Basic knowledge of air separation plant

air A mixture of gases present at the Earth's surface. The density of air close to the ground is 1.29kg/m3 under standard conditions. The main components are oxygen, nitrogen and argon; By volume, oxygen, nitrogen and argon account for 20.95 percent, 78.09 percent and 0.932 percent, respectively. In addition, it also contains trace amounts of hydrogen and other rare gases such as neon, helium, krypton and xenon. According to different regional conditions, it also contains unquantified carbon dioxide, water vapor and acetylene.

feed air is the raw gas used to separate gases and make liquids.

Molecular formula O2, molecular weight 31.9988 (according to 1979 international atomic weight), colorless, odorless gas. Under the standard condition, the density is 1.429kg/m3, the melting point is 54.75K, and the boiling point is 90.17K at 101.325kPa. Very active chemical properties, is a strong oxygen agent. It doesn't burn, it helps.

industrial process oxygen made by air separation equipment, the oxygen content (volume ratio) is generally less than 98%.

gaseous oxygen for industrial use was prepared from gaseous air separation equipment, with the oxygen content (volume ratio) greater than or equal to 99.2%.

oxygen made in an air separation equipment with an oxygen content (volume ratio) greater than or equal to 99.995%.

nitrogen nitrogen formula N2, molecular weight 28.0134 (according to the 1979 international atomic weight), is a colorless, odorless, inert gas. The density under standard condition is 1.251kg/m3, the melting point is 63.29K, and the boiling point is 77.35K under the power of 101.325kPa. Chemical properties are not active, can not burn, is a kind of asphyxiating gas.

gaseous nitrogen for industry was obtained from industrial gaseous nitrogen using an air separation device, the nitrogen content (volume ratio) was greater than or equal to 98.5%.

nitrogen collected on pure nitrogen nitrogen separation equipment, whose nitrogen retention amount (volume ratio) was greater than or equal to 99.995%.

nitrogen collected by air separation equipment was purity nitrogen, whose nitrogen retention (volume ratio) was greater than or equal to 99.9995%.

liquid oxygen(liquefied oxygen) is the oxygen that is in the liquid state of liquefied oxygen. It is a sky-blue, transparent, and liquid that can flow easily. The boiling point at 101.325kPa is 90.17K and the density is 1140kg/m3. It can be made liquid by air separation equipment at low temperature or liquefied by gaseous oxygen.

liquid nitrogen(liqued nitrogen) nitrogen in a liquid state, is a transparent and easily flowing liquid. The boiling point is 77.35K and the density is 810kg/m3 at 101.325kPa pressure. Low temperature can be used
Method Using air separation equipment to prepare liquid nitrogen or gas nitrogen to liquefy.

liquid air(liquefied air) is the air that is in the liquid state of liquefied. It is light blue, liquid that can flow easily. The boiling point at 101.325kPa is 78.8K and the density is 873kg/m3. Liquid air is an intermediate product in the process of air separation.

oxgen-enriched liquid air refers to liquid air with oxygen content (volume ratio) exceeding 20.95%.

liquid nitrogen fraction extracted at an appropriate position in the lower column with a nitrogen content (volume ratio) generally of 95% to 96%.

nitrogen waste nitrogen liquid, generally 95%~96% in nitrogen content (volume ratio), extracted from the upper column.

normal state refers to the gas state when the temperature is 0°C and the pressure is 101.325kPa.
The process of separating its components from air for the production of oxygen and nitrogen and the extraction of gases such as argon, neon, helium, krypton, and xenon.

throttling The throttling fluid expands through a sharp hole without effort or pressure reduction.

throttling effect(Joule-Thomsoneffect) Throttling effect(Joule-Thomsoneffect) Temperature change caused by gas expansion without work.

The pressure of the expansion fluid decreases while the volume increases.
isentropic expansion effect Temperature change due to pressure change of a gas during isentropic expansion.

The process of adiabatic expansion of air in the expansion machine and external work at the same time.

nitrogen expansion A process of adiabatic expansion of nitrogen in the expansion machine and external work at the same time.

A gas liquefaction cycle based on high-pressure throttling expansion, characterized by both liquefaction and freezing of the circulating gas.

high pressure liquefaction cycle with expander (Heyland cycle) Gas liquefaction cycle that works in combination with expansion and throttle expansion, Its characteristic is that the gas state of the expander inlet is high pressure and normal temperature.

medium pressure liquefaction cycle with expander (Claude cycle) A gas liquefaction cycle that isused in combination with expansion and throttling expansion for workforces, Its characteristic is that the gas state of the expander inlet is medium pressure and low temperature.

low pressure liquefaction cycle with expander(Kapitza cycle) Gas liquefaction cycle in which adiabatic expansion and throttle expansion work together, It is characterized by low pressure and low temperature of the gas inlet of the expander.

The stirling cycle is a theoretical thermodynamic cycle consisting of two isothermal and two isovolumic processes. The whole cycle is completed by isothermal compression, isovolumic cooling, isothermal expansion and isovolumic heating.
A flow of low-temperature backflow gas is entered at the cold end of the switching heat exchanger (or regenerator) to reduce the temperature difference at the cold end to ensure the non-freezing of the switching handle.

In the switching channel of switching heat exchangers (or recoolers), the ability of the back flow gas to bring carbon dioxide and water out of each section per unit time is greater than the value of the forward flow air to bring carbon dioxide and water through the section. Make the switching heat exchanger (or regenerator) air channel is not blocked by carbon dioxide, water freezing.

sublimation is a phase transformation process that sublimates directly from solid phase to vapor phase.

Process by which carbon dioxide and moisture in the air are frozen on the surface of the channel and blown back out of the facility by the backflow gas in the next cycle. It consists of two stages: freezing and clearing.

temperature difference refers to the temperature difference between hot and cold fluids when heat is transferred between two surfaces or between two environments.

warm end temperature difference refers to the warm end temperature difference between hot and cold fluids at the hot end of the heat exchanger.

The middle portion temperature difference between hot and cold fluids in the heat exchanger.

cold end temperature difference refers to the temperature difference between hot and cold fluids at the cold end of the heat exchanger.

Part of the liquid oxygen is drawn out from the bottom of the condensing evaporator and flows through the adsorber. After removing the hydrocarbons in this part of the liquid oxygen, the liquid oxygen is returned to the condensing evaporator.

expanded air to upper column(Lachman air) expanded air to upper column(Lachman air)
Part OF the air is extracted from the bottom of the lower tower, reheated by the cold section of the switching heat exchanger, and is directly sent to the upper tower for rectification after thermal expansion of the turbine expansion mechanism.

vapour ratio The ratio of fluid vapour vapour to vapour vapour vapour in a rectifying tower.

The steam opening speed was too high in the rectifying tower, which prevented the liquid flooding.

A condition in which liquid leaks from sieve plates due to low rising steam velocity in a sieve plate rectification tower.

Using the adsorption process of pressure effect in the adsorption-regeneration operation cycle, adsorption under higher pressure and regeneration under lower pressure (or negative pressure).

cold loss caused by the temperature difference between a device and the surrounding medium operating at a temperature lower than the ambient temperature.

The temperature difference between the hot and cold fluids at the hot end of the heat exchanger exists in the cold loss carsed by insufficient patients to warm up, which results in the incomplete recovery of cold volume.

refrigeration capacity refers to the refrigeration capacity loss in refrigeration of air separation equipment due to refrigeration loss and insufficient reheating loss.

recovery rate Ratio of the total content of the gas component of the product to the stingy content of the component in the processed air.

specific power consumption refers to the electrical energy consumed by air separation equipment to produce gas per unit of product.

Normal operating pressure greater than or equal to 1.0MPa process flow.

Normal operation pressure greater than 1.0MPa to less than or equal to 5.0MPa process flow.

Normal operation pressure greater than 5.0MPa process

high pressure process combined with low pressure process.

With low voltage switch heat exchanger process low pressure process with reversing heat exchangers switch heat exchanger is used to remove moisture and carbon dioxide in the air of low pressure process.

Wateractivated low pressure process with molecular sieve adsorber to remove water and carbon dioxide and hydrocarbons in the air.

air separation plant is a complete set of equipment that uses air as raw material and uses low temperature technology to separate air into oxygen, nitrogen, argon and other rare gases.