Biomethane

The composition of bio-methane and the upgrading process required is a function of the specifications of final use of biogas. For instance, only H2S must be removed below 1000 ppmv if biogas is intended to be used in boilers for on-site heat generation. Internal combustion engines for combined heat and power generation (CHP) require prior removal of H2O, H2S < 200-1000 ppmv, NH3 < 32-50 mg/m3, siloxanes < 5-28 mg/m3 and halocarbons < 65-100 mg/m3. These values are often set by manufacturers based on previous operational experiences or on specifications of the materials used for their construction. Turbines and micro-turbines require very low levels of siloxanes (0.03-0.1 ppmv) and water (pressurized dew point -6.7 °C below biogas temperature), but can cope with H2S concentrations in the range of 10000-70000 ppmv and halocarbons levels as high as 1500 ppmv Cl-/F-. Finally, the generation of bio-methane for injection into natural gas networks and use as vehicle fuel entails the most rigorous quality specifications: CH4 > 80-96 %, CO2 < 2-3 %, O2 < 0.2-0.5 %, H2S < 5 mg/m3, NH3 < 3-20 mg/m3 and siloxanes < 5-10 mg/m3.

The market for physical/chemical and biological technologies for biogas upgrading is rapidly evolving due to the ever-stricter specifications for biogas use worldwide. Biogas upgrading based on physical/chemical methods has traditionally exhibited high energy and/or chemical requirements, which has promoted an intensive research on biotechnologies for biogas upgrading based on their lower operating cost and environmentally friendliness.