Utilization of Biogas as a Renewable Energy

Introduction to Biogas

Biogas is a type of renewable energy that belongs to the category of biofuel, 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. With technological advancements, various beneficial biogas utilization options are now available. The most common uses for biogas are electricity production, heat generation, and conversion to renewable natural gas and compressed renewable natural gas for use as vehicle fuels (Rutz, 2012).

Utilization of Biogas as a Renewable Energy

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 the "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 utilization of heat. Basically, it is a gas-powered engine with a generator connected to it. The engine drives the generator, which in turn produces electricity.

As a result of internal combustion, the gas engine also generates heat. This heat leaves the engine through the exhaust gases and the cooling liquid. By using heat exchangers, this thermal energy can be captured and used productively. An engine-based CHP unit has an efficiency of up to 90% and produces approximately 35% electricity and 65% heat. Compared to natural gas, biogas generally has a lower quality. Its heating value is lower. Furthermore, biogas can also contain contaminants that are harmful to the engine, such as sulfur compounds, halide compounds, acids, and solids. This often leads to biogas being treated to reduce contamination levels and enhance the gas engine's performance and lifetime (Rutz, 2012).

Biogas as Vehicle Fuel

This renewable energy is already used for heat and electricity production, but the best upgrading solution of this clean energy is its use as vehicle fuel. Gasoline vehicles can use biogas as a fuel, but biogas has to be upgraded to natural gas quality to be used in standard vehicles designed to use natural gas. Gas upgrading is normally performed in two steps, where the main step is the process that removes CO2. Minor contaminants are normally removed before the CO2 removal, and the water dew point can be adjusted before or after the upgrading, depending on the process (Shaha, 2021).

The second step is the removal of H2S, in which ferrous material (material consisting of iron) is placed in a closed gas-tight container to be purified. Suryavanshi N. D. Shaha, a professor at S.V.P.M’s College of Engineering, stated that biogas has a very high octane number, approximately 130. By comparison, gasoline is 90 to 94, and alcohol is 105 at best. This means that a higher compression ratio can be used with biogas than with petrol. An engine's compression ratio is the ratio of the volume of gas in the cylinder when the piston is at the top of its stroke (top dead center, or TDC) to the volume of gas when the piston's at the bottom of its stroke (bottom dead center, 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 a longer expansion cycle, creating more mechanical power output, and lowering the exhaust temperature. Biogas is a non-fossil gas produced from the decomposition of organic waste, recognized as an important component of the renewable energy program worldwide. It has the real potential to replace fossil energy (Shaha, 2021).

Conclusion

Biogas can be a valuable energy resource that can potentially be 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 developed for natural gas, such as heat production, electricity generation, and even as vehicle fuel.

References

Rutz, D. (2012). Sustainable Heat Use of Biogas Plants. WIP Renewable Energies.

Shaha, S. N. D. (2021). Biogas Utilization in Vehicles. S.V.P.M’s College of Engineering.