The oxygen and nitrogen products produced by the general air separation unit come from the low pressure oxygen and nitrogen bodies of the upper tower, and come out of the air separation cold box after reheating by the heat exchanger, and the absolute pressure is about 0.12MPa. Then the oxygen compressor compresses it to the required pressure (3.1MPa) and supplies it to users. The internal compression process of liquid oxygen is to extract the liquid oxygen product from the condensing evaporator, compress it to the required pressure (about 3.1MPa) through the liquid oxygen pump, and then reheat it through the heat exchanger and supply it to users after gasification. That is, it is compressed to the required pressure in the cold box. Compared with the original process, it has the following features:
1) no oxygen compressor is needed. The power consumed by compressing the liquid to the same pressure is much smaller than compressing the same amount of gas. Moreover, the volume of the liquid oxygen pump is small, the structure is simple, and the cost is much cheaper than that of the oxygen compressor.
2) liquid oxygen compression is safer than air oxygen compression.
3) because a large amount of liquid oxygen is continuously discharged from the main cooling, the hydrocarbon is not easy to be concentrated in the main cooling, which is conducive to the safe operation of the equipment.
4) due to the high pressure of reheating liquid oxygen and gasification, the Oxygen channel of the heat exchanger needs to bear high pressure. Therefore, the cost of the heat exchanger will
Improved than the original process. In addition, the safety of the strength of the heat exchanger should be fully considered in the design.
5) the cooling capacity of liquid oxygen gasification is sufficient, and the temperature difference at the hot end of the heat exchanger is relatively large, that is, the cooling loss is relatively large. In order to maintain the balance of cooling capacity, the pressure of raw material air is required to be higher, the energy consumption of air compressor has increased.
Generally speaking, the increased energy consumption of air compressor is roughly equal to the reduced energy consumption of liquid oxygen pump, or slightly increased. Equipment costs are roughly the same, or slightly reduced. But in terms of security and reliability, the internal compression process has its advantages. With the application of variable frequency liquid pump, the adjustment of the flow of oxygen and nitrogen of the product is very flexible, and the purity stability of the product is also relatively good, which is a process widely used internationally at present.
