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Double Membrane Biogas Holder
| MOQ: | 1 SET |
| Price: | Please contact us |
| Standard Packaging: | Standard export wooden box |
| Delivery Period: | 5~45 days |
| Payment Method: | L/C,T/T |
| Supply Capacity: | 20 sets per month |
Double Membrane Biogas Holder: What Drives the Price, the Life, and the Quote
A double membrane biogas holder stores the methane your digester makes and feeds it to the engine at a steady pressure. This guide explains the parts, the six cost drivers, and the five line items you should check before you sign.
What a double membrane biogas holder actually is
It is a low-pressure, dry-seal gas store built from flexible fabric films instead of steel plates. Most units use three films: a bottom membrane that seals the concrete base, an inner membrane that holds the biogas, and an outer membrane that forms the weatherproof shell. A small blower keeps the air space between the inner and outer films at a steady low pressure, so the gas leaves the holder at a near-constant pressure no matter how much is stored.
On an integrated unit the holder sits on top of the digester tank and uses the tank roof as the base. A standalone unit stands on its own ring foundation beside the tank. Both do the same job: decouple gas production from gas use.
Six things that decide the price
Suppliers quote the same keyword at very different numbers. The gap almost always comes from these six points, not from one being "expensive".
1. Usable volume. This is the single biggest line. A 500 m³ holder and a 3,000 m³ holder are different fabrication jobs, different film area, and different blower duty. Volume sets roughly 60% of the hardware cost.
2. Membrane material. Standard modified-PVC fabric is the economy choice. PVDF-coated fabric costs more but resists UV and H₂S far longer. PTFE sits at the top of the range and is specified when the site is hot, sunny, or highly corrosive.
3. Integrated vs standalone. Putting the holder on the digester roof removes the need for a separate foundation and anchor ring, but it limits diameter to the tank top. A standalone unit costs more in civil works yet scales freely.
4. Blower and control cabinet. A constant-duty blower with a pressure-relief valve and a control cabinet sounds minor, but a poorly specified blower is the most common cause of early failure. Quotes that cut here usually cost more later.
5. Site wind and snow rating. Wind belts, tensioning systems, and snow ropes are added for exposed or cold sites. A holder rated for a coastal wind zone is not the same product as one rated for a sheltered yard.
6. Safety accessories. Over/under-pressure valves, flame-retardant fabric to DIN 4102 B1, and gas-level alarms are often quoted as options. Treat them as required, not optional.
What actually sets the service life
The films, not the frame, wear out first. A standard PVC holder in an exposed site typically runs 10 to 15 years. Better fabric and a shaded, well-tensioned installation push that to 15 to 20 years. PTFE membranes are rated around 50 years in supplier literature, though most operators replace the gas-contact film well before that on maintenance cycles.
Three things shorten life: uninterrupted UV exposure, heavy hydrogen sulfide in the raw biogas, and slack tensioning that lets the outer film flap. Ask the supplier for the UV-aging and H₂S-resistance test data, not just a year number.
How to read a quote without missing the risk
A useful quote lists more than a price. Check these five line items:
Membrane spec sheet: fabric type, coating, total weight (g/m²), and the fire class (DIN 4102 B1 or equivalent).
Design pressure: most holders run 0.5 to 1.5 kPa; confirm the value and the relief set point.
Blower duty and spares: rated airflow, power, and whether a spare is included.
Warranty years: film warranty and structure warranty are usually different; read both.
Anchor ring and civil scope: confirm whether the foundation ring, anchor bolts, and penetration seals are in the supplier's scope or yours.
Where plants use them
Any site that makes biogas and needs to buffer it before use is a fit:
• Farm biogas: dairy and pig manure digesters, buffering gas for cooking fuel or a generator.
• Food-waste AD: storing high-quality biogas before upgrading to bio-CNG or generating power.
• Industrial wastewater: biogas from IC, UASB, and EGSB reactors in food, brewing, and pharma plants.
• Municipal sludge: digestion gas used for plant heat and power.
• Landfill gas: low-pressure collection and buffering at the wellhead.
Double membrane vs the other two options
| Attribute | Double membrane holder | Single-balloon bag | Fixed-dome tank |
|---|---|---|---|
| Pressure control | Constant, air-blower regulated | Floats with volume | Near fixed, little buffer |
| Corrosion | None in steel parts | None | H₂S attacks coating |
| Install time | Days, modular | Hours | Weeks, civil heavy |
| Best fit | Steady engine feed | Small, low-budget | Cheap gas cap, no buffer |
Frequently asked questions
Can it sit on an existing digester tank?
Yes. An integrated unit bolts to the tank roof and uses it as the base, which saves the foundation cost of a standalone holder. The tank top diameter then sets the maximum holder diameter.
How big should the holder be for a 100 kW engine?
A 100 kW unit burns roughly 50 to 60 Nm³/h of biogas. A 4 to 6 hour buffer means about 250 to 350 m³ of holder volume. Daytime-only running about doubles that. Start from your engine datasheet.
What pressure does it hold?
Most holders run a low 0.5 to 1.5 kPa, held steady by the blower. That is enough to feed a generator or flare without a booster, and low enough to stay safe in a methane environment.
Is the membrane flame retardant?
Reputable fabric is polyester with a PVC or PVDF coating tested to a fire class such as DIN 4102 B1. Ask for the certificate; do not accept a verbal claim.
Who handles the foundation?
For a standalone holder the supplier usually provides the anchor-ring design and you build the concrete ring. For an integrated unit the tank roof already serves as the base, so civil work is minimal.
Get a quote you can read line by line
Send your digester volume, gas production rate, and site wind zone. We return a spec'd quote with the six cost drivers broken out.
Email: richie@scmondes.com
