A biogas holder is an indispensable part of the biogas system. It regulates the pressure and flow, which is key for the stable operation of other equipment in the gas line. The storage level is used to control the distribution of biogas to each consumers.
Due to the corrosive natural of biogas, membrane (fabric with PVC/PVDF coating) is the preferred material to steel. An external structure is used to the membrane gas bag. This external structure can be membrane as well, supported by air blower. It is commonly known as double-membrane gas holder.
The biogas is stored between internal (2) and bottom membrane (3), which are anchored to the foundation with guiding rails (4). The space between external (1) and internal (2) membrane is filled with air, supplied by the blower (5) via non-return valve (8). The pressure in this space is stable with the regulating valve (9). This maintains a positive pressure for the external membrane, which can withstand the wind and snow load. It also exert pressure to the biogas, which goes to various consumers. The internal membrane can moves up and down while the pressure is relatively consistent. The ultrasonic sensor detects the height of internal membrane and storage level is calculated accordingly.
To avoid the damage from overpressure, a hydraulic relief valve is equipped at the biogas inlet line. The blower and sensor must be ex-proof.
The external structural can also be steel tank. It is not very often used due to the extra maintenance cost. It is used for area with heavy snow.