Adding gas from biomass to the gas grid - SGC

Selexol from the flash tank is depressurised to atmospheric pressure and fed into the top of adesorption column. Air is blown from the bottom of the desorption column to remove dissolvedcarbon dioxide from the Selexol solution. The desorption column is equipped with internals andpacking in the same way as the absorption column. The regenerated liquid is cooled in a heatexchanger to maintain the absorption temperature and recycled to the absorption column.The vent gas is either released to the atmosphere or treated in some kind of gas filter to removeodours.Hydrogen sulphide is absorbed together with carbon dioxide in the absorption column. The solubilityfor H 2 S in Selexol is very high and H 2 S cannot be removed in the desorption column. To removeH 2 S from a Selexol solution, heating with steam is needed. It is therefore desirable that H 2 S isremoved before the absorption to minimise energy costs. If very large gas flows are treated, it canbe economically interesting to use Selexol for H 2 S removal. The recovered H 2 S is then processedfurther to produce sulphur.The product gas has a low water content since Selexol absorbs water. Further drying is normally notneeded.Figure 8: Biogas cleaning and upgrading with ‘SulfaTreat’ and ‘Selexol’page: 42