Biogas Storage Tanks
Pioneers for a clean environment
Biogas storage systems are an active contribution to the generation of renewable energies, and thus to environmental protection in general. At SATTLER, concepts for the storage of biogas, liquid manure, or brewery residues have a long tradition. In 1981 SATTLER invented the double membrane gas holder for storing digester gas from waste water treatment plants. This biogas storage design has been tested and proven over the decades and now is an integral feature in the design of any modern waste water treatment plant worldwide.
As the leading supplier of such storage systems, we keep the value chain as long as possible in our own company. Thus our own weaving and coating units ensure outstanding quality for the supply of the base material, PVC-coated polyester fabrics. Download the Sattler Biogas Storage Tanks Brochure
The perfect storage tank for every challenge.
WHICH VOLUME DO I CHOOSE?
Storage tanks are designed to compensate for fluctuations in production and consumption, for volume changes due to varying temperatures and for stagnating consumption; furthermore, gas holders store gas for later use. With these parameters the optimal dimensioning can be determined. The ideal storage volume varies according to the plant design, the substrate mixture, and the management of the plant.
BASE LOAD OPERATION
The goal is to enable consumers to operate at high capacity. Consumers’ performance should neither be influenced nor determined by fluctuating gas production, but should constantly operate at full load. Flaring excess gas should be avoided. Therefore excess gas production is buffer stored and lack of gas production is replaced by the stored gas. Conventional storage tanks hold volumes corresponding to a gas production of three to four hours.
The storage tank serves to balance out the continuous gas production and the discontinuous consumption. Low gas production will be stored over a longer period of time, followed by a shorter and higher-powered consumption period. That is why bigger storage tanks are required.
WHICH PRESSURE DO I CHOOSE?
The operating pressure is predetermined by the plant design and the dimensioning of the various components. We are talking about low-pressure systems, starting from zero pressure to 50 mbar. The operating pressure influences the dimensioning of the entire gas line. Among them are: gas ducts, safety devices for protection against over-pressure, condensate traps, flares, devices for gas purification, and gas pressure intensifiers.
WHICH EXTERNAL LOADS DOES A STORAGE TANK HAVE TO WITHSTAND?
Depending on its location, wind load, temperature and sun radiation all have an impact on the gas holder. The impact of snow loads depends both on the location and operating conditions since waste heat from the digester results in de-icing in regular operation. When not in operation, the digester does not produce any waste heat. In this case the full snow load must be taken into account.
UP TO WHICH TANK DIAMETER DO WE BUILD GAS STORAGE TANKS?
Textile gas storage tanks and coverings can be built to very large dimensions. The tank diameter basically does not pose any limitation as to the choice of a suitable gas storage tank.
WHICH KIND OF AGITATOR TECHNOLOGY CAN BE USED?
There is a suitable storage system for each type of stirring device. Submersible mixers are accessible via service manholes or service shafts in the membrane. It is not necessary to remove membranes for service purposes.
WHICH COSTS DO I HAVE TO TAKE INTO ACCOUNT?
In terms of economic evaluation of a storage system, not only the initial investment and the running costs play a major role, but also the replacement investment and opportunity costs are to be considered. Opportunity costs arise from lesser yields in power and heat generation and from a higher use of substrate in less suitable storage systems.
The highest costs arise when the CHP (combined heat & power) does not operate at full capacity! These opportunity costs can exceed the initial costs of the biogas storage tank after only a few years of operation.
Sattler Double Membrane Gas Storage Tanks
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 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. And 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.
Sattler/Ceno DMGS TM
The Sattler double membrane gas storage tank that is mounted on an existing tank consists of an external membrane which forms the outer shape, and an internal membrane which seals the digester gas-tight. A permanently running support air blower provides air to the space between the inner and outer membranes, thus keeping the pressure at a constant level – irrespective of gas production and gas withdrawal. The pressurised air keeps the outer membrane in shape to withstand external wind- and snow loads. And it exerts a constant pressure on the inner membrane and thus pushes gas at constant volume and pressure into the outlet pipe. 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 by means of 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 combination of storage tanks and covers offers an ideal storage volume at lowest total costs.
This kind of gas holder also offers a wide range of possible shapes, from the quarter sphere to the hemisphere and to conic shapes – everything is possible to ensure a customer- and needs-oriented design.
The double-shell CENO biogas roof is mounted onto an existing tank and consists of an external membrane which provides the outer shape, and an internal membrane that seals the digester gas-tight. The central pole leads up to the maximum turning point and keeps the external membrane in place. This enables the gas holder to withstand all external loads such as snow, wind, or rain. The biaxial bending of the roof prevents fluttering and ballooning at strong winds. Both membranes are anchored to the external wall of steel or concrete tanks. The safety valves protect the gas holder against over- and low gas pressure.
Level meter systems provide electronic signals showing the filling level of the gas membrane that can then be processed by the customer to control the plant. The single-shell cover consists of one membrane supported by a central pole. It is used as a cover for permanent storage tanks and for fermenters.
The combination of gas holder and single-shell cover offers ideal storage volumes at lowest total costs.
Plant designs with more than one gas holder offer the possibility to combine gastight single-shell CENO biogas roofs, air-supported external double membrane gas holders SATTLER/CENO DGMS, and SATTLER/CENO DMGS TM mounted on tanks. In this case, the single-shell cover is constructed to meet the pressure requirements of the DMGS.
Various patented mountings and openings ensure that maintenance can be carried out without removing the biogas roofs. For example the withdrawal of biogas can be done via a gas outlet in the membrane. Manholes for maintenance of e.g. immersed agitators or feeders of solid matter are possible. Special rainwater deflectors ensure that rainwater is kept off the insulation of the tank.