我們知道了沼氣是非常好的能源物質，可以用來燒鍋爐、發電、提純生物天然氣或者重整制氫。但是沼氣中含有很多雜質，需要先經過一定程度的凈化才能進行利用。凈化程度一般需要根據沼氣用途確定，通常需要去除的主要是水、硫化氫和粉塵顆粒。另外如果沼氣用于提純天然氣或者重整制氫，氧氣、氮氣及揮發性有機物等雜質也是需要去除的。? ?注：本表部分信息引自鄧良偉等《沼氣工程》；

　　We know that biogas is a very good energy material that can be used to burn boilers, generate electricity, purify natural gas, or produce hydrogen through reforming. However, biogas contains many impurities and requires a certain degree of purification before it can be utilized. The degree of purification generally needs to be determined based on the use of biogas, and the main substances that need to be removed are water, hydrogen sulfide, and dust particles. In addition, if biogas is used for purifying natural gas or reforming hydrogen, impurities such as oxygen, nitrogen, and volatile organic compounds also need to be removed.? Note: Some information in this table is quoted from Deng Liangwei et al.'s "Biogas Engineering";

　　沼氣凈化環節，雖然在整個沼氣工程中占比不大，但又是一個不可忽略的環節，也需要專業的廠家去做。這部分項目額度不高，工作瑣碎，愿意去做精做好的廠家其實并不多。但是沼氣工程就是這樣，由一個又一個的環節串聯而成，只有每個環節都做好了，整個項目才可能好。

　　The biogas purification process, although accounting for a small proportion in the entire biogas project, is still an essential step that cannot be ignored and requires professional manufacturers to do it. This part of the project does not have a high budget, and the work is tedious. There are actually not many manufacturers willing to do it well. But biogas engineering is like this, consisting of one link after another, and only when each link is done well, can the entire project be successful.

　　本篇，我主要總結了沼氣凈化環節中最重要的三塊內容：硫化氫的去除、水蒸氣的去除和粉塵顆粒的去除。

　　In this article, I mainly summarized the three most important aspects of biogas purification: removal of hydrogen sulfide, removal of water vapor, and removal of dust particles.

　　1沼氣中硫化氫去除

　　1. Removal of hydrogen sulfide from biogas

　　沼氣中最討厭的一個雜質就是硫化氫，尤其蛋白質含量比較高的物料產出的沼氣，硫化氫含量也會比較高。硫化氫具有較強的腐蝕性和毒性，應最先被去除。硫化氫去除一般分為：生物脫硫、化學脫硫、物理脫硫。化學脫硫又分為濕法脫硫和干法脫硫。物理脫硫法一般是采用活性炭吸附，這種方法成本較高，一般較少采用。目前采用較多的是生物脫硫、濕法脫硫和干法脫硫。

　　The most disliked impurity in biogas is hydrogen sulfide, especially in biogas produced from materials with high protein content, where the hydrogen sulfide content is also relatively high. Hydrogen sulfide has strong corrosiveness and toxicity, and should be removed first. Hydrogen sulfide removal is generally divided into biological desulfurization, chemical desulfurization, and physical desulfurization. Chemical desulfurization is divided into wet desulfurization and dry desulfurization. The physical desulfurization method generally uses activated carbon adsorption, which is costly and rarely used. At present, biological desulfurization, wet desulfurization, and dry desulfurization are commonly used.

　　（1）生物脫硫生物脫硫是利用特定微生物將沼氣中的H2S轉化為單質硫或硫酸鹽的脫硫方式。基本原理是：H2S被微生物吸收轉移至微生物體內，作為營養物質被特定的微生物分解、轉化、利用，微生物得以生長繁殖。常見的生物脫硫有原位生物脫硫（即厭氧罐內生物脫硫），滴濾工藝（也稱酸式/一體式生物脫硫），洗滌再生工藝（也稱堿式生物脫硫/分離式生物脫硫）。

　　(1) Biological desulfurization is a desulfurization method that uses specific microorganisms to convert H2S in biogas into elemental sulfur or sulfate. The basic principle is that H2S is absorbed and transferred by microorganisms into their bodies, and as a nutrient, it is decomposed, transformed, and utilized by specific microorganisms, allowing them to grow and reproduce. Common biological desulfurization methods include in-situ biological desulfurization (i.e. anaerobic tank biological desulfurization), drip filtration process (also known as acid/integrated biological desulfurization), and washing regeneration process (also known as alkaline biological desulfurization/separated biological desulfurization).

　　（2）濕法脫硫濕法脫硫是利用特定的溶劑與氣體接觸而吸收其中的H2S，溶劑失效后通過再生重新使用。濕法脫硫按溶液的吸收與再生性質又可分為氧化法、吸收法。氧化法是借助溶液中載氧體的催化作用，將吸收的硫化氫轉化為硫磺，使溶液獲得再生。氧化法主要有氨水法、砷堿法、蒽醌二磺酸鈉法等。吸收法以弱堿性溶液為吸收劑，與硫化氫進行化學反應形成化合物，當富液溫度升高、壓力降低時，該化合物就分解，放出硫化氫。這類方法有烷基醇胺法、堿性溶液法等。其中最常用的是碳酸鈉吸收法。由于碳酸鈉溶液在吸收酸性氣體時，pH 不會很快發生變化，保證了系統的操作穩定性。此外，碳酸鈉溶液吸收硫化氫比吸收二氧化碳快，可以部分地選擇吸收硫化氫。該法通常用于脫除氣體中大量二氧化碳，也可以用來脫除含二氧化碳和硫化氫的天然氣及沼氣中的酸性氣體。

　　(2) Wet flue gas desulfurization is the process of using a specific solvent to absorb H2S from a gas, which is then regenerated and reused after the solvent has failed. Wet desulfurization can be divided into oxidation method and absorption method according to the absorption and regeneration properties of the solution. The oxidation method utilizes the catalytic effect of oxygen carriers in the solution to convert absorbed hydrogen sulfide into sulfur, thereby regenerating the solution. The oxidation methods mainly include ammonia method, arsenic alkali method, sodium anthraquinone disulfonate method, etc. The absorption method uses a weakly alkaline solution as an absorbent and reacts chemically with hydrogen sulfide to form a compound. When the temperature of the rich solution increases and the pressure decreases, the compound decomposes and releases hydrogen sulfide. This type of method includes alkyl alcohol amine method, alkaline solution method, etc. The most commonly used method is the sodium carbonate absorption method. Due to the fact that the pH of sodium carbonate solution does not change quickly when absorbing acidic gases, the operational stability of the system is ensured. In addition, sodium carbonate solution absorbs hydrogen sulfide faster than carbon dioxide, and can partially selectively absorb hydrogen sulfide. This method is usually used to remove large amounts of carbon dioxide from gases, and can also be used to remove acidic gases from natural gas and biogas containing carbon dioxide and hydrogen sulfide.

　　（3）干法脫硫：干法脫硫按原理可分為化學吸附法和化學吸收法。化學吸附法即采用脫硫劑吸附氣體中的硫化物從而達到脫硫的目的，活性炭和分子篩吸附即屬此類。化學吸收法即采用脫硫劑與氣體中的硫化氫反應將硫化物脫除的過程，其脫硫劑有氧化鐵、氧化鋅、氧化錳等。近代工業上也常用干法脫硫作為脫除有機硫和精細脫硫的手段。其中氧化鐵資源豐富，價廉易得，是目前使用最多的沼氣干法脫硫方法。三種脫硫工藝總結如下圖：

　　(3) Dry desulfurization: Dry desulfurization can be divided into chemical adsorption method and chemical absorption method according to the principle. Chemical adsorption method uses desulfurizers to adsorb sulfides in gases to achieve desulfurization, and activated carbon and molecular sieve adsorption belong to this category. Chemical absorption method is the process of removing sulfides by reacting desulfurizers with hydrogen sulfide in the gas. The desulfurizers include iron oxide, zinc oxide, manganese oxide, etc. Dry desulfurization is also commonly used in modern industry as a means of removing organic sulfur and fine desulfurization. Among them, iron oxide resources are abundant, inexpensive and easy to obtain, and it is currently the most commonly used dry desulfurization method for biogas. The summary of three desulfurization processes is shown in the following figure:

　　2沼氣中水蒸氣去除

　　2. Removal of water vapor from biogas

　　前面說到，沼氣中還含有水蒸氣，一般發酵罐中沼氣相對濕度達到 100%，這也意味著沼氣中水蒸氣是飽和狀態。水蒸氣與H2S、NH3、CO2反應，會引起后續設備嚴重磨損和損壞，因此沼氣必須進行干燥處理，去除過多的水分。一般可使用的干燥沼氣的方法有:冷凝脫水、溶劑吸收脫水、干燥劑吸附脫水。三種脫水工藝總結如下。

　　As mentioned earlier, biogas also contains water vapor. Generally, the relative humidity of biogas in a fermentation tank reaches 100%, which also means that the water vapor in biogas is saturated. The reaction between water vapor and H2S, NH3, CO2 can cause severe wear and damage to subsequent equipment, so biogas must be dried to remove excessive moisture. The commonly used methods for drying biogas include condensation dehydration, solvent absorption dehydration, and desiccant adsorption dehydration. The three dehydration processes are summarized as follows.

　　（1）冷凝脫水：

　　(1) Condensation dehydration:

　　①原理：冷凝法的原理是將沼氣冷卻到水蒸氣露點溫度以下，再進行水的分離。

　　① Principle: The principle of condensation method is to cool biogas to below the dew point temperature of water vapor, and then separate the water.

　　②常用形式：氣水分離器、沼氣凝水器、冷干機/冷水機組+換熱器

　　② Common forms: gas water separator, biogas condenser, refrigerated dryer/chiller+heat exchanger

　　③適用性：冷卻脫水精度取決于冷卻溫度和分離手段，冷卻溫度越低，脫水效果越好，但能耗也越高，因此，適合用在脫水精度要求不高的場合，特別適用于“大氣量，大分離”的工況，在脫水精度較高的工況可作為初步脫水

　　③ Applicability: The accuracy of cooling and dehydration depends on the cooling temperature and separation method. The lower the cooling temperature, the better the dehydration effect, but the higher the energy consumption. Therefore, it is suitable for use in situations where dehydration accuracy is not high, especially for "atmospheric volume, large separation" conditions. In conditions with high dehydration accuracy, it can be used as a preliminary dehydration

　　④優點：流程簡單、操作簡便、處理能力大、運行穩定、投資及運行費用低。除水蒸氣外，其他雜質(如水溶氣體、氣落膠)也會在冷凝中被去除。

　　④ Advantages: Simple process, easy operation, large processing capacity, stable operation, low investment and operating costs. In addition to water vapor, other impurities such as water-soluble gases and gas droplets will also be removed during condensation.

　　⑤缺點：由于降溫程度有限，該方法無法做到100%脫水(即脫水精度低)，在脫水精度要求較高的工況只能作為氣體深度脫水干燥的初步處理手段。

　　⑤ Disadvantages: Due to limited cooling, this method cannot achieve 100% dehydration (i.e. low dehydration accuracy), and can only be used as a preliminary treatment method for gas deep dehydration and drying in working conditions with high dehydration accuracy requirements.

　　（2）溶劑吸收脫水：

　　(2) Solvent absorption dehydration:

　　①原理：溶劑吸收法是利用吸水性能高的液體作為干燥劑，與通過吸收塔的氣體逆流接觸，從而進行氣液傳質以脫除氣體中的水分的方法。常用的吸收劑有乙二醇、二甘醇、三甘醇、可吸濕鹽類等。

　　① Principle: Solvent absorption method is a method of removing water from gas by using a liquid with high water absorption performance as a desiccant and contacting it in reverse flow with gas passing through an absorption tower, thereby performing gas-liquid mass transfer. Common absorbents include ethylene glycol, diethylene glycol, triethylene glycol, and hygroscopic salts.

　　②適用性：適用于“大氣量、小吸收”的工況，在大氣量脫水干爆的工業生產中可以按先冷凝脫水，再溶劑脫水的工藝進行搭配使用

　　② Applicability: Suitable for working conditions of "atmospheric volume, small absorption", it can be used in combination with the process of first condensing dehydration and then solvent dehydration in industrial production of large volume dehydration and dry explosion

　　③優點：流程簡單、處理能力大、氣體壓降較小、運行穩定、運行費用較低;溶劑吸收的脫水精度較冷凝法的高。

　　③ Advantages: simple process, large processing capacity, low gas pressure drop, stable operation, and low operating costs; The dehydration accuracy of solvent absorption is higher than that of condensation method.

　　④缺點：濕氣的流量、溫度、壓力和溶劑的濃度、溫度、循環量以及干燥塔的設備結構都會對溶劑吸收法脫水效果造成一定的影響，運行成本相對冷凝法高。

　　④ Disadvantages: The flow rate, temperature, pressure of moisture, concentration, temperature, circulation rate of solvent, and equipment structure of the drying tower will all have a certain impact on the dehydration effect of solvent absorption method, and the operating cost is relatively high compared to condensation method.

　　（3）干燥劑吸附脫水

　　(3) Desiccant adsorption dehydration

　　①原理：干燥劑吸附脫水是利用多孔性的固體材料吸附沼氣中的水蒸氣，如二氧化硅、氧化鉬、氧化鎂、活性炭和沸石等。

　　① Principle: Desiccant adsorption dehydration is the use of porous solid materials to adsorb water vapor from biogas, such as silica, molybdenum oxide, magnesium oxide, activated carbon, and zeolite.

　　②適用性：適用于中小氣量脫水，或作為另外兩種脫水方式的補充

　　② Applicability: Suitable for dehydration of small and medium gas volumes, or as a supplement to the other two dehydration methods

　　③優點：脫水精度高，對氣體溫度、壓力、流量變化不敏感，操作彈性大，占地面積小，操作易于程序化控制

　　③ Advantages: High dehydration accuracy, insensitivity to changes in gas temperature, pressure, and flow rate, high operational flexibility, small footprint, easy to program control operation

　　④缺點：工藝復雜、氣體壓降較大、吸附劑需定期更換、運行能耗較高;對于處理氣量大的氣體，設備投資較大，運行費用也比較高。

　　④ Disadvantages: complex process, high gas pressure drop, adsorbent needs to be replaced regularly, high operating energy consumption; For gases with large processing volumes, equipment investment is relatively high and operating costs are also relatively high.

　　3沼氣中粉塵去除

　　3. Dust removal from biogas

　　水洗除塵：

　　Water washing and dust removal:

　　①原理：通過洗滌方式，將沼氣中粉塵去除

　　① Principle: Remove dust from biogas through washing method

　　②適用范圍：沼氣脫硫前，去除大顆粒雜質

　　② Scope of application: Removing large particle impurities before biogas desulfurization

　　③優點：不需要更換濾芯，運行成本低，可自動化控制

　　③ Advantages: No need to replace filter element, low operating cost, and can be automatically controlled

　　④缺點：去除精度低;無法用于干燥后除塵

　　④ Disadvantages: Low removal accuracy; Cannot be used for dust removal after drying

　　過濾除塵：

　　Filtering and dust removal:

　　①原理沼氣通過過濾器，將沼氣中的粉塵去除

　　① Principle: Biogas is filtered to remove dust from the biogas

　　②適用范圍：脫硫后，沼氣利用前，以及對進氣有較高要求的情況

　　② Scope of application: After desulfurization, before biogas utilization, and situations with high requirements for intake air

　　③優點：設備簡單，去除效率高，去除精度高，可用于各階段除塵

　　③ Advantages: Simple equipment, high removal efficiency, high removal accuracy, can be used for dust removal in various stages

　　④缺點：過濾器濾芯需要經常更換，成本稍高

　　④ Disadvantage: The filter cartridge needs to be replaced frequently, resulting in slightly higher costs

　　前文我們說到，一部分固體顆粒會被水蒸氣或者沼氣帶出，我們稱之為粉塵，這些粉塵如不去除，會在壓縮機、氣體儲罐、發電機中沉積，引起管道堵塞、增大磨損、降低設備壽命等。沼氣中的粉塵去主要有兩種方式：洗滌除塵和過濾除塵。

　　As mentioned earlier, some solid particles are carried out by water vapor or biogas, which we call dust. If these dust particles are not removed, they will deposit in compressors, gas storage tanks, and generators, causing pipeline blockage, increased wear, and reduced equipment life. There are two main ways to remove dust from biogas: washing and filtering.

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