沼氣提純有很關(guān)鍵的一步，就是沼氣。沼氣有多種實(shí)現(xiàn)方法，主要包括升溫、冷凝、吸附、吸收、膜法等。
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，升溫是通過(guò)加熱氣體使其相對(duì)濕度降低，通過(guò)控制溫度來(lái)實(shí)現(xiàn)相對(duì)濕度的控制。對(duì)沼氣加熱升溫，沼氣的相對(duì)濕度隨著溫度的升高而降低，盡管這種方法并不能真正減少沼氣中的水蒸氣的含量，即沼氣中含濕量是不變的，但可以有效避免液態(tài)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.
冷凝是利用制冷系統(tǒng)提供的冷媒把沼氣溫度降低到其露點(diǎn)溫度以下，使沼氣中的水蒸氣凝結(jié)出來(lái)，而凝結(jié)熱被制冷設(shè)備帶走，達(dá)到減少沼氣含濕量的目的。冷卻是將濕沼氣流經(jīng)低溫表面使沼氣冷卻到露點(diǎn)溫度以下，從而將濕沼氣中水蒸氣去除的方法。由于用冷凍機(jī)進(jìn)行冷卻，所以又稱(chēng)冷凍。它是目前比較常用的方法。由于常常需要再加熱，冷卻的能耗較高。
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.
吸附是指利用吸附劑（如硅膠、鋁膠、分子篩等）對(duì)水分子的極性吸附作用而將沼氣中的水分降低到一定的含量。吸附是一個(gè)復(fù)雜的物質(zhì)轉(zhuǎn)移過(guò)程，分為化學(xué)吸附和物理吸附。物理吸附是指被吸附的物質(zhì)與吸附劑之間的吸附力是由范德華力產(chǎn)生的，將被吸附物質(zhì)的分子吸附到吸附劑表面或分子晶格之間，吸附過(guò)程中不發(fā)生任何化學(xué)反應(yīng)，吸附具有可逆性；化學(xué)吸附是指被吸附的物質(zhì)與吸附劑之間的吸附力是由化學(xué)鍵力產(chǎn)生的，吸附后吸附劑的化學(xué)性質(zhì)發(fā)生了變化，吸附具有不可逆性。在吸附中吸附劑以物理吸附為主，適用于相對(duì)濕度較低的沼氣，可使露點(diǎn)達(dá)到-40℃以下，因此該方法多用于干燥處理中。
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.
吸附在實(shí)際應(yīng)用中，多采用固定床方式，即濕沼氣流經(jīng)由固體吸附劑堆積而成的吸附床時(shí)，利用毛細(xì)管作用將水蒸氣吸附在固體吸濕劑上，沼氣中所含水量降低，從而達(dá)到的目的。選擇適當(dāng)吸附劑和操作流程，可將沼氣的濕度降得很低。吸附劑經(jīng)再生后循環(huán)使用。這種方法用于濕度較小而要求較高的場(chǎng)合。固體吸附床不受露點(diǎn)溫度的影響而達(dá)到很低的濕度，在低溫低濕工況下效率顯著高于其它方式，并且結(jié)構(gòu)簡(jiǎn)單，維護(hù)方便，運(yùn)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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