The purification of biogas generally includes dehydration, desulfurization, and decarbonization of biogas. The combined action of moisture and hydrogen sulfide in biogas can accelerate the corrosion of pipelines, valves, and flow meters. Hydrogen sulfide also causes pollution to the atmosphere, so it needs to be removed.
How to dehydrate biogas: The biogas from the fermentation device contains saturated water vapor, which can be removed using three methods.
(1)冷分离法。是利用压力能变化引起温度变化，使水蒸气从气相中冷凝下来的方法。常用 的有两种流程：A．节流膨胀冷脱水法。一般用于高压燃气，经过节流膨胀或低温分离，使 部分水冷凝下来。B．加压后冷却法。如净化气在08MPa压力下的冷却脱水。
(1) Cold separation method. It is a method of using pressure energy changes to cause temperature changes, causing water vapor to condense from the gas phase. There are two commonly used processes: A. Throttling expansion cold dehydration method. Generally used for high-pressure gas, it undergoes throttling expansion or low-temperature separation to condense some water. B. Cooling method after pressurization. For example, cooling and dehydration of purified gas at a pressure of 0.8MPa.
(2) Solvent absorption method. Among these dehydration solvents are calcium chloride, lithium chloride, and glycols.
(3) Solid state physical water absorption method. Adsorption is generated under the action of solid surface forces, and can be divided into chemical adsorption (which cannot be regenerated after dehydration) and physical adsorption (which can be regenerated after dehydration) based on the properties of surface forces.
沼气的脱硫：沼气中的有害物质主要是硫化氢，它危害人体健康，对管道阀门及应用设备有较强的腐蚀作 用。目前，国内大部分用户均未安装脱硫器，已造成严重后果。为减轻硫化氢对灶具及配套 用具的腐蚀损害，延长设备使用寿命，保证人身健康，必须安装脱硫器。脱硫原理：在常温下含有H2S的沼气通过脱硫剂床层，沼气中H2S与活性物质(如氧化铁)接触，生成 硫化铁和亚硫化铁，然后含有硫化物的脱硫剂与空气中的氧接触，当有水存在时，铁的硫化 物又转化为氧化铁和单体硫。
Desulfurization of biogas: The harmful substance in biogas is mainly hydrogen sulfide, which is harmful to human health and has a strong corrosive effect on pipeline valves and application equipment. At present, most users in China have not installed desulfurizers, which has caused serious consequences. To reduce the corrosion damage of hydrogen sulfide to stoves and supporting appliances, extend the service life of equipment, and ensure personal health, it is necessary to install a desulfurization device. Desulfurization principle: At room temperature, biogas containing H2 2S passes through the desulfurization agent bed. H2 2S in the biogas comes into contact with active substances (such as iron oxide) to generate iron sulfide and ferrous sulfides. Then, the desulfurization agent containing sulfides comes into contact with oxygen in the air. When water is present, the sulfide of iron is converted into iron oxide and monomer sulfur.
这种脱硫和再生过程可循环进行多次，直至氧化铁脱硫剂表面 大部分被硫或其他杂质覆盖而失去活性为止。脱硫方法：脱硫的方法有湿法脱硫和干法脱硫两种。干法脱硫具有工艺简单，成熟可靠、造价低等优点 ，并能达到较好的交货程度。目前家用沼气脱硫基本上采用这种方法。干法脱硫剂有活性炭、氧化锌、氧化锰及氧化铁等，从运转时间、使用温度、公害、价格等 综合考虑，目前采用多的脱硫剂是氧化铁。
This desulfurization and regeneration process can be repeated multiple times until the surface of the iron oxide desulfurizer is mostly covered by sulfur or other impurities and loses its activity. Desulfurization methods: There are two types of desulfurization methods: wet desulfurization and dry desulfurization. Dry desulfurization has the advantages of simple process, mature and reliable, low cost, and can achieve good delivery level. At present, this method is mainly used for household biogas desulfurization. Dry desulfurization agents include activated carbon, zinc oxide, manganese oxide, and iron oxide. Considering the operating time, operating temperature, environmental hazards, and price, the most commonly used desulfurization agent is iron oxide.