How Does A Double Membrane Roof Work?
OUR ROLE IN ADVANCING RENEWABLE ENERGY PRODUCTION
In this article, we delve into the working principles of a double-membrane biogas roof. In efforts to combat global climate change, an alternative form of renewable energy has emerged alongside solar and wind power: biogas. One of the major benefits of biogas is its independence from weather conditions. Unlike solar and wind energy, biogas can be generated continuously, day and night. To produce biogas, a proper biogas system is required, which must be fitted with a gas-tight cover, typically a double-layer membrane roof.
FROM COW MANURE TO ELECTRICITY
Before we can explain how a double layer biogas roof works, it is helpful to know how a biogas plant works in the basics. In order to produce biogas, organic material is needed. This can be manure from a cow, but can also consist of crop or ‘wet waste’, such as compostable waste from the kitchen container. Low-value residual (waste) streams are preferably used, as they often have no other application than the generation of bioenergy1. This organic material is stored in a silo, also called a digester or fermenter.
SO HOW DOES GAS FORM FROM ORGANIC MATTER?
A digester is home to bacteria and other microorganisms that do their work best at a temperature of about 42°C. These ensure that the organic material is broken down into gas consisting mainly of methane and carbon dioxide1. In this way, gas is formed in the biogas plant which is fed through pipes to a gas engine. When the gas engine is on, it is able to generate electricity from the biogas produced in the plant. The heat that is subsequently released from this process can again be used to heat the plant, thus forming a circular process.
HOW DOES A DOUBLE MEMBRANE ROOF CONTRIBUTE TO THIS PROCESS?
A double-layer biogas roof basically consists of the following components: an outer membrane, a variable-movement inner membrane, a fan and a substructure consisting of a center column, a tension band construction and a desulfurization net. The main purpose of the outer membrane is to “keep out” the outside and the main purpose of the inner membrane is to achieve a variable gas volume. In order to ensure that the outer membrane remains tightly stretched, a fan blows outside air between the outer and inner membrane and in this way a constant pressure is maintained (standard approx. 2 mbar) which allows the spherical shape of the outer membrane to be realized.
HOW A DOUBLE MEMBRANE BIOGAS ROOF OPERATES
When no biogas is being generated, the inner membrane rests directly on the substructure. Once biogas production commences and exceeds the rate of biogas consumption — for instance, when the gas engine is inactive — the pressure from the accumulating biogas lifts the inner membrane. Typically, this movement starts when the biogas pressure reaches between approximately 2.2 and 2.4 mbar, assuming a set inter-membrane pressure of 2 mbar. The surplus air trapped between the two membranes is then vented through an outlet valve.
Conversely, when biogas production falls below consumption levels, the inner membrane descends. In this case, a fan supplies additional air to maintain the outer membrane’s shape, ensuring it can resist external environmental forces such as wind and rainfall.
By efficiently managing the variable gas volume with a double membrane biogas cover, users can optimize biogas storage and renewable energy production to meet specific operational needs. Compared to traditional concrete slab covers, double membrane systems offer a more cost-effective and flexible solution.
This is the fundamental principle behind the operation of a double membrane biogas roof. Interested in learning how we can support the success of your project? Please do not hesitate to contact us!