1 The method of air separation
The methods of air separation can be divided into two types: low temperature and non-low temperature, among which the methods of non-low temperature air separation include adsorption, membrane separation and chemical separation. Because the low temperature separation method has an irreplaceable competitive advantage in the aspect of large-scale production of oxygen and nitrogen liquid products, especially high-purity products, and only the low temperature separation method can produce rare gas products such as argon at the same time, so the low temperature separation method plays a very important role in the industrial application of air separation. Variable Pressure absorption method was developed successfully in the late 1950s S. Due to its unique advantages of flexibility and convenience, low investment and low energy consumption, in recent years, the oxygen-enriched technology of variable pressure adsorption air separation has been applied more and more in the field of medium and small scale oxygen-enriched application. Membrane separation separation is a high-tech emerging abroad in 1980s S, which belongs to polymer materials science, and it is one of the ten new science and technology industries in the 21st century. Although this technology started late, it developed rapidly.
2 The current situation of cooling and air separation equipment in China
The global industrial gas market is monopolized by seven multinational gas companies. In 2001, the market shares of each company were respectively AL (France liquefied air company) accounting for 18%, BOC14 %, Praxair 13%, ap 11%, linde/AGA (German Linde company) 10%, Japan acid (NSC) 5%, Messer (Mailer) 4%, others 25%.
After decades of development, China's air separation equipment manufacturing industry has formed a tripartite confrontation of Hangzhou Hangyang Co., Ltd., Sichuan air separation equipment (Group) Co., Ltd. and Kaifeng Air separation Group Co., Ltd. In addition, some multinational companies such as France Air France and Linde have established joint ventures or sole proprietorship air separation equipment manufacturing enterprises in China, which has added new strength to the development of China Air separation equipment manufacturing enterprises. At the end of 2004, Hangzhou Hangyang signed a joint promotion and development agreement with the German Messel group, which made the manufacture of air separation plant in our country hopeful to challenge the world monopoly market.
In the field of air separation plant manufacturing, there is at least a ten-year gap between domestic enterprises and foreign advanced level. Large air separation plant is still the advantage of multinational gas companies. With the rapid development of China's economy, iron and steel, Petrifaction and chemical industry are even more unconventional. The growth rate of industrial gases is 12% ~ 15%. For this purpose, more than 100 sets of large air separation plants have been introduced, and Baosteel has also introduced 72000 m3/H air separation equipment. However, domestic enterprises have received very few orders, and the 52000 m designed and manufactured by Hangzhou Hangyang Co., Ltd.3/H air separation plant represents the highest level in China.
3 Low temperature air separation process
Low-temperature separation of air use the multi-tower low-temperature rectification process to produce high-purity products of oxygen, nitrogen and argon from the compressed air. Compressed air passes through the molecular sieve adsorber to remove the impurities contained, including water, CO2, Hydrocarbon, etc. Then it is cooled to low temperature through heat exchanger, and can be separated into oxygen, nitrogen, argon and other products in the distillation column. The cooling required by the unit is made by compressed air or compressed nitrogen expansion.
According to the pressure method of gas products, the low temperature separation process of air can be divided into two types: external compression and internal compression. In the external compression process, the temperature of the pneumatic product produced by the air separation unit is close to the ambient temperature. Because its pressure is only a little higher than that of the atmospheric pressure, it needs to be compressed to the pressure required by users through the compressor. In the internal compression process, the liquid pump is used to press the product liquid from the distillation tower, and then it is sent into the steam exchanger and the air separation unit after reheating. The process of using the liquid pump to pump the product liquid to the pressure required by users is the whole internal compression process; the process of lifting the product liquid pressure to a middle pressure in the device is the partial internal compression process, this process can reduce the compression series of centrifugal compressor.
4 Technical development of low temperature separation of air in China
With the rapid development of science and technology, the low temperature separation technology of air has achieved great development. The early development mainly focused on the improvement of product extraction rate, the purification of raw material air, the improvement of Heat Exchanger efficiency, the optimization control of the unit, the improvement of compressor and expansion machine efficiency, etc. The recent development focuses on the use of stuffing distillation column, the use of molecular sieve adsorber for air purification, computer simulation and control, the improvement of mechanical efficiency of unit equipment, etc.
In 1998, Hangzhou Hangyang Group developed the air separation technology with the core of regulating stuffing on the tower and fully rectifying argon production. In 2000, Hangyang Enterprise successfully designed and manufactured a set of "1600" internal compressed air separation equipment of Yunnan Copper Industry with completely independent intellectual property rights. These technologies have reached the modern international advanced level. Hangyang is the 52000 m manufactured by Henan Zhongyuan Dahua Group3/H air separation plant is an air separation plant with maximum internal compression process designed and manufactured independently in China at present. It adopts the internal compression process of oxygen and nitrogen pumps with air pressurization and air expansion into the tower, that is to say, the pressurized air compressor + liquid oxygen (nitrogen) pump is adopted and the oxygen (nitrogen) compressor is replaced by the reasonable organization of heat exchanger system, and the process of air purification by molecular sieve and argon production by full rectification is adopted. According to users' needs, we can choose the best process which is safe, reliable, economical and reasonable. The whole set of equipment has the remarkable features of advanced design parameters, mature technology, good operation reliability, convenient operation, low energy consumption, high safety, etc.
In recent years. Under the guidance of technology innovation strategy, China's air separation technology has made great progress, which not only consolidates the domestic middle-end market, but also gradually enters the high-end market to compete with foreign big companies. In December 2003, Hangzhou Hangyang company won the bidding for two sets of "48000" compressed air separation project contracts of Sinopec Hubei chemical fertilizer and Anqing branch, breaking the monopoly of foreign companies. In 2004, Hangzhou Hangyang won the bid of "52000" compressed air separation equipment of Henan Zhongyuan Dahua, making the manufacture of compressed air separation equipment within 50 thousand grade no longer belong to the patent of foreign companies. More and more domestic large-scale air separation plants are adopted by domestic petrochemical, chemical and steel users.
