technological parameters in selecting systems to...

Enhancing Capacity – Empowering Nation

New Delhi Jan 2017

Technological Parameters in selecting systems to control emissions in Thermal Power Plants


New Delhi Jan 2017

Environmental Gazette Notification 2015Part A-NOX1. NOx Fundamentals2. Major NOx Reduction Techniques3. SCR Design Features4. SCR Technical Issues5. Modification for SCR and SNCR6. Summary

Part B - SOX1. Purpose of FGD2. Types of FGD3. Wet Limestone based FGD4. BHEL Experience


New Delhi Jan 2017

WaterRequirement(withcoolingtower)

:

:

3.5 m3/Mwh (max.) (current)

2.5 m3/Mwh (> 2017)

TechnologyOptions(Boiler)

: (i) Air‐cooled condenser (ii) Dry bottom ash handling system

Particulatematter :::

100 mg/Nm3 (vintage plants before 31.12.2003)50 mg/Nm3 (2003 – 2016) 30 mg/Nm3 (> 2017)

Technology options : Already available

Sulphur Di‐oxide ::

200 mg/Nm3 (upto 2016)100 mg/Nm3 (> 2017)

Technology options : BAP having collaboration with MHI

NOx :::

600 mg/Nm3 (vintage plants)300 mg/Nm3 (2003 – 2016)*100 mg/Nm3 (> 2017)**

Technology options : *Modification of firing system (to be checked based on existing layout and structural arrangement)** Separate De NOx Plant

Environmental Gazette Notification


New Delhi Jan 2017

Comparison of Emission Norms

World Bank Norms2008

Environmental Protection

Agency, USA2012

EU2012

China The Gazette of India

2016

Particulate Matter mg/Nm3

30 22.5 50 30 30

Sulphur Dioxide (SO2) mg/Nm3

200 160 200 100 100

Oxides of Nitrogen ( NOx) mg/Nm3

200 117 200 100 100

Mercury ( Hg) mg/Nm3 - 0.001 - 0.03 0.03


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NOx Fundamentals– Forms of NOx


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Thermal NOx:

• Combustion process above 1300 deg C form “Thermal Nox” and this process is defined

by Zeldovitch Mechanism

• Formation of thermal NOx depends on oxygen concentration and temperature and

insignificant below 760 deg C

NOx Fundamentals– IntroductionFuel NOx:

• Forms when Nitrogen that is chemically bound in the fuel reacts with oxygen in the

combustion air.

• This process is not significantly temperature dependent but does depend on Air Fuel ratio .

Prompt NOx:

• Forms when Nitrogen in combustion air or fuel reacts with Hydrocarbon radicals

from the combusting fuel or when some of the fuel bound Nitrogen forms HCN. This

process is dependent on fuel rich conditions. - Negligible


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Intensity of various NOX Components in Boiler


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Major NOx Reduction Techniques


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NOX Control using Combustion Process Modification


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Low NOx Burners and Furnace Air Staging

Design features that regulate the aerodynamic distribution and mixing of the fuel and air.


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Furnace Air‐staging

Furnace leakage

OFA, separated

OFA, close coupled

Primary air and Secondary air

• Combustion is made tooccur in two zones• Fuel rich zone near the

flame. (70‐90% air issupplied here)

• Remaining combustionin the low temperaturezone above the flame


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NOx control using Flue Gas Treatment – Post Combustion


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SELECTIVE NON CATALYTIC REDUCTION

CombustionProcess


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SNCR Reaction Equation

Ammonia reaction equation

Reaction for urea

4NO + 2CO(NH2)2 + O2 4N2 + 4H2O + 2CO2

2NO + 2NH3 + (1/2)O2 2N2 + 3H2O


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• In Furnace Post Combustion Control

• Injection in Upper Furnace

• Temperature Range: 900‐1100 deg C

• NOx reduction Range for Utility Boilers ‐ 25 to 50 %

• Urea or ammonia can be used as the reagent.

SELECTIVE NON CATALYTIC REDUCTION


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SNCR Design Temp Window

Source EPA


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SNCR Critical Process Parameters

• Reaction temperature (sp.: furnace temp)

• Residence time (reagent injection location)

• Degree of mixing

• NOx concentration

• Ammonia slip (which is strongly influenced by the ratio of injected reagent to uncontrolled NOx)


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SELECTIVE CATALYTIC REDUCTION


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4 NO + 4 NH3 + O2 4 N2 + 6 H2O2 NO2 + 4 NH3 + O2 3 N2 + 6 H2O

Undesired Parallel Reactions

SO2 + 1/2 O2 SO3

NH3 + SO3 + H2O NH4HSO4

NOX NH3

N2 H2O

Basic Reactions

In an SCR system, vaporised ammonia (NH3) is injected into the flue‐gas stream at about 300–400°C,

which is then passed over a catalyst. The catalyst promotes reactions between NOx and NH3 to form

molecular nitrogen and water vapour.

SELECTIVE CATALYTIC REDUCTION


New Delhi Jan 2017

Option‐1 * :Introduction of Over Fired Air and /or Concentric Firing System without disturbing existing WB

Option‐2 * :Introduction of New WB with additional level Separated Over Fired Air without changing total furnace height.

Option‐3 * :SNCR in boiler to reduce Nox

Option‐4 * :Introduction of SCR

* Can be decided based on the site measured values

Options to reduce NOx emission: Case to Case Basis


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SCR DESIGN PROCESS


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Basic SCR Configurations

HOT-SIDE, HIGH DUST SCR

HOT-SIDE, LOW DUST SCR

COLD-SIDE SCR

NH3

NH3

NH3

BOILERSCR

BOILER

BOILER

SCR

SCR

STA

CK

STA

CK

STA

CK

AIRHEATER

AIRHEATER

AIRHEATER

ELECTROSTATICPRECIPITATOR



DUCT BURNER

FLUE GAS DESULFURIZATION



GAS TO GAS HEAT EXCHANGER

Recommended

Hot ESP technology not successful

Very costly Including GGH


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SCR Process Flow Diagram


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The primary base material of catalyst is titanium dioxide (TiO2), with smaller amounts of othermetal oxides including tungsten oxide (WO2) for thermal support and vanadium pentoxide(V2O5), which is the primary active material.

Two predominant styles of catalyst are used in SCRs ‐ honeycomb and plate type.

Honeycomb catalyst provides the greater surface area of the two designs, but can besusceptible to fly ash fouling.

BHEL has capability to manufacture both honey comb as well as plate type catalysts

HONEY COMB PLATE TYPE

SCR Catalyst


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Comparison Of SCR Reagent Injection Systems

Anhydrous Ammonia

Lowest capital cost

Lowest operating cost

Fewest product deliveries

Highest safety risk

Highest permitting costs

Largest number of regulatory issues

Aqueous Ammonia(19 or 29% by weight NH3)

Moderate capital cost

High energy usage

Largest number of product deliveries

Lower risks than anhydrous

Moderate permitting issues

Moderate regulatory issues

Urea to Ammonia

Highest capital costs

Moderate energy consumption

Moderate product deliveries

Lowest safety risk

Lowest permitting issues

Lowest regulatory issues


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NH3 Slip• NH3 may reduce NOx, oxidize to form NOx, or remain unreacted

and pass through the stack. This unreacted portion is referred to as “NH3 slip”.

• Inadequate flue gas temperature and/or reaction time for SNCR kinetics and mixing of the reagent with flue gas can contribute to an increase in NH3 slip.

• Relatively high concentrations of NH3 slip can react with SO2 and sulphur trioxide (SO3) in the flue gas and form ammonium sulfatesand bisulfates, which, in turn, can cause plugging of the air preheater (APH) passages.

• The potential for APH fouling can be alleviated by maintaining NH3 slip levels between 2 and 5 ppm.


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SCR System : to be installed with associated design modifications

The main SCR components & subsystems are as given below, considering anhydrous ammonia as reagent

Reactor

Catalyst

Ammonia Unloading

Ammonia Storage

Vaporisers

Dilution Fans

Ammonia Distribution

Ammonia Injection

Static Mixing

Turning Vanes

Soot Blowing

Ammonia Tank : to be designed and located as per the IS 4544 code. Tank location to be identified in the existing Power Plant area, considering the existing structures, structures, facilities, pipes, drains, overhead lines etc.

SCR systemNOx Emission of 100 mg/Nm3 at SCR outlet


New Delhi Jan 2017

SCR System : to be installed with associated design modifications

SCR system would reduce the stack outlet NOx emission to 100 mg/Nm3 from 500 mg/Nm3

SCR system Installation : installed in the Flue Gas between Eco & APH. Temperature range in this zoneis optimal for NOx reduction.

SCR system Location : located between Economiser and APH

SCR system Ducting : optimally designed Inlet & Outlet Ducting with suitable internals for uniformdistribution of Flue Gas and proper mixing of the reagent.

SCR system Structurals : adequate & suitable for support and maintenance of the SCR & its allied subsystems.

SCR systemNOx Emission of 100 mg/Nm3 at SCR outlet


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TYPICAL PLANT WITH SCR


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Technical Issues• NOx measurement –Avg or Instantaneous; Location of measurement-

Clarity required in Gazette notification• Type of reagent for SCR to be chosen• Anhydrous Ammonia-Transportation/Handling. • Aqueous Ammonia- Storage space• Urea-Technical grade urea required (Total Nitrogen by weight min.

46%)-IS 1781 ; currently to be imported.• Location of Ammonia storage tank-a)Static and Mobile Pressure

Vessels b)IS4544 c) ANSI K61.1d)IS 662/799


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A) Boiler Back End system : modifications required to accommodate the SCR System.

B) ID system to be modified to handle the additional pressure drop due to the SCR System.

Modification Required for SCR


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Boiler Back End system : modifications required to accommodate the SCR System.

Boiler Back End to be modified to accommodate the SCR & and its sub Systems.

Ducting system : additional Ducting from Eco‐Out to SCR‐In and from SCR‐Out to APH In.

Dampers : additional Biplane Dampers for Isolation & Control. Existing Gates atAPH Flue Gas Inlet would be replaced with Dampers.

Ash Handling system : additional provision of Ash Handling from SCR Inlet & Outlet Ducts.

Air Preheaters : upgraded APH Rotor, Housing, and Elements capable of handling the Flue Gasfrom the SCR. Adequate provision for APH Internals Cleaning.

Supporting Structures : augmented Supporting Structures to support the additional equipment &loads by providing additional / replacement / strengthening structures.

Foundation Design : redesigned and augmented to complement the structural changes.

Boiler Back Endcomplementing the SCR installation


New Delhi Jan 2017

ID system : modifications required to complement the introduction of SCR System.

ID system to be modified to handle the additional pressure drop due to the SCR System.

ID Fan : ID Fans & Motor with higher capacity, to handle the additionalpressure drop in the SCR system and or Cyclone seperator.

Dampers : higher torque actuators for the Dampers in the ID system, to take care ofthe higher negative pressures inside duct due to the addition of the SCR.

Ash Handling system : additional provision of Ash Handling.

Supporting Structures : Supporting Structures to support the additional equipment &loads by providing additional structures.

Foundation Design : redesigned and augmented to complement the structural changes.

ID systemcomplementing the SCR installation


New Delhi Jan 2017

Modification Required for SNCR

• Adequate wall space within the boiler for installation of injectors have to be checked.

• The injectors have to be installed in the upper regions of the boiler, the boiler radiant cavity, and the convective cavity.

• Existing water tubes may need to be moved or removed fromthe boiler housing.

• Adequate space adjacent to the boiler for the distribution systemequipment and for performing maintenance have to be checked.


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Modifications required to meet latest MoEF norms for Nox

Boiler Modification (Furnace / Backpass / Pressure Parts / Circulation system).

Windbox.

Primary & Secondary Air system.

SCR to be installed between Eco Outlet & APH

Additional Ducting & Dampers for the new SCR System to be provided.

APH (with new internals & height) if required.

ID fan & motor with higher capacity.

ID system Dampers to be provided with higher rated actuators.

Structures and its foundation to be done.

Ammonia Unloading and Storage system to be located and designed according to the Code.

NOx Emission reduction Summary


New Delhi Jan 2017

Environmental Gazette Notification 2015

Part A-NOX

1. NOx Fundamentals

2. Major NOx Reduction Techniques

3. SCR Design Features

4. SCR Technical Issues

5. Modification for SCR and SNCR

6. Summary

Part B - SOX

1. Purpose of FGD

2. Types of FGD

3. Wet Limestone based FGD

4. BHEL Experience


New Delhi Jan 2017

PURPOSE OF FGD

The Flue Gas Desulphurization(FGD) is a process of removal of sulphur dioxide(SO2) from the flue gas.

Sulphur content in Indian coal ranges from 0.25 to 0.5 % and in imported coalit is more than 0.6 %.

95 – 96 % of sulphur is converted into SO2

Coal with 0.5 % Sulphur, generates SO2 of range 1500 - 2000 mg/Nm3

SO2 emission results in Acid Rain, corrosion of Buildings & Structures andaffect human health.


New Delhi Jan 2017

Water Requirement(with cooling tower)

:

:

3.5 m3/Mwh (max.) (current)

2.5 m3/Mwh (> 2017)

Technology Options(Boiler)

: (i) Air-cooled condenser (North Karanpura 660 MW)(ii) Dry bottom ash handling system (Durgapur 250 MW)

Particulate matter :

:

:

100 mg/Nm3 (vintage plants before 31.12.2003)50 mg/Nm3 (2003 – 2016) 30 mg/Nm3 (> 2017)

Technology options : Already available

Sulphur Di-oxide :

:

100 mg/Nm3 (> 2017) 200 mg/Nm3 ≥500MW and 600 mg/Nm3 < 500MW (up to 2016)

Technology options : BAP having collaboration with MHI

NOx :

:

:

600 mg/Nm3 (vintage plants)300 mg/Nm3 (2003 – 2016)*100 mg/Nm3 (> 2017)**

Technology options : *Modification of firing system (to be checked based on existing layout and structural arrangement)** Separate De NOx Plant

Environmental Gazette Notification


New Delhi Jan 2017


Part A-NOX

1. NOx Fundamentals





6. Summary

Part B - SOX

1. Purpose of FGD

2. Types of FGD


4. BHEL Experience


New Delhi Jan 2017

TYPES OF FGD

1) Dry FGD (Lime based)

2) Seawater based FGD

3) Wet Limestone based FGD process Reagent : Limestone slurry Most widely used FGD system, having a share of about 80%.


New Delhi Jan 2017


Part A-NOX

1. NOx Fundamentals





6. Summary

Part B - SOX

1. Purpose of FGD

2. Types of FGD


4. BHEL Experience


New Delhi Jan 2017

WET LIMESTONE BASED FGD

• Limestone is used as a reagent for the removal of SO2 from the exhaust flue

gas.

• The SO2 laden flue gas reacts with the limestone slurry sprayed in the

scrubber.

• The removal of SO2 takes place in the Absorber system and Gypsum is

collected as final product.

• Clean gas passes through the mist eliminator to remove moisture, gets

reheated in GGH and then discharged to chimney


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WET LIMESTONE BASED FGD


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DCFS – Double Contact Flow Scrubber


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Critical Equipment of FGD system

Booster Fan

Gas to Gas Heater (GGH)

Slurry Recirculation pump

Wet Ball Mill

Gypsum de-watering system

Oxidation Blower

Mist eliminator

Agitator


New Delhi Jan 2017


Part A-NOX

1. NOx Fundamentals





6. Summary

Part B - SOX

1. Purpose of FGD

2. Types of FGD


4. BHEL Experience


New Delhi Jan 2017

BHEL EXPERIENCE

Successfully commissioned sea water based FGD at Trombay

unit#8 250 MW of MHI Technology in 2010

Supplied Wet Limestone based FGD to NTPC Bongaigaon

3X250MW of Ducon Technology in 2012.

BHEL has signed a TCA with M/s MHPS for Wet FGD

technology in April 2013 valid upto 2028.

Received NOA for Maitree Bangladesh 2X660 MW EPC

contract which includes FGD system.


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Inputs from customer

13

Type of coal used/planned for boiler Customer input

Lime stone sourcing Customer input

Gypsum sales / disposal plan Customer to decide


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FGD Design inputs

• Coal analysis report & Flue gas characteristics

• Lime stone characteristics

• Process water characteristics

• Plot plan


New Delhi Jan 2017

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