Synthesis Gas from Biomass –Problems and Solutions en route to TechnicalRealizationBy N. DAHMEN, E. DINJUS and E. HENRICH*

AbstractA thermochemical two-step processcalled bioliq® for the conversion of bio-

mass in tailored synthetic fuels and organicchemicals via the production of syngas as aversatile intermediate is being developed.The research and development work has beenfocused on synthesis gas generation from liq-uefied biomass in a pressurized entrainedflow gasifier. The sequential process stepshave been successfully investigated in thelaboratory and on the pilot plant scale. Fastpyrolysis for liquefaction of the ligno-cellu-losic biomass has been conducted with theLurgi twin-screw mixing reactor success-fully. Pumpable, homogenous slurries of thepyrolysis liquids with high loadings of pyrol-ysis char powder have been prepared withcolloid mixers for subsequent gasification.Efficient and smooth slurry gasification to atar-free, low methane synthesis gas has beenobtained with a number of different slurriesin four testing campaigns in the 3–5 MWth en-trained flow pilot gasifier of Future Energy,Freiberg, at 26 bar. A complete process linewith around 2 MWth capacity from fast pyrol-ysis to synthesis with an 80 bar gasifier is un-der design, the pyrolysis plant already underconstruction in co-operation with Lurgi AG.

IntroductionLignocellulose in the form of straw, hay orresidual wood is the most inexpensive and

abundant biomass by far. Presently, biomassis covering about 3% of the primary energyneed in Germany. Consistent use of allbiogenous residual and waste materials willincrease this proportion to about 12% [1]. Asbiomass is the only renewable carbon source,it may replace part of the fossil resources andenergy carriers in the long term. Transition oforganic chemical industry to biomass as araw material represents a long-term and greatchallenge in chemical research and develop-ment. Apart from the already practiced utili-

zation of natural substances, there is hardlyany economic incentive to intensify thechemical use of biomass for mass produc-tion. Early development of the correspond-ing technologies, however, is a precautionthat may reduce today’s dependence on pe-troleum and improve our competitiveness.Use of biomass for the production of tailoredsynthetic fuels and organic chemicals shouldtherefore be given priority to its use on theelectricity or heat market.Synthetic chemicals and fuels from biomassmight replace part of fossil energy carriersin the short term already and, hence, contrib-ute to reducing CO2 emissions. Further in-creasing crude oil prices, aspects of supplysecurity as well as existing emission limitsgive new political and economic impulses inthe search for solutions. For example, theEuropean Union wishes to increase the cur-rent share of biofuels to 5.75% in 2010.In principle, the method of producing syn-thetic chemicals and fuels from fossil mate-rials, mainly coal and natural gas, has beenknown for a long time. For biogenous solidfuels, however, an adequate technology stillremains to be developed. Coal or natural gasare first converted into a synthetic raw gasby a reaction with water vapor and oxygen.After cleaning and conditioning, the productdesired is obtained by a catalytic conversion

at increased pressures and temperatures.The main chemical processes established forthe production of synthetic chemicals andfuels are the Fischer-Tropsch synthesis(FTS) and methanol synthesis (Fig. 1) [2, 3].The FT raw product consists of a large spec-trum of hydrocarbons that are separated andprocessed depending on the target productdesired. Methanol is the intermediate prod-uct of the MtG process (methanol to gaso-line). However, it can also be used directly asa fuel. It is applied for the synthesis of theanti-knock additive MTBE (methyl-tert.butylether), the production of RME (rapemethyl ester, biodiesel) by esterification ofrape oil, and as a direct fuel and hydrogencarrier in DMFC fuel cells. Fully syntheticfuels or 2nd generation biofuels have a higherpurity and environmental compatibility thanpetroleum-based fuels and may be tailoredto specific requirements of e. g. automotivemanufacturers and stricter emission stan-dards.

ProblemCompared to the use of fossil fuels,synthesis gas production from biomass

is more complex and sophisticated. For useon a large technical scale, the following prob-lems have to be solved:

OIL GAS European Magazine 1/2007 OG 31

SYNTHETIC FUELS

0179-3187/07/I© 2007 URBAN-VERLAG Hamburg/Wien GmbH

*N. Dahmen, E. Dinjus, E. Henrich, ForschungszentrumKarlsruhe Institute for Technical Chemistry, CPV (E-mail:Nicolaus.Dahmen@itc-cpr.fzk.de).Lecture, presented at the DGMK/SCI Conference “Synthe-sis Gas Chemistry”, October 4–6, 2006, Dresden, Germany.

Fig. 1 Utilization paths of synthesis gas

SYNTHETIC FUELS

OG 32 OIL GAS European Magazine 1/2007

– Biomass arises in a regionally distributedmanner, i. e. it has to be collected overlarge areas and transported over accord-ingly long distances

– The less valuable, ash-rich biomass in par-ticular has a low volumetric energy density(e. g. straw bales about 2 GJ/m3). Alsohere, the problem of economically accept-able transport distances has to be solved

– A large variety of usable biomasses exists.It must be ensured that the processes ap-plied are suited for a maximum number offeed stocks

– Biomass is taken from the biosphere; forlong-term use, an ecologically compatibleextraction of the raw material must be en-sured

– Biomasses are heterogeneous solid fuelsof partly variable chemical composition;solid fuels in principle require a highertechnical expenditure. Use of existingtechnologies for the processing of fossilmaterials, for instance, helps to shortendevelopment times and reduce the risks

– The high ash contents of fast growingbiomasses (straw, hay, etc.) in particularcause problems in thermochemical pro-cesses due to corrosion, sticking, andplugging of the technical components

– Fuel syntheses require a tar-free, meth-ane-depleted synthesis gas at high pres-sures (FTS up to 30 bar, methanol andDME up to 80 bar) and a crucial elimina-tion of trace substances to avoid poisoningof the catalyst

– Gasification of biomass of an averagechemical composition of C6H9O4 results ina C/H ratio of about 1 that is insufficientfor direct production of hydrocarbons. Anadditional step, the water-gas shift reac-tion, is necessary, in which part of the COis converted into hydrogen and CO2 by theaddition of water

– The use of biomass also has social aspects,as new logistics and income and laborstructures have to be established in the ag-

ricultural, grassland, and forestry sectorsfor them to be able to supply and processenergy materials.

The bioliq® ProcessThe Karlsruhe bioslurry gasificationprocess has been designed for the con-

version of ligno-cellulosic biomass into or-ganic chemicals and tailored synfuels withelectricity and power as inevitable by-prod-ucts [4, 5]. The development has been fo-cused on the front-end steps for syngas gen-eration. The tail-end steps for syngas clean-ing, synthesis and product conditioning arewell known from many technical applica-tions in the chemical industry and the hugeCTL and GTL plants of Sasol and Shell. Thebioliq® concept meets the logistical and tech-nical requirements resulting from the widelydistributed occurrence of biomass and theneeds for an economic production of chemi-cals and fuels in industrial scale (Fig. 2).Syngas production is the key issue of the pro-cess: a slagging entrained flow gasifier oper-ating at high pressure above downstreamsynthesis pressure and temperatures abovethe ash melting pointhas been selected be-cause of the follow-ing advantages: (1)tar-free, low meth-ane syngas, (2) highcarbon conversion>99%, (3) high po-tential throughput upto the GWth range,(4) short start-up andsudden shut-down,(5) high feed flexi-bility. For pre-treat-ment of biomass, itsliquefaction by fastpyrolysis can servedifferent aims: (1) togenerate valuable

chemicals, (2) to prepare a liquid fuel formore convenient and efficient combustionfor heat, power or electricity, (3) to prepare apumpable fuel for convenient and efficientgasification to produce syngas. Usual objec-tive of flash pyrolysis is a high yield of a sta-ble, clean and ash-free bio-oil for direct usein boilers, diesel engines or turbines. Highquality oil for these applications requiresmuch effort during production and eventualdownstream upgrading procedures. For gasi-fication however, high purity is not needed.Any suspension of pulverised pyrolysis charand liquids with LHV >10 MJ/kg which canbe pumped and pneumatically atomised withpure oxygen is suited for the gasifier.

Step 1: Bio slurry productionIn a first step of the bioliq® process, pyroly-sis oil and pyrolysis char are generated fromthe biomass by de-centralized flash pyroly-sis (Fig. 2). The transported bed LR-type(Lurgi-Ruhrgas) mixing reactor applied forthis purpose has been used as a “sandcracker” in the industrial flash pyrolysis ofvarious refinery products for about 40 yearsalready [7]. In the present process, the finelychopped biomass particles are heated uprapidly to about 500 °C by hot sand in thetwin screw mixing reactor (Fig. 4). After ashort residence time of a few seconds, thehot pyrolysis vapors leave the reactor to-gether with the fine char powder [6]. Themain portion of gas is cooled to form liquidpyrolysis products: a single step condensedbio-oil phase is less stable than a separatedtar and aqueous phase. The remaining pyrol-ysis gas produced may be used in the processfor heating up the heat carrier. The pyrolysischar and condensates are mixed in a colloi-dal mixer to a transport-stable, pumpableslurry, the volumetric energy density ofwhich is higher by more than a factor of 10compared to the original biomass. Theseslurries are stable mixtures of organic tarand aqueous condensate with more than30 wt.% of char. Main objective of the fastpyrolysis is the production of sufficient or-ganic and aqueous liquid for complete charsuspension [8, 9]. In addition to the ca.

Fig. 2 The decentralized/central slurry gasification concept

Fig. 3 Yields of the flash pyrolysis of different kinds of wood meal andstraw

50–65% energy in the liquid condensatesnow also the ca. 25–40% fraction in the charis contained in the slurry ready for gasifica-tion. Some results of fast pyrolysis obtainedfor various feedstocks are plotted in Figure3. The materials 1–4 are different types ofwood, materials 5–8 are different types ofstraw. The yields differ significantly for dif-ferent materials, but also for materials of thesame group of biomass.

Step 2: Bio slurry gasificationThe slurry prepared from the pyroylsis prod-ucts is then transported to a central plant forsyngas production and conversion andsprayed into a large-scale high-pressure en-trained-flow gasifier together with oxygenand converted substoichiometrically (λ ≈1/3) at temperatures above 1200°C to atar-free and methane-depleted raw synthesisgas [10–12]. Gasification takes place at apressure exceeding that of the downstreamsynthesis, such that no complex interimcompression is needed. The entrained-flowgasifier of the GSP type (Gaskombinat“Schwarze Pumpe”) is suited in particularfor the gasification of ash-rich biomasses. Itwas developed originally for the gasificationof the salt lignite existing in Central Ger-many [13]. The gasifier is equipped with acooling screen, onto which the molten ash isdeposited in the form of a liquid slag leavingthe reactor (Fig. 5). Suitability of this type ofgasifier has been demonstrated by four testcampaigns with various bio-slurries and op-eration parameters using the only 3–5 MWpilot gasifier of Future Energy, Freiberg.The test runs have been conducted with slur-

ries from different pyroylsis products fromhard and softwood as well as from wheat andrice straw. The slurry properties ranged be-tween LHV from 10–24 MJ/kg, densities of1100–1300 kg/m3 and viscosities (20 °C) of1–10 Pas. In all experiments, a practicallytar-free, methane-depleted (<0.1 vol.%)synthesis gas was produced. It typically con-sisted of 43–50 vol.% carbon monoxide,20–30 vol.% hydrogen, and 15–18 vol.%CO2.The synthesis gas is cleaned, conditioned,and transferred to chemical synthesis at pro-cess pressure already. By the above men-tioned routes (Fig. 1) synthetic chemicalsand fuels can then be produced. This processallows to generate about 1 t synthetic fuelfrom about 7 t air-dried straw or wood.Nearly 50% of the energy initially contained

in the biomasses remains in the liquid prod-uct. As by-products, heat and electricity aregenerated, by means of which the energyconsumption of the process can be coveredcompletely.After technical feasibility of the process hadbeen confirmed by demonstrating the suit-ability of all process steps, it is now concen-trated on the further development of the pro-cess. For this purpose, a pilot plant along thecomplete process chain with a biomassthroughput of 500 kg/h is being built at theForschungszentrum Karlsruhe with supportby the Agency of Renewable Resources(Fachagentur Nachwachsende Rohstoffe,FNR). This pilot plant will serve to demon-strate and further develop the process, pre-pare upscaling to a commercially relevantscale, demonstrate the feasibility of the pro-

SYNTHETIC FUELS

OIL GAS European Magazine 1/2007 OG 33

Fig. 4 Flowchart of flash pyrolysis with a twin-screw mixing reactor Fig. 5 Flowchart of the GSP high-pressure entrained-flow gasifier

Fig. 6 Process building for biomass conditioning, fast pyroylsis and slurry preparation

SYNTHETIC FUELS

OG 34 OIL GAS European Magazine 1/2007

cesses used, and help to make a reliable costestimation. The first construction phase,comprising biomass cutting, flash pyrolysis,and continuous slurry mixing, was started in2005. Figure 6 shows the process buildingunder construction. The clearly visibletower-like construction accommodates thepyrolysis plant that will be operated from2007 together with the Lurgi AG, Frankfurt.

Cost Study and PotentialThe Karlsruhe bioliq® process is tai-lored to the distributed biomass

arisings in agriculture. Fast pyrolysis andslurry production with energy densificationof the feedstock may take place in a largernumber of decentralized plants, whereasgasification and subsequent gas conditioningand synthesis will be carried out centrally ineconomically efficient large-scale plants forfuel or chemical synthesis. The slurry will betransported to these plants favourably by rail-way. When assuming about 40 flash pyroly-sis plants with a capacity of 200,000 t/a eachthat produce slurries for a central syngas andfuel production plant with a capacity of1 million t fuel and a price of the feedstock of70 Euro/t air-dry material, production costsof less than 1 Euro per kg fuel result. The sur-vey of the costs (Fig. 7) shows that about halfis due to the supply of biomass in Germany.Today, the production costs of syntheticchemicals and fuels from biogenousfeedstocks correspond to or exceed those offossil fuels. The high specific mass through-put, feeding of the solids and residues andtheir discharge from the process zones aswell as complex cleaning of the synthesisgas, however, lead to higher process costs.The gas generation and synthesis plants

should have the size of refinement facilities,but will probably remain at the lower sizelimit. As a result of cost degression these fa-cilities will be more expensive. A widerspectrum of feedstocks will improve theflexibility, utilization, and economic effi-ciency of the plants. In this respect, thefeedstocks are by no means limited to purebiomass. In principle, any mixtures of bio-mass, fossil fuels or organic wastes and anymixtures with calorific values in excess of10 MJ/kg are suited. By integrating thegasifier in a plant complex of chemical in-dustry, diversification and value of the us-able products may be increased.Process development is presently focusingon so far hardly used, low-value biomass,such as excessive straw, low-quality hay orresidual wood. Use of whole wood is consid-ered a non-profitable solution in the longterm. Although this less problematicfeedstock may facilitate an earlier technicalimplementation, increasing consumption asconstruction material, for cellulose produc-tion, and for decentralized and domesticpower and heat production is expected. Useof whole plants seems to be more reasonablefor cereals or specially grown energy plants.According to accompanying systems analy-sis [1, 14] about 5 million t of synthesis fuelcould be expected to be produced from a to-tal of about 30 million t dry matter of resid-ual wood and excessive straw already today.This corresponds to about 10% of the cur-rent consumption of gasoline and diesel fu-els in Germany [15].

Support and funding of the work by the Federal Ministryof Education and Research, Ministerium für Ernährungund Ländlichen Raum Baden-Württemberg, theAgency for Renewable Resources FNR, and the Euro-pean Commission are gratefully acknowledged.

Literature[1] E. Henrich, L. Leible, L. Malcher, H. J. Wiemer: Fi-

nal project report “Gaserzeugung aus Bio-masse”, Forschungszentrum Karlsruhe, 2005.

[2] R. L. Espinoza, A. P. Steynberg, B. Jager, and A.C. Vosloo: Applied Catalysis A: General, Volume186 (1999) 13–26 and 41–54.

[3] W. Liebner, M. Wagner; Erdöl Erdgas Kohle 120(2004) 323–326.

[4] E. Henrich, E. Dinjus, D. Meier; DGMK Proceed-ings 2002-2, 95.

[5] E. Henrich, E. Dinjus; Nachwachsende Rohstof-fe, no. 24, Landwirtschaftsverlag Münster, 2004,298–337.

[6] C.Kornmayer, E.Dinjus, E.Henrich, F.Weirich, R.Reimert;DGMK Proceedings, 2006-2, 185–192.

[7] R. W. Rammler; Oil & Gas Journal, Nov. 9, 1981,p. 291.

[8] K. Raffelt, E. Henrich, J. Steinhardt; DGMK Pro-ceedings 2004-1, 333–340.

[9] K. Raffelt, E. Henrich, C. Kornmayer, C. Renck, R.Stahl, J. Steinhard, E. Dinjus; DGMK Proceed-ings 2006-2, 121–128.

[10] E. Henrich, E. Dinjus, D. Meier; DGMK Proceed-ings 2004-1, 105.

[11] M. Schingnitz, D. Volkmann; DGMK Proceedings2004-1, 29–38.

[12] M. Schingnitz; Chemie-Ingenieur-Technik 74(2002) 976–984.

[13] M. Schingnitz, H. Brandt, F. Berger, P. Göhler, H.Kretschmer; Fuel Processing Technology, 16(1987), 289–302.

[14] L. Leible, S. Kälber, G. Kappler, S. Lange, E.Nieke, P.Proplesch, D.Wintzer, B.Fürniß;DGMKProceedings 2006-2, 23–30.

[15] S. Lange, R. Reimert, L. Leible; DGMK Proceed-ings 2006-2, 107–114.

Dr. Nicolaus Dahmen hasstudied chemistry at theRuhr-University Bochum, fin-ishing his PhD and changing tothe Forschungszentrum Karls-ruhe in 1992. Today he is work-ing in the field of thermo-chemical conversion of bio-

mass to hydrogen and synthesis gas. As a projectleader he is responsible for the construction of thebioliq pilot plant.

Prof. Dr. Eckhard Dinjus fin-ished his study of chemistry atthe Friedrich-Schiller-Univer-sity in Jena with a PhD degreein 1973. In 1989 he made hishabilitation, after which he be-come the leader of the Max-Planck working group “CO2-

Chemistry”. Since 1996 he is leader of the Institutefor Technical Chemistry of the ForschungszentrumKarlsruhe and holds the chair for the same at the Uni-versity of Heidelberg.

Prof. Dr. Edmund Henrichstudied chemistry at the uni-versities of Mainz and Heidel-berg. Here he finished his dis-sertation in 1971 and habilita-tion in 1993 in the field ofradiochemistry. Since 1974 heworks at the Forschungs-

zentrum Karlsruhe and has been involved in the con-ception and design of the BtL-process. Since 2005 hehas an apl. professorship at the University of Heidel-berg.

Fig. 7 Percentage shares in the costs ofproduction of BTL synthesis fuel by theKarlsruhe bioliq® process