The air separation plant is a large complex system, mainly composed of the following subsystems: power system, purification system, refrigeration system, heat exchange system, distillation system, product delivery system, liquid storage system and control system.
Power system: mainly refers to raw material air compressor.
The air separation plant separates air at low temperature to obtain oxygen, nitrogen and other products, which is essentially completed by energy conversion. The energy of the device is mainly input by the original air compressor. Therefore, most of the total energy consumption of air separation is the energy consumption of the original air compressor.
Purification system: it is composed of air pre cooling system (air cooling system) and molecular sieve purification system (purification system). The temperature of the compressed raw air is very high. The air precooling system can reduce the air temperature through contact heat transfer, and can wash the harmful impurities such as acid substances. The molecular sieve purification system further removes moisture, carbon dioxide, acetylene, propylene, propane and nitrous oxide in the air, which are harmful to the operation of the air separation unit.
Refrigeration system: the air separation unit adopts expansion refrigeration, and the refrigeration of the whole air separation unit strictly follows the classical refrigeration cycle. Generally speaking, the air separation refrigeration equipment only refers to the expander.
Heat exchange system: the heat balance of air separation unit is completed by refrigeration system and heat exchange system. With the development of technology, aluminum plate heat exchanger is the main heat exchanger at present.
The key point of the low temperature distillation system is to realize the separation equipment. Generally, high and low pressure two-stage distillation is used. It includes low pressure tower, medium pressure tower and condensing evaporator.
Product delivery system: oxygen and nitrogen produced by air separation unit need a certain pressure to meet the use of subsequent systems. As long as the compressor is composed of nitrogen and oxygen.
Liquid storage system: the air separation plant can produce some liquid oxygen, liquid nitrogen and other products into the liquid storage system for use when necessary. It can be composed of different specifications of storage tank, cryogenic liquid pump, evaporator, etc.
Control system: all large air separation plants adopt computer distributed control system, which can realize automatic control.