The growth potential of biogas upgrading is large. There are about 20.000 biogas plants in Europe today, but only 400 upgrading installations as of 2015. The capacity of new biogas plants tends to increase, resulting in lower specific investment costs of biogas upgrading.
Biomethane has methane content greater than 95% w/w up to the standard of substitute natural gas (SNG) or compressed natural gas (CNG). In particular, other parameters as Wobbe index, put limits on concentration of some impurities, such as sulfur, oxygen, dust, water, NH3 and siloxanes. Biomethane can be applied as fuel sources for stove/boilers devices, vehicles, engines and gas turbines to produce heat and electricity. Also, it can be injected into the natural gas distribution system. Moreover, biogas needs to be purified in order to increase the specific heat, minimize corrosion problems caused by acid gases and other impurities. Currently, the biogas upgrading technologies are at the stage of development and performance improvement. Some novel biogas upgrading technologies such as cryogenic separations, in-situ and ex-situ biological upgrading, hydrate separations, are the recent developments. Nevertheless, most of the technical parameters and information have been obtained either in laboratory-scale reactor or pilot tests. Therefore, more research works needs to be performed to bridge the knowledge gap between such tests and large-scale operational biogas plants.
Specifying lower methane contents in the range of 90-98% does not change much in terms of capital expenditure (CAPEX), according to equipment suppliers. More significant parameters in terms of CAPEX are the requirements for pretreatment of the raw gas and quality parameters other than methane content. Obviously, lower methane purity means that more inert carbon dioxide (CO2) has to be transported and stored in the gas system and the direct compatibility with natural gas is lost.
Membranes (including membrane hybrids), pressure swing adsorption (PSA), and physical scrubbing all appear to be operationally flexible regarding product gas methane content and operating expense (OPEX), whereas chemical scrubbing has very high CO2 selectivity.