What Is a Basic Oxygen Furnace?

In the early 19th century, with the rapid development of the industrial revolution, the demand for the quantity and quality of steel became higher and higher. As a result, people began to seek new and more effective methods of steelmaking. In 1879, British metallurgist Thomas proposed an alkaline converter steelmaking method, which uses dolomite high-temperature firing clinker and mixed tar to make an alkaline refractory brick lining. During the smelting process, air is added and quicklime is added. In this way, the entire reaction proceeds under alkaline high temperature conditions, and the oxidized phosphorus is combined with lime and remains in the slag without returning to the steel, so the problem of dephosphorization is solved.

Converter steelmaking is a steelmaking method that does not require an external heating source and mainly uses liquid pig iron as a raw material. The main characteristics of converter steelmaking are: the physical heat of the liquid pig iron in the converter and the heat generated by the chemical reaction between the various components of the pig iron (such as carbon, manganese, silicon, phosphorus, etc.) and the oxygen sent into the furnace, so that The metal has the composition and temperature required for tapping. The charge is mainly hot metal and slag-making materials (such as lime, quartz, fluorite, etc.). To adjust the temperature, scrap steel and a small amount of cold pig iron and ore can be added. The converter is divided into alkaline (lined with magnesia or dolomite) and acidic (lined with siliceous material) according to the properties of the refractory material of the furnace lining; it is divided into bottom blowing, top blowing and Side blowing; According to the gas used for blowing, it is divided into air converter and oxygen converter. The acid converter cannot remove sulfur and phosphorus in pig iron, and high-quality pig iron must be used, so the application range is limited. Alkaline converters are suitable for making steel with high phosphorus pig iron, and have been greatly developed in Western Europe. Air-blown converter steel, because of its high nitrogen content, is not as good as open-hearth steel, and its raw materials are limited, and it cannot be used with more scrap steel. It has not been widely adopted worldwide like open-hearth furnaces. The introduction of oxygen top-blown converters in 1952 gradually replaced air-blown converters and flat furnaces, and has now become the world's main steelmaking method.

The main difference between converter steelmaking and other steelmaking methods is that he does not rely on external energy, and only uses the exothermic oxidation reaction of air or oxygen blown into the molten pool and various elements in pig iron to complete the tasks of decarburization and removal of impurities, and Heating molten steel to tapping temperature (1600 or higher) ^[1]

British military engineer Bessemer gave a speech to the British Science Association in 1856, entitled "Iron can be turned into steel without using fuel and just blowing in air". He proposed putting molten pig iron into a converter and blowing high-pressure air to burn off the silicon, manganese, carbon, and phosphorus contained in the pig iron, thereby refining the steel. Bessemer invented the pear-shaped movable converter, which can take 10 to 15 tons of molten iron to steel in only 10 minutes. It takes a few days to complete it with agitation. Therefore, this is a steelmaking method with high productivity and low cost, which has become a great initiative in the history of metallurgy. However, the converter invented by Bessemer is an acid converter. In an acid converter environment, phosphorus is difficult to be removed by oxidation. Therefore, Bessemer converters in Europe are only suitable for countries such as Sweden and Austria, which have large amounts of low-phosphorus and low-sulfur iron ore.

The superiority of replacing air with oxygen has long been recognized, but it has not been achieved for a long time due to the failure to obtain a large amount of cheap industrial pure oxygen. By the 1940s, after air separation to produce oxygen on an industrial scale, it was possible to use a large amount of oxygen in steelmaking. However, the old converter was converted to oxygen blowing, and the air holes at the bottom of the furnace burned quickly, making the blowing impossible. In 1948, R. Durrer used a water-cooled oxygen lance to insert molten iron into a furnace in Switzerland to blow molten iron successfully. In 1952, Linz and Donawiz steel plants in Austria established a 30-ton oxygen cap. Blowing converter workshop. Later, according to the first letter of these two place names, the oxygen top-blown converter steelmaking method was called LD steelmaking method. In the 1950s, the LD steelmaking method spread to countries around the world, gradually replacing the open hearth steelmaking method. With the advent of top-blown oxygen converters, other types of oxygen-blown steelmaking methods have appeared, such as the Kaldo steelmaking method and the Rotor steelmaking method, but they have not been promoted. Lime powder-sprayed oxygen top-blown converter steelmaking method, called LD-AC method, can blow pig iron with high phosphorus content. It was used in high-phosphorus pig iron steelmaking production before the introduction of oxygen bottom-blown converter.

In 1879, British metallurgist Thomas proposed an alkaline converter steelmaking method, which uses dolomite high-temperature firing clinker and mixed tar to make an alkaline refractory brick lining. During the smelting process, air is added and quicklime is added. In this way, the entire reaction proceeds under alkaline high temperature conditions, and the oxidized phosphorus is combined with lime and remains in the slag without returning to the steel, so the problem of dephosphorization is solved. Thomas's method was soon widely used in Germany and France, which are rich in phosphorus-containing iron ore, thereby further promoting the development of steelmaking.

After World War II, many countries began to experiment with pure oxygen instead of air to make steel. In 1948 Austria made the first technological breakthrough. This method is to mix pig iron with scrap steel, pour it into a converter, and then blow oxygen to quickly burn off carbon and impurities. The quality of steel produced by this method is comparable to that of open hearth steel, but the time required is only one tenth of that of open hearth steel.

Our country

China used side-blown acid converter steelmaking in various places in the 1930s and 1940s, with a total production capacity of about 100,000 tons / year. In the 1950s, the trial of alkaline lining blowing in Tangshan Steel Plant was successfully carried out and spread to all parts of the country. In the 1950s and 1960s, the steel output of side-blown converters reached more than 20% of China's total steel output. At the end of the 1950s, a 30-ton oxygen top-blown converter workshop was first built in Beijing and production started. In the future, it has been completed and put into production in various places. In 1980, the output of oxygen converter steel accounted for 40.64% of the national steel output.