Fluidized Bed Gasification as a Mature And Reliable Technology for the Production of Bio-Syngas and Applied in the Production of Liquid Transportation Fuels—A Review

Marcin Siedlecki, Wiebren De Jong, Adrian H.M. Verkooijen
2011 Energies  
Biomass is one of the renewable and potentially sustainable energy sources and has many possible applications varying from heat generation to the production of advanced secondary energy carriers. The latter option would allow mobile services like the transportation sector to reduce its dependency on the fossil fuel supply. This article reviews the state-of-the-art of the fluidization technology applied for the gasification of biomass aimed at the production of gas for subsequent synthesis of
more » ... liquid energy carriers via, e.g., the Fischer-Tropsch process. It discusses the advantages of the gasification technology over combustion, considers the size of the conversion plant in view of the local biomass availability, assesses the pros and cons of different gasifier types in view of the application of the product gas. Subsequently the article focuses on the fluidized bed technology to discuss the main process parameters and their influence on the product composition and the operability of the gasifier. Finally a synthesis process (FT) is introduced shortly to illustrate the necessary gas cleaning steps in view of the purity requirements for the FT feed gas. When considered as a primary energy carrier, each category will have its specific benefits and problems, depending on the conversion technique. The main issues are: • The amount of ash. Ash refers to the inorganic part of a solid fuel. In analytical chemistry it refers to the remaining solid matter after complete oxidation of the combustible fraction, mostly consisting of metal oxides. A high amount of ash will lower the energy content of the fuel and may cause handling problems during and after the conversion process (solid residues); • The composition and the structure of ash. The interaction of ash with the remaining species in the process will depend on its composition. Often ash will show an inert behavior, not leading to any chemical interaction with the process. Some metal oxides, like CaO, MgO, Fe x O y may act as catalysts for some chemical reactions during and after the conversion process (see Section 3.2.-bed materials and additives part). This can be beneficial (faster conversion of species) or problematic (smouldering of disposed off ashes). In addition it is well known, that the presence of alkali metals in the ash, promoted by the presence of chlorine, will lead to the formation of low-melting, "sticky" compounds that are likely to cause problems, in particular during high temperature conversion processes. Furthermore, the presence of heavy trace metals (e.g., lead, mercury) may cause environmental and health problems irrespective of the conversion process applied. The structure of the ash may have negative influence on the volatile release and the burn-out of a fuel particle, leading to higher emissions or lower conversion efficiencies (e.g., the case of pepper plant residue, PPR [12, 13] ); • The moisture content of raw biomass. Moisture, naturally present in raw biomass-just like ash-will lower the energy content of the fuel. However, for some conversion processes the presence of moisture is desired or even essential. The "classical" thermal conversion processes in particular, however, will not accept biomass of which the moisture content is too high ( typically maximum 30% wt [14]; Demirbas [11] quotes 10% wt moisture, which in practice would not be realistic, as drying below 10% wt moisture is expensive [15]; Hofbauer [16] indicates test runs 1. Technology scale-up; 2. Size distribution of raw biomass;
doi:10.3390/en4030389 fatcat:pfaxoxklcnddrjotcdb2qfio4m