How to Size a Double Membrane Gas Holder for Biogas

Define what the gas holder must do

An anaerobic digester is a process vessel; the gas holder provides a gas-storage volume. A tank-top arrangement may integrate storage above a digester, while a ground-mounted holder forms a separate storage unit. Identify whether the requirement is buffering, accommodating a planned gas-use interruption or another defined operating scenario.

Low-pressure biogas storage and high-pressure biomethane storage require different equipment. State the gas condition and the point in the process where the holder will be installed.

Calculate the usable storage capacity

Put hourly gas production and consumption figures side by side for a complete operating cycle. Calculate the surplus or shortfall in each period, then add these changes over time to find the storage space needed. This matters particularly where biogas is produced continuously but used only at certain times.

Specify starting inventory, permitted high and low levels, reserve and shutdown scenarios. Distinguish geometric volume from usable storage and agree whether figures are operating m³ or normalised volumes, including reference temperature, absolute pressure and dry or wet basis.

Agree pressure limits and downstream interfaces

A double membrane gas holder buffers gas at the designed low pressure; it is not a substitute for a high-pressure compressor. Pressure and inventory are separate design inputs. Level measurement and its calibration are needed to relate membrane position to stored volume.

Provide normal and allowable pressure limits, gas inlet and outlet conditions, pressure losses and the requirements of the engine, treatment system or other consumer. Agree pressure regulation, protective functions and the flare interface in the project design.

Match the membrane to the actual biogas

Supply the gas analysis, including methane, carbon dioxide, hydrogen sulphide and moisture, together with operating temperature and expected condensate. Review gas compatibility, permeability, flexing behaviour, seams and connections as one system.

Material comparisons need the same test gas, method and conditions. An oxygen-permeability result does not establish methane tightness. If the stored gas changes to industrial fuel gas or oxygen, the gas-contact materials and configuration require a separate assessment.

Compare ground-mounted and tank-top arrangements

Choose by site layout and structural interfaces rather than appearance alone. A tank-top membrane cannot be selected independently of the supporting tank and its approved design.

Ground-mounted and tank-top project examples

The MOTET portfolio includes a 3,000 m³ ground-mounted holder in Krabi and a 1,500 m³ tank-top holder in Nakhon Ratchasima, Thailand. These projects illustrate differences in site layout, foundations and tank-top connections.

The Anhui tank-top double membrane biogas holder repair is documented in 29 site photographs. They show local repair and reinstallation of the existing membrane, including crown-plate connections, clamping plates and lifting. Allow space for this maintenance work when planning a new installation.

Prepare a quotation that can be compared

Send a common design basis to each supplier. An equipment price is meaningful only when usable storage, gas duty and delivery boundaries are comparable.

• Gas analysis, flow profiles, volume basis and required operating reserve.
• Pressure and temperature limits, site loads and layout drawings.
• Membranes, support air, instruments, controls and piping interfaces.
• Civil works, transport, installation and commissioning responsibilities.
• Required drawings, material records, inspection criteria and service scope.

Selection questions

Is a biogas storage tank the same as an anaerobic digester?

Not necessarily. A digester contains the biological process; the holder provides gas storage. Tank-top systems can combine these functions within an integrated arrangement, but the liquid-process and gas-storage duties remain distinct.

Can I choose capacity from daily biogas output alone?

Daily output is a starting input. Use the production and consumption profiles, operating reserve and permitted storage range to establish usable capacity.

Does pressure tell me how much gas is stored?

Pressure alone is insufficient in a regulated low-pressure holder. Use the specified level measurement and volume calibration.

Can the same membrane be used for biogas, industrial fuel gas and oxygen?

Material and equipment suitability must be confirmed for each gas and operating duty. Oxygen service requires its own compatibility and cleanliness assessment; a biogas configuration is not automatically transferable.