Biogas is a type of renewable energy that belongs to the category of biofuel that is naturally produced from the decomposition of organic waste in the absence of oxygen, which is referred to as anaerobic digestion. Anaerobic digestion is a natural form of waste-to-energy that uses the process of fermentation to break down organic matter. Biogas generated from anaerobic digestion processes is a clean and environmentally friendly renewable fuel. Currently there are various beneficial biogas utilization options available with the advancement of the technologies. The most common uses for biogas are electricity production, heat generation and with the new technologies, it can be converted to renewable natural gas and compressed renewable natural gas as well to be used as vehicle fuels.

The most common use of biogas is for thermal (heat) energy. A small biogas system can provide the heat energy for simple household activities by simply adjusting the air-to-gas ratio in a conventional gas burner. According to “Sustainable Heat Use of Biogas Plants” handbook by Dominik Rutz, biogas can be used as fuel for a combined heat and power (CHP) installation, which is a simultaneous production of electricity with the recovery and utilisation heat. Basically, it is a gas powered engine with a generator connected to it. The engine drives the generator, which in turn produces electricity.

The gas engine produces heat as a result of internal combustion. This heat escapes from the engine via the exhaust gases and the cooling liquid. This thermal energy can be captured and used productively by using heat exchangers. An engine-based CHP unit can achieve up to 90% efficiency and generates approximately 35% electricity and 65% heat. Biogas is generally of lower quality than natural gas. It has a lower heating value. Furthermore, biogas can contain contaminants that are harmful to the engine, such as sulphur compounds, halide compounds, acids, and solids, so biogas is frequently treated to reduce contamination and improve the performance and lifetime of the gas engine.

This renewable energy is already used for heat and electricity production, but the best upgrading solution of this clean energy is the use as vehicle fuel. Gasoline vehicles can use biogas as a fuel, but biogas has to be upgraded to natural gas quality in order to be used in normal vehicles designed to use natural gas.

Gas upgrading is typically done in two steps, the first of which is the CO2 removal process. Minor contaminants are typically removed prior to CO2 removal, and the water dew point can be adjusted either before or after the upgrade (depending on the process).

The second step is to remove H2S by placing the ferrous material (iron-containing material) in a closed gas tight container to be purified.

Suryavanshi N. D. Shaha, professor of mechanical engineering at S.V.P.M, stated that biogas has a very high octane number of around 130. In comparison, gasoline has a pH of 90 to 94 and alcohol has a pH of 105 at best. This means that biogas can have a higher compression ratio than petrol. The compression ratio of an engine is the ratio of the volume of gas in the cylinder at the top of its stroke (top dead center, or TDC) to the volume of gas at the bottom of its stroke (bottom dead centre or BDC). A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency with less fuel, while giving longer expnasion cycle, creating more mechanical power output and lowering the exhaust temperature. Biogas is a non-fossil gas which is produced from the decomposition of organic waste that has been recognized as an important component of the renewable energy program in the world. It has a real potential of fossil energy replacement.

Biogas can be a valuable energy resource that can be potentially used in many types of equipment. There are a variety of end uses for biogas. Except for the simplest thermal uses such as odor flaring or some types of heating, biogas needs to be cleaned or processed prior to use. With appropriate cleaning or upgrade, biogas can be used in all applications that were developed for natural gas such as production oh heat and electricity generation and even as vehicle fuel.