Learn air separation plant basic system and principle

What is an air separation plant?

Air separation equipment is a device that uses air as raw material, converts the air into liquid state by means of compression cycle deep freezing, and then gradually separates it from liquid air to produce inert gases such as oxygen, nitrogen and argon through rectification.

Air separation unit purification principle

In the equipment that uses the principle of low temperature rectification to produce oxygen, in order to ensure the normal rectification and separation of air in the low temperature area, the air must be filtered, pre-cooled and purified in the normal temperature area.

There is a lot of dust in the air. During the long-term high-speed operation of the air turbine compressor (air compressor), the dust will cause wear, corrosion and scaling of the impeller, blades and other parts inside the machine, shorten the service life of the machine, Therefore, a raw material air filter must be installed to remove dust from the air.

The temperature of the air compressed by the air turbine compressor rises to more than 80 degrees, which causes the subsequent adsorption and heat exchange to not proceed normally. By setting up an air pre-cooling system, the air temperature entering the air separation plant can be effectively reduced.

In addition to a large amount of dust in the raw air, there are also hydrocarbons such as moisture, carbon dioxide, and acetylene. Most modern air separation plants use molecular sieve purification systems to remove these impurities to improve the cleanliness of the air entering the cold box and prevent moisture. And carbon dioxide concentration threatens the normal operation of the air separation plant. Therefore, gas filtration, pre-cooling and purification equipment is an indispensable part of the air separation plant.

Air separation unit air products basic system

Air separation plant is a large and complex system, mainly composed of the following subsystems: power system, purification system, refrigeration system, heat exchange system, rectification system, product delivery system, liquid storage system and control system, etc.

1. Power system

Mainly refers to the raw material air compressor. The air separation plant separates the air at low temperature to obtain oxygen, nitrogen and other products, which is essentially completed through energy conversion. The energy of the device is mainly input by the raw air compressor. Correspondingly, most of the total energy consumption required for air separation is the energy consumption of the raw air compressor.

2. Purification system

It consists of air pre-cooling system (air cooling system) and molecular sieve purification system (purification system). The compressed raw air has a high temperature, and the air pre-cooling system reduces the temperature of the air through contact heat exchange, and at the same time can wash the harmful impurities such as acidic substances. The molecular sieve purification system further removes moisture, carbon dioxide, acetylene, propylene, propane and nitrous oxide in the air and other substances that are harmful to the operation of the air separation plant.

3. Refrigeration system

The air separation plant is refrigerated by expansion, and the refrigeration of the entire air separation plant strictly follows the classic refrigeration cycle. However, the air separation refrigeration equipment usually mentioned mainly refers to: the expander.

4. Heat Exchange System

The heat balance of the air separation plant is accomplished through the refrigeration system and the heat exchange system. With the development of technology, heat exchangers mainly use aluminum plate-fin heat exchangers.

5. Rectification system

The core of the air separation plant is an important equipment for realizing low temperature separation. Usually high and low pressure two-stage rectification is adopted. It is mainly composed of low pressure column, medium pressure column and condensing evaporator.

6. Product delivery system

The oxygen and nitrogen produced by the air separation plant require a certain pressure to meet the use of the subsequent system. As long as it consists of oxygen compressors and nitrogen compressors of various specifications.

7. Liquid storage system

The air separation plant can produce certain products such as liquid oxygen and liquid nitrogen, and enter the liquid storage system for use when needed. As long as it is composed of storage tanks, cryogenic liquid pumps and vaporizers of various specifications.

Air separation plant can be divided into 5 basic systems in terms of process flow:

1. Purification system of impurities

It mainly purifies mechanical impurities, moisture, carbon dioxide, acetylene, etc. mixed in the air through devices such as air filters and molecular sieve absorbers.

2. Air cooling and liquefaction system

It is mainly composed of air compressor, heat exchanger, expander and air throttle valve, etc., which play the role of deep freezing of air.

3. Air distillation system

The main components are rectification tower (upper tower, lower tower), condensing evaporator, subcooler, liquid air and liquid nitrogen throttle valve. It plays the role of separating various components in the air.

4. Heating blowing system

The purification system is regenerated by heating and blowing off.

5. Instrument control system

The entire process is controlled by various instruments.