|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Converter. History of invention and production
Directory / The history of technology, technology, objects around us Converter - an apparatus (type of furnace) for producing steel from pig molten iron and charge by blowing with air or commercially pure oxygen. Oxygen is now more commonly used. Oxygen is supplied to the working space of the converter through tuyeres (at a pressure of about 1,5 MPa). This method of obtaining steel is called converter or oxygen-converter. The converter is a container consisting of three parts: the top - the helmet, the middle - the cylinder and the bottom - the bottom. The bottom can be attached, plug-in or integral with a cylindrical part. In this case, the converter is called deaf-bottom. In 1855, the Englishman Henry Bessemer conducted an interesting experiment: he melted a piece of blast-furnace iron in a crucible and blew it with air. Brittle cast iron turned into malleable steel. Everything was explained very simply - the oxygen of the air burned carbon out of the melt, which was removed into the atmosphere in the form of oxide and dioxide. For the first time in the history of metallurgy, additional heating of raw materials was not required to obtain a product. This is understandable, because Bessemer realized the exothermic reaction of carbon combustion. The process was surprisingly fast. In a puddling furnace, steel was produced in only a few hours, but here in a matter of minutes. So Bessemer created a converter - a unit that turns molten iron into steel without additional heating. DI. Mendeleev called the Bessemer converters furnaces without fuel. And since the shape of the Bessemer aggregate resembled a pear, it was called so - "Bessemer pear".
In the Bessemer converter, not every cast iron can be melted, but only one that contains silicon and manganese. Combining with the oxygen of the supplied air, they release a large amount of heat, which ensures the rapid burning of carbon. Still, there is not enough heat to melt solid pieces of metal. Therefore, scrap iron or hard cast iron cannot be processed in a Bessemer converter. This severely limits the possibilities of its application. The Bessemer process is a fast, cheap and easy way to make steel, but it also has big drawbacks. Since the chemical reactions in the converter are very fast, carbon burns out, and harmful impurities - sulfur and phosphorus - remain in the steel and degrade its properties. In addition, when blowing, the steel is saturated with air nitrogen, and this degrades the metal. That is why, as soon as open-hearth furnaces appeared, the Bessemer converter was rarely used for steel smelting. Much more converters were used for smelting non-ferrous metals - copper and nickel.
Today's converter, of course, can in a certain sense be called a descendant of Bessemer's offspring, because, as before, steel is obtained in it by blowing through liquid iron. But not air, but technically pure oxygen. It turned out to be much more efficient. The oxygen-converter method of steel smelting came into metallurgy more than half a century ago. Created in the Soviet Union at the suggestion of metallurgical engineer N.I. Mozgovoy, he completely replaced the Bessemer process. And the world's first ton of oxygen-converter steel was successfully smelted in 1936 at the Bolshevik plant in Kiev. It turned out that in this way it is possible not only to process liquid pig iron, but also to add significant amounts of solid pig iron and iron scrap to it, which could previously only be processed in open-hearth furnaces. That is why oxygen converters have become so widespread. But it wasn't until the 1950s that steel converters finally came to the fore. The degree of heat utilization in an oxygen converter is much higher than in hearth-type steelmaking units. The thermal efficiency of the converter is 70 percent, and for open-hearth furnaces it is not more than 30. In addition, the exhaust gases from the converter are used for afterburning in waste heat boilers, or as fuel when gases are removed from the converter without afterburning. There are three types of converters: bottom blown, top blown and combined. Currently, the most common in the world are top blown oxygen converters - units are very productive and relatively easy to operate. However, in recent years, all over the world, bottom-blown and combined (top and bottom) blast converters are beginning to crowd out top-blown converters.
Let's consider the device of the oxygen converter with the top purge. The middle part of the converter body is cylindrical, the walls of the bath are spherical, the bottom is flat. The upper part of the helmet is conical. The casing of the converter is made of steel sheets with a thickness of 30-90 millimeters. In converters with a cage up to 150 tons, the bottom is detachable; it is bolted to the hull, which facilitates repair work. With a load of 250-350 tons, the converter is made dead-bottomed, which is caused by the need to create a rigid hull structure that guarantees against cases of liquid metal breakthrough. The converter housing is attached to a special support ring, to which the trunnions are welded. One of the trunnions is connected to the rotation mechanism through a gear coupling. In converters with a capacity of more than two hundred and fifty tons, both pins are driven. The converter is supported by trunnions on bearings mounted on the beds. The rotation mechanism allows you to rotate the converter around a horizontal axis. The body and bottom of the converter are lined with refractory bricks. Oxygen is supplied to the converter bath for metal purging through a special lance inserted into the converter neck. The first operation of the converter process is loading the scrap. The converter is tilted at a certain angle from the vertical axis and a special box-scoop with a capacity through the neck is loaded into the converter scrap - iron and steel scrap. Usually load 20-25 percent of scrap per melt. If the scrap is not heated in the converter, then liquid iron is immediately poured. After that, the converter is placed in a vertical position, and an oxygen lance is introduced into the converter through the neck. Slag-forming materials are introduced into the converter through a special chute to induce slag: lime and a small amount of iron ore and fluorspar. After oxidation of iron impurities and heating of the metal to the specified values, the purge is stopped, the lance is removed from the converter, and the metal and slag are poured into the ladles. Alloy additives and deoxidizers are introduced into the ladle. The duration of melting in well-functioning converters is almost independent of their capacity and is 45 minutes, the duration of the purge is 15-25 minutes. Each converter gives 800-1000 melts per month. The durability of the converter is 600-800 melts. The movement of the metal in the converter is very complex; in addition to the oxygen jet, bubbles of carbon monoxide act on the liquid bath. The mixing process is further complicated by the fact that the slag is pushed by a gas jet into the thickness of the metal and mixed with it. The movement of the bath and its swelling by the released carbon monoxide bring a significant part of the liquid melt into an emulsion state, in which the metal and slag drops are intimately mixed with each other. As a result, a large contact surface of the metal with the slag is created, which ensures high rates of carbon oxidation. Oxygen bottom-blown converters, due to less iron waste, make it possible to obtain a higher (by 1,5–2 percent) yield of good steel compared to top-blown converters. Melting in a 180-ton bottom blown converter lasts 32-39 minutes, blowdown - 12-14 minutes, that is, the productivity is higher than that of top blown converters. However, the need for intermediate replacement of the bottoms eliminates this difference in performance. The first bottom blown converters abroad were built in 1966-1967. The need to create such a converter is mainly due to two reasons. Firstly, the need to process cast irons with a high content of manganese, silicon and phosphorus, since the processing of such cast iron in converters with top blowing is accompanied by metal emissions during blowing and does not ensure the proper stability of the chemical composition of the finished steel. Secondly, the fact that the converter with such a purge is the most acceptable design that allows the reconstruction of the existing Bessemer and Thomas shops, and fits into the building of the existing open-hearth shops. This converter is characterized by the presence of a large number of reaction zones, intensive oxidation of carbon from the first minutes of melting, and a low content of iron oxides in the slag. Due to the specifics of the operation of the steel-smelting bath during bottom blowing, in converters of this type, the yield of good is somewhat higher than in other converters, and the dust content of the exhaust gases is lower. In bottom blown converters with a large number of tuyeres, all technological processes proceed more intensively than in top blown converters. However, the overall performance of bottom blown converters does not significantly exceed that of top blown converters due to the limited stability of the bottoms. To protect the laying of the bottom of the converter from high temperatures, the lance is made in the form of two coaxial tubes - oxygen is supplied through the central one, and some hydrocarbon fuel, most often natural gas, is supplied through the peripheral one. There are usually 16-22 such lances. A large number of smaller tuyeres ensures better mixing of the bath and a smoother melting process. The fuel jet separates the reaction zone from the bottom, lowers the temperature near the bottom at the exit point of the oxygen jets due to heat extraction for fuel heating, cracking and dissociation of the fuel components and their oxidation products. The cooling effect is also provided by powdered lime, which is fed into the oxygen jet. Thus, blowing the molten metal with several jets of oxygen from below creates a number of favorable features in the operation of the converter. Provides a larger number of reaction zones and a large interfacial contact surface of oxygen jets with metal. This makes it possible to increase the blowing intensity and increase the rate of carbon oxidation. The mixing of the bath is improved, the degree of oxygen utilization is increased. As a result, it becomes possible to melt large pieces of scrap. The better hydrodynamics of the bath ensures a smoother and quieter course of the entire melt, virtually eliminating emissions. Because of this, bottom-blown converters can process cast irons with a high content of manganese and phosphorus. The desire to increase the productivity of the units simultaneously with the need to increase the homogeneity of the composition and temperature of the metal with the possibility of manufacturing steels of a wide range led to the use of combined blowing with a relatively small (compared to only bottom blowing) amount of gases blown through tuyeres installed in the bottom of the converter. Recently, two main variants of such a process have appeared, when oxygen or inert gases are supplied from below in order to provide intensive mixing of the bath and accelerate the process of removing impurities. In this case, as in the case of bottom blowing, powdered lime can be supplied from below along with the gases. According to such an important indicator as the possible consumption of scrap, converters with top, bottom and combined blowing are approximately on the same level, with a slightly higher yield of bottom blown. At present, many different methods of combined blowing of a molten bath are being used and developed in the world, rationally combining top and bottom blowing, the latter using both oxygen and inert gases (argon, nitrogen). In the BOF process with top blowing, sufficiently intensive mixing is achieved only in the middle of the melt with intensive carbon oxidation. At the beginning and at the end of the melt, mixing is insufficient, which makes it difficult to deep refine the metal from sulfur and phosphorus. The combined supply of oxygen through the top and bottom tuyeres even more than with one bottom purge accelerates the process of carbon oxidation and increases the productivity of the converter. Compared to pure bottom blowing, in the case of a combined process under comparable conditions, the temperature of the metal is higher. In addition, with combined blowing, reducing the flow of oxygen through the upper tuyere reduces dust and spatter. And one more advantage of oxygen converters: here all processes are mechanized and automated, more and more often the management of converters is entrusted to computers. Author: Musskiy S.A.
▪ Bakelite ▪ Elevator
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Sensor for biometric breath authentication ▪ Hard drive capacity to double by 2016 ▪ Food emulsifiers harm the intestines
▪ section of the site Firmware. Article selection ▪ article To spread the thought along the tree. Popular expression ▪ article Which animals have an internal clock set to a 47-hour life cycle? Detailed answer ▪ article Electromechanic of power supply. Standard instruction on labor protection ▪ article Transformation of three cards. Focus secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page