Adding gas from biomass to the gas grid - SGC

Figure 4 illustrates reported investments for membrane upgrading systems as a function of the plantcapacity. Some of the figures are budgets while others are data from realised plants.Since the construction of membrane systems is of a modular nature, the specific costs perprocessed volume of gas is more competitive for smaller units than for larger.Figure 4: Specific investment of membrane upgrading system versus capacity [lit.9,15,17]4.3.3 Upgrading by Pressure Swing AdsorptionPressure Swing Adsorption, or PSA, is a method for the separation of carbon dioxide from methaneby adsorption/desorption of carbon dioxide on zeolites or activated carbon at different pressurelevels. The adsorption material adsorbs hydrogen sulphide irreversibly and is thus poisoned byhydrogen sulphide. For this reason a hydrogen sulphide removing step is often included in the PSAprocess.The PSA process requires dry gas and the crude biogas is dried before it enters the upgradingprocess.The upgrading system consists of four adsorber vessels filled with adsorption material. This materialcan be zeolites from carbon for example. During normal operation each adsorber operates in analternating cycle of adsorption, regeneration and pressure build-up. During the adsorption phasebiogas enters from the bottom into one of the adsorbers. When passing the adsorber vessel, carbondioxide, oxygen and nitrogen are adsorbed on the adsorbent material surface. The gas leaving thetop of the adsorber vessel contains > 97% methane.Before the adsorbent material is completely saturated with the adsorbed feed gas components, theadsorption phase is stopped and another adsorber vessel that has been regenerated is switchedinto adsorption mode to achieve continuous operation.page: 36