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General design requirements of large air separation equipment
2017-03-08863
Air separation equipment is a separation equipment which can liquefy, distill and filter air into oxygen, nitrogen and other useful gases. It is a complete set of equipment composed of a variety of machinery and equipment. The complete set of equipment includes: air filtration system, air compression system, air precooling system, molecular sieve purification system, fractionator system, full distillation hydrogen free argon production system, instrument control system, electric control system Systems, etc., often classified by air pressure. There are three kinds of commonly used ones: high pressure, medium pressure and low pressure. The following details the design and requirements of each air separation system.
I. the flowmeter needs temperature and pressure compensation because it is greatly affected by the change of atmospheric pressure.
II. Flowmeter: electromagnetic flowmeter is generally used for medium water, with allowable pressure loss of 5kpa and placed horizontally; orifice plate or Vespa is generally used for medium gas, with allowable pressure loss of 3kpa; the pressure loss of orifice plate is larger.
III. for air-cooled tower and water-cooled tower, the resistance of Bauer ring is generally 500-800pa per meter, generally 600Pa, the packing height of air-cooled tower is 12m (1 + 3 + 8), generally about 7.2kpa, and that of water-cooled tower is 7m, generally about 4.2kpa. The adsorber is generally 1.5m high, with a resistance of 5kpa per meter and a resistance of 7.5kpa. The resistance of regular packing per meter of operation is 20-25mmh2o, 5mmh20 for each tray, 90-100 trays for the upper tower, 4-5kpa for the upper tower, 25-26mmh2o for each sieve plate tower, and 60 trays for the lower tower, about 15kpa for the lower tower. 225 trays of crude argon tower, with resistance of 12kpa; 60 trays of refined argon tower, with packing of 12m high, with resistance of 2.5 to 3kpa. 10KPA of refined argon waste gas
IV. instrument air volume: instrument air during startup and shutdown: 500nm3 / h; pressure: 0.5MPa (g); dew point: - 30 ℃; dust content: ＜ 1 μ m ＜ 1mg / m3; oil content: ＜ 10mg / m3; organic content: ＜ 1 μ m; carbon impurities: ＜ 1mg / M3; note: instrument gas is provided by the user during startup and shutdown
V. the air entering the plate of the self pressurization process is wet air. The height of the liquid oxygen evaporator is required to be lower than the plate, and the inlet of the liquid air in the lower tower is lower than the outlet of the liquid oxygen evaporator from the liquid air, otherwise the liquid will accumulate. At the same time, the liquid inlet shall be provided with a gas seal, otherwise the throttle valve will be blocked
6. The shrinkage of aluminum pipe per meter is 3.8% at low temperature, and that of stainless steel is 2% at low temperature.
VII. Protection grade of motor, ip-x y, in which x-dustproof and y-waterproof. There are 0-6 levels of dustproof, 0-unprotected, 1-50mM diameter object, 2-12mm diameter object, 3-2.5mm diameter object, 4-1mm diameter object, 5-dustproof, a small amount of dust does not hinder the normal operation of electrical components, 6-absolute dustproof. There are 0-8 levels of waterproof, 0-unprotected, 1-anti dripping, 2-anti dripping at 15 ℃, 3-anti dripping, 4-anti splashing, 5-anti spraying, 6-anti wave, 7-anti flooding, 8-anti diving
VIII. External compression process
A. for the device without argon, the purity of oxygen decreases with the increase of the amount of expansion air entering the upper tower.
B. for the unit with argon, with the increase of expansion air volume into the tower (partial bypass), oxygen is more than argon (the purity of oxygen extracted from argon becomes higher), and with the decrease of expansion air volume, argon is more than oxygen; it is recommended that expansion air accounts for 7-10% of the total air volume, when it is less than 7%, oxygen purity becomes worse, more than 10%, and argon gas volume sharply decreases.
C. the expansion air double extraction port of the main heat exchanger, when the liquid production volume is large, the extraction temperature in the expansion air is low, the liquid production volume is small, and the middle extraction temperature is high, which is mainly to meet the heat exchange above the middle extraction section.
D. when the liquid volume is small, the extraction temperature in expansion is higher, which can reduce the expansion air, and the large amount of expansion air is harmful to the distillation oxygen production. Generally 165K, superheated after expansion 15-20K
E. when the liquid volume accounts for less than 8% of the oxygen volume, if the domestic product cannot meet the requirements, it shall be imported. 8-11% shall be divided into two parts from the booster end of the expander; 11-15% shall be increased by small booster, with the discharge pressure of 14barg, divided into two parts.
F. for external compression, due to the total evaporation of liquid oxygen in the main cooling, the hydrocarbon concentration is high, and 1% of liquid oxygen is required to be discharged. For the self pressurization process, 1% of liquid oxygen at the bottom of the liquid oxygen evaporator is discharged, and the liquid oxygen spray evaporator is set.
G. due to the low-pressure expansion mechanism used in the external compression process, the refrigeration capacity is weak. It is generally recommended that the temperature difference at the hot end of the heat exchanger be 3k, 2.5k, not too large.
IX. internal compression process
A. without argon or with argon device, the purity of oxygen decreases with the increase of nitrogen extraction from the lower tower; with argon (or synergist) is conducive to improving the purity of oxygen, and at the same time, pumping a stream of waste liquid nitrogen from the lower tower is beneficial to argon extraction and oxygen, saving energy consumption.
B. the internal pressure is limited by the liquid volume behind the low-temperature expander. Generally, the middle extraction temperature is fixed. The increase or decrease of flow rate is used to increase or decrease the cooling capacity to see whether the cooling capacity is balanced.
C. the temperature difference at the hot end of the internal compression process is recommended to be 4-7k. When the pressure is low, the temperature difference at the hot end is smaller. When the pressure is high, the temperature difference at the hot end is larger, which is beneficial to heat exchange.
D. for large-scale air separation units with more than 40000 units and large expansion capacity, it is recommended to use high-temperature expander. The expansion air enters the main heat exchanger for cooling and then enters the lower tower, so as to reduce the irreversible loss of the heat section of the heat exchanger and save energy consumption.
E. the larger the liquid volume behind the expander is, the lower the energy consumption is. 0-10% can save about 2% of the energy consumption. Generally, 3-7% is recommended, and 8-12% is recommended for foreign operation devices.
F. there is an optimal pressure point for supercharged air under supercritical pressure, and an optimal pressure area for supercharged air above supercritical pressure. The final stage discharge pressure should be related to the unit investment, so as to prevent the increase of investment caused by machine span.
G. if there is any condition, for many pressure levels
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