As an alternative to conventional fuels, biogas is produced from the processing of biomass resources as an industrial feedstock. Biogas is a renewable and local energy source that contributes to sustainable heat and power production. Besides making use of agricultural wastes such as crop and forest residues and animal manure, biogas production converts organic wastes from industrial and municipal waste to energy. This is usually achieved by the implementation of the anaerobic digestion process.
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Anaerobic digestion is a process of decomposition of organic material in the absence of oxygen. During anaerobic fermentation of organic matter, the feedstock material breaks and degrades; in the meanwhile, different bacteria populations generate biogas. The produced biogas is in general a mixture of mostly methane, carbon dioxide, nitrogen, hydrogen, oxygen, and water vapor. The high concentration of methane in biogas indicates its potential to be injected into existing gas grids thanks to biogas purification and upgrading technology.
Upgrading biogas to biomethane
When biogas comes out from the digestion tanks, is a mixture of methane, carbon dioxide, hydrogen sulfide, air, hydrogen, Volatile Organic Components (VOCs), and siloxanes. Upgrading or purifying biogas means removing any CO2 and other contaminants present in biogas to produce biomethane.
In the membrane separation process, biogas produced in an anaerobic digestion plant enters the installation and is cooled and dehumidified. It is then transported to the active carbon filter system where it is purified by removing hydrogen sulfide and other contaminants. Once cleaned, the gas is compressed to the required pressure. The biogas flows to the membrane system in which methane is separated from carbon dioxide. The actual separation takes place because CO2 diffuses more easily than methane through the membrane straws, leading to separation.
Anaerobic digestion is the process through which organic matter is broken down in an oxygen-free environment to create biogas. Therefore, biogas is created by food waste, wastewater, animal manure, and various other organic wastes and is used to generate electricity and to provide heat.
When organic waste arrives at the plant, it is pre-treated and mixed with liquid waste to create a slurry. Then, it is fed into the digestion tank where there is no oxygen. Bacteria within this slurry eat organic matter. As they eat and break down organic matter, they create biogas (methane, carbon dioxide, and other gases). Gas flows at the top of the tank and is captured to create electricity and heat. Methane can also be cleaned up and used as vehicle fuel. The remaining slurry can be collected to act as manure for plants.
Convert waste to energy
Biogas is considered a solution to biomass and sustainability. The basic form of biomass comes mainly from firewood, charcoal, and crop residues, which is commonly used in the combustion process of dry raw materials to generate heat and power. However, biogas production through anaerobic digestion reduces greenhouse gas emissions. And, it is widely used for the valorization of wet residues and liquid effluents, such as municipal wastes and sewage, and moist residues of agricultural crops and animal wastes. Biogas production technology allows for waste conversion into gaseous fuels. It is an environmentally friendly, renewable, clean biofuel. Biogas technology is also a source of nutrient-rich organic fertilizer.
Upgrading biogas to produce biomethane can help to fully utilize the potential of biogas as a vehicle fuel or as a substitute for natural gas. Therefore, it is important to improve the quality of the raw biogas to separate unwanted substances such as nitrogen, hydrogen, oxygen, and water. Finally, by removing carbon dioxide in the biogas upgrading process, the energy content of the gas is increased, making it ready for grid injection. The removed carbon dioxide can be recovered and stored for other industrial use.