Tips for membrane-based biogas purification technology

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This post was last edited by HaiChuanZhiYou on 2016-3-21 at 16:13. There are many methods for purifying biogas; traditional ones include pressure swing adsorption and the ammonia method, while membrane technology and high-pressure water washing are new technologies developed in recent years. Many people think that purifying biogas using membrane technology is simple. Membrane technology is already widely used in various gas separation applications, and it can be applied to biogas separation by simply adopting the existing processes; the membrane modules can also be chosen as long as they have the necessary separation capabilities. However, this is not the case – there is a great deal of complexity involved in using membrane technology for biogas separation! Let me go through them one by one slowly. Firstly, carbon dioxide in biogas has a plasticizing effect on many polymer membrane materials, and many gas separation membranes are not suitable for use in biogas separation systems. Therefore, separation membranes made from polymers resistant to plasticization must be used; although their performance also degrades over time during use, this degradation occurs much more slowly compared to membranes made from materials that are not resistant to plasticization. Therefore, its service life is much longer. However, this type of membrane is relatively expensive and is often overlooked by many people. If you want to build a good reputation in the industry, you should opt for this gas separation membrane designed specifically for biogas separation. If you use it for personal use, this type of film offers great value for money. Choosing the right separation membrane is important, but the design of the associated process is equally crucial. Biogas contains many impurities that can be harmful to the membrane material; if a process design is developed without accurate test reports on the types and concentrations of these impurities, such a design will fail as well. Of course, you need to know in advance what the membrane fears; in fact, membranes are quite delicate and have many natural enemies, and even trace amounts of these can be fatal to them. But if you keep the membrane away from its natural predators, it will become extremely strong, and it can last for ten or eight years without any problem. In membrane processes, cooling and heating are required; with these back-and-forth operations, energy is wasted. A good process design should enable the comprehensive utilization of this energy, so as to reduce the operating costs of the equipment and make it more competitive when compared to other separation technologies such as pressure swing adsorption. The membrane separation process takes place under pressure; biogas, however, has no pressure, so it is necessary to increase the pressure before carrying out the separation. Determining the optimal pressure level involves a great deal of complexity. Before designing, an economic model must be established; through comprehensive calculations, the optimal operating pressure is determined. Generally, using a single membrane only yields methane gas at a relatively low concentration; to achieve a high recovery rate, a two-stage or three-stage process is necessary. The more stages there are, the more complex the technology becomes. How many membranes are used in one stage? How many segments are there in the double membrane? How many membranes are there in three segments? The optimal ratio of membrane roots not only reduces investment but, more importantly, lowers energy consumption; this is because to implement a two-stage or three-stage process, reflux is required, and the gas undergoing reflux needs to be re-compressed, which consumes a large amount of compression energy. The optimal ratio helps to reduce the amount of reflux. The two important parameters of membranes are the permeability coefficient and the separation coefficient. The parameters of membranes available on the market vary greatly, and of course the prices also differ. Membranes that are inexpensive do not necessarily mean that the devices built using them will be cost-effective; there is much to consider here. To see through the confusion and understand the reality, one needs to have membrane calculation software of their own. Only results obtained through one’s own design are truly reliable, and they prevent one from being misled by the apparent prices of membrane components. Biogas is a flammable and explosive gas; when designing such systems, not only technical specifications need to be taken into account, but safety also comes first. Many people overlook the issue of the explosion limit of exhaust gases, which creates ongoing safety hazards during the operation of the device. Some designs, in an effort to achieve aesthetics, are made in container-style form, ignoring ventilation and exhaust within the containers, which can also pose safety hazards. There are many more tips related to membrane-based biogas purification technology, but they won’t all be listed here. Those who are interested can get in touch with me. My email address is: wanghai@bgas.com.cn.