Biogas Production Process Explained

Bio Gas processing is among the biological methods of waste management. It is commonly used in the management of plant waste worldwide. The main difference of the Bio Gas processing is that instead of letting the gases produced during the fermentation process to escape into the environment, they are collected and used as a gaseous fuel product.

In the process of producing biogas, organic liquid wastes, animal manure, and solid organic wastes are directed into a digester. In the digester system, bacteria ferment the wastes in an anaerobic process to produce biogas, a gaseous bi-product. The non-digestible solids in the digester are removed as sludge which can later be returned to the ground. After the treatment process, the liquid from the waste treatment plant will be made harmless to the environment; and it can then be released into the rivers.

The gases contained biogas produced in an ordinary plant approximately contains the following:
- 60%~70% methane
- 30%~40% carbon dioxide
- Some trace of hydrogen sulphide

This biogas manufactured is further refined so that the carbon dioxide and hydrogen sulphide gases are eliminated. The outcome is a gas that mostly contains methane. This is very homogeneous to the natural gas obtained from the oil and gas fields. By employing the use compressors in a bottling plant, both the methane and carbon dioxide gases can be kept in highly pressurized cylinders. The two gases can be made use of in other industrial applications processes. The biogas gas can be used as fuel in electrical power generators, vehicles, and for general heating purposes.

With a well-designed and converted gas engine, electrical power generation is very feasible. When compressed under high Glycol purification pressures, the methane gas can be carried along as fuel for CNG motor vehicles. Methane can also be liquefied and carried along to power LNG vehicles. The natural gas can be mixed with diesel oil and used in running special bio-fuel engines.

Gas Holder and Metering

the produced biogas is collected in inverted floating vessels sealed at the bottom with water. As the quantity of the gas increases, the floating vessel raises thus creating room for a larger volume.

Scrubbing

Scrubbing is a process that gets rid of an unwanted compound from the biogas prior to being used. The main compound to be scrubbed is hydrogen sulphide (it has a smell similar to that of  (the rotten egg). Hydrogen sulphide usually reacts with the moisture in the biogas to form corrosive sulphurous acids. Sulphuric acid can corrode almost anything.

Hydrogen Sulphide Scrubbing

One of the ways of getting rid of hydrogen sulphide is by letting it to react with something worth getting rid of; for example some steel wool for instance. Due to the extreme corrosive nature of hydrogen sulphide gas, the piping used must be made of transparent glass having gas inlet pipe running down to the bottom of the container; and an outlet pipe leading up way near the top. The whole assemblage must be gas-tight.

Regeneration of Iron Sulphide

The Bio Gas processing  process regeneration is slower compared the initial scrubbing action. As soon as the black corrosion is at approximately 75% of the height of the container, change the ferric oxide or steel wool for a fresh sacrificial material. Usually, it is advisable to run two or more similar containers connected to increase the scrubbing capability.

2-Stage Scrubber

The 2-stage scrubber illustrated below requires the gas to be highly pressurized to enable it to bubble into aqueous solutions of ferric and calcium hydroxides. This further gets rid of the unwanted impurities contained in the biogas.