Anaerobic digestion of sludge can not only reduce the amount of sludge, but also produce a large amount of biogas with high calorific value. Biogas is an easily accessible bioenergy. It can be used for heating and power generation, etc. to realize the resource utilization of sludge. The components of the biogas system are as follows:
Gas collecting chamber: The gas collecting chamber is built on the top of the anaerobic digestion reactor. The biogas is led out from the highest point of the gas collecting chamber by pipeline. The gas collecting chamber should maintain a certain volume; it can maintain the relative stability of the biogas pressure; it can prevent scum or digestion liquid from entering the biogas discharge pipe. When there is a three-phase separator, it is also necessary to prevent biogas from jumping into the sedimentation tank. The gas collecting chamber has good air tightness to prevent biogas from escaping and air from entering.
Transmission and distribution system: The transmission and distribution system includes gas transmission pipes and gas distribution pipes. The biogas between the gas collecting chamber and the gas storage cabinet is called a gas storage tank, and the biogas pipe between the gas storage cabinet and the user is called a gas distribution pipe. The hydrogen sulfide content in the gas transmission pipe is high, and anti-corrosion measures should be taken. Usually, the biogas in the gas phase of the digester is in a saturated state with steam and water, which carries a large amount of water, making it have a high humidity. The humidity of biogas can produce the following adverse effects: water and hydrogen sulfide in biogas produce hydrosulfuric acid to corrode pipelines and equipment; water condenses on the diaphragms and diaphragms of equipment such as check valves, safety valves, flow meters, and regulators, affecting their accuracy; moisture can increase the air flow resistance of the pipeline; moisture can reduce the calorific value of biogas. Therefore, dehumidification measures should be taken in the biogas distribution system.
Purification unit: Biogas purification mainly includes desulfurization and filtration. Hydrogen sulfide in biogas is a corrosive gas. Desulfurization is to remove hydrogen sulfide in biogas, otherwise the hydrosulfuric acid formed by hydrogen sulfide and water vapor will corrode equipment or pipelines and reduce the service life. There are two types of desulfurization: dry and wet. Dry desulfurization is to fill multiple layers of absorption materials in the desulfurization tower to absorb and desulfurize hydrogen sulfide. Wet desulfurization generally uses liquid absorbent to absorb hydrogen sulfide in biogas in the desulfurization tower. The absorption liquid is generally sprayed from the top of the tower downward, and the biogas rises from the bottom of the tower, and hydrogen sulfide enters the absorption liquid. Regardless of the desulfurization method, the desulfurization effect should be checked regularly, and the filler should be replaced or the concentration of the absorption liquid should be adjusted in time according to the situation.
Gas storage cabinet: The most commonly used gas storage cabinet is a low-pressure covered gas storage cabinet. For large-scale treatment plants, due to the large production volume, all gas storage cabinets are required to have a large capacity or a large number. In view of this situation, some large treatment plants also use medium-pressure spherical tanks to store biogas in order to reduce the capacity of storage equipment.
Flame arrester: Biogas is mixed with a certain proportion of air, and it will burn in time when it encounters an open flame or reaches the ignition temperature. If there is negative pressure in the biogas system, the negative pressure prevention valve will open, allowing part of the air to enter the biogas system. After these mixed gases composed of air and biogas reach the combustion points such as boilers, engines and burners through the distribution system, they will flash back in the biogas pipe. Backfire will increase the temperature and cause gas expansion, thus damaging pipelines and equipment. In severe cases, it will cause biogas leakage and explosion. Therefore, fire-blocking devices should be installed on boilers, engines and pipelines before combustion in the biogas system.
Gas-using equipment: In addition to being used in biogas circulation and mixing, biogas is mainly used as power fuel, such as for burning boilers or driving gas turbines, etc. In some cases, it is used to manufacture chemical raw materials.
