modelling of trace element release in oxyfuel pf coal combustion reed.pdf · 2017-02-21 ·...
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Modelling of trace element release in oxyfuel PF coal combustion
SupervisorsDr. Marcos Millan-AgorioDr. Graham Reed
Marco A. Jano Itomarco.jano-ito10@imperial.ac.uk
Background: IC involvement in FECUNDUS
Researchers currently involved in FECUNDUS:
• Prof Nigel Brandon (ESE - Professor). • Dr Marcos Millan (CE - Lecturer).• Dr Nigel Paterson (CE - Research Fellow).• Dr Graham Reed (CE - Research Fellow).• Mr Hamish Spender (CE - PhD student).
Groups at IC Involved in Fecundus• Department of Chemical Engineering.
• Pyrolysis and Gasification of Solid Fuels.» Integration of Gasification with Carbon Storage (Flexgas).» Biomass Chars for Steel Production in Electric Arc Furnaces
(Green EAF).• Gas Cleaning.
» Catalytic Tar Cracking.• Fuel Catalytic Upgrading and Characterisation.
» Synthesis and Testing of Hydrocracking Catalysts.
• Department of Earth Sciences and Engineering.• Fuel Cells.
» Fuel Cell Design and Optimisation.» Effect of Gas Contaminants on Fuel Cells.
Background: IC and FECUNDUS
• WP2 - Oxyfuel plus Steam Gasification and Integration with the ICFB Process Scheme.
• WP3 - Selection and Characterisation of Alternative Fuels For Entrained Flow Gasification.
• WP4 - Development and Test of Materials for Advance Gasification Processes.
Up to 1000°C and 30 bar.Resistance-heated reactor shell.Solid feed rate of up to 6 g/min.Gas flow rates of up to 15 ln /min.
Pressurised Fluidised Bed Reactor
V-5
V-4
I-6 I-1 I-4 I-7 I-3 I-5
V-1
V-3
V-2
E-1
D1
M2
E-2
I-2
C2C1 C3
M1
O1
H1
I1
Z1
S1
F1
V1 F2F3
X1
V3
V2
V4
V5
E1
G1
R1
T1
Modelling of trace element release in oxyfuel PF coal combustion
SupervisorsDr. Marcos Millan-AgorioDr. Graham Reed
Marco A. Jano Itomarco.jano-ito10@imperial.ac.uk
Modelling of trace element release in oxyfuel PF coal combustion
Introduction
Objectives
Methodology
Results
Conclusions
Presentation contents
Introduction
- Carbon capture and storage
- Oxy-fuel combustion
- Trace elements in coal and their behaviour in combustion
Conventional PC combustion
Source: Based on Vattenfall (2010) and Centro Mario Molina (2010)
Conventional power generating systems use air to burn coal and produce steam.
Coal is burned in a boiler and flue gases in some cases are cleaned before being emitted into the atmosphere.
Bottom ash
Coal
Boiler
Precipitator
Sulphur removal
Fly ashNOx
Steam turbine
Condenser
Electricity
DeNOX
SOx
Flue gases
Air
Oxy-fuel combustion
Source: Based on Vattenfall (2010) and Centro Mario Molina (2010)
Bottom ash
Coal
Boiler
Steam turbine
Condenser
Electricity
Precipitator
Fly ash
Sulphur removal
SOxWater
Cooler and condenser
Air separation
Air
N2
O2
Recycled flue gases
Oxy-fuel combustion uses oxygen and recycled flue gases instead of air. Recycled flue gases control temperature.
Addition of an Air Separation Unit (ASU), flue gas cleaning and CO2 compression.
The purity of CO2 can be as high as 95%.
Compressor CO2
Trace elements in coal
Source: Clarke, L.B. (1993) The fate of trace elements during coal combustion and gasification: and overview. Fuel, 72 (6), 731 – 736.
These elements are found as traces (less than 1000ppm by weight) in coal.
Their emission during combustion is considered to be a threat to the environment, human health and process operation as well.
These elements can be found as:
Included in coal particles or as minerals and rock fragments.
Associated to organic or inorganic matter.
Trace element behaviour under combustion
Source: Atalla, M., Morgan, S., Riley, K., Bryant, G. and Nelson, P. (2007) Trace element deportment in combustion processes. Cooperative Research Centre for Coal in Sustainable Development (CCSD), Research report 70.
Complex transformations at rapid heating and high temperatures.
Combustion:
Non-volatile trace elements in organic matter transferred to gas phase.
In the mineral matter, volatile elements vaporise.
Non-combustible material is in the bottom-ash, fly-ash and vapour.
Oxy-fuel combustion
Higher heat capacities of CO2 and H2 O (in case flue gas is recycled before being dried).
Higher gas emissivities.
Higher flue gas density.
Hindered diffusion of CO2 from the particle.
Hindered diffusion of O2 to the char surface.
Reaction between CO2 and carbon.
The formation of NOx , SOx and ash particles, as well as the fate of trace elements may be altered
What potential to form carbonate deposits?
Main features of oxy-fuel combustion
Objectives
Development of a procedure to evaluate trace element release in an oxy-fuel combustion system that may be similar to a real plant.
Use MTDATA as a thermodynamic tool to model trace element behaviour at different temperatures.
Analysis of the speciation of trace elements in combustion under O2 /N2 and O2 /CO2 environments, different stages of the processes and different coal compositions.
Analysis of the impact of trace element release on process equipment corrosion.
Air-fired and Oxy-fuel systems
• System based on: “Conceptual design of supercritical O2 -based PC boiler” prepared by Foster Wheeler to the U.S. Department of Energy.
• Provides industry data for air-fired and oxy-fuel processes as well as coal composition (Illinois #6).
• Cases: Air-fired case, Oxy-fuel with 72.1% recycled flue gases and Oxy-fuel with 65.5% recycled flue gases.
Source: Seltzer, A., Fan, Z. and Robertson, A. (2006) Conceptual design of supercritical O2-based PC boiler. Foster Wheeler Power Group, Inc., DE-FC26-04NT42207.
Oxy-fuel cases
Coal analysis
Illinois No 6 bituminous coal (US DOE 2008), % db
Ash 10.9
S 2.82
Cl 0.33
ash minerals, % on ash db
Silica 45
Alumina 18
Iron Oxide 20
Calcium Oxide 7
Trace element composition
Average for Illinois mines shipped coal (USDOE 2008), ppm (db)
As 7.5 Mn 38
B 90 Mo 8.4
Be 0.7 Ni 14
Cd 0.9 Pb 24
Co 1.3 Sb 0.8
Cr 14 Se 1.9
Cu 9.2 V 31
Hg 0.09 Zn 84.4
Activities performed
Air-fired and oxy-fuel modelling
Trace element release
• Simulation of the behaviour of 15 trace elements using MTDATA.
• Preliminary analysis of the behaviour of trace element speciation for the air-case and oxy-fuel cases.
• Mass balance of the processes.
• Adiabatic flame temperature.
Modelling of trace element release
• Chemical equilibrium calculations provide an initial understanding of speciation.
• MTDATA minimizes the Gibbs energy function in complicated multiphase multicomponent systems.
• Scientific Group Thermodata Europe (SGTE) for element properties.
Main species formed
Vapour Condensed
140°C-380°C 380°C-800°C 800°C- 1200°C
140°C-380°C 380°C-800°C 800°C-1200°C
Mercury HgCl2HgCl2 , Hg,
HgO Hg, HgO ------ ------ ------
Arsenic As4 O10As4 O10 ,
As4 O7, As4 O8,AsO, AsO2 As2 O5 ------ ------
Selenium SeO2 SeO2 , SeO SeO2 , SeO, Se,SeH ------ ------ ------
Lead ------ PbCl2PbO, PbCl, PbCl2 , Pb PbSO4 PbSO4 ------
Antimony SbCl3 SbCl3 , Sb4 O6SbCl, SbO,
Sb4 O6Sb2 O5 , SbO2 SbO2 ------
Chromium ------ CrH2 O4 , CrO2 Cl, CrO2
CrH2 O4 , CrO2 Cl, CrO2
Cr2 S3 O12Cr2 S3 O12 ,
Cr2 O3Cr2 O3
Cadmium ------ CdH2 O2 , CdCl2
Cd, CdH2 O2 , CdCl2 , CdOH CdSO4 ------ ------
Nickel ------ NiCl2 ,NiO2 H2 , NiCl2 ,
NiOH, NiCl NiSO4NiSO4 , Ni2 SiO4
Ni2 SiO4
Main species formed
Vapour Condensed
140°C-380°C 380°C-800°C 800°C- 1200°C
140°C-380°C 380°C-800°C 800°C-1200°C
Manganese ------ MnCl2 MnCl2 , MnCl MnSO4MnSO4 ,
Mn2 O3 , Mn3 O4Mn2 SiO4
Cobalt ------ CoCl2 , CoH2 O2
CoCl2 , CoH2 O2
CoSO4CoSO4 , Co2 SiO4
Co2 SiO4
Beryllium ------ BeH2 O2BeH2 O2 , BeSO4
BeSO4BeSO4 , Be2 SiO4
------
Boron BH3 O3 , BClH2 O2
BH3 O3 , BHO2 , BClH2 O2
BHO2 , BKO2 , BH3 O3 , BO2
BHO2 ------ ------
Copper ------ CuCl, CuCl2 , Cu3 Cl3
CuCl, CuCl2 , Cu, CuOH CuSO4 CuSO4 ------
Vanadium VOCl3 V4 O10 , VOCl3 ------ V2 O5 V2 O5Ca2 O7 V2 ,
V4 O10 , VO2
Zinc------ ZnCl2
Zn, ZnCl2 , ZnH2 O2 , ZnO, ZnCl, ZnOH
H2 O5 SZn, ZnSO4
ZnSO4 ,Zn2 SiO4
Zn2 SiO4
Interactions between minor and trace elements
Considerable interaction
No interactionInteraction
Condensed species formed at convection zone tube wall temperatures (800 to 380oC)
Element Condensed form
Element Condensed form
Sb SbO2 Cu CuSO4
As As2 O5 Pb PbSO4
Be Be2 SO4 , Be2 SiO4
Mn MnSO4
Cd CdSO4 Ni NiSO4
Cr Cr2 O3 , Cr2 O12 S3
V V2 O5
Co CoSO4 Zn ZnSO4
Conclusions (1)
• Air-fired and oxy-fuel cases present similar trace element speciation trends and small differences were found.
• At high temperatures, trace elements were primarily found in the chlorinated and oxidised forms.
• At low temperatures, trace elements condensed as sulphates and silicates.
• Trace elements interacted primarily with chloride, sulphur and silicon.
Conclusions (2)
For the coal studied, trace element speciation is unchanged between conventional PC and oxyfuel PC boilers, but:
The recycle configuration (wet or dry) can affect S concentration
Coal Cl, S and Si concentration sensitivity studies show:
• decreased Cl lowers Pb, Cd and Cu volatility
• decreased S allows carbonate to form if:
– Ca:S>1
and
– temperatures are low ( ~ 140oC)
• decreased Si (i.e. low ash) increases Co, Ni and Zn volatility at high temperatures
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