Air separation plant information about basic system and application

Air separation plant working principle 

Cryogenic large-scale air separation equipment is referred to as "air separation equipment", which uses air as raw material, converts air into liquid state by means of compression cycle deep freezing, and then gradually separates it from liquid air through rectification to produce oxygen, nitrogen and Inert gases such as argon.

Air separation equipment is an important instrument and equipment used in the production and manufacturing process of the coal chemical industry and petrochemical industry. The difference in boiling point between the constituent gases in the air allows the liquefied substance to fully contact and react with the gas, and realize the separation of high-purity gases under the action of the principle of heat and mass exchange.

Air separation equipment basic system

Air separation plant is a large and complex system, mainly composed of power system, purification system, refrigeration system, heat exchange system, rectification system, product conveying system, liquid storage system, instrument and electrical control system and safety guarantee system.

1. Power system

It mainly refers to the raw 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. It is mainly composed 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. It is mainly composed of storage tanks of various specifications, cryogenic liquid pumps and vaporizers.

8. Control system

Large-scale air separation plants adopt computer distributed control system, which can realize automatic control.

Air separation plant application field

Because of its uniqueness, air separation equipment is widely used in various important national economic fields such as machinery, metallurgy, petrochemical, new coal chemical industry, building materials, aerospace and medical care.

For a long time, the main users of the air separation plant industry have been metallurgical enterprises, especially iron and steel enterprises. After 2010, the steel industry entered a period of structural adjustment, and demand slowed down. In recent years, policies have promoted the industrial integration of iron and steel enterprises, increased investment in technological transformation, eliminated outdated production capacity, improved industrial concentration and the effect of energy saving and emission reduction. Since 2014, the investment in fixed assets in my country's steel industry has continued to decrease, with an average annual decline of 9%. From 2010 to 2015, my country has eliminated a total of 240 million tons of backward steel production capacity, accounting for 20% of the crude steel production capacity in 2015.

The application of air separation equipment in the chemical industry is subdivided into coal chemical, petrochemical and fertilizer. my country's traditional coal chemical industry has entered a mature stage, and most of them are facing the pressure of overcapacity. Its main products include coke, calcium carbide, and methanol. Taking methanol as an example, the overall operating rate of methanol enterprises is mainly concentrated at 40-60%, while the new coal chemical industry represented by coal gasification and coal liquefaction is in its infancy and has a broad space for future development.

Elsewhere in the chemical industry, demand for air separation plants is stable. In the fertilizer industry, air separation equipment is mainly used for the production of nitrogen fertilizers, accounting for 65-70% of the fertilizer structure in my country. The main raw material of chemical fertilizer is synthetic ammonia. The development direction of my country's synthetic ammonia production mainly uses coal as the raw material. New coal gasification technology is used to build large-scale synthetic ammonia production enterprises, and small-scale high-energy consumption and high-polluting enterprises are eliminated. Coal gasification produces synthetic ammonia. First, pure oxygen is used as an oxidant to gasify coal to produce hydrogen. After the hydrogen reacts with pure nitrogen, synthetic ammonia is produced. Therefore, air filtration equipment is indispensable. The oxygen production capacity of the air separation equipment that needs to be configured for every 300,000 tons of synthetic ammonia annual production capacity is about 30,000 m³/h.

The petrochemical and chemical industry development plan points out that the nitrogen fertilizer industry should adjust the raw material and power structure, and develop low-rank coal such as bituminous coal and lignite to make fertilizers. It will also bring adjustments to the air separation plant.

In terms of petrochemicals, due to the continuous decline of oil prices in the past few years, the investment in fixed assets in the oil industry has been greatly reduced. At present, oil prices have slowly recovered, and the 2017 CAPEX announced by CNOOC has increased by about 30% compared with 2016, and the refining industry will grow. my country's ethylene production has also developed at a stable level in the past three years, and the overall demand for air separation equipment in the petrochemical industry is expected to grow steadily.