Notwithstanding the complexity of the FT plants, all XTL (where X = C for coal, G for natural gas or B for biomass) processes consist of the three main sections illustrated in Fig. 19.1: gasification to syngas and gas cleaning/conditioning, FT synthesis reactor and product upgrading section. Variations and different available options for biomass gasification (pressure, use of oxygen, air medium, etc.), type of FT reactor and catalyst and target products lead to large number of possible process configurations to produce FT liquids from biomass (Tijmensen et al., 2002). All concepts, however, can be grouped into two main categories: full conversion FT, aimed at maximizing FT liquids production, and once through FT, with co-firing of the off gas with natural gas in a gas turbine for electricity production, aimed at maximizing energy efficiency.

Several studies have investigated the technical feasibility and economics of the different BTL-FT processes in order to identify the most promising system configurations (Hamelinck et al., 2004; Henrich et al., 2009; Tijmensen et al., 2002; van Vliet et al., 2009). The outcome of these studies is not conclusive as there are large uncertainties concerning technology status and economic values. Although both biomass gasification technologies and syngas conversion technologies are commercially available and have been demonstrated at a commercial scale, there is very limited commercial experience in integrating biomass gasification with downstream processes for the production of liquid transportation fuels. There is, in general, a common consensus that R&D efforts should focus on the following key issues: gasifier designs, syngas quality, product selectivity in chemical synthesis and process integration and scale (E4tech, 2008).

The following paragraphs consist of a description of the main processes, reactor types and catalytic materials employed in these three main sections of the BTL-FT process.