3MW Pilot-Scale Oxy-Fuel Combustion of Victorian Brown Coal

Transcription

1 3MW Pilot-Scale Oxy-Fuel Combustion of Victorian Brown Coal Jian Zhang 1,2, Xiaojiang Wu 3, Yoshihiko Ninomiya 4, Lian Zhang 1, * 1)Department of Chemical Engineering, Monash University, Australia 2) School of Mechanical Engineering, Shanghai Jiaotong University, China 3) R&D Division, Shanghai Boiler Works Ltd., China 4) Department of Applied Chemistry, Chubu University, Japan *: Corresponding author: lian.zhang@monash.edu Sept , Panferrada, Spain

2 Presentation Topics Significance of Victorian brown coal (VBC) R&D of Victorian brown coal Monash 3MW oxy-fuel combustion experiments CFD numerical simulation Conclusions Acknowledgment

3 Characteristics of Victorian Brown Coal (VBC) The single power source in Victoria, Australia, forming backbone of the local Industry. Typical properties: VM (%db): ~50%; Ash (% db): <1 ~ 3%; S (% db): <0.5 %; Moisture (% ar): 50~65 wt%. The CO 2 emission rate of VBC is higher as 1.3 ton-co 2 /MWhelectricity in the existing brown coal air-fired power plant, relative to 0.9 t-co 2 /MWh for the black coal. Fuel type In 2004 Efficiency (tonnes CO 2 -e/mwh sent out) Brown Coal (Hazelwood 2004) 1.58 Brown Coal (Yallourn 2004) Brown Coal (Loy Yang A 2004) Black Coal Gas Co-geneation Wind

4 R&D on Oxy-firing of Victorian Brown Coal Same as black coal, oxy-firing is significant for a GREEN VBC future Basic research supported by ETIS, Victorian Government 2014 Research Consortium: Monash Univ, Shanghai Boiler Works Co Ltd Chubu Univ, Japan, Shanghai Jiaotong Univ, Int l Power Pty Ltd, Energy Australia Pty, Ltd Basic research supported by Australian Research Council (ARC) Pilot-scale (3 MW) by ANLEC R&D, BCIA 2020 Large scale (>30 MW)? Victorian brown coal Target to align with Australian Carbon reduction strategy

5 Research Challenges and Methodologies Abundant tri-atomic moisture in original coal and oxy-firing flue gas; Abundant alkali, alkaline earth metals and iron: cause for slagging/fouling. Issue Tool Measurement Flowsheeting, Technoeconomic analysis Experiments Thermoflex 23 TG-DTA Flat flame burner reactor (FFBR) Drop-tube furnace Wet vs. semi-dry or dried coal Wet vs. dried flue gas recycle C-O 2, C-CO 2 and C-H 2 O kinetics Ignition of wet,semi-wet and dry coal Combustibility and ash formation 3 MW pilot furnace Validification and scale-up test Char/ash Sample Characterisation XRF, ICP-OES XRD, SEM-EDX Mössbauer Spectroscopy Synchrotron XAS Elemental compositions Structure of overall and individual spots Chemical forms of iron-based species Speciation of trace metals (Cr, As) and major (Fe, S)

6 CFD Modelling approach OFA cross section Burner cross section Mesh generation of 3MW pilot-scale boiler Mathematic sub-models: Gaseous turbulence: Realizable k-ε model Particle motion: Random trajectory model Radiation: Discrete ordinate model + refined WSGGM proposed by Yin C.G Devolatilisation : Single reaction model Volatile combustion: Finite-rate/eddydissipation model+ Refined methane (mimic volatiles) oxidation mechanism in CO 2 by Westbrook and Dryer Char combustion: Single-film model with C-O 2, C-CO 2 and C-H 2 O reactions Moisture release: surface and inherent moisture are treat separately

7 Two Probable Oxy-firing Modes for VBC (1) Retrofit of existing power plant Incorporating internal pre-drying: via the use of hot flue gas, and/or integration with supercritical/ultrasupercritical steam condition o C circulated flue gas O 2 from ASU Raw brown coal boiler Condenser Flue gas Wet / semidried coal (moisture 30~40wt%) (2) Purpose-designed greenfield oxyfiring boiler Incorporating external pre-drying: Via the use of low-temp steam/flue gas, and integration with supercritical/ultrasupercritical steam condition. Raw brown coal Low-temp Steam from steam turbine dryer Condensate O 2 from ASU 2 nd gas 1 st gas boiler Flue gas from economiser Dried /airdried coal (moisture 10~25wt%)

8 System Assessment by using Thermoflex MW th supercritical oxy-firing plant with/without external coal drying condenser 2 nd hot flue gas 1 st dried flue gas Process scheme Net LHV efficiency, % External coal dryer Net HHV Efficiency, % Black Coal Bituminous Externally Dried VBC Internally dried VBC Air-firing Oxy-firing 27 Wet VBC existing air-firing 300 MW th boiler Supercritical system subcritical system Wet as-mined VBC: lower efficiency due to moisture evaporation in the boiler; Externally dried VBC with supercritical technology: higher efficiency to offset the ASU Penalty, that is comparable with existing air-firing plant.

9 Quick ignition of Wet vs Dry VBC Lab-scale FFBR O 2 /CO 2 air 16% 21% 26% 31% Air-dried VBC Quick ignition of dried VBC even in O 2 /CO 2 Adjustable/flexible O 2 % in boiler/ burner favours the ignition and combustion of wet coal Wet VBC 40 wt% moisture O /CO 2 2 air 16% 21% 26% 31% 36% (Wirhan P, Fuel submitted)

10 High gasification reactivity of VBC oxy-firing Lab-scale DTF Coal feeder Primary gas Mass flow controllers Air O 2 CO 2 AirO 2 CO 2 ON OFF Secondary gas High-speed camera Pyrometer Oscilloscope PC Water in Thimble filter T p, K H 2 O Water outdry ice To gas analyser (O 2, CO 2, CO, NO, SO 2 ) Burning Coal Particle 27% O 2 in CO 2, T w = 1073K C-CO 2 /C-H 2 O contribution Measured data 105µm 130µm 153µm No C-CO 2 and C-H 2 O reactions for 130µm Distance from Coal Injector Tip, m (Energy and fuels 2013, 27 (8), pp ) Strong gasification reactions (~ 20%) during oxy-firing lower particle temperature.

11 Verification by Using Pilot-Scale Boiler Process Flowsheet O 2 (~95%) inlet Thermocouples for flue gas temp measurement Heat-transfer Gas preheater Bag filter De-SO x flue gas condenser Stack gas Front View Flame observation/ Measurement port Wet flue gas recycle Dry flue gas recycle Probe for ash deposition Flue gas/o 2 mixer Secondary gas Primary gas Mill Features: Up to 3 MW th for both air-firing and oxy-firing; Recirculation of both wet and dry flue gas; Ash sampling along the furnace; Sampling of emissions (CO, CO 2, O 2, H 2 O, SO 2, NO x, SO 3, Hg, trace metals).

12 Coal Samples Tested Properties of Victorian brown coal (VBC) samples, wt% air-dry basis coal Victorian Brown Coal Hazelwood Yallourn Loy Yang proximate analysis, % Moisture (ar) Volatile Matter, (db) Fixed Carbon (db) Ash (db) Ultimate analysis, %, (db) Carbon Hydrogen Nitrogen Sulphur Specific energy (gross dry,mj/kg) Wet coal samples moisture is 30~40% in experiments.

13 Experimental Conditions Tested June 2012 date: Dried coal (~24%moisture) and wet coal (30-40%) samples Wet flue gas recycle; Varying O 2 % in 1 st gas. various VBCs Oxy firing Airfiring Coal Coal Yallourn Moisture in coal (wt%) 23.1 Hazelwood 24.6 Loy Yang 24.0 XJ coal ( lignite ) Moisture in coal (wt%) Thermal power, Mw Coal feeding rate, kg/h total air, Nm 3 /h Thermal power, MW Coal feeding rate, kg/h Pure O2 flux, Nm3/h Recycled gas flux, Nm3/h O2 in furnace, vol% Hazelwood Hazelwood Yallourn Yallourn Loy Yang

14 Smooth Shift Between Two Modes Coal feeding rate (kg/h) (1) (2) (3) (4) (5) (1) Preheating stage: The furnace heated up by burning natural gas. Coal was milled and ready in the bunker. (2) Air combustion stage Gas temperature in combustion zone, o C (3) Transition stage to oxy-fuel combustion (4) Oxy-fuel combustion stage When steady, sample collection started. (5) Shut-off stage.

15 High-Purity CO 2 in Flue Gas Air ingress ratio 5%, air-dried Hazelwood coal, Thermal load 0.9 MW Flue gas temp: ~160 o C Typical measurement Flue gas components,vol% Predicted CO2 dry% measured O2 dry% Predicted O2 dry% 0 18: : : : :00 Time measured CO2 dry% Predicted H2O wet% This study Callide oxy-fuel project Energy Conversion and Management 2007, 48, Comparison with literature Coal Hazewood coal (24.6%, moisture) Australian black coal Dried lignite (15%,moisture) CO 2, dry% 80.0 (air 15.0) O 2, wet% 4.0 (air 4.0) H 2 O, wet% 35.0 (air 10.0 ) Air ingress was mainly caused from natural burner surroundings and air-preheater

16 Flue Gas Amount and Recycle Ratio Wet coal (42% H 2 O) with a feeding rate of ~220 kg/h, 0.9 MW, exit-o 2 % ~5% Recycle Percentage % Recycle Percentage, % O 2 % in Furnace Flue gas flux, Nm3/h air Flue gas amount, Nm 3 /h 30%O 2 /CO 2 flue gas in furnace flue gas emitted 35%O 2 /CO 2 40%O 2 /CO 2 A significant cut on flue gas amount by using higher O 2 % for wet coal in oxy-fuel Mode; The inherent moisture acts as a dilutant as well, reducing flue gas recirculation ratio and energy consumption for the RFG forward fan.

17 Oxy-Firing Stability of Dried VBC Hazelwood coal: 23 wt% moisture, wet RFG, same O 2 % in 1st and 2nd gas Temperature, o C Air 27%O 2 /CO 2 30%O 2 /CO 2 Radiation transferheat flux, W/m 2 rad-heat-flux

18 Oxy-Firing Stability of Wet VBC Hazelwood coal: 42 wt% moisture, wet RFG, same O 2 % in 1st and 2nd gas Temperature, o C 21%O 2 /CO 2 Air 26%O 2 /CO 2 30%O 2 /CO 2 35%O 2 /CO 2 Radiation transferheat flux, W/m 2 rad-heat-flux For wet coal, 30% O 2 in furnace is essential to stabilise its combustion

19 Influence of 1st gas O2% on VBC Ignition Char burnout rate (kg/s) 1st The presence of >21% O2 in gas is essential for wet VBC to ignite stably. Char ignition point Air firing (Ignition time is 10.5ms for mean particle size) 4%O2 in 1st gas, only recycled gas (13.5ms) Oxy-fuel firing Burner zone 21%O2 in 1st gas (12.2ms) 30%O2 in 1st gas, (11.5ms)

20 Flue Gas Temperature Profile air-firing oxy-firing (30% O 2 ) Average gas temperature, o C Dry coal wet coal ~150 o C Furnace height, m Average gas temperature, o C Dry brown coal wet brown coal 50 o C Furnace height, m Air-firing: lower temp for wet coal case due to moisture evaporation; Oxy-firing: narrower difference between dry and wet coal due to local higher radiation transfer-heat in burner zone, which makes effect to keep wet-coal burning stability.

21 Conclusions 1) Integration of external drying and supercritical steam conditions is able to offset the energy penalty related to ASU for wet VBC. 2) Oxy-fuel combustion of Victorian brown coal, dry or wet, is achievable, leading to the purity of 80% (dry) CO 2 in flue gas, with a minimum 60% recycle ratio for flue gas. 3) Good matching conditions of VBC oxy-firing with air-firing: Retrofit of existing power plant Purpose-designed oxy-firing boiler Proper oxygen concentration, vol% 30% 27% Proper oxygen concentration in 1 st gas, vol% >21% - RFG recycle ratio ~65% ~75% Temperature / Radiation flux distribution Similar with air-firing Unburned carbon in fly ash Non-detectable, fully burnt out (4) CFD modelling was developed to clarify the oxy-fuel characteristics of VBC. And the results was well verified by the experimental data.

22 Thank-You to All Team Members Manager X Zhang Mr. XL Ge Mr. XX Cheng Dr. XJ Wu Prof. Y Ninomiya Mr. BQ Dai Dr. L Zhang Prof. MC Zhang Dr. K Yan Mr. Y Meng Mr. Chen Prof. ZX Zhang Dr. J Zhang Ms. YW Zhang Mr. Nan Chen Mr. F Chen

23 Acknowledgement Monash Colleagues: Andrew Hoadley, Baiqian Dai, Fiona Low, Wirhan Prationo, Anthony De Girolamo; Energy Australia (Geoff Gay) and International Power (Garry Smith and Tony Innocenzi) for coal supply and project feedback; Huazhong Univ of Sci and Technol (HUST, Wuhan, China) for analysis support; ANLEC R&D and BCIA for financial support; Australian Research Council (ARC); Australian Academy of Technological Science and Engineering (ATSE) Joint Co-ordination Grant (JCG).

24 Many thanks for your attention!