5000m³ Ground Mounted Dual Membrane Biogas Balloon For Methane Storage

Product Description

The Mondes Process Double Membrane Gas Holder is a robust air-supported structure specifically engineered for biogas storage applications. This innovative design allows for efficient gas containment while minimizing the risk of leakage, which is crucial in maintaining the integrity of biogas as an energy source. Typically, this Gas Holder is integrated into anaerobic digestion systems within wastewater treatment facilities, agricultural digestion projects, landfill sites, and combined heat-and-power plants that utilize digested organic materials to produce biogas as an energy source.

In wastewater treatment facilities, the integration of the Gas Holder enhances operational efficiency by providing a reliable method for storing methane produced during anaerobic digestion processes. The stored biogas can be utilized on-site to power generators or heating systems, thereby reducing reliance on external energy sources and contributing to overall sustainability goals.

In agricultural settings, these structures facilitate the management of organic waste from livestock operations and crop residues. By capturing and storing biogas generated through controlled fermentation processes, farmers can convert waste into valuable renewable energy while simultaneously mitigating greenhouse gas emissions associated with traditional waste disposal methods.

Landfill sites benefit from the use of Double Membrane Gas Holders by effectively managing landfill gas production. As organic materials decompose in landfills over time, significant amounts of methane are released; utilizing a Gas Holder system helps capture this potent greenhouse gas for conversion into usable energy rather than allowing it to escape into the atmosphere.

Furthermore, in combined heat-and-power plants that leverage digested organic materials for electricity generation and thermal output, incorporating such advanced storage solutions optimizes fuel utilization rates. The ability to store excess biogas ensures consistent operation even when feedstock availability fluctuates or during periods of high demand.

Main Technical Parameters

Typical Installation

The gasholder is installed between the digester and the gas consumption equipment:

A Typical Gas-Holder installation is designed to store approximately 20 hours worth of gas production volume. Storage volumes can be designed to suit the process production and consumption requirements; Smaller units may be required as a buffer storage on a continuously operated plant, but larger gas storage units may be specified to hold the gas for use during the local peak-power requirement period, when energy produced can be sold on at a better price.

Main Structure

Outer Membrane

The Gas Holder structure comprises two spherically shaped membranes and a flat bottom membrane mounted onto a concrete base slab.

The outer membrane is a permanently inflated textile structure. The membrane is inflated by the use of electrically operated blowers – usually specified in matched pairs for Duty/Standby cycles. Non-return valves are fitted in the air supply line to isolate each blower when in standby mode. A regulator valve is fitted on the outer membrane exhaust duct.

The outer membrane is designed to all appropriate intenational codes for air-supported structures. The textile membrane is designed to withstand the internal air pressure forces as well as external dynamic forces from wind and snow. MONDES uses a range of membrane materials of up to 1,011 lbf/2 inches (9,000 N/5cm breaking strain) – the strongest textile membrane currently commercially available. The membranes are manufactured from polyester yarn with a PVC+PVDF coating. The coating is applied to our own specifications with additives and treatments for protection against sulphur and other components found in biogas. The membrane is specified for a low methane permeability of 167-ml/m²/day/bar pressure. The external membrane receives additional additives for increased protection against Ultra Violet radiation. Typical life expectancy of the external membrane is 20 years in an exposed, high-UV location. Longer durations can be expected in countries where UV levels are reduced. Over the lifetime of the structure, the outer membrane will become embrittled and begin to crack up, exposing the polyester yarns. At the end of its lifespan, the outer membrane can be easily replaced. Inner membranes (see later discussion) do not suffer from the same UV aging process and will outlast the outer membrane by a minimum factor of 2:1. Each roll of membrane material is 100% tested by both computer and human visual inspection techniques.

The membrane shape is manufactured in standard sizes to use the most economical use of standard base material widths. Alternative, specific sizes can be produced but it may not be commercially advantageous to do so.

The membrane form is achieved by precisely cutting the textile roll to accurate design patterns. These patterns are based on over 20 years experience of the behaviour of the textile under pressurised conditions, and have become a very specialised shape to ensure even stress distribution throughout the structure. The lapped joints between the components are high frequency welded under controlled conditions to ISO.9001. Total traceability is maintained for every metre of membrane weld for our quality records. Test welds are produced before each new roll of fabric is set up on the welding machine, and every 82 feet (25m) of weld throughout the construction of the welded membrane.

Fittings through the membrane, such as the viewing port, crown, inlets and outlets, and the base peripheral joint are reinforced with encapsulated stainless steel endless ropes. Each rope is manufactured to the exact size required for each individual project:

Inner Membrane

The inner membrane forms the variable volume gas containment within the outer membrane. The inner membrane and bottom membranes are sealed with a gas-tight compression seal around the periphery of the structure on the concrete base. As the volume of stored gas increases, the inner membrane rises to accommodate it. The pressure within the gas containment, and therefore the gas pipelines, is maintained by the air pressure within the outer membrane bearing on the surface of the inner membrane. The pressure differential across the outer air containment and inner gas containment is minimal – due only to the weight of the inner membrane (the gas containment pressure is 0.145 – 0.022psi (1 to 1.5 mBar higher)).

The inner membrane is made from the same textile fabric as the outer membrane. The inner membrane has reduced UV protection because it is not exposed to this radiation, but has an additional anti-static coating to eliminate the possibility of static being caused by the movement of the membrane during operation. Despite the unstressed service condition of the inner membrane, it is always specified to be the same strength as the outer membrane. In the unlikely even of an outside membrane failure, the inner membrane will maintain structural integrity against all loading conditions (internal pressure and environmental).

Gas Pipework & Pressure Relief

With over 20 years of development and a wide range of installations throughout the world we believe this system is the optimum arrangement of the gas supply pipework and pressure relief.

It is important that gas is supplied by one pipeline and consumed through a second pipeline – even in a system where the gasholder is used as a simple buffer. Biogas is a mixture of methane and carbon dioxide, and this mixture can settle out during periods of stagnation. With a two-pipeline system the gas within the containment is continually in motion – even during periods when production and consumption are equally matched.

The gas supply and consumption pipes are routed underneath the base slab to the centre of the base. The pipes and membranes are sealed using bolted compression sealing flanges. For diagrammatic purposes below, the two pipes are shown opposing each other. In practice, these two pipes would run parallel to each other, radially across the base. The pipework must be specified at the correct size to accommodate the volume flow rate and pressure of each individual plant’s requirements.

The Hydraulic Pressure Relief valve must always be installed on the gas supply line to the Double Membrane Gas Holder. When installed on the supply line, the valve will protect the membrane structure from over-pressure within as well as over-pressure situations caused by a rapid surge in gas production. Each valve is individually manufactured to fixed dimensions to provide the pressure relief necessary for each installation’s combinations of pressure and flowrates. The valve is constructed from type 304 stainless steel, and uses a 100% glycol antifreeze fluid inside to maintain the pressure trap. The fail-safe valve operates on the simple principle of hydraulic pressure differentials. The valve must be regularly maintained and checked for level of the fluid contents. In the event of a blow-off situation, humidity suspended within the biogas will condense out in the colder valve fluid and the level will increase. The valve body is supplied complete with a level viewing window, ball-valve drain cock, and a filllevel plug.

Both the supply and consumption pipes must be laid to falls so that any condensate forming within the pipes drains away. Condensate traps must be fitted close to the gasholder to facilitate the removal of the condensate. Typically, the condensate traps are installed in a pit just outside the tank base slab

Control Equipment

The standard scope of supply for Double Membrane Gas Holders includes:

1) Ultrasonic Level transducer and instrument.

2) Gas detector transducer and instrument.

• The Ultrasonic level transducer is situated in a housing at the crown of the Outer membrane. The transducer is hard-wired back to the instrument from where the readings can be read and control signals supplied via a 4-24mA control circuit interface for other PLC control equipment. The instrument provides for up to six relays for switching control circuits, for example, for starting the waste gas burner when the gas storage is nearing maximum, etc.

• The Gas Detector transducer is mounted in the outer membrane pressure regulation valve. The unit serves to maintain a continuous check for methane leakage into the outer membrane air containment. The transducer must be hard wired back to the instrument that provides for alarm and relay switching. The instrument is typically configured to provide alarms at 20%, 40% and 60% of the LEL (Lower Explosive Limit) for methane in air. In the event of the third alarm condition, the control system should shut the plant down so that the alarm can be investigated before any leakage reaches a flammable concentration of methane in the outer containment.

System/Plant Design Considerations

As noted above, the Gas Holder maintains the pressure throughout the gas production and consumption system. It is vital that the required operating pressure of the Gas Holder is determined at an early stage in the design of the plant and process so that an accurate quotation can be provided first time.

In any system related to the flow of gas or fluids, there are pressure drops caused by friction of the fluid in motion against the walls of the pipes, through valves and fittings, etc. In a system such as a biogas digestion and POWER PLANT, the pressure will not be the same at any point whilst the gas is flowing. The plant will have a pressure profile that is directly related to the design of the pipework, valves, and plant items involved:

As can be seen in the above diagram, the pressure at the Gas holder is less than at the digester, but greater than at any point throughout the gas consumption distribution. The pressure drop across each section of the plant is directly related to the size and length of the pipework involved, and the number of valves and other fitting through which the gas must flow.

In the simple example provided, the actual pressure required at the digester and gasholder must be worked backwards through the system from the specifications and requirements at the POWER PLANT. Depending upon the length and complexity of the system, the pressure at the digester might be considerably higher than that needed at the POWER PLANT in order that system as a whole can flow the gas at the volume and pressure required.

The use of a gas booster situated before the POWER PLANT is always worthy of consideration. A booster can provide the pressure required at the consumption unit whist allowing the rest of the system up-stream to be configured for reduced operating pressures. Introducing a gas booster can have a significant effect on reducing over-all plant investment costs as both the gas holder and digester will become cheaper when designed for lower operating pressures. The additional running costs of a gas booster are usually fairly well balanced against the reduced running costs of the smaller blowers required to maintain the pressure at the gasholder. In addition, a gas booster will only need to operate when there is a demand on the consumption side, thereby contributing further to the balancing of the operating costs.

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