Biogas dehumidification is a key step in biogas purification. There are many ways to dehumidify biogas, including heating dehumidification, condensation dehumidification, adsorption dehumidification, absorption dehumidification and membrane dehumidification.

在上述方法中，升温除湿是通过加热气体使其相对湿度降低，通过控制温度来实现相对湿度的控制。对沼气加热升温，沼气的相对湿度随着温度的升高而降低，尽管这种方法并不能真正减少沼气中的水蒸气的含量，即沼气中含湿量是不变的，但可以有效避免液态水的形成。

In the above methods, heating and dehumidification is to reduce the relative humidity by heating the gas, and control the temperature to achieve the control of the relative humidity. For the heating of biogas, the relative humidity of biogas decreases with the increase of temperature. Although this method can not really reduce the content of water vapor in biogas, that is, the moisture content of biogas is unchanged, it can effectively avoid the formation of liquid water.

冷凝除湿是利用制冷系统提供的冷媒把沼气温度降低到其露点温度以下，使沼气中的水蒸气凝结出来，而凝结热被制冷设备带走，达到减少沼气含湿量的目的。冷却除湿是将湿沼气流经低温表面使沼气冷却到露点温度以下，从而将湿沼气中水蒸气去除的方法。由于用冷冻机进行冷却，所以又称冷冻除湿。它是目前比较常用的除湿方法。由于常常需要再加热，冷却除湿的能耗较高。

Condensation dehumidification is to use refrigerant provided by refrigeration system to reduce the temperature of biogas below its dew point, so that the steam in biogas condenses out, and the condensation heat is taken away by refrigeration equipment, so as to reduce the moisture content of biogas. Cooling dehumidification is a method of removing water vapor from wet methane by cooling it below dew point temperature through low temperature surface. Because it is cooled by a refrigerator, it is also called freezing dehumidification. It is a commonly used dehumidification method at present. The energy consumption of cooling and dehumidification is high because of the need for reheating.

吸附除湿是指利用吸附剂（如硅胶、铝胶、分子筛等）对水分子的极性吸附作用而将沼气中的水分降低到一定的含量。吸附是一个复杂的物质转移过程，分为化学吸附和物理吸附。物理吸附是指被吸附的物质与吸附剂之间的吸附力是由范德华力产生的，将被吸附物质的分子吸附到吸附剂表面或分子晶格之间，吸附过程中不发生任何化学反应，吸附具有可逆性；化学吸附是指被吸附的物质与吸附剂之间的吸附力是由化学键力产生的，吸附后吸附剂的化学性质发生了变化，吸附具有不可逆性。在吸附除湿中吸附剂以物理吸附为主，适用于相对湿度较低的沼气除湿，可使露点达到-40℃以下，因此该方法多用于除湿干燥处理中。

Adsorption dehumidification refers to the use of adsorbents (such as silica gel, aluminium gel, molecular sieve, etc.) to adsorb water molecules POLARLY and reduce the moisture content of biogas to a certain level. Adsorption is a complex material transfer process, which is divided into chemical adsorption and physical adsorption. Physical adsorption means that the adsorption force between adsorbed substances and adsorbents is generated by van der Waals force, and the molecules of adsorbed substances are adsorbed to the surface of adsorbents or between molecular lattices. No chemical reaction occurs during the adsorption process, and the adsorption is reversible. Chemical adsorption means that the adsorption force between adsorbed substances and adsorbents is generated by chemical bonding force, and then adsorbed. The chemical properties of adsorbents have changed and the adsorption is irreversible. Physical adsorption is the main adsorbent in adsorption dehumidification, which is suitable for biogas dehumidification with low relative humidity, and can make dew point below - 40 C. Therefore, this method is mostly used in dehumidification and drying treatment.

吸附除湿在实际应用中，多采用固定床除湿方式，即湿沼气流经由固体吸附剂堆积而成的吸附床时，利用毛细管作用将水蒸气吸附在固体吸湿剂上，沼气中所含水量降低，从而达到除湿的目的。选择适当吸附剂和操作流程，可将沼气的湿度降得很低。吸附剂经再生后循环使用。这种方法用于湿度较小而除湿要求较高的场合。固体吸附床除湿不受露点温度的影响而达到很低的湿度，在低温低湿工况下除湿效率显着高于其它除湿方式，并且结构简单，维护方便，运行可靠。

In practical application, fixed bed dehumidification is often used, that is, when wet methane flow is accumulated by solid adsorbent, water vapor is adsorbed on solid adsorbent by capillary action, water content in methane is reduced, so as to achieve the purpose of dehumidification. The humidity of biogas can be reduced very low by choosing proper adsorbent and operation process. The adsorbent is recycled after regeneration. This method is used in the case of low humidity and high dehumidification requirement. Solid adsorbent dehumidification is not affected by dew point temperature and achieves very low humidity. Under low temperature and humidity conditions, the dehumidification efficiency is significantly higher than other dehumidification methods, and it has simple structure, convenient maintenance and reliable operation.

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