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.
