Large air separation FAQ

In the upper column fractionation, below the liquid air inlet is called the stripping section, and above the liquid air inlet is called the distillation section. The stripping section realizes the separation of oxygen and argon, and the distillation section realizes the separation of oxygen and nitrogen. Because the boiling points of oxygen and argon are relatively close, the separation is difficult. In order to ensure the purity of oxygen, the separation of oxygen in the distillation section is not clean, and argon escapes with oxygen and nitrogen. If high purity nitrogen is to be obtained, argon will condense with oxygen in the distillation section, which will affect the purity of oxygen. In order to ensure the purity of oxygen and obtain high purity nitrogen, it is necessary to extract part of the gas with high argon concentration in the distillation section.

Fluid resistance refers to the pressure drop of fluid flowing through pipes, valves or equipment. The actual process pressure gradually decreased. In order to ensure the final pressure required by the process, a pressure source (gas compressor or pump) is needed to provide higher pressure, that is, more energy is consumed. Therefore, the amount of resistance reflects the amount of energy loss. In oxygen production, flow resistance is also closely related to the production process. For example, the resistance measurement of switching heat exchanger is the basis to judge whether self-cleaning is good. If the resistance of the distillation column is too large, the normal distillation conditions will be destroyed. The magnitude of resistance (i.e. energy loss) can be expressed by the pressure drop before and after the fluid flows through the vessel. For example, the gauge pressure at the bottom of the tower is 0.038 MPa, the gauge pressure at the top of the tower is 0.025 MPa, and the p

In the process of operation, especially in the start-up and shutdown of the air separation unit, one-way force should be avoided on the instrument. During the start-up of the equipment, close the high pressure and low pressure valves firstly, then open the balance valve, and then slowly open the high pressure (or low pressure) valve, so that the measured medium can enter the positive (negative) pressure chamber of the transmitter. If the liquid is to be measured, the gas in the positive (negative) pressure chamber should be discharged from the upper vent. If the gas is measured, drain the liquid accumulated in the positive (negative) pressure chamber from the lower drain screw hole. After discharging the gas (liquid), close the balance valve, and then open the valve on the other side. When the equipment is shut down, the high pressure (or low pressure) valve should be closed first, then the balance valve should be opened, and then the valve should be closed on the other side. Someti

When the amount of treated air increases, the rising steam in the distillation column will increase, and the amount of liquid to be condensed in the main cooler will increase accordingly, so it has no effect on the reflux ratio in the column. The purity of oxygen and nitrogen remained unchanged in a certain range with the increase of gas volume, and the output increased proportionally with the increase of gas volume. However, with the increase of the amount of condensate in the main cooler, the heat load of the main cooler increases. When the heat transfer area is insufficient, the temperature difference of the main cooler will inevitably expand, and the pressure of the lower column will increase accordingly. At the same time, with the increase of gas velocity in the column, the amount of downflow liquid increases, and the liquid layer on the tray thickens, which increases the resistance of the tray and the pressure of the upper and lower columns. This will adversely affect the sepa

In the main column of the air separation column, the distribution of argon varies with the position of the liquid air inlet. With the increase of liquid air inlet position, the maximum concentration of argon enrichment zone in the stripping section also increases, and the nitrogen content in the distillate can be reduced. However, the argon content in the downstream also increases. In order to ensure the purity of oxygen, more trays are needed under the extraction port of argon fraction. Therefore, in the case of producing argon, the position of liquid air supply E1 should be appropriately increased compared with the case of not producing argon. Some unit is equipped with two liquid air inlet positions to meet the conditions of argon production and non argon production respectively. In the production of argon, in order to improve the extraction rate of argon, the content of argon in oxygen and nitrogen must be reduced. When the content of argon in exhaust nitrogen is more than 0.3%

There are 10 ways to transilluminate the welding seam of air separation unit, which are suitable for different occasions. Single wall is the most commonly used transilluminating method, but when the radiation source or film cannot enter the inside small diameter vessel and pipeline, double wall transilluminating method is adopted. The selection of transillumination method should consider all factors synthetically. For example, according to the principle of selecting the transillumination method which is beneficial and improves the sensitivity, single wall transillumination should be selected as far as possible. According to the principle which is conducive to the detection of corresponding defects, the outside radiation source is preferred for the detection of cracks on the inner wall of the container.

If the temperature after the expander of the air separation unit is too low, it should find out the cause of the low temperature and take measures to increase the temperature after the expander. If the low temperature of expander is caused by liquid air in front of expander, appropriate measures should be taken to reduce the liquid air level of lower column. If it is caused by other reasons, the more effective method is generally throttling in front of the expander. Throttling will not increase the temperature in front of the expander, but throttling will reduce the pressure in front of the expander, so the pressure difference between the front and the back of the expander will be reduced, the expander will do less work and the temperature will be reduced, so the temperature at the after of the expander can be increased.

1.The purpose of purging is to purge the welding slag and dirt left in the pipeline and container. 2.The principle of purging is doing the outside columnfirstly,and the inside column after. The purging should be carried out one pipeline by one. 3.When purging the system, the filter core on the equipment inlet pipe should be removed. 4.When purging the pipe outside the cold box, all the valves connected with the cold box should be disconnected to prevent dirt from entering the valve and column. 5.The purging of each system should be repeated for many times. The purging time shall not be less than 4 hours. 6.To check whether the purging is complete, wet white filter paper or white cloth shouldbe used to placeat the outlet of purging. After 5 minutes, it is qualified if it is clean and free of obvious mechanical impurities.

1.In the process of preparation and implementation of hoisting construction, the safety and quality assurance system must ensure the normal operation,to ensure that the hoisting project meets the requirements of safety and quality. Before hoisting, safety and quality inspection must be carried out, and it must comply with the code forLifting construction of chemical engineering construction (HG20201-2000) and other regulations and specifications. 2.The crane performance shall meet the requirements of hoisting process, and the alarm and hydraulic system must be reliable. 3.Strictly implement the provisions of the technical documents attached to the crane. 4.The hoisting schedule of auxiliary crane should match that of main crane. 5.The hook deflection angle shall not be greater than 3°. 6.It is forbidden to drag the unitdirectly on the ground with crane. 7.Before unithoisting, trial hoisting shall be carried out. The clear hoisting distance and the foundation change at

1.The cold box foundation is divided into frame type and non frame type. The levelness of top surface of frame type frame shall not exceed 1 / 1000. All sections of the frame shall be placed vertically. All bottom plates of non frame type cold box shall be kept at the same level, and the levelness shall not exceed 1 / 1000.   2.When installing the cold box plate, the adjacent two sides can beassembled into a whole piece or angle type on the ground. The length error of each diagonal line a...

When the amount of processing air is reduced, the rising steam and reflux liquid in the upper column will be reduced, but the reflux ratio will not change. Therefore, the reduction of processing air in a small range will not affect the purity of oxygen and nitrogen, and the reduction of processing air volume will help to reduce the pressure of the upper and lower columns. However, according to the material balance, the production of oxygen and nitrogen will naturally decrease when the amount of processing air is reduced. If the amount of processing air is too small, there will be leakage on the tray. If the heat and mass exchange of the leaked liquid is not sufficient, the purity of oxygen and nitrogen will be greatly affected, and even the normal production can not be realized. Therefore, the minimum allowable load of distillation column is generally specified.

Air separation unit is a kind of unit that takes air as raw material, transforms air into liquid by low temperature cryogenic method which compresses and circulates air, and then gradually separates oxygen, nitrogen, argon and other inert gases from liquid air by distillation. At present, the air separation unit produced in China has many forms and types. There are unit for the production of gaseous oxygen and nitrogen, as well as unit for the production of liquid oxygen and nitrogen. However, there are four types of basic processes: high pressure, medium pressure and low pressure, and full low pressure process. The production scale of air separation unit in China has developed from the original oxygen generator which can only produce 20m³/ h (oxygen) to the current large-scale air production capacity of 20000 m³/ h, 30000 m³/ h and 50000 m³/ h (oxygen). The air separation unit can be divided into 5 basic systems in terms of process 1. Impurity purification system: the mechani