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BIO-SNG FEASIBILITY STUDY – ESTABLISHMENT OF A REGIONAL PROJECTFigure 5.2 Fixed Bed Gasifiers 35Entrained flow gasifiers represent the state-of–the-art for gasification of pulverised hard solid fuels suchas coal or petroleum coke, or liquids such as residual oils, but are unsuitable for raw biomass or wastederivedfuels which can not be pulverised in the same manner as coal or coke. However, biomass can bepre-treated by a process such as Torrefaction, which is in effect a low temperature pyrolysis stage formanufacturing charcoal. Indeed the Choren Carbo-V gasifier undertakes this reaction within the process,thereby utilising the energy value of both the volatile carbon that is evolved in a pyrolysis step and thefixed carbon (charcoal) in an entrained gasification stage – see Figure 5.3. The heat of the gasificationreaction in a gasifier is provided by the oxidation of part of the fuel, and in an entrained flow gasifier theprocess is blown with oxygen rather than air. This is essential if it is required to minimise the nitrogenlevels in the syngas, a condition in SNG production that becomes paramount because it is very difficult(i.e. costly) to separate nitrogen from the SNG later in the process train.35 Olofsson et al, “ Initial Review and Evaluation of Process Technologies and Systems Suitable for Cost-EfficientMedium-Scale Gasification for Biomass to Liquid Fuels” (2005)34