Large air separation FAQ

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.

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

The air separation column mainly includes main heat exchanger, liquefier, distillation column, condensing evaporator, etc. The main heat exchanger, condensing evaporator and liquefier are plate type of heat exchangers. It is a new type of all aluminum metal composite partition heat exchanger. The average temperature difference is small, and the heat exchange efficiency is as high as 98-99%. Distillation column is the unit of air separation. The types of column unit are classified according to the internal parts. The sieve plate column with sieve plate, the bubble cap column with bubble cap plate, and the packed column with packing material. The sieve plate is widely used in air separation distillation column because of its simple structure, easy manufacture and high efficiency. Packed column is mainly used for distillation column with diameter less than 0.8m and height less than 7m. Bubble column is seldom used because of its complicated structure and difficult manufacture. Turbine

Special pressure-bearing equipment generally bears internal pressure, that will cause tensile stress inside the shell, which is called working stress. The working stress is directly proportional to the pressure and diameter, and inversely proportional to the vessel wall thickness. The axial stress is half of the circumferential stress. Therefore, for cylindrical vessels, the stress of longitudinal weld is twice that of girth weld. Because the geometric shape of the spherical shell is symmetrical to the spherical center, and the axial stress is equal to the circumferential stress in numerical value. Therefore, the wall thickness of the spherical vessel can be reduced by half as much as that of the cylindrical vessel under the same pressure and diameter.

When the air separation unit is in normal operation, the liquid flows down and can only flow on the tray and flow to the lower tray through the overflow bucket because the supporting force of the rising steam prevents the liquid from flowing down from the small hole of the tray. After shutdown, due to the interruption of rising gas flow, the liquid on the tray can flow from the overflow bucket to the lower tray, and also can flow through the small hole on the tray to the lower tray. This will cause the surface of liquid oxygen and liquid air rise, which may exceed the position of the expansion air outlet pipe, resulting in liquid carrying accident of the expander during restart. Therefore, pay attention to the liquid level position when stopping.

The plant operation cycle between two large heating is related to many factors. From an operational point of view, this mainly depends on when the air passage of the main heat exchanger is blocked. The main reason for the blockage is that the moisture and carbon dioxide content in the air entering the unit exceeds the standard, which accumulates and freezes in the main heat exchanger until it is blocked. The abnormal operation of molecular sieve purification system will shorten the operation cycle of the unit. It is mainly caused by the following reasons: 1. The molecular sieve adsorption bed is short circuited. In the process of operation, due to the unstable gas velocity control or switching, the pressure difference between the two tanks is too large, which will affect the bed layer, make the molecular sieve bed uneven and make the bed layer short circuit. In serious cases, the dust screen of the adsorber will break and the molecular sieve powder will enter the heat exchanger c

Screw compressor is a positive displacement compressor from the mechanical type, which is composed of the driving rotor and driven rotor, the main body and a pair of synchronous gears. Therefore, the common faults of screw compressor are as follows: 1. The bearing is burnt out. Because of the foreign matter in the oil system, the oil pressure and the quality of the oil are reduced, resulting in the bearing burning out. The main treatment methods are: check the oil supply system; clean the oil filter and the cooling pipe of the oil cooler; check and adjust the oil pressure regulating valve; test the oil quality, and replace the oil when it is not good; check and deal with the oil leakage points. 2. The rotor is burnt out. When foreign matters enter into the compressed medium system, the temperature of the rotor rises, the temperature of the cooling oil of the rotor increases due to the high temperature of the inhaled medium, and the compression ratio increases, which may cause the

1. Before connecting the pipe orifice of each container, clean white cloth shall be used to tie the orifice to prevent grease and dirt from entering. 2. When welding in the cold box and in the condensing evaporator, it is strictly forbidden for flame or arc to touch the surface of vessels and pipes. 3. The containers, valves, pipes and corresponding supports in the cold box, the surface of the cold box and the foundation surface shall not be stained with grease after installation, otherwise, degreasing treatment shall be carried out.

Air cooling column is a mixed heat exchange device. The function is to make the cooling water fully contact with the air and being mixed fully to increase the heat transfer area and enhance the heat transfer, usually using "packed column" or "sieve plate". The packed column is a round steel container with packing (ceramic ring, plastic ring, etc.). Cooling water is ejected from the top of the column and mixed with air flowing upward from the bottom for heat and mass exchange. Air transfers heat to the cooling water, lowering its temperature and raising its temperature. In order to prevent the generation of water droplets in the air, the raschig ring (or stainless steel wire mesh) packing separator (also known as trapping layer) and mechanical water separator (inertial separation) are usually installed on the upper part of the column. The cooling water ejected from the spray device flows downward to the packing layer through the distributor, and an overflow ring is provided to redist

All low pressure air separation units are usually equipped with nitrogen water precoolers. It mainly uses the unsaturation of nitrogen in sewage to evaporate part of water. As the water evaporates, it absorbs the latent heat of vaporization to lower the temperature of the cooling water, which is then used to cool the treated air and lower the temperature of the air entering the column. Therefore, it includes air cooling column and water cooling column. The basic purpose of setting up nitrogen precooler is to reduce the air temperature entering the air separation column and avoid the temperature fluctuation greatly. Because the inlet air temperature directly affects the operation conditions of the switching heat ex-changer and distillation column, as well as the economy of the whole air separation unit. In the design, the air temperature entering the column is usually set at 30 ° C. When the inlet temperature of the column is higher than the design index during operation, the throttl

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