沼气的主要成分是CH4和CO2，将CO2从混合气中分离得到的高纯度甲烷气被称为生物天然气。生物天然气可以直接作为石化天然气的替代燃料，发展沼气已成为增加天然气供应量的一个重要方向。人类对天然气需求量的增加推动了生物天然气技术的发展。沼气提纯生物天然气可高值化利用沼气，有效减少沼气工程因沼气利用不充分而排空造成的温室效应，具有环保和能源双重效益。本文概述了沼气提纯技术及国内外发展现状，以期为沼气提纯技术的发展提供参考。
The main components of biogas are CH4 and CO2. The high-purity methane gas obtained by separating CO2 from the mixture is called biogas. Biogas can be directly used as an alternative fuel for Petrochemical Natural gas. The development of biogas has become an important direction to increase the supply of natural gas. The increase of human demand for natural gas has promoted the development of biogas technology. Biogas purification of biogas can make high-value use of biogas, effectively reduce the greenhouse effect caused by the emptying of biogas projects due to insufficient utilization of biogas, and have dual benefits of environmental protection and energy. This paper summarizes the biogas purification technology and its development status at home and abroad, in order to provide reference for the development of biogas purification technology.
1、沼气特性
1. Biogas characteristics
沼气是一种混合气体，其组成不仅取决于发酵原料的种类及其相对含量，而且随发酵条件及发酵阶段的不同而变化。当沼气厌氧反应器处于正常稳定发酵阶段时，沼气的体积组成大致为：甲烷（CH4）50%～75%，二氧化碳（CO2）25%～45%，水（H2O，20～40℃下）2%～7%，氮气（N2）0～2%，少量的氧气（O2），以及少于1%的氢气（H2）和硫化氢（H2S）。
Biogas is a kind of mixed gas. Its composition depends not only on the type and relative content of fermentation raw materials, but also on the different fermentation conditions and fermentation stages. When the biogas anaerobic reactor is in the normal stable fermentation stage, the volume composition of biogas is roughly: methane (CH4) 50% ~ 75%, carbon dioxide (CO2) 25% ~ 45%, water (H2O, at 20 ~ 40 ℃) 2% ~ 7%, nitrogen (N2) 0 ~ 2%, a small amount of oxygen (O2), and less than 1% of hydrogen (H2) and hydrogen sulfide (H2S).
与其它可燃气体相比，沼气具有抗爆性良好和燃烧产物清洁等特点。目前，沼气主要应用在发电、供热和炊事方面，沼气中的CO2降低了沼气的能量密度和热值，限制了沼气的利用范围，要去除沼气中的CO2、H2S 和水蒸气等将沼气提纯为生物天然气（BNG）。生物天然气可压缩用于车用燃料（CNG）、热电联产（CHP）、并入天然气管网、燃料电池以及化工原料等领域。汽车使用生物天然气不仅可以降低尾气排放造成的空气污染，而且温室气体的净排放量减少75%～200%，生物天然气可混入现有的天然气管网，降低对石化能源的依赖。
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 scope of its utilization. It is necessary to remove CO2, H2S and water vapor in biogas and purify biogas into biological natural gas (bng). Biogas can be compressed for vehicle fuel (CNG), cogeneration (CHP), incorporation into natural gas pipelines, fuel cells, chemical raw materials and other fields. The use of biogas in automobiles can not only reduce the air pollution caused by exhaust emissions, but also reduce the net emission of greenhouse gases by 75% - 200%. Biogas can be mixed into the existing natural gas pipeline network, reducing the dependence on petrochemical energy.
2、沼气提纯技术
2. Biogas purification technology
目前填埋气提纯工艺有变压吸附法（PSA）、水洗法、化学吸收法、膜分离法、选择分离法等，在目前世界范围内工艺较为成熟、应用相对较多的方法是变压吸附法（PSA）、化学吸收法（胺法净化）、膜分离法。
At present, landfill gas purification processes 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变压吸附法（PSA）
2.1 pressure swing adsorption (PSA)
变压吸附法（PSA）是在加压条件下，利用沼气中的CH4、CO2以及N2在吸附剂表面被吸附的能力不同而实现分离气体成分的一种方法。组分的吸附量受压力及温度的影响，压力升高时吸附量增加，压力降低时吸附量减少；当温度升高时吸附量减小，温度降低时吸附量增加。变压吸附对气体来源的要求非常严格，H2S的存在会导致吸附剂永久性中毒，并且变压吸附要求气体干燥，所以变压吸附前要先脱除H2S和H2。
Pressure swing adsorption (PSA) is a method to separate gas components under pressurized conditions by using the different adsorption capacities of CH4, CO2 and N2 in biogas on the surface of adsorbent. The adsorption capacity of components is affected by pressure and temperature. When the pressure increases, the adsorption capacity increases, and when the pressure decreases, the adsorption capacity decreases; When the temperature increases, the adsorption capacity decreases, and when the temperature decreases, the adsorption capacity increases. PSA has very strict requirements on gas source. The presence of H2S will cause permanent poisoning of adsorbent, and PSA requires gas drying, so H2S and H2 should be removed before PSA.
吸附材料在该技术中起到关键的作用，一般采用不同类型的活性炭、沸石、硅胶、氧化铝和分子筛作为吸附材料。不同的吸附材料对沼气的纯化效果各不相同。目前，以活性炭和分子筛为主的碳基吸附剂，在研究沼气提纯方面经常被使用。近年来出现的一些新型吸附材料，如有序介孔材料、胺修饰吸附剂和金属框架物（MOFs）对CO2具有很高吸附选择性，应用前景广阔，而且MOFs被认为是在CO2分离方面具潜力。
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 based on activated carbon and molecular sieve are often used in the study 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 broad application prospects, and MOFs are considered to have the most potential in CO2 separation.
2.2化学吸收法
2.2 chemical absorption method
化学吸收法是利用胺溶液将CO2从CH4中分离的方法，分离过程中CO2被吸收后进一步与胺溶液发生化学反应，通过加热完成胺溶液的再生。由于化学反应具有很强的选择性，而CH4被胺溶液吸收的量又非常低，所以这种方法CH4的损失率低于0.1%。该技术操作压力一般为1atm。
Chemical absorption method uses amine solution to separate CO2 from CH4. After CO2 is absorbed in the separation process, it further reacts with amine solution and completes 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 1atm.
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被吸收后与胺溶液发生了化学反应，因此吸收过程可以在较低的压力条件下进行，一般情况下只需在沼气已有压力的基础上稍微提高一些压力即可。胺溶液的再生过程比较困难，需要160℃的温度条件，因此运行过程需要消耗大量的工艺用热，存在运行能耗高的弊端。此外，由于存在蒸发损失，运行过程需要经常补充胺溶液。
Commonly used amine solutions mainly include ethanolamine (MEA), diethanolamine (DEA) and methyl diethanolamine (MDEA) [13]. Since CO2 reacts with amine solution after being absorbed, the absorption process can be carried out under low 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 a temperature of 160 ℃, so the operation process needs to consume a lot 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膜分离法
2.3 membrane separation method
膜技术被认为是21世纪工业技术改造中的一项极为重要的技术，有专家指出：谁掌握了膜技术谁就掌握了化学工业的明天。膜分离法原理是利用各气体组分在膜表面的吸附能力不同，溶解、扩散速率不同，在膜两侧分压差的推动下，大部分CO2等组分和少量的CH4透过膜壁进入渗透侧分离出去，大部分CH4在高压侧作为生物天然气输出。
Membrane technology is considered to be a very 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 use the different adsorption capacity of each gas component on the membrane surface and the different dissolution and diffusion rates. Driven by the differential pressure 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 and are separated out, and most of CH4 is output as biological natural gas on the high-pressure side.
适合沼气提纯的有聚酰亚胺膜、聚砜膜和醋酸纤维素膜，后者的耐水性不佳，使用过程中需要严格脱水，沼气提纯膜元件使用中空纤维、螺旋卷类型的较多，封套式较少。沼气提纯膜分离技术有两套基本的膜分离系统：气体渗透模块系统和气液膜分离系统。对于气体渗透模块系统来说，在阶段，CH4含量高可达到92%。但若经过多级膜处理后，CH4含量高会超过96%。沼气气液膜分离提纯技术是近年才发展起来的，对于CO2的去除非常有效，特别是采用碱性溶液的膜系统，能够在阶段中将55%CH4含量的沼气纯化到CH4含量96%。
Polyimide membrane, polysulfone membrane and cellulose acetate membrane are suitable for biogas purification. The latter has poor water resistance and requires strict dehydration in the process of use. Biogas purification membrane components use more hollow fibers and spiral rolls, and less envelopes. There are two basic membrane separation systems for biogas purification membrane separation technology: gas permeation module system and gas-liquid membrane separation system. For the gas permeation module system, the maximum CH4 content can reach 92% in the first stage. However, after multi-stage membrane treatment, the maximum CH4 content will exceed 96%. Biogas gas-liquid membrane separation and purification technology has only been developed in recent years, which is very effective for CO2 removal. Especially, the membrane system using alkaline solution can purify biogas with 55% CH4 content to 96% CH4 content in the first stage.
The above is a detailed introduction to biogas purification, which I hope will help you. If you have any questions, please contact us. We will provide services for you with a professional attitude https://www.hneee.net
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