fluidised bed methanation technology for improved ... · fluidised bed methanation technology ......

T.J. Schildhauer, May 2009

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. BiollazPaul 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)

• In operation since 1984, input is lignite• 14 Lurgi-Gasifiers (150 MWth each)• Fixed bed methanation (Lurgi)

Great Plains Synfuels Plant

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

FeedstockProducer gas CH4 , CO2

Heat

Heat

Autothermal Gasification:Losses depend on the gasifier outlettemperature.

Exothermic Methanation:Losses depend on selectivity and producergas composition. The higher the methanefraction, the higher the chemical efficiency!

Gasifier Methanation


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 H2 S and COS, but also organic sulphur compounds such asmercaptans, thiophenes

- potentially higher ethylene (C2 H4 ) 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 MWSNG scale running on CO/H2 mixtures


Operation experience of demo & pilot plants (Comflux) Good starting point for bio syngas investigations

0

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2 kW Pilot plant

H2 /CO ratio [-]

Target area for biomass

Target area for biomass


Methane from wood: Producing SNG in pipeline quality

CHP Plant Güssing; 8 MWth , 2 MWel

Gas conditioning

SNG (CH4 )

FluidizedCatalyst

Bed

H2 4%CO 0.5%CO2 47.5%CH4 40%C2H4 0%N2 8% Gas

cleaning

H2 37%CO 25%CO2 18%CH4 10%C2H4 3%N2 6%S-speciestars


FluidizedCatalyst

Bed

Gas cleaning

> 1000h stable run with real gas (10 kW slip stream)

fully automated set-up of PSI


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[vol

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s_co

Stable run with real gas on 10 kW scale

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

GAS

Sampling points

Seemann et al., Applied Catalysis A: General 313 (2006) 14 – 21


Why does it work ? (Dominant effects)

At end of catalyst bed, mixing of dense and bubble phase

Mass transfer between dense and bubble phase

Hydrogen reacts with Cs on catalyst surface (internal regeneration)

CO2 first by Boudouard (Cs !), 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

C2 H4 present in the feed

+ Good temperature control+ No formation of carbon whiskers

if C2 H4 present in the feed- Attrition resistant catalyst necessary- Scale-up more complex


Acquiring experience in up scaling PSI does R&D on methanation and gas cleaning in Güssing (A)

1 MWSNG PDU:• gas pre-treatment• methanation• H2 /CO2 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

KonsortiumMethan aus Holz

Bio-SNG

CCEM2nd Gen. Biogas

Swisselectric research

EU DG TREN

Swiss Federal Office of Energy (BFE)VSGEGOGVM

Gaznat

ETH-Domain


Carbon- and sulphur-species in raw gas from gasifiers Mainly depending on gasification temperature

C1 C2 – C5 BTEX >C7 (tars)

C

S

H2 S

COS

mercaptanes

thiophenes

Low temperature gasification: (800 - 900 °C)High temperature

gasification: (1200 - 1600 °C)

fluidised bed methanation technology for improved ... · fluidised bed methanation technology ......

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