隨著我國對可再生能源的開發(fā)和利用的不斷深入發(fā)展, 利用畜禽糞便厭氧發(fā)酵產(chǎn)沼氣是一種非常有前景的能源利用途徑，但所產(chǎn)生的沼氣中都含有H2S氣體，由于它是一種腐蝕性很強(qiáng)的化合物，所以沼氣脫硫是沼氣利用的關(guān)鍵環(huán)節(jié)。本文以某工程調(diào)試與運(yùn)行實(shí)例分析了大型沼氣工程中的生物脫硫技術(shù)，以為同類型工程提供參考。

With the continuous development and utilization of renewable energy in China, anaerobic fermentation of livestock and poultry manure to produce biogas is a very promising energy utilization pathway. However, the biogas produced contains H2S gas, which is a highly corrosive compound. Therefore, biogas desulfurization is a key link in biogas utilization. This article analyzes the biological desulfurization technology in large-scale biogas projects through a case study of commissioning and operation, providing reference for similar projects.

目前沼氣脫硫的方法有兩大類，即物理化學(xué)法和生物法。物理化學(xué)法包括干法脫硫和濕法脫硫，已被廣泛地應(yīng)用且積累了豐富的經(jīng)驗(yàn)，但該方法存在運(yùn)行費(fèi)用高、投資大、產(chǎn)生二次污染等缺點(diǎn)；而生物法以不需催化劑和氧化劑、不需處理化學(xué)污泥、少污染、低能耗、率、可回收單質(zhì)硫等優(yōu)點(diǎn)，引起了人們的廣泛關(guān)注。為此，筆者以某公司熱電聯(lián)產(chǎn)沼氣工程為例，介紹了該沼氣工程調(diào)試與運(yùn)行時(shí)生物脫硫技術(shù)的具體運(yùn)用。

At present, there are two main methods for desulfurization of biogas, namely physical and chemical methods and biological methods. Physical and chemical methods, including dry desulfurization and wet desulfurization, have been widely applied and accumulated rich experience. However, this method has disadvantages such as high operating costs, large investment, and secondary pollution; Biological methods have attracted widespread attention due to their advantages such as no need for catalysts and oxidants, no need to treat chemical sludge, low pollution, low energy consumption, high efficiency, and recyclability of elemental sulfur. Therefore, the author takes a company's cogeneration biogas project as an example to introduce the specific application of biological desulfurization technology during the commissioning and operation of the biogas project.

生物脫硫的裝置主要由生物脫硫塔和曝氣水箱構(gòu)成，從厭氧罐內(nèi)導(dǎo)出的沼氣由脫硫塔底部進(jìn)入，脫硫循環(huán)水由泵打入脫硫塔頂，兩者在塔內(nèi)逆向接觸反應(yīng)，且塔內(nèi)充有填料以供脫硫菌附著生長，同時(shí)也利于氣水均勻分布以充分接觸。生物脫硫塔及曝氣水箱都采用耐酸玻璃鋼制作，循環(huán)泵也使用耐酸性泵。脫硫塔的負(fù)荷為8m3 (沼氣) /（m3·h）左右。

The device for biological desulfurization mainly consists of a biological desulfurization tower and an aeration water tank. The biogas exported from the anaerobic tank enters from the bottom of the desulfurization tower, and the desulfurization circulating water is pumped into the top of the desulfurization tower. The two react in reverse contact inside the tower, and the tower is filled with packing material for the attachment and growth of desulfurization bacteria. At the same time, it is also conducive to the uniform distribution of gas and water for sufficient contact. The biological desulfurization tower and aeration water tank are made of acid resistant fiberglass, and the circulation pump also uses acid resistant pumps. The load of the desulfurization tower is about 8m3 (biogas)/(m3 · h).

本工程采用生物脫硫的方法對沼氣進(jìn)行脫硫處理，主要利用無色硫細(xì)菌在適宜的溫度、濕度和微氧條件下的代謝作用將H2S氧化成單質(zhì)硫或亞硫酸。生物脫硫分為3個(gè)階段 :

This project adopts the method of biological desulfurization to desulfurize biogas, mainly utilizing the metabolic action of colorless sulfur bacteria under suitable temperature, humidity, and micro oxygen conditions to oxidize H2S into elemental sulfur or sulfurous acid. Biological desulfurization is divided into three stages:

1.H2S 氣體的溶解過程，即由氣相轉(zhuǎn)化為液相；

The dissolution process of H2S gas, that is, the transformation from gas phase to liquid phase;

2.溶解后的H2S被微生物吸收，轉(zhuǎn)移微生物的體內(nèi)；

2. The dissolved H2S is absorbed by microorganisms and transferred into their bodies;

3.進(jìn)入微生物細(xì)胞內(nèi)的H2S作為營養(yǎng)物被微生物分解、轉(zhuǎn)化和利用，從而達(dá)到去除H2S的目的。

3. H2S entering microbial cells is decomposed, transformed, and utilized by microorganisms as nutrients, thereby achieving the goal of removing H2S.

雖然生物脫硫具有能耗少、去除率高等特點(diǎn)，但必須給硫細(xì)菌營造一個(gè)適宜的環(huán)境，才能確保其具有較高的生物活性，以達(dá)到的脫硫效果。而在該工程調(diào)試與運(yùn)行中影響生物脫硫效率的主要因素有pH值、DO、溫度、H2S負(fù)荷，因此必須對這些因素進(jìn)行控制。

Although biological desulfurization has the characteristics of low energy consumption and high removal rate, it is necessary to create a suitable environment for sulfur bacteria to ensure their high biological activity and achieve the best desulfurization effect. The main factors that affect the efficiency of biological desulfurization during the commissioning and operation of the project are pH value, DO, temperature, and H2S load, so these factors must be controlled.

1、pH值的控制

1. Control of pH value

硫細(xì)菌種類繁多，且各自具有不同的生理學(xué)、形態(tài)學(xué)和生態(tài)學(xué)特性，對環(huán)境條件的要求也各異。有研究表明，硫細(xì)菌可生存的范圍很廣，在pH值為1.0～9.0、溫度為 4～95℃的條件下都可生長和運(yùn)動，但各自都有適宜的pH值范圍，如硫化葉菌屬的硫細(xì)菌在pH值為2～3下生存才有較好的生物活性，若環(huán)境的pH值不在其適宜的范圍，其活性將會 受到很大的影響，一般大多數(shù)硫細(xì)菌適宜的pH值范圍為6～8。

There are various types of sulfur bacteria, each with different physiological, morphological, and ecological characteristics, and different requirements for environmental conditions. Studies have shown that sulfur bacteria can survive in a wide range, growing and moving under conditions of pH 1.0-9.0 and temperature 4-95 ℃, but each has a suitable pH range. For example, sulfur bacteria belonging to the sulfur leaf fungus genus have good biological activity only when they survive at pH 2-3. If the pH value of the environment is not within their suitable range, their activity will be greatly affected. Generally, the pH range suitable for most sulfur bacteria is 6-8.

本工程試運(yùn)行初期，將脫硫循環(huán)水的pH值維持在2～3之間，達(dá)到了較好的脫硫效果，可能是硫化葉菌屬的硫細(xì)菌起的作用，但隨著產(chǎn)氣量的增加，循環(huán)水中有限的DO濃度難以將pH值維持在較低水平，所以在試運(yùn)行后期將循環(huán)水的pH值維持在5～7之間，在此期間主要通過控制較小的曝氣量(即較低的DO)和更換新鮮循環(huán)水來防止pH值的波動。因?yàn)楫?dāng)pH值發(fā)生較大波動時(shí)，硫細(xì)菌的活性急劇下降甚失去活性，如本工程中當(dāng)pH值由2～3調(diào)整到5～7時(shí)，生物脫硫塔幾乎完全失去了脫硫效果。所以在生物脫硫中，維持穩(wěn)定的pH值是關(guān)重要的，它將直接影響脫硫效果的好壞。

In the early stage of the trial operation of this project, the pH value of the desulfurization circulating water was maintained between 2 and 3, achieving good desulfurization effect, which may be due to the role of sulfur bacteria in the sulfur leaf fungus genus. However, with the increase of gas production, the limited DO concentration in the circulating water makes it difficult to maintain the pH value at a low level. Therefore, in the later stage of the trial operation, the pH value of the circulating water was maintained between 5 and 7. During this period, the main measures to prevent pH fluctuations were to control the aeration rate (i.e., lower DO) and replace fresh circulating water. Because when the pH value fluctuates significantly, the activity of sulfur bacteria decreases sharply or even loses its activity. For example, in this project, when the pH value is adjusted from 2-3 to 5-7, the biological desulfurization tower almost completely loses its desulfurization effect. Therefore, maintaining a stable pH value is crucial in biological desulfurization, as it will directly affect the effectiveness of desulfurization.

2、DO濃度的控制

2. Control of DO concentration

氣相中H2S和O2難以發(fā)生反應(yīng)，生物脫硫反應(yīng)過程主要發(fā)生在液相中，所以脫硫塔內(nèi)循環(huán)噴淋水中的DO（溶解氧）濃度是影響生物脫硫的一個(gè)重要因素。C.J.N.Busiman等在生物脫硫反應(yīng)器中研究了單質(zhì)硫產(chǎn)生的條件，在硫化物濃度為90mg/L、停留時(shí)間為45 min、DO濃度低于1mg/L時(shí)，產(chǎn)生極少的硫酸（<10%）；在DO濃度超過5mg/L 時(shí)，生成的硫酸鹽穩(wěn)定在52%；而在DO濃度為1mg/L時(shí)，單質(zhì)硫產(chǎn)率。所以控制噴淋水中的DO濃度是氣相中H2S能否變?yōu)閱钨|(zhì)硫的關(guān)鍵因素之一。經(jīng)過該工程試運(yùn)行發(fā)現(xiàn)，在不同的H2S負(fù)荷下，循環(huán)液中都存在一個(gè)的DO濃度。

H2S and O2 are difficult to react in the gas phase, and the biological desulfurization reaction mainly occurs in the liquid phase. Therefore, the dissolved oxygen (DO) concentration in the circulating spray water inside the desulfurization tower is an important factor affecting biological desulfurization. C. J.N. Busiman et al. studied the optimal conditions for the production of elemental sulfur in a biological desulfurization reactor. When the sulfide concentration was 90 mg/L, the residence time was 45 min, and the DO concentration was below 1 mg/L, very little sulfuric acid (<10%) was produced; When the DO concentration exceeds 5mg/L, the generated sulfate remains stable at 52%; At a DO concentration of 1mg/L, the yield of elemental sulfur is highest. So controlling the DO concentration in the spray water is one of the key factors determining whether H2S in the gas phase can be converted into elemental sulfur. After the trial operation of the project, it was found that there is an optimal DO concentration in the circulating liquid under different H2S loads.

當(dāng)DO濃度過低時(shí)主要發(fā)生個(gè)反應(yīng)，因S2-轉(zhuǎn)化為S0的過程是一個(gè)產(chǎn)堿的過程，會引起循環(huán)水pH值的上升; 當(dāng)DO濃度過大時(shí)發(fā)生第二個(gè)反應(yīng)，產(chǎn)生的酸過多，循環(huán)液的 pH 值會加速下降。pH值的上升與下降都會對脫硫效果有影響，所以合適的DO濃度是控制反應(yīng)進(jìn)行到哪一步的關(guān)鍵，也是使產(chǎn)物主要為單質(zhì)硫，并使循環(huán)液的pH值穩(wěn) 定維持在5～7，即脫硫效果的關(guān)鍵。由于理論上氧化1分子H2S生成單質(zhì)硫需要1/2分子的O2 ，所以在工程調(diào)試與運(yùn)行中, 需要根據(jù)不同的H2S負(fù)荷對循環(huán)液中的DO 濃度進(jìn)行調(diào)整，以防止DO過少pH值上升、DO過量生成大量酸，造成pH值劇烈變化而影響脫硫效果。而DO控制主要是通過調(diào)整曝氣風(fēng)量加以控制。

When the DO concentration is too low, the first reaction mainly occurs, as the process of S2- conversion to S0 is an alkali production process, which can cause an increase in the pH value of the circulating water; When the concentration of DO is too high, a second reaction occurs, producing too much acid and accelerating the decrease in pH value of the circulating solution. The rise and fall of pH value will have an impact on the desulfurization effect, so the appropriate DO concentration is the key to controlling which step of the reaction is carried out, and it is also the key to making the product mainly elemental sulfur and maintaining the pH value of the circulating liquid stable at 5-7, which is the best desulfurization effect. Due to the theoretical requirement of 1/2 molecule of O2 for the oxidation of 1 molecule of H2S to produce elemental sulfur, it is necessary to adjust the DO concentration in the circulating liquid according to different H2S loads during engineering debugging and operation, in order to prevent the pH value from rising due to insufficient DO and the generation of a large amount of acid due to excessive DO, which may cause a drastic change in pH value and affect the desulfurization effect. And DO control is mainly controlled by adjusting the aeration air volume.

3、H2S負(fù)荷的控制

3. Control of H2S load

H2S負(fù)荷對脫硫產(chǎn)物也有較大影響。當(dāng)脫硫塔在低負(fù)荷的條件下運(yùn)行時(shí)，H2S容易被過氧化，生成大量的酸使循環(huán)水pH值急劇下降；當(dāng)反應(yīng)器在高負(fù)荷的條件下運(yùn)行時(shí)，脫硫產(chǎn)物主要為單質(zhì)硫，循環(huán)液pH值穩(wěn)定甚還會上升。生物脫硫塔在啟動時(shí)需向循環(huán)水中加入約1%的厭氧罐發(fā)酵液，以提供生物脫硫所需的菌種；啟動初期菌種有將近30d適應(yīng)過程，期間脫硫效果會出現(xiàn)較大的波動；但調(diào)試運(yùn)行穩(wěn)定后，經(jīng)過脫硫后的沼氣中 H2S濃度可維持在200×10-6以下，去除率將達(dá)到90%以上。

The H2S load also has a significant impact on desulfurization products. When the desulfurization tower operates under low load conditions, H2S is prone to peroxidation, generating a large amount of acid and causing a sharp drop in the pH value of the circulating water; When the reactor operates under high load conditions, the main desulfurization product is elemental sulfur, and the pH value of the circulating liquid remains stable or even increases. When starting the biological desulfurization tower, about 1% of anaerobic tank fermentation broth needs to be added to the circulating water to provide the required bacterial strains for biological desulfurization; During the initial start-up phase, the bacterial strain undergoes an adaptation process of nearly 30 days, during which there may be significant fluctuations in desulfurization efficiency; But after stable debugging and operation, the H2S concentration in the desulfurized biogas can be maintained below 200 × 10-6, and the removal rate will reach over 90%.

實(shí)際工程運(yùn)行發(fā)現(xiàn)，在硫細(xì)菌所能承受范圍內(nèi)，H2S容積負(fù)荷越高，微生物脫硫反應(yīng)越能保持良好的運(yùn)行效果，且不易發(fā)生循環(huán)水急劇酸化的現(xiàn)象。有研究發(fā)現(xiàn)，無色硫細(xì)菌在營養(yǎng)物質(zhì)受限制而有足夠硫化物時(shí)，可在幾乎無明顯生長的情況下，地將硫化物氧化。所以在工程運(yùn)營中，當(dāng)H2S負(fù)荷發(fā)生變化時(shí)，主要通過控制pH值、DO濃度等運(yùn)行條件就能確保運(yùn)行效果的穩(wěn)定。

In actual engineering operation, it has been found that within the range that sulfur bacteria can withstand, the higher the H2S volumetric load, the better the microbial desulfurization reaction can maintain good operating efficiency, and the phenomenon of rapid acidification of circulating water is less likely to occur. A study has found that colorless sulfur bacteria can efficiently oxidize sulfides with almost no significant growth when there are sufficient sulfides due to nutrient limitations. So in engineering operation, when the H2S load changes, the stability of the operating effect can be ensured mainly by controlling operating conditions such as pH value and DO concentration.