The process of biogas compression and utilization generally includes biogas generation, purification, compression and final utilization. The following is a detailed introduction:
Biogas generation
Raw material collection: Select agricultural waste (such as straw, livestock and poultry manure), industrial organic wastewater, urban domestic sewage and garbage and other organic-rich materials as raw materials. These raw materials contain a large amount of carbohydrates, proteins and fats, which are the material basis for the production of biogas.
Anaerobic fermentation: The collected raw materials are placed in a biogas pool or an anaerobic fermentation tank, and fermented by anaerobic microorganisms under anaerobic conditions. This process is generally divided into four stages: hydrolysis, acidification, acetic acid production and methane production, and finally produces biogas with methane and carbon dioxide as the main components, and also contains a small amount of impurities such as hydrogen sulfide and water vapor.
Biogas purification
Desulfurization: Hydrogen sulfide in biogas is corrosive and toxic, which will cause harm to equipment and human body. Common desulfurization methods are dry desulfurization and wet desulfurization. Dry desulfurization generally uses adsorbents such as iron oxide and activated carbon to react chemically with hydrogen sulfide to remove it. Wet desulfurization uses alkaline solution or oxidizing solution to react with hydrogen sulfide to achieve the purpose of desulfurization.
Dehydration: The water in biogas will reduce the calorific value of biogas, and may also form condensed water in pipes and equipment, causing corrosion and blockage. Common dehydration methods include cooling, adsorption and membrane separation. The cooling method is to remove water vapor by lowering the temperature of biogas to condense into water droplets; the adsorption method is to use silica gel, molecular sieves and other adsorbents to adsorb water in biogas; the membrane separation method is to use special membrane materials to allow water to pass through the membrane first to achieve separation.
Removal of carbon dioxide: In order to improve the calorific value and quality of biogas, it is usually necessary to remove part of the carbon dioxide. Common methods include chemical absorption, physical absorption and membrane separation. The chemical absorption method uses alkaline solution to react with carbon dioxide for absorption; the physical absorption method uses organic solvents to dissolve carbon dioxide under certain conditions to achieve separation; the membrane separation method is to separate carbon dioxide and methane according to the different permeation rates of carbon dioxide and methane in the membrane material.
Biogas compression
Boosting: The purified biogas first enters the air inlet of the compressor, and is compressed by the compressor's impeller or piston and other components to increase the pressure of the biogas, generally from normal pressure to a certain high pressure level, such as 20MPa - 25MPa.
Cooling: During the compression process, the temperature of the biogas will rise. Excessive temperature will affect the performance of the compressor and the quality of the biogas, and may even bring safety hazards. Therefore, it is necessary to cool the compressed biogas through a cooling system to reduce its temperature to a suitable range, generally below 40°C.
Storage: Compressed biogas is usually stored in special gas storage equipment, such as high-pressure gas storage tanks, gas cylinders, etc., for subsequent transportation and use.
Biogas is a clean and renewable energy source with a variety of utilization methods, mainly including the following aspects:
Energy utilization
Cooking and heating: In rural areas or some places with conditions, biogas can be directly transported to family kitchens through pipelines for stove combustion to meet the needs of cooking and hot water supply. In winter, the heat generated by biogas combustion can also be used to heat houses and provide residents with a warm and comfortable living environment.
Power generation: Biogas power generation is one of the important ways to use biogas on a large scale. Through biogas generators, the chemical energy of biogas is converted into electrical energy, which can provide electricity supply for enterprises, communities or remote areas and achieve energy self-sufficiency. Excess electricity can also be connected to the power grid to provide clean energy for society.
Automobile fuel: The content and properties of the main component methane of purified and compressed biogas are similar to those of natural gas, and can be used as fuel for cars. Cars fueled by biogas have the advantages of low cost and low pollution, which can effectively reduce dependence on traditional fossil fuels and reduce exhaust emissions.
Agricultural use
Biogas fertilizer return to the field: The residues after biogas fermentation, namely biogas residue and biogas liquid, are high-quality organic fertilizers. Biogas fertilizer contains rich nutrients such as nitrogen, phosphorus, potassium, and a large amount of organic matter and microorganisms, which can improve soil structure, increase soil fertility, increase the yield and quality of crops, reduce the use of chemical fertilizers, and is conducive to the sustainable development of agriculture.
Greenhouse gas fertilizer: In greenhouses, introducing an appropriate amount of carbon dioxide produced by biogas combustion can increase the concentration of carbon dioxide in the greenhouse, provide more raw materials for plant photosynthesis, promote plant growth and development, and improve the yield and quality of crops such as vegetables and fruits. It can also play a certain role in warming.
Aquaculture bedding: After treatment, biogas residue can be used as bedding for farmed animals. It has good water absorption and air permeability, can keep the pens dry, and reduce the occurrence of animal diseases. At the same time, the beneficial microorganisms in biogas residue can also improve the breeding environment and promote the healthy growth of animals.
Industrial use
Chemical raw materials: Methane in biogas can be used as a chemical raw material for the production of a variety of chemical products. For example, synthesis gas can be produced through the reforming reaction of methane. Synthesis gas is an important raw material for the production of chemical products such as methanol and synthetic ammonia. In addition, methane can also be used to produce organic chemical raw materials such as acetylene and methyl chloride, further extending the industrial chain to produce a variety of chemical products such as plastics, rubber, and fibers.
Fuel cells: With the continuous development of fuel cell technology, biogas can also be used as fuel for fuel cells. Fuel cells convert chemical energy in biogas directly into electrical energy through electrochemical reactions. They have the advantages of high energy conversion efficiency, no pollution, and low noise. They can be used in distributed power generation, backup power supply and other fields to provide stable power supply for industrial production and life.
Other uses
Lighting: In some remote areas or places where power supply is insufficient, biogas can be used for lighting through biogas lamps. Biogas lamps use the high temperature generated by biogas combustion to make the fluorescent material in the lamp glow, providing a certain brightness to meet people's basic lighting needs.
Refrigeration and preservation: The absorption refrigeration technology driven by biogas combustion can realize the refrigeration and preservation of agricultural products. This refrigeration method has the advantages of low energy consumption, stable operation, and environmental friendliness. It can extend the storage period of agricultural products, reduce the loss of agricultural products, and increase the added value of agricultural products.
