Adding gas from biomass to the gas grid - SGC

In the gasification process the first degradation stage is often followed by an additional hightemperature gasification stage for the conversion of remaining tars and carbon rich solids to gasesand carbon free ash. This essential clean up is generally considered as a part of the gasificationprocess. Also the first cyclone to separate the gas and solids is often designed as a part of thegasifier.Syngas cleaning starts with an already relatively clean synthesis gas with a low amount ofaccompanying liquids and solids. The cleaning train consists of a sequence of cleaning units, eachunit removing some of the contaminating components.The general lay out is to cool down the raw syngas and to remove the bulk of the entrained solidsand liquids with a cyclone, a filter removes remaining solids (solid and liquid separation). The nextstep is to remove, when necessary, the sulphurous components (desulphurisation).The clean syngas is used for heat and power production. The clean syngas is also used for theconversion to higher value chemicals, as for example, methanol. Conversion of syngas to methanemakes it possible to produce a pipeline quality gas. This process is widely studied anddemonstrated and is considered as mature. Due to the abundant and low cost availability of naturalgas there are currently however no commercial pipeline quality gas production plants.A recent study by Gastec [lit.21] compares the production of power and pipeline quality gas fromsyngas. A projected thermal biomass gasification unit produces 70 MWth of clean syngas at nearlyatmospheric pressure. In this specific case 50% of the syngas was obtained from biomass and theremaining was obtained from (fossil derived) organic wastes. Four potential roads for the final use ofthe syngas were compared:• production of power by a steam turbine• production of power by a gas turbine• production of power by combined cycle system• production of pipeline quality gas for delivery at 40 bar to the gas transport gridTable 21 summarises some of the results of this study.page: 50