Ash Formation and Speciation of Trace Metals During Oxy-Fuel - PowerPoint PPT Presentation

Ash Formation and Speciation of Trace Metals During Oxy-Fuel Combustion Lian Zhang, Yong Sun, et al Department of Chemical Engineering, Monash University, Clayton, Vic 3800, Australia Tel: +61-3-9905-2592, Fax: +61-3-9905-5686 Email: lian.zhang@monash.edu

Victorian Brown Coal (Lignite) Open cut in the Latrobe Valley, Morwell, Victoria The single largest source meeting >80% of the electricity needs in Victoria; Open cut deposits to last another 500 years; Cheap-$3/MWh-e from it, relative to $9-15 from black coal and >$20 from natural gas, forming ‘backbone’ of the industry in Victoria.

High Greenhouse Gas Emission Typical properties of brown coal: In 2004 VM (%db): ~50; Ash (% db): <1 ~ 3%; Efficiency (tonnes Fuel type CO 2 -e/MWh sent out) S (% db): <0.5 %; Brown Coal (Hazelwood 2004) 1.58 Moisture: 50~60%. Brown Coal (Yallourn 2004) 1.404 Brown Coal (Loy Yang A 2004) 1.158 Black Coal 0.8-1.1 Gas 0.4-0.55 Co-geneation 0.25-0.4 Low efficiency (~30%) Wind 0.02 http://www.envict.org.au/file/Greenhouse_Brown_Coal_05.pdf and high emission rate due to prevalence of moisture. Carbon tax of $ ∼ 23/t to be implemented next July would worsen the the position of Victorian brown coal in the energy market -- the Sunday Age News April 2011

Oxy-Fuel R&D in Monash 2007 2009 Basic research supported by ETIS, Victorian Government 2014 Basic research supported by ARC 2011 2013 Pilot-scale (3 MW) by ANLEC R&D 2020 Large scale (>30 MWe)? Victorian brown coal Target to align with Australian Carbon reduction strategy

Oxy-Fuel Combustion of Victorian Brown Coal Air separation unit (ASU) for oxygen purification reduces the net efficiency by 9%. For Victorian brown coal with a HHV net efficiency of approx 29% in existing power plant, the retrofitted oxy-fuel plant will Show a new efficiency less than 20% HHV – too bad to accept. High cost for retrofitting to existing air-fired subcritical plant. So, how to offset the ASU’ s energy penalty? -- increase the steam condition severity to super and/or ultra-supercritical (USC) condition; -- integrate external (internal) coal-drying into oxy-fuel combustion process.

Major Research Topics • Retrofit case : burning of as-mined wet brown coal under subcritical steam condition; • Purpose-designed new oxy-fuel plant : burning of as-mined wet coal under high-oxygen content and ultra supercritical steam (USC) condition; • Purpose-designed new oxy-fuel plant : burning of externally dried coal under USC steam condition. For each case, the heat flux (flue gas recycle) and ash formation and pollutant emissions are the two major concerns of us.

Advanced/Unique Drop-Tube Furnace Coal feeder Built in 2007 Primary gas Pyrometer Mass flow Oscilloscope controllers Air O 2 CO 2 High-speed camera Air O 2 CO 2 ON PC OFF Water in Thimble filter Secondary gas Water out Dry ice H 2 O To gas analyser (O 2 , CO 2 , CO, NO, SO 2 )

Ash Collection in DTF Coarse Fine fraction Coarse fraction Coarse : heavy, >5.0 µm for Fine primary particles/clusters; Formation route: solid-to-solid . Fine : light, ≤ 1.0 µm for primary particles, agglomerated upon quenching on filter. Formation route: gas-to-solid .

Advanced Analytical Instruments ICP – OES and XRF for Major, minor and trace elements quantification; FactSage and HSC Chemistry for thermodynamic equilibrium prediction on ash formation; Computer-controlled SEM (CCSEM) for mineral speciation; Synchrotron-based X-ray Adsorption Spectroscopy (XAS) for speciation of trace metals toxicity (Cr, As, Cd, Mn and Hg). 1.5 (a) 1.2 Normalised Adsorption 6+ Cr 0.9 0.6 Standard CaCrO 4 Oxy-ash-1 collected in DTF 0.3 Oxy-ash-2 collected in DTF Oxy-ash-3 collected in DTF 0.0 5980 6000 6020 6040 6060 6080 Energy, eV

Any Effect of Oxy-Firing on Ash Formation? Yes, First – O 2 % In CO 2 to match air must be higher than 21%, so higher coal-O 2 oxidation rate will be achieved. Formation of Ca/Mg-Al-Si-O Ash PSD 100 16 12 10 Wt% 8 Wt% 1 Raw mineral 4 Air Air 21% O 2 /79% CO 2 21% O 2 /79% CO 2 27% O 2 /73% CO 2 0.1 27% O 2 /73% CO 2 0 0 1 2 3 4 0.1 1 10 100 τ p ,s Particle Diameter, µ m Fuel 2011, 90: 1361-69

Any Effect of Oxy-Firing on Ash Formation? Higher P O2 however affects little on the oxidation of trace metals such as Cr. VBC, oxy, fine BL, oxy-ash Normalized Absorption Cr 6+ VBC, air, fine BL, air-ash VBC, oxy, coarse VBC, air, coarse 0 20 40 60 80 0 20 40 60 80 Energy, eV Energy, eV ES & T, 2011, 45 (15), pp 6640–6646

Any Effect of Oxy-Firing on Ash Formation? Second – due to O 2 diffusion control, does char react with CO 2 on its surface? Boundary layer CO emission profile rich in CO 2 10 Air O 2 diffusion 21% O 2 / 79% CO 2 CO fraction on the mass control 27% O 2 / 73% CO 2 basis of feed coal, % 8 6 4 2 0 Char particle 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Residence time, s Energy & Fuels 2010, 24: 4803-11

Strong Reducing Atmospheres on Char Surface affects the mineral melting propensity Q 1000 o C 27% O 2 /73% CO 2 9000 M Relative Intensity, [-] H H Q M M M Q L Q Q Q Q M Q Q M 6000 K-Si is leucite (KAlSi 2 O 6 ) 21% O 2 /79% CO 2 3000 K-Si K-Si Air 0 0 10 20 30 40 50 60 70 80 90 2 Theta Fuel 2011, 90: 1361-69

Strong Reducing Atmospheres on Char Surface Promote the vaporisation extent of volatile metals 10 Reducing Condition 8 % of NaCl (g) in total Na Preferential formation of NaCl (g ) under oxy-fuel 6 conditions Oxidizing Condition 4 2 0 1100 1200 1300 1400 Temperature, K Proc. Combust. Inst. 2011, 33: 2795-2802

Dirty Gas Recirculation Brown Coal air-/oxy-firing system Wet Coal Stack De-SO x boiler Precipitator mill Case 3 Case 1 Case 2 Case 4 Water Condenser Case 1 : dehydrated, de-dusted, De-SO 2 /HCl, clean flue gas recirculation; Case 2 : dehydrated, de-dusted SO 2 /HCl recirculation; Case 3 : dehydrated flue gas prior to precipitator and De-SO x; Case 4 : wet dirty flue.

Formation of Fine Ash Upon SO 2 /HCl Recycle 100 Conditions : Brown coal, 1000 o C (furnace temp) 80 4 sec (gas) Fine Ash Yield, wt% SO 2 60 40 Sulfate deposition may affect the HCl fouling on superheater; 20 0 200 400 600 800 1000 1200 Vaporisation of metals upon HCl recycle affects the Conc. of SO 2 /HCl in RFG, ppmV pollutant emission. Fuel 2011, 90(6): 2207-16

3 MW Pilot-Scale Oxy-Fuel Facility To be collaborated with Shanghai boiler Works Limited (SBWL) O 2 inlet flue gas Convection Fabric condenser section filter Thermocouples Gas- for flue gas temp Stack gas De-SO x gas measurement heater Dry flue gas Flame observation/ Wet flue gas recycle Measurement port recycle Flue gas/O 2 mixer Secondary gas Primary gas Observation/ Sampling ports Mill

3 MW Pilot-Scale Oxy-Fuel Facility Milestone of this Project: First Operation ( 28 March 2011 ) Start to Operate ( 10 May, 2011 ) First Experiment ( 24 May, 2011 )

3 MW Pilot-Scale Oxy-Fuel Facility Coal Drying System Experimental Building Furnace Experimental Building Coal Bin Room

Ash Research in Pilot-Scale Facility Ash deposition behavior High-temperature small drop-tube furnace (to 1500 o C) under construction; • Cooling water-jacketed probe (500-650 o C) attached with metal substrates • on the top: carbon steel, Martensitic alloy P91 and X20CrMoV121. Pollutant Emission behavior • Trace metal sampling and characterisation; • Fine particulate sampling and characterisation; • Bottom ash sampling and characterisation.

Summary • Monash targets the scale-up of oxy-fuel combustion for Victorian brown coal through both fundamental and large-scale R&D. • Victorian brown coal ash formation is susceptible to coal combustion environment and flue gas recirculation. A similar situation is predictable for other coals either high-rank or low- rank. • Lab-scale investigation confirmed the changes on ash properties upon gas swap and recirculation, need to be further confirmed in pilot-scale facility.

Acknowledgment Funding granters : ARC (FT & LIEF) and ANLEC R&D (BCIA); Collaborators : A/Prof Sankar Bhatacharya, Monash, Australia; Prof Yoshihiko NInomiya, Chubu Univ, Japan; Prof ZX Zhang, Shanghai Jiao Tong Univ, China; Shanghai Boiler Works Limited, China; International Power Hazelwood, Australia; International Power Loy Yang B, Australia; TRUenergy, Australia. Australian National Beamlime Facility (ANBF), KEK, Japan; National Synchrotron Radiation Research Center (NSRRC), Taiwan, China.