Enhancing Capacity Empowering Nation. Technological Parameters in selecting systems to control emissions in Thermal Power Plants

Transcription

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

2 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 Enhancing Capacity Empowering Nation Part B - SOX 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

3 Environmental Gazette Notification Water Requirement (with cooling tower) Technology Options (Boiler) Particulate matter : : : : : 3.5 m 3 /Mwh (max.) (current) 2.5 m 3 /Mwh (> 2017) : (i) Air cooled condenser (ii) Dry bottom ash handling system Technology options : Already available Sulphur Di oxide : : 100 mg/nm 3 (vintage plants before ) 50 mg/nm 3 ( ) 30 mg/nm 3 (> 2017) 200 mg/nm 3 (upto 2016) 100 mg/nm 3 (> 2017) Technology options : BAP having collaboration with MHI NOx : : : 600 mg/nm 3 (vintage plants) 300 mg/nm 3 ( )* 100 mg/nm 3 (> 2017)** Technology options : *Modification of firing system (to be checked based on existing layout and structural arrangement) ** Separate De NOx Plant

4 Comparison of Emission Norms World Bank Norms 2008 Environmental Protection Agency, USA 2012 EU 2012 China Particulate Matter mg/nm 3 Sulphur Dioxide (SO 2 ) mg/nm 3 Oxides of Nitrogen ( NOx) mg/nm 3 Mercury ( Hg) mg/nm The Gazette of India 2016

5 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 Enhancing Capacity Empowering Nation Part B - SOX 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

6 NOx Fundamentals Forms of NOx

7 NOx Fundamentals Introduction Fuel 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. 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 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

8 Intensity of various NOX Components in Boiler

9 Environmental Gazette Notification 2015 Part A-NO X 1. NOx Fundamentals 2. Major NOx Reduction Techniques 3. SCR Design Features 4. SCR Technical Issues 5. Modification for SCR and SNCR 6. Summary Enhancing Capacity Empowering Nation Part B - SO X 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

10 Major NOx Reduction Techniques

11 NOX Control using Combustion Process Modification

12 Enhancing Capacity Empowering Nation Low NOx Burners and Furnace Air Staging Design features that regulate the aerodynamic distribution and mixing of the fuel and air. New Delhi Jan 2017

13 Furnace Air staging Enhancing Capacity Empowering Nation Combustion is made to occur in two zones Fuel rich zone near the flame. (70 90% air is supplied here) Remaining combustion in the low temperature zone above the flame OFA, separated OFA, close coupled Primary air and Secondary air Furnace leakage

14 NOx control using Flue Gas Treatment Post Combustion

15 SELECTIVE NON CATALYTIC REDUCTION Combustion Process

16 SNCR Reaction Equation Enhancing Capacity Empowering Nation Ammonia reaction equation 2NO + 2NH 3 + (1/2)O 2 2N 2 + 3H 2 O Reaction for urea 4NO + 2CO(NH2) 2 + O 2 4N 2 + 4H 2 O+ 2CO 2

17 SELECTIVE NON CATALYTIC REDUCTION In Furnace Post Combustion Control Injection in Upper Furnace Temperature Range: deg C NOx reduction Range for Utility Boilers 25 to 50 % Urea or ammonia can be used as the reagent.

18 SNCR Design Temp Window Enhancing Capacity Empowering Nation Source EPA

19 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)

20 SELECTIVE CATALYTIC REDUCTION

21 SELECTIVE CATALYTIC REDUCTION In an SCR system, vaporised ammonia (NH3) is injected into the flue gas stream at about C, which is then passed over a catalyst. The catalyst promotes reactions between NOx and NH3 to form molecular nitrogen and water vapour. NO X NH 3 Basic Reactions 4 NO + 4 NH 3 + O 2 4 N H 2 O 2 NO NH 3 + O 2 3 N H 2 O Undesired Parallel Reactions SO 2 + 1/2 O 2 SO 3 N 2 H 2 O NH 3 + SO 3 + H 2 O NH 4 HSO 4

22 Options to reduce NOx emission: Case to Case Basis 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

23 Environmental Gazette Notification 2015 Part A-NO X 1. NOx Fundamentals 2. Major NOx Reduction Techniques 3. SCR Design Features 4. SCR Technical Issues 5. Modification for SCR and SNCR 6. Summary Enhancing Capacity Empowering Nation Part B - SO X 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

24 SCR DESIGN PROCESS Enhancing Capacity Empowering Nation

25 Basic SCR Configurations Enhancing Capacity Empowering Nation HOT-SIDE, HIGH DUST SCR BOILER NH 3 SCR AIR HEATER ELECTROSTATIC PRECIPITATOR FLUE GAS DESULFURIZATION STACK Recommended HOT-SIDE, LOW DUST SCR BOILER NH 3 ELECTROSTATIC PRECIPITATOR SCR AIR HEATER FLUE GAS DESULFURIZATION STACK Hot ESP technology not successful COLD-SIDE SCR BOILER AIR HEATER ELECTROSTATIC PRECIPITATOR FLUE GAS DESULFURIZATION GAS TO GAS HEAT EXCHANGER STACK Very costly Including GGH DUCT BURNER NH 3 SCR

26 SCR Process Flow Diagram Enhancing Capacity Empowering Nation

27 SCR Catalyst Enhancing Capacity Empowering Nation The primary base material of catalyst is titanium dioxide (TiO2), with smaller amounts of other metal 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 be susceptible to fly ash fouling. BHEL has capability to manufacture both honey comb as well as plate type catalysts HONEY COMB PLATE TYPE

28 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 NH 3 ) 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

29 NH3 Slip Enhancing Capacity Empowering Nation NH 3 may reduce NOx, oxidize to form NOx, or remain unreacted and pass through the stack. This unreacted portion is referred to as NH 3 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 NH 3 slip. Relatively high concentrations of NH 3 slip can react with SO 2 and sulphur trioxide (SO 3 ) in the flue gas and form ammonium sulfates and bisulfates, which, in turn, can cause plugging of the air preheater (APH) passages. The potential for APH fouling can be alleviated by maintaining NH 3 slip levels between 2 and 5 ppm.

30 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. Enhancing Capacity Empowering Nation SCR system NOx Emission of 100 mg/nm3 at SCR outlet

31 SCR system NOx Emission of 100 mg/nm3 at SCR outlet SCR System : to be installed with associated design modifications SCR system would reduce the stack outlet NOx emission to 100 mg/nm 3 from 500 mg/nm 3 SCR system Installation : installed in the Flue Gas between Eco & APH. Temperature range in this zone is optimal for NOx reduction. SCR system Location : located between Economiser and APH SCR system Ducting : optimally designed Inlet & Outlet Ducting with suitable internals for uniform distribution of Flue Gas and proper mixing of the reagent. SCR system Structurals : adequate & suitable for support and maintenance of the SCR & its allied sub systems.

32 TYPICAL PLANT WITH SCR Enhancing Capacity Empowering Nation

33 TYPICAL PLANT WITH SCR Enhancing Capacity Empowering Nation

34 TYPICAL PLANT WITH SCR Enhancing Capacity Empowering Nation

35 Environmental Gazette Notification 2015 Part A-NO X 1. NOx Fundamentals 2. Major NOx Reduction Techniques 3. SCR Design Features 4. SCR Technical Issues 5. Modification for SCR and SNCR 6. Summary Enhancing Capacity Empowering Nation Part B - SO X 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

36 Technical Issues Enhancing Capacity Empowering Nation 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

37 Environmental Gazette Notification 2015 Part A-NO X 1. NOx Fundamentals 2. Major NOx Reduction Techniques 3. SCR Design Features 4. SCR Technical Issues 5. Modification for SCR and SNCR 6. Summary Enhancing Capacity Empowering Nation Part B - SO X 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

38 Modification Required for SCR 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.

39 Boiler Back End complementing the SCR installation 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 at APH 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 Gas from 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.

40 ID system complementing the SCR installation 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 additional pressure drop in the SCR system and or Cyclone seperator. Dampers : higher torque actuators for the Dampers in the ID system, to take care of the 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.

41 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 from the boiler housing. Adequate space adjacent to the boiler for the distribution system equipment and for performing maintenance have to be checked.

42 Environmental Gazette Notification 2015 Part A-NO X 1. NOx Fundamentals 2. Major NOx Reduction Techniques 3. SCR Design Features 4. SCR Technical Issues 5. Modification for SCR and SNCR 6. Summary Enhancing Capacity Empowering Nation Part B - SO X 1. Purpose of FGD 2. Types of FGD 3. Wet Limestone based FGD 4. BHEL Experience

43 NOx Emission reduction Summary 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.

44 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

45 PURPOSE OF FGD The Flue Gas Desulphurization(FGD) is a process of removal of sulphur dioxide (SO 2 ) from the flue gas. Sulphur content in Indian coal ranges from 0.25 to 0.5 % and in imported coal it is more than 0.6 % % of sulphur is converted into SO 2 Coal with 0.5 % Sulphur, generates SO 2 of range mg/nm 3 SO 2 emission results in Acid Rain, corrosion of Buildings & Structures and affect human health.

46 Environmental Gazette Notification Water Requirement (with cooling tower) Technology Options (Boiler) Particulate matter : : : : : 3.5 m 3 /Mwh (max.) (current) 2.5 m 3 /Mwh (> 2017) Technology options : Already available Sulphur Di-oxide : : : (i) Air-cooled condenser (North Karanpura 660 MW) (ii) Dry bottom ash handling system (Durgapur 250 MW) 100 mg/nm 3 (vintage plants before ) 50 mg/nm 3 ( ) 30 mg/nm 3 (> 2017) 100 mg/nm 3 (> 2017) 200 mg/nm 3 500MW and 600 mg/nm 3 < 500MW (up to 2016) Technology options : BAP having collaboration with MHI NOx : : : 600 mg/nm 3 (vintage plants) 300 mg/nm 3 ( )* 100 mg/nm 3 (> 2017)** Technology options : *Modification of firing system (to be checked based on existing layout and structural arrangement) ** Separate De NOx Plant

47 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

48 1) Dry FGD (Lime based) 2) Seawater based FGD TYPES OF FGD 3) Wet Limestone based FGD process Reagent : Limestone slurry Most widely used FGD system, having a share of about 80%.

49 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

50 WET LIMESTONE BASED FGD Limestone is used as a reagent for the removal of SO 2 from the exhaust flue gas. The SO 2 laden flue gas reacts with the limestone slurry sprayed in the scrubber. The removal of SO 2 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

51 WET LIMESTONE BASED FGD

52 DCFS Double Contact Flow Scrubber

53 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

54 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

55 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 BHEL has signed a TCA with M/s MHPS for Wet FGD technology in April 2013 valid upto Received NOA for Maitree Bangladesh 2X660 MW EPC contract which includes FGD system.

56 Inputs from customer Enhancing Capacity Empowering Nation Type of coal used/planned for boiler Lime stone sourcing Gypsum sales / disposal plan Customer input Customer input Customer to decide 13

57 FGD Design inputs Coal analysis report & Flue gas characteristics Lime stone characteristics Process water characteristics Plot plan

58