Biomass thermochemical gasification

Cox et al. (1995) portray a new approach to thermochemical gasification of biomass to hydrogen. The process is based on catalytic steam gasification of biomass with concurrent separation of hydrogen in a membrane reactor that employs a permselective membrane to separate the hydrogen as it is produced. The process is particularly well-suited for wet biomass and may be conducted at temperatures as low as 575 K. 

Keywords Packed-bed combustion, thermochemical conversion of biomass, solid-fuel combustion, fuel-bed combustion, grate combustion, biomass combustion, gasification, pyrolysis, drying. 

This overview reports on the progress achieved over the past five years in thermochemical gasification of biomass and waste recovered fuels. The status of all major projects is reviewed while new trends are briefly presented. The paper concludes with recommendations for fumre R D needs and demonstration requirements while attempting to present a strategy for the commercialisation of gasification technologies. 

Fluidized bed application is fairly popular in biomass thermochemical conversions. The one of reason is due to the high efficient heat and mass transfers between particles and gases in the reactor. The initial and essential step of biomass thermochemical conversions such as combustion and gasification in a fluidized bed is pyrolysis. Directly experimental study on the pyrolytic process is limited. Numerical simulation can be an effective way for understanding of the first step of biomass combustion and gasification in applications. 

Ctirbon monoxide for the water-gas shift reaction may derive from a synthesis gas (predominantly CO) obtained by a thermochemical gasification of biomass (e.g., wood waste). Growth and H2 production using this synthesis gas was recently reported for another purple nonsulfur bacterium Rhodospirillum rubrum [8]. 

The data in this paper are drawn from a number of studies performed at Pacific Northwest Laboratory (3,7-9). We have examined biomass pyrolysis tar samples from many types of pyrolytic gasification and liquefaction systems through the U.S. Department of Energy support of domestic biomass thermochemical conversion research and international cooperative efforts. Many of these can be compared directly as a function of temperature since they are all produced at short residence time, approximately one second. Others produced at longer residence time or pressure require discussion separately. 

As biomaterials are structurally and chemically complex, biomass thermochemical conversion processes (1,2) produce complex fractions including a liquid fraction which, dep>ending on the process, can be obtained in large (liquefaction, pyrolysis) or small yields (gasification). These liquids have found little utility because of their large contents in oxygen which implies low heat values, instability and corrosive prop>erties. Two routes have been tested (3,4) in order to produce hydrocarbons from these liquids. The first one involves hydrotreatment with either H2 or H2 + CO over classical hydrotreatment catalysts. The second route is the simultaneous dehydration and decarboxylation over HZSM-5 zeolite catalyst in the absence of any reducing gas. 

Baker, E. Mudge, L. Wilcox, W. A., Catalysis of gas phase reactions in steam gasification of biomass. In Fundamentals of Thermochemical Biomass Conversion, Overend, R. P. et al., Ed., Elsevier Applied Science, London, 1985, pp. 1194-1208. 

Direct production of hydrogen from gasification is the simplest route. Gasification is a two-step process in which the solid feedstock is thermochemically converted to a low- or medium-energy-content gas. Natural gas contains 35 MJ/Nm3. Air-blown biomass gasification results in approximately 5 MJ/m3 oxygen-blown in 15 MJ/m3. 

Chaudhari, S.T., Ferdous, D., Dalai, A.K, Bej, S.K, Thring, R.W., and Bakhshi, N.N. (2000). Pyrolysis and Steam Gasification of Westvaco Kraft Lignin for the Production of Hydrogen and Medium Btu Gas, Abstracts Progress in Thermochemical Biomass Conversion, Tyrol, Austria, 17-22 September. 

Thermochemical conversion processes use heat in an oxygen controlled environment that produce chemical changes in the biomass. The process can produce electricity, gas, methanol and other products. Gasification, pyrolysis, and liquefaction are thermochemical methods for converting biomass into energy. 

Thermochemical biomass-to-liquid (BtL) conversion, involving thermal gasification of the biomass and subsequent synthesis of biofuels by the Fischer-Tropsch process. Various aspects of the use of catalysis in this process are discussed in the several chapters. 

The biomass is first processed by thermochemical methods (gasification, pyrolysis), for example, to form synthesis gas, which can be processed further to methanol or Fischer-Tropsch (FT-) hydrocarbons. To gasify solid biomass, both circu-... 

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