Key points of air separation technology

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Basic terms for air separation units in coal chemical industry 1. Air: A gas mixture present on the Earth’s surface. The density of air near the ground under standard conditions is 1.29 kg/m3. The main components are oxygen, nitrogen, and argon ； By volume, oxygen accounts for about 20.95%, nitrogen for about 78.09%, and argon for about 0.932%; in addition, trace amounts of hydrogen and rare gases such as neon, helium, krypton, and xenon are also present. Depending on regional conditions, it also contains variable amounts of carbon dioxide, water vapor, and hydrocarbons such as acetylene. 2. Process air refers to the raw air used for gas separation and liquid production. 3. Oxygen, with the molecular formula O2 and a molecular weight of 31.9988 (according to the 1979 International Atomic Weights), is a colorless and odorless gas. Its density at standard conditions is 1.429 kg/m3, the melting point is 54.75 K, and the boiling point at a pressure of 101.325 kPa is 90.17 K. It has extremely reactive chemical properties and is a strong oxidizing agent. It cannot burn, but it can support combustion. 4. Process oxygen for industrial use: Process oxygen intended for industrial use, produced by air separation equipment, generally has an oxygen content of less than 98%. (Volume ratio) 5. Industrial gaseous oxygen: Industrial gaseous oxygen produced by air separation equipment, with an oxygen content of 99.2% or higher. (Volume ratio) 6. High-purity oxygen: Oxygen produced by air separation equipment, with an oxygen content of 99.995% or higher (by volume ratio). 7. Nitrogen, with the molecular formula N2 and a molecular weight of 28.0134 (according to the 1979 International Atomic Weights), is a colorless, odorless inert gas. Its density under standard conditions is 1.251 kg/m³; its melting point is 63.29 K, and its boiling point at a pressure of 101.325 kPa is 77.35 K. It has inert chemical properties, does not burn, and is an asphyxiating gas. 8. Industrial gaseous nitrogen: Industrial gaseous nitrogen produced by air separation equipment, with a nitrogen content of 98.5% or more (on a volume basis). 9. Pure nitrogen: Nitrogen produced by air separation equipment, with a nitrogen content of 99.995% or higher (on a volume basis). 10. High-purity nitrogen: Nitrogen produced by air separation equipment, with a nitrogen content (on a volume basis) of 99.9995% or higher. 11. Liquid oxygen: Oxygen in a liquid state; it is sky-blue, transparent, and flows easily. At a pressure of 101.325 kPa, the boiling point is 90.17 K and the density is 1140 kg/m3. It can be produced using cryogenic air separation equipment to obtain a liquid form, or by liquefying gaseous oxygen. 12. Liquid nitrogen: Nitrogen in a liquid state; it is a transparent and easily flowable liquid. The boiling point at a pressure of 101.325 kPa is 77.35 K, and the density is 810 kg/m3. Liquid nitrogen can be produced using cryogenic air separation equipment, or by liquefying gaseous nitrogen. 13. Liquid air: Air in liquid form, a light blue, fluid liquid. The boiling point at a pressure of 101.325 kPa is 78.8 K, and the density is 873 kg/m3. Liquefied air is an intermediate product in the air separation process. 14. Oxygen-enriched liquid air refers to liquid air with an oxygen content of over 20.95% (by volume). 15. Fractionated liquid nitrogen (waste nitrogen) is a liquid drawn from an appropriate location in the lower column, with a nitrogen content of generally 95%~96% (on a volume basis). 16. Impure nitrogen: A gaseous substance drawn off from the upper part of the upper column; its nitrogen content is generally 95%–96% (by volume). 17. Standard state refers to the state of a gas at a temperature of 0°C and a pressure of 101.325 kPa. 18. Air separation: The process of separating the components of air to produce oxygen and nitrogen, as well as to extract gases such as argon, neon, helium, krypton, and xenon. 19. Throttling: The pressure of a fluid is reduced as it expands through a sharp orifice without doing work. 20. Throttling effect (Joule-Thomson effect): The temperature change that occurs when a gas expands without doing any work. 21. Expansion: The pressure of the fluid decreases while its volume increases. 22. Isentropic expansion effect: The temperature change that occurs in a gas during isentropic expansion due to pressure changes. 23. Air expansion: The process in which air expands adiabatically within an expander while doing work on the outside. 24. A throttling-based liquefaction cycle (Linde cycle): A gas liquefaction cycle that relies on high-pressure throttling expansion, characterized by the cycle gas being both liquefied and used for cooling. 25. High-pressure liquefaction cycle with an expander (Hyrland cycle): A cycle in which adiabatic expansion and throttling expansion are used together to liquefy gas, characterized by the gas at the inlet of the expander being in a high-pressure and normal-temperature state. 26. Medium-pressure liquefaction cycle with expander (Linde cycle): A cycle in which adiabatic expansion and throttling expansion, both of which perform work on the surroundings, are combined to liquefy gas. Its characteristic is that the gas at the inlet of the expander is at medium pressure and low temperature. 27. Low-pressure liquefaction cycle with an expander (Kapitsa cycle): A gas liquefaction cycle in which adiabatic expansion and throttling expansion, both of which generate external work, are utilized in combination. Its characteristic feature is that the gas at the inlet of the expander is at low pressure and low temperature. 28. Sterling cycle: A theoretical thermodynamic cycle consisting of two isothermal processes and two isochoric processes. The entire cycle is completed through four processes: isothermal compression, isochoric cooling, isothermal expansion, and isochoric heating. 29. Sublimation: A phase transition process in which a substance changes directly from the solid state to the gas state. 30. Temperature difference: Refers to the temperature difference that occurs when heat is transferred between the surfaces of two fluids with different temperatures, or between two different environments. 31. Hot-side temperature difference: Refers to the temperature difference between the cold and hot fluids at the hot side of the heat exchanger. 32. Temperature difference in the middle section: Refers to the temperature difference between the hot and cold fluids in the middle part of the heat exchanger. 33. Cold-side temperature difference: Refers to the temperature difference between the hot and cold fluids at the cold side of the heat exchanger. 34. Rahman Air: Air drawn from the bottom of the lower column, rewarmed in the cold section of the switching heat exchanger, and after adiabatic expansion in the turbine expander, is directly fed into the upper column to participate in distillation. 35. Liquid-vapor ratio (reflux ratio): The ratio of the amount of liquid flowing downward to the amount of vapor rising in a distillation column. 36. Flooding: A condition in a distillation column where the upward velocity of steam is too high, preventing the liquid from flowing downward normally. 37. Liquid leakage: A condition in a sieve-plate distillation column where liquid leaks through the sieve pores due to an excessively low velocity of the rising vapor. 38. Pressure swing adsorption: An adsorption process that utilizes pressure effects; in each adsorption-regeneration cycle, adsorption occurs at higher pressure, while regeneration takes place at lower pressure (or under negative pressure). 39. Run-down heat loss: The loss of cooling effect that occurs due to the temperature difference between equipment operating at temperatures lower than the ambient temperature and the surrounding medium. 40. Sub-reheat loss: The loss resulting from incomplete recovery of cold energy due to the temperature difference between the hot and cold fluids on the hot side of the heat exchanger. 41. Cooling loss refers to the loss of cooling capacity in the cryogenic tank of air separation equipment due to cooling leakage and insufficient reheat. 42. Extraction rate: The ratio of the total content of a particular component in the product gas to its total content in the process air. 43. Energy consumption per unit: Refers to the electrical energy consumed by air separation equipment to produce a unit amount of gas. 44. Low-pressure process: A process in which the normal operating pressure of air separation is greater than, less than, or equal to 1.0 MPa. 45. Medium-pressure process: A process in which the normal operating pressure of air separation is greater than 1.0 MPa and less than or equal to 5.0 MPa. 46. High-pressure process: A process in which the normal operating pressure of air separation is greater than 5.0 MPa. 47. High-and-low-pressure process: A process that combines a high-pressure process with a low-pressure process. 48. Low-pressure process with molecular sieve adsorber: A low-pressure process that uses molecular sieve adsorbers to remove moisture, carbon dioxide, and hydrocarbons from the air. 49. Air separation equipment: A set of devices that uses air as raw material and low-temperature technology to separate air into oxygen, nitrogen, argon, and other rare gases. 50. Large-scale air separation equipment refers to complete sets of air separation equipment whose oxygen production capacity is 10,000 m3/h or more (under standard conditions). 51. Medium-sized air separation equipment refers to complete sets of air separation equipment capable of producing oxygen at a rate of 1,000 m³/h or more but less than 10,000 m³/h (under standard conditions). 52. Small air separation equipment refers to complete sets of air separation equipment that produce less than 1000 m3/h of oxygen (under standard conditions)