BIOGAS PRODUCTION & BOTTLING PLANT

Biogas is a clean, un-polluting, smoke and soot free fuel. It contains 55 to 70 per cent methane which is inflammable. Biogas is produced from cattle dung, human excreta and organic matter in a “Biogas Plant” commonly known as “gobar gas plant” through a process called “digestion”. The manorial value of the dung is also enhanced by this process. It helps in simultaneously obtaining both cooking fuel and enriched manure from cattle dung. Besides, women and children are saved from hardship and drudgery of collecting and head solid loading of heavy bundles of firewood, explore to smoke in the kitchen and time consuming cooking. It has also improved village / urban sanitation.

Haryana, with cattle population of about 7.6 million, has the potential a potential of generation of about 3.8 million cubic meters of biogas which can be used to generate about 300 MW power or can be purified, compressed and bottled for production of about 1.2 million Kg of compressed biogas.

One tone cattle dung by about 100 adult animals produces about 50 cu.m. biogas per da .This gas can be utilized for thermal as well as power generation besides producing rich manure as a bye product. The gas generated can also be purified and compressed further to produce bio-CNG, which can find application for commercial purposes.

The current use of fossil fuels is rapidly depleting the natural reserves. The natural formation of coal and oil however, is a very slow process which takes ages. Therefore, a lot of research effort is put into finding renewable fuels nowadays to replace fossil fuels. Renewable fuels are in balance with the environment and contribute to a far lesser extent to the greenhouse effect.

Biogas is a renewable fuel, an energy source that can be applied in many different settings. It is defined as a combustible gas mixture produced by the anaerobic fermentation of biomass by bacteria and takes only a relatively short time to form. In nature, the fermentation process occurs in places where biological material is fermented in an oxygen deprived environment such as swamps and waterbeds. The two main sources of biogas from human activities are domestic garbage landfills and fermentation of manure and raw sewage. The advantage of processing these waste products anaerobically, compared to aerobically, is the larger decrease in volume of waste product.

For this reason, the industry nowadays prefers anaerobic fermentation to process waste streams.

Biogas is a mixture of methane, CO2 and small quantities of other gases produced by anaerobic digestion of organic matter in an oxygen-free environment. The precise composition of biogas depends on the type of feedstock and the production pathway; these include the following main technologies:

• Biodigesters: These are airtight systems (e.g. containers or tanks) in which organic material, diluted in water, is broken down by naturally occurring micro‑organisms. Contaminants and moisture are usually removed prior to use of the biogas.

• Landfill gas recovery systems: The decomposition of municipal solid waste (MSW) under anaerobic conditions at landfill sites produces biogas. This can be captured using pipes and extraction wells along with compressors to induce flow to a central collection point.

• Wastewater treatment plants: These plants can be equipped to recover organic matter, solids, and nutrients such as nitrogen and phosphorus from sewage sludge. With further treatment, the sewage sludge can be used as an input to produce biogas in an anaerobic digester.

The bio-gas produced from food waste, decomposable organic material and kitchen waste, consisting of methane and a little amount of carbon di oxide is an alternative fuel for cooking gas (LPG). Also, the waste materials can be disposed of efficiently without any odor or flies and the digested slurry from the bio-gas unit can be used as an organic manure in the garden. The major components of the bio-gas plant are a digester tank, an inlet for feeding the kitchen waste, gas holder tank, an outlet for the digested slurry and the gas delivery system for taking out and utilizing the produced gas. This project is also useful for students to have a hands-on learning experience in constructing a Mini Bio-Gas Plant, using locally available material.

Basics behind biogas production

Biogas is gained from organic materials. The origin of the substrates can vary, ranging from livestock waste, harvest surplus, vegetable oil remains (Oil Cakes), materials from household organic waste collection containers.

The evaluation of materials for implementation in the biogas process depends on their potential attainable yield. The inflammable biogas is a versatile source of energy, which is now preferably converted into electricity and heat. In recent years, several biogas plants were taken in operation in India, with animal manure and organic wastes from industry and households are fermented.

Apart from conventional materials, Grass can also be fermented due to progress in the fermentation method: Farmers become “energy hosts” due to the fermentation of green material. The clean energy from grasslands can easily be transported and contributes to the reduction of greenhouse gases. Fermentation of grass can provide an ecologically and economically smart contribution to energy production of the future.

Biogas mainly consists of combustible methane (CH4) and non-combustible carbon dioxide (CO2). Besides CH4 and CO2, biogas also contains small amounts of hydrogen sulphide (H2S) and some other pollutants. The composition of biogas strongly depends on its source. Table below shows the composition of biogas from various sources. It can be seen that biogas from a garbage landfill also contains some nitrogen (N2).

CH4 combusts very cleanly with hardly any soot particles or other pollutants, making it a clean fuel. But CO2, the non-combustible part of the biogas, lowers the calorific value of the biogas. Biogas containing 60% CH4 has a calorific value of 21.5 MJ/Nm3 while pure CH4 has a calorific value of 35.8 MJ/Nm3.

Overview of compositions of biogas from different sources

Besides CO2, biogas also contains small amounts of H2S. H2S is poisonous when inhaled. Furthermore, when water is present, H2S forms sulphuric acid (H2SO4), which is highly corrosive, resulting in extra costs for maintenance when using the biogas.

Depending on the source of the biogas, it can contain other pollutants. Common pollutants are water vapor, ammonia (NH3) and siloxanes. Water vapor in biogas forms, combined with NH3 or H2S, a corrosive solvent. Siloxanes are silicate compounds that have oxygen groups replaced by organic groups like CH3. When this compound is burned, it will form SiO2 (sand) which can cause severe damage to equipment.

There are a number of uses for biogas. Currently, biogas which has been stripped of H2S is mainly used in gas turbines to produce electricity. However, most energy is lost as heat in this process, which results in a low overall efficiency. But biogas can also be used for injection in the gas grid or as a car fuel. The requirements for the end product depend on the final use of the biogas.