SLIDE 1
Ash Formation and Speciation of Trace Metals During Oxy-Fuel - - PowerPoint PPT Presentation
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:
SLIDE 2
SLIDE 3
High Greenhouse Gas Emission
Low efficiency (~30%) and high emission rate due to prevalence
- f moisture.
Fuel type Efficiency (tonnes CO2-e/MWh sent out) Brown Coal (Hazelwood 2004) 1.58 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 Wind 0.02
In 2004
http://www.envict.org.au/file/Greenhouse_Brown_Coal_05.pdf
Typical properties of brown coal:
VM (%db): ~50; Ash (% db): <1 ~ 3%; S (% db): <0.5 %; Moisture: 50~60%.
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
SLIDE 4
Oxy-Fuel R&D in Monash
2007 2009 Basic research supported by ETIS, Victorian Government Basic research supported by ARC 2014 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
SLIDE 5
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.
SLIDE 6
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.
SLIDE 7
Mass flow controllers Coal feeder Primary gas
ON OFF
Oscilloscope Pyrometer Secondary gas Thimble filter
Air O2 CO2 Air O2 CO2
PC To gas analyser (O2, CO2, CO, NO, SO2) High-speed camera H2O Water in Water out Dry ice
Advanced/Unique Drop-Tube Furnace
Built in 2007
SLIDE 8
Ash Collection in DTF
Coarse fraction Fine fraction Coarse Fine
Coarse: heavy, >5.0 µm for 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.
SLIDE 9
Advanced Analytical Instruments
ICP – OES and XRF for Major, minor and trace elements quantification; FactSage and HSC Chemistry for thermodynamic equilibrium prediction
- n ash formation;
Computer-controlled SEM (CCSEM) for mineral speciation; Synchrotron-based X-ray Adsorption Spectroscopy (XAS) for speciation
- f trace metals toxicity (Cr, As, Cd, Mn and Hg).
5980 6000 6020 6040 6060 6080
0.0 0.3 0.6 0.9 1.2 1.5
(a)
Standard CaCrO4 Oxy-ash-1 collected in DTF Oxy-ash-2 collected in DTF Oxy-ash-3 collected in DTF
Normalised Adsorption Energy, eV
Cr
6+
SLIDE 10
Any Effect of Oxy-Firing on Ash Formation?
Yes, First – O2 % In CO2 to match air must be higher than 21%, so higher coal-O2 oxidation rate will be achieved.
0.1 1 10 100 0.1 1 10 100
Wt% Particle Diameter, µm
Raw mineral Air 21% O2/79% CO2 27% O2/73% CO2
Ash PSD
1 2 3 4 4 8 12 16 Air 21% O2/79% CO2 27% O2/73% CO2
Wt%
τp,s
Formation of Ca/Mg-Al-Si-O
Fuel 2011, 90: 1361-69
SLIDE 11
Any Effect of Oxy-Firing on Ash Formation?
Higher PO2 however affects little on the oxidation of trace metals such as Cr.
20 40 60 80 20 40 60 80
BL, oxy-ash Energy, eV BL, air-ash VBC, air, fine VBC, oxy, fine VBC, oxy, coarse Energy, eV VBC, air, coarse
Normalized Absorption
Cr6+
ES & T, 2011, 45 (15), pp 6640–6646
SLIDE 12
Any Effect of Oxy-Firing on Ash Formation?
Second – due to O2 diffusion control, does char react with CO2 on its surface?
Boundary layer rich in CO2 Char particle O2 diffusion control CO emission profile
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 2 4 6 8 10
CO fraction on the mass basis of feed coal, % Residence time, s
Air 21% O2 / 79% CO2 27% O2 / 73% CO2
Energy & Fuels 2010, 24: 4803-11
SLIDE 13
Strong Reducing Atmospheres on Char Surface
affects the mineral melting propensity
10 20 30 40 50 60 70 80 90 3000 6000 9000
K-Si K-Si L M H H M M M M M Q Q Q Q Q Q Q Q Q
27% O2/73% CO2 21% O2/79% CO2
Relative Intensity, [-] 2 Theta
Air 1000oC
K-Si is leucite (KAlSi2O6)
Fuel 2011, 90: 1361-69
SLIDE 14
Strong Reducing Atmospheres on Char Surface
Promote the vaporisation extent of volatile metals
1100 1200 1300 1400 2 4 6 8 10 Oxidizing Condition
% of NaCl(g) in total Na Temperature, K
Reducing Condition
Preferential formation
- f NaCl(g) under oxy-fuel
conditions
- Proc. Combust. Inst. 2011, 33: 2795-2802
SLIDE 15
Dirty Gas Recirculation
Case 1: dehydrated, de-dusted, De-SO2/HCl, clean flue gas recirculation; Case 2: dehydrated, de-dusted SO2/HCl recirculation; Case 3: dehydrated flue gas prior to precipitator and De-SOx; Case 4: wet dirty flue. Brown Coal air-/oxy-firing system Wet Coal boiler Precipitator De-SOx mill Water Condenser Case 1 Case 2 Case 3 Stack Case 4
SLIDE 16
Fuel 2011, 90(6): 2207-16
Formation of Fine Ash Upon SO2/HCl Recycle
200 400 600 800 1000 1200 20 40 60 80 100
Fine Ash Yield, wt%
- Conc. of SO2/HCl in RFG, ppmV
SO2 HCl Conditions: Brown coal, 1000oC (furnace temp) 4 sec (gas) Sulfate deposition may affect the fouling on superheater; Vaporisation of metals upon HCl recycle affects the pollutant emission.
SLIDE 17
3 MW Pilot-Scale Oxy-Fuel Facility
Fabric filter flue gas condenser Stack gas Dry flue gas recycle O2 inlet De-SOx Convection section Flame observation/ Measurement port Gas- gas heater Flue gas/O2 mixer Wet flue gas recycle Mill Primary gas Secondary gas Observation/ Sampling ports Thermocouples for flue gas temp measurement
To be collaborated with Shanghai boiler Works Limited (SBWL)
SLIDE 18
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
SLIDE 19
Coal Drying System Coal Bin Room Furnace Experimental Building Experimental Building
3 MW Pilot-Scale Oxy-Fuel Facility
SLIDE 20
Ash Research in Pilot-Scale Facility
- High-temperature small drop-tube furnace (to 1500oC) under construction;
- Cooling water-jacketed probe (500-650oC) attached with metal substrates
- n the top: carbon steel, Martensitic alloy P91 and X20CrMoV121.
Ash deposition behavior Pollutant Emission behavior
- Trace metal sampling and characterisation;
- Fine particulate sampling and characterisation;
- Bottom ash sampling and characterisation.
SLIDE 21
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.
SLIDE 22