The Tank-Mounted Double Membrane Gasholder, H = D/4 combines a tank cover with flexible biogas storage. It is mounted on the upper rim of a digester, post-digester or suitable storage tank and buffers differences between gas production and consumption. Stored gas can be supplied to CHP engines or gas treatment equipment according to plant demand.

Geometry and model range

H = D/4 defines the nominal dome height H relative to tank diameter D. For a 20 m tank the height is 5 m; for a 30 m tank it is 7.5 m. The range covers diameters of 10–40 m and dome heights of 2.5–10 m.

The model table gives indicative usable gas volumes of 89–5,320 m³. These are working storage volumes, not the geometric volume of the roof. Final capacity depends on the membrane configuration and tank internals; the stored volume changes as the inner membrane rises and falls.

How the system works

The flexible inner membrane contains biogas above the tank contents. Gas inflow raises it; withdrawal lowers it. A blower supplies supporting air between the membranes, while the exhaust assembly regulates air discharge. This maintains the outer roof shape as the gas volume changes. The air system is sized for the required gas withdrawal rate and operating pressure.

Membranes, fastening and support

The outer membrane is UV-protected PVC-coated polyester fabric. The black, biogas-resistant inner membrane is low-density polyethylene (PE-LD). Strength, colour and material specification are selected for site conditions.

The membranes are secured to the tank rim with stainless steel profiles: a U-profile with a clamping hose or a bolted double flat profile. Installation on new or existing concrete or steel tanks requires structural suitability. A belt-and-net substructure supports the membranes when empty and prevents contact with the substrate. The centre support is matched to the tank.

Level measurement and pressure protection

The 4–20 mA filling level indicator connects to the plant control system. The measurement method and membrane stabilisation are selected for the installation. Stabilisation reduces uneven movement and improves measurement reliability.

Overpressure and vacuum protection is included. Valve size, quantity and settings depend on gas production, withdrawal and permitted pressure. The standard pressure range is −1 to +3 mbar; other requirements need a dedicated design.

Complete equipment package

The package includes membranes, rim fastening, support structure, support air supply and exhaust, level measurement and pressure protection. It also includes the centre support, external belt reinforcement, service opening, valve heating and an agitator-area support bracket with splash protection. Ratings and dimensions are matched to the project. Thermal insulation and special membrane materials are optional.

Selection requires tank dimensions, buffer volume, gas production and withdrawal rates, operating pressure, wind and snow loads. The detailed equipment list and model table support selection of the installation.