Thermodynamic modelling of gasification processes with consideration of alkali metals

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Institute of Energy Process Engineering and Chemical

with consideration of alkali metals Stefan Guhl, Prof.

1 Institute of Energy Process Engineering and Chemical Engineering Thermodynamic modelling of gasification processes with consideration of alkali metals Stefan Guhl, Prof. Bernd Meyer 2 nd International Freiberg Conference on IGCC & XtL Technologies, Freiberg TU Bergakademie Freiberg I Institute of Energy Process Engineering and Chemical Engineering Reiche Zeche I Freiberg I Tel. +49(0)3731/ I Fax +49(0)3731/ evt@iec.tu-freiberg.de I Web

2 Motivation conversion of MSW and coal via gasification generates CO- and H 2 -rich synthesis gas and volatile ash components like Na, K, Zn volatile ash components will condensate at cooler parts in gasifiers - heat exchangers - raw gas outlet - refractory lining - formation of deposits - reduced efficiency - blockages evaluation of the pathway of volatile ash components in the BGL-Gasification process by thermochemical calculations application of the validated model for entrained flow- or fluidized bed gasification processes 2

oxygen: steam: steamoxygen ratio: 24-30 t/h = 180-230 MW 4000-6000 m³/h

3 The BGL - Gasification Process operating pressure: 24 bar raw gas temperature at discharge: 550 C after scrubber: 200 C In: MSW + coal: oxygen: steam: steamoxygen ratio: t/h = MW m³/h STP t/h kg/m³ STP Out: raw gas: Slag: m³/h STP, wf. 3 5 t/h 3

4 Preparation of the data file in FactSage TM selection of elements: Ar, Al, C, Ca, Cl, Fe, H, K, Mg, N, Na, O, P, S, Si, Ti selection of possible products from the databases FACT 5.3, FACToxide, FACTmisc, FACTsalt (update August 2005) stoichiometric pure condensed substances ( C_graphite(s), Al 2 O 3 (s) ) gas treated ideally with solution phase gas_ideal non-ideal solution phases e.g. ASlag-liq, BAlkCl-ss_rocksalt, BSalt-liquid, Pyrrhotite, Fe-liq 4

5 Partial examination of thermodynamic data for capturing and volatilisation of Na and K, especially the components and solution phases of the metal oxides are important: Al 2 O 3, CaO, FeO/Fe 2 O 3, K 2 O, MgO, Na 2 O, SiO 2, TiO 2 /Ti 2 O 3 calculation of 28 binary systems (phase diagrams) and comparison to literature (Slag Atlas 2nd Edition, 1995 Verlag Stahleisen GmbH) calculation of characteristic points of ternary systems and comparison to ternary phase diagrams from literature data file (database with cp(t), H 298 and S 298 for each stoichiometric substance, parameters for non-ideal solution phases) for equilibrium calculation in SimuSage TM 5

6 Buildup of the thermochemical model in SimuSage TM definition of isobaric and isothermal local equilibrium stages (equilibrium composition obtained by Gibbs energy minimisation) connecting the local equilibrium stages by material streams, usage of mixer, splitter, iterator interacting of single stages, material cycles definition of amount and composition of input streams fitting of the model via process data X 1 X 2 T p p, T, (ΔH) calculation of local equilibrium X 1 X 2 T mixer splitter 6

Model development 2 equilibrium stages, alkali condensation in Devolatilisation stage, alkali evaporation in lower stage accumulation in alkali

$compensation Phosphor solution in slag stream only described in liquid iron phase Fe-liq, absent in used slag phase ASlag-liq fractional$

7 Model development 2 equilibrium stages, alkali condensation in Devolatilisation stage, alkali evaporation in lower stage accumulation in alkali cycle bypass for CO due to temperature dependence of Boudouard reaction, compensation with argon alkali bypass represents condensed alkali chlorides in the raw gas, verified by mass balance of feedstock and slag samples variation of the temperature of the lower stage argon compensation Phosphor solution in slag stream only described in liquid iron phase Fe-liq, absent in used slag phase ASlag-liq fractional release of Phosphor 7

8 Composition of MSW-coal-mixture for calculations Ultimate Analysis MSW-coal mixture in wt.-%, dry Ash composition in wt.-% Ash Na 2 O 3.25 Carbon 52.1 MgO 2.47 Hydrogen 5.72 Al 2 O Nitrogen 1.22 SiO Oxygen P 2 O Sulphur combustion 0.26 SO Chlorine org 0.29 Cl 3.31 K 2 O 1.76 CaO TiO Fe 2 O

9 Results phases in slag stream Slag-liquid 91.6 wt.% of slag stream Iron-liquid 5.0 wt.% of slag stream Constituents wt.-% Constituents wt.-% SiO CaO 28.8 Al 2 O MgO 2.7 FeO 0.3 TiO Na 2 O 2.8 K 2 O 1.0 CaS 1.0 MgS 0.1 Na 2 S 0.1 K 2 S 0.1 CaCl NaCl 0.3 KCl 0.1 MgCl Fe 82.1 C 2.3 P 14.4 FeS 1.1 Carbon 2.4 wt.% of slag stream Constituents wt.-% C 100 9

10 Results retention of ash components Comparison of results with measured retention rates higher retention of Chlorine than for Sulphur qualitatively calculated less precise for Chlorine 10

11 Results cycle of alkalies Distribution of K and Na on outlet streams and accumulation in alkali cycle 100 % K 100 % Na % K % Na 50 % K 24 % Na 1590 % K 130 % Na 800 % Cl 1540 % K 54 % Na 760 % Cl 50 % K 76 % Na 11

-%: solid/liquid phases: gas phase: KCaCl 3 _chlorocalcite(s) BAlkCl-ss_rocksalt

12 Results cycle of alkalies Distribution of K and Na on phases down- and upstream in wt.-%: solid/liquid phases: gas phase: KCaCl 3 _chlorocalcite(s) BAlkCl-ss_rocksalt BSalt-liquid 11% 25% K KCl (KCl)2 11% KCaCl 3 K 64% 29% 60% Na 2 Ca 3 Si 6 O 16 (s) BAlkCl-ss_rocksalt 13% Na BSalt-liquid NaCl (NaCl)2 7% Na 45% 42% 93% 12

13 Results - Influence of temperature Partial pressure of Na- and K-compounds for a constant retention rate: increasing accumulation of alkalis by temperature increase 13

14 Influence of partial pressure Retention of K for changing partial pressure of K-compounds at 1400 C: increasing K-retention by increasing K- partial pressure Temperature near the ash flow temperature promotes the alkali retention 14

15 Conclusion The BGL-gasification process was simulated with thermochemical calculations using the software FactSage TM and SimuSage TM. The results were validated with process data from the BGL-Gasifier of the Sustec Schwarze Pumpe plant. The Potassium and Sodium retention in the slag can be described. Temperatures near the ash flow temperature promote the Alkali retention in the slag. The Phosphor retention can be described for the liquid iron phase. The higher retention of Chlorine than for Sulphur in the slag phase is described in a qualitative way. 15

16 Thank you for your attention! Questions? Stefan Guhl Institute of Energy Process Engineering and Chemical Engineering TU Bergakademie Freiberg Reiche Zeche Phone: Freiberg Fax: Germany 16

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