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沼气提纯生物天然气技术

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 biological natural gas. 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 biological natural gas technology. Biogas purification of biogas can make high-value use of biogas, effectively reduce the greenhouse effect caused by insufficient utilization of biogas in biogas projects, and have the 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 not only depends on the type and relative content of fermentation raw materials, but also changes with 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, 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 good explosion resistance and clean combustion products. At present, biogas is mainly used in power generation, heat supply and cooking. The CO2 in biogas reduces the energy density and calorific value of biogas and limits the scope of biogas utilization. It is necessary to remove CO2, H2S and water vapor in biogas and purify biogas into biological natural gas (bng). Bio natural gas can be compressed for vehicle fuel (CNG), cogeneration (CHP), integration into natural gas pipeline network, fuel cell, 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 adsorbent surface. 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. Therefore, 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分离方面最具潜力。
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. Moreover, MOFs are considered to have the most potential in CO2 separation.

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