The material used for the double-membrane roof system is a PVC-coated polyester fabric, which has been especially developed and produced for use with biogas tanks. The material is flame-retardant according to DIN 4102 B1 and UV-resistant. Materials with a weight of 800 g/m² to 1,500 g/m² are used. The gas permeability of the membrane is between <200 cm³/(m² d bar) and <500 cm³/(m² d bar). It is available in the standard colours of silver grey (similar to RAL 7001) and moose green (similar to RAL 6005). However, the double-membrane roof system can also be delivered in special colours on request. The material is high-frequency welded. Air inlets and outlets, as well as a condensate drain plug, are incorporated into the outer membrane. Hemmed sleeves are built into the inner membrane to act as guides for the filling level belt and hose. A protective weatherproof film is attached to the container edge and serves to drain off rainwater. The volume of the gas tank can be individually agreed with the customer.
The dbds double-membrane roof systems are designed for containers
- up to a diameter of 40 m
- up to a gas operating pressure of 20 mbar
- up to a gas storage volume of 6,500 m³
The roof systems can be fitted to containers made out of concrete, steel or enamelled steel. Depending on the customer's wishes and requirements, the following components on the roof system can be individually adapted, selected and manufactured.
The attachment system serves the purpose of gas-tight attachment of the double membrane on the container dome and attachment of the substructure to the top edge of the container. The double membrane is attached by means of threaded anchors bonded into the concrete or, in the case of steel containers, with bolts. The sealing is provided by a foamed self-adhesive PE tape. On concrete containers the lower clamping rail serves as a bracket for the double membrane and has attachment points (tabs) for the substructure (belt system). The double membrane is held in place by the upper clamping rail on both concrete and steel containers. All metal components are made of corrosion-resistant stainless steel.
The centre support in combination with the crown ring supports the substructure and is used to attach the belt system. The centre support is fixed to the base of the container with four anchor bolts. All components are made of corrosion-resistant stainless steel.
The crown ring in combination with the centre support supports the substructure and is used to attach the belt system. The crown ring is mounted on the centre support. All components are made of corrosion-resistant stainless steel.
The substructure provides the structure on which the double membrane is mounted, and prevents the double membrane from being immersed in the substrate if the gas pressure drops because of operating conditions. The substructure comprises a polyester belt system that is attached to the crown ring in the centre of the container and to the upper edge of the container. On concrete containers the belt system is attached to the upper edge of the container on the tabs of the lower clamping profiles, and on steel containers on metal brackets fixed to the container wall. All metal components are made of corrosion-resistant stainless steel.
The support air blower provides for the build-up of pressure in the support air space. The required air flow is pumped through the air inlet pipe between the membranes by one or two fans. Excess air can escape through a safety valve in the air inlet pipe or via the air outlet. The air inlet and air outlet can be partially or fully shut off with gate valves. The supply of support air (gas operating pressure, gas withdrawal, gas production, etc.) is agreed with the customer on a case-by-case basis.
A structural analysis is performed on the dbds double membrane roof systems with due attention to the currently applicable standards (DIN, EC, BSJ).
The documentation comprises the installation and operating instructions based on the machinery directive, the operating instructions for the support air blower, the overpressure/underpressure safety unit and the gas level measurement devices, the verifiable structural analysis, factory certificates and test certificates.
The dbds double membrane roof systems can be supplied with either full installation or supervised installation including a gas leak test. Four installation engineers are provided for full installation, and two installation engineers for supervised installation. A crane, telescopic work platforms and scaffolding are required for installation.