainability Consideration

The use of bio energy therefore has the capacity to impact on land use and demands that the

sustainability case be thought through extremely rigorously. ‘Renewable’ ‘Low greenhouse gas

emission’ and ‘Sustainable’ are not synonymous terms and none can be guaranteed with biomass

projects. Biomass is a renewable resource as long as the average rate of harvest is less than or

equal to the average rate of re-growth. Biomass production systems are nutrient dependent,

hence nonrenewable if they systematically degrade the material value of finite nutrient resources.

Biomass use for energy purposes has low net greenhouse gas emissions despite CO2 emissions

during combustion, because the carbon in the biomass was sourced from the atmosphere as CO2

during plant growth, as shown in the schematic below. This is particularly attractive as it allows

for continued use of high energy density carbon based fuels in dispersed applications, such as

transport, where carbon capture and storage is not practically possible.

5 Biomass technology review by crucible carbon consulting

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Figure 5 Schematic of balanced carbon cycle

Table 2 Primary processing technologies and the ability to process different bio molecules

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RESEARCH OBJECTIVE & METHODOLOGY

Background:

Biomass is an energy source that is easily available in the rural areas of India. It would give the

country a form of energy security by reducing its dependence on fossil fuel imports. Biomass

power is a clean energy and would thus, provide sustainability benefits. With increasing

realization of the same there are investments in the biomass power sector for the generation of

electricity however better technology is required for the effective utilization of the biomass fuel

energy. Improved technology in the gasifier is needed for the maximum conversion of the

biomass fuel energy into the various gas. The efficiency of the biomass plants are still very low

of about 13-20 % and maximum energy are wasted in the form of flue gas energy to the

atmosphere. Hence to improve the efficiency of the biomass power plant is the need of an hour

and can be done with the help of combined heat and power.VAM can be added in the system to

tap the exhaust heat of the flue gases and used for cooling purpose meanwhile improving the

efficiency and reducing environmental impact due to hot flue gases. There is a need to boost

these investments. This project report emphasis on the technology available in the market to

improve the efficiency of the system and to tap the unutilized flue gas energy into some utilized

form of cooling energy.

Business Objectives:

The company may find useful this project report when doing a market analysis related to the

technology available in the biomass conversion into useful energy and increasing the efficiency

of the biomass power sector by effective utilization of the exhaust flue gas energy for cooling

purpose by the application of combined heat and power in the form of vapour absorption system,

henceforth making business in selling the cooling power to the consumers from the waste energy

of the flue gas.

Research Objectives:

The research objectives are:

To analyze existing biomass power plants technology available ( mainly gasification )

To do an analysis of various technologies available in vapour absorption system

To effectively use the waste heat energy from the biomass power plant as of combined

heat and power to raise the efficiency of the system.

To do cost-economic analysis of the integration of VAM with the smaller biomass plant

Research Methodology:

Primary research has been done by meeting various people of different organizations like PUSA,

Teri etc. Secondary data has been heavily used in the project from different vendors such as

diagrams and technical specifications.

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Information required:

Biomass technology available in India and abroad

Engine specification

Heat and mass balance of process flow sheet of biomass plant

Specifications of vapour absorption machine

Financial modeling of biomass power plant

Financial modelling of VAM

Challenges faced by those already in the market

Process:

Limitations:

The research is limited at the point of the non-availability of the detailed specifications of VAM

and the detailed step by step specification of the various technical factors like temperature and

pressure of the process flow heat and mass balance of the biomass power plant.. Some values

like that for cost of project, O&M expenses are not found within the time constraints.

Objective: techno-commercial analysis of the integration of VAM with smaller

biomass plant in order to improve efficiency

Quantitative study

Interaction with:

Biomass Power Plant

research people of

TERI, PUSA

Information from:

MNRE, CEA, State Renewable

Energy development agencies

Published reports of IIT journal

papers

Process flow diagram of the

vendors of rice husk, woody

based biomass power plant

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COMPANY PROFILE

TATA Power is India’s largest integrated power company with a significant international

presence. The Company has an installed generation capacity of 8521 MW in India and a

presence in all the segments of the power sector viz. Fuel Security and Logistics, Generation

(thermal, hydro, solar and wind), Transmission, Distribution and Trading. It has successful

public-private partnerships in Generation, Transmission and Distribution in India. It is one of the

largest renewable energy players in India and is developing country’s first 4000 MW Ultra Mega

Power Project at Mundra (Gujarat) based on super-critical technology.

Its international presence includes strategic investments in Indonesia through 30% stake in coal

mines and a geothermal project; in Singapore through Trust Energy Resources; in South Africa

through a joint venture called ‘Cennergi’; in Australia through investments in enhanced

geothermal and clean coal technologies and in Bhutan through a hydro project in partnership

with The Royal Government of Bhutan.

The Company has an installed hydro capacity of 447 MW in Maharashtra. Through its

partnerships and joint ventures the company currently has 462MW of hydro projects(Dugar

236MW, Dagachhu 126MW) under way. The Company is prospecting further opportunities to

bid and acquire hydro projects. The company has a strong portfolio of 28+ MW of solar

generation capacity. The Company has partnered with the Australian company, Sunengy Pty.

Ltd. to build the first floating solar plant in India. It has an installed wind generation capacity of

397 MW. Another 180 MW of wind projects are under construction in the states of Rajasthan

(Dalot 100.5) and Maharashtra (Pethshivpur 49.5, Visapur 32 MW). The company is also

exploring Geothermal Power in Australia. The consortium led by it has won the Sorik Marapi

geothermal project of approximately 240MW in Northern Sumatra, Indonesia.

The company has set up various plants at Haldia and in Jamshedpur (Power 6) based on the blast

furnace and coke oven gases which are waste gases from steel making process which help in

reducing greenhouse gas emission significantly. It is also experimenting with unique pilot

projects with a focus on clean energy. Some of them are:

Concentrated photovoltaic (C-PV): A 13.5kW pilot unit is being developed in

which sunrays are concentrated on PV cells and the assembly floats on Walwhan

lake (Maharashtra) in order to cool the cells. If successful, this technology can be

scaled up across all the lakes that provide hydro power to TATA plants in West

Maharashtra and thus generate about 1,000 MW.

Solar powered telecom towers: More than 600,000 telecom towers in India use

diesel generator sets to provide power to their antennas. TATA Power Solar

Solutions Ltd., a 100% subsidiary of TATA Power is providing solar PV panels

26

that can replace the gensets on 25 such installations. This technology can be

upgraded to augment power to local grids.

High altitude wind: TATA Power will test a 35kW turbine mounted on a blimp

that will float 333m above the ground to catch winds that are more intense and

sustained at that altitude.

Micro wind turbine: The company will test a 2kW wind turbine that can be

mounted on roof tops and provide power to homes

A 250kW Biomass gasification system using rice husk will be installed at the

TATA hydro power plant near Karjat. If successful, this technology can be taken

to hundreds of villages.

The company is a pioneer in Power production in the private sector and in addition, has many

firsts to its credit:

First to bring UMPP in India (at Mundra, Gujarat) based on super- critical

technology and unit size of 800 MW each.

First 150 MW thermal unit in the country · First 500 MW thermal unit in the

country.

First to Commission Gas Insulated Switchgear 220 KV and 110 KV.

Touch screen-based Distributed Digital Control and Energy Management

Systems.

Computerised Grid Control and Energy Management Systems.

220 kV Transmission Lines in Four-Circuit Towers.

220 kV Cable Transmission Network. Flue Gas De-sulphurisation Plant using sea

water.

First 275 meter tall chimney for Unit No. 6. 500 MW power plant.

First Operational Pumped Storage Unit in the country of 150 MW capacity.

First to install Fly Ash Aggregate Plant to convert waste product (fly ash) into a

useful building material.

Training Simulators for 150 MW, 500 MW Thermal Power Plants and High

Voltage Switchyard Operations.

First to introduce SCADA and Fibre Optic Ground Wire Communication.

TATA Power's Load Despatch Center is the First ever Load Despatch Center in

India to have gotten ISO Certification (11 August 2004).

The Company is on a multi-fold growth path and is committed to ‘responsible growth’ . Some of

the projects that are under implementation include: 236 MW Dugar Hydro Project, 1600 MW

Coastal Maharashtra Project, 1980 MW Tiruldih Power Project, Jharkhand, 660 MW Naraj

Marthapur, Orissa, Kalinganagar, Orissa 3X67.5 MW (Gas based) +3X150 MW (Coal+gas

based, 126 MW Dagachhu Hydro Project, 240 MW Sorik Marapi Geothermal Project,

Distribution Franchisee in Jamshedpur.

27

Vision: “To be the most admired and responsible Integrated Power Company with international

footprint, delivering sustainable value to all stakeholders.”

Mission: “We will become the most admired and responsible Power Company delivering sustainable

value by:

Operating our assets at benchmark levels

Executing projects safely, with predictable benchmark quality, cost and time

Growing the TATA Power businesses, be it across the value chain or across

geographies, and also in allied or new businesses

Driving Organizational Transformation that will make us have the conviction and

capabilities to deliver on our strategic intent

Achieving our sustainability intent of 'Leadership with Care', by having leading

and best practices on Care for the Environment, Care for the Community, Care for

the Customers and Shareholders, and Care for the People.”

Values: “Our Values are SACRED to us

Safety - Safety is a core value over which no business objective can have a higher

priority

Agility - Speed, Responsiveness and being Proactive, achieved through

Collaboration and Empowering Employees

Care - Care for Stakeholders - our Environment, Customers & Shareholders –

both existing and potential, our Community and our People (our employees and

partners)

Respect - Treat all stakeholders with respect and dignity

Ethics - Achieve the most admired standards of Ethics, through Integrity and

mutual Trust

Diligence - Do everything (set direction, deploy actions, analyze, review, plan

and mitigate risks etc) with a thoroughness that delivers quality and Excellence –

in all areas, and especially in Operations, Execution and Growth”

Strategic Intent: By 2020, to be a Company with 26,000 MW Power Generation, 4,000 MW of Retail Distribution

Business and with 50 MTPA of Energy Resources

Business

The company does it all to carry forward its green legacy right from focusing on producing clean

and green power to investing and implementing eco-friendly technologies; reducing carbon

footprint to joining global initiatives to combat climate change; scouting for clean power sources

28

internationally to driving energy conservation and efficiency; to creating sustainable livelihood

for communities to green buildings and villages.

Generation

TATA Power generates about 8521 MW of power of which 7407 MW is from Thermal Power

plant. TATA Power has an installed generation capacity of 1112 MW through green resources.

Transmission

Powerlinks Transmission Limited (Powerlinks) is India's first transmission project to be executed

as a Public-Private-Partnership. Powerlinks transmit power from the Bhutan based Tala

Hydroelectric Project (in Nilgiri, West Bengal), through the Eastern/North-Eastern Region of

India to Mandola in Uttar Pradesh (near New Delhi) a total distance of 1,200 km.

TATA Power's transmission operations in Mumbai License Area stretch from Colaba in South

Mumbai to Bassein Creek in North Mumbai and to Vikhroli in North-East Mumbai (bypassing

Bhandup and Mulund).

Distribution

Mumbai Distribution: TATA Power has a customer base of over 3.5 Lakh direct customers in

Mumbai and on, average about 12,000 million units (MU) are sold in a year. At the core of

reliable power supply to the city is the unique ‘Islanding System' pioneered by TATA Power,

due to which the city of Mumbai has the advantage of assured uninterrupted reliable supply of

power.

Delhi Distribution: The Company has partnered with the State Government of Delhi for

distribution to its North Delhi customers, as the North Delhi Power Limited (NDPL). This

company serves over 1 million customers (from a population of 4.5 million) spread over in an

area of 510 sq. kms and has a peak load of 1050 MW. Measures like energy audits, replacement

of old meters with theft-proof electronic meters, automated meter reading, aggressive

enforcement and public awareness drives have reduced the current ATC loss percentage to well

below the target loss level percentage that has been committed to the regulatory authorities.

Distribution franchise for Jamshedpur Circle: Subsequent to winning the bid for the

Distribution Franchisee (DF) of Jamshedpur circle, a Special Purpose Company (SPC) ‘TP

Power Distribution Ltd.’ has been formed and executed the Distribution Franchise Agreement

(DFA) with Jharkhand State Electricity Board (JSEB).

29

Tata Power Trading Company Limited (TPTCL), a wholly owned subsidiary, is the first

company to have been awarded a power trading licence by the Central Electricity Regulatory

Commission enabling it to carry out transactions all over India.

The Strategic Engineering Division (SED), It has been in operation for over 30 years and has

been pursuing development and production activities for the Indian defence sector. Over 90% of

the company's strategic electronic efforts are executed for the defence sector. The division has

long-standing relationships with the Armed Forces and DRDO. The Division has developed

specialised equipment for Air Defence and Naval Combat Systems. It is also developing a

program to modernize the Airfield Infrastructure for the Indian Air Force.

TATA Power Solar, It is a 100% subsidiary of TATA Power, and is a market leader in Solar

Photovoltaic technology in India. Nearly 75% of sales is achieved from exports to Europe and

USA.

30

BIOMASS TECHNOLOGIES FOR ENERGY AND MATERIALS

The majority of biomass that is in principle available for bio energy projects exists as solid

unprocessed plant material with a moisture content typically around 50 per cent. In addition there

is a diverse range of available biomass resources associated with human activity, particularly

residues and wastes from agricultural, industrial, municipal, forest and other economic activities.

There are six generic biomass processing technologies based on direct combustion (for power),

anaerobic digestion (for methane rich gas), fermentation (of sugars for alcohols), oil exaction

(for biodiesel), pyrolysis (for biochar, gas and oils) and gasification (for carbon monoxide (CO)

and hydrogen (H2) rich syngas). These technologies can then be followed by an array of

secondary treatments (stabilisation, dewatering, upgrading, refining) depending on specific final

products.

The versatility of biomass processing technologies to produce energy and materials in heat, gas,

liquids and solid forms is highlighted in Table below.

Table 3 Overview of biomass technology6

6 Biomass technology review by crucible carbon consulting

31

Direct Combustion

Biomass combustion can produce heat or steam. Dry woody biomass has an energy content of

approximately 20 Giga Joules per tonne (GJ/t), slightly higher for softwoods due to higher lignin

content. This is comparable to lower ranked coals, making biomass suitable for electricity

generation. Lower grade waste heat from biomass combustion can also be used in combined heat

and power applications.

The direct combustion of woody biomass for power production is currently the highest volume

bio energy market worldwide. Biomass may be the sole fuel for heat and power generation or

may be blended with coal in a process known as co-firing. The residues from biomass

combustion are essentially ash, which can be process wastes or better utilized as soil conditioners

to close nutrient cycles. The key features of biomass combustion are summarized in the table

below.

Table 4 Direct combustion technology

Combustion is designed to capture the calorific value of biomass only. As biomass resources

become more constrained, with increasing demand for renewable energy, they can be expected to

be directed more to applications that capture additional value from their inherent material

qualities.

32

Combustion of biomass for process heat or electricity production may also be conducted

indirectly via the combustion of pre-processed biomass products such as compressed or torrefied

wood pellets, pyrolysis oil and pyrolysis char.

The principle advantage of the indirect combustion route is the transportability of the

intermediate products which have a lower bulk density than green biomass, allowing a greater

area for biomass sourcing

Figure 6 One of the largest heat and power plants is the Alholmens Kraft facility in Finland, which generates

560 megawatts thermal (MWth) and 240 megawatts electrical (MWe) from woody biomass

Anaerobic Digestion

Anaerobic digestion is conducted by prokaryotic microbes (Eubacteria and Archaea) that

evolved their metabolic pathways prior to the development of an oxygen rich atmosphere.

Prokaryotes have the necessary enzymes to catalyze a range of organic polymer decomposition

reactions at benign temperatures and pressures. These reactions include the generation of

hydrogen (H2) and methane (CH4) from biomass.

Anaerobic digestion for methane production is mainly used as a waste processing technique for

biomass with high nitrogen and low lignin content. If untreated, the biological breakdown of this

waste will produce CO2 and CH4. Deliberate anaerobic digestion is a way of ensuring that CH4

emissions are controlled and captured while recovering energy from the biomass. This can

reduce greenhouse gas emissions from water treatment plants and landfill. Anaerobic digestion

residues can be returned to the landscape to help close nutrient cycles and be a net benefit where

land is used for food production.

33

Digesters are typically run at 35 degrees Celsius to 60 degrees Celsius with higher temperatures

giving a faster reaction rate but with increased heating costs. They may be operated under

continuous, plug or batch conditions with higher production coming from continuous or plug

flow. Digesters may often accept waste from a number of sources and this variety of inputs may

aid in digester function through better nutrition of the microbes. Rapid and large scale changes in

the composition of the feed may reduce digester performance.

Table 5 Anaerobic Digestion technology summary7

An example of commercial anaerobic digestion at the Carrum sewage treatment plant of

Melbourne Water is shown in Figure below. This facility generates 3.4 megawatts (MW) of

electricity and the digester are partly underground to improve thermal regulation

Figure 7 Anaerobic digestion at the Carrum sewage treatment plant of Melbourne Water

7 Biomass technology review by crucible carbon consulting

34

Fermentation

Biomass fermentation of glucose or fructose sugar rich feed stocks produces ethanol. This is the

most commercially established of the liquid bio fuel technologies. Ethanol is usually blended

with standard petrolor diesel. Blending requires anhydrous ethanol in order to mix effectively

with hydrocarbons without water deposits. Dehydration of ethanol and growing high productivity

crops can be very energy intensive processes, which significantly reduce the net energy returns

for bio-ethanol.

Technologies are under active development for conversion of cellulosic materials to sugars so

that they can be used as a feedstock source. This process will be far less feedstock constrained

because of the abundance of lingo cellulosic biomass. The production of Butanol rather than

Ethanol via fermentation is also under development

.

There is considerable public debate about the use of first generation bio fuels such as bio ethanol

and calls have been made for a moratorium on expansion of production capacity. Debate has

focussed on the diversion of staple food crops to bio fuel use in the first world and the

corresponding increase in food prices for the worlds poor. Exaggerated Greenhouse reduction

claims (since energy intensity is high) have also been a point of debate and improvements over

the use of fossil based fuels for some cases may be negligible. The high profile US corn based

bio-ethanol industry is driven more by energy security than climate change. Brazil is a global

leader in bio ethanol use based on sugar cane feed

Table 6 Fermentation technology summary

35

Figure 8 The world’s largest fuel ethanol plant, Jilin, China, processes close to 2 M tonnes of corn per year to

produce some 2.3 Ml per day ethanol

Oil Extraction

Animal and plant oils are especially suited as a liquid fuel feedstock as unlike carbohydrates they

are largely deoxygenated and similar in structure to the long chain hydrocarbons of diesel and jet

fuel. Chemical conversion to fuel substitutes is therefore relatively simple with high energy and

process efficiency once oils are separated from the bulk biomass.

Oil can be extracted directly from biomass by mechanical separation or solvent extraction.

Mechanical separation can extract up to 90 per cent of available oils (typically 70-80 per cent).

This is the preferred technology for the extraction of high value food oils75 and for processing

high oil content feed stocks.

Solvent extraction is mainly used with lower oil yielding biomasses or following mechanical

separation. The oil is recovered by evaporating the solvent, which is then re-condensed and

reused. Solvent losses are usually small and form a negligible cost when compared to the cost of

the biomass feedstock.

Vegetable oils and animal fats are also available in concentrated form as recycled cooking oils

and tallow. While plant oils can directly be used in diesel engines, there are storage and

temperature related viscosity issues. Trans-esterification or hydrogenation, the process of

converting oils to biodiesel, alters the viscosity so that transport fuel standards can be met. The

physical and chemical properties of the resultant biodiesel is dependent on both the qualities of

the oil feedstock and the processing technology.

36

Table 7 Oil extraction summary

The biodiesel industry in Australia is severely feedstock constrained, with the drought, food and

export competition greatly increasing costs of feed over recent years. Many facilities are

operating well below capacity and several have recently had to close. Australian biodiesel

production is dominated by tallow and waste oil processing; capacity is around 525 Ml per year

(total annual Australian use is 14 gigalitres (Gl) fossil diesel per year)

Pyrolysis

Pyrolysis is thermal decomposition of organic material with no or limited oxygen. It can be

applied in principal to any forms of biomass. The main products of pyrolysis are gas, oil/tar

liquids and char, with flexibility to vary the amounts oil, gas and char. Slow pyrolysis increases

char yields and fast (or ‘flash’) pyrolysis increases the liquid fraction The energy contents of

pyrolysis gas, oil and char are about 6, 18 and 36 GJ/tonne respectively. Pyrolysis oil has about

half the energy content of crude oil. There are well established commercial char making facilities

focused on high value metallurgical applications, using high quality biomass inputs, such as

eucalyptus chips, with capacities around 35,000 tonnes of char per annum. This high cost regime

is not generally scalable to the emerging bioenergy industry.

The pyrolysis of biomass for bioenergy is a relatively undeveloped technology although the

pyrolysis of coal is well established for the production of town gas. Existing commercial slow

pyrolysis units for biomass are based on kiln type technologies and produce only gas and char

37

outputs. Fast pyrolysis technologies take a number of different approaches such as fluidised

beds, ablation and mixing with heat distribution sources such as sand, but all require a small

input particle size of less than 2mm and quench the oil and char outputs together which causes

difficulties with particulates in the oil. Hot filtration is being investigated in an effort to reduce

this as an issue.

Pyrolysis technologies using a wider range of lower cost biomass feeds, including woody crops

and wastes and residues, are under active development with several operating commercially.

Reducing the capital intensity and improving the energy efficiency of pyrolysis is important in

facilitating technology uptake.

Table 8 Pyrolysis technology summary

The largest flash pyrolysis plant (Dynamotive, West Lorne, Canada – see Figure below. It

processes 200 tonnes per day (t/day) wood waste in a bubbling fluid bed to generate primarily

fuel oil, while the largest commercial slow pyrolysis plant (MTK, Japan) processes 100 t/day

woodchips in a rotary kiln. Although oil is an intrinsic product of pyrolysis (approximately one

third of output), current commercial operations remove the ‘oil’ fraction in a gaseous phase.

38

Figure 9 Dynamotive flash pyrolysis plant in West Lorne Canada

A Note on Pyrolysis Char - ‘Biochar’

Pyrolysis is the only biomass processing option that produces char. Biochar formation, which is

optimisedby slow pyrolysis conditions, represents one of the very few value adding opportunities

for removal of CO2 from the atmosphere. ‘Biochar’ is very stable in soils and therefore has the

potential to be a major carbon sink. Char rich soils, such as the Amazonian ‘terra preta’ have

retained their carbon for thousands of years. A ‘carbon pump’ in the reverse direction to

greenhouse gas emissions is therefore created by the sequence: photosynthesis - biomass -

pyrolysis – biochar in soil

The high surface area of chars contributes to their beneficial effects on soil quality by providing

a substrate for microbial growth, improving soil structure, reducing soil tensile strength and

enhancing water and nutrient retention. Terra preta soils are highly productive and require less

water and fertiliser

Figure 10 Soil regeneration through ‘terra preta’

39

Biochar is a strategic opportunity in a carbon constrained world where significant soil

degradation has occurred through clearances and intensive agricultural practices, which

themselves have contributed to greenhouse emissions and climate change. In pyrolysis, the

nutrients in biomass report to the char, so that ‘biochar’ provides a pathway for nutrient recycling

back into soils

Given the sustainability advantages of biochar in soils there is little doubt that there will be

increasing activities in this area. These benefits will act as an additional driver for higher volume

and/or low capital cost pyrolysis technologies. Biochar is not yet a developed market and in the

shorter term the selling price of biochar may be underpinned by its energy value

Gasification

Gasification is a process in which oxygen-deficient thermal decomposition of organic matter

(coal, oil or biomass) produces non-condensable fuel or synthesis gases. Gasification combines

pyrolysis with partial combustion to provide heat for the endothermic decomposition reactions.

Unless the gas is combusted directly for power, it is cooled, filtered and scrubbed to remove

condensables and carry-over particles. The syn-gas produced can be used in a variety of energy

conversion devices (for example, internal combustion engines, gas turbines and fuel cells) or

converted to high value fuels and chemicals.

Biomass gasifiers based on packed/moving bed configurations are limited to small scale

operations, typically less than 1 MWe. Fluidised bed gasifiers offer much higher throughput

capacity and have demonstrated commercial viability on a range of biomass sources. The largest

biomass gasifier is 70 MWth fed by around 200,000 tonnes per annum of forestry products

40

Table 9 Gasification technology summary

Integration of Technology Aspects

A synthesis of the key factors for biomass processing technologies is presented in the table

below.

Thermal technologies are the least sensitive to the qualities of the feedstock and are able to

effectively process lingo cellulosic materials. These technologies are inherently the most scalable

and do not require purpose grown biomass.

Established technologies other than Direct Combustion are significantly limited in scale through

dependence on specific and limited feed stocks. Technologies that provide high volume and

value opportunities are currently the most immature and are the most likely candidates for future

innovation.The analysis highlights the strategic attractiveness of thermal processing to solid,

liquid and gas energy products, while recognizing that immediate term projects are likely to be

limited in scale

41

Table 10 Sustainability Considerations of Biomass Processing Technologies

Integration of Sustainability Aspects

There is a logical alignment between biomass resources and their constituents, the selection of

processing technology and the downstream product application, as shown in the figure below.

The objective in specific projects is to maximize the value of the system as a whole

42

Figure 11 Strategic platform for maximum value capture from bio energy resources

43

Figure 12 Biomass Energy Conversion Overview

44

BIOMASS GASIFICATION

The production of generator gas (producer gas) called gasification, is partial combustion of solid fuel (biomass) and takes place at temperatures of about 1000

0

C. The reactor is called a gasifier. The combustion products from complete combustion of biomass generally contain nitrogen, water vapor, carbon dioxide and surplus of oxygen. However in gasification where there is a surplus of solid fuel (incomplete combustion) the products of combustion are combustible gases like Carbon monoxide (CO), Hydrogen (H2) and traces of Methane and non- useful products like tar and dust. The production of these gases is by reaction of water vapor and carbon dioxide through a glowing layer of charcoal. Thus the key to gasifier design is to create conditions such that a) biomass is reduced to charcoal and, b) charcoal is converted at suitable temperature to produce CO

Types of Gasifiers

Since there is an interaction of air or oxygen and biomass in the gasifier, they are classified

according to the way air or oxygen is introduced in it. There are three types of gasifiers given in

fig below- Downdraft, Updraft and Crossdraft. And as the classification implies updraft gasifier

has air passing through the biomass from bottom and the combustible gases come out from the

top of the gasifier. Similarly in the downdraft gasifier the air is passed from the tuyers in the

downdraft direction.

Figure 13 Products of gasification

45

Figure 14 Various types of gasifier

With slight variation almost all the gasifiers fall in the above categories.

Sr.

No.

Gasifier

Type

Advantage Disadvantages

1. Updraft - Small pressure drop

- good thermal efficiency

- little tendency towards slag

formation

- Great sensitivity to tar and moisture and

moisture content of fuel

- relatively long time required for start up

of IC engine

- poor reaction capability with heavy gas

load

2. Downdraft - Flexible adaptation of gas

production to load

- low sensitivity to charcoal dust and

tar content of fuel

- Design tends to be tall

- not feasible for very small particle size

of fuel

3. Crossdraft - Short design height

- very fast response time to load

- flexible gas production

- Very high sensitivity to slag formation

- high pressure drop

Table 11 Advantage and disadvantage of various gasifier

46

Table 12 Comparison of biomass gasifier

Process Zones

Four distinct processes take place in a gasifier as the fuel makes its way to gasification. They are

:

a) Drying of fuel

b) Pyrolysis – a process in which tar and other volatiles are driven off

c) Combustion

d) Reduction

Though there is a considerable overlap of the processes, each can be assumed to occupy a

separate zone where fundamentally different chemical and thermal reactions take place. Figure

given below shows schematically an updraft gasifier with different zones and their respective

temperatures.

47

Figure 15various zones in updraft gasifier & gasification process in downdraft gasifier

Figure 16 gasification process in cross-draft gasifier& single & double throat gasifier

In the downdraft gasifiers there are two types :

Single throat

Double throat

Single throat gasifiers are mainly used for stationary applications whereas double throat are for

varying loads as well as automotive purposes.

48

Reaction Chemistry

The following major reactions take place in combustion and reduction zone

1. Combustion zone The combustible substance of a solid fuel is usually composed of elements carbon, hydrogen and

oxygen. In complete combustion carbon dioxide is obtained from carbon in fuel and water is

obtained from the hydrogen, usually as steam. The combustion reaction is exothermic and yields

a theoretical oxidation temperature of 14500

C. The main reactions, therefore, are:

C + O2

= CO2

(+ 393 MJ/kg mole) (1)

2H2

+ O2

= 2H2 O (- 242 MJ/kg mole) (2)

2. Reaction zone The products of partial combustion (water, carbon dioxide and uncombusted partially cracked

pyrolysis products) now pass through a red-hot charcoal bed where the following reduction

reactions take place

C + CO2

= 2CO (- 164.9 MJ/kg mole) (3)

C + H2O = CO + H

2 (- 122.6 MJ/kg mole) (4)

CO + H2O = CO + H

2 (+ 42 MJ/kg mole) (5)

C + 2H2

= CH4

(+ 75 MJ/kg mole) (6)

CO2

+ H2

= CO + H2O (- 42.3 MJ/kg mole) (7)

Reactions (3) and (4) are main reduction reactions and being endothermic have the capability of

reducing gas temperature. Consequently the temperatures in the reduction zone are normally

800-10000

C. Lower the reduction zone temperature (~ 700-8000

C), lower is the calorific value of

gas.

3. Pyrolysis zone Wood pyrolysis is an intricate process that is still not completely understood. The products

depend upon temperature, pressure, residence time and heat losses. However following general

remarks can be made about them.

Upto the temperature of 2000

C only water is driven off. Between 200 to 2800

C carbon dioxide,

acetic acid and water are given off. The real pyrolysis, which takes place between 280 to 5000

C,

produces large quantities of tar and gases containing carbon dioxide. Besides light tars, some

methyl alcohol is also formed. Between 500 to 7000

C the gas production is small and contains

hydrogen.

49

Thus it is easy to see that updraft gasifier will produce much more tar than downdraft one. In

downdraft gasifier the tars have to go through combustion and reduction zone and are partially

broken down.

Since majority of fuels like wood and biomass residue do have large quantities of tar, downdraft

gasifier is preferred over others. Indeed majority of gasifiers, both in World War II and presently

are of downdraft type.

Finally in the drying zone the main process is of drying of wood. Wood entering the gasifier has

moisture content of 10-30%. Various experiments on different gasifiers in different conditions

have shown that on an average the condensate formed is 6-10% of the weight of gasified wood.

Some organic acids also come out during the drying process. These acids give rise to corrosion

of gasifiers.

Properties of Producer gas

The producer gas is affected by various processes as outlined above hence one can expect

variations in the gas produced from various biomass sources. Table 13 lists the composition of

gas produced from various sources. The gas composition is also a function of gasifier design and

thus, the same fuel may give different calorific value as when used in two different gasifiers.

Table-13 therefore shows approximate values of gas from different fuels and table-14 shows the

comparative properties of producer gas with other gases like biogas and natural gas.

The maximum dilution of gas takes place because of presence of nitrogen. Almost 50-60% of gas

is composed of noncombustible nitrogen. Thus it may be beneficial to use oxygen instead of air

for gasification. However the cost and availability of oxygen may be a limiting factor in this

regard. Nevertheless where the end product is methanol – a high energy quality item, then the

cost and use of oxygen can be justified.

On an average 1 kg of biomass produces about 2.5 m3 of producer gas at S.T.P. In this process it

consumes about 1.5 m3 of air for combustion. For complete combustion of wood about 4.5 m3

of air is required. Thus biomass gasification consumes about 33% of theoretical stoichiometeric

ratio for wood burning. The average energy conversion efficiency of rice husk gasifiers is about

70-80%

50

Temperature of Gas

On an average the temperature of gas leaving the gasifier is about 300 to 4000C . If the

temperature is higher than this (~ 5000C) it is an indication that partial combustion of gas is

taking place. This generally happens when the air flow rate through the gasifier is higher than the

design value.

Table 13 Composition of Producer Gas from various fuels

51

.

Table 14 Comparison of producer gas with biogas & natural gas

52

HEAT AND MASS TRANSFER

Material quantities, as they pass through processing operations, can be described by material

balances. Such balances are statements on the conservation of mass. Similarly, energy quantities

can be described by energy balances, which are statements on the conservation of energy. If

there is no accumulation, what goes into a process must come out. This is true for batch

operation. It is equally true for continuous operation over any chosen time interval.

Material and energy balances are very important in an industry. Material balances are

fundamental to the control of processing, particularly in the control of yields of the products.

The first material balances are determined in the exploratory stages of a new process, improved

during pilot plant experiments when the process is being planned and tested, checked out when

the plant is commissioned and then refined and maintained as a control instrument as production

continues. When any changes occur in the process, the material balances need to be determined

again.

The increasing cost of energy has caused the industries to examine means of reducing energy

consumption in processing. Energy balances are used in the examination of the various stages of

a process, over the whole process and even extending over the total production system from the

raw material to the finished product.

Material and energy balances can be simple, at times they can be very complicated, but the basic

approach is general. Experience in working with the simpler systems such as individual unit

operations will develop the facility to extend the methods to the more complicated situations,

which do arise. The increasing availability of computers has meant that very complex mass and

energy balances can be set up and manipulated quite readily and therefore used in everyday

process management to maximize product yields and minimize costs.

Basic Principles

If the unit operation, whatever its nature is seen as a whole it may be represented

diagrammatically as a box, as shown in Figure below The mass and energy going into the box

must balance with the mass and energy coming out.

53

Figure 17 mass and energy balance

The law of conservation of mass leads to what is called a mass or a material balance.

Mass In = Mass Out + Mass Stored

Raw Materials = Products + Wastes + Stored Materials.

ΣmR

= ΣmP

+ Σ mW

+ ΣmS

(where Σ (sigma) denotes the sum of all terms).

ΣmR

= ΣmR1

+ Σ mR2

+ ΣmR3

= Total Raw Materials

ΣmP

= ΣmP1

+ Σ mP2

+ ΣmP3

= Total Products.

ΣmW

= ΣmW1

+ Σ mW2

+ ΣmW3

= Total Waste Products

ΣmS

= ΣmS1

+ Σ mS2

+ ΣmS3

= Total Stored Products.

If there are no chemical changes occurring in the plant, the law of conservation of mass will

apply also to each component, so that for component A:

mA

in entering materials = mA

in the exit materials + mA

stored in plant.

For example, in a plant that is producing sugar, if the total quantity of sugar going into the plant

is not equalled by the total of the purified sugar and the sugar in the waste liquors, then there is

something wrong. Sugar is either being burned (chemically changed) or accumulating in the

plant or else it is going unnoticed down the drain somewhere.

54

In this case:

MA= (mAP

+ mAW

+ mAU

)

where mAU

is the unknown loss and needs to be identified. So the material balance is now:

Raw Materials = Products + Waste Products + Stored Products + Losses

where Losses are the unidentified materials.

Just as mass is conserved, so is energy conserved in food-processing operations. The energy

coming into a unit operation can be balanced with the energy coming out and the energy stored.

Energy In = Energy Out + Energy Stored

ΣER

= ΣEP

+ ΣEW

+ ΣEL

+ ΣES

where

ΣER

= ER1

+ ER2

+ ER3

+ ……. = Total Energy Entering

ΣEp

= EP1

+ EP2

+ EP3

+ ……. = Total Energy Leaving with Products

ΣEW

= EW1

+ EW2

+ EW3

+ … = Total Energy Leaving with Waste Materials

ΣEL

= EL1

+ EL2

+ EL3

+ ……. = Total Energy Lost to Surroundings

ΣES

= ES1

+ ES2

+ ES3

+ ……. = Total Energy Stored

Energy balances are often complicated because forms of energy can be inter converted, for

example mechanical energy to heat energy, but overall the quantities must balance

Method for Preparing Process Flow Chart

The identification and drawing up a unit operation/process is prerequisite for energy and material

balance. The procedure for drawing up the process flow diagrams is explained below.

Flow charts are schematic representation of the production process, involving various input

resources, conversion steps and output and recycle streams. The process flow may be constructed

stepwise i.e. by identifying the inputs / output / wastes at each stage of the process, as shown in

the Figure below

55

Figure 18 Process Flow Chart

Inputs of the process could include raw materials, water, steam, energy (electricity, etc);

Process Steps should be sequentially drawn from raw material to finished product. Intermediates

and any other byproduct should also be represented. The operating process parameters such as

temperature, pressure, % concentration, etc. should be represented

The flow rate of various streams should also be represented in appropriate units like m3

/h or

kg/h. In case of batch process the total cycle time should be included.

Wastes / by products could include solids, water, chemicals, energy etc. For each process steps

(unit operation) as well as for an entire plant, energy and mass balance diagram should be drawn.

Output of the process is the final product produced in the plant.

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VAPOUR ABSORPTION MACHINE

A vapor absorption chiller machine (VAM) is a machine that produces chilled water using a heat

source rather than electrical input as in the more familiar vapor compression cycle. It seems

unreasonable that cooling can be achieved with heat, but that is what occurs within an absorption

chiller.

Both vapor compression and absorption refrigeration cycles accomplish the removal of heat

through the evaporation of a refrigerant at a low pressure and the rejection of heat through the

condensation of the refrigerant at a higher pressure. The basic difference is that an electric chiller

employs a mechanical compressor to create the pressure differences necessary to circulate the

refrigerant whereas the absorption chillers use heat source and do not use a mechanical

compressor. The differences cause an absorption system to use little to no work input, but energy

must be supplied in the form of heat. This makes the system very attractive when there is a cheap

source of heat, such as solar heat or waste heat from electricity or heat from generation.

Absorption chillers have recently gained widespread acceptance due to their capability of not

only integrating with cogeneration systems but also because they can operate with industrial

waste heat streams.

What is Absorption?

Comparing the absorption refrigeration cycle with the more familiar vapor compression

refrigeration cycle is often an easy way to introduce it. The standard vapor compression

refrigeration system is a condenser, evaporator, throttling valve, and a compressor. Figure below

is a schematic of the components and flow arrangements for the vapor compression cycle

Figure 19 Vapour compression cycle

In the vapor-compression refrigeration cycle, refrigerant enters the evaporator in the form of a

cool, low-pressure mixture of liquid and vapor (4). Heat is transferred from the relatively warm

air or water to the refrigerant, causing the liquid refrigerant to boil. The resulting vapor (1) is

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then pumped from the evaporator by the compressor, which increases the pressure and

temperature of the refrigerant vapor. The hot, high-pressure refrigerant vapor (2) leaving the

compressor enters the condenser where heat is transferred to ambient air or water at a lower

temperature. Inside the condenser, the refrigerant vapor condenses into a liquid. This liquid

refrigerant (3) then flows to the expansion device, which creates a pressure drop that reduces the

pressure of the refrigerant to that of the evaporator. At this low pressure, a small portion of the

refrigerant boils (or flashes), cooling the remaining liquid refrigerant to the desired evaporator

temperature. The cool mixture of liquid and vapor refrigerant (4) travels to the evaporator to

repeat the cycle. Much like in the vapor compression cycle, refrigerant in the absorption cycle

flows through a condenser, expansion valve, and an evaporator. However, the absorption cycle

uses different refrigerants and a different method of compression than the vapor compression

cycle.

Figure 20 Vapor Absorption Cycle

Absorption refrigeration systems replace the compressor with a generator and an absorber.

Refrigerant enters the evaporator in the form of a cool, low-pressure mixture of liquid and vapor

(4). Heat is transferred from the relatively warm water to the refrigerant, causing the liquid

refrigerant to boil. Using an analogy of the vapor compression cycle, the absorber acts like the

suction side of the compressor—it draws in the refrigerant vapor (1) to mix with the absorbent.

The pump acts like the compression process itself—it pushes the mixture of refrigerant and

absorbent up to the high-pressure side of the system. The generator acts like the discharge of the

compressor—it delivers the refrigerant vapor (2) to the rest of the system. The refrigerant vapor

(2) leaving the generator enters the condenser, where heat is transferred to water at a lower

temperature, causing the refrigerant vapor to condense into a liquid. This liquid refrigerant (3)

then flows to the expansion device, which creates a pressure drop that reduces the pressure of the

refrigerant to that of the evaporator. The resulting mixture of liquid and vapor refrigerant (4)

travels to the evaporator to repeat the cycle

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Similarities between Vapor compression and Vapor absorption cycles

The basic absorption chiller cycle is similar to the traditional vapor compression

chiller cycle in that

1. Both cycles circulate refrigerant inside the chiller to transfer heat from one fluid to the

other

2. Both cycles include a device to increase the pressure of the refrigerant and an expansion

device to maintain the internal pressure difference, which is critical to the overall heat

transfer process;

3. Refrigerant vapor is condensed at high pressure and temperature, rejecting heat to the

surroundings

4. Refrigerant vapor is vaporized at low pressure and temperature, absorbing heat from the

chilled water flow

Differences between Vapor compression and Vapor absorption cycles

The basic absorption chiller cycle is different to the vapor compression chiller cycle.

In that

1. The absorption systems use heat energy in form of steam, direct fuel firing or waste heat

to achieve the refrigerant effect;

2. The absorption cycle use a liquid pump, NOT a compressor to create the pressure rise

between evaporator and condenser. Pumping a liquid is much easier and cheaper than

compressing a gas, so the system takes less work input. However, there is a large heat

input in the generator. So, the system basically replaces the work input of a vapor-

compression cycle with a heat input;

3. The absorption cycle uses different refrigerants that have no associated environment

hazard, ozone depletion or global warming potential (for example lithium bromide

absorption system use distilled water as the refrigerant). The vapor compression

refrigeration cycle generally uses a halocarbon (such as HCFC-123, HCFC-22, HFC-

134a, etc) as the refrigerant;

4. Compared to compression chillers, absorption systems contain very few moving parts,

offer less noise and vibration, are compact for large capacities and require little

maintenance

5. Compared to compression chillers, the performance of absorption systems is not sensitive

to load variations and does not depend very much on evaporator superheat;

6. Compared with mechanical chillers, absorption systems have a low coefficient of

performance (COP = chiller load/heat input). However, absorption chillers can

substantially reduce operating costs because they are powered by low-grade waste heat.

The COP of absorption chiller is NOT sensitive to load variations and does not reduce

significantly at part loads

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From the standpoint of thermodynamics, the vapor compression chiller is a heat pump, using

mechanical energy and work, to move heat from a low to a high temperature. An absorption

chiller is the equivalent of a heat engine – absorbing heat at a high temperature, rejecting heat at

a lower temperature, producing work – driving a heat pump.

Applications of Absorption Systems

The main advantage of absorption chillers is their ability to utilize waste heat streams that would

be otherwise discarded. In terms of energy performance, motor-driven vapor compression

chillers will beat absorption chillers every time. Still there are specific applications where

absorption chillers have a substantial advantage over motor-driven vapor compression chillers.

Some of those applications include

1. For facilities that use lot of thermal energy for their processes, a large chunk of heat is

usually discarded to the surrounding as waste. This waste heat can be converted to useful

refrigeration by using a VAM.

2. For facilities that have a simultaneous need for heat and power (cogeneration system),

absorption chillers can utilize the thermal energy to produce chilled water.

3. For facilities that have high electrical demand charges. Absorption chillers minimize or

flatten the sharp spikes in a building’s electric load profile can be used as part of a peak

shaving strategy.

4. For facilities where the electrical supply is not robust, expensive, unreliable, or

unavailable, it is easier to achieve heat input with a flame than with electricity.

Absorption chillers uses very little electricity compared to an electric motor driven

compression cycle chiller

5. For facilities, where the cost of electricity verses fuel oil/gas tips the scale in favor of

fuel/gas. Various studies indicate that the absorption chillers provide economic benefit in

most geographical areas, due to the differential in the cost between gas and electric

energy.

6. For facilities wanting to use a “natural refrigerant and aspiring for LEED certification

(Leadership in Energy and Environmental Design) absorption chillers are a good choice.

Absorption chillers do not use CFCs or HCFCs - the compounds known for causing

Ozone depletion.

7. For facilities implementing clean development mechanism (CDM) and accumulating

carbon credits, the absorption use coupled to waste heat recovery and cogeneration

system help reduce problems related to greenhouse effect from CO2 emission.

Vapor absorption system allows use of variable heat sources: directly using a gas burner,

recovering waste heat in the form of hot water or low-pressure steam, or boiler-generated hot

water or steam

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The Basic Principle of Absorption Cooling

Water boils and evaporates at 212 °F [100 °C] at standard atmospheric pressure (14.7psia

[101.3kPa]). When the pressure is reduced, water boils at a lower temperature. The following

table gives the total pressure in inches of mercury and the corresponding approximate water

boiling temperature at different pressures:

The fundamental principle of VAM is that water boils at about 40°F at the low pressure vacuum

condition of 6.5 mm-Hg. Let’s examine this closely.

Consider a closed vessel placed under a vacuum of say, 6.5 mm Hg (refer to the figure below).

Assume the closed vessel contains a high quality absorbent material such as dry silica gel, and a

heat transfer coiled tube through which warm water is circulated. When water is sprayed on the

outer wall of the heat transfer tube

1. It gets boiled at low temperature 40°F (4°C) under vacuum, and in doing so, absorbs heat

from the running water in the heat transfer tube. (The sprayed water is also called the

refrigerant).

2. The running water in the heat transfer tube is optimally cooled equivalent to the heat of

evaporation

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Figure 21Vapor Absorption System with Silica Gel Absorbent

The vapors produced, as a result of evaporation, will immediately be absorbed by the silica gel.

But when the silica gel reaches the limit of its absorbing capacity, the process continuity cannot

be maintained. To ensure a continuous process, some means of converting the absorbent to its

original concentration is necessary

In commercial practice, silica gel is replaced with an aqueous absorbent solution. Continuing

with the same explanation, as the aqueous absorbent solution absorbs refrigerant vapors; it

becomes diluted and has less ability to absorb any further water vapor. To complete the cycle

and sustain operation, the dilute solution is pumped to higher pressure where with application of

heat, the water vapor is driven off and the re-concentrated absorbent is recycled back to the

absorber vessel. The released refrigerant vapor is condensed in a separate vessel and returned for

evaporation.

The simplified diagram here illustrates the overall flow path.

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Figure 22 Vapor Absorption System with Aqueous Absorbent

Most commercial absorption chillers use pure water as refrigerant and lithium bromide (LiBr) as

absorbent salt. Another common refrigerant–absorbent pair is ammonia as the refrigerant and

water as the absorbent. There are other refrigerant– absorbent combinations; but in this course

will focus on lithium bromide VAM.

How Absorption Machine Works

Absorption system employs heat and a concentrated salt solution (lithium bromide) to produce

chilled water. In its simplest design the absorption machine consists of 4 basic components

1. Generator

2. Condenser

3. Evaporator

4. Absorber

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Figure 23 Vapour absorption cycle

Just like the vapor-compression refrigeration cycle, the absorption machine operates under two

pressures – one corresponding to the condenser-generator (high pressure refrigerant separation

side) and the other corresponding to evaporator-absorber (low pressure absorption process in

vacuum). For air-conditioning applications, the evaporator-absorber is at a pressure of 6.5 mmHg

and temperature of about 40ºF. The pressure on the high-pressure side of the system (condenser)

is approximately ten times greater than that on the low-pressure side to allow the refrigerant to

reject heat to water at normally available temperatures. Typically the condensation of water in

the condenser-generator takes place at a pressure of 75 mmHg and temperature of about 113ºF.

Function of Components

Generator:

The purpose of the generator is to deliver the refrigerant vapor to the rest of the system. It

accomplishes this by separating the water (refrigerant) from the lithium bromide-and-water

solution. In the generator, a high-temperature energy source, typically steam or hot water, flows

through tubes that are immersed in a dilute solution of refrigerant and absorbent. The solution

absorbs heat from the warmer steam or water, causing the refrigerant to boil (vaporize) and

separate from the absorbent solution. As the refrigerant is boiled away, the absorbent solution

64

becomes more concentrated. The concentrated absorbent solution returns to the absorber and the

refrigerant vapor migrates to the condenser

Condenser:

The purpose of condenser is to condense the refrigerant vapors. Inside the condenser, cooling

water flows through tubes and the hot refrigerant vapor fills the surrounding space. As heat

transfers from the refrigerant vapor to the water, refrigerant condenses on the tube surfaces. The

condensed liquid refrigerant collects in the bottom of the condenser before traveling to the

expansion device. The cooling water system is typically connected to a cooling tower. Generally,

the generator and condenser are contained inside of the same shell.

Expansion Device:

From the condenser, the liquid refrigerant flows through an expansion device into the evaporator.

The expansion device is used to maintain the pressure difference between the high-pressure

(condenser) and low-pressure (evaporator) sides of the refrigeration system by creating a liquid

seal that separates the high-pressure and low pressure sides of the cycle. As the high-pressure

liquid refrigerant flows through the expansion device, it causes a pressure drop that reduces the

refrigerant pressure to that of the evaporator. This pressure reduction causes a small portion of

the liquid refrigerant to boil off, cooling the remaining refrigerant to the desired evaporator

temperature. The cooled mixture of liquid and vapor refrigerant then flows into the evaporator

Evaporator:

The purpose of evaporator is to cool the circulating water. The evaporator contains a bundle of

tubes that carry the system water to be cooled/chilled. High pressure liquid condensate

(refrigerant) is throttled down to the evaporator pressure (typically around 6.5 mm Hg absolute).

At this low pressure, the refrigerant absorbs heat from the circulating water and evaporates. The

refrigerant vapors thus formed tend to increase the pressure in the vessel. This will in turn

increase the boiling temperature and the desired cooling effect will not be obtained. So, it is

necessary to remove the refrigerant vapors from the vessel into the lower pressure absorber.

Physically, the evaporator and absorber are contained inside the same shell, allowing refrigerant

vapors generated in the evaporator to migrate continuously to the absorber

Absorber:

Inside the absorber, the refrigerant vapor is absorbed by the lithium bromide solution. As the

refrigerant vapor is absorbed, it condenses from a vapor to a liquid, releasing the heat it acquired

in the evaporator.

The absorption process creates a lower pressure within the absorber. This lower pressure, along

with the absorbent’s affinity for water, induces a continuous flow of refrigerant vapor from the

evaporator. In addition, the absorption process condenses the refrigerant vapors and releases the

heat removed from the evaporator by the refrigerant. The heat released from the condensation of

65

refrigerant vapors and their absorption in the solution is removed to the cooling water that is

circulated through the absorber tube bundle.

As the concentrated solution absorbs more and more refrigerant; its absorption ability decreases.

The weak absorbent solution is then pumped to the generator where heat is used to drive off the

refrigerant. The hot refrigerant vapors created in the generator migrate to the condenser. The

cooling tower water circulating through the condenser turns the refrigerant vapors to a liquid

state and picks up the heat of condensation, which it rejects to the cooling tower. The liquid

refrigerant returns to the evaporator and completes the cycle

TYPES OF VAM

Absorption chillers are classified as:

1. Single effect absorption chiller

2. Double effect absorption chiller

Single Effect Absorption Chillers

The single-effect absorption chiller includes a single generator, condenser, evaporator, absorber,

heat exchanger, and pumps. Fig. below shows a Single Effect Chiller.

Figure 24 Basic Cycle of Single Effect Chiller

We have already discussed the operational principle of VAM. Physically in a single effect VAM,

the evaporator and absorber are contained inside the same shell, allowing refrigerant vapors

generated in the evaporator to migrate continuously to the absorber. Also the condenser and

generator are in same shell.

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The basic absorption cycle as discussed earlier may be modified in several ways to reduce the

heat required to operate the chiller and to reduce the extent of heat transfer surface incorporated

in the machine. One is to utilize all possible opportunities for heat recovery within the cycle in

order to improve the heat economy within the cycle. For example, a heat exchanger is placed to

recover some of heat from the concentrated hot lithium bromide solution going from the

generator to the absorber to heat the dilute cold lithium bromide solution going from the absorber

to the generator. Heat exchangers optimize the energy transfer between the hot,

concentrated lithium bromide that is recycling and the cooler, dilute sorbent solution that is yet to

be boiled.

Also the modifications are possible in cooling circuit; for example, the cooling water is arranged

in series i.e. made to pass through absorber first followed by condenser. Some absorption chiller

designs split the cooling water and deliver it directly to both the absorber and the condenser

A typical single effect system use low pressure steam (20 psig or less) or hot water at 185°F to

200°F, as the driving force. These units typically require about 18 pounds per hour (pph) of 9 psi

steam at the generator flange (after control valve) per ton of refrigeration at ARI standard rating

conditions.

Figure 25 Single Effect Steam Fired Vapor Absorption Chiller Machine

Double Effect (2-Stage) Absorption Systems

A double-effect chiller is very similar to the single-effect chiller, except that it contains an

additional generator

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Figure 26 Basic Cycle of Double Effect Type Chillers

In a single-effect absorption chiller, the heat released during the chemical process of absorbing

refrigerant vapor into the liquid stream, rich in absorbent, is rejected to the cooling water. In a

multiple-effect absorption chiller, some of this energy is used as the driving force to generate

more refrigerant vapor. The more vapor generated per unit of heat or fuel input, the greater the

cooling capacity and the higher the overall operating efficiency.

Operation of Double Effect VAM

Before we discuss the operation of double effect indirect fired VAM, it is important to

understand some terminology that defines the physical and chemical properties of absorbent

solution during absorption process.

Dilute Solution: The term dilute solution refers to a mixture that has a relatively high

refrigerant content and low absorbent content.

Concentrated Solution: A concentrated solution has a relatively low refrigerant content

and high absorbent content.

Intermediate Solution: An intermediate solution is a mixture of dilute and concentrated

solutions.

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Figure 27 Two Stage Vapor Absorption Chiller Machine

In the high-temperature generator, very high temperature steam or hot water flows through tubes

that are immersed in an absorbent solution that is at an intermediate concentration. The solution

absorbs heat from the warmer steam or water, causing the refrigerant to boil and separate from

the absorbent solution. As the refrigerant boils away, the absorbent solution becomes

concentrated and returns to the absorber

The hot refrigerant vapor produced in the high-temperature generator migrates to the low-

temperature generator, where it flows through tubes that are immersed in a dilute solution. The

solution absorbs heat from the high temperature refrigerant vapor, causing the refrigerant in the

low-temperature generator to boil and separate from the absorbent solution. As that refrigerant

boils away, the concentration of the absorbent solution increases and the concentrated solution

returns to the absorber.

The low-temperature refrigerant vapor produced in the low-temperature generator migrates to the

cooler condenser. Additionally, the liquid refrigerant that condensed inside the tubes of the low-

temperature generator also flows into the condenser. Next, the refrigerant travels through the

condenser, expansion device, evaporator and absorber in a manner similar to refrigerant travel in

the single effect absorption chiller.

Double-effect systems can be configured either in series or parallel flow. The difference between

the two systems is the fluid path taken by the solution through the generators.

Series flow cycle: In the series flow cycle, the dilute solution from the absorber is

pumped entirely to the high-temperature generator. As the refrigerant boils away and

migrates to the low-temperature generator, the absorbent solution becomes concentrated.

The resulting intermediate solution then flows to the low temperature generator, where it

is further concentrated by the refrigerant vapor that was created in the high temperature

generator. The concentrated solution then flows back to the absorber to repeat the cycle.

The series flow cycle has been the mainstay of most double-effect absorption chiller

69

designs for many years. It is simple because it requires only one generator pump and is

fairly straightforward to control. The series cycle, however, requires a significantly larger

heat exchanger to obtain similar COPs to the other cycles.

Parallel flow cycle: In the parallel flow cycle, the dilute solution from the absorber is

split between the low-temperature and high-temperature generators. Both streams of

dilute solution are concentrated in the generators and mix together again before returning

to the absorber. The parallel flow cycle can be implemented using one generator pump, if

a throttling device is used to control the flow of solution to the low-temperature

generator. Separate generator pumps should be used for control over the full range of

operating conditions

The performance of a double-effect absorption chiller mainly depends on the choice of operating

conditions, the amount of heat transfer surface area, the effectiveness of the purge system, the

materials of construction, the design of the controls, and the manufacturing techniques

Efficiency of Vapor Absorption Machine (VAM)

Efficiencies of absorption chillers is described in terms of Coefficient of Performance (COP),

and is defined as the refrigeration effect, in Btu, divided by the net heat input, in Btu.

The COP can be thought of as a sort of index of the efficiency of the machine. The absorption

systems with a COP of 1.0 will burn 12,000 BTUs of heat energy for each ton-hour of cooling.

For example, a 500-ton absorption chiller operating at a COP of 0.70 would require: (500 x

12,000 Btu/h) divided by 0.70 = 8,571,429 Btu/h heat input.

Cooling capacity is measured in tons of refrigeration. A ton of refrigeration is defined as the

capacity to remove heat at a rate of 12,000 Btu/hr at the evaporator

What do you need to run a VAM?

1. Heat Source

2. Refrigerant-Absorbent Working Pair

3. Cooling Water

Heat Source

Absorption chillers are classified by the firing method—that is, how the generator is heated and

whether it has a single- or a multiple-effect generator

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Indirect Fired Systems

"Indirect-fired" absorption chillers use steam, hot water or hot gases steam from a boiler, turbine

or engine generator, or fuel cell as their primary power input. These chillers can be well suited

for integration into combined heat and power (CHP) cogeneration system by utilizing rejected

heat from gas turbine, steam turbine (non condensing and extraction type) or engine generator.

COGENERATION – Combine Heat and Power (CHP)

Cogeneration is the sequential generation of two different forms of useful energy from a single

primary energy source.

The concept of power and absorption cooling arises from the industries where there is a need for

continuous reliable electricity and heating/cooling. As electricity costs rise, producing power at

the point of use is far more economical and reliable than generating and transmitting electricity

from a remote power plant. In fact, a facility operating a Combined Heating and Power (CHP)

system is about three times more efficient, and it reduces greenhouse gases by similar amounts.

But to realize these benefits, all the heat by-products of cogeneration must be used all the time.

Using the heat from a CHP system is usually straightforward during winter, but this same heat

can be used in summer months to drive an absorption chiller to provide chilled water for cooling

Lithium Bromide (LiBr) – Water Absorption System

Key Characteristics

1. Lithium bromide is a salt and desiccant (drying agent). The lithium ion (Li+) in the

lithium bromide solution and the water molecules have a strong association, producing

the absorption essential for the chiller to operate. Water is the refrigerant and LiBr is

the absorbent

2. LiBr system operates under vacuum; the vacuum pumps are needed only for short

duration while starting the machine; after that, equilibrium condition is maintained by

physical and chemical phenomena

3. Since water is the refrigerant for the LiBr absorption system, the minimum possible

chilled water temperature, at its lowest, is about 44° F; consequently, LiBr absorption

chillers are used in large air-conditioning applications;

4. The advantage of the water-LiBr pair includes its stability, safety, and high volatility

ratio.

Cautions:

1. At high concentrations, the solution is prone to crystallization.

2. The lithium bromide solution is corrosive to some metals. Corrosion inhibitors may be

added to protect the metal parts and to improve heat-mass transfer performance.

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Cooling Water

Cooling water is required to remove the heat that the LiBr solution absorbs from the refrigerant

vapor in the absorber and also condenses the refrigerant vapor from the generator. The heat gain

in the cooling water is finally rejected in a cooling tower.

Absorption systems require larger cooling tower capacity and greater pump energy than electric

chillers due to larger quantities of cooling water needed for the cycle. An absorption refrigeration

system that removes 12,000 Btu/hr (does 1 ton of air conditioning) requires heat energy input of

approximately 18,000 Btu/hr to drive the absorption process. This means that the heat rejection

at the cooling tower approximates 30,000 Btu/hr per ton of refrigeration. With a 15°F (8°C)

temperature drop across the tower, the heat rejection of an absorption system requires circulation

of approximately 4 gpm of water per ton of air conditioning. [Gpm/ton = Btu/hr / (500

* DT)]. In comparison heat rejection in a compression system is approximately 15,000 Btu/hr per

ton of refrigeration [12000 + 3000 Btu/hr per ton of refrigeration due to heat of compression].

The vapor compression system requires approximately 3 gpm of cooling water per ton of

refrigeration, with a 10°F temperature drop across the cooling tower

Key Characteristics

Cooling water in absorption machine passes through both the absorber and condenser. Any

deficiency in the cooling water system can affect the cooling capacity and the COP of the

machine

1. Lower temperature cooling water: The absorption power of a LiBr solution is stronger

at lower temperatures of cooling water. When the temperature of the cooling water in the

condenser is low, condensing temperature of the refrigerant decreases. Therefore,

condenser pressure becomes low. As the boiling temperature (generator temperature) of

the LiBr solution decreases when the condensing pressure is low, the calorific value of

the driving heat source can decrease. This will result in energy savings.

2. The cooling water temperature is too low: It is not acceptable if the temperature of the

cooling water is too low. A lithium bromide solution of a given concentration will

crystallize at a certain low temperature. For example, at a concentration of 65% LiBr, the

absorbent solution crystallizes at a temperature lower than 42°C (108°F), with 60%, at a

temperature lower than 17°C (63°F), and with a concentration of 55%, at a temperature

lower than 15°C (59°F). As the absorbent crystallizes it become a non-flowing solid,

rendering the chiller inoperable. Additionally, crystallization events require cleaning of

the entire system.

3. The cooling water temperature is too high: Some problems occur when cooling water

temperature becomes too high. With the increase of cooling water temperature, the

absorption power of the LiBr solution is degraded. This prevents the machine from

producing the normal chilled water temperature while a higher amount of fuel is

consumed. In order to prevent this, the stability of the cooling water system, preventive

maintenance of the cooling tower system/equipment, and proper water treatment are

essential.

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4. Water treatment of cooling water: Water treatment of cooling water is an important

factor for the VAM. If the water quality is poor, the heat transfer tubes may form a scale

on the interior surfaces in addition to becoming corroded. The heat transfer capability

will decrease, causing abrupt changes in chilled water temperature and a waste of source

energy

Practical Problem

Practical problems typical to water-lithium bromide systems are:

1. Crystallization

2. Air leakage

3. Corrosion

Crystallization

Lithium Bromide absorbent is prone to crystallization. Crystallization is a phenomenon that

causes aqueous solution of LiBr to permanently separate into salt at low cooling water

temperatures. As the absorbent crystallizes, it becomes a non flowing solid, rendering the chiller

inoperable. Currently, modern controls fairly well prevent this from happening; nevertheless, it is

important to have an understanding of the concept.

Crystallization is likely to occur when condenser pressure falls and when there is sudden drop in

condenser water temperature. While reducing condenser water temperature does improve

performance, it could cause a low enough temperature in the heat exchanger to crystallize the

concentrate.

Power failures can cause crystallization as well. A normal absorption chiller shutdown uses a

dilution cycle that lowers the concentration throughout the machine. At this reduced

concentration, the machine may cool to ambient temperature without crystallization. However, if

power is lost when the machine is under full load and highly concentrated solution is passing

through the heat exchanger, crystallization can occur. The longer the power is out, the greater the

probability of crystallization.

Crystallization is avoided by:

Maintaining artificially high condensing pressures even though the temperature of the

available heat sink is low;

Regulating cooling water flow rate to condenser;

By adding additives;

An air purging system is used to maintain vacuum.

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Air Leakage and Maintenance Needs

Lithium Bromide absorption systems operate below atmosphere pressure. Any system pressure

increase due to leakage of air into the system or the collection of non-condensable gases (NCG)

causes a partial pressure that is additive to the vapor pressure of the LiBr-H2O solution. As the

pressure increases, so does the evaporator

temperature.

Air leakage into the machine can be controlled by:

Designing the machine with hermetic integrity and

Routinely purging the unit using a vacuum pump.

Corrosion of Components

Lithium Bromide is corrosive to metals. Corrosion can occur inside the chiller due to the nature

of the LiBr solution or on exterior components due to the heat source used to drive the system.

The corrosive action of the LiBr solution increases with its temperature. In general, as the

number of stages in an absorption system increases the temperature at the first generator also

increases. This implies that special care must be used to combat corrosion in multiple-stage

absorption systems.

As a safeguard, and to have complete protection, a corrosion inhibitor is generally added to the

absorbent and the alkalinity is adjusted. Alcohol, namely octyl alcohol, generally is added to the

system to increase the absorption effect of the absorbent

CHALLENGES IN THE BIOMASS POWER PLANT

Biomass is the renewable energy sources & available in the rural areas of the country in

abundance. These biomass are converted into several gases of high calorific value which is used

in the generation of power at biomass based power plant but the efficiency of these power plant

is quiet low and varies from (10 - 20 %) as compared to thermal power plant of efficiency

varying from (34-40%). The technology used in the conversion of biomass into producer gas or

biogas by the gasifier is required to be modernized and made it effective so as to increase the

efficiency of the biomass based power plant. The gas used in the engine after burning exits as

flue gas containing high amount of thermal energy which is found to be liberated in the

atmosphere increasing the environmental temperature and dissolving the ecological balance.

These high source of liberated energy from the engine is still untapped and can be used for

various other purpose like heating, air conditioning or process cooling. Hence some technology

is required to trap that waste energy and convert it into some useful form hence increasing the

overall efficiency of the system and decreasing the negative impact on the environment.

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INTEGRATION OF SMALLER BIOMASS PLANT & VAM

For improving the efficiency of the rice husk, woody straw based biomass power plant and for

the maximum utilization of the waste heat as exhaust gases, hot water VAM has been clubbed

with the biomass power plant for raising the efficiency and minimizing the waste heat released to

the atmosphere, henceforth helps in saving the ecological balance & improving the overall

efficiency of the system.

The process flow chart of heat and mass balance of rice husk, woody straw and various other

fuel based biomass power plant of different capacity sizes has been studied and on the basis of

that the heat & mass balance of 250 KW capacity rice husk based power plant has been made .

The heat and mass balance of the rice husk based power plant has been done as shown in

annexure-1

The various calculations and formulas involved in the heat and mass balance has been discussed

below:

Energy input into gasifier = GCV of rice husk * mass of the rice husk/hr

Mass of air required for burning = density of air * volume of air

Total energy input into the gasifier = energy of the rice husk biomass

Total mass input into the gasifier = mass of rice husk + mass of the air

Total energy o/p from the gasifier = GCV of producer gas * volume of the gas

Energy lost from the gasifier are in terms of = bio char + energy loss to the surrounding

After exit from the gasifier the producer gas goes to the venturi scrubber where the moisture

present in the gas is separated & the loses are in the form of tar & particulates, condensate water,

circulating cooling water & energy loss to the surrounding.

Energy loss by condensate water = °C of condensate * specific heat * mass

Energy loss by CW = mass of CW* specific heat * temp. difference

After venture scrubber the gas goes into the separation box where loses are in the form of tar &

particulates, then it goes to mist eliminator via the heat exchanger and finally to the engine.

The box diagram of the heat and mass balance of the rice husk based biomass power plant is

given in annexure -2

On the basis of the reference heat and mass balance of 250KW rice husk based power plant, the

efficiency of the various equipments used in the power plant has been identified and a derived

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heat and mass balance of 39.5 KW rice husk based biomass power plant has been calculated

which is shown in annexure-3

The exhaust flue gas is trapped via a heat exchanger in which the water @ 85 °C is heated to

90.6 °C. this hot water goes to the generator of VAM where it exchanges heat for the heating of

the LIBR solution.

Heat gained by hot water in H.E. = mass of hot water * specific heat* ∆ T

The heat and mass balance of the 5TR vapour absorption machine integrated with the 39.5 KW

rice husk based power plant has been given in annexure-4

The financial modelling of the biomass based power plant has been done and shown in annexure

-5 from which the capital cost of 39.5 KW biomass power plant has been calculated which

comes as 18.61 lakh and the per unit selling cost of electricity is 5.87 Rs/unit

The financial modelling of the VAM has been done and shown in annexure -6, in which the

target costing of the VAM has been calculated which is equal to 0.5 lakh/KW (0.4lakh/KW +

0.1lakh as the capital cost for vapour compression system using grid electricity) cooling energy,

which is the project capital cost for VAM.

Hence the total cost of the VAM of 5 TR refrigeration is calculated, which is equal to 8.50 lakh

TECHNO-COMMERCIAL ANALYSIS & CALCULATIONS

For cold storage system:

1TR of cooling consumes 1300We

3550W of cooling consumes 1300We

3.5 unit of cooling consumes 1.3 unit of electrical energy

3.5 unit of cooling requires 4.55 Rs @ 3.50 Rs/unit thermal energy from the

grid

1 unit of cooling requires 1.28Rs

3.55 unit of cooling capacity capital cost of the cold storage is equal to

30000Rs

1 unit capital cost = 30000/3.55 = 8450 Rs

Hence for the selling of cooling energy by VAM @ 1.28Rs/unit, the target costing of the VAM

has been calculated as 0.395lakh/KW as shown in annexure-6. This compensate the electrical

76

energy part of the cold storage, and hence the capital cost/KW of cold storage has been added to

the VAM capital cost for the final project capital cost/KW of VAM which is equal to =

(0.395+.08450) = 0.4795 lakh/KW

Hence, if any vendor provides VAM at less then the calculated project cost then it should be

accepted else rejected.

For commercial aspect and its viability, TERI has developed a technology on 5TR VAM which

is available commercially, hence the project cost calculated for the 5TR VAM =

0.4795lakh/KW*17.7378KW = 8.50 lakh. So, if the 5TR VAM is available in the market at less

than 8.50 lakh , then the project is viable for commercial selling of the cooling energy using 39.5

KWe producer gas engine available in the market.

FINDINGS & CONCLUSION

The various technologies available in the market for biomass gasification and biomass power

generation and VAM has been found and the exhaust of the biomass power plant flue gas has

been trapped and utilized for the cooling purpose by using VAM and the target costing of the

VAM has been calculated for making the project of combined heat and power viable in the

market. The calculated project cost of VAM for 5TR is equal to 8.50 lakh. For different capacity

biomass plant, different capacity of VAM can be installed for improving the efficiency which

can be calculated very easily by the heat and mass balance.

FUTURE SCOPE

Technology assessment of other energy sources can be done such as in solar, geothermal, and

other renewable energy sources and scope for combined heat and power with those technology

can be assessed for further improvement in the effective utilization of the waste energy.

Efficiency improvement can also be done in the biomass power plant generation by tapping

waste energy at various points other than the energy of the exhaust flue gas.

BIBLIOGRAPHY

www.teriin.org

www.iisc.ernet.in/

www.thermax.com

http://indiacoldchainshow.com/contact/

ANNEXURE