Biogas as an ecological source of energy. Energetic safety.


Biogas, originally called mud or swamp gas, due to the place of natural secretion of swamps. It is also often called a landfill gas because it is created in municipal waste landfills.

Biogas is an unconventional fuel produced from organic matter under anaerobic conditions in the methane fermentation process where methane is the main component. Methane is a chemical organic compound used as a fuel gas in the energy industry, automotive engines and households. In comparison to natural gas, biogas contains 40-85% v / v methane, where 90-91% v / v methane is found in conventional natural gas. The calorific value of methane obtained from the biomass distribution is 39.7 MJ / m3, thanks to which it can be used for the production of heat and electricity. However, before using it, it must be dried and cleaned of hydrogen sulphide and carbon dioxide. Biogas is produced in a closed fermentation chamber without access to light and oxygen. The fermentation chamber must have adequate load, i.e. about 3 – 5 kg SSO / m3 / d. In popular biogas plants, temperatures in the range of 35 – 400C are used, maintaining the right temperature is a very important task when operating the installation. When the limits of appropriate temperatures are disturbed, this may lead to bacterial activity or damage that is irreversible.

To keep the substrate in the liquid phase, its dry matter content should not exceed 12 – 15%. Another very important condition that must be ensured in the fermentation chamber is the pH, which should be between 7 and 7.7 pH. Insufficient stability of the process caused by incorrect dosing of too much easily decomposed organic matter may cause a sudden drop in pH, which will lead to inhibition of bacterial activity, which will disrupt the operation of the biogas plant for a long time. In modern biogas plants, control-measurement and automation devices are used, which guarantee the stability of the fermentation process in these biogas plants, using 100% of the generation capacity. The resulting biogas in agricultural biogas plants in the methane fermentation process, in addition to methane and carbon dioxide, contain small amounts of water vapor, hydrogen sulphide and other compounds. The above-mentioned compounds reduce the energy value of the produced biogas and limit its technical use. Water vapor and hydrogen sulfide act corrosively on biogas transport devices, which is a major disadvantage of biogas. Biogas can be pressed into the gas network or used for drives must be properly cleaned. Technological purification of biogas involves the removal of water vapor from the gas. Biogas, before being pumped into the absorption column, is compressed to a pressure of 7 bar, resulting in a higher gas temperature. The gas must be cooled to obtain the optimum gas temperature before going into the absorption process. The absorption column contains a material that ensures a good contact time for the biogas with the absorption medium. The absorption medium is forced up the column and flows down counter-currently to the gas being forced down. The gas leaving the absorption column is 95-98% methane. The treated biogas in the absorption column is subjected to drying to a level that prevents condensate from falling out. For the drying of biogas, an absorption dryer with filling is used. It is common to use two dryers installed in parallel, then we will get higher quality biogas. The filling of one dryer is regenerated with the dry gas of the second dryer.

The use of bed regeneration ensures continuity of installation work. The siloxane filter is the last stage of biogas purification. Siloxanes are silicon compounds that are responsible for the formation of waste, removal of siloxanes from biogas is provided by active carbon filters. After passing the above mentioned stages, the treated biogas can be used in the network in a compressed form and is used as a fuel for cars. The treated biogas contains 98 – 99% v / v methane.

The final products of methane fermentation are post-fermentation residue, which is used as a fertilizer, which has such advantages as:

limits the burning of plants during fertilization;
is easily absorbable nitrogen (ammonium) fertilizer for plants.
The largest biogas producers in the European Union is Great Britain, followed by Germany much later, France is in third place in terms of biogas production.

The biogas produced can be used for:

electricity production;
thermal energy production in adapted gas boilers;
production of electricity and heat in associated units;
transmission in the gas network;
traction motors and vehicles drives as fuel;
technological processes, e.g. methanol production;
production of dry ice.
Environmental effects of agricultural biogas production:

reducing the consumption of fossil energy resources;
reduction of emissions of compounds generated during combustion of non-renewable energy resources;
improvement of conditions for fertilization of arable land with waste from biogas plants as compared to non-fermented liquid manure;
the ability to maintain the soil humus balance when using by-products (waste);
the destruction of weed seeds, and hence the reduction of the amount of used plant protection products;
elimination of pathogens through the process of hygienization;
odor reduction by over 80%;
reduction of pollution of ground and surface water;
reduction of greenhouse gas emissions of nitrous oxide and methane.