How to measure biogas production?

Previously we explained how a biogas digester works and how it produces gas. In this article we will explain why it is important to measure the biogas production and provide 3 ways on how this can be done.

Why measure biogas?

When biogas is produced as a source of renewable energy, It is important to be aware of how much gas is produced inside the fermenter. with a double membrane roof, you cannot see the inner membrane. Therefore it is not possible to visually attain the amount of gas inside the tank.

There are some dangers to not knowing the amount of gas in your fermenter. Once a fermenter is too full you will start to loose precious gas through the previously mentioned over – under pressure relieve valve. This valve lets the gas escape once the pressure inside the fermenter gets to high. The obvious negative effect of this is the loss of revenue. But if, through circumstances, the relieve valve is unable to sufficiently blow of enough gas, the membrane might even tear or rupture, causing even more monetary damage.

The same goes for the extraction of the gas. Once the pressure inside the tank is too low, the same over – under pressure relieve valve sucks in air, to prevent the roof from  vacuuming. This is also not good for the concentration of the gas within the tank. Oxygen will disrupt the composition of the gas, and it may yield a less pure concentration. So when extracting gas it is also good to know how much percentage is still inside the tank.

3 ways of measuring biogas

At Membrane Systems Europe we use 3 different ways of measuring biogas production inside the digester: the GasH meter; an Ultrasonic measurement device; or a Weight + Tape(+sensor). We will explain these 3 gas level measurements below.

1. GasH meter

A GasH meter consists of a tube that is attached to the middle of the upper side of the inner membrane. This tube (filled with liquids) measures the distance between the middle of the inner membrane and the case that hangs on the wall. This distance is measured by the pressure of the liquid inside the tube.

2. Ultrasonic measurement device

An Ultrasonic level measurement is a system that measures the distance between the outer and inner membrane by means of sending out signals from the inner side of the outer membrane to the upper side of the inner membrane. This system provides the possibility to set a maximum and minimum distance between the inner and outer membrane.

3. Weight + Tape (+ sensor)

This measurement system of MSE measures the height of the inner membrane. The product consists of a belt, which goes from one side of the tank to the other and lies exactly in the middle, on the upper side of the inner membrane. At the end of the tape, a weight will determine the height of the membrane. If the inner membrane goes up, the belt will also be dragged up, pulling the weight.

The weight is guided through a transparent tube on the outside of the tank. This gives a visual indication on how much gas is in the tank. The higher the weight, the more gas. Of course the weight is also attached to a digital measurement device, which translates the height of the weight to a 4 -20 mA signal, detailing the exact amount of gas produced.

Wrap up

All the gas level measurement systems can be integrated in the complete double membrane roofs of Membrane Systems Europe. All systems provide a detailed insight into how much gas is present in the tanks, which prevents there being too much or too little inside the tank. Thus preventing possible damages.