technological parameters in selecting systems to...
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Enhancing Capacity – Empowering Nation
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Technological Parameters in selecting systems to control emissions in Thermal Power Plants
Enhancing Capacity – Empowering Nation
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
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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
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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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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
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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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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
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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 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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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
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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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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
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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
ELECTROSTATICPRECIPITATOR
ELECTROSTATICPRECIPITATOR
DUCT BURNER
FLUE GAS DESULFURIZATION
FLUE GAS DESULFURIZATION
FLUE GAS DESULFURIZATION
GAS TO GAS HEAT EXCHANGER
Recommended
Hot ESP technology not successful
Very costly Including GGH
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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
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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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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
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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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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
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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
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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
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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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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
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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
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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
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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.
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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
Enhancing Capacity – Empowering Nation
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
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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%.
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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
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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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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
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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
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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