Modelling of trace element release in oxyfuel PF coal combustion

Transcription

1 Modelling of trace element release in oxyfuel PF coal combustion Marco A. Jano Ito Supervisors Dr. Marcos Millan-Agorio Dr. Graham Reed

2 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).

3 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.

4 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.

5 Pressurised Fluidised Bed Reactor I-2 T1 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 l n /min. F1 V1 V-5 F2 F3 V5 V-2 E1 E-2 Z1 I1 X1 V3 V-1 V4 V-3 I-6 I-1 I-4 I-7 I-3 I-5 V-4 V2 M1 R1 H1 M2 G1 S1 O1 E-1 D1 C1 C2 C3

6 Modelling of trace element release in oxyfuel PF coal combustion Marco A. Jano Ito Supervisors Dr. Marcos Millan-Agorio Dr. Graham Reed

7 Modelling of trace element release in oxyfuel PF coal combustion Introduction Objectives Methodology Results Conclusions

8 Presentation contents Introduction - Carbon capture and storage - Oxy-fuel combustion - Trace elements in coal and their behaviour in combustion

9 Conventional PC combustion Steam turbine Electricity Condenser Boiler DeNOX Sulphur removal Flue gases Coal Precipitator Air NOx Fly ash SOx Bottom ash 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. Source: Based on Vattenfall (2010) and Centro Mario Molina (2010)

10 Oxy-fuel combustion Steam turbine Electricity Condenser Boiler Sulphur removal Coal Compressor CO 2 Air separation Air N 2 O 2 Bottom ash Precipitator Fly ash SOx Water Cooler and condenser 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 CO 2 compression. The purity of CO 2 can be as high as 95%. Source: Based on Vattenfall (2010) and Centro Mario Molina (2010)

11 Trace elements in coal 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. Source: Clarke, L.B. (1993) The fate of trace elements during coal combustion and gasification: and overview. Fuel, 72 (6),

12 Trace element behaviour under combustion 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. 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.

13 Oxy-fuel combustion Main features of oxy-fuel combustion Higher heat capacities of CO 2 and H 2 O (in case flue gas is recycled before being dried). Higher gas emissivities. Higher flue gas density. Hindered diffusion of CO 2 from the particle. Hindered diffusion of O 2 to the char surface. Reaction between CO 2 and carbon. The formation of NO x, SO x and ash particles, as well as the fate of trace elements may be altered What potential to form carbonate deposits?

14 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 O 2 /N 2 and O 2 /CO 2 environments, different stages of the processes and different coal compositions. Analysis of the impact of trace element release on process equipment corrosion.

15 Air-fired and Oxy-fuel systems System based on: Conceptual design of supercritical O 2 -based PC boiler prepared by Foster Wheeler to the U.S. Department of Energy. Oxy-fuel cases 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.

16 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

17 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

18 Activities performed Air-fired and oxy-fuel modelling Mass balance of the processes. Adiabatic flame temperature. 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.

19 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.

20 Main species formed Vapour Condensed 140 C-380 C 380 C-800 C 800 C C Mercury HgCl 2 HgCl 2, Hg, HgO 140 C-380 C 380 C-800 C 800 C-1200 C Hg, HgO Arsenic As 4 O 10 As 4 O 10, As 4 O 7, As 4 O 8, AsO, AsO 2 As 2 O Selenium SeO 2 SeO 2, SeO SeO 2, SeO, Se,SeH Lead PbCl 2 PbO, PbCl, PbCl 2, Pb PbSO 4 PbSO Antimony SbCl 3 SbCl 3, Sb 4 O 6 SbCl, SbO, Sb 4 O 6 Sb 2 O 5, SbO 2 SbO Chromium Cadmium Nickel NiCl 2, CrH 2 O 4, CrH 2 O 4, Cr Cr CrO 2 Cl, CrO 2 CrO 2 Cl, CrO 2 S 3 O 2 S 3 O 12, 12 Cr 2 Cr 2 O 2 O 3 3 CdH 2 O 2, CdCl 2 Cd, CdH 2 O 2, CdCl 2, CdOH NiO 2 H 2, NiCl 2, NiOH, NiCl CdSO NiSO 4 NiSO 4, Ni 2 SiO 4 Ni 2 SiO 4

21 Main species formed Vapour Condensed 140 C-380 C 380 C-800 C 800 C C 140 C-380 C 380 C-800 C 800 C-1200 C Manganese MnCl 2 MnCl 2, MnCl MnSO 4 MnSO 4, Mn 2 O 3, Mn 3 O 4 Mn 2 SiO 4 Cobalt Beryllium CoCl 2, CoCl 2, CoSO CoSO 4, CoH 2 O 2 CoH 2 O 4 Co 2 Co 2 SiO 2 SiO BeH 2 O 2 BeH 2 O 2, BeSO 4 BeSO 4 BeSO 4, Be 2 SiO Boron BH 3 O 3, BClH 2 O 2 BH 3 O 3, BHO 2, BClH 2 O 2 BHO 2, BKO 2, BH 3 O 3, BO 2 BHO Copper Vanadium Zinc CuCl, CuCl 2, CuCl, CuCl 2, Cu 3 Cl 3 Cu, CuOH CuSO 4 CuSO VOCl 3 V 4 O 10, VOCl V 2 O 5 V 2 O 5 Ca 2 O 7 V 2, V 4 O 10, VO ZnCl 2 ZnH 2 O 2, ZnO, Zn, ZnCl 2, ZnCl, ZnOH H 2 O 5 SZn, ZnSO 4 ZnSO 4, Zn 2 SiO 4 Zn 2 SiO 4

22 Interactions between minor and trace elements Considerable interaction Interaction No interaction

23 Condensed species formed at convection zone tube wall temperatures (800 to 380 o C) Element Condensed form Element Condensed form Sb SbO 2 Cu CuSO 4 As As 2 O 5 Pb PbSO 4 Be Be 2 SO 4, Be 2 SiO 4 Mn MnSO 4 Cd CdSO 4 Ni NiSO 4 Cr Cr 2 O 3, Cr 2 O 12 S 3 V V 2 O 5 Co CoSO 4 Zn ZnSO 4

24 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.

25 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 ( ~ 140 o C) decreased Si (i.e. low ash) increases Co, Ni and Zn volatility at high temperatures