The reason for the dehydration of biogas is that if water accumulates in the gas conduit, it will dissolve hydrogen sulfide and corrode the pipeline. In addition, when the biogas is stored under pressure, the water in the biogas will condense and freeze the gas storage tank. The removal method is as follows:
The content of saturated water vapor in biogas is different under different temperatures. At 35 ℃, the content of water is close to 5%. The water in biogas must be removed before it is put into the natural gas network. For different purification processes, there are different methods in each stage. The condensate needs to be removed before compression, so that there is no need to dry the gas in the process of washing and removing carbon dioxide and hydrogen sulfide. Before the absorption and purification process, it is often necessary to dry the gas, mainly including condensation method and adsorption method. The most commonly used method is condensation method, which is to remove the condensate water by cooling the gas through the cooler in the heat exchange system. This method is usually 0.5 ℃ - 1 ℃ lower than the dew point due to the surface cooling of the heat exchanger. In order to obtain a lower dew point, the gas must be compressed before condensation, and then released to the required pressure.
Adsorption drying refers to the absorption of water in the gas through silica gel, alumina or magnesium oxide, and the gas to be dried is dried through the desiccant in the adsorption bed. Usually two sets of devices are used. When one works, the other can be regenerated. There are two ways to regenerate desiccant. One is that a part of high-pressure dry gas (3% - 8%) can be used to regenerate the desiccant, which can be returned to the compressor population. The other is to use air and vacuum pump to regenerate desiccant under normal pressure. This method will mix air into biogas, generally not.
Water can be absorbed by glycol, triethylene glycol and water absorbing salt. There are many kinds of salts with different water absorption properties. Usually, small salt particles are filled in the drying adsorption tower. When the dry biogas is introduced from the bottom, the saturated salt solution dissolved by water accumulates at the bottom of the adsorption tower, and is discharged through the valve, and then replaced with new salt particles. Generally, salt does not need to be regenerated. In general industrial dryer, different salt dew point is usually between 10 ℃ and 15 ℃.