The tank-mounted double membrane gasholder with a dome height of H = D/2 combines a tank cover with flexible biogas storage. It is installed on the upper rim of a digester, post-digester or suitable storage tank and buffers differences between gas production and consumption. The stored biogas can be supplied to a CHP unit or downstream gas treatment equipment according to the plant operating schedule.

Dome geometry and model range

H = D/2 means that the nominal dome height above the tank rim is half the tank diameter. For example, a 20 m tank has a 10 m dome; a 30 m tank has a 15 m dome. The catalogue range covers diameters from 10 to 40 m and corresponding dome heights from 5 to 20 m.

The usable gas volume depends on diameter, membrane geometry and the arrangement inside the tank. It changes as the inner membrane rises and falls. The model table provides indicative usable storage volumes; the selected configuration determines the final capacity.

How the double membrane system works

The flexible inner gas storage membrane contains the biogas above the tank contents. It rises as gas enters and descends as gas is withdrawn. The outer weather protection membrane retains its shape through supporting air pressure in the space between the membranes.

A support air blower system supplies this space, while the exhaust air assembly regulates air discharge. This allows the gas storage volume to change while maintaining the outer dome shape. The air system is selected for the required gas withdrawal rate and operating pressure.

Membranes, fastening and support

The outer membrane is made of PVC-coated polyester fabric with UV protection. The black, biogas-resistant inner membrane is made of low-density polyethylene (PE-LD). Material specification, membrane strength and colour are selected for the project and site conditions.

The membranes are fastened around the upper tank rim using a stainless steel profile system. Available arrangements include a U-profile with a clamping hose or a bolted double flat profile. The fastening system is matched to the tank structure. Installation is possible on new or existing concrete and steel tanks, subject to structural suitability.

A belt-and-net substructure supports the membranes when the gas storage is empty and helps prevent contact with the substrate. A centre support or an adaptation of the existing support is specified to suit the tank design.

Filling level measurement and pressure protection

A filling level indicator with a 4–20 mA signal allows the storage level to be integrated into the plant control system. The measurement method and membrane stabilisation arrangement are selected for the installation. Stabilisation reduces uneven membrane movement and improves the reliability of level measurement.

Overpressure and vacuum protection forms part of the gas storage system. Valve size, number and settings are matched to gas production, withdrawal and the permitted pressure. The standard pressure range is −1 to +3 mbar; other pressure requirements are addressed by a dedicated design.

Configuration for the installation

The common system components are the two membranes, rim fastening, support structure, support air supply and exhaust, filling level measurement and pressure/vacuum protection. The complete package also includes a centre support, service opening, external belt reinforcement and heating for the pressure protection valve. Thermal insulation and special membrane materials are available as project-specific options.

Selecting the gasholder requires the tank dimensions, required buffer volume, gas production and withdrawal rates, operating pressure and site wind and snow loads. These data determine the equipment configuration and its connection to the existing tank.

Biogas gasholder sizes and prices

Compare 31 tank-mounted double membrane gasholders with indicative usable storage volumes of 228–13,789 m³. Complete equipment packages cost 28.400–106.400 €. Select the tank diameter and required gas buffer volume in the model table below.