Biogas Storage Tank: Gasholders, Digestate And Buffer Capacity

A biogas storage tank is not one vessel but three storage functions around the digester: a gasholder that buffers methane at 5-30 mbar, a digestate tank that stores nutrient-rich outflow to the spreading season, and a feedstock buffer that smooths feed interruptions. Treating storage as a single digester-sized tank is the most common design error, because each function has its own driver - gas pressure, regulation, or feed continuity. Center Enamel supplies the GFS, FBE, stainless-steel and carbon-steel bolted tanks for all three storage roles.

The gasholder decouples biogas production from biogas use, letting the combined-heat-and-power unit or upgrading train draw steady flow while the digester keeps running. The digestate tank stores the outflow, sized to spreading windows and local rules rather than daily volume. The feedstock buffer holds one to two weeks of feed so a delivery gap does not stall the reactor. Each is a distinct tank with its own coating and roof logic.

• Gasholder: 5-30 mbar flexible membrane, decouples gas use.
• Digestate: sized to season plus regulation, not daily flow.
• Feedstock buffer: one to two weeks of feed continuity.
• Three distinct tanks, not one digester-sized vessel.

A gasholder's usable volume is only what sits above the low-pressure setpoint, not the full geometric tank volume, because below the setpoint the gas cannot be extracted. The roof must also carry flame arrester, water seal or relief, and hazardous-area classification. Sizing to recoverable volume, with the venting and methane and H2S detection basis confirmed, is what makes the storage actually usable.

• Usable gas = volume above the low-pressure setpoint.
• Flame arrester, relief and detection required.
• Methane and H2S detection in the hazardous area.
• Size to recoverable volume, not geometric volume.

Pin down these storage-sizing numbers so each of the three functions is specified correctly: gasholder pressure of 5-30 mbar, recoverable gas volume above the low-pressure setpoint, digestate storage to the spreading season, a feed buffer of 1-2 weeks, CSTR retention of 20-40 days at 35-38 C for 8-12% total solids feed, and per-zone coating - GFS 2C2F at 0.25-0.45 mm or FBE - verified by a 1,500 V holiday-spark test and a shell calculation to AWWA D103-19 and ISO 28765. Each function has its own driver and its own tank.

A 2021 biogas project in Beijing, China, used a single Glass-Fused-to-Steel bolted tank of 1,587 m3 with a gas-membrane roof. As a digester-plus-gas-storage delivery it demonstrates a tank engineered with a membrane roof for the biogas duty. Diameter and height are not recorded in the verified project data and are reported Not Provided.

Biogas storage introduces safety duties a digester alone does not. The gasholder operates at 5-30 mbar but the gas is flammable and contains H2S, so the roof needs a flame arrester, a relief and a water seal or equivalent, and the area needs methane and H2S detection with a hazardous-area classification. The digestate tank is simpler but still an agitated, often alkaline, nutrient liquor that demands its own coating logic. Storage safety is part of the tank specification, not an add-on, and the manufacturer should state the detection and venting basis explicitly.

• Flame arrester, relief and water seal on the holder.
• Methane and H2S detection in the hazardous area.
• Hazardous-area classification applied to storage.
• Digestate coating logic kept separate from gas.
• Venting and detection basis stated by the supplier.

Center Enamel supplies biogas storage tanks across all three functions - gasholder, digestate and feedstock buffer - in GFS, FBE, stainless-steel and carbon-steel bolted construction. The company has produced GFS tanks since 2008, holds ISO 9001, ISO 45001, NSF/ANSI 61, EN 1090 (CE), ISO 28765 and WRAS approvals, and has delivered more than 30,000 storage projects across 100+ countries, with a standard ex-works lead time of about 30 days for 1,000 to 10,000 m3 tanks.

• Membrane-roof and gas-tight options for holders.
• Per-zone coating for gas, digestate and feed.
• Shell to AWWA D103-19 and ISO 28765.
• 100% 1,500 V holiday-spark test on panels.

It is three storage functions around the digester: a gasholder buffering methane at 5-30 mbar, a digestate tank storing outflow to the spreading season, and a feedstock buffer holding one to two weeks of feed. They are separate tanks, not one digester-sized vessel.

Because each function has a different driver - gas pressure for the holder, regulation for digestate, feed continuity for the buffer. Sizing them all to the digester volume either over-builds or under-builds one of them.

To recoverable volume - only the gas above the low-pressure setpoint can be extracted, not the full geometric tank volume. The roof also needs flame arrester, relief and methane and H2S detection in the hazardous area.

To the spreading season plus local regulation, not to daily output. Digestate accumulates and is stored then land-applied, so the tank is often larger than intuition suggests.

It holds one to two weeks of feed so a delivery gap or quality swing does not stall the reactor. Smoothing feed continuity protects the 20-40 day retention process.

Yes. Center Enamel supplies gasholder, digestate and feedstock-buffer tanks in GFS, FBE, stainless-steel and carbon-steel bolted construction, with membrane-roof and gas-tight options for holders.

Bolted tanks to AWWA D103-19 and ISO 28765; coatings to NSF/ANSI 61 or WRAS where potable contact applies; EN 1090 (CE) marking for Europe. Gas-zone safety follows the local hazardous-area code.

A 2021 Beijing biogas project used a single GFS bolted tank of 1,587 m3 with a gas-membrane roof - a digester engineered with a membrane roof for biogas duty.

Sizing the gasholder to the full geometric tank volume. Usable gas is only what sits above the low-pressure setpoint, so the holder must be sized to recoverable volume with the venting basis confirmed.

A biogas storage tank is three functions - a gasholder buffering methane at 5-30 mbar, a digestate tank sized to the spreading season plus regulation, and a feedstock buffer of one to two weeks - and each is a distinct tank with its own coating and roof logic. The gasholder must be sized to recoverable volume above the low-pressure setpoint, not geometric volume, with flame arrester, relief and gas detection. Center Enamel supplies all three in GFS, FBE, stainless-steel and carbon-steel bolted construction, as demonstrated by a 2021 Beijing digester of 1,587 m3 with a gas-membrane roof.