Internal compression air separation equipment: the internal compression process air separation is to cancel the oxygen press, extract liquid oxygen from the main condensation evaporator of the rectification tower, pressurize through the liquid oxygen pump, and then heat the high-pressure air with liquid oxygen, so that it is vaporized out of the cold box as a product gas.

Hot spots of internal compression air separation equipment: 1. Safety and economy; 2. High automation control; 3. Small footprint.

What is the external compression process, the internal compression process
The external compression process is the production of low-pressure oxygen by the air separation equipment, and then pressurized by the oxygen press to the required pressure to the user, also known as conventional air separation.
The internal compression process is to cancel the oxygen press and directly produce medium-high pressure oxygen to the user from the shunt tower of the air separation equipment.
The main difference between the two is that the oxygen supply pressure of the product oxygen is reached by the liquid oxygen in the cold box through the liquid oxygen pump, and the liquid oxygen is heated in the high pressure plate fin heat exchanger and the high pressure air to vaporize and recover heat.
Compared with the external compression process, the main technical changes in the internal compression process are in two parts: rectification and heat transfer. In the external compression process, the air separation is directly generated by the rectification tower and then reheated by the main heat exchanger to the cold box. The internal compression process air separation is the extraction of liquid oxygen from the main condensing evaporator of the rectification tower, and then pressurized by the liquid oxygen pump to the required pressure, and then a high-pressure air and liquid oxygen heat exchange, so that it is vaporized out of the cold box as a product gas. It can be simply considered that the internal compression process is to replace the oxygen press of the external compression process with a liquid oxygen pump and an air booster.

The application of internal compression process technology in the industry mainly has the following three factors:
(1) Security considerations, in theory, the safety of the internal compression process is higher, and the safety requirements of the air separation industry are very high.
(2) The cost of the liquid oxygen pump required by the internal compression process and the air booster is correspondingly much lower; Oxygen press in the design and manufacturing need to consider more safety factors, the price is very expensive.
(3) The internal compression process is convenient for pipeline gas supply, and gas companies usually sell a large number of liquid products while operating on-site gas supply business.

Principle and application of internal and external compression in cryogenic air separation

The principle of internal compression is that because the cryogenic air separation lists strict physical laws, the compression process is completed internally by a piston with a certain control system, so the cost of internal compression is relatively low, but also easier to control and maintain. The external compression needs to be completed by centrifugal compression or axial flow compressor, and its cost is relatively higher, but it also has a high compression efficiency, which can accelerate the compression process of air, and also improve the production efficiency and purity of deep cooling air separation.

What are the configuration of the external compression process of the air separation device

According to the oxygen requirements, the configuration of the external compression process of the air separation unit supporting the metallurgical and chemical industries is as follows:

1, air compressor and filter system: the use of domestic or imported machines with domestic self-cleaning filter;

2, nitrogen water pre-cooling system: make full use of the cold capacity of dry nitrogen, reduce the temperature of chilled water, cancel the chiller (or with a spare chiller);

3, purification system: the use of electric heating or steam heating, automatic switching; Using molecular sieve + alumina bunk bed structure, prolong the life of molecular sieve;

4, refrigeration system: 2 sets of domestic expansion machine, 1 use 1 standby;

5, heat exchange system: domestic low pressure plate;

6. Main rectification system: sieve plate lower tower or packing lower tower, regular packing upper tower, plate-fin multilayer or falling film main cooling;

7, argon production system: structured packed argon tower, full rectification of three towers to produce argon;

8, pressure oxygen system: domestic oxygen penetration or oxygen piston;

9, nitrogen pressure system: nitrogen penetration or nitrogen piston;

10, instrument control system: domestic or imported DCS.

The advantages of external compression process: low supporting requirements, low price of supporting units or valves, and less investment.

The difference between internal compression devices and external compression devices

1. Different spatial layout: the internal compression equipment is installed inside the air separation equipment, which covers a small area, directly compressors the gas, and the process is simple; The external compression device is usually installed outside the air separation device and occupies large space and device configuration.
2. The compression medium is different: the internal compression device directly compresses the gas, while the external compression device requires the use of lubricating oil and other media to assist compression, which may have limitations on the compression of some gases.
3. Different pressure ranges: The pressure range of the internal compression equipment is usually limited by the pressure of the location and is limited to a certain extent; External compression equipment is not subject to such limitations, and appropriate exhaust can be carried out when the pressure reaches a certain range.
4. Different functions and uses: internal compression equipment is usually installed in the air separation equipment, used to compress oxygen, nitrogen, rare gases, etc., widely used; External compression equipment is not only used for air separation, but also widely used in petrochemical, steel, fertilizer and other industries.

Advantages and disadvantages of the two devices

1. Advantages of internal compression equipment: small footprint, simple equipment structure, relatively low price, easy operation, moderate pressure range.
2. Disadvantages of internal compression equipment: gas purity has more strict requirements, compression power is relatively small, pressure and flow fluctuation.
3. The advantages of external compression equipment: good stability, large range of pressure and flow, flexible operation, and wide range of adaptation.
4. Disadvantages of external compression equipment: large area, complex equipment, high price, need to be equipped with lubricating oil and other auxiliary equipment.

The selection of air separation equipment in the metallurgical industry

The requirement for oxygen pressure in the metallurgical industry is usually between 2.0 and 3.0 MPa, which can be achieved by internal compression process air separation equipment or external compression process air separation equipment.
At present, a typical process in domestically manufactured internal compression process air separation equipment is the process of expanding air into the lower tower. Its characteristics are: firstly, it is suitable for producing large liquid volumes, and secondly, the extraction rate of argon is high.
Nowadays, in the domestic metallurgical industry, all users who order internal compression process air separation equipment choose this process, and these users have the same demand: they need a large amount of liquid products to operate gas sales business while meeting production needs.
At the same time, another advantage of this process is that it requires less land, and the raw material air compressor and air booster can be combined into an integrated machine.
For some parts that have not considered gas sales business, it is very reasonable to choose conventional external compression process air separation equipment.

The selection of air separation equipment in the chemical industry

The chemical (petrochemical) industry generally requires much higher oxygen pressure than steelmaking, usually between 4.0MPa and 9.0MPa, and the required oxygen production scale is also very large, often exceeding 30000. In this way, air separation equipment using internal compression process is the only choice. Moreover, due to the complex product structure of chemical type air separation equipment, it is required to produce multiple pressure levels of oxygen and nitrogen products simultaneously. Therefore, multiple schemes need to be compared according to specific requirements, such as using single pump or dual pump internal compression, air circulation or nitrogen circulation, etc. The best scheme must follow the principle of the optimal combination of one-time investment cost and long-term operating cost.
Of course, if the customer’s requirements for air separation equipment are not too complex, similar to metallurgical air separation equipment, then the usual internal compression process or external compression process can be considered.