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April 2004 ECN-RX--04-024 BIOMASS AND WASTE-RELATED SNG PRODUCTION TECHNOLOGIES Technical, economic and ecological feasibility M. Mozaffarian R.W.R. Zwart H. Boerrigter E.P. Deurwaarder Contribution to the “2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection ” 10-14 May 2004, Rome, Italy

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Page 1: Biomass and waste-related SNG production technologies€¦ · based hydrogen lowers the market price for SNG from hydrogasification process, as only a part of the produced SNG can

April 2004 ECN-RX--04-024

BIOMASS AND WASTE-RELATEDSNG PRODUCTION TECHNOLOGIES

Technical, economic and ecological feasibility

M. MozaffarianR.W.R. ZwartH. Boerrigter

E.P. Deurwaarder

Contribution to the “2nd World Conference and Technology Exhibition on Biomass for Energy,Industry and Climate Protection ”

10-14 May 2004, Rome, Italy

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Page 3: Biomass and waste-related SNG production technologies€¦ · based hydrogen lowers the market price for SNG from hydrogasification process, as only a part of the produced SNG can

ECN-RX--04-024 3

BIOMASS AND WASTE-RELATED SNG PRODUCTION TECHNOLOGIESTECHNICAL, ECONOMIC AND ECOLOGICAL FEASIBILITY

M. Mozaffarian, R.W.R. Zwart, H. Boerrigter, E.P. DeurwaarderEnergy research Centre of the Netherlands (ECN)

P.O. Box 1, 1755 ZG Petten, The NetherlandsPhone: +31 224 564262 / Fax: +31 224 568504

E-mail: [email protected]

ABSTRACT: Based on comparable assumptions, a technical, economic, and ecological assessment has beenperformed for several biomass/waste-related SNG production technologies, with the objective to make a selectionfor future implementation of the most promising options. Based on the modelling results, the upstreampressurised oxygen-blown CFB or indirect atmospheric steam-blown gasification with downstream methanationroutes were identified to be the most promising options for SNG production from biomass. In combination withdownstream methanation, SNG production efficiencies up to 70% (LHV) can be achieved. The successfulintegrated lab-scale demonstration of “Green Gas” production confirmed the potential of the ECN gas cleanupconcept to deliver a product gas, that can satisfy among others the specifications for downstream methanation.For a 100 MWth system and biomass costs of 2.3 ¼�*-��WKH�61*�SURGXFWLRQ�FRVWV�UDQJH�IURP�����WR�����¼�*-�DQGthe CO2 emission reduction costs range from approximately 80 to 95 ¼�WRQQH�� ³*UHHQ� *DV´� SURGXFWLRQ� YLDbiomass gasification with downstream methanation can be an economic feasible process in the Netherlands, ifcomparable stimulating measures would be considered for green gas, as are now the case for green power.Keywords: green gas, substitute natural gas (SNG), methanation

1 INTRODUCTION

“Green Gas” (or Substitute Natural Gas, SNG) isa sustainable gas from biomass with natural gasspecifications. Therefore, it can be transportedthrough the existing gas infrastructure, substitutingnatural gas in all existing applications.

Within the Dutch sustainable energy policy animportant role is foreseen for the application ofbiomass and waste. 10% of the total primary energysupply in 2020 should be delivered by renewableenergy sources[1][2]. About 50% of this policy targethas to be realised by biomass and waste. For the long-term (2040) the Dutch Ministry of Economic Affairshas proposed a Biomass Vision within the EnergyTransition activities, declaring that 30% of the fossilfuels in the electricity and transportation sectors, and20-45% of the fossil-based raw materials in thechemical industry has to be substituted by biomass[3].

Compared to other biomass conversion routes, themajor advantage of the “Green Gas” concept is thepotential to use the existing dense Dutch andEuropean gas infrastructure for large-scaleintroduction of bio-energy. For Europe this willcontribute to the security of gas supply, which will bemore and more dependent from import, while for theNetherlands it will save the natural gas resources fora longer period.

Large amounts of primary fuels are consumed fordistributed heat production. The use of centralisedproduced SNG (economy of scale) for heatproduction in households and small and mediumsized enterprises is economic competitive withalternative options like distributed CHP plants andelectrical heating. SNG can also be stored in old gasfields for (seasonal) peak shaving. Promising nearfuture applications for “Green Gas” are co-generationat household level (especially in fuel cells), and asalternative fuel for transportation (i.e. CNG, LNG).Concerning the future use of alternativetransportation fuels in the EU, the EuropeanCommission has a targeted natural gas market share

for road transport of 10% by 2020 (based onpercentage of the total fuel consumption fortransportation). A main driving force for the large-scale introduction of CNG as motor fuel is concernfor the security of supply for the transport sector,currently solely dependent on oil products[4][5].Besides, application of CNG will result in lessemissions of NOx, CO2, aromatics, and sulphurcompounds, compared to petrol or diesel[5][6]. Similarto CNG, “Green Gas” can also be used as a motorfuel, with the advantage of being an almost CO2-neutral fuel.

The objective of this project, which is carried outin co-operation with the Dutch Gasunie Trade &Supply, was to make a selection for futureimplementation of the most promising technologiesfor the production of SNG from biomass and waste.

The following gasification-based SNG productionroutes have been considered within this study[7]:• Pressurised O2-blown CFB gasification followed

by methanation.• Atmospheric indirect steam-blown gasification

followed by methanation.• Pressurised BFB hydrogasification followed by

methanation.• Pressurised O2-blown CFB gasification followed

by Fischer-Tropsch synthesis and methanation.• Atmospheric indirect gasification followed by

Fischer-Tropsch synthesis and methanation.

The first three stand-alone SNG productionconcepts are considered in this paper. In the co-production FT-SNG concept the off-gases from FTsynthesis are used for SNG production throughmethanation. This concept can be considered as analternative route to stand-alone FT synthesis, inwhich large amounts of off-gases would be recycledto the gasification step, requiring a large amount ofauxiliary power. The co-production FT-SNG concepthas been evaluated in the paper “High efficiency co-production of SNG and FT transportation fuels frombiomass” by Zwart and Boerrigter[8].

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The main pre-conditions for the stand-alonegasification concepts were production of a tar-free,low-nitrogen, and high methane content product gas,and the up-scaling potential of the technology to acommercial scale. Air-blown CFB gasification due toa high nitrogen content of the produced gas, andentrained-flow gasification due to zero methanecontent of the produced gas have, therefore, been leftout of consideration.

2 MODELLING WORK

A block scheme of the stand-alone SNGproduction systems is presented in figure 1. In allcases the product gas from gasifier, after a low-temperature cleanup, and passing through amethanation step, is used for the production of SNGas main product.

Figure 1: “ Green Gas” (SNG) production by biomass gasification / hydrogasification

In order to determine the mass and energybalances of these processes, three Aspen Plus modelswere developed. The operating temperature of thegasifiers is 850°C. The gasifier pressure isrespectively 1 bar for indirect gasification, 15 bar foroxygen-blown gasification, and 30 bar forhydrogasification. In case of indirect gasification, theproduct gas after cleanup is compressed to 15 bar,before entering the methanation section. In case ofpressurised options a CO2 stream is used as transportgas. The cleanup step consists of a dust filter, deep tarremoval with the ECN oil-based gas washer (theOLGA unit), water scrubbing for removal of NH3 andhalides, and guard beds for final protection ofmethanation catalyst. The methanation process isbased on the inter-cooled methanation process, usedwithin the Lurgi coal-to-SNG process[9]. Theconditioning step consists of gas cooling and drying,followed by partial removal of CO2 (if necessary), inorder to bring the Wobbe-index of the gas within theDutch natural gas specification (i.e. between 43.46and 44.41 MJ/Nm3). The heat generated at variouspoints in each process is used for steam andelectricity generation in a steam cycle, in order tosatisfy the demand within the system.

The modelling results show, that the upstreamatmospheric steam-blown indirect gasification orpressurised oxygen-blown gasification withdownstream methanation routes are the mostpromising options for SNG production from biomass.In combination with downstream methanation, SNGproduction efficiencies up to approximately 70% (onLHV basis) can be achieved. The specific investmentcosts of a system with a thermal biomass input of 100

MW are higher for pressurised oxygen-blowngasification (480 ¼�N:th) compared to indirect steam-blown gasification (450 ¼�N:th), mainly due to therequirement of an oxygen plant. The SNG productioncosts for a 100 MWth system and biomass costs of 2.3¼�*-�UDQJH� IURP����� WR�����¼�*-��ZKLOH�EDVHG�RQ� WKHDutch stimulating measures, valid in 2002, the actualmarket price for green gas was calculated to be in therange of 8.5 to 8.9 ¼�*-��7KH�&22 emission reductioncosts range from approximately 80 to 95 ¼�WRQQH�which is lower than the 100 ¼�WRQQH� WD[� H[HPSWLRQfor green power.

The up-scaling potential of the indirectgasification technology is expected to be less than thepressurised oxygen-blown gasification, due to thecomplicated heat exchange between the gasifier andthe combustor. This makes the technology mainlysuitable for decentralised SNG plants (< 100 MWth).The fact that this technology does not require anoxygen plant is another positive aspect of thistechnology for decentralised applications. In contrary,the pressurised oxygen-blown gasification will bemore suitable for centralised applications (> 100MWth).

With respect to biomass hydrogasification, higherSNG production efficiencies (up to 80% LHV) andlower SNG production costs (5.6 ¼�*-�� FDQ� EHachieved, compared to biomass gasification/methanation routes. However, the limited availability(until 2020), as well as the origin (fossil-based) of theapplied hydrogen result in lower SNG productionpotential and CO2 emission reduction, and higherCO2 emission reduction costs (115 ¼�WRQQH��� )RVVLO�based hydrogen lowers the market price for SNGfrom hydrogasification process, as only a part of theproduced SNG can be considered green.

3 EXPERIMENTAL WORK

“ Green Gas” production via biomass gasification,gas cleaning, and methanation was successfullydemonstrated in December 2003.

Gas cleaning is the major technical challenge inthe application of product gases from biomassgasification for SNG production, as the methanationcatalysts are very sensitive to impurities, especiallysulphur, halides, and tar compounds. In the integratedtest, beech wood (1 kg/hr) was converted into aproduct gas (composition: CH4 (11%), CO (31%), H2(21%), C2H4 (3.6%), CO2 (29%), with balance mainlyN2, C2H6, and C2H2) by oxygen/steam-blowngasification in one of the ECN biomass lab-scale(bubbling) fluidised bed gasifiers. The gas wascompletely de-dusted with a high-temperatureceramic filter (400°C), followed by deep tar removalwith the lab-scale OLGA unit, and water scrubbingfor removal of NH3 and halides. In order to achievethe desired H2/CO ratio for methanation, extrahydrogen was added to the gas. Then the gas was ledto the so-called AGAF facility (Advanced GasApplication Facility), consisting of respectively awater condensor, a compressor (up to 60 bar), ZnOfilters for sulphur removal, and active carbon filtersfor final protection. The clean gas was then used asfeed for our micro-flow fixed-bed methanation

Indirect gasification

MethanationSNGGas

conditioningO2-blown

gasification

Hydro-gasification

Heat / steam

O2 / steam

Hydrogen

Biomass

Biomass

Biomass

Gascleanup

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ECN-RX--04-024 5

reactor with a Ru-based catalyst, operated at 30 barand 260°C.

The suitability of the cleaned biomass product gasfor SNG synthesis was proven by stable catalystperformance during the 150-hours integratedmethanation test. The deactivation rate wascomparable with our reference case, in which a“ clean” synthetic mixed gas was used as feed stream.

4 CONCLUSIONS

• Atmospheric indirect steam-blown gasification orpressurised oxygen-blown CFB gasification withdownstream methanation are the most promisingroutes for SNG production from biomass,resulting in SNG production efficiencies up to70% LHV.

• Atmospheric indirect steam-blown gasification ismore suitable for decentralised (< 100 MWth)applications, while pressurised oxygen-blownCFB gasification is more suitable for centralised(> 100 MWth) applications.

• The successful integrated lab-scale demonstrationof “ Green Gas” production confirms the potentialof the ECN gas cleanup concept to deliver aproduct gas, that can satisfy among others thespecifications for downstream methanation.

• For a 100 MWth system and biomass costs of 2.3¼�*-�WKH�61*�SURGXFWLRQ�FRVWV�UDQJH�IURP�����WR8.5 ¼�*-� DQG� WKH� &22 emission reduction costsrange from approximately 80 to 95 ¼�WRQQH�which is lower than the 100 ¼�WRQQH� WD[exemption for green power.

• “ Green Gas” production by atmospheric indirectsteam-blown gasification or pressurised oxygen-blown CFB gasification with downstreammethanation can be economic feasible processesin the Netherlands, if comparable stimulatingmeasures would be considered for green gas, as isnow the case for green electricity.

5 FUTURE WORK

The “ Green Gas” technology developments atECN will be continued in 2004-2005, in co-operationwith the Dutch Gasunie Trade & Supply (GU T&S)and Gastransport Services (GtS). A bench-scaleintegrated gasification, gas cleaning, and methanationsystem will be constructed and operated. The new so-called MILENA gasifier, with thermal inputs up to 25kW (5 kg/hr biomass), can be operated at directoxygen-blown gasification mode, as well as atindirect steam-blown gasification mode. Theintegrated system should enable the proof ofproduction of a gas, that satisfies the specificationsfor downstream methanation. The R&D activities areaimed at optimisation of the gasification conditions

(agglomeration behaviour, gas composition), gascleaning (removal of tar and other components) andconditioning, and an extensive methanation testprogramme. The R&D activities should result in aconceptual design for a pilot-scale integrated biomassgasification SNG plant, to be realised and operated in2005-2008. Commercial units are expected after2008.

6 ACKNOWLEDGEMENTS

Financial supports from the Dutch organisationfor energy and the environment (Novem) and theDutch Gasunie Trade & Supply are gratefullyacknowledged

7 REFERENCES

[1] Derde energienota. Ministerie van EconomischeZaken, Den Haag, 1995.

[2] Duurzame energie in opmars, actieprogramma1997-2000. Ministerie van Economische Zaken,Den Haag, 1997.

[3] Biomassa: de groene motor in transitie; standvan zaken na de tweede etappe. Ministerie vanEconomische Zaken, Den Haag, December 2003.

[4] Communication from the Commission to theEuropean Parliament, the Council, the Economicand Social Committee and the Committee of theRegions on alternative fuels for roadtransportation and on a set of measures topromote the use of biofuels. Commission of theEuropean Communities, COM (2001) 547 final,Brussels, November 2001.

[5] Market development of alternative fuels. Reportof the European Commission’s alternative fuelsContact Group, December 2003.

[6] Hendriksen, P., R.J. Vermeulen, R.C. Rijkeboer,D. Bremmers, R.T.M. Smokers, R.G. Winkel:Evaluation of the environmental impact ofmodern passenger car on petrol, diesel,automotive LPG and CNG, TNO report:03.OR.VM.055.1/PHE, December 2003.

[7] Mozaffarian, M., Zwart, R.W.R.: Feasibility ofbiomass/waste-related SNG production technolo-gies. Final report, ECN-C--03-066, ECN, Petten,The Netherlands, July 2003.

[8] Zwart, R.W.R., Boerrigter, H.: High efficiencyco-production of substitute natural gas (SNG)and Fischer-Tropsch (FT) transportation fuelsfrom biomass. Oral presentation (B4.2) at the 2ndworld conference and technology exhibition onbiomass for energy, industry and climateprotection, Rome, Italy, 10-14 May 2004.

[9] Catalyst Handbook. Second edition, edited byM.V. Twigg, ISBN 1874545359, 1996.

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