1、沼氣特性
1. Characteristics of biogas
沼氣是一種混合氣體，其組成不僅取決于發(fā)酵原料的種類及其相對(duì)含量，而且隨發(fā)酵條件及發(fā)酵階段的不同而變化。當(dāng)沼氣厭氧反應(yīng)器處于正常穩(wěn)定發(fā)酵階段時(shí)，沼氣的體積組成大致為：甲烷（CH4）50%～75%，二氧化碳（CO2）25%～45%，水（H2O，20～40℃下）2%～7%，氮?dú)猓∟2）0～2%，少量的氧氣（O2），以及少于1%的氫氣（H2）和硫化氫（H2S）。
Biogas is a kind of mixed gas. Its composition depends not only on the type and relative content of fermentation materials, but also on the fermentation conditions and fermentation stages. When the biogas anaerobic reactor is in the normal and stable fermentation stage, the volume composition of biogas is roughly 50% - 75% of methane (CH4), 25% - 45% of carbon dioxide (CO2), 2% - 7% of water (H2O, at 20 - 40 ℃), 0 - 2% of nitrogen (N2), a small amount of oxygen (O2), and less than 1% of hydrogen (H2) and hydrogen sulfide (H2S).
與其它可燃?xì)怏w相比，沼氣具有抗爆性良好和燃燒產(chǎn)物清潔等特點(diǎn)。目前，沼氣主要應(yīng)用在發(fā)電、供熱和炊事方面，沼氣中的CO2降低了沼氣的能量密度和熱值，限制了沼氣的利用范圍，要去除沼氣中的CO2、H2S 和水蒸氣等將沼氣提純?yōu)樯锾烊粴猓˙NG）。生物天然氣可壓縮用于車用燃料（CNG）、熱電聯(lián)產(chǎn)（CHP）、并入天然氣管網(wǎng)、燃料電池以及化工原料等領(lǐng)域。汽車使用生物天然氣不僅可以降低尾氣排放造成的空氣污染，而且溫室氣體的凈排放量減少75%～200%，生物天然氣可混入現(xiàn)有的天然氣管網(wǎng)，降低對(duì)石化能源的依賴。
Compared with other combustible gases, biogas has the characteristics of good explosion resistance and clean combustion products. At present, biogas is mainly used in power generation, heating and cooking. The CO2 in biogas reduces the energy density and calorific value of biogas, and limits the utilization range of biogas. It is necessary to remove CO2, H2S and water vapor in biogas to purify biogas into biological natural gas (BNG). Biogas can be compressed and used in the fields of vehicle fuel (CNG), cogeneration (CHP), integration into natural gas pipeline network, fuel cell and chemical raw materials. The use of biological natural gas in automobiles can not only reduce the air pollution caused by tail gas emissions, but also reduce the net emissions of greenhouse gases by 75% to 200%. Biological natural gas can be mixed into the existing natural gas pipeline network, reducing the dependence on petrochemical energy.
2、沼氣提純技術(shù)
2. Biogas purification technology
目前填埋氣提純工藝有變壓吸附法（PSA）、水洗法、化學(xué)吸收法、膜分離法、選擇分離法等，在目前世界范圍內(nèi)工藝較為成熟、應(yīng)用相對(duì)較多的方法是變壓吸附法（PSA）、化學(xué)吸收法（胺法凈化）、膜分離法。
At present, the purification processes of landfill gas include pressure swing adsorption (PSA), water washing, chemical absorption, membrane separation, selective separation, etc. At present, the more mature and widely used methods in the world are pressure swing adsorption (PSA), chemical absorption (amine purification), and membrane separation.
2.1變壓吸附法（PSA）
2.1 Pressure swing adsorption (PSA)
變壓吸附法（PSA）是在加壓條件下，利用沼氣中的CH4、CO2以及N2在吸附劑表面被吸附的能力不同而實(shí)現(xiàn)分離氣體成分的一種方法。組分的吸附量受壓力及溫度的影響，壓力升高時(shí)吸附量增加，壓力降低時(shí)吸附量減少；當(dāng)溫度升高時(shí)吸附量減小，溫度降低時(shí)吸附量增加。變壓吸附對(duì)氣體來源的要求非常嚴(yán)格，H2S的存在會(huì)導(dǎo)致吸附劑永久性中毒，并且變壓吸附要求氣體干燥，所以變壓吸附前要先脫除H2S和H2。
Pressure swing adsorption (PSA) is a method to separate gas components under pressure by using the different adsorption capacities of CH4, CO2 and N2 in biogas on the adsorbent surface. The adsorption capacity of components is affected by pressure and temperature. The adsorption capacity increases when the pressure increases, and decreases when the pressure decreases; The adsorption capacity decreases when the temperature increases, and increases when the temperature decreases. PSA has very strict requirements on the gas source. The presence of H2S will cause permanent poisoning of the adsorbent, and PSA requires gas drying, so H2S and H2 must be removed before PSA.
吸附材料在該技術(shù)中起到關(guān)鍵的作用，一般采用不同類型的活性炭、沸石、硅膠、氧化鋁和分子篩作為吸附材料。不同的吸附材料對(duì)沼氣的純化效果各不相同。目前，以活性炭和分子篩為主的碳基吸附劑，在研究沼氣提純方面經(jīng)常被使用。近年來出現(xiàn)的一些新型吸附材料，如有序介孔材料、胺修飾吸附劑和金屬框架物（MOFs）對(duì)CO2具有很高吸附選擇性，應(yīng)用前景廣闊，而且MOFs被認(rèn)為是在CO2分離方面具潛力。
Adsorption materials play a key role in this technology. Generally, different types of activated carbon, zeolite, silica gel, alumina and molecular sieve are used as adsorption materials. Different adsorption materials have different purification effects on biogas. At present, carbon-based adsorbents, mainly activated carbon and molecular sieve, are often used in the research of biogas purification. In recent years, some new adsorption materials, such as ordered mesoporous materials, amine modified adsorbents and metal frameworks (MOFs), have high adsorption selectivity for CO2, and have broad application prospects, and MOFs are considered to have the most potential in CO2 separation.
2.2化學(xué)吸收法
2.2 Chemical absorption method
化學(xué)吸收法是利用胺溶液將CO2從CH4中分離的方法，分離過程中CO2被吸收后進(jìn)一步與胺溶液發(fā)生化學(xué)反應(yīng)，通過加熱完成胺溶液的再生。由于化學(xué)反應(yīng)具有良好的選擇性，而CH4被胺溶液吸收的量又非常低，所以這種方法CH4的損失率低于0.1%。該技術(shù)操作壓力一般為1atm。
Chemical absorption method is a method that uses amine solution to separate CO2 from CH4. During the separation process, CO2 is absorbed and then chemically reacts with amine solution to complete the regeneration of amine solution by heating. Because the chemical reaction has strong selectivity and the amount of CH4 absorbed by amine solution is very low, the loss rate of CH4 in this method is less than 0.1%. The operating pressure of this technology is generally 1 atm.
常用的胺溶液主要有乙醇胺（MEA）、二乙醇胺（DEA）和甲基二乙醇胺（MDEA）[13]。由于CO2被吸收后與胺溶液發(fā)生了化學(xué)反應(yīng)，因此吸收過程可以在較低的壓力條件下進(jìn)行，一般情況下只需在沼氣已有壓力的基礎(chǔ)上稍微提高一些壓力即可。胺溶液的再生過程比較困難，需要160℃的溫度條件，因此運(yùn)行過程需要消耗大量的工藝用熱，存在運(yùn)行能耗高的弊端。此外，由于存在蒸發(fā)損失，運(yùn)行過程需要經(jīng)常補(bǔ)充胺溶液。
The commonly used amine solutions mainly include ethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) [13]. Since CO2 is absorbed and chemically reacts with amine solution, the absorption process can be carried out at a lower pressure. Generally, it is only necessary to slightly increase the pressure on the basis of the existing pressure of biogas. The regeneration process of amine solution is relatively difficult, requiring 160 ℃ temperature conditions, so the operation process needs to consume a large amount of process heat, which has the disadvantage of high operation energy consumption. In addition, due to evaporation loss, amine solution needs to be supplemented frequently during operation.
2.3膜分離法
2.3 Membrane separation method
膜技術(shù)被認(rèn)為是21世紀(jì)工業(yè)技術(shù)改造中的一項(xiàng)出彩為重要的技術(shù)，有專家指出：誰掌握了膜技術(shù)誰就掌握了化學(xué)工業(yè)的明天。膜分離法原理是利用各氣體組分在膜表面的吸附能力不同，溶解、擴(kuò)散速率不同，在膜兩側(cè)分壓差的推動(dòng)下，大部分CO2等組分和少量的CH4透過膜壁進(jìn)入滲透?jìng)?cè)分離出去，大部分CH4在高壓側(cè)作為生物天然氣輸出。
Membrane technology is considered to be an extremely important technology in the industrial technological transformation in the 21st century. Some experts pointed out that whoever masters membrane technology will master the future of chemical industry. The principle of membrane separation method is to make use of the different adsorption capacity of each gas component on the membrane surface and the different dissolution and diffusion rates. Under the promotion of the partial pressure difference on both sides of the membrane, most of the components such as CO2 and a small amount of CH4 enter the permeation side through the membrane wall for separation, and most of CH4 is exported as biological natural gas at the high pressure side.
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2023-03-02
