Fuel Variability Effects in Pilot Scale Oxy-Combustion Hamidreza G. Darabkhani, (Coal and Cereal Co-Product (CCP) Nigel A. Legrave, Nigel Simms and John Oakey Centre for Energy and Resource Technology (CERT), School of Applied Sciences, Cranfield University, UK 2nd Oxyfuel Combustion Conference Queensland, Australia 12-16 September 2011
Outline Introduction Experimental Set-up Experimental Conditions and Test Matrix of Fuels Gas Emissions (major and minor species) Temperature Profiles Ash Deposition Results Rig Modifications Summary and Future Works 1/20
Introduction Oxy-firing of Pulverised Fuel (PF) in boilers involves the combustion of pulverised coal in a mixture of oxygen and recycled flue gas (RFG). Cranfield University is working with five other universities to improve Britain's knowledge base for oxyfuel combustion technology. Cranfield Contribution to the OxyCap project: • Operation of Oxy-fired Combustor to determine process environments and impacts on ash behaviour as conditions change. • Modelling of the boiler environment based on rig data. • Impact of boiler environment and ash behaviour on corrosion of boiler components. This study presents the results of investigations into the gaseous emissions, temperature profiles and ash deposition from combustion of El-Cerrejon coal mixed with Cereal Co-product (CCP) biomass in a 150 kW th oxy-firing PF combustor. 2/20
Diagram of Multi-fuel Combustion Rig 3/20
Flue Gas Recirculation Ducting and Fan Installation of flue gas recirculation ducting and fan 0.65 m Recycled Flue Gas (RFG) pipe 3.9 m Extra fan & pipe work for flue gas recycle 4/20
Oxygen and CO 2 Supply Systems Installation of Oxygen and CO 2 flow pipes and flow metres (varying O 2 levels) O 2 supply system 5/20
Gas Analyser, Thermocouples and Deposition probes Gas Analyser, Thermocouples and deposition probes for measurement of process environment Protea Unit (ProtIR) A fully assembled deposit capture probe including the ‘K’ type thermocouples connection plugs 6/20
Trace Heating of Pipework To prevent acid/water condensation inside the pipework 7/20
Experimental Conditions Fuel: pulverised El-Cerrejon coal mixed with Cereal Co-product (CCP) RFG: Test matrix of fuels Recirculated without previous (fuels are supplied by E.ON) treatment (e.g. H 2 O or SO x removal) Mix Ratio Percentage: 60-70% Fuel type (wt %) Temperature: 90-130 ⁰ C Case 1: 100:0 ‘El-Cerrejon’ (South Case 2: 80:20 American coal ) + Addition of CO 2 (35 l/min) to feed the Case 3: 60:40 Cereal Co-product pulverised fuel from hopper to chamber Case 4: 20:80 (CCP) Case 5: 0:100 PULVERISED FUEL RATE: 9-12 kg/h Pure O 2 Injection: 175 l/min Major flue gases species including CO 2 , H 2 O and O 2 and the minor gaseous species (e.g. CO, SO 2 , NO, HCl, N 2 O, NO x , etc.) during 1-2 hours of stable combustion will be presented and compared in the full paper. 8/20
Gas Emissions Case 2: COAL 80%+ CCP MAIN SPECIES CONCENTRATION 20% COAL/CCP: 80/20% 45 CO 2 : good concentration (~35%) 40 35 H2O: 16% (almost half of CO2 concentration) Vol % 30 CO2 25 O 2 : high oxygen concentration in the exhaust (~ 8%) H2O 20 O2 CO: medium(~2040ppm) 15 10 SO 2 : higher than air-firing mode (~660ppm) 5 0 N 2 : ingress into the system (~40%) 0 7 14 22 29 36 43 50 58 65 72 79 86 94 101 Time(min) MINOR SPECIES CONCENTRATION MINOR SPECIES CONCENTRATION COAL/CCP: 80/20% COAL/CCP: 80/20% (without CO) 12000 1400 1200 CO 10000 SO2 SO2 1000 N2O N2O 8000 NO NO 800 ppm ppm HCl HCl 6000 NO2 NO2 600 CH4 CH4 4000 400 2000 200 0 0 0 7 14 22 29 36 43 50 58 65 72 79 86 94 101 0 7 14 22 29 36 43 50 58 65 72 79 86 94 101 Time(min) Time(min) 9/20
Gas Emissions during the burner operation MAIN SPECIES 40.00 64.5%RFG 35.00 64.8%RFG CO2 100% COAL 59.3%RFG 30.00 CO2 80% COAL- 20% CCP 65.5%RFG CO2 60% COAL- 25.00 40% CCP 70.2%RFG CO2 20% COAL- Vol % 80% CCP 20.00 CO2 100% CCP H2O 100% COAL 15.00 H2O 80% COAL- 10.00 20% CCP H2O 60% COAL- 40% CCP 5.00 H2O 20% COAL- 80% CCP H2O 100% CCP 0.00 0 4 7 11 15 18 22 25 29 32 36 40 43 47 Time(min) 10/20
Temperature profile in the vertical chamber IN FURNACE TEMPERATURE 900 850 800 Temperature (°C) 750 700 650 Vertical chamber 80% COAL-20% CCP Vertical chamber 60% 600 COAL-40% CCP Vertical chamber 20% 550 COAL-80% CCP Vertical chamber 100% CCP 500 0 2 3 5 7 8 10 12 13 15 17 18 20 22 23 25 27 28 30 32 33 35 37 38 40 42 43 45 47 48 Time(min) 11/20 Trend to achieve lower temperature when increasing the content of CCP
Gas Emissions vs. Fuel Type MAIN SPECIES (Average) 40 H2O MAIN SPECIES. 35 CO2 • CO 2 the trend of CO 2 and fuel fed is the same (except in O2 30 case 1) 25 • O 2 no much effects related to fuel feeding (due to O 2 %Vol 20 adjustments during the experiments) • H 2 O concentration increases by increasing the percentage 15 of CCP in the fuel composition. 10 5 So 2 concentration dramatically decreases by adding more CCP 0 into the fuel mixture. CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 100%COAL 80%COAL-20%CCP 60%COAL-40%CCP 20%COAL-80%CCP 100%CCP MINOR SPECIES MINOR SPECIES CO NO (Average) (Average) 18000 800 NO NO2 NO2 16000 N2O 700 N2O SO2 14000 SO2 600 HCl HCl 12000 500 CH4 CH4 10000 ppm ppm 400 8000 300 6000 200 4000 100 2000 0 0 CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 100%COAL 80%COAL-20%CCP 60%COAL-40%CCP 20%COAL-80%CCP 100%CCP 100%COAL 80%COAL-20%CCP 60%COAL-40%CCP 20%COAL-80%CCP 100%CCP 12/20
Ash Deposition Case 1: COAL 100% Deposits from the ceramic sections of the three deposition probes with surface temperatures of 700 °C (probe 1), 600 °C (probe 2) and 500 °C (probe 3) were collected after combustion runs. Oxy-firing deposition - 100% El Cerrejon - Elemental Analysis (RFG 70.2%) Probe 1- top Probe 1- side Probe 1 underside Probe 2 - top Probe 2- side Probe 2 - underside Probe 3- top Probe 3- side Probe 3 - underside 100 10 Element (Wt %) 1 0.1 O Na Mg Al Si Cl P S K Ca Ti Fe Cu 13/20 Element
Ash Deposition (probes at 500, 600 and 700 C) Higher K content in case 5 compared to case 1, (as expected from the ash composition analyses of the parent fuels) For several elements, their presence depend of the location of the deposits more than the type of fuel used (e.g. Si, S) Probe 3-Top 60 Distribution of elements: 50 Main: P, Si, K, Al, Fe CASE 1 100%COAL Medium: S , Ca, P 40 CASE 2 Minor: Na , Mg, Ti, Cu, Cl, Pt % (Weight) 80%COAL-20%CCP CASE 3 30 60%COAL-40%CCP CASE 4 20%COAL-80%CCP 20 CASE 5 100%CCP 10 Probe 3-Top 0 14/20 O Na Mg Al Si P S K Ca Ti Fe Cu Cl Pt Element
Ash Deposit Composition Oxy-firing vs. Air-firing • Comparing air and oxy-firing, the deposit S contents do not follow the levels expected from simple mixing of the fuel ashes, indicating that complex interactions are taking place. • The ashes generated may have more acid nature and the acid gases in the boiler also higher than in air-firing and both are influenced by recycle rate. • Further work is required to understand the interactions. Probe 1-Top 60 50 OXY-FIRING 40 100%COAL % (Weight) AIR-FIRING 100%COAL 30 OXY-FIRING 80%COAL-20%CCP 20 AIR-FIRING 80%COAL-20%CCP 10 0 O Na Mg Al Si P S K Ca Ti Fe Cu Cl Pt Ni 15/20 Element
New Rig Modifications: 1- Installation of an Axial Air Swirler at the Air Inlet Port • Swirler served to create a toroidal flow reversal that entrained and recirculated a portion of the hot combustion products to mix with the incoming air and fuel. • This will help to improve the burning efficiency and as a result the effective flame temperature and also to drag the flame itself closer to the fuel nozzle (as it is in air firing). Main Flow Region 16/20 Recirculation *Gas Turbine Combustion- Region Lefebvre
2 - Sealed RFG Fan • Despite the efforts consumed to resolve the problem, some air leakage still exists mainly from the recirculation fan box. • The new gas tight fans with HT grease lubricated and double lip seal at shaft entry is fitted in the near future. • The Capsis system is prepared to measure the acid dew point of the recycled flue gases. Capsis Box Gas Tight Capsis RFG Fan Probe Exhaust Fan 17/20
3- Improved Fuel Feeding System A gas tight and accurate fuel feeding system is under construction which will help to prevent the blockage in the feeding pipe and also the ingress of air into the rig Venturi Gaseous fuel feed pipe Pulverised coal feed pipe CO 2 supply hose Pilot flame input port
4- The Primary Oxygen Line • A primary line of oxygen is installed in order to introduce excess oxygen to the burner to improve the burning efficiency and obtaining a higher effective flame temperature. • This primary O 2 will be introduced through a venturi attached to the pulverised coal feed hopper. Recycled Flue Gas Dry Recycle Wet Recycle Secondary O 2 Flow Oxy xy-Fu Fuel CO 2 Rich Flue Gas Combus bustor or CO 2 + O 2 Primary Flow Water and Sox Pulverised Removal Fuel Flow diagram of the Cranfield oxy-fuel pulverised fuel fired combustor (red: ongoing modifications) 19/20
Recommend
More recommend
