The raw gas from a fluidized-bed biomass gasifier should have very low tar, ammonia, and particulates content, to make it easy to clean for its eventual use in gas engines or gas turbines. Besides an optimized design and operation of the gasifier, it requires the use of in-bed catalytic additives. Four available and competitive additives have been compared in this work:  a calcined dolomite (OCa·OMg), natural and sintered olivines ((Mg,Fe)2SiO4), and a Ni-olivine catalyst that was developed at the University of Strasbourg. They were tested under very similar experimental conditions in two small-scale pilot plants:  the first pilot plant was based on a circulating fluidized-bed (CFB) gasifier, and the second pilot plant was based on a bubbling fluidized-bed (BFB) gasifier. The tar content at the gasifier exit when using dolomite was, on average, only 60% (±10%) of the tar content when natural or raw olivine was used. This showed that dolomite was 1.40 times more active than olivine in biomass gasification with air. Nevertheless, dolomite generates 4−6 times more particulates or dust and also some extra NH3 in the gasification gas than olivine. Under the conditions used in this work (gasification with air), the Ni-olivine catalyst was not very active for tar elimination and it deactivated very quickly. Much of the data on gasification gas provided in this paper was obtained under operations similar to those found in commercial biomass gasifiers.

Biomass gasification with pure steam in a fluidized bed is a highly endothermal process that has been connected in several ways to a fluidized-bed combustor to burn the char that is generated in the gasifier. This resulted in what currently is called dual fluidized-bed (DFB) biomass gasifiers. This review starts by describing the pioneering DFB biomass gasifiers that were operated during the period of 1975-1990 by Kunii's group in Japan, Battelle-Columbus and FERCO in the United States, TNEE in France, AVSA in Belgium, etc., ... and Corella and Herguido's gasifier, which was operated during the period of 1989-1991. A description of the gasifiers operated today in Europe (TU Wien and Gu ¨ssing in Austria and ECN in The Netherlands), Japan (IHI Co., EBARA, AIST-Tsukuba), and the People's Republic of China (Dalian, Hangzhou, and Beijing) then is given. Their most-relevant operation data, and the results from these gasifiers (mainly, the gaseous hydrogen (H 2 ) and tar contents in the raw produced gas), are finally presented briefly.

Full-size 15 × 15 × 30 cm nickel-based monoliths are tested for tar elimination in fuel gas produced by biomass gasification in a fluidized bed at a small pilot-plant scale. The feedstocks used were mixtures of pine wood chips and "orujillo", the residue from olive oil production. Temperatures at the front or face of the monolith ranged from 820 to 956 °C, gas hourly space velocities in the monolith ranged from 1280 to 4550 h -1 (normal conditions, nc), area velocities ranged from 2.7 to 7.1 m/h, and superficial or face gas velocities at the inlet of the monolith ranged from 0.34 to 1.3 m/s. Samples of gas and tar were taken before and after the monolith reactor, and variations in gas composition and tar content were determined. Using a macrokinetic model presented elsewhere, some key kinetic constants for the tar-removal reaction are calculated for the monolith and used as indexes of its activity. The effects of some important operating conditions on the activity and sometimes on the deactivation of the monolith are presented here. The intrinsic activity of the monolith for tar abatement is finally compared with those of other competing catalysts such as dolomites and commercial steam-reforming catalysts. It is concluded that these monoliths are not very high in activity, but they can operate with a fuel gas containing particulates, thereby avoiding the use of hot filters, which are problematic when used in biomass gasification.

Seven different commercial nickel-based catalysts for steam reforming of light hydrocarbons and of heavier hydrocarbons were tested for tar removal in a flue gas from an atmospheric fluidized bed biomass gasifier, using air as the gasifying agent. The catalysts were provided by BASF AG, ICI-Katalco, Haldor Topsoe a/s, and United Catalyst Inc. The facility used is a small pilot plant, and the catalytic reactor operates in full flow with a real gasification gas. A guard bed with a calcined dolomite is used to decrease the tar content at the inlet of the catalytic bed to a level below 2 g/m 3 n . The variables studied include the temperature (730-850 °C) of the catalytic bed, gas residence time, steam content in the flue gas, and composition of the reacting atmosphere. All catalysts for steam reforming of naphthas provide a similar and very high activity. Values of the apparent activation energy and preexponential factor are given and analyzed for the most active catalysts. The catalyst life is also studied. No deactivation is observed with times-onstream of up to 65 h.

This paper addresses the H 2 production with simultaneous CO 2 capture by steam gasification of coal in a fluidized bed, at low/medium temperatures (600-800 °C) and atmospheric pressure. This work is mainly aimed at reviewing the effects of the inorganic species present in the matrix of the coal or added to the gasifier bed. The most promising species seems to be the calcined limestone (CaO), which intervenes in the overall gasification reaction network in at least five different types of reactions. The effectiveness of the CaO for CO 2 capture in the coal gasifier is, therefore, affected/influenced by the other four simultaneous or competitive types of reactions in the gasifier. The effects of the temperature in the gasifier and of the (CaO/ coal) ratio fed to the gasifier are finally reviewed and discussed in detail.