Development of catalytic tar decomposition downstream from a dual fluidized bed biomass steam gasifier

Gasification of biomass is an attractive technology for combined heat and power production. Although a lot of research and development work has been carried out during the past decade the commercial breakthrough for this technology is still to come. One problem that has not been completely solved so far is the tar content in the product gas, which can cause plugging in the colder parts of the plant. Among the possible gas cleaning methods, catalytic hot gas cleaning is rather promising because of the complete destruction of the tars instead of creating a waste stream which is difficult to dispose. Different catalysts were measured in laboratory scale reactors fed by synthetic gas mixtures and tar model compounds. Commercial steam-reforming catalysts for heavy hydrocarbons (particularly naphthas) proved best as tar decomposing catalysts. Based on these results 3 nickel-based monolith type of catalyst were produced and afterwards tested in a laboratory scale reactor fed by slip streams taken from the 8 MW dual fluidized bed steam gasifier plant in Güssing, Austria. Almost complete tar and considerable ammonia decomposition could be achieved over this catalyst at temperatures above 850 °C and space velocities of about 1100 h− 1.