Fluidised Bed Methanation Technology for Improved Production of SNG from Coal International Conference on Clean Coal Technologies, Dresden, 18 May 2009 T.J. Schildhauer, S. Biollaz Paul Scherrer Institut Villigen, Switzerland
Outline Why convert coal to SNG? (What is SNG?) State of art in SNG from coal: fixed bed methanation Learnings from coal gasification and methanation for biomass-to-sng Learnings from biomass-to-sng for future coal gasification and methanation Conclusions and Outlook
Why convert carbonaceous material to SNG? Synthetic Natural Gas (SNG) is a versatile energy carrier that is interchangeable with Natural Gas (> 95% methane, high HHV) SNG can be distributed via the NG grid Many applications in industry, for de-central electricity production and as fuel, e.g. in CNG cars Higher chemical efficiency achievable than for FT Less selectivity issues Process is less complex (not necessarily high pressure process)
State of the art: Fixed bed methanation (I) Great Plains Synfuels Plant In operation since 1984, input is lignite 14 Lurgi-Gasifiers (150 MW th each) Fixed bed methanation (Lurgi) http://www.dakotagas.com/
State of the art: Fixed bed methanation (II) Adiabatic fixed bed reactors with intermediate cooling and product gas recycle (here the TREMP process by Haldor Topsoe A/S, Denmark) Temperature profiles show catalyst deactivation due to sintering Rostrup-Nielsen et al., Applied Catalysis A: General 330 (2007) 134 138
Chemical/cold gas efficiency along the process chain Feedstock Gasifier Producer gas Methanation CH 4, CO 2 Heat Autothermal Gasification: Losses depend on the gasifier outlet temperature. Heat Exothermic Methanation: Losses depend on selectivity and producer gas composition. The higher the methane fraction, the higher the chemical efficiency!
Is there a price to pay for higher efficiency? Higher chemical or cold gas efficiency asks for lower gasifier outlet temperatures and higher methane content in the producer gas From the Biomass-to-SNG process we know that lower temperatures in the gasifier and more methane means: - not only H 2 S and COS, but also organic sulphur compounds such as mercaptans, thiophenes - potentially higher ethylene (C 2 H 4 ) contents Under fixed bed conditions, ethylene tends to form carbon whiskers on nickel catalysts Additional potential for catalyst deactivation! Czekaj et al., Applied Catalysis A: General 329 (2007) 68 78
How about fluidised bed methanation? Comflux methanation technology for SNG production (70 & 80ies) Demo plant in 20 MW SNG scale running on CO/H 2 mixtures
Operation experience of demo & pilot plants (Comflux) Good starting point for bio syngas investigations 50 1,4 Reaction pressure [bar] 40 30 20 10 20 MW Demo plant 2 kw Pilot plant Target area for biomass Steam ratio D v [-] 1,2 1,0 0,8 0,6 0,4 0,2 2 kw Pilot plant Target area for biomass 0 1,0 2,0 3,0 4,0 H 2 /CO ratio [-] 0,0 1,0 1,5 2,0 2,5 3,0 H 2 /CO ratio [-]
Methane from wood: Producing SNG in pipeline quality H 2 4% CO 0.5% CO 2 47.5% CH 4 40% C 2 H 4 0% N 2 8% Gas conditioning Fluidized Catalyst Bed Gas cleaning H 2 37% CO 25% CO 2 18% CH 4 10% C 2 H 4 3% N 2 6% S-species tars SNG (CH 4 ) CHP Plant Güssing; 8 MW th, 2 MW el
> 1000h stable run with real gas (10 kw slip stream) Fluidized Catalyst Bed Gas cleaning fully automated set-up of PSI
Stable run with real gas on 10 kw scale 50 5.0 45 4.5 40 4.0 CH 4, CO 2 [vol%] 35 30 25 20 15 s_co2 s_ch4 s_co 3.5 3.0 2.5 2.0 1.5 CO [vol%] 10 1.0 5 0.5 0 0.0 0 100 200 300 400 500 600 700 800 900 1000 1100 operating hours [h] Schildhauer et al., Annual Scientific Report PSI (2008)
Why does it work? (Toolbox for investigation) - Measuring dense phase concentration profiles by means of a moveable sampling tube allows to gain insight into the heart of methanation - Taking catalyst samples oxygen-free from the reactor allows sample characterisation by: XRD, chemisorption, TPO/TPR etc. GC Sampling points GAS Seemann et al., Applied Catalysis A: General 313 (2006) 14 21
Whydoesitwork? (Dominant effects) At end of catalyst bed, mixing of dense and bubble phase Mass transfer between dense and bubble phase Hydrogen reacts with C s on catalyst surface (internal regeneration) CO 2 first by Boudouard (C s!), then readsorption, then by methanation Kopyscinski et al., Chemical Engineering Technology 32 (2007) 343 347
Methanation Options for SNG Synthesis Fixed bed vs. fluidised bed methanation Fixed Bed Fluidised bed + State of the art - Hot spot - Formation of carbon whiskers if C 2 H 4 present in the feed + Good temperature control + No formation of carbon whiskers if C 2 H 4 present in the feed - Attrition resistant catalyst necessary - Scale-upmorecomplex
Acquiring experience in up scaling PSI does R&D on methanation and gas cleaning in Güssing (A) 1 MW SNG PDU: gas pre-treatment methanation H 2 /CO 2 separation Process Development Unit (PDU)
Conclusion and Outlook In SNG production, higher overall chemical efficiency asks for lower gasifier outlet temperatures and higher methane contents Lower gasifier temperatures and more methane means often: more ethylene contents (catalyst deactivation due to carbon formation!) Fluidised bed methanation allows converting (unsaturated) hydrocarbons into SNG, without harming the methanation catalyst (experiment in 10 kw scale during 1000h) It is expected that PSI s methanation technology is quite robust towards producer gases from e.g. low temperature coal gasification A proof-of-concept of PSI s first generation methanation technology on the 1 MW scale is on the way (commissioning ongoing, 60h run so far)
Acknowledgments Our partners: CTU, TU Vienna, repotec, Biomassekraftwerk Güssing European Union (DG TREN) swisselectric research, VSG, EGO, GVM, Gaznat Swiss Federal Office of Energy (BfE) CCEM, ETH domain (ETH-Rat)
Research cooperations in SNG from wood EU DG TREN Bio-SNG Swisselectric research Konsortium Methan aus Holz VSG EGO GVM Gaznat CCEM 2nd Gen. Biogas Swiss Federal Office of Energy (BFE) ETH-Domain
Carbon- and sulphur-species in raw gas from gasifiers Mainly depending on gasification temperature S thiophenes mercaptanes High temperature gasification: (1200-1600 C) COS H 2 S C 1 C 2 C 5 BTEX >C 7 (tars) Low temperature gasification: (800-900 C) C