Wang Qian explained the principle of membrane dehumidification and introduced the type and shape of membrane materials. The application of membrane dehumidification technology in the field of compressed air drying and air conditioning (full heat recovery, air dehumidification) is reviewed.
-), female, Nanchang, Jiangxi, professor, master, mainly engaged in teaching and research and engineering design work in air conditioning and refrigeration.
Membrane separation technology is a new separation technology, which uses selective permeation membrane as separation medium. Under the action of driving force (such as pressure difference, concentration difference, temperature difference) on both sides of the membrane, the components on the raw material side are selective. Through the membrane, separation and purification are realized. It has the advantages of convenient operation, high separation efficiency and low energy consumption. It is widely used in the fields of water treatment, organic solvent mixture separation and gas separation. H. Dehumidification of air conditioning system The energy consumption is large, and the application of membrane dehumidification technology is expected to reduce the dehumidification energy consumption of the air conditioning system. This paper reviews the application of membrane dehumidification technology in the field of compressed air drying and air conditioning.
1 membrane dehumidification principle For a specific membrane material, the water vapor transmission rate is at least two orders of magnitude higher than nitrogen, oxygen, etc. The membrane dehumidification technology utilizes this characteristic of water vapor, so that the humid air passes through the membrane surface, the water vapor The gas enters the permeate side and the other gases are impermeable, so that the water vapor is separated from the dry air. On the permeate side, if the infiltrated water vapor cannot be removed in time, due to the hydrophilicity of the membrane material, the water molecules will easily accumulate on the permeate side, causing the subsequent permeation rate to decrease, resulting in a sharp drop in dehumidification performance (ie, production of rich Differential polarization phenomenon, generally can use the purge, vacuum method to solve the concentration polarization problem. 0. The purge method can be divided into external purge, self-purge. The external purge is to remove part of the dry air after treatment as the purge gas, and remove the water vapor on the permeate side; the self-purge is to adjust the porosity of the membrane, so that a small part of the dry air also permeates through the membrane to the permeate side, and penetrates. The dry air acts as a purge gas to remove the water vapor from the permeate side, ensuring continuous infiltration. The vacuuming method means that the water vapor is removed by vacuuming on the permeate side. Of course, a combination of purging and vacuuming can also be used to solve the concentration polarization problem. Taking the hollow fiber tube membrane as an example, the principle of various methods for solving the concentration polarization problem can be seen in the wet air hollow fiber tube membrane wet air hollow fiber tube membrane water vapor J water vapor purge gas | | purge gas dry air | wet air h empty fiber tube membrane vacuum steam vacuum vacuum steam drying air There is no doubt that membrane material is the core of membrane dehumidification technology, excellent membrane material should have high separation factor, strong corrosion resistance, good flexibility, high mechanical strength Long service life, reasonable cost and easy industrial production. According to the physical structure and chemical properties of the membrane, the membrane can be divided into microporous membrane, homogeneous membrane and composite membrane: 1 microporous membrane is a loose structure membrane with a pore size range of 3100 nm, and the separation principle is similar to the traditional filtration mechanism. That is, the filtration effect is determined by the particle size of the material to be filtered and the pore size of the membrane, and the diameter of the water molecules is about. 4nm, it is easy to pass through the microporous membrane. 2 Homogeneous membrane is also called dense membrane, its pore diameter is generally below 1.5nm, the structure is very tight, and its separation effect depends on the diffusion coefficient and solubility of the component in the membrane. The homogeneous membrane can be divided into two types: symmetric membrane and asymmetric membrane: the cross-sectional structure of the symmetric membrane is the same; the asymmetric membrane is different, generally the lower layer is a porous bottom layer, and the upper layer is a dense skin layer. 3 composite membrane is a thin layer (thickness about 0.2pm), dense and special active membrane layer on the porous support layer. The separation characteristics of the composite membrane are mainly determined by the active membrane layer, and the porous support layer only plays a supporting role. .
According to the material, it can be divided into inorganic film and organic film. The inorganic film includes a ceramic film, a metal film, a glass film, a molecular sieve composite film, a zeolite film, etc., although the inorganic film has advantages of high temperature resistance, organic solvent resistance, acid and alkali resistance, antimicrobial corrosion resistance, rigidity, and mechanical strength, The filling density, manufacturing cost and industrial application penetration rate have yet to be improved and improved. Therefore, the membranes used in the current membrane dehumidification technology are mainly organic membranes. There are many organic materials that can be formed into a film. Generally, they are polymer materials with special mass transfer functions. The main types are cellulose and its derivatives, polysulfones, polyamides, polyimides and other categories. Among them, polysulfone membrane materials have developed rapidly in recent years and have become one of the most widely used polymer membrane materials in modern industry. Its advantages are good mechanical properties, stable chemical properties, corrosion resistance and high temperature, making up for the tradition. Most of the organic film is not resistant to high temperature, acid and alkali, and is often used as a porous support layer of the composite film. The polysulfone membrane material has a low surface free energy and a large water contact angle, which is characterized by strong hydrophobicity. Xing Danmin et al. conducted an experimental study on the dehumidification performance of polysulfone hollow fiber tube membrane and sulfonated polysulfone-polysulfone composite hollow fiber tube membrane. It is considered that polysulfone hollow fiber tube membrane is suitable for medium-demand air dehumidification conditions, using sulphur. The polysulfone-polysulfone composite hollow fiber tube membrane can significantly improve the dehumidification performance of the membrane.
When preparing the film, in addition to the solvent and the film material, the casting agent may also have additives or other modified substances, and the mass fraction of the film material, the added U, the modified substance and the like, and the total amount of the casting agent is called Solid content. Ma Wenbao et al. studied the effect of solid content on the moisture permeability of polysulfone membrane materials and proposed a method to improve its moisture permeability. Zhang Xinru et al. considered the complexity of the asymmetric membrane manufacturing process and was not conducive to industrial production. The wet film formation method was used to test the moisture permeability of the asymmetric membrane prepared by the process, and the layers (porous bottom layer and cortex) were carried out. Analysis of mass transfer resistance. Wang Hongda et al. conducted a comprehensive discussion on the mechanism of membrane moisture permeability and the research progress of membranes.
There are two basic forms of the membrane: flat plate, hollow fiber tube.
The flat membrane has a simple structure, small flow resistance and simple preparation process. The hollow fiber tube membrane is tubular, and the preparation process is relatively complicated. Compared with the flat membrane, the membrane has the advantages of simple assembly membrane, large specific surface area and good reproducibility. The hollow fiber tube membrane module has a high packing density, and the 0.3 m3 hollow fiber tube membrane module can provide an effective membrane area of ​​500 m2, while the flat membrane module under the same conditions is only 20 m2. In foreign countries, the membrane dehumidification technology is in the field of compressed air drying. Has entered the industrial application era, widely used in medical compressed air, valves and pneumatic machine gas, communication cable pressurization process gas, instrument test experimental gas, mining equipment compressed air, ozone gas machine raw material gas, ship supply Gas, nuclear power station gas, clean air for car painting.
The structure of the compressed air dryer using the hollow fiber tube membrane is shown in Fig. 0. The hollow fiber tube membrane module is filled in the dryer, and the structure is similar to the tube heat exchanger. The wet compressed air enters the hollow fiber tube membrane from one end of the dryer. The water vapor permeates outside the hollow fiber tube membrane and is finally discharged into the atmosphere. The condensed water accumulates at the bottom of the dryer and is finally discharged. The dry compressed air is output from the other end of the dryer. .
Water vapor is an inflator made by ANDREW with a membrane dryer as a drying device, with a treatment capacity of 56.6 L/min and a dry air (product gas) dew point of -45 ft. More than 5,000 sets of Prism membrane dryers from Permea are used worldwide to remove moisture from compressed air using hollow fiber membranes. The treatment range is 1 3000m3/h, the dehydration rate is over 99%, and the dry air dew point is -40 feet. Under certain conditions of compressed air pressure, the lower the dehydration rate, the larger the flow rate of dry air obtained; the higher the pressure of compressed air, the higher the flow rate of dry air obtained. The compressed air membrane dryer developed by the 71st Research Institute of China Shipbuilding Industry Corporation can work under the conditions of inlet temperature of -1050 °C, inlet pressure of 20700 kPa and ambient temperature of -10 50 °C. Dry air dew point reaches -40 body loss ratio is 040%, noise is less than 45dB. Many scholars have studied the application of membrane dehumidification technology in air conditioning field. Full heat exchanger is one of the important directions, and it has entered the practical stage. In the air conditioning system, in order to ensure indoor air quality, it is necessary to introduce a certain amount of fresh air, and also to discharge part of the indoor air out of the room. Since the fresh air load accounts for a large proportion of the air conditioning system load, the heat recovery method is an effective means to reduce the energy consumption of the fresh air treatment and effectively utilize the exhaust energy. Because the summer fresh air is hot and humid, and the air is cooled at a low temperature, the use of a full heat exchanger can achieve better energy saving than the use of a sensible heat exchanger. Due to the limitation of civil construction space, the exhaust air (heat) recovery generally adopts a plate type or plate-fin type full heat exchanger instead of a rotary type full heat exchanger. The plate full heat exchanger is mainly composed of a heat exchange material, a corrugated corrugated paper support structure and a frame, and the most important component affecting the total heat exchange efficiency is a heat exchange material. For a long time, heat and mass exchange materials have generally been specially treated papers with moisture absorption and heat transfer characteristics.
With the development of membrane technology, people began to apply membrane materials as heat exchange materials to total heat exchangers.
Research was carried out, mathematical models were established and experimental verification was carried out. JLNm et al. established a thermal mass transfer model of the membrane and defined a new dimensionless number, which makes the analysis of the hot-humid coupled membrane total heat exchanger easier. LZZhang et al. studied the energy conservation of membrane heat exchangers under the hot and humid conditions in Hong Kong. Yin Ping selected a membrane with a pore diameter of less than 2 nm and a thickness of 3050|xm, which has good water vapor permeability. It is compounded on a fiber material with strong moisture permeability, good heat transfer effect and certain strength (as a support layer). The corrugated corrugated paper support structure was abolished, and the material thickness and aperture of the support layer were optimized several times to determine the combined form, and the full heat exchange efficiency and suitability of the membrane total heat exchanger using the novel membrane were suitable. Oncoming wind speed, resistance, leak rate, etc. were measured.
Wang Huiyong et al. studied the heat and mass transfer performance of a membrane-based total heat exchanger based on a hydrophilic-hydrophobic composite membrane, and established a heat and mass transfer calculation model for the countercurrent membrane heat exchanger. The experimental results agree well with the theoretical results. . Liang Caihang et al. used the membrane total heat exchanger for the refrigeration dehumidifier, and studied the dehumidification capacity of the outdoor air temperature, relative humidity and flow rate to the refrigeration dehumidifier under the conditions of indoor dry bulb temperature of 27 feet and wet bulb temperature of 19 feet. The effect of the coefficient of refrigeration performance. Compared with the traditional refrigeration dehumidifier, the dehumidification and refrigeration performance coefficients of the refrigeration dehumidifier equipped with the membrane total heat exchanger are 3.2 times and 1.8 times that of the conventional refrigeration dehumidifier, respectively.
In the field of air conditioning, the conventional dehumidification methods include cooling and dehumidification, moisture dehumidifying agent dehumidification, solid adsorption dehumidification, and the like. For the application of membrane dehumidification technology in air dehumidification of air conditioning systems, many methods currently studied include membrane-hygroscopic method, recirculating membrane contactor method, membrane wet pump method, and purge-vacuum combination method.
The membrane-hygroscopic method means that the wet air to be treated flows on one side of the membrane, and the moisture absorbent flows on the other side. Since only water vapor can permeate through the membrane, the method can dehumidify the air without The phenomenon that tiny droplets caused by the direct spray of air from the moisture absorbent enters the treated air is generated, and the dehumidifying device used in the membrane-hygroscopic method is a membrane contactor (see). The membrane-hygroscopic method has a better dehumidifying effect and avoids the problem of entrainment of the moisture absorbent. However, like the conventional method for dehumidifying the moisture absorbent, the hygroscopic agent also has a problem of reduced concentration and regeneration after moisture absorption.
In order to solve the problem of membrane-hygroscopic hygroscopic agent regeneration and continuous dehumidification, scholars have proposed a recycling membrane contactor method. For the working principle, the regeneration gas can be indoor return air or dry air. The dehumidification method is still a membrane-hygroscopic method, but a regenerative membrane contactor is provided in the system to regenerate the diluted moisture absorbent so that the moisture absorbent circulates in the two membrane contactors. V.Usachov et al. used triethylene glycol as a moisture absorbent to conduct an experimental study on an air conditioning system equipped with a recirculating membrane contactor. Under the dehumidification and regeneration temperature difference of less than 30, the dew point was -30 °C. Dry air.
S. Bergem et al. combine a recirculating membrane contactor process with a compression chiller to form an all-air air conditioning system (see). The mixed wind of fresh air and return air is dehumidified by the dehumidifying membrane contactor and sent to the air conditioning area. The lithium chloride solution as a moisture absorbent is cooled by the evaporator and then enters the dehumidifying membrane contactor to absorb the moisture in the mixed air, and the diluted lithium chloride is used. The solution flows into the liquid tank, and the upper lithium chloride dilute solution is then taken out by the solution circulation pump 9 and preheated by the economizer to enter the condenser. After further heating, the lithium chloride dilute solution is transferred to the fresh air and the exhaust air in the regenerative membrane contactor. The mixed air, the concentrated lithium chloride concentrated solution is divided into two parts, one part is sent to the liquid tank after being cooled by the economizer, and the other part is mixed with the dilute lithium chloride solution (adjusting the concentration of the lithium chloride solution entering the regenerative membrane contactor) After entering the condenser, the three-way valve acts to regulate the flow. The simulation calculation shows that the energy saving effect of the system is obvious.
The method of obtaining a 10% purge ratio (the amount of sweeping air accounts for the amount of dry air) combined with vacuuming can greatly improve the dehumidification performance of the membrane contactor.
See the air treatment system combined with surface cooler and hydrophobic surface cooler. The fresh air is dried by hollow fiber tube membranes, then cooled by an indirect surface cooler, and finally cooled and controlled by relative humidity using a hydrophobic surface cooler.
Compared with the application of the hydration cold water circulation pump in the total heat exchanger, the research on membrane dehumidification technology in air dehumidification is still far away from the practical application. This is mainly due to the application of membrane dehumidification technology to air dehumidification, which has certain difficulties in mass transfer driving force. Membrane dehumidification technology can be widely used in the field of compressed air drying. Thanks to compressed air, a certain pressure difference can be established on both sides of the membrane. However, in the air conditioning field, the treated air is basically atmospheric pressure, and it is impossible to boost the air. Process it. If the permeation side vacuuming method is adopted, the vacuum pump must consume electric energy, and the sealing of the membrane contactor is very high.
In some places with special requirements, membrane dehumidification technology also has application space. Taking the environmental control requirements of aircraft flight cabins as an example, with the continuous improvement of aviation technology level, the number of various electronic devices in the aircraft is increasing, the humidity control of the environment is becoming more and more important, and the high-humidity environment will reduce the electronic equipment. The reliability will also reduce the efficiency of the refrigeration equipment. At present, many advanced aircraft in the world use high-pressure water-removing environmental control systems. The key components of air removal are air condensers (condensing moisture in the air) and high-pressure water separators. The high-pressure water separators are mainly centrifugal. Water separation, the tangential velocity is obtained after the airflow passes through the cyclone, and the rotating flow field is formed in the separation section. 7j membrane dehumidification is an emerging dehumidification technology, which has many unique advantages compared with the traditional dehumidification method. The field of air conditioning has a good development and application prospects. Although membrane dehumidification technology still has shortcomings such as narrow dehumidification application, small scale and high cost, with the deepening of membrane technology research and integration with other technologies, membrane dehumidification technology will surely become more in air conditioning and other fields. development of.
Wang Baoguo, Lu Hongling, Yang Yi. The application of membrane separation technology in the petrochemical industry. Petrochemical, 2006 (8): 705-710. Zhang Qi, Tang Weihua, Zhang Longlong. Membrane dehumidification technology in gas drying Wang Yong, Wang Hongru. Research progress on polysulfone separation membrane materials and their modification Xing Danmin, Cao Yiming, Xu Renxian. Study on air dehumidification by polysulfone hollow fiber membrane method. Membrane Science and Technology, 1997 (2): 38-42, 63. Ma Wenbao, Zhang Lizhi. Effect of solid content on the moisture permeability of polysulfone membranes Zhang Xinru, Zhang Lizhi, Yan Lixia. Mass transfer performance of asymmetric dehumidification membranes Wang Hongda, Zhang Lizhi. The moisture permeability mechanism of the moisture permeable membrane and the research overview of the membrane. Refrigeration and Air Conditioning and Electric Machinery, 2002 (2): 28 Wang Baoguo, Jiang Weiwei. Research status and development of hollow fiber membranes U. Yan Wancheng. Cartes membrane air dehumidification new technology ZHANG Yinping. Development of a new type of plate heat exchanger - product development and real Wang Huiyong, Lu Yuanwei, Ma Chongfang. Experimental study on factors affecting heat transfer efficiency of membrane type full heat exchanger DG. Building thermal ventilation and air conditioning, 2008 Zhang Yan, Zhang Lizhi, Xiang Hui, et al. Heat exchange and heat exchange performance of total heat exchanger based on hydrophilic-hydrophobic composite membrane. Journal of Chemical Industry and Engineering, 2007(2): 294-298, Liang Caihang, Zhang Lizhi. Experimental study on refrigeration dehumidifier based on membrane heat recovery DO. Chemical Journal, 2012 Dong Juntao, Zhang Lizhi. The principle and research progress of membrane air conditioning dehumidification Zhang Lizhi, Wang Hongda. The application of membranes in air dehumidification - pressure dehumidification and wet pumps. Refrigeration and Air Conditioning and Electric Machinery, 2002 (3): 7-M Li National, Li Junfeng, Liu Jingzhi, and so on. Elimination of concentration polarization to improve the dehumidification efficiency of membrane modules C0. Chemical Industry and Engineering Technology, 2007 (1): 37-39. 3 Yuan Weixing, Yuan Xiuqian. A new high-pressure dehumidification aircraft environmental control system using membrane modules//a large-scale aircraft key technology high-level forum and the Proceedings of the 2007 Annual Conference of the Chinese Aviation Society. Shenzhen: China M Yuan Satellite, Wang Chenjie, Li Yunxiang. Simulation study of a new environmental control system for aircraft based on membrane dehumidification. Journal of Aeronautics, 2011 (4): 589-597. 5 Ding Cheng, Liu Shuzi. Research on Atmospheric Environmental Membrane Dehumidification Technology in Submarine Cabin//The 6th National Conference on Human-Machine-Environment System Engineering
R417a Refrigerant is a cost-effective, non-ozone-depleting HFC retrofit refrigerant in direct expansion stationary air conditioning and medium-temperature commercial refrigeration systems. it can Replace R22 directly.
R417a Freon Gas Features:
Boiling Point(1ATMS): -41.8o
CDensity(25oC) kg/m3: 1152
ODP: 0
Critical temperature(K): 363.1
Critical pressure Pisa: 615
Flammability: No
Advantages:safe ,save energy and protect environment
R417a Refrigerant, also known as ISCEON® MO59, is an HFC retrofit refrigerant for R22 in direct expansion stationary air conditioning (AC) and medium temperature commercial refrigeration systems.
High purity refrigerant gas r417a with good price
R417a Refrigerant
R417a Refrigerant,R417a Gas,R417a Freon Gas
QuZhou Bingcool Refrigerant Manufacture Co.,LTD , https://www.refrigerant-supplier.com