Biogas Holder Design for Commercial CSTR AD Plants

Biogas Holder Design is synonymous with the term “double membrane gas holder” and the suppliers and contractors that apply this description to their biogas storage products tailor their gas holders for use on large commercial circular-walled digesters. These are by far the most common type of commercial AD plants,  and most of those follow the description of mesophilic type single stage continuously stirred biogas reactors (CSTRs).

You can find more information on our web, so please take a look.

Biogas holders designed for Wastewater Treatment plants (WWTPs – “sewage works”) sludge digestion plants, while also being “mesophilic type single stage continuously stirred biogas reactors (CSTRs)“, differ from the designs discussed here. Many WWTP sludge digestion plants have a rigid fixed roof and biogas holder designs are sold as stand-alone gas storage units for those.

Similarly, dry anaerobic digestion plants (SSADs) also need biogas storage, but again, those biogas holder designs are not covered in this article, unless provided as stand-alone membrane biogas holders.

Although the size of biogas holders is considerable, they are not provided for long-term gas storage. Typically, biogas holders provide storage capacity for no more than a few hours of gas production capacity.

The gas compression in gas holders is low compared with gas grid network pressures. They would not be an economical choice for long-term storage at any AD facility. If used for that purpose the biogas holders would need to be too large to be economically justifiable.

Instead, the biogas from AD plants is used 24/7, either to run a generator feeding electricity into the electrical grid or is fed into a biogas upgrading system to make biomethane continuously.

This makes the power from biogas plants unique among mainstream renewable energy sources because the supply is not intermittent. It is an always-on supply and very valuable as baseload energy.

Correcting a Common Misconception Necessary Before Starting Any Biogas Holder Design Article

To all normal purpose it is a mistake to assume (although many do) that masonry, mortar and concrete are gas-tight. They are not. The use of mortar additives to improve gas tight properties is not sufficient. Gas-tightness can only be achieved through a combination of good, careful workmanship and special coatings.

Special coatings can be applied to masonry and plaster that is strong and free of cracks, and these may be gas tight when constructed. However, masonry and plaster are stiff material which will eventually crack at some location. A coating which has been applied to such surfaces would have to be very special not to also crack. Once cracks have developed, many experts say that not even the best seal coating can render cracks permanently gas-tight thereafter.

List of Biogas Holder Suppliers and Installers

Now let us look at the manufacturers and suppliers that Design and Build digester gas holders, and what they have to say about their gas holding systems:

1. Dystor® Double Membrane Digester Gas Holder Systems

The Dystor® biogas holder design uses a dome-shaped, engineered membrane system to store biogas and prevent odours.

The Dystor system’s outer membrane remains inflated in a fixed position. The inner membrane moves freely as it stores or releases biogas generated from the anaerobic digestion process. This system can hold up to six times as much gas as conventional steel digester covers, maximising the energy benefits of the process and providing cost savings. Via Dystor® Double Membrane Digester Gas Holder Systems

2. DMG – Biogas Storage – Double Membrane Biogas Holder by Bilgeri EnvironTec GmbH

Each store is individually calculated in terms of the loads (internal pressure, wind and snow loads). As a result, in accordance with good biogas holder design methods, membranes are selected with high tensile strength.

The PVC-coated membranes are hardly combustible according to DIN B1, fungicidal treatment and equipped with UV protection. To protect the membranes from the substances contained in the biogas (CH4, CO2, H2S, etc.), the interior and bottom membranes have a special coating.

In [this biogas holder design,] the supporting air blower provides the necessary pressure of the gas reservoir to absorb the external forces such as snow and wind load and to generate the form on the gas system. A separate air hose connects the fan to the memory.

In this biogas holder design, the check valve prevents air leakage in case of failure of the blower. For safety, a pressure control valve is installed in the air system.

This valve controls the operating pressure and closes automatically at a minimum required pressure (static stability, failure of the fan) in the outer membrane. By this device, the membrane remains stable at existing gas production. A [digester substrate level] level measurement sensor enables an optimum utilisation of the storage volume, and control of the slave devices (e.g. flare, motor, burner, etc.). via DMG – Double Membrane Holder

3. Tecon Double Membrane Biogas Storage

Custom-Made Biogas Storage For Wastewater Treatment Plants and Energy Recovery Facilities — The TECON gasholder may be mounted on the ground typically in the form of a ¾ sphere, or mounted on the top of an anaerobic digester or tank functioning as a durable tank cover and storage vessel.

The double membrane gasholder consists of an outer and inner membrane.

The outer membrane is the protection layer and is always under pressure to withstand wind and snow loads, no matter climate extremes.

The inner membrane expands and contracts beneath the outer membrane according to gas generation and usage.

If the gasholder is ground-mounted on a concrete foundation, there is a third, bottom membrane which seals the gas storage to the foundation.

Every gas holder is designed in conformance with the strictest European and U.S. standards (e.g. materials of construction, structural design, storage capacity, snow load, wind load, operating pressure fire resistance).

Also, all membrane gasholders are custom-designed and manufactured in accordance with the specific project requirements for size, configuration (e.g. dome, rectangular, square, doughnut, ¾ sphere) and strength using high-quality PVC-coated polyester fabrics. Product design and manufacturing principles place a priority on system safety, reliability and control simplicity. via TECON – Biogas Storage System – Treatment Solutions …

4. Biogas Storage Tanks from Sattler BioGas

Sattler Double Membrane Gas Storage Tank Design Principles

The SATTLER double-membrane gas storage tank consists of an external membrane which forms the outer shape of the tank, as well as an internal membrane and a bottom membrane which make up the actual gas space.

A permanently running support air blower provides air to the space between the inner and outer membrane and thus keeps the gas pressure up at a constant level – irrespective of gas supply and gas withdrawal.

The pressurised air keeps the outer membrane in shape to withstand external wind and snow loads.

It exerts a constant pressure on the inner membrane and thus pushes gas at constant volume and pressure into the outlet pipe. The gas charge and discharge pipes are cast into the concrete foundations that are usually supplied by the customer. All three membranes are then clamped to the foundation by means of an anchor ring.

The safety valve prevents the gas holder from over-pressure on the gas side. To maintain a constant pressure within the gas holder, a pressure control valve is mounted on the air side. Filling levels are measured by means of ultrasonic and wire length measurement systems.

As the leading supplier of such biogas holder storage systems, we keep the value chain as long as possible in our own company. Thus their own weaving and coating units [are stated by them to] ensure outstanding quality for the supply of the base material, PVC-coated polyester fabrics.

More About Sattler/Ceno DMGS TM

Both membranes are clamped to the crown of the storage tank or anchored to the external wall of steel or concrete tanks.

A supporting structure prevents the inner membrane from immersing into the substrate and being damaged by the stirring device. The safety valves protect the gas holders against over- or low gas pressure. The pressure regulation is carried out by an airside pressure control valve.

Filling levels are measured using hydraulic and wire length measurement systems. Where plants are designed with more than one storage tank, you can combine Sattler double membrane gas storage tanks and single membrane gastight covers.

The intention is that variation in the combination of storage tanks and covers, and the numbers sold should offer an ideal storage volume, at the lowest total costs. Via Biogas Storage Tanks | Sattler BioGas | Utile Engineering

5. JDV Double Membrane Biogas Holder

The unique design allows for variable biogas storage within the inner membrane at constant pressure during gas production and utilisation, while the air-inflated outer membrane provides gas pressure and protection. The outer membrane is constructed of a high-tech cross woven fabric, coated with PVC and Ultraviolet (UV) ray protection, which has proven to endure the weather elements.

An ultrasonic sensor is positioned at the centre of the sphere to monitor the volume of gas present. This gives the operators full control of optimising the utilisation of biogas to feed generators and/or heating systems.

Storing digester biogas and eliminating or reducing ‘flaming' from the digester(s), can help your facility reduce or eliminate the need for electric grid power when generators and/or hot water boilers are incorporated into the system/facility design.

via JDV Double Membrane Biogas Holder – JDV Equipment

If you are looking for more details, kindly visit Wansheng.

6. DuoSphere Double Membrane Biogas Holder Design for Gas Storage

Over the years, WesTech has supplied customers with anaerobic digestion equipment that has added value to their plant operations. WesTech provides the DuoSphere™ Dual Membrane Gasholder biogas holder design.

The DuoSphere™ offers innovative designs for digester gas storage and alternatives for conventional digester covers.

By storing biogas, the plants can have a constant feed of gas to their generator.

DuoSphere™ Biogas Holder Design

Slab-mounted dual membranes provide convenient digester gas storage for your plant operation needs.

• Simple gas storage capability
• Mounts to flat concrete slab
• Constant pressure regulation
• Inner membrane access
• Custom flow and sizes

Tank-mounted digester covers provide an innovative and cost-effective solution for new and replacement covers, in this biogas holder design.

• Lower capital and installation costs
• Absolute odor containment
• New or existing digesters
• Variable liquid level

DuoSphere™ Biogas Holder Design Features

• The critical inner gas-holding membrane is independent of the outer membrane
• Membranes are manufactured from the highest quality materials available
• Access is available to inspect the inner membrane at all times
• Airflow between the membranes is accurately controlled
• Gas detection equipment monitors the air between the membranes
• Spark-resistant and explosion-proof pressurization fans
• Complete service from design to fabrication to installation and commissioning
• Fast installation (two to five days)
• Gasholder volumes from 700 ft3 to 176,000 ft3 (20m3 to m3)
• Volume is measured ultrasonically. via DuoSphere Holder

7. BIODOME® Double Membrane Gas Holder

This was one of the first designs installed in the UK. Other AD plants now also have digester tanks incorporating the now industry-leading BIODOME® Double Membrane Gas Holder roof biogas holder design to store the biogas produced during the treatment of their food waste, ready for conversion to renewable electricity. via ANAEROBIC DIGESTION « KIRK GROUP BLOG

We hope you found this biogas holder design article useful. Please leave your comments in our comments section below.

[Biogas Holder Design – Article first published 12 February .]

During the cold season, we would like to draw your attention to special care when operating your double diaphragm gas cylinder in winter weather conditions. To ensure trouble-free operation, system components that are particularly sensitive to weather conditions should be checked and maintained regularly.

To this end, we would like to provide you with the following information and recommendations:

Observe the WEATHER FORECAST

To prevent the negative effects of heavy snowfall and extreme frost, it is advisable to keep an eye on the current weather forecast, especially in winter. If heavy snowfall and/or frost is forecast, precautionary measures can be taken and particularly sensitive parts of the system can be checked as a precaution.

▶ Check the support air pressure. Is the support air blower working properly?

▶ Are all exhaust air flaps free to move?

▶ Are the intake openings of the fans clear?

▶ Is there sufficient antifreeze in the overpressure/underpressure protection?

▶ Is it possible to install a snow clearing cable on the roof as a precaution?

▶ Can the gas storage tank be filled to use the heat from the stored gas?

SUPPORT AIR BLOWER

▶ The roof of the double membrane gas storage tank must be checked regularly for snow.

▶ In the case of double diaphragm gas storage tanks, all fan intake grilles should be checked regularly in winter for frost formation and icing. In addition, exhaust air flaps should be checked for free movement. Icing can restrict the performance of the blowers and therefore the support air pressure recommended by us may not be maintained.

▶ If heavy snowfall is forecast, the support air pressure of the double diaphragm gas cylinder should be checked as a precaution. One mbar of pressure can carry 10 kg of snow load per m². If there is still a risk of the weather protection membrane being pushed in, countermeasures must be taken. In warm fermenters and secondary fermenters, the snow can be melted by filling the gas storage space. Depending on the moisture of the snow and the outside temperature, the snow can melt or slide off. In addition, tapping on the outside of the weather protection membrane can help the snow to slide off. Suitable tools for knocking off would be, for example, a broom with a telescopic handle or a 50 mm HT pipe. Caution: Do not use any sharp-edged tools.

▶ If the center of the weather protection membrane is dented by snow and/or water pockets, the gas storage membrane must be emptied in suitable weather conditions (no wind, no rain). The supporting air fan is then switched off. A rope or tensioning strap is thrown over the weather protection membrane and a channel is created by tying it in, through which the water can run off. Accumulations of snow can also be removed via this channel. Caution: Do not use any sharp-edged tools.

OVERPRESSURE / UNDERPRESSURE PROTECTION

The vacuum/overpressure safety device should be checked for free movement at least once a day in winter temperatures – or several times a day in extremely cold weather (please refer to the maintenance and care schedule in the ÜUDS operating instructions).

▶ Please avoid blowing off biogas over a longer period of time (also for environmental reasons).

▶ Despite the use of very pure or very highly concentrated antifreeze in the pressure/vacuum relief device (recommendation down to -30°C), this can be diluted so much by internal condensation (condensation of water vapor on the cold surfaces) that the pressure/vacuum relief devices lose their frost protection. If an overpressure/underpressure safety device blows off for a longer period of time during frost, pipes and the technology can freeze due to the condensate freezing.

▶ In unheated “cold” fermentation product storage facilities, overpressure/underpressure safety devices are particularly susceptible to winter temperature conditions due to the lack of a heat source. They should therefore be checked before each frost period. The dilution effect due to condensate formation is less pronounced in fermentation residue stores than in relatively warm fermenters. If attention is paid to an exact fill level when filling the overpressure/underpressure safety device (see scale), it is immediately apparent if the fill level decreases due to evaporation or after blowing off. It is also immediately apparent if the fill level increases due to condensation.

▶ For safe operation, we strongly recommend the use of trace heating, especially for tanks with increased condensate formation and in areas with expected heavy and prolonged frost. We offer trace heating systems for overpressure/underpressure safety devices. For further information, please contact us on +49 (0) 915 66-0

CAUTION: If the vacuum/overpressure safety device is frozen, please do not attempt to defrost it, e.g. with a hot air gun/gas burner. There is a risk of a biogas/air mixture igniting. A hazardous explosive atmosphere can occur at the chimney opening of the overpressure protection both in normal operation and in the event of faults. Non-explosion-proof devices may not be used there.

Defrosting with hot water is safer.

LEVEL MEASUREMENT

The mechanical level measuring device (especially draw-wire sensors) can freeze and therefore give unreliable values. Corresponding overpressure or underpressure can cause damage to the double diaphragm gas cylinder.

Depending on the weather conditions, these system components must be checked regularly for icing. Spraying the cord with silicone spray in the area of the deflection pulleys also prevents it from freezing.

FLAT PROFILE FASTENINGS

With membranes screwed on with a flat profile, the slipping snow can accumulate on the top of the wall and lead to the membrane being pushed in sideways, unlike with clamp hose fastenings. For this reason, the top of the wall must be cleared if large amounts of snow have accumulated and any water pockets that have formed must be skimmed off.

Caution: Do not use any sharp-edged tools!

PRESSURE AIR CONNECTION SET for the clamping hose

Glykoler: As a preventative measure, approx. 0.6 liters of pure antifreeze should be flushed into the system annually before the frost period (for the procedure, see Glykoler operating instructions, page 7). Only the supplied antifreeze (ALGOREX radiator antifreeze -40°C) or agents with the same specifications may be used!

Screw and clamp connections should be checked regularly and retightened if necessary.

HEAT PROTECTION FILM

The use of thermal insulation film can reduce heat loss by up to approx. 30 % and thus save heating energy. Retrofitting is possible. For further information, please contact us on +49 (0) 915 66-0

SNOW REMOVAL CONCEPT

Depending on the shape of the roof and the size of the container, a rope can be thrown over the container. For roofs with a spherical cap shape and center flange, several cables can be attached to the center flange at the high point using eyebolts. The snow can slide off by pulling the cable sideways. Caution: Caution is required if a level sensor with the weather protection membrane is installed at the high point. After the snow has slid off, the supply air ducts and the exhaust air flaps must be checked for functionality.

For further information, please contact us on +49 (0) 915 66-0

GENERAL SAFETY INFORMATION

When working on and around the double diaphragm gas cylinder, please take care to protect yourself against accidents, in particular against slipping on frozen ground or slipping and falling on black ice. Make sure you wear gloves to protect against frostbite when touching metal parts. Always watch out for icicles or roof avalanches falling from roofs or the tops of containers.