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The air separation unit is a set of air separation unit with pressurized turbine expander, which is used for absorption and purification of molecular sieve at normal temperature, and regulating the filling tower without hydrogen to produce argon. The technological process is as follows:
1 filtration, compression, precooling and purification
Raw material process air is inhaled through the suction inlet, enters into the self-cleaning air filter, filters out dust and mechanical impurities, enters into the centrifugal air compressor for compression, and the compressed air enters into the air cooling tower of the air precooling system, it is cooled and washed by water. The air cooling tower is cooled by circulating cooling water and low temperature chilled water cooled by water cooling tower and further cooled by ice machine. The top of the air cooling tower is equipped with inertia separator and screen separator to prevent free water in the process air from coming out.
The process air of the air precooling system enters into the air purification system which is used to absorb and remove water, carbon dioxide and hydrocarbon. The adsorber in the purification system is composed of two vertical containers, and the two adsorption containers adopt the double bed structure, the bottom is activated alumina, and the top is molecular sieve. When one is running, the other is regenerated after the nitrogen from the cold box is heated by the heater.
2 Air rectification
Most of the clean process air of the air purification system enters into the main heat exchanger in the cold box, and is cooled by the air flowing back. The air close to the dew point enters into the bottom of the lower tower and conducts the first distillation. In the distillation column, the rising gas fully contacts with the downstream liquid. After heat and mass transfer, the concentration of nitrogen in the rising gas gradually increases. In the evaporator of main condensing, nitrogen condenses and liquid oxygen gasification. The liquid space and liquid nitrogen produced in the lower tower will go into the upper tower after being cooled by the cooler and throttling. As the recirculation fluid of the upper tower, they will be rectified again in the upper tower, get product nitrogen, product oxygen, liquid oxygen and dirt nitrogen.
3 The preparation of cold volume
Most of the cooling capacity required by the unit is provided by the turbine expander. The rest part of the clean air of the air purification system enters into the booster driven by the turbine expander to increase its pressure. Then, the cooler is cooled down after pressurization, enters into the main heat exchanger in the cold box, and enters into the turbine expander after cooling to a certain temperature. This kind of inflated air enters the upper tower after expanding and refrigerating in the expansion machine, and participates in rectification.
4 purification of argon
The extraction of argon adopts the latest technology of whole rectification to produce argon. In order to produce argon, a stream of argon distillation gas is extracted from the proper position of the top and bottom of the distillation tower and sent to the crude argon Tower I for rectification, reduce the content of oxygen; the recirculation liquid of crude argon Tower I is liquid crude argon transported by the liquid pump from the bottom of crude argon Tower II. The gas coming out from the top of the crude argon Tower I enters the crude argon Tower II and conducts deep argon-oxygen separation in it. After the rectification of the crude argon Tower II, the crude argon gas with oxygen content ≤1ppm is obtained on the top of the crude argon Tower II, and the condensation evaporator is installed on the top of the crude argon Tower II, which is sent into the air as the cold source after the air flow from the supercooler is cut off, most of the crude argon gas is used as the recirculation fluid of the crude argon tower after condensation by the condensing evaporator. The rest part is extracted from the top of the crude argon Tower (the crude argon with oxygen content ≤1ppm) and sent to the refined argon tower. An evaporator is installed at the bottom of the refined argon tower, the medium-pressure nitrogen from the bottom of the tower below is used as heat source to make liquid argon evaporate, and the nitrogen is liquefied at the same time. A condenser is installed on the top of the refined argon tower. Liquid nitrogen extracted from the refined argon evaporator is used as the cold source to make most of the rising gas condense as the recirculation liquid of the refined argon tower. After being rectified by the refined argon tower, the 99.999% Ar liquid argon obtained from the bottom of the refined argon tower leads out the cold box as the product liquid argon.
5. Device design and technical features:
(1) adopt the whole low pressure process of molecular sieve adsorption, pressurized turbine expansion machine refrigeration, full rectification argon production, oxygen external compression process. Advanced process, mature technology, reliable operation, convenient operation, safety and low consumption.
(2) the precooling system uses nitrogen and dirty nitrogen to enter the water cooling tower to lower the temperature of cooling water, and the structure of the air cooling tower adopts reliable measures to prevent liquid flooding.
(3) Special structure is adopted for the channel of main condensing evaporator to prevent acetylene from gathering in liquid oxygen and ensure the safety of main condensing evaporator and system.
(4) the upper tower, the crude argon Tower and the refined argon Tower all adopt the structured packing tower.
(5) the device has the ability to change working condition and load, and the range of the device load capacity is 75% ~ 105%.
(6) DCS distributed control system is adopted.
