Large air separation FAQ

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

The amount of liquid nitrogen removed from the lower column of the air separation unit will affect the purity of the liquid nitrogen in the lower column and the oxygen enriched liquid air at the bottom of the column. When the liquid nitrogen removal amount of the lower column increases, the reflux liquid participating in the heat and mass exchange of the lower column will be reduced, the temperature rise of the rising steam on the column plate will be correspondingly reduced, the condensation of the rising steam will not be sufficient, the oxygen component will be condensed less, the purity of nitrogen at the column top will be reduced, and the purity of liquid nitrogen will be naturally reduced. At the same time, the temperature rise of the downflow liquid will increase, the liquid evaporation will be more sufficient, more nitrogen components will be evaporated to the top of the column, and the purity of the liquid air at the bottom of the column will be improved accordingly.

Lean alloy steel is often used in special pressure-bearing equipment. The alloying elements often added include manganese, silicon, chromium, nickel, molybdenum, vanadium, boron and rare earth elements. Most of silicon and manganese melt into ferrite, only a small amount into cementite, which are commonly used strengthening elements in lean alloy steel. The amount of chromium and nickel is generally small, and the main role of chromium and nickel is to increase the undercooling degree of austenite and refine the microstructure. Part of chromium is dissolved in ferrite and some in cementite, which can improve the stability of cementite. Molybdenum is dissolved in ferrite slightly, and has the effect of solid solution strengthening. It is a strong carbide forming element, which can improve the high temperature strength of steel and improve the temper brittleness.

Cryogenic air separation nitrogen production uses air as raw material, which is compressed, purified and heat exchanged to liquefy gas air into liquid air. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. Liquid oxygen and liquid nitrogen have different boiling points and are separated by distillation to obtain nitrogen. 1. Air compression and purification The air passes through the air strainer to remove dust and mechanical impurities, then enters the air compressor, compresses to the required pressure, and then goes to the air cooler to reduce the air temperature. It then enters the air drying purifier to remove moisture, carbon dioxide, acetylene and other hydrocarbons from the air. 2. Air separation The purified air enters the main heat exchanger in the air separation column, and is cooled to the saturation temperature by the reflux gas (production nitrogen gas, waste gas), and is sent to the bottom of the distillation column. The nitrogen is obtained fr