bio-energy transport fuel generation from municipal solid wastes and sewage sludge

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Bio Energy Generation Generation of Transport Energy from Biodegradable

Municipal Solid Waste and Sewage Sludge

EG400 ADVANCED ENERGY SYSTEMS ENGINEERING GROUP 6 DANIEL BRESLIN, JONATHAN CONWAY, NIALL RABBITTE AND COLM FLYNN

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Table of Contents Table of Figures ....................................................................................................................................... 3

Table of Tables ........................................................................................................................................ 3

Table of Equations .................................................................................................................................. 4

Abstract ................................................................................................................................................... 5

Introduction ............................................................................................................................................ 6

Literature review ..................................................................................................................................... 7

Transport in Ireland ............................................................................................................................ 7

Resources in Ireland ............................................................................................................................ 8

Why Biodegradable Municipal Solid Waste and Sewage Sludge ........................................................ 9

Bio Gas Plants .................................................................................................................................... 10

Bio-Methane Plants .......................................................................................................................... 12

Chemical Processes and Breakdown ............................................................................................. 12

Biodegradable Municipal Solid Waste and Sewage Sludge to Bio Gas ......................................... 12

Bio-Methane Plant Design ............................................................................................................ 13

Biogas Refinery Process ................................................................................................................ 15

Overall Bio-Methane Plant Processes ................................................................................................... 18

Modelling Techniques used .................................................................................................................. 19

Matlab as a Modelling Software ....................................................................................................... 19

Matlab Modelling Method ................................................................................................................ 19

Modelling Methods Description ........................................................................................................... 20

Mathematical Model ........................................................................................................................ 20

First Order Differential Model .......................................................................................................... 21

Design Model Constants ................................................................................................................... 22

Molar Mass Calculation .................................................................................................................... 22

Design Model Initial Conditions ........................................................................................................ 23

Design Model Results ............................................................................................................................ 24

Design Model Inputs ......................................................................................................................... 24

Design Assumptions .......................................................................................................................... 24

Design Results ................................................................................................................................... 27

Annual Design results .................................................................................................................... 28

Biogas Refinery ................................................................................................................................. 28

Bio-Methane to Liquid Methane Gas ................................................................................................ 29

Bio-Methane Combustion ................................................................................................................. 31

Model Manipulation and Simulation for different Feed Stock types ............................................... 32

Cost Analysis ......................................................................................................................................... 33

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Capital Expenses ............................................................................................................................... 33

Running costs .................................................................................................................................... 33

Pasteurisation of the Digestate..................................................................................................... 33

Water Scrubbing ........................................................................................................................... 34

Refrigeration of bio-methane ....................................................................................................... 34

Other expenses ............................................................................................................................. 34

Liquefied Methane Sale .................................................................................................................... 35

Life Cycle Assessment ........................................................................................................................... 36

Content ............................................................................................................................................. 36

Project Objectives ............................................................................................................................. 36

Marco-Scale Study ............................................................................................................................ 37

Goal ............................................................................................................................................... 37

Raw Material Transportation ........................................................................................................ 37

Electrical running cost ................................................................................................................... 38

Transportation to services stations .............................................................................................. 38

Methane and Diesel comparison .................................................................................................. 39

Discussion.............................................................................................................................................. 40

Design operation ............................................................................................................................... 40

Design Parameters ............................................................................................................................ 40

Bio-Methane as a Transport Fuel ...................................................................................................... 40

Life Cycle Assessment of the Plant .................................................................................................... 41

Plant Cost .......................................................................................................................................... 41

Conclusion ............................................................................................................................................. 42

References ............................................................................................................................................ 43

Appendix ............................................................................................................................................... 45

Matlab Model Code .......................................................................................................................... 45

Digester Code ................................................................................................................................ 45

Combustion Code .......................................................................................................................... 47

Thermodynamic Tables for Methane Gas ..................................................................................... 48

Project Gantt chart ........................................................................................................................ 50

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Table of Figures Figure 1Total CO2 produced in Ireland per year for each sector (Dineen et al., 2014) .......................... 7

Figure 2 Fuel Breakdown for vehicles in Ireland for 2013 (Dineen et al., 2014) .................................... 7

Figure 3 Tonnes of BMW that Ireland has sent to landfills each year (EPA, 2015) ................................ 8

Figure 4 Sewage Sludge produced in Ireland between 2005 and 2013 (Irish Water, 2014). ................. 8

Figure 5 Biogas facilities in Ireland by feedstock type (Murphy 2015) ................................................. 10

Figure 6 Bio Gas production process .................................................................................................... 11

Figure 7 Anaerobic Digester Design (NRCS, 2009) ................................................................................ 13

Figure 8 Bio-methane Plant processes ................................................................................................. 14

Figure 9 Requirements needed for different applications of biogas/bio-methane (Persson et al.,

2007) ..................................................................................................................................................... 15

Figure 10 Water Scrubbing design process (Persson et al., 2007) ........................................................ 16

Figure 11 Pressure Swing Adsorption design process (Persson et al., 2007) ....................................... 17

Figure 12 Overall Plant Processes ......................................................................................................... 18

Figure 13 Flow diagram of the Matlab Model for the Design............................................................... 19

Figure 14 Flow Diagram of the operation process ................................................................................ 26

Figure 15 Raw biogas produced in the digester over three weeks ....................................................... 27

Figure 16 Breakdown of the production of each component in the raw biogas over three weeks ..... 27

Figure 17 T-s Diagram for methane gas ................................................................................................ 29

Figure 18 Methane Combustion of 1 fuel mole .................................................................................... 31

Figure 19 Diesel Combustion of 1 fuel mole ......................................................................................... 31

Figure 20 Biogas Components produced from Cattle Manure as a feedstock ..................................... 32

Figure 21 Biogas Components produced from SS and BMW as a feedstock ........................................ 32

Figure 22 Rate for the Water Scrubbing process .................................................................................. 34

Figure 23 Cumulative Cash Flow ........................................................................................................... 35

Figure 24 LCA: System boundaries for Production ............................................................................... 37

Figure 25 Total GHG produced over a year’s production of methane ................................................. 38

Figure 26 Comparison of GHG produced for Methane and Diesel production .................................... 39

Table of Tables Table 1 Composition of Bio Gas ............................................................................................................ 12

Table 2 Biomass Feed Stock Percentage Break Down .......................................................................... 20

Table 3 Molar Mass of the Elements .................................................................................................... 22

Table 4 Fuel consumption for cars in Ireland........................................................................................ 25

Table 5 Annual Production Results ....................................................................................................... 28

Table 6 Annual Refinery Production Results ......................................................................................... 28

Table 7 Refrigeration Process ............................................................................................................... 30

Table 8 Modelled Results for certain feedstock types .......................................................................... 32

Table 9 Finances of the Plant ................................................................................................................ 35

Table 10 LCA Emissions Analysis ........................................................................................................... 38

Table 11 LCA Comparison Analysis ....................................................................................................... 39

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Table of Equations Equation 1 Chemical Reaction .............................................................................................................. 20

Equation 2 Constant 1 of the Equation ................................................................................................. 20




Equation 6 First Order Equation for the Feedstock .............................................................................. 21

Equation 7 First Order Equation for Water ........................................................................................... 21

Equation 8 First Order Equation for CO2 ............................................................................................... 21

Equation 9 First Order Equation for Methane ...................................................................................... 21

Equation 10 First Order Equation for Ammonia ................................................................................... 21

Equation 11 Reaction Rate Equation for the Feedstock ....................................................................... 22

Equation 12 Reaction Rate Equation for Water ................................................................................... 22

Equation 13 Reaction Rate Equation for CO2 ....................................................................................... 22

Equation 14 Reaction Rate Equation for Methane .............................................................................. 22

Equation 15 Reaction Rate Equation for Ammonia ............................................................................. 22

Equation 16 Initial Conditions for the feedstock .................................................................................. 23

Equation 17 Initial Conditions for water ............................................................................................... 23

Equation 18 Mass of Methane Produced ............................................................................................. 23

Equation 19 Mass of CO2 Produced ...................................................................................................... 23

Equation 20 Mass of Ammonia Produced ............................................................................................ 23

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Abstract

The main objective of this report was to design a system that creates Transport Energy out of a

biomass feedstock which in this case was determined as Biodegradable Municipal Solid Waste

(BMW) and Sewage Sludge (SS). The process of anaerobic digestion was used in order to create

energy from the biomass feedstock used. Due to anaerobic digestion, a gas called bio-gas is

produced from the biological breakdown of the organic components of the biomass feedstock. This

biogas consists of mainly 50-70% methane and 30-50% carbon dioxide. This gas can then be refined

and cleaned which will give almost 100% methane gas. This methane gas due to its high calorific

value can then be liquefied and used as a transport fuel.

A bio-methane plant was designed based on the amount of BMW and SS created in Connaught. This

gave an annual figure of roughly 93,000 tonnes of combined BMW and SS that could be used as a

feedstock for the bio-methane plant. A mathematical model was created that mimicked the

breakdown of the feedstock in the anaerobic digester over a period of time. This model allowed for a

comprehensive analysis of the amount of biogas that could be produced from digesting the available

feedstock. The modelled design results showed an annual raw biogas production of 36,000 tonnes.

Refinery processes where then used in order to allow the gas to be suitable as a transport fuel. After

refinery processes such as water scrubbing and refrigeration the annual liquid methane gas available

for transport use amounted to 29,700 m3.

From comparing the energy equivalent needed to run a car for a year it was calculated that a total of

12,600 cars could be ran annually off the bio-methane produced from Connaught’s SS and BMW. By

running 12,600 cars for a year on bio-methane it resulted in a 32% decrease in carbon dioxide

released when compared to equivalent number of cars ran on diesel.

From the costing analysis perspective of this design the capital cost required to build this plant was

found to be totalling up on €15 million. The overall running cost for this bio-methane production

facility amounted to roughly €4 million per annum. The expected payback was estimated to be

roughly 9.5 years based Liquefied Methane sales and disregarding government incentives and gate

fees obtained.

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Introduction The main purpose behind this report is to design, model and perform a cost analysis on a bioenergy

conversion and supply system in Ireland. This report will look in detail at the conversion of the

biomass resources, BMW and SS into an energy product suitable to meet the demand of Irelands

transport needs.

Ireland like all developed countries throughout the world produces massive amounts of BMW and SS

per annum. The common practice is to dispose of these through landfills or through agriculture. But

both of these biomass resources can release large amounts of biogas during digestion. Using

processes such as water scrubbing the raw biogas can be cleaned to roughly 98-100% methane gas.

Iron chloride may also be added to the digester in order to remove the hydrogen sulphide from the

gas. The methane gas can then be liquefied and has the ability to power vehicles.

In 1995 Ireland signed a protocol along with the majority of other developed countries to reduce the

amount of waste being sent to landfills as the numbers for each country were increasing rapidly.

Over the following 20 plus years each individual country were given targets to meet for these

reductions.

Ireland has also signed up to the Paris Agreement which is an International agreement of emission

reduction targets. Similar to the landfill protocol, Ireland has been given targets to reduce their

Green House Gas (GHG) emissions. Carbon dioxide (CO2) is a major contributor to Irelands GHG

emissions and it is found that in 2013 the Irish transport industry created the largest quantity of CO2

for Ireland (4,326 ktoe, (Dineen et al., 2014)). Therefore this CO2 figure created by the transport

sector must be looked upon to be reduced. The transport industry is mainly made from the fossil

fuels of diesel (55.3%) and petrol (28.0%) (Dineen et al., 2014), which create large amounts of CO2

when combusted.

Overall if these biomass resources can be used to produce a transport energy it would be of great

benefit to Ireland as the process involves reducing the amount of waste going to landfills while

creating a “clean” and “renewable” fuel to reduce the amount fossil fuels being used in the Irish

transport sector.

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Literature review

Transport in Ireland Over the years Irelands transport sector has increased vastly, between 1990 and 2008 the

energy consumption and CO2 production in the sector nearly tripled. It has now become the

largest sector in Ireland for CO2 production as shown in figure 1. Due to attempts to reduce

CO2 emissions through the Paris agreement and the economic recession these figures

reduced slightly after 2007. However as Ireland begin to rise from the recession again recent

figures suggest another increase in the CO2 production but this time only from the transport

sector. Although new cars registered in Ireland have been more economical, the increase in

cars on the roads has also increased therefore no change has been seen.

Figure 1Total CO2 produced in Ireland per year for each sector (Dineen et al., 2014)

By breaking down the transport sector into the different types of fuels, shows the reliance

Ireland has on the fossil fuels of diesel and petrol. When burned diesel and petrol release

very large amounts CO2. Figure 2 represents this breakdown of fuels used in Ireland during

the 2013 year. It clearly shows this reliance on fossil fuels and shows that not enough

“renewable fuels” are being processed like liquefied petroleum gas (LPG).

Figure 2 Fuel Breakdown for vehicles in Ireland for 2013 (Dineen et al., 2014)

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Resources in Ireland BMW compromises of waste that will rot or degrade biologically. The majority of this waste is usually

garden waste, food waste, timber and paper.

In 1995 the bulk of all of Ireland’s BMW along with the rest of its municipal solid waste (MSW) was

sent to landfills around the country. Due to these extremely large figures of waste going to landfills

not only in Ireland but across Europe an initiative was taken to reduce the amount of waste going to

landfills. Targets of reduction were made for each country and the amount of BMW they were sending

to landfills. So far Ireland has met its first two targets in 2010 and 2013, it is also currently on track to

meet its 2016 target (EPA, 2015). Figure 3 below shows the progression of Irelands BMW figures going

to landfills and how it has met its targets.

Figure 3 Tonnes of BMW that Ireland has sent to landfills each year (EPA, 2015)

Ireland has reduced its figures of BMW in four main ways, prevention and minimisation of BMW,

recycling of paper and cardboard, biological treatment of food and garden waste and the treatment

of residual waste. These four methods are good for the reduction of these wastes but if energy could

be created from this waste it would be extremely beneficial. This is possible by using the BMW to

create a biogas.

SS is similar to BMW and has the ability to be used in the production of energy, as it can be used to

create more of this biogas. This SS is formed during the treatment of wastewater. This SS is most

commonly disposed of by agriculture purposes as a soil conditioner, sent to a landfill or incinerated.

Figure 4 below shows the amount of sludge produced in Ireland between 2005 and 2013.

Figure 4 Sewage Sludge produced in Ireland between 2005 and 2013 (Irish Water, 2014).

0

200000

400000

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2003 2005 2007 2009 2011 2013 2015

Ton

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Sweden has been running a project for over the past 10 years, where they have produced biogas to

run their city buses on (Persson et al., 2007). Some of this biogas is made from SS and BMW. According

to Persson, Sweden was able to produce 1.35 TWh/year of biogas. Sewage treatment plants were the

largest contributors to this figure (44% 594 GWh). This biogas was mostly used for heating purposes

but a proportion of 36% (486 GWh) was upgraded, the majority of this upgraded gas was used as

vehicle fuel. Further study says that approximately 100 GWh/year are currently used in the sector of

vehicle fuel. Therefore it can be concluded biogas created from sewage treatment plants has the

potential to fuel all vehicles in Sweden.

Why Biodegradable Municipal Solid Waste and Sewage Sludge BMW and SS have the potential to become a great future solution to the diminishing fossil

fuel resources. These products are currently being intensely studied to find a way for them

to be used in the production of energy. The two main reasons for this are one the global

energy crisis which is becoming an ever increasing issue as well as the disposal of these

wastes. These were previously the waste that were sent to landfill to be buried, however

this is no longer an option so being able to retrieve some of the energy from this and

therefore decrease the overall volume that has to be disposed of will greatly benefit the

future of the world.

A study done on the energy potential of a city in India saw that the waste had the possibility

of being decreased by 60% to 90% by the processes used to achieve energy return from it.

This study looked at the composition of the MSW which they found to be around 30%

biodegradable and 45% non-biodegradable and an average amount of 25% moisture weight

in the waste (EPA, 2015). Testing of samples got a range of calorific values of the material

which was averaged out and calculated that the city had approximately a power generation

potential of 8073kW per day. This is only a single study in a single city but BMW is seen to

have a great energy potential within it and the emission look to be lower than those of a

similar thermal plant. From this study it’s clear that the potential for energy is there within

the BMW however this study concentrated on simple energy creation and not on how this

potential could be harnessed to be used for energy within transport.

The production of methane is the most researched process for harnessing energy for SS. It

currently is being researched worldwide to improve the pre-treatment processes and the

post-treatment processes. A lot of studies are concentrating on the pre-treatment process

with an end goal of improving the overall performance of the methane extracted from SS.

Currently incineration is one of the highly used methods of disposing of SS along with

treating it and using it for land use on farms.

SS like BMW has the potential to be harnessed for energy through a number of processes

that are mainly at a research stage. There is potential for their use with the energy transport

area with modifications to the current engines and introducing further treatments to make

it transport ready.

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Bio Gas Plants Currently there are 30 anaerobic digesters operating in the Republic of Ireland (Murphy, 2015). 15 of

these plants use industrial bio waste i.e. MSW and SS as a feedstock.

Figure 5 Biogas facilities in Ireland by feedstock type (Murphy 2015)

Anaerobic digestion is the biological breakdown of organic matter in the absence of oxygen to

produce a combustible biogas. This gas can be upgraded and used for the generation of electricity,

heat or use as a transport fuel. Anaerobic digestion is preferable to composting for quantities of

waste exceeding 50 ktonnes per annum. For this analysis, with a large central plant to serve the

Republic, the available resource for composting is roughly 300,000 tonnes. In 2014, 53,543 tonnes

dry solids of SS was generated in Ireland and 150,000 tonnes of MSW (EPA, 2015). 20% of this overall

figure was used for anaerobic digestion (EPA, 2015). Of the 53,543 tonnes of SS collected in 2014,

4,590 tonnes (8.5%) was used for anaerobic digestion (Irish Water, 2014). The overall capacity for

anaerobic digestion in Ireland is currently 60 ktonnes per annum.

There are many different types of anaerobic digestion plants, for example anaerobic lagoons,

continuously stirred, landfill bioreactor, and dry batch. The wet batch continuously stirred tank

reactors (CSTR) is generally seen as the most suited to the co-digestion of MSW and SS (Braun,

2004). This report looks primarily at the wet batch CSTR type digester particularly one to handle

300,000 tonnes per annum. The Agrivert anaerobic digestion plant, a large scale co-digestion plant

with a capacity of 50 ktonnes per annum operates at Cassington, UK. One of the merits of wet batch

anaerobic digestion is the high energy return. For this plant the total primary energy yield is 150 m3

per tonne. It was built at a cost of £10 million (E. Angelonidi, S.R. Smith 2014).

The economic viability of an aerobic digester depends on set up cost and service duration, alternate

fuel prices (e.g. natural gas), the availability of feedstock for the digester, feedstock moisture

content, plant efficiency, and other factors. Natural gas is the main competitor to the synthetic

natural gas market.

Undoubtedly with fossil fuels dwindling, greater awareness of the causes of global warming,

regulations and continuous improvements in technology there will be more anaerobic digesters

built.

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Biomass Feedstock

Biodegradable Municipal Solid

wasteSewage Sludge

Anaerobic Digester

Temperature Control in the

Mesophilic Range

PH Control

Constant Mixing

Biogas Produced

Figure 6 Bio Gas production process

The flow diagram above depicts the normal process for an anaerobic digestion plant producing

biogas.

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Bio-Methane Plants

Chemical Processes and Breakdown Converting MSW and SS into a substance that can be used for transport fuel will be quite a similar

process when converting it to biogas. This process involves using fermentation and anaerobic

techniques to break down the biological waste, which in turn will create biogas. This biogas can then

be converted into bio-methane which can be used for transport Energy.

Utilisation of biogas in the transport sector is a technology with great potential and with important

socio-economic benefits. Biogas is already used as vehicle fuel in countries like Sweden, Germany and

Switzerland (Persson et al., 2007).

Biodegradable Municipal Solid Waste and Sewage Sludge to Bio Gas There are many different types of processes in which BMW and SS are broken down into biogas. The

main technique used is anaerobic digestion which consists of fermenting the waste in an oxygen free

environment.

Composition of Bio Gas

Constituent Composition

Methane (CH4) 55-75%

Carbon dioxide (CO2) 30-45%

Hydrogen Sulphide (H2S) 1-2%

Nitrogen (N2) 0-1%

Hydrogen (H2) 0-1%

Carbon Monoxide (CO) Traces

Oxygen (O2) Traces Table 1 Composition of Bio Gas

Biological break down of organic matter creates biogas through four different phases

Anaerobic Hydrolysis

Polymeric compounds of polysaccharides, fats and proteins are decomposed into monomers. During

this phase the oxygen present in the void spaces of freshly buried waste is rapidly consumed, resulting

in a production of CO2 and often an increase in waste temperature.

Acidogene Phase

Monomers from the first phase result act as a substrate for the bacteria which then produce CO2, H2

and Acids

BMW and SS

Bio GasBio

Methane

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Acetogenetic Phase

This phase involves using the products of the Acidogene phase and converting them into compounds

that can be used by methanogen bacteria which creates the gas methane.

Methanogenic Phase

This phase consists of the methanogen bacteria converting the products of the Acetogenetic Phase

into CO2 and methane. This process is known as Methanogenesis and the product of this phase results

in biogas.

Bio-Methane Plant Design The main factors of the anaerobic digestion plant design are the fermenter, feedstock, gas refinery

and the compressor.

The fermenter is a key part of the anaerobic digestion process. The fermenter allows for the

chemical breakdown of the feedstock into biogas. This break down can only take place in an oxygen

free environment. It is imperative that the fermenter is air tight to allow for maximum biogas

creation.

The fermenters design consists of a large air tight tank with inlets to allow the feedstock to be

pumped in. There is also an agitator which mixes the feedstock to allow for an even breakdown. The

biogas is collected through an opening at the top of the tank where it is then chemically washed and

refined during the refinery process. An opening in the tank also allows for the left over digestate or

substrate to be removed.

Figure 7 Anaerobic Digester Design (NRCS, 2009)

In order to achieve stability and maximum efficiency when it comes to the breakdown of organic

material, many factors can have a large bearing on this. PH and Temperature are the two main

contributors to the rate in which the waste is broken down.

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Bio-Methane Plant Processes

Figure 8 Bio-methane Plant processes

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Fermenter Temperature control

Methane bacteria experiences optimum growth between 38-45°C (mesophilic). Many biogas

facilities operate within this temperature range due to high gas yields and good process stability

(Seai.ie, 2016). Hot water may be passed around through pipes inside of the digester. This then acts

as a heat exchanger and can maintain the mesophilic temperature for maximum bacteria growth

and hence maximum biogas yield.

Fermenter PH Control

The level of pH has an effect on the enzymatic activity in the micro-organisms, since each enzyme is

in activity only in one specific range of pH, and it has its maximum activity with its optimal pH. A

stable pH indicates system equilibrium and digester stability. A falling pH decrease can point toward

acid accumulation and digester instability. Gas production is the only parameter that shows digester

instability faster than pH (Ahring et al., 2003).

Biomass Feedstocks

The biomass feedstock types is the single most influential component for biogas generation. The

chemical breakdown for each feedstock can vary depending on whether its cattle manure, pig

manure, SS or BMW. Most of these feedstocks will have different volatile solids contents, moisture

content as well as chemical composition percentages.

The percentage of carbon in the feedstock plays a major role in determining the output of biogas

from the fermenter. The higher the carbon content in the feedstock the more efficient the anaerobic

process will be in terms of producing methane gas. On the other hand the higher the oxygen content

in the feedstock the lower the efficiency of methane production. This is down to the fact that

anaerobic digestion requires an oxygen free environment and by increasing the oxygen percentage it

has a negative effect on the methane produced.

Biogas Refinery Process Biogas to bio-methane comprises of mainly two main steps, a cleaning process that will remove any

trace elements and components in the gas as well an upgrading process which increases the calorific

value of the substance. This will then create bio-methane which can be used as a transportation fuel.

Figure 9 shows the requirements needed for different applications of biogas/bio-methane. This shows

that for upgrading biogas so it can be used as transportation fuel, all of the trace elements of hydrogen

sulphide (H2S), water and CO2 have to be removed.

Figure 9 Requirements needed for different applications of biogas/bio-methane (Persson et al., 2007)

Most manufacturers of gas engines set maximum limits of halogenated hydrocarbons and siloxanes in

biogas. When using biogas for vehicle fuel both contaminants as well as CO2 need to be removed to

reach a sufficient gas quality

There are many state of the art processes and technologies out there for removing H2S, CO2 and H2O

from biogas.

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Carbon Dioxide Removal

By removing CO2 from the gas the calorific value of the gas can be greatly increased. By increasing the

heating value of the gas this will increase the driving distance and efficiency of vehicles for a specific

gas storage value.

The most common methods for removing CO2 from gas are by adsorption, absorption processes. New

technologies like membrane separation can also be used.

Absorption

Both H2S and CO2 can be removed from biogas using absorption processes.

Water Scrubbing

Water scrubbing involves using water as a solvent that dissolves the CO2 and H2S into the water. This

processes involves compressing the biogas into a column where it is met with a counter flow of water.

The packing’s in the column allow for a large surface of area where the water can react with the biogas.

The biogas is then fed out through the top of the column where it is enriched with methane. As this

gas is now saturated it must be dried in order to remove the water content.

The CO2 rich water is then brought to a flash tank where the pressure is dramatically decreased in

order to release the CO2. Some H2S can be released into the atmosphere which can create emission

problems. Because of this it is recommended that the H2S is removed at an earlier stage for example

during the fermentation process.

Figure 10 Water Scrubbing design process (Persson et al., 2007)

Organic Solvents

Organic solvents can also be used in the same way water was used during the water scrubbing phase.

Organic solvents like polyethylene glycol and mono ethanol amine can be used as replacements for

water. As CO2 and H2S are even more soluble in thee organic substances than water a higher quality

of methane gas is produced. This allows for a smaller refinery when compared to the use of water but

regeneration of the substance involves mixing it with steam which is energy consuming and costly.

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Adsorption

Pressure swing adsorption

Activated carbon can be used or molecular sieves can be used to separate the CO2 from the biogas

using an adsorption technique. Pressure swing adsorption occurs at high pressures, and the material

is regenerated by lowering the pressure. For this technique the H2S must be removed from the gas

before treatment.

This technique involves using pressure vessels in parallel. ‘Regeneration of the saturated vessel is

achieved through stepwise depressurisation. First the pressure is reduced through linking the vessel

with an already regenerated vessel. Then the pressure is reduced to almost atmospheric pressure. The

gas released in this step contains significant amounts of methane and is therefore recycled to the gas

inlet. Finally the vessel is completely evacuated with a vacuum pump. The gas that leaves the vessel

in this step mainly consists of carbon dioxide which is released to the atmosphere’ (Persson et

al.,2007).

Figure 11 Pressure Swing Adsorption design process (Persson et al., 2007)

Membrane Separation

This technique involves creating a pressure difference across a membrane. This membrane will then

allow the H2S and CO2 to cross the membrane as their molecules have a different permeability when

compared to methane. This means that the methane would then be separated from both H2S and CO2.

This process is completed a couple of times until all of the CO2 and H2S are separated from the gas.

This process involves drying and compressing the gas after every occasion it is passed through the

membrane (Perrson et. al, 2007).

Hydrogen Sulphide Removal

As Perrson et al have stated, H2S is mostly removed during the fermentation process and the reason

for this is the fact that it is a highly corrosive substance can cause problems such as corrosion and

plugging of pipes (2007). The most common way of removing H2S from biogas is by dosing the digester

with iron chloride.

Water Removal

When the gas leaves the digestion chamber it is saturated with water vapour. This water vapour must

be removed before the gas can be refined. The most common way of removing water is by drying the

gas is by refrigeration. This process involves compressing (if necessary) the gas and chilling it to about

-40˚C, this allows the water to hit its dew point and condense. The water is then separated from the

gas and in the case of water scrubbing method this water can be recycled and used.

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Overall Bio-Methane Plant Processes

Waste Management Site

Bio Methane Production

Biodegradable MSW Sewage Sludge

Held at Fuel Sites

Digestate Pasteurisation for farm use

Resources produced from farming

LANDFILL

Fertiliser used on farm

Fuel burned in cars

Consumed by human race

Atmosphere

Transport Transport

Transport to Plant

Transport of waste

Goods produced

MSWRecycled

Methanetransported

UnusableWaste

Bought by farners

Used on land

Figure 12 Overall Plant Processes

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Modelling Techniques used

Matlab as a Modelling Software MATLAB is a high-performance language for technical computing. It integrates computation,

visualization, and programming in an easy-to-use environment where problems and solutions are

expressed in familiar mathematical notation. Typical uses include: mathematics, computation,

algorithm development, modelling, simulation, prototyping, data analysis, exploration, visualization,

scientific and engineering graphics, application development, including Graphical User Interface

building (Cimss.ssec.wisc.edu, 2016).

Matlab Modelling Method

% Element composition of

biomass feedstock

Molar mass calculation

Equation Constants calculation

Initial First Order

Condition

First Order Equation

Varying with time

For Loop Set varying with

time

Mass of each component

calculated with time

Results of the gas produced plotted

against time in the digester

Mass of Methane Produced

Combustion Model of

Methane in Air

Mass of CO2 released from

burning the Methane created

Figure 13 Flow diagram of the Matlab Model for the Design

20 | P a g e

Modelling Methods Description

Mathematical Model The purpose of this model was to simulate the biogas production inside an anaerobic digester. This

model allowed for the amount of biogas produced over a period of time to be calculated for a given

input of feedstock. For the purpose of this experiment the feedstock used was SS and BMW

The Phyllis website allowed the composition of both SS and BMW to be found. This gave us an

approximation of the percentages of carbon, oxygen, nitrogen and hydrogen in the feedstock. This

website also allowed the composition percentages of the elements to be tested at different water

content percentages. For the purpose of this experiment both water content percentages for SS and

BMW were set constant at 25%.

A weighted average of both compositions for SS and BMW was calculated. Table 2 shows the

breakdown of the percentage of elements in the biomass feedstock according to the Phyllis

Database for biomass feedstock types.

Biomass Feed Stock Percentage Break Down

Element % Composition

Carbon 38.58%

Hydrogen 4.70%

Oxygen 28.24%

Nitrogen 3.48%

Water 25% Table 2 Biomass Feed Stock Percentage Break Down

The chemical equation used to model the anaerobic digestion process consisted of a simplified

anaerobic process where the feedstock was converted directly to methane, carbon dioxide and

ammonia. Equation 1 depicts the chemical equation used for the model.

CcHhOoNn + (c-(h/2)-(o/2)+(3*n)/4)H2O = (c/2)-(h/8)+(o/4)+((3*n)/8)CH4 + (c/2)+(h/8)-(o/4)-

((3*n)/8)CO2 + nNH3

Equation 1 Chemical Reaction

Where the equation constants are

c1 = (c-(h/2)-(o/2)+(3*n)/4

Equation 2 Constant 1 of the Equation

c2 = (c/2)-(h/8)+(o/4)+((3*n)/8)


c3 = (c/2)+(h/8)-(o/4)-((3*n)/8)


c4 = n


21 | P a g e

This theoretical chemical equation breakdown allows for no losses and gives 100% creation of

biogas. In reality this is not the case and in most cases only 40% of the feedstock is created into

biogas and the later 60% is digestate left over.

For the model the overall production of biogas was set to a real life scenario of 40% to give a more

applicable and accurate biogas and bio methane production.

First Order Differential Model The differential equation allowed the biochemical reaction of the anaerobic process to be calculated

with respect to time. This model was based on previous studies conducted by (Rea, J., 2014).

The reaction rate constant can be calculated from experiment but for this model it was taken from

literature. According to Rea, the kinetic coefficient k was calculated as 1.8𝑥10−6 (𝑚𝑜𝑙

𝐿∗ 𝑡)−1 for an

ideal reaction of BMW conducted in a laboratory (2014).

For this first order model, equations were set up as shown below

𝑑(𝐴)

𝑑𝑡=

𝑑(𝐴)

𝑑𝑡 𝑖𝑛−

𝑑(𝐴)

𝑑𝑡 𝑜𝑢𝑡− 𝑘𝐴𝐵𝑐1

Equation 6 First Order Equation for the Feedstock

𝑑(𝐵)

𝑑𝑡=

𝑑(𝐵)


𝑑(𝐵)

𝑑𝑡 𝑜𝑢𝑡− 𝑐1𝑘𝐴𝐵𝑐1

Equation 7 First Order Equation for Water

𝑑(𝐶)

𝑑𝑡=

𝑑(𝐶)


𝑑(𝐶)

𝑑𝑡 𝑜𝑢𝑡+ 𝑐2𝑘𝐴𝐵𝑐1

Equation 8 First Order Equation for CO2

𝑑(𝐷)

𝑑𝑡=

𝑑(𝐷)


𝑑(𝐷)


Equation 9 First Order Equation for Methane

𝑑(𝐸)

𝑑𝑡=

𝑑(𝐸)


𝑑(𝐸)


Equation 10 First Order Equation for Ammonia

Where A is the biomass input, B is the water content of the biomass, C is the methane produced, D is

carbon dioxide produced and E is the ammonia produced in the reaction.

22 | P a g e

For this model there was no feeding or extraction rates from the digester until fully digested, so this

then simplified the equations into

Design Model Constants For this model the overall densities of both the SS and BMW were combined using a weighted

average approach. This allowed the volume of the waste to be calculated which in turn calculated

the mass of biogas produced with respect to time.

The densities for each feedstock was found from the EPA website and were calculated based on the

values given for BMW and SS.

The chemical equation is based on the Buswell equation. This equation will give the theoretical mass

of each product component of the bio gas.

The quantity of CO2 present in the biogas generally is significantly lower than follows from the

Buswell equation. This is because of a relatively high solubility of CO2 in water and part of the CO2

may become chemically bound in the water phase (de Mes, T.Z.D. et al., 2003).

Molar Mass Calculation

Element Molar Mass (g/mol)

Oxygen 16

Carbon 12

Hydrogen 1

Nitrogen 14 Table 3 Molar Mass of the Elements

The molar mass for the feedstock of the model was calculated by multiplying the composition of the

elements in the feedstock by each elements molar mass. This then allowed the constants for each

product to be calculated using equation 1.

𝑑(𝐴)

𝑑𝑡= −𝑘𝐴𝐵𝑐1

Equation 11 Reaction Rate Equation for the Feedstock

𝑑(𝐵)

𝑑𝑡= −𝑐1𝑘𝐴𝐵𝑐1

Equation 12 Reaction Rate Equation for Water

𝑑(𝐶)

𝑑𝑡= 𝑐2𝑘𝐴𝐵𝑐1

Equation 13 Reaction Rate Equation for CO2

𝑑(𝐷)


Equation 14 Reaction Rate Equation for Methane

𝑑(𝐸)


Equation 15 Reaction Rate Equation for Ammonia

23 | P a g e

Design Model Initial Conditions The models initial conditions comprised of the feedstock in the digester at time equal to zero

seconds, where no biogas is produced.

The initial conditions for the models biomass (A), water content (B), Methane produced (C), Carbon

dioxide produced (D) and Ammonia (E) was as follows

A0 = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑤𝑎𝑠𝑡𝑒

𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒∗𝑜𝑣𝑒𝑟𝑎𝑙𝑙 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒

Equation 16 Initial Conditions for the feedstock

B0 = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡

𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡∗𝑜𝑣𝑒𝑟𝑎𝑙𝑙 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒

Equation 17 Initial Conditions for water

As there was no products created initially then C, D and E were all equal to zero.

Where mass is in grams and volume is in litres.

The above conditions could then be applied to the mathematical model where the overall biomass

volume, mass and water content were known.

As this model calculates the change in concentration of each gas mole per litre, the mass of each of

the products could be calculated at shown below

Mass CH4 = (Ct=x)*Biomass Volume*Molar Mass (C)

Equation 18 Mass of Methane Produced

Mass CO2 = (Dt=x)*Biomass Volume*Molar Mass (D)

Equation 19 Mass of CO2 Produced

Mass NH3 = (Et=x)*Biomass Volume*Molar Mass (E)

Equation 20 Mass of Ammonia Produced

From running the simulation over a period of time, this allowed for the mass of each of the products

to be calculated.

24 | P a g e

Design Model Results

Design Model Inputs Overall accessible mass of biomass waste per week per digester – 601 tonnes

Water content of the waste – 25%

Reaction rate constant (k) – 1.8𝑥10−6 (𝑚𝑜𝑙

𝐿∗ 𝑡)−1

Percentage biogas produced – 40%

Design Assumptions It was decided that the range of the SS and BMW collection would take into account the entire

region of Connacht.

In 2010 a figure was calculated of 625kg of MSW was produced per capita in Ireland (SEAI, 2010).

The Central Statistics Office of Ireland states that the population of Connacht in 2011 was 542,547

(Cso.ie., 2011). Therefore the tonnes available of MSW in Connacht is calculated below:

542547 ×625

1000= 339091.875 𝑇

This figure is the total amount of MSW produced in Connacht per annum. However only a

percentage of this is actually BMW therefore only 30% of this can be used in the process of

fermentation.

Also it is unlikely that all the available BMW will actually be collected due to factors such as people

illegally dumping or burning waste instead of making it available for collection. To include this into

our calculation we have made an assumption that 85% of the BMW will be available to be collected.

Therefore the annual amount of waste coming to the plant should be:

339091.875 × 30% × 80% = 86468.428 𝑇

From Figure 4 from Irish Water states that the total annual amount of SS produced in Ireland is

approximately 62,000 tonnes. As we are only concerned with the region of Connacht, this figure

must be divided by the population of Ireland and multiplied by the population of Connacht to get the

total available SS for the proposed plant as shown below:

62000

4595000× 542547 = 7320.547 𝑇

Now the total amount of BMW and SS is found to be 93,788.975 tonnes. This is the total amount of

waste which can enter the plant per year. Obviously all this will waste will not land on site at the one

time, therefore dividing by the 52 weeks in a year gives us 1,803.634 tonnes per week entering the

site and available to begin the process of fermentation.

To compare how many cars could run off this fuel instead of petrol or diesel the average annual

diesel/petrol consumption per car in Ireland must be calculated. Using figures calculated in 2005 the

below table 4 gives an indication of the amount of litres consumed by a diesel or petrol car in Ireland

as stated by the SEAI. (Seai.ie, 2016)

25 | P a g e

Combined Average Mileage

Fuel consumption Efficiency figure for

new cars

Average annual fuel consumption per car

Diesel 23811 km 6.3 L /100 km 1500 L

Petrol 15966 km 7.2 L /100 km 1150 L

Table 4 Fuel consumption for cars in Ireland

From running the simulation model for 1804 tonnes of feedstock this amounted in an overall feed

stock volume of 1964 m3 of waste. The would then require a square digester size of roughly 12.5 m

cubed which is extremely oversized, costly to run and expensive to build.

Alternatively a rotation digester process could be used. This process allows for smaller sized

anaerobic digesters to be used, but will require nine digesters in order to meet the requirement of

waste each week.

This process will involve dividing each weekly total of waste among three digesters. As there will be

nine digesters and the anaerobic process only lasts for three weeks in each digester can be emptied

and filled again.

Figure 14 depicts the design process for this bio-methane production plant.

26 | P a g e

1 weeks BMW and SS Enters Plant

Feedstock is sorted, shredded and divided

among the first 3 digesters

Digester 1 Digester 2 Digester 3

Refrigeration Stage

Storage Tank

Figure 14 Flow Diagram of the operation process

Week 2

Digester 4, 5 and 6 filled

Week 3


Week 1


27 | P a g e

Design Results The results were calculated for 1 digester over a digestion period of roughly 3 weeks with a feed

stock mass of 601 tonnes.

Figure 15 Raw biogas produced in the digester over three weeks

Figure 15 depicts the raw biogas produced in the digester over a period of roughly three weeks. The

graphs shows how at roughly 1.4𝑥106 seconds the gas has reached almost 98% of its final value of

140 tonnes of raw biogas. As this is the raw biogas produced it has mixtures of methane, carbon

dioxide and ammonia.

Figure 16 Breakdown of the production of each component in the raw biogas over three weeks

28 | P a g e

Figure 16 shows the breakdown of production for each component of the raw biogas. This graph

shows how methane has the largest fraction of roughly about 60% with CO2 at about 31% and

ammonia following with roughly 9%.

From the graph it is clear that there is quite a substantial amount of methane gas produced through

anaerobic digestion in the digester.

Since only pure methane can be used for transport fuel it is clear that there is quite a lot of refining

and cleaning that must take place in order to get rid of both the ammonia and carbon dioxide

percentage in the raw biogas.

Annual Design results

Annual Production for the Anaerobic Process in tonnes

Raw Biogas 36000

Methane content 18200

Carbon dioxide content 15600

Ammonia content 2200 Table 5 Annual Production Results

Table 5 shows the annual production of raw biogas and its constituents for a total of 93,789 tonnes

of combined SS and BMW biomass feedstock.

Biogas Refinery To make the biogas into bio-methane a process called water scrubbing was used. From literature it

was found that this technique was the most common and had a very small percentage of methane

loss. The losses of methane due to this process is roughly 5% (Niesner, J et al., 2013). This was

prorated into our model and the results for our bio-methane production are listed below.

Table 6 Annual Refinery Production Results

Table 6 shows the refinery production of bio-methane after both carbon dioxide and ammonia are

removed due to the water scrubbing process. From a report conducted by the SEAI, the average

annual fuel consumption for diesel cars in Ireland which amounts to 1,500 litres or 0.015 GWh

energy equivalent (Seai.ie, 2016).

The annual energy production for the bio-methane amounted to 17,500,000 m3 or 192.990 GWh

energy equivalent. By equating the energy equivalent of both sets of data for the bio – methane

produced and the average annual energy consumption for a diesel car, this gives a value of roughly

12,600 cars that could be ran on bio-methane.

Fossil Fuel Consumption

kWh MWh GWh

17,500,000 Cubic Meter (m3) 192,990,000 192,990.000 192.990

1,500 Litre (l) 15,248 15.248 0.015

Unit

Bio - Methane annual production

Average annual Diesel consumption per car

Fossil Fuels Quantity

29 | P a g e

Bio-Methane to Liquid Methane Gas A refrigeration cycle will be used in order to lower the temperature of the bio-methane gas to a

liquid for both transportation and use as a transport fuel for cars. This refrigeration cycle consists of

one refrigerator used for 168 hours per week. This means that the refrigerator is running 24/7 in

order to convert the gas into liquid for sale to the service stations. As there are nine digesters in a

working process as described in the design assumptions section this means that there will be one

main refrigerator used in order to fulfil the work process.

Figure 17 depicts the T-s diagram for methane gas. The diagram shows how at atmospheric pressure

methane is a gas at 20°C or 293 Kelvin. Similarly methane at atmospheric pressure transforms into a

compressed liquid at a temperature of -162°C or 111 Kelvin. This gives a clear indication that the gas

does not require compression as it can reach its liquid state and correct temperature according to

Chevron at atmospheric pressure.

Tem

per

atu

re (

K)

Entropy (kJ/kgK)

Saturation Dome Patm

293

3

111

Figure 17 T-s Diagram for methane gas

30 | P a g e

Weekly Refrigeration Cycle

Mass of Bio-Methane per week 241298

Number of Refrigerators 1

Temperature

Pressure kPa

Specific Volume (m3/kg)

Enthalpy kJ/kg

State 1 Methane Gas 20 100 1.9347 627.58

State 2 Liquid Methane -162 100 0.002367 -286.5

Change in Enthalpy kJ/kg 914

Gas Mass flow Rate kg/s 0.3990

Rated Refrigeration Cycle kW 365

Running Hours per week 168

Energy Consumption kWh 61268

Volume of Liquid Gas m3 571

Cost at 0.15c/kWh per Refrigerator € 9,190

Total weekly cost for refrigeration € 27,571

Annual Cost € 1,433,677 Table 7 Refrigeration Process

Table 7 shows the calculated specifications need for the refrigeration cycle. Chevron states that for

liquid natural gas (LNG) must be chilled to a value of -162°C (Chevron Policy, 2016). From viewing the

physical property table for methane gas it showed that at atmospheric pressure the liquid saturation

temperature was in fact -162°C.

The overall weekly refrigeration energy requirement amounts to 61,268 kWh for a 168 hour running

cycle. This is quite a substantial running requirement and will contribute greatly to the running cost

of the bio-methane plant.

31 | P a g e

Bio-Methane Combustion A mathematical model was also created in order to simulate the combustion of the bio-methane

produced when used as a transport fuel. This also allowed the mass of CO2 released into the

atmosphere due to combustion to be calculated.

As stated in previously approximately 12,600 diesel cars could fuelled with bio-methane. From the

mathematical model a value of 2.75 grams of CO2was released per gram of bio-methane fuel

burned. By burning our 17,500,000 m3 or 12,451 tonnes of bio-methane produced this would

amount to approximately 34,240 tonnes of CO2 released.

The CO2 emissions from a burning diesel amount to 2.63 kg per litre of diesel burned (Seai.ie, 2016).

Using this conversion factor and applying it to 12,600 cars, the annual equivalent diesel CO2

emissions amount to 50,000 tonnes. This results in a reduction of 32% when burning methane

instead of diesel for 12,600 cars annually. By burning bio-methane it is clear that there is a significant

decrease in the mass of CO2 emitted into the atmosphere.

The above graphs show the mole fraction of carbon dioxide, water, oxygen and nitrogen due to

changing fuel to air ratios for combustion of one fuel mole of diesel and methane. The average fuel

to air ratio for automobiles is roughly fifteen and a comparison of both fuels will be done on this

basis.

The two main pollutants of fuel combustion area carbon dioxide and nitrogen/nitrogen oxide. These

gases are harmful to the environment and can cause pollution such as smog, global warming and

acid rain.

It can be clearly seen that nitrogen fraction is roughly the same for both types of fuel. The carbon

dioxide fraction is considerably lower for methane than that of diesel. This also shows that

combusting diesel will always create more carbon dioxide when compared to methane.

Overall by replacing diesel with methane or bio-methane as a transport fuel it will have a positive

impact on lowering the amount of carbon dioxide released through combustion.

Figure 19 Diesel Combustion of 1 fuel mole Figure 18 Methane Combustion of 1 fuel mole

32 | P a g e

Model Manipulation and Simulation for different Feed Stock types The model was ran for different types of biomass waste such as cattle manure and pig manure.

These feedstock wastes consisted of different compositions of carbon, nitrogen, hydrogen and

oxygen.

From these results the most bio-methane producing biomass feed stock for anaerobic digestion

could be found.

Biomass Composition %

Element Cattle Manure Pig Manure MSW and Sludge

Carbon 48.39% 43.66% 38.58%

Hydrogen 5.35% 4.18% 4.70%

Nitrogen 9.60% 2.47% 3.48%

Oxygen 25.98% 33.51% 28.24%

Bio-Methane Produced by 1000 tonnes of waste

200,000 m3 180,000 m3 183,000 m3

Table 8 Modelled Results for certain feedstock types

Table 8 compares the biomass composition for BMW and SS against cattle manure and pig manure.

Taking 1,000 tonnes of waste as a constant, figures are calculated for the bio-methane that can be

produced for each waste type. Cattle manure has the potential to create 20,000 m3 more than the

pig manure, and in fact can produce 17,000 m3 more bio-methane than BMW and SS. Therefore

these results show that cattle manure has more potential to produce bio-methane than the pig

manure.

To further compare between the BMW and SS against the cattle manure, graphs of the gas produced

by each against the time taken inside the digester is shown in figures 19 and 20. It is clear to see that

the cattle manure produces a higher amount of gas quicker than the BMW and SS. After one week

Figure 20 Biogas Components produced from Cattle Manure as a feedstock

Figure 21 Biogas Components produced from SS and BMW as a feedstock

33 | P a g e

(0.6𝑥106 seconds), around 130 tonnes of biogas is already produced which is over 90% of the total

that will be produced. Comparing this to using the BMW and SS only over 100 tonnes is produced

which is around 70% of the potential biogas that could be produced.

From table 8 the biomass composition shows that cattle manure has significantly higher values of

carbon, nitrogen and hydrogen along with lower values of oxygen. Due to this it will produce more

bio-methane in comparison to the compositions of pig manure and BMW and SS.

Cost Analysis

Capital Expenses A 50 ktonne capacity anaerobic digester takes 2 years to build (Golkowska et al., 2014). The plant in

this study is designed to handle 94 ktonnes of waste. The estimated build time is 2 years and the

capital cost is for the biogas plant is €14.6 million (Anaerobic Digestion Community Website, 2016).

As discussed previously biogas is not suited for use as a transport fuel and therefore must be

upgraded. A biogas upgrading facility capable of handling 2000m3/h would cost €900,000. The plant

is estimated to have a service life of 30 years.

Running costs One tank holds about 600 tonnes of feedstock. The feedstock from BMW and SS is subject to strict

regulations laid down by the Department of Agriculture as part of Regulation (EC) No 1774/2002 of

the European Parliament and laying down health rules concerning animal by-products not intended

for human consumption. The feedstock must be screened. The material for the digester must be

shredded to a maximum particle size of 12mm. This shredding cost has being included in the overall

running cost.

The biogas can be upgraded to fuel suitable for ICE by reducing the CO2 to below 3.5% and the H2S

content to below 100ppm. This study does not consider sulphur in the model. In reality the biogas

will require desulphurisation. This can be achieved by dosing iron chloride (FeCl3).Iron chloride is

available at a cost of 600 USD/tonne.

Pasteurisation of the Digestate The digestate left over from the AD process has a residual value as N, P and K (Nitrogen, Phosphorus

and Potassium) fertiliser.

‘The treatment costs for the pre-dried solid fraction of digestate ranged from €19 /tonne to

€23/tonne output. These costs may be covered by vending treatment products at a price reaching at

least 34-41% of their potential fertilizing and humus value (PFHV) (ca €55/tonne). Treatment of raw

digestate generates high operating costs (€216-247/tonne output), much higher than the PFHV of

the products (ca €35-51/tonne). For such systems either the treatment has to be financially

subsidized by the authorities or €13-32/tonne input should be covered by the substrate deliverers as

a disposal fee.’ (Golkowska et al., 2014)

34 | P a g e

Water Scrubbing The resulting biogas from the anaerobic digestion process is not suitable for transport fuel. First it

must be purified. One technique is to use water scrubbing. The H2S should be removed prior to

water scrubbing when in the biogas storage tank.

A small amount of methane is lost in the purification process. In the case of water scrubbing it is

about 1-5%. To operate the water scrubber processing 2000m3/h would cost €900,000 assuming a

processing cost of 5c/m3 (Vienna University, 2012).

Figure 22 Rate for the Water Scrubbing process

Figure 22 shows results for certain case studies completed. As our plant is designed to refine up on

2000 m3/h of biogas, this allowed an overall trend to calculated and a running cost could be then

determined for our plant. This annual running cost amounted to roughly 5 ct/m3 of biogas refined.

Refrigeration of bio-methane According to Chevron, liquid natural gas must be stored at a temperature of -162°C (Chevron Policy,

2016). Methane at atmospheric pressure is a liquid at -162˚C, meant that no decompression or

compression of the liquid was required and hence less energy requirement needed in the refinery

process. The annual running cost for a refrigerator to cool the bio-methane to this temperature

would cost €1,433,677.

Other expenses If there were 30 workers earning minimum wage of €9.36 per hour working 40 hours a week, the

total wages would be €585,000 per annum. Other expenses are estimated at €215,000 per annum.

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000 2500

An

nu

al R

un

nin

g C

ost

ct/

m3

Volume of Gas Refined per Hour (m3/h)

Running Cost for Volume of Gas Refined

35 | P a g e

Liquefied Methane Sale The available resource for Connaught is 93,870 tonnes as calculated previously. From the MATLAB

model this would yield 17,500,000m3 of refined bio-methane gas and 29,700 m3 of liquid methane

gas. This volume at atmospheric pressure has an energy content of 192,990MWh. Then the energy

for 1 m3 of bio-methane at atmospheric pressure is 11kWh. This is slightly higher than the range

given in text books of 9.6 to 10.6 kWh.

Assuming a constant sale price over the 30 years of 20 ct/litre of liquid methane gas, the annual

income from the sale of bio-methane would be roughly €5,939,987. The price of 20 ct/litre was

found to be roughly 60 ct/litre for liquid petroleum gas (Mylpg.eu, 2016). As we are using liquid

methane gas we estimated the price per litre to be roughly similar to that of liquid petroleum gas. Of

this 60 ct/litre approximately two thirds of the price was due to government taxes (Dccae.gov.ie,

2016).

Figure 23 Cumulative Cash Flow

Plants Costs and Sales

Capital Construction Cost €14,605,000

Running Cost €977,500

Bio-Methane Upgrading Cost €900,000

Refrigeration Cost €1,433,677

Miscellaneous Cost €800,000

Total Running Costs €4,111,177

Sales Income € 5,939,987 Table 9 Finances of the Plant

Figure 22 and table 9 show both the payback in years as well as the annual sales and running costs.

From figure 22 it can be clearly seen that the payback time is roughly nine years. This is a relatively

quick payback time and after its thirty year life span a profit of roughly €38,000,000. This shows how

profitable anaerobic digestion can be in terms of creating transport fuel.

-€20,000,000

-€10,000,000

€0

€10,000,000

€20,000,000

€30,000,000

€40,000,000

€50,000,000

0 5 10 15 20 25 30

Years

36 | P a g e

From table 9 it is clear that the main annual cost requirement is refrigeration. This is needed in order

to make the gas saleable on the market. If this design just required methane/natural gas production

there would be even more profit available as there would be no need for refrigeration and instead

the gas could be pumped into the national gas grid.

Life Cycle Assessment

Above represents the life cycle of the plant from the raw materials used to manufacture the plants

materials to the construction of the plant right through production, maintenance and the end of life.

Each element of the cycle has a large production of GHG. The cycle however represents that ability

of raw materials to be recycled from the plant and reused.

Content Project Objectives

Macro-scale study

o GHG emissions comparison to diesel.

Discussion

Project Objectives Decided on assessment boundaries.

Carry out a CO2 study for the yearly production of fuel from the plant.

Compare these with the equivalent diesel production.

37 | P a g e

Marco-Scale Study

Goal Assess the GHG emissions associated with a yearly production in the plant.

LCA methodologies: ISO 14040, ISO 14044

System boundaries: Gate to processing to fuel station to car exhaust

Functional unit: tonnes of CO2

Data resources: 2012 Guidelines to Defra / DECC's GHG Conversion Factors for Company Reporting.

Figure 24 LCA: System boundaries for Production

Process of calculating figures for GHG for the production of bio-methane

Raw Material Transportation The average distance the waste travels from three sites across Connacht was measured. Sites in

Sligo, Casltebar and Carrick-on-Shannon gives an average journey length of 109km. By multiplying

the number of journeys needed annually to the plant to facilitate the max waste available for

methane production in Connacht gives 311,740km. This will be the total distance travelled by the

trucks in order to bring the waste to site.

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Electrical running cost By taking the total operational cost of the plant and dividing it by €0.15 the average cost per kilowatt

hour gives the kilowatts used each year.

Transportation to services stations Taking the total tonnes produced of methane to be transported per annum and using the same

average distance to provide the whole of Connacht with methane fuel, we get the number of

kilometres travelled per year to provide the fuel to the consumer

Emissions from cars: Figures taken from Matlab results.

Figure 25 Total GHG produced over a year’s production of methane

Figure 25 is a representation of the figures calculated in table 10. From the chart it is clear the

electrical running cost of the plant is the largest producing factor of GHG in the production of the

production of methane fuel. This high cost results from the refrigeration process as it needs a large

amount of electricity to complete the process. However the electrical running cost in GHG can be

reduced if the plant switches to totally green produced electricity. This would see the emissions

decrease dramatically but the cost of production would increase as the cost of this electricity is

significantly greater.

Product Raw Material transporatation Electrical running of Plant Transport to Service Stations Emmissions from Cars Total GHG per year

Total tonnes CO2e Total tonnes CO2e Total tonnes CO2e Total tonnes CO2e Total tonnes CO2e

Biodegradble MSW

Sewage Sludge

Diesel Na Na 195801 50000

GHG assoicated with yearly production of transport energy from 93700 tonnes of MSW & Sewage Sludge

Comparsion to diesel production to same sites

245801.2852

444218 9830334 153768 34240.0000 10462559

Table 10 LCA Emissions Analysis

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Methane and Diesel comparison Assuming diesel is produced and bought from Saudi Arabia. Taking a rough approximation of the

distance it must travel from there to Dublin port to be 5,408km, where it will then be held and

transported by tankers to Galway. The total litres needed of diesel to accommodate the same

number of vehicles as the methane a year is 18 million litres, dividing this into tankers with a

capacity to transport 30,000 litres and taking the distance from Dublin Port to Galway City as 220

km. This gives a total of 600 trips per year meaning 137,408 total kilometres travelled by the diesel

from production site to fuel stations.

Taking the figures for methane production from the above study to compare the GHG of both

products shows that methane produces less CO2 a year then the diesel equivalent. Also seen from

the chart is the emissions produced by the burning of diesel against the emissions produced by the

burning for methane.

Table 11 LCA Comparison Analysis

Figure 26 Comparison of GHG produced for Methane and Diesel production

From Figure 26 it can be clearly seen from the above bar chart that the GHG emissions produced

from the diesel is greater than that of methane.

Transport to Service Stations Emmissions from Cars Total GHG per year

Total tonnes CO2e Total tonnes CO2e Total tonnes CO2e

Biodegradble MSW

Sewage Sludge

Diesel 195801 50000 245801

188008

Comparsion of Methane and diesel

153768 34240

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Discussion

Design operation The design operation as described in the design section is a process that takes a weekly load of BMW

and SS and distributes it evenly among three digesters. As the time calculated for maximum biogas

production was roughly three weeks this meant that the waste had to fermented for this time. This

is where the other six digesters had to be used in order to meet the weekly waste requirement.

Overall this operation process works well but there is slight problems when it comes to liquefying

the gas to liquefied natural gas or liquefied bio-methane.

The refrigeration process is running 24/7 and has an extremely high energy requirement. This is

down to the 182°C temperature drop it has to meet. In reality the gas should be stored and then

liquefied to help save on the running energy and cost requirement.

For this design the thermal energy requirement for keeping the digesters in the mesophilic range of

40°C was assumed as being met via an external gas fired boiler and because of this there are

increased running costs. In theory a certain percentage of the created biogas or bio-methane could

be fed back to a boiler and used to meet the thermal energy requirement of the plant. This idea was

not part of this project but could be of real importance when considering the running and

operational costs of the plant.

Design Parameters From the design results of the model it is clear that the feedstock type has a significant bearing on

both the quantity of bio-methane produced as well as the time required to fully digest the biomass

feedstock.

It is clear that the greater the amount of carbon percentage in the chemical breakdown of the feed

stock the more biogas produced. From the comparison study of cattle manure and combined BMW

and SS, it was clear that the cattle manure had a lot more potential in terms of bio-methane

production. This was solely due to the high carbon content in the cattle manure when compared to

the BMW and SS. The time required to reach 98% of its final biogas production also took roughly two

thirds of the time of that for the BMW and SS.

Therefore a conclusion can be made that cattle manure has a greater potential in comparison to the

BMW and SS. Theoretically the cattle manure can produce a larger quantity of bio-methane in

roughly one third of the time for the equivalent of that for BMW and SS. This results in lower

operational costs, smaller biogas plants and lower construction costs therefore it may have a huge

potential. Further research into this is definitely worthwhile and may be more beneficial than BMW

and SS.

Bio-Methane as a Transport Fuel It is found that Connacht’s BMW and SS has great potential. The results show that it has the ability to

approximately fuel 12,600 cars from the bio methane liquid produced. Using this “renewable” fuel

would reduce the carbon dioxide production for Ireland. It is calculated that from the 12,451 tonnes

of bio-methane burned, only 34,240 tonnes of carbon dioxide is released. In comparison to the

burning of diesel as a fuel in 12,600 cars, the carbon dioxide released would be in the region of

50,000 tonnes. Therefore changing from a diesel fuel to bio-methane fuel can result in a 32%

decrease in carbon dioxide emissions for the 12,600 cars.

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Life Cycle Assessment of the Plant The LCA shows that the yearly GHG emissions in relation to the plant are mostly due to the electrical

running costs of the plant. Over 95% of the plants yearly GHG emissions are due to electrical running

of the plant. This figure is extremely high and is due to the fact that the electricity is being purchased

from the grid at the cheapest rate of €0.15, this cheap rate of electricity is generated from fossil fuel

plants such as the coal plant in Money Point Co. Clare which produces extremely high values of CO2

when burning coal as a fuel. Although it is possible to obtain the electricity needed to run the plant

from renewable energy sources such as the wind farm in Knockacummer in Co. Cork. Using this

“green electricity” would see a significant decrease in the GHG emissions associated with the plant’s

production of liquefied methane gas. However this “green electricity” comes at a price as the energy

production plants charge extra per kWh in comparison to fossil fuels. This increase will lead to the

plants operational costs being significantly higher, therefore the annual profit being reduced.

As stated previously the refrigeration process to liquefy the methane gas is the largest energy

consumer in the plant. Therefore it could be more beneficial and profitable to introduce a combined

cycle gas turbine (CCGT) and sell electricity directly to the grid instead of liquefying the gas. This

would significantly reduce the GHG emissions and the running cost of the overall plant as the

refrigeration is removed. However the cost of the CCGT plant would need to be taken into

consideration.

Plant Cost It is clear from the cost analysis of this bio-methane production plant that there is a considerable

amount of revenue that can be generated over its lifespan. The single main cost requirement of this

plant is in its liquefying stage. If for example a combined CCGT plant or direct injection of gas into

the grid was used, refrigeration would not be needed and the running costs of the plant would be

drastically reduced.

From a cost perspective a CCGT of roughly 45% efficiency, running on the bio-methane gas produced

would create roughly the same income on sales with no refrigeration cost. This would results in a

faster payback time and increased revenue income over its lifespan.

Currently the Waste Management Regulations 2015 set the Landfill Levy at €75/tonne of waste.

Feedstock sourced from BMW and SS can have a gate fee for disposing of the waste that would have

gone to landfill. This fee of course should be lower than the landfill fee to act as an incentive for

using the anaerobic digestion process facility. This analysis does not consider this fee and if this

design is considered for real life application a gate fee should be included which will considerably

increase the revenue of the plant.

42 | P a g e

Conclusion 99% of Irelands transport industry is dependent on oil. Every year Ireland produces 300 ktonnes of

biodegradable waste. This could reduce our reliance on fossil fuels while diverting waste from

landfills. The waste resource for Connaught can be used to produce 17.5 million standard m3 of bio-

methane, enough to power 12,600 cars.

Several processes were examined in this study to convert this waste to energy. The gasification

process requires materials that can withstand temperatures in excess of 1000°C. Harmful waste

products such as tar, sulphur and ash is produced by this process. However anaerobic digestion is

relatively simple, cheaper to produce and has less harmful waste products than other SNG

processes.

The cost of electricity for refrigeration of the bio-methane can be eliminated if the bio-methane was

used in a CCGT plant (for example).

To run the refrigeration process for this facility it costs €1.5 million. The additional expense of

cooling the bio-methane to a liquefied state was found to not be cost beneficial. In a real world

scenario it would make more sense to sell the gas directly to the gas grid. Replacing the electric

heaters and the refrigeration will reduce the payback time from 7.5 years to 5.5 years.

From the LCA the GHG emissions produced from methane and diesel are investigated. This

comparison looks at the GHG produced during the transport to the service stations and the total

emissions from the 12,600 cars. Both these figures are then totalled and compared. The findings

prove that using BMW and SS reduces the GHG emissions by 57,793 tonnes or a reduction of 24% in

comparison to diesel.

The model is also used to compare different types of biomass, such as cattle manure and pig manure

against the BMW and SS. It is found that cattle manure has the greatest potential from the three as

1,000 tonnes can produce 200,000 m3 of bio-methane, compared to 183,000 m3 for 1,000 tonnes of

BMW and SS waste. The model also shows that the days required inside the digester for cattle

manure is only one week to reach 90% of biogas production, meanwhile it takes the BMW and SS

three weeks to reach a figure in this region.

However there is some limitations to the model used, the kinetic reaction constant rate was taken

from a literature. This figure was found under laboratory conditions, therefore ideal conditions. In

real life scenarios due to human error and varying climate conditions this figure would not be exact

for digesters. This would lead to some inaccuracy in the results of duration in the digester and the

tonnes of biogas produced and comparisons between real life digester figures and the modelled may

be slightly different. Another limitation of the model is a water content of 25% for BMW and SS was

taken at all times, this in theory would not be the case as the composition for each week would be

different due to different compositions of the feedstock arriving to the plant. As seen in the cattle

manure comparison different compositions can lead to less time needed in the digester and more

bio-methane produced. The Buswell equation does not account for the CO2 produced by anaerobic

digestion being dissolved in the water, in reality this is not the case as the majority of the CO2 will be

dissolved in the water. A constant figure from the literature was taken but this will vary in real life

depending on the moisture content of the feedstock at the time of arriving to the plant.

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Appendix

Matlab Model Code

Digester Code % kinetic bacteria growth coefficient k = 1.8*10^-6 ;

% molar masses of each element molar_carbon = 12 ; molar_hydrogen = 1 ; molar_oxygen = 16; molar_nitrogen = 14; overall_atomicmass =

molar_carbon+molar_hydrogen+molar_oxygen+molar_nitrogen;

carbon_percent = 0.3858; hydrogen_percent = 0.047; nitrogen_percent=0.0348; oxygen_percent = 0.2824;

av_weight =

1/((carbon_percent/molar_carbon)+(hydrogen_percent/molar_hydrogen)+(oxygen_

percent/molar_oxygen)+(nitrogen_percent/molar_nitrogen)); % to get molar ratios we divide by molar mass c = (carbon_percent*overall_atomicmass)/molar_carbon ; h = (hydrogen_percent*overall_atomicmass)/molar_hydrogen ;

o = (oxygen_percent*overall_atomicmass)/molar_oxygen ; n = (nitrogen_percent*overall_atomicmass)/molar_nitrogen; water_c=1; % These are the molar masses of each component molar_mass_A = molar_carbon*c + molar_hydrogen*h + molar_oxygen*o +

molar_nitrogen*n; molar_mass_B = 2*molar_hydrogen + molar_oxygen ; molar_mass_C = molar_carbon + 2*molar_oxygen ; molar_mass_D = molar_carbon + 4*molar_hydrogen ; molar_mass_E = molar_nitrogen + 3*molar_hydrogen;

% C_c H_h O_o N_n + c_1*H20 -- c_2*CO2 + c_3*CH4 +c_4*NH3 constant1 = (water_c)*(c-(h/2)-(o/2)+(3*n)/4);%water constant2 = (c/2)-(h/8)+(o/4)+((3*n)/8); % C02 producedc2 constant3 = (c/2)+(h/8)-(o/4)-((3*n)/8); % CH4 producedc3 constant4 = (n); %NH3

N_total = constant1+constant2+constant3+constant4; % Total number of

product moles X_CO2 = constant2/N_total; % Mole fraction of co2 X_CH4 = constant3/N_total; % Mole fraction of ch4 X_NH3 = constant4/N_total; % Masses of each component per mol of Bio Feed m_A = molar_mass_A ; m_B = constant1*molar_mass_B ; m_C = constant2*molar_mass_C ;%co2 m_D = constant3*molar_mass_D ;%ch4 m_E = constant4*molar_mass_E;

% mass in grams, capacity in Litres, volume of reaction in Litres mass_of_waste = 1804*1000*1000;

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mass_of_water = mass_of_waste*0.25 ; density_of_waste = 1.2 ;

density_of_water = 1 ; volume_reaction = (((mass_of_waste/1000)/density_of_waste) +

((mass_of_water/1000)/density_of_water)) ; digester_capacity = volume_reaction+10000; digester_capacity_m3 = digester_capacity*0.001; %Initial Conditions A_0 = mass_of_waste/(molar_mass_A*(volume_reaction*1)) ; B_0 = mass_of_water/(molar_mass_B*(volume_reaction*1)) ; C_0 = 0; D_0 = 0; E_0 = 0; %Initial conditions with time dAdt_0 = -k*A_0*(B_0^(constant1)) ; dBdt_0 = -k*A_0*(B_0^(constant1))*constant1 ; dCdt_0 = k*A_0*(B_0^(constant1))*constant2 ; dDdt_0 = k*A_0*(B_0^(constant1))*constant3 ; dEdt_0 = k*A_0*(B_0^(constant1))*constant4 ; %concentration of each element with time assigning them into a vector tfinal = 2000000 ; t = (1:tfinal) ; A = zeros(1,tfinal) ; B = zeros(1,tfinal) ; C = zeros(1,tfinal) ; D = zeros(1,tfinal) ; E = zeros(1,tfinal) ; % Rate of concentration of each component put into a row vector dA_dt = zeros(1,tfinal) ; dB_dt = zeros(1,tfinal) ; dC_dt = zeros(1,tfinal) ; dD_dt = zeros(1,tfinal) ; dE_dt = zeros(1,tfinal) ; % initial conditions put into the first index of the vectors A(1) = A_0 ; B(1) = B_0 ; C(1) = C_0 ; D(1) = D_0 ; E(1) = E_0 ; dA_dt(1) = dAdt_0 ; dB_dt(1) = dBdt_0 ; dC_dt(1) = dCdt_0 ; dD_dt(1) = dDdt_0 ; dE_dt(1) = dEdt_0 ; % Loop run in relation to time for i = 2:tfinal A(i) = A(i-1) + dA_dt(i-1) ; B(i) = B(i-1) + dB_dt(i-1) ; C(i) = C(i-1) + dC_dt(i-1) ; D(i) = D(i-1) + dD_dt(i-1) ; E(i) = E(i-1) + dE_dt(i-1) ; dA_dt(i) = -k*A(i)*(B(i)^(constant1)) ; dB_dt(i) = -k*A(i)*(B(i)^(constant1))*constant1 ; dC_dt(i) = k*A(i)*(B(i)^(constant1))*constant2 ; dD_dt(i) = k*A(i)*(B(i)^(constant1))*constant3 ; dE_dt(i) = k*A(i)*(B(i)^(constant1))*constant4 ; end

% mass of gas components produced mols_of_c = C*volume_reaction*(0.4*0.2) ;

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mols_of_d = D*volume_reaction*0.4 ; mols_of_e = E*volume_reaction*0.4 ; mass_of_CO2 = (mols_of_c*molar_mass_C)/(1000*1000) ; mass_of_CH4 = (mols_of_d*molar_mass_D)/(1000*1000) ; mass_of_NH3 = (mols_of_e*molar_mass_E)/(1000*1000) ; mass_of_Raw_BioGas =

((mols_of_c*molar_mass_C)/(1000*1000))+((mols_of_d*molar_mass_D)/(1000*1000

))+((mols_of_e*molar_mass_E)/(1000*1000)); Metres_Cubed_Raw=(((mols_of_c*molar_mass_C)/(1000))+((mols_of_d*molar_mass_

D)/(1000))+((mols_of_e*molar_mass_E)/(1000)))/(0.9); water_scrubbing_loss=0.05; Meters_CubedGas=((mols_of_d*molar_mass_D)/(1000)/0.717)*(1-

water_scrubbing_loss); Mass_Bio_Methane = (mols_of_d*molar_mass_D)/(1000*1000)*(1-

water_scrubbing_loss);

% plot data figure(1) plot(t,mass_of_CH4,'b', t, mass_of_CO2, 'r', t, mass_of_NH3,'k') xlabel('Time(seconds)') ylabel('Gas Produced (Tonnes)') legend('CH4 Model' , 'CO2 model','NH3 Model','Raw BioGas Produced') figure(2) plot(t, Meters_CubedGas,'r') xlabel('Time(seconds)') ylabel('Bio-Methane Produced (Cubic Meters)') figure(3) plot(t,Metres_Cubed_Raw,'r') xlabel('Time(seconds)') ylabel('Raw Biogas Produced (Cubic Meters)') figure(4) plot(t,mass_of_Raw_BioGas,'k') xlabel('Time (seconds)') ylabel('Raw BioGas Produced (Tonnes)')

Combustion Code n = 1; % Number of C atoms in fuel(were changed for methane and diesel) m = 4; % Number of H atoms in fuel(were changed for methane and diesel)

a = 1; % Number of fuel moles

b_min = 2; % Minimum number of O2 moles b_max = 16; % Maximum number of O2 moles b_inc = 1; % Increment in number of O2 moles b = [b_min:b_inc:b_max]; % Values of number of O2 moles num_b = length(b); % Number of values of O2 moles

for i=1:num_b ba_ratio(i) = b(i)/a; % Mole ratio of O2 to fuel

% Element balance equations c(i) = a*n; % C balance d(i) = a*m/2; % H balance e(i) = b(i)-a*n-a*m/4; % O balance f(i) = 3.76*b(i); % N balance

% Mole fraction calculation

48 | P a g e

N_total(i) = c(i)+d(i)+e(i)+f(i); % Total number of product moles X_CO2(i) = c(i)/N_total(i); % Mole fraction of CO2 X_H2O(i) = d(i)/N_total(i); % Mole fraction of H2O X_O2(i) = e(i)/N_total(i); % Mole fraction of O2 X_N2(i) = f(i)/N_total(i); % Mole fraction of N2

end Mass_of_CO2_released_perFuelBurned = (44*n)/((12*n)+m);%(grams)/mass of

fuel oxidiesed grams tonnes_of_CO2_released_perFuelBurned =

Mass_of_CO2_released_perFuelBurned/(1000*1000);%fuel in grams tonnes_fuel = 12451; tonnes_released =

(tonnes_of_CO2_released_perFuelBurned*tonnes_fuel)*1000*1000; % Plot results figure(1) plot(ba_ratio,X_CO2,ba_ratio,X_H2O,ba_ratio,X_O2,ba_ratio,X_N2) title('Methane Combustion Mole fractions'); xlabel('Oxygen-Fuel ratio'); ylabel('Mole fraction'); legend('CO2','H2O','O2','N2');

Thermodynamic Tables for Methane Gas

49 | P a g e

50 | P a g e

Project Gantt chart

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