沼氣提純技術(shù)

　　Biogas purification technology

　　根據(jù)分離原理不同，目前常見的沼氣提純技術(shù)有：吸附法、高壓水洗法（物理吸收法）、化學(xué)吸收法（胺洗法）、膜分離法等。

　　According to different separation principles, common biogas purification technologies currently include adsorption method, high-pressure water washing method (physical absorption method), chemical absorption method (amine washing method), membrane separation method, etc.

　　1.1吸附法

　　1.1 Adsorption method

　　吸附法是一種物理提純方法，包括變壓吸附法（PSA）和變溫吸附法（TSA），其中用于沼氣提純的主要是PSA法。

　　Adsorption method is a physical purification method, including pressure swing adsorption (PSA) and temperature swing adsorption (TSA), among which PSA method is mainly used for biogas purification.

　　變壓吸附法（PSA）主要是利用吸附劑（如活性炭、硅膠、氧化鋁和沸石等）根據(jù)不同氣體的吸附量不同或氣體分子大小不同的特點(diǎn)，來脫除沼氣中的雜質(zhì)氣體，實(shí)現(xiàn)氣體的分離（如圖1）。在變壓吸附過程中，沼氣經(jīng)過過濾、脫水、脫氨、脫硫和壓縮等預(yù)處理后，沼氣在變壓吸附裝置（吸附塔）內(nèi)分別處于吸附、減壓、脫附、加壓的一個(gè)循環(huán)狀態(tài)，通過加壓將沼氣中的CO2和N2等吸附在吸附塔內(nèi)，而CH4為輕組分由變壓吸附塔頂部排出，并作為產(chǎn)品進(jìn)行收集，直至吸附塔達(dá)到飽和狀態(tài)，進(jìn)行減壓將吸附柱減壓甚至抽成真空，這時(shí)被吸附的CO2和N2等雜質(zhì)氣體就會(huì)被脫附出來，由塔底排出。如此循環(huán)往復(fù)去除沼氣中的雜質(zhì)氣體來提純沼氣。

　　The pressure swing adsorption (PSA) method mainly uses adsorbents (such as activated carbon, silica gel, alumina, zeolite, etc.) to remove impurity gases from biogas according to the characteristics of different gas adsorption capacities or gas molecule sizes, and achieve gas separation (as shown in Figure 1). In the process of pressure swing adsorption, after pre-treatment such as filtration, dehydration, deamination, desulfurization, and compression, the biogas is in a cycle of adsorption, depressurization, desorption, and pressurization in the pressure swing adsorption device (adsorption tower). CO2 and N2 in the biogas are adsorbed in the adsorption tower by pressurization, while CH4, as a light component, is discharged from the top of the pressure swing adsorption tower and collected as a product until the adsorption tower reaches saturation. The adsorption column is depressurized or even evacuated by depressurization. At this time, the adsorbed impurity gases such as CO2 and N2 will be desorbed and discharged from the bottom of the tower. Repeat this process to remove impurities from biogas and purify it.

　　變壓吸附法（PSA）占地面積小，一般為集成裝置，運(yùn)輸、安裝方便，甲烷回收率為97%左右，但需要一定的壓力，對(duì)原料中H2S的含量有一定的要求（一般＜50ppm），且對(duì)控制元件及閥門的精度要求較高。相比于水洗法和化學(xué)吸收法，PSA法更為靈活，適用于中、小規(guī)模的沼氣提純工程項(xiàng)目。

　　The pressure swing adsorption (PSA) method has a small footprint, is generally an integrated device, is easy to transport and install, and has a methane recovery rate of about 97%. However, it requires a certain pressure and has certain requirements for the H2S content in the raw materials (generally<50ppm), and has high precision requirements for control components and valves. Compared to water washing and chemical absorption methods, PSA method is more flexible and suitable for medium and small-scale biogas purification projects.

　　1.2高壓水洗法

　　1.2 High pressure water washing method

　　高壓水洗法主要利用CO2和CH4在水中溶解度的差異，通過物理吸收將CO2和CH4進(jìn)行分離。在外部條件相同的情況下，CO2在水中的溶解度是CH4的30倍左右，當(dāng)沼氣通過水體后，CO2被水吸收從而達(dá)到提純沼氣的目的。同時(shí)，經(jīng)過試驗(yàn)證明，CH4與CO2在水中的溶解度隨著壓力的加大，沼氣提純的效果更加顯著。

　　The high-pressure water washing method mainly utilizes the difference in solubility between CO2 and CH4 in water to separate them through physical absorption. Under the same external conditions, the solubility of CO2 in water is about 30 times that of CH4. When biogas passes through the water, CO2 is absorbed by the water to achieve the goal of purifying biogas. Meanwhile, it has been experimentally proven that the solubility of CH4 and CO2 in water increases with increasing pressure, resulting in a more significant purification effect of biogas.

　　圖2為高壓水洗法工藝流程，通常沼氣通過壓縮后從吸收塔底部進(jìn)入，水從頂部進(jìn)入實(shí)現(xiàn)錯(cuò)流吸收。為提高CO2在水中的溶解度，水洗工藝一般采用較高的壓力，CO2在水中的溶解度隨著壓力的升高逐漸增大，甲烷損失少。但是，在CO2的吸收過程中需要大量工業(yè)用水，同時(shí)產(chǎn)生的廢液需通過CO2再生裝置進(jìn)行回收處理，凈化后的CH4也需通過脫水裝置進(jìn)行干燥處理。

　　Figure 2 shows the process flow of high-pressure water washing method. Usually, biogas enters from the bottom of the absorption tower after compression, and water enters from the top to achieve cross flow absorption. To improve the solubility of CO2 in water, the water washing process generally uses higher pressure, and the solubility of CO2 in water gradually increases with the increase of pressure, resulting in less methane loss. However, a large amount of industrial water is required in the absorption process of CO2, and the waste liquid generated at the same time needs to be recovered and treated through a CO2 regeneration device. The purified CH4 also needs to be dried through a dehydration device.

　　高壓水洗法主要適用于處理規(guī)模較大的氣體，提純純度高（＞97%CH4），甲烷損失小（0.05%~6%）；該方法所使用的溶劑是可再生的，并且可以耐受一定的雜質(zhì)；主要通過改變裝置的壓力和溫度來調(diào)整

　　The high-pressure water washing method is mainly suitable for processing large-scale gases, with high purification purity (>97% CH4) and low methane loss (0.05%~6%); The solvent used in this method is renewable and can tolerate certain impurities; Mainly adjusted by changing the pressure and temperature of the device

　　胺洗法適用于規(guī)模較大的沼氣提純工程（沼氣處理量達(dá)到每小時(shí)萬立方米），規(guī)模越大，經(jīng)濟(jì)性越好，提純純度高（＞99%CH4），甲烷損失小（＜0.1%）。在提純過程中具有設(shè)備成本低、操作簡(jiǎn)便、凈化效果好以及操作壓力低等優(yōu)點(diǎn)，其操作壓力一般為0.1MPa，操作壓力低于水洗法沼氣提純工藝，該方法所使用的溶劑是可再生的。但同時(shí)，使用該方法能源消耗高，且由于有機(jī)胺存在一定的毒性，回收后的CO2不適合再利用，不適用于含O2的沼氣提純。

　　The amine washing method is suitable for large-scale biogas purification projects (with a biogas processing capacity of up to 10000 cubic meters per hour). The larger the scale, the better the economy, the higher the purification purity (>99% CH4), and the smaller the methane loss (<0.1%). In the purification process, it has the advantages of low equipment cost, easy operation, good purification effect, and low operating pressure. The operating pressure is generally 0.1 MPa, which is lower than the water washing method for biogas purification. The solvent used in this method is renewable. However, at the same time, using this method consumes high energy, and due to the toxicity of organic amines, the recovered CO2 is not suitable for reuse and purification of biogas containing O2.

　　1.4膜分離法

　　1.4 Membrane Separation Method

　　膜分離法的基本原理是依靠氣體在膜表面的吸附能力不同、溶解度不同和擴(kuò)散速率差異，來選擇“過濾”氣體中的各組分，即利用薄膜材料對(duì)各種氣體的滲透率不同來達(dá)到分離的目的，常用的分離膜材料有：高分子材料、無機(jī)材料和金屬材料，但是在沼氣的CO2和CH4的分離中常用的是中空纖維膜。在膜兩側(cè)分壓差的作用下，大部分的CO2以及少量的CH4作為快氣通過膜壁滲透分離排出，剩下大部分的CH4以透余氣形式獲得提純，為提高CH4的濃度，通常采用多級(jí)膜分離工藝。膜分離法工藝流程如圖4所示。

　　The basic principle of membrane separation method relies on the different adsorption capacity, solubility, and diffusion rate of gases on the membrane surface to select the various components in the "filtered" gas, that is, to achieve separation by using the different permeability of membrane materials to various gases. Commonly used separation membrane materials include polymer materials, inorganic materials, and metal materials, but hollow fiber membranes are commonly used in the separation of CO2 and CH4 in biogas. Under the action of the pressure difference on both sides of the membrane, most of the CO2 and a small amount of CH4 are separated and discharged through the membrane wall as fast gas, while the remaining CH4 is purified in the form of permeate gas. To increase the concentration of CH4, a multi-stage membrane separation process is usually used. The process flow of membrane separation is shown in Figure 4.

　　常見的膜分離法主要有高壓氣相分離和氣相-液相吸收膜分離兩種。采用高壓氣相分離方法時(shí)，由于膜的兩側(cè)都是氣相，所需的操作壓力較大，CH4的純度最高只有92%，經(jīng)多級(jí)膜分離，CH4的純度可達(dá)99.5%。氣相-液相吸收膜分離一側(cè)為氣相，一側(cè)為液相，不需要較高壓力，沼氣從膜的一側(cè)流過，其中的H2S和CO2分子能夠擴(kuò)散穿過膜，在另一側(cè)被相反方向流過的液體吸收，吸收膜的工作壓力僅為0.1MPa，溫度為25~35℃，液相的吸收劑可以用化學(xué)吸收法中提到的胺溶液和堿溶液。

　　The common membrane separation methods mainly include high-pressure gas phase separation and gas liquid phase absorption membrane separation. When using high-pressure gas phase separation method, due to the fact that both sides of the membrane are in the gas phase, a high operating pressure is required, and the highest purity of CH4 is only 92%. After multi-stage membrane separation, the purity of CH4 can reach 99.5%. The gas-liquid absorption membrane separates the gas phase on one side and the liquid phase on the other side, without requiring high pressure. Biogas flows through one side of the membrane, and H2S and CO2 molecules can diffuse through the membrane and be absorbed by the liquid flowing in the opposite direction on the other side. The working pressure of the absorption membrane is only 0.1 MPa and the temperature is 25-35 ℃. The absorbent for the liquid phase can be amine solution and alkali solution mentioned in chemical absorption method.

　　膜法裝置工藝簡(jiǎn)單、操作簡(jiǎn)便，設(shè)備占地面積小、自動(dòng)化程度較高，安裝方便，較適用于規(guī)模較小和中等規(guī)模的沼氣提純工程，對(duì)其擴(kuò)容也較易操作。但操作壓力高，投資運(yùn)行費(fèi)用較高，且對(duì)原料中H2S的含量有較高的要求（一般＜10ppm）。

　　The membrane method device has a simple process, easy operation, small equipment footprint, high degree of automation, easy installation, and is suitable for small-scale and medium-sized biogas purification projects. Its expansion is also easy to operate. But the operating pressure is high, the investment and operating costs are high, and there are high requirements for the content of H2S in the raw materials (generally<10ppm).

　　從上述論述可以看出，各種提純技術(shù)各有優(yōu)缺點(diǎn)，在實(shí)際應(yīng)用中需根據(jù)建設(shè)項(xiàng)目自身的情況，如對(duì)回收率的要求、占地面積、對(duì)產(chǎn)品中甲烷含量的要求等來選擇相應(yīng)的技術(shù)，以達(dá)到最佳的效果。

　　From the above discussion, it can be seen that various purification technologies have their own advantages and disadvantages. In practical applications, the corresponding technology should be selected according to the situation of the construction project itself, such as the requirements for recovery rate, land area, and methane content in the product, in order to achieve the best effect.

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