Influence of the biomass gasification processes on the final composition of syngas

Interest in the technology of gasification has shown a number of ups and downs since its first appearance. It appears that interest in gasification research correlates closely with the relative cost and availability of liquid and gaseous fossil fuels. Gasification is a versatile thermo-chemical conversion process which produces a gas mixture of H-2, CO and CH4 the proportions being determined by the use of air, oxygen or steam as oxidizer, with a concomitant range of heat values, low (4-6 MJ/Nm(3)), medium (12-18 MJ/Nm(3)) and high (40 MJ/Nm(3)). A variety of biomass gasifiers have been developed. Differentiation is based on the means of supporting the biomass in the reactor vessel, the direction of flow of both the biomass and oxidant, and the way heat is supplied to the reactor. Gases formed by gasification are contaminated by some constituents such as particles, alkali metals, nitrogen components, tars, sulfurs and chlorides. The level of contamination varies, depending on the gasification process and the feedstock. Gas cleaning must be applied to prevent erosion, corrosion and environmental problems in downstream equipment. In this work, a global perspective about the producer gas final composition dependence, the so-called syngas, from the biomass, oxidizer, reactor type, temperature and pressure is given based on a literature benchmarking. This study shows that there are some discrepancies in the values given by various authors. This highlights the strong dependence of the syngas final composition from the biomass conditions, type of gasifier and pressure and temperature of the process. Thus, in order to make precise studies on the use of syngas it will be necessary to consider that its composition will be rather constant. The development of mathematical models for numerical simulation fully validated experimentally are strongly desirable and may be a very useful tool to determine the final composition of syngas by changes in initial conditions without laborious and expensive experimental tests. (C) 2013 The Authors. Published by Elsevier Ltd.