Fundamental oxy-fuel combustion research carried out within the ENCAP project

Transcription

1 Oxy-fuel workshop, Cottbus, 29-3 th November 25 Fundamental oxy-fuel combustion research carried out within the ENCAP project KLAS ANDERSSON Department of Energy and Environment, Chalmers University of Technology

2 ENCAP Oxyfuel Boiler technologies - Participating Organizations Vattenfall AB, Sweden University of Stuttgart, Germany Energi E2 AS, Denmark Chalmers University of Technology, Sweden Mitsui Babcock Energy Limited, UK Siemens Aktiengesellschaft, Germany L Air Liquide, France ALSTOM Power Centrales Steam Power Plant, France ALSTOM Power Boilers SA, France ALSTOM Power Boiler GmbH, Germany RWE Power AG, Germany Public Power Corporation S.A., Greece University of Ulster, United Kingdom

3 Research on combustion fundamentals in Encap University Stuttgart Increased knowledge on fundamentals of combustion behaviour and emission formation/reduction Basic combustion characteristics, data for validation of CFD modeling and to support selection of flue gas treatment technology. coal combustion tests to characterize emission behavior, ash quality, particle temperatures etc under oxyfuel combustion conditions compared to air combustion gas fired tests to identify and characterize differences in flame properties; gas concentrations, temperatures and radiation characteristics, between oxyfuel and air combustion conditions The results and experiences gained to be summarized januari 26 (18 Month) Input to the other partners within the consortium and to continued experimental activities in 1kW and 5 kw test units

4 IVD 2kW coal combustion reactor General caracteristics: Furnace: Ceramic tube Length of furnace: 2,5 mm Diameter: 2 mm 5 electrically heated zones (up to 14 C) Synthetic feed gas mixtures no flue gas recycling Measurements performed with oil-cooled probe introduced from the bottom

5 CHALMERS 1 kw oxy-fuel combustion unit University Stuttgart 1 kw unit Specifically designed for Oxyfuel research Flue gas recycling applied FI FI Pilot burner Cylindrical furnace Direct O2 injection Primary/secondary register air/o2/co2 fan SC FI TI Measurement ports R1, R2...R7 pre-heater mixing point O2/flue gas Wet flue gas recycle FI Dry flue gas recycle FI Air inlet Cylindrical, refractory lined combustion chamber: D = 8 mm H = 24 O2 C3 H 8 Cooling tube 1/4 8 mm 24 mm Flue gas cooler TI TC TC Flue gas condenser PIC TI SC FI Stack gas 7x4 measurement ports along reactor sides Cooling water

6 Test conditions in 2 and 1 kw units University Stuttgart Same test conditions used in both reactors: Three different combustion environments Air as reference case OF 21, same volumetric cond. as for air: 21% O 2 and 79% CO 2 OF 27, similar temperature cond. as for air: 27% O 2 and 73% CO 2 Same stoichiometric conditions in all test set-ups λ = 1.15 Three different fuels tested: Gas (C 3 H 8 ) Lausitz, lignite Kleinkopje, bituminous coal

7 Measurements performed at IVD (Oct 25) Coal combustion characteristics - 2 kw th unit Gas emission behaviour under oxyfuel conditions NO X reduction potential through staging with oxyfuel NO X and SO 2 behaviour under simulated flue gas recycling conditions Particle ignition and combustion particle temperatures of three different size fractions: 9-15 µm, µm, µm Ash and burnout characterisation

8 Gas emissions and temperature profiles: air vs. 27% oxyfuel SO 2, NO X in mg/mj 1 baseline gas temperature gas temp. in C 15 SO 2, NO X in mg/mj 1 27% oxyfuel gas temperature gas temp. in C SO SO 2 4 NO X 6 4 NO X distance from burner in m distance from burner in m

9 Effect of HNO 3 injection on NO X emission NOx in ppm 2, 1,8 1,6 1,4 1,2 1, measured NOx conc calculated NOx conc NOx from HNO3 injection molarity in mol/l

10 Effect of oxyfuel staging on NO X emission University Stuttgart Kleinkopje NO X in mg/mj 4 35 baseline un-staged λ = 1.15 c(no X ) = 382 mg/mj 27% oxyfuel un-staged λ = 1.15 c(no X ) = 322 mg/mj 4 35 NO X in mg/mj λ = λ =.85 λ = λ =.85 λ = λ = residence time in reduction zone in seconds residence time in reduction zone in seconds NO X is given referred to NO 2

11 Measurements performed at Chalmers Flame characteristics: Gas concentration profiles O 2, CO, HC, CO 2 suction probe/online gas analysis Cooling water outlet Heated tube: to prevent condensation Gas suction tube Cooling water inlet 162 mm 4 mm A A Section A-A Ø45,/41,mm Ø33,/29,mm Ø18,/14,mm Ø8,/6, mm 19 mm Temperature profiles suction pyrometer (thermocouple type B, 2K) Cooling water outlet Cooling water inlet A Thermocouple Type B: D=3mm A 2mm Suction inlet flue gas: D=6mm Section A-A Ø45,/41,mm Ø3,/26,mm Ø17,2/13,mm 1,x1, mm Ø13,mm Radiation Intensity profiles Narrow angle radiometer (IFRF type) High broadband reflectance mirror Electronic shutter Collimating tube Cooling water PT-1 Thermopile Cooling water

12 Start-up sequence from air to Oxy-fuel in the Chalmers Unit Stack gas concentrations of O 2 and CO Start from air to oxy-fuel: stabilized conditions after some 4 to 5 hours 3.% Oxygen excess reached 94-95% CO 2 in stack gas O 2 concentration [vol %] Furnace exit concentration CO 2 O CO 2 concentration [vol%] 1 Shift from air to O 2 /CO 2 combustion Time [min]

13 Radial temperature profiles: 215 mm from burner inlet University Stuttgart 16 Gas temperature [oc] Measurement port: R2 215mm from burner Distance from centreline [mm] Profile: centre line to furnace wall Reaction zone Oxyfuel combustion: temperature control by flue gas recycle rate:. OF27 OF 21

14 Radial temperature and radiation profiles Radiation intensity q [kw/m 2 sr] mm from burner Meas. port: R2 Air - q 1 OF 21 - q 1 OF 27 - q 1 Air - T g OF 21 - T g OF 27 - T g Gas temperature T g [ o C] Temperature level of OF 21 case decreases drastically compared to air-fired conditions, but similar radiation intensity. OF 27 case similar temperature levels as for air. Radiation intensity from the flame increases 2-3% Change in emissivity Distance from centreline [mm]

15 Radiation measurements Comparison of measured radiation intensity for Air, OF 21 and OF 27 Determine flame/gas layer emissivity from measurement data gas emissivity (CO 2, H 2 O) with model (Leckner) Deviation form expected results? Other effects on radiative properties in oxy-fuel flames?

16 Mean emissivity Radiation received from flame and wall during measurements with hot background q1 = ε λ Rλ Tgdλ + ε b (1 ε λ ) Rλ Tsdλ + (1 ε b ) ε λ (1 ε λ ) R If ε b is equal to unity the signal can be rewritten as q1 = ε λ RλTg dλ + (1 ε λ ) R λts dλ λtg dλ

17 Mean emissivity Emissivity is assumed grey: q = σεmtmr + σ ( 1 ε m) Ts Schmidt method Three separate intensity measurements from 1. The flame and hot furnace wall, q 1, 2. the flame alone with a cold background target, q 2 3. and the hot furnace wall alone q 3

18 Mean emissivity - furnace cross section OF 27 conditions - T s [ o C] Mean emissivity m = f(ts) Measurement port: R3 Air: ε mh2o OF 27: m ε m Air:T mr OF 27:T mr Mean radiation temperature, Tmr = f(ts) Air case: -ε m =.4 -T s = 65ºC -T mr = 93ºC OF 27 case: -ε m =.52 -T s = 68ºC -T mr = 95ºC Air conditions - T s [ o C]

19 Gas emissivity Using available model by (B. Leckner, 1972) to determine the total gas emissivity according to: ε = ε + ε ε ( CO H O) g CO2 H 2O CO 2 and H 2 O emissivities are treated separately Band overlap correction term Any arbitrary partial pressures of CO 2 and H 2 O can be applied in the model. Maximum error of 5% for H 2 O and 1% for CO 2 emissivities at a temperature above 4 K

20 Gas emissivity Air case Test case: Air OF 27 case Gas emissivity =f(t g ) CO 2 ε CO2 ε H2O ε tot H2 O tot ε tot Gas emissivity =f(tg) Test case: OF ε CO CO ε H2O H2 O ε tot tot Average gas temperature T g [ o C] Average gas temperature T g [ o C] Test case p CO2 p H2O T s [K] L [m] Air,1,14 928,8 OF 27,82,18 953,8

21 Comparison mean and total gas emissivity Gas emissivity, ε g Air case: ε g =.24 T mr = 93ºC (calculated) OF 27 case: ε g =.3 T mr = 95ºC (calculated) Mean emissivity, ε m Air case: ε m =.4 T s = 65 ºC (measured) OF 27 case: ε m.52 T s = 68ºC (measured)

22 Conclusions from gas fired tests Compared to reference tests with air in the 1 kw unit: University Stuttgart The temperature level of OF 21 case drops drastically and leads to a delayed burn-out as detected from HC and O2-profiles The OF 27 case shows similar temperature levels, which together with an increase in O 2 -concentration in the recycled feed gas results in similar combustion intensity and burn-out behavior The radiation intensity of the OF 27 flame increases with about 2-3% despite similar temperature profiles. Increased emissivity not only due to the increased band radiation from CO 2. The soot formation for various oxy-fuel conditions and fuels need to be studied in detail for use in RT-modeling.

23 Conclusions from coal fired tests University Stuttgart Gas emissions: Small decrease in NO X emission rate for OF 27 without flue gas recycle No difference in SO 2 generation Negligleble CO emissions, identical for air and oxyfuel case Oxyfuel staging: Reduction of NO X emission rate equal or better for oxyfuel case compared to air case Ignition behavior: Particle ignition and burnout is accelerated with higher oxyfuel concentrations Temperatures reached for 27% oxyfuel are comparable to those for air Ash quality: Little change in oxyfuel ashes compared to ashes from air combustion

24 Up-coming activities within the ENCAP experimental programme: 1 kw and 5 kw units 1. Burner concepts and design - burner adaptation - start-up/ shut-down procedures 2. Radiation characteristics -radiation measurements coal-firing 3. Burnout and emission behavior - ash sampling - re-circulation vs. NO X /SO 2 behavior 4. Slagging, fouling and fly ash behavior - deposition behavior of the coals - particle load behavior

25 IVD.5 MW th unit modified for oxyfuel operation burner coal + primary air/ gas additional fuel + conveyor air/ gas secondary air/ gas, flue gas recirculation vertical furnace staging gas re-circulated flue gas part-stream O 2 / CO 2 tanks by-pass options ESP stack fabric filter staging gaso2 injection bottom ash SCR Catalyst APH ash three ash hoppers filter ash O 2 / CO 2 mixing

26 CHALMERS 1 kw th unit modified for oxy-coal operation University Stuttgart Modified for coal tests summer 25 Dry, pressurized flue gas as carrier gas Coal feed Coal from pneumatic feed system Direct O2 injection Initial tests with dried lignite (Lausitz) performed autumn 25 FI FI Pilot burner Cylindrical furnace Primary/secondary register air/o2/co2 fan SC FI TI Measurement ports R1, R2...R7 mixing point O2/flue gas pre-heater Wet flue gas recycle FI Dry flue gas recycle Air inlet FI SC Cooling tube 1/4 24 mm TI PIC FI 8 mm Flue gas cooler Fabric Filter TC TC Flue gas condenser TI Stack gas C3 H 8 O2 Dry, pressurized flue gas for dust control and fuel carrier gas Cooling water

27 Oxyfuel pilot testing in phase 2 of ENCAP The Oxyfuel boiler technology subproject will nominate two candidates for pilot testing in phase 2 Phase 2: August 26-March 29 3 MW th Oxyfuel PF plant New-built plant located next to the Schwarze Pumpe power station Investment decision taken by Vattenfall in May 25 1 MW th Oxyfuel CFB plant Based on modifications to an existing test-facility Decision on which of the pilot options that will be financed within the ENCAP project will be taken the next few months