The oxygen and nitrogen products produced by the air separation unit in the external compression process are low-pressure oxygen and nitrogen from the upper column, which are sent out of the cold box after being reheated by the heat exchanger. The product gas pressure out of the cold box is generally 0.12MPa. After being compressed to the pressure required by the user by the oxygen compressor, it is sent to the user’s pipeline.
The internal compression process of oxygen is that liquid oxygen products are directly extracted from the condensing evaporator, compressed to the user's required pressure by the liquid oxygen pump in the cold box, and then sent to the user's pipeline after reheating and gasification by the heat exchanger.
Compared with the external compression process, the internal compression process of liquid oxygen has the following characteristics:
1.There is noneed to configure the oxygen compressor, only need to configure the liquid oxygen pump. Compared with the oxygen compressor, the liquid oxygen pump has the advantages of small volume, simple structure and low cost.
2.Due to the continuous discharge of large amount of liquid oxygen from the condensing evaporator, hydrocarbons are not easy to accumulate in the condenser evaporator, which is conducive to the safe operation of the equipment. The safety factor of compressed liquid oxygen is greater than that of compressed gaseous oxygen.
3.Due to the high pressure of liquid oxygen reheating and gasification, the oxygen channel of heat exchanger is required to have higher pressure bearing performance, so the cost of heat exchanger in internal compression process is correspondingly increased.
4.The cooling capacity of liquid oxygen gasification in internal compression process is sufficient, and the cold loss is relatively large.In order to keep the balance of cooling capacity, high pressure of raw air is required, which increases the energy consumption of air compressor.
Compared with the comprehensive process, the internal compression process of liquid oxygen has higher safety and reliability. With the application of frequency conversion liquid oxygen pump, the flow regulation of nitrogen and oxygen is more flexible, and the purity of the product is also higher.
