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Study on interlock control of air separation unit in internal compression process
2017-04-241192
Since the 21st century, China's air separation equipment industry has produced nearly 1000 sets of large and medium-sized air separation equipment, of which the external compressed air separation equipment is generally used in the metallurgical (steel and non-ferrous) industry; the internal compressed air separation equipment is generally used in the chemical industry (represented by the coal chemical industry to methanol dimethyl ether, synthetic ammonia, coal to natural gas and coal to methanol); the high-purity nitrogen device is generally used in the petrochemical industry and manufacturing In recent years, the paper, glass, lithium battery and other industries, as well as the organization and application of three tower distillation low-purity oxygen technology, high-purity oxygen nitrogen gas and rare gas total extraction process, have made rapid development, making China's air separation technology to a new higher stage.
The instrument and control system of air separation equipment is very important for a set of air separation equipment, even the key to the success of an air separation equipment. At the same time, the advanced instrument and control system is also the symbol of modern air separation equipment. At present, China's air separation equipment has jumped to the scale of 120000-150000 after 50-60 years of development from the early hundreds of the people's Republic of China, and the gap with foreign countries has been further narrowed. The I & C system is also upgraded rapidly, including large-scale air separation I & C system, such as PLC (programmable control system), DCS (Advanced Distributed Control System), ESD (emergency stop system technology), ALC (automatic load change technology), FCS (field bus control technology), SIS (safety instrument system), MMS (vibration protection system), ITCC (compressor unit integrated control system) And the extensive application of CCS (compressor unit coordinated control system) and so on, also signifies that the advanced nature of air separation equipment in China is heading for the international first-class level.
Generally, a set of air separation equipment consists of process system, instrument control system and electric control system. The design of instrument control system is based on the principle of reliability, practicality, advancement and high cost performance. The instrument control system adopts the control principle of combination of distributed control system (DCS), local instrument control and local instrument control, i.e. field instrument + DCS control system. Each unit of the complete air separation equipment includes each unit, such as air compressor, precooling system, purification system, fractionator system, oxygen compressor, nitrogen compressor, liquid storage system, and the utility measurement points of the air separation unit all adopt a set of DCS system to monitor, control and interlock the process parameters.
For each system of air separation unit: air filter system, self-cleaning air filter is equipped with automatic control system, which can automatically reverse blow at fixed time and adjust the program according to the resistance of filter; precooling system, chilled water pump and cooling water pump are domestic reliable products, which are all one in use and one for standby, to ensure the reliability of the unit; purification system, which adopts long cycle, The double bed purification and switching system adopts impact free switching control technology. The switching system adopts DCS automatic control, and is equipped with automatic judgment of pressure difference, and then cooperates with valve position feedback signal. It can fully ensure the reliability of the switching system. The imported valves with similar positive and negative flow capacity and good regulation performance are used for the pressure equalizing to ensure the relative stability of the working conditions during the regeneration process of the device. The rectification system and low-temperature liquid pump are imported famous brand products, one for use and one for standby, one for operation and the other for low-speed operation. If the operating pump fails, the standby pump is 15-20 The workload is automatically reached within seconds. The waste nitrogen vent valve is pre opened to prevent "pressure holding" on the tower.
If all the talents in the world are used by me, then the world will be owned by me. The United States is a country which has been founded for more than 200 years. It has developed rapidly in a short time and become a global superpower. It is precisely because of the origin of this idea. If domestic enterprises want to have a place in the current international competition of industry, they must vigorously carry forward the spirit of overcoming difficulties and striving for success; they must further emancipate their minds, break the shackles and allow them to do so to a greater extent; they must actively innovate, accelerate their development and growth, and make contributions to the development and progress of science and technology in the world.
Enterprise innovation is generally divided into three stages, the first stage is to catch up with and learn foreign advanced technology, and the second stage is to compete with foreign leading enterprises. The third stage is to surpass foreign leading enterprises and make contributions to the world's scientific and technological progress. Nowadays, many equipment manufacturing enterprises in China have made some achievements. There is no doubt that by the middle of the 21st century, China will become the three major innovation centers in the world with Europe and the United States. Therefore, domestic enterprises must be confident in innovation and boldly release their talent advantages.
Gas industry is a new industry in China. At present, the annual marketing of Linde and Air France, the world's leading enterprises, has reached 10 billion euros, and that of American air chemical industry and Praxair has reached 10 billion dollars. Now, although China's air separation technology has reached the world's advanced level, China's gas industry is relatively weak compared with Europe and the United States, and it needs to be vigorously developed.
The process parameters in the instrument control system of air separation plant generally include: temperature, pressure, flow, liquid level and analysis instrument. According to experience, they are generally classified as follows: local and remote instruments according to operation requirements; control valves and cut-off valves according to control requirements; pneumatic, electric and hydraulic instruments (less used) according to energy consumption of instruments; analog meters and digital instruments according to instrument signals; in-line and on-line instruments according to installation position of instruments.
The reasonable setting of the instrument interlocking control system can not only meet the requirements of the process system, but also make the whole air separation unit run more safely and reliably, which is particularly important for the design of the air separation system. In recent years
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