Thermal Gasification of Biomass Introduction

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CanadaBIOSYN Gasification and Gas Conditioning TechnologiesThe BIOSYN gasification process was developed during the 1980s by BIOSYN Inc, asubsidiary of Nouveler Inc, and a division of Hydro-Quebec. The process is based on abubbling fluidised bed gasifier containing a bed of silica or alumina capable ofoperating up to 1.6 MPa. Extensive oxygen-blown biomass gasification tests wereconducted during 1984-88, in a 10 t/hour demonstration plant located at St-Juste deBretennieres, Québec, to produce synthesis gas for methanol production. Air blownatmospheric gasification tests were also conducted for evaluating cogeneration. TheBIOSYN process proved the technical feasibility of gasifying biomass from forest andagricultural residues. Subsequently, by using a 50 kg/h process development unit, theBIOSYN process has also proven the feasibility of gasifying primary sludges, refusederived fuel (RDF), rubber residues (containing 5-15% Kevlar), and granulatedpolyethylene and propylene residues.The process accepts feed particle sizes upto 5 cm, feed bulk densities higher than0.2 kg/l and feed moisture content up to20%. The thermal efficiency for biomassgasification varies from 70-80%. The fuelgas composition ranges from 30-55% N 2 ,16-30% CO 2 , 12-30% CO, and 2-10%H 2 . Air blown gasification produces 2Nm 3 fuel gas/kg of dry biomass. The gasyield reaches 4 Nm 3 of fuel gas/kg ofpolyethylene. With air as the gasifyingagent the higher heating value (HHV) of the fuel gas is about 6 MJ/Nm 3 . Enrichedair, with 40% oxygen, can produce a fuel gas having a HHV of about 12 MJ/Nm 3at half the gas yield. The raw gas cyclones remove 85-95% of entrainedparticulates.Courtesy of BIOSYNInc, CanadaThe supporting research and development includes gas scrubbing for efficient tarremoval with reduced water requirements, recycling the insoluble tars to the gasifier,wet oxidation and adsorption of dissolved organic compounds in the scrubbing water,and recycling carbon-rich ashes and carry over carbon with adsorbed organiccompounds to the gasifier. This effort also includes hot-gas filtration of entrained dustusing a static bed of perlite particles and a moving sand bed filter, and catalytic steamcracking of tar. Proprietary catalysts can decompose 99% of tars and 97% ofnaphthalene compounds. The BIOSYN technology is commercialized by EnerkemTechnologies Inc, a subsidiary of the Kemestrie Group, a spin-off company of theUniversity of Sherbrooke. A commercial installation to gasify 2.2 t/hour of granulatedpolypropylene residues is now under construction in Spain. The electricity output will besold to the grid. Environmental International Engineering SL, a Spanish-baseddevelopment and engineering group, in partnership with Enerkem, will erect andcommission the plant in late 2000.7
DenmarkHarboøre ProjectBetween 1988 and 1992, the Danish boilermanufacturer Ansaldo Vølund Energy choseto build an updraft, counter current, movingbed gasifier for the Harboøre DistrictHeating Project located on the west coast ofJutland. The updraft gasifier was selected tocircumvent feed drying, to achieve 99% carbon conversion, and to produce a highheating value fuel gas with low dust content. The Vølund gasifier is based on aGerman design and it is now operated with woody biomass, at 4 MW th capacity, toprovide heat to about 550 homes. The raw gas containing condensible tar and otherorganic compounds is cooled and scrubbed to separate and recycle these combustiblecondensates back to the gasifier. Extensive research and technology development wasconducted in support of this facility to test novel heat exchangers, tar crackingschemes, minimization and disposal of emissions and effluents, and operation of ICengines. The gasifier could be operated at higher capacity in the future forcogeneration applications. In January 2000, two 1.5 MW e gas engines were installedto cogenerate electricity and district heat.Courtesy of Voeland Research Centre, DenmarkHøgild ProjectThis 0.5 MW th capacity CHP project supplying heatand power for 120 homes and residences in Høgild nearHerning, started with the French Martezo co-currentdowndraft moving bed gasifier. The project owner HerningMunicipality, contracted the Hollesen Engineering Company toreconstruct the gasifier. Since December 1998, the gasifier has beenoperating satisfactorily. The feed stock for gasification is double screeneddry wood residues (15% or less moisture content) and waste fromwoodworking factories. The raw gas from the gasifier is cooled andcleaned using a wet scrubber, a sawdust filter, and a filter type waterseparator. The fuel gas with a lower heating value of 4-4.8 MJ/Nm 3 isburnt and consumed in a Mercedes gas engine to produce heat and power.The efficiency of electricity production is about 24%.Blære ProjectThe Department of Energy Engineering at the Technical University of Denmark (DTU)has developed a two-stage gasification process. Based on this technology a cogenerationplant producing 250 kW th and 100 kW e was built at Blære, Aars by the Danish REKAMaskinfabrikken company. Wood or straw is pyrolysed in a first stage screw-conveyedreactor by external heating at 600°C. The resulting volatiles react with preheatedair/steam mixture to produce a low-tar-containing fuel gas which is used to gasify the8
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Thermal Gasification of Biomass Introduction

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