This method is a new technology developed after 1952. It is a method that is more advanced and more advanced in the world. Pure oxygen top-blown converter steelmaking has the following advantages:
(i) Fast production speed Because it is blown with pure oxygen, it will reduce carbon at high speed and increase temperature quickly, which will greatly shorten the smelting time. A 300t converter has a blowing time of less than 20 minutes, including auxiliary working hours, and no more than 1 hour.
(ii) Multi-variety, good quality Pure oxygen top-blown converter can both refine ordinary steel and ordinary low-carbon steel. For example, the capital steel mill successfully tested more than 100 kinds of steel products by this method. Due to the use of pure oxygen blowing, the content of harmful gases such as nitrogen and hydrogen in the steel is low.
(iii) Infrastructure investment and production costs The capital investment of low-purity oxygen top-blown converters is equivalent to 60-70% of the open-air furnaces of the same production capacity, and the production cost is also lower than that of open-hearth furnaces.
At present, the pure oxygen top-blown converter has successfully improved the oxygen supply per unit time with the successful development of the porous nozzle of the oxygen lance, and due to the innovation of operation technology (for example, using electronic computing technology to regulate and control the smelting process), Regardless of the size of the converter, the blowing time is basically the same. Even in the 300t converter, the net oxygen blowing time can be shortened to about 12 minutes. Within a certain limit, the larger the furnace capacity, the better the economic effect, so the top-blown converter is rapidly moving toward large-scale. The largest converter in the world is now 350t, and 400-450t converters are being researched.
(2) Electric furnace steelmaking method
The electric furnace steelmaking method mainly uses arc heat, and the temperature in the arc action zone is as high as 4000 °C. The smelting process is generally divided into a melting period, an oxidation period and a reduction period. In the furnace, not only an oxidizing atmosphere but also a reducing atmosphere can be caused, so the efficiency of dephosphorization and desulfurization is high.
The electric steelmaking steel with scrap steel as raw material has less investment than the blast furnace converter method. At the same time, due to the development of direct reduction, metallized pellets are provided instead of most of the scrap steel for the electric furnace, thus greatly promoting the electric steelmaking. There are about 1,400 large electric furnaces in the world. At present, electric furnaces are developing in large-scale, ultra-high-power and electronic computer automatic control. The maximum electric furnace capacity is 400t.
Almost all electric furnaces above 150t are used to smelt ordinary steel. In many countries, 60-80% of the output of electric furnace steel is low carbon steel. Due to the shortage of electricity and scrap, China is currently mainly used for smelting high-quality steel and alloy steel.
(3) Open hearth steelmaking method
Before the 1950s, open hearth steel accounted for 85% of world steel production. In recent years, in addition to casting large steel ingots such as large castings or water supply presses, open hearth steelmaking is still playing its role. Due to the development of pure oxygen top-blown converter steelmaking technology, the output of converter steel has increased significantly. Steel production has only declined year by year. The biggest disadvantage of the open hearth steelmaking method is that the smelting time is long (generally 6 to 8 hours), the fuel consumption is large (the utilization of heat energy is only 20 to 25%), and the capital investment and production cost are high. A steel plant with an annual output of 12 million tons of steel is enough to build six 250-300t pure oxygen top-blown converters. If a flat furnace is built, it needs 30 to 40 large flat furnaces. Although the flat furnaces currently in production in the world have generally adopted oxygen steelmaking, the productivity has been greatly improved, but the dust removal system is complicated and the investment is high. Therefore, the open hearth steelmaking is no longer developed, and even the demolition is converted into a top or bottom blowing converter. the trend of.
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