Oxygen is the substance on which all living organisms on Earth depend for survival. It readily reacts chemically with other substances to form oxides, and oxidation reactions generate a large amount of heat. Therefore, oxygen, as an oxidizing agent and combustion supporter, is widely used in metallurgy, the chemical industry, energy, machinery, national defense, and other industrial sectors.
(1) Iron and steel industry. The largest consumer of oxygen in steel enterprises is the converter steelmaking shop. By blowing in high-purity oxygen, impurities in molten iron such as carbon, phosphorus, sulfur, and silicon are oxidized. The heat generated by this oxidation is sufficient to maintain the temperature required for the steelmaking process. Blowing with pure oxygen (>99.2%) greatly shortens the smelting time and improves the quality of steel.
During electric furnace steelmaking, oxygen blowing accelerates the melting of furnace charge and the oxidation of impurities, saving electric power consumption, and electric furnaces have gradually become established oxygen users.
In blast furnace ironmaking, oxygen-enriched blast allows a greater amount of pulverized coal to be injected, saving coke and reducing the fuel ratio. Although the purity of the oxygen enrichment is not high (24–25% O₂), the enormous blast volume makes oxygen consumption quite considerable-nearly one-third of that used in steelmaking. Blast furnaces therefore also rank as major oxygen users.
Non-ferrous metal smelting. In heavy metal smelting, pyrometallurgical processes dominate. In addition to heat released by the oxidation of sulfur and iron, additional heat must be supplied by fuel combustion. To intensify the smelting process, reduce energy consumption, and decrease the volume of harmful off-gas, oxygen-enriched air is used instead of air for smelting, while simultaneously increasing production capacity. The oxygen concentration ranges from 35% to 90%. A flash furnace with an annual output of 3,600 t/a of copper requires an air separation unit with a production capacity of 3,000 m³/h and an oxygen purity of 95%. A lead-zinc smelter with 100,000 t/a capacity requires an air separation unit of 1,500 m³/h at 95% oxygen purity. Since the required oxygen purity is not high, the capacity of the air separation unit needed is relatively small, and a pressure swing adsorption (PSA) oxygen generation unit can be used.
(2) Chemical industry. In the production of synthetic ammonia for fertilizer, nitrogen is the main feedstock gas, while oxygen is used in processes such as high-temperature cracking of heavy oil and gasification of pulverized coal to intensify the process and increase fertilizer output. Generally, a synthetic ammonia plant of 100,000 t/a capacity requires an air separation unit of 70,000 m³/h.
In addition, large quantities of oxygen are consumed in natural gas reforming to produce methanol, in the oxidation of ethylene and propylene to their oxides, and in desulfurization and sulfur recovery. Oxygen consumption per ton of product ranges from 300 to 1,000 m³/t, requiring air separation units of 10,000–30,000 m³/h.
(3) Energy industry. During pressurized coal gasification, sufficient oxygen must be supplied to maintain the temperature of the oxidation layer in the gasifier. Oxygen purity must be no less than 95%, and oxygen consumption per kilogram of coal varies with coal type and quality: 0.14–0.18 m³/kg for lignite and 0.17–0.22 m³/kg for bituminous coal. Gasification pressure is determined by process requirements; the higher the pressure, the lower the oxygen consumption.
For Integrated Gasification Combined Cycle (IGCC) power generation plants, approximately 5.6 m³ of oxygen is required per kW.
(4) Machinery industry. Oxygen is mainly used for metal cutting and welding. As a combustion supporter for acetylene, it produces a high-temperature flame that melts the metal.
(5) National defense industry. Liquid oxygen is often used as a rocket propellant oxidizer. Combustible materials soaked in liquid oxygen become highly explosive and can be used to make liquid oxygen explosives.
In addition, in the medical field, oxygen is also an indispensable substance for emergency treatment and adjuvant therapy of patients. Oxygen production has therefore become an essential and important link in the national economy.
