OUR CONTRIBUTION TO THE GENERATION OF RENEWABLE ENERGY
In this blog, we explain how a double-layer biogas roof works. Out of the desire to limit the climate change in the world, there is -besides generating energy through solar panels and wind turbines- another form of renewable energy has been developed: biogas. The great advantage of biogas is that it is not dependent on weather conditions. Biogas can be produced at any time of the day. For this you need a biogas installation and this should be equipped with a gas tight cover or double mebrane 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.
When no biogas is produced, the inner membrane rests on the substructure. The moment biogas production takes place and the biogas production is greater than the biogas withdrawal, for example when the gas engine is off, the force created by the pressure of the biogas will cause the inner membrane to rise. As a rule, the inner membrane will begin to move at a biogas pressure between approximately 2.2 and 2.4 mbar (at a set pressure of 2 mbar between the membranes). The excess air present between the two membranes disappears through the outlet valve. On the other hand, if the biogas production is lower than the biogas withdrawal, the inner membrane will drop and the air supply through the fan will ensure that the outer membrane keeps its desired shape and can absorb external forces, such as rain and wind.
By making optimal use of the variable gas volume available through a double membrane biogas cover, optimal biogas can be produced as well as renewable energy generated according to the user’s wishes. This is the advantage of using a variable biogas roof over using, for example, a concrete slab cover. It is also better for the wallet, because a concrete slab cover is a lot more expensive.
This is how a double membrane roof works. Are you curious as to how we can make your project a success too? Then get in touch with us!
By: Laura Nieuwmeijer, MSc Industrial Engineering & Management, Martin Nieuwmeijer, MSc Chemical Engineering.
References  Vergisting en vergassing (2020, juli 30). Geraadpleegd van Rijksdienst voor Ondernemend Nederland: https://www.rvo.nl/onderwerpen/duurzaam-ondernemen/duurzame-energie-opwekken/bio-energie/vergisting-en-vergassing