Generally, rivers, lakes or groundwater are used as cooling water for air separation units. This kind of water usually contains suspended solids (sediment and other pollutants) and bicarbonates such as calcium and magnesium [- Ca (HCO3) 2 and Mg (HCO3) 2], which is called hard water. When there are many suspended solids, it is easy to block the channels, filters and valves of the cooler. Calcium, magnesium and other bicarbonates are easy to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitates when the water temperature rises, that is to say scale. Generally, water temperature above 45 ℃ will start to form scale, and the higher the water temperature is, the easier it is to scale.Water cooling tower is a kind of hybrid heat exchanger. The cooling water with higher temperature (about 35 ℃) from the air cooling tower flows downward from the top spray, and the sewage nitrogen with lower temperature (about 27 ℃) from the switching heat exchanger flows from bottom to top. The two are in direct contact, which is a complex heat transfer process with heat and mass transfer.
When the temperature of sewage nitrogen in the cold end is reduced, the temperature difference in the hot end will be enlarged, so that the insufficient reheating will increase the cold loss, the expansion will increase, and the product quantity will decrease; liquid hammer may occur, and the automatic valve will be easily damaged. In a word, air liquefaction at the cold end is harmful but not beneficial, and the expansion of temperature difference at the cold end is the most harmful.Air separation plant.In the distillation column, because N2O is a high boiling point component relative to N2, O2 and AR components, it will be dissolved in liquid oxygen, resulting in the inability to obtain high purity liquid oxygen and gaseous oxygen products at the bottom of the upper column. According to the determination, when the purity of oxygen product is 99.5%, the average content of N2O is 1.4 × 10-5. Moreover, when the liquid oxygen is not discharged sufficiently, N2O accumulates continuously in the liquid oxygen. When the N2O content in the liquid oxygen is more than 50 × 10-6, it will precipitate as a solid state and block the main condenser evaporator channel.
The determination of the operation cycle of air separation unit is mainly based on the time interval when the trace carbon dioxide is gradually accumulated after it is brought into the air separation tower until it cannot continue to operate due to blockage. Under normal conditions, the continuous operation time of the full low pressure oxygen generator should be more than one year, and the continuous operation time of the new molecular sieve adsorption process can be more than two years.After the air compressor stopped automatically, the pressure in the air cooling tower decreased, and when the air compressor was started again, the molecular sieve purifier water inflow accident occurred. The reason is that the automatic regulating valve of water level and the check valve of backwater system are out of order. When the air compressor stops automatically, the check valve from the air inlet of the air cooling tower to the outlet of the air compressor is full of water, and the air compressor starts again.
Air separation plant.In the aspect of metal smelting, oxygen and argon blowing is an important measure to produce high-quality steel. The argon consumption per ton of steel is 1-3m3. In addition, argon is also needed in the smelting of special metals such as titanium, zirconium and germanium, and in the electronic industry.When the resistance of a group or a unit increases, the middle temperature should be controlled slightly lower to reduce the temperature difference at the cold end. But this kind of adjustment method can only be used when the resistance increases little, and can only be eliminated under the condition of long-term operation. It can also be eliminated by short-term parking and back blowing. If the resistance is too large, it can only be stopped for heating treatment.If the nitrogen content of the argon fraction is too much, the purity of the crude argon will be reduced, and the temperature difference of the crude argon condenser will be reduced, or even zero, and the crude argon tower will stop working. Moreover, too much nitrogen in the crude argon will bring difficulties to the production of refined argon, so the argon fraction should be located in the place with as little nitrogen as possible.
