硫化氫（H2S）從哪里來？

　　Where does hydrogen sulfide (H2S) come from?

　　沼氣中不止含有甲烷，二氧化碳和水，還包括一些少量的其他化合物。雖然，沼氣中雜質的含量相對較低，但是在沼氣的利用中會產生比較明顯的副作用。沼氣中的雜質會對沼氣應用的設備造成問題，包括腐蝕和機械磨損。在沼氣的燃燒中，雜質還會產生無用污染物的排放。未經凈化的沼氣中非常常見的雜質有硫化氫，氨氣，氧氣和氮氣。硫化氫是由細菌（微生物）生化過程產生的，可以減少發(fā)酵罐中硫化物的含量并轉化為硫化氫。這些細菌也出現(xiàn)在發(fā)酵罐中，同時和形成甲烷的細菌爭奪相同的基質，造成甲烷形成的減少和硫化氫的形成。富含硫元素的發(fā)酵原料主要包括富含蛋白質的原料，例如雞糞、酒糟等。

　　Biogas contains not only methane, carbon dioxide, and water, but also small amounts of other compounds. Although the content of impurities in biogas is relatively low, there will be significant side effects in the utilization of biogas. Impurities in biogas can cause problems for equipment used in biogas applications, including corrosion and mechanical wear. In the combustion of biogas, impurities can also generate the emission of useless pollutants. The most common impurities in unpurified biogas are hydrogen sulfide, ammonia, oxygen, and nitrogen. Hydrogen sulfide is produced by biochemical processes of bacteria (microorganisms), which can reduce the content of sulfides in fermentation tanks and convert them into hydrogen sulfide. These bacteria also appear in the fermentation tank, competing with methane forming bacteria for the same substrate, resulting in a reduction in methane formation and the formation of hydrogen sulfide. Fermentation materials rich in sulfur mainly include protein rich materials, such as chicken manure, distiller's grains, etc.

　　在利用禽類糞污為發(fā)酵原料的項目中，粗沼氣中的H2S的含量能達到5000ppm甚至更高，而沼氣利用設備，如有的沼氣CHP機組要求H2S的含量低于100ppm，有的沼氣鍋爐要求低于20ppm，而有的沼氣提純設備要求低于15ppm。因此沼氣脫硫是沼氣凈化工藝環(huán)節(jié)的重中之重，也是沼氣凈化工藝環(huán)節(jié)投資非常大的部分。常見的沼氣脫硫技術包括干法脫硫、濕法脫硫和生物脫硫，對于規(guī)模化的沼氣項目來說，常采用生物脫硫（粗脫硫）+干法脫硫（精脫硫）的組合工藝，以達到后端沼氣利用設備的硫化氫入口要求。

　　In projects that use poultry manure as fermentation raw material, the content of H2S in crude biogas can reach 5000ppm or even higher, while biogas utilization equipment such as some biogas CHP units require H2S content below 100ppm, some biogas boilers require H2S content below 20ppm, and some biogas purification equipment requires H2S content below 15ppm. Therefore, biogas desulfurization is the top priority in the biogas purification process and also the largest investment in the biogas purification process. Common biogas desulfurization technologies include dry desulfurization, wet desulfurization, and biological desulfurization. For large-scale biogas projects, a combination process of biological desulfurization (coarse desulfurization) and dry desulfurization (fine desulfurization) is often used to meet the hydrogen sulfide inlet requirements of the back-end biogas utilization equipment.

　　何為生物脫硫？

　　What is biological desulfurization?

　　生物脫硫法又被叫做生物催化脫硫(Biocatalytic Desulfurizaton，簡稱?BDS),是一種常溫常壓下利用脫硫細菌將硫化物轉化為單質硫或硫酸鹽的脫硫方法。生物脫硫法的基本原理是：H2S氣體被吸收液吸收轉化為硫化物，然后被脫硫細菌吸收至體內，作為營養(yǎng)物質被脫硫細菌分解、氧化、利用。在脫硫的同時為脫硫細菌的生長繁衍提供能量。生物脫硫的過程主要分為3個階段：

　　Biological desulfurization, also known as biocatalytic desulfurization, abbreviated as? BDS), It is a desulfurization method that uses desulfurization bacteria to convert sulfides into elemental sulfur or sulfate under normal temperature and pressure. The basic principle of biological desulfurization method is that H2S gas is absorbed and converted into sulfides by the absorption solution, and then absorbed into the body by desulfurization bacteria as nutrients, which are decomposed, oxidized, and utilized by desulfurization bacteria. Provide energy for the growth and reproduction of desulfurization bacteria while desulfurizing. The process of biological desulfurization is mainly divided into three stages:

　　（1）H2S氣體的吸收過程：硫化氫氣體由氣相轉移至液相，被吸收液吸收轉變?yōu)榱蚧铮?/p>

　　(1) The absorption process of H2S gas: Hydrogen sulfide gas is transferred from the gas phase to the liquid phase, and is absorbed by the absorption liquid to transform into sulfides;

　?。?）硫化物的吸附吸收過程：溶解至水溶液中的硫化物被脫硫細菌吸收吸附，從水溶液中轉移至脫硫細菌的體內；

　　(2) The adsorption and absorption process of sulfides: sulfides dissolved in aqueous solution are absorbed and adsorbed by desulfurization bacteria, and transferred from the aqueous solution to the bodies of desulfurization bacteria;

　?。?）生物氧化的過程：進入脫硫細菌體內的硫化物被用作能源或養(yǎng)分在細菌體內酶作用下氧化分解和利用，從而達到去除H2S的目的。

　　(3) The process of biological oxidation: Sulfides entering the desulfurization bacteria are used as energy or nutrients, and are oxidized, decomposed, and utilized by enzymes in the bacteria to achieve the goal of removing H2S.

　　常用的生物脫硫工藝技術

　　Common biological desulfurization process technologies

　　根據(jù)吸收液pH值的不同，生物脫硫法可分為酸法生物脫硫和堿法生物脫硫。

　　According to the different pH values of the absorption solution, biological desulfurization can be divided into acid based biological desulfurization and alkaline based biological desulfurization.

　　（1）酸法生物脫硫

　　(1) Acid based biological desulfurization

　　酸法生物脫硫通常采用氧化硫硫桿菌和氧化亞鐵硫桿菌進行硫化物的氧化，這些細菌具有嗜酸性，生物反應器中的溶液環(huán)境呈酸性，pH值通常為2-6，氧化產物主要是SO42-，發(fā)生的化學反應為：常見的酸法生物脫硫工藝流程如下：

　　Acid based biological desulfurization usually uses sulfur oxidizing bacteria and ferrous oxidizing bacteria for the oxidation of sulfides. These bacteria are acidophilic, and the solution environment in the bioreactor is acidic, with a pH value usually between 2-6. The oxidation product is mainly SO42-, and the chemical reaction that occurs is as follows: The common process flow of acid based biological desulfurization is as follows:

　　工藝流程描述：沼氣進入吸收反應器底端，并從底端穿過填料層到達頂部?？諝馔ㄟ^變頻控制添加。尾氣成分分析儀對余氧濃度監(jiān)控并與空氣風機連鎖。營養(yǎng)液通過計量泵定時添加。液位開關控制整體的液位平衡。為了脫硫細菌的活性，采用熱交換器和溫度監(jiān)測對系統(tǒng)的溫度調節(jié)控制。PH儀用于控制營養(yǎng)液的質量（酸堿度），例如當PH低于設定值時，新鮮的營養(yǎng)液和稀釋用水自動加入脫硫塔中，在此同時，廢液自動排出，并保持液位平衡。有研究和工程運行表明，在酸法生物脫硫穩(wěn)定運行階段，營養(yǎng)液的溫度宜控制在30-35℃，pH值宜控制在1.45 – 1.55，空氣供應需要根據(jù)現(xiàn)場產氣情況來設置，宜按實際產氣量的1/9-1/10供入空氣，采用變頻器來實現(xiàn)風機變頻供氧，根據(jù)實際產氣量設置變頻器參數(shù)。

　　Process description: Biogas enters the bottom of the absorption reactor and passes through the packing layer from the bottom to the top. Air is added through variable frequency control. The exhaust gas composition analyzer monitors the residual oxygen concentration and is interlocked with the air fan. Nutrients are added at regular intervals through a metering pump. The liquid level switch controls the overall liquid level balance. In order to enhance the activity of desulfurization bacteria, a heat exchanger and temperature monitoring are used to regulate and control the temperature of the system. PH meter is used to control the quality (acidity and alkalinity) of nutrient solution. For example, when the pH is lower than the set value, fresh nutrient solution and dilution water are automatically added to the desulfurization tower. At the same time, the waste liquid is automatically discharged and the liquid level is maintained in equilibrium. Research and engineering operations have shown that during the stable operation stage of acid based biological desulfurization, the temperature of the nutrient solution should be controlled at 30-35 ℃, the pH value should be controlled at 1.45-1.55, and the air supply should be set according to the on-site gas production situation. It is recommended to supply air at 1/9-1/10 of the actual gas production rate, and use a frequency converter to achieve variable frequency oxygen supply for the fan. The parameters of the frequency converter should be set according to the actual gas production rate.

　?。?）堿法生物脫硫堿法生物脫硫是指采用排硫硫桿菌作為脫硫細菌進行生物脫硫的方法。生物反應中的環(huán)境呈中性或堿性。生物反應器中溶液呈堿性，氧化產物主要是單質S，對H2S?的吸收效率高，與酸法相比，堿法停留時間較短，吸收塔體積較小。堿法生物脫硫反應方程式如下：

　　(2) Alkali based biological desulfurization refers to the method of using sulfur releasing bacteria as desulfurization bacteria for biological desulfurization. The environment in biological reactions is neutral or alkaline. The solution in the bioreactor is alkaline, and the oxidation product is mainly elemental S. Does it affect H2S? The absorption efficiency is high, and compared with the acid method, the alkaline method has a shorter residence time and a smaller absorption tower volume. The reaction equation for alkaline biological desulfurization is as follows:

　　常見的堿法生物脫硫工藝流程如下：

　　The common alkaline biological desulfurization process is as follows:

　　工藝流程描述：

　　Process description:

　　①洗滌吸收：

　?、?Washing and absorption:

　　沼氣經增壓風機輸送至洗滌塔，與自上而下的洗滌液逆流接觸，過程中H2S?被液相吸收，其余氣體從洗滌塔頂排出進入后續(xù)單元，完成沼氣吸收、脫除過程。生物反應器洗滌液通過循環(huán)泵噴淋至洗滌塔進行H2S?吸收，洗滌塔吸收H2S?后的洗滌液也通過洗滌塔與生物反應器構成的連通器回流至生物反應器，達到洗滌液的循環(huán)。

　　Biogas is transported to the washing tower by a booster fan and comes into countercurrent contact with the washing solution from top to bottom. During the process, H2S? Absorbed by the liquid phase, the remaining gas is discharged from the top of the washing tower into the subsequent unit, completing the process of biogas absorption and removal. The washing solution of the bioreactor is sprayed into the washing tower through a circulating pump for H2S treatment? Absorption, does the washing tower absorb H2S? The subsequent washing solution also flows back to the bioreactor through the connecting vessel between the washing tower and the bioreactor, achieving the circulation of the washing solution.

　　②生物轉化

　?、?Biotransformation

　　生物反應器內溶液依靠曝氣實現(xiàn)全混和充氧，吸收H2S?后的洗滌液在硫桿菌的作用下可將硫化物轉化為單質硫，實現(xiàn)硫的脫除。

　　Does the solution in the bioreactor rely on aeration to achieve full mixing and oxygenation, and absorb H2S? The washing solution can convert sulfides into elemental sulfur under the action of sulfur bacteria, achieving sulfur removal.

　?、哿蚍蛛x

　?、?Sulfur separation

　　生物反應器內部分溶液流入硫沉淀器，硫產物在此單元沉淀后進入壓濾系統(tǒng)，完成硫單質的非常終分離。液相回流至生物反應器。

　　Part of the solution in the bioreactor flows into the sulfur precipitator, and the sulfur product is precipitated in this unit and then enters the pressure filtration system to complete the final separation of elemental sulfur. Reflux the liquid phase to the bioreactor.

　　有研究和工程運行表明，在堿法生物脫硫穩(wěn)定運行階段，循環(huán)液的氧化還原電位(ORP)?值宜保持在-380 mV至-400?mV內，生物反應器內溶解氧(DO )濃度宜控制在1-2 mg/L，循環(huán)液的堿度宜保持在0.30 mol/L?左右，溫度宜保持在30℃左右。

　　Research and engineering operations have shown that during the stable operation stage of alkaline biological desulfurization, what is the oxidation-reduction potential (ORP) of the circulating liquid? Should the value be maintained between -380 mV and -400 mV? Within mV, the dissolved oxygen (DO) concentration in the bioreactor should be controlled at 1-2 mg/L, and the alkalinity of the circulating liquid should be maintained at 0.30 mol/L? The temperature should be maintained at around 30 ℃.

　　在目前市場上規(guī)模化的沼氣工程通常采用堿法生物脫硫，這主要是由于凈化后的沼氣用于提純利用的較多。酸法生物脫硫中，進入吸收反應塔中的空氣中的氮氣，若后端采用膜提純技術時很難被分離出來，造成提純后的產品氣中甲烷含量很難進一步提高。從技術的角度，若后端沼氣用于熱電聯(lián)產（CHP）時，酸法和堿法生物脫硫都可以采用。

　　At present, large-scale biogas projects in the market usually use alkaline biological desulfurization, mainly because purified biogas is widely used for purification and utilization. In acid based biological desulfurization, the nitrogen in the air entering the absorption reaction tower is difficult to separate if membrane purification technology is used at the back end, resulting in difficulty in further increasing the methane content in the purified product gas. From a technical perspective, both acid and alkali based biological desulfurization methods can be used when using backend biogas for combined heat and power (CHP).