RU2027777C1 - Method of continuous steel smelting and unit for its accomplishment - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: the unit may be positioned in the existing open-hearth plant with employment of the available production equipment. The movable hearth of the steel-making unit has a number of successively extending bath, in which production operations with isolated amounts of metal are accomplished in a conveyer succession, and flue gases move from the "hotter" zone to the "colder" one. A large amount (up to 100%) of large-sized scrap can be processed in the unit at a capacity exceeding the converter capacity. EFFECT: facilitated procedure. 2 cl, 3 dwg

Description

 The invention relates to metallurgy, and specifically to methods for the continuous smelting of steel.

 Known continuous methods for the production of steel, carried out in single-stage and multi-stage units of continuous operation.

 The essence of these methods lies in the fact that liquid cast iron is continuously poured into the working space of the unit, consisting of one or more melting zones, filled with scrap metal and slag-forming materials, oxygen and thermal energy are supplied (if necessary).

 Metal (in the case of a multi-stage process) flows by gravity from one workspace to another, and the finished steel goes to the digger bucket or to a special drive in the unit.

 The disadvantage of these methods is that the heat of the exhaust gases is used ineffectively, it is impossible to inspect and repair the metal-enclosed part of the unit, which does not make it possible to timely prevent an emergency. A continuous supply of molten iron and scrap metal is required to withstand the required level of metal in the unit, which in turn places stringent conditions for the supply of molten cast iron, as well as the thorough preparation of scrap metal by the fractional composition and geometrical form of its pieces (the latter is due to the known scrap feeding devices in such aggregates, as a rule, are bunkers with vibration leaks; batch feeding of individual pieces of bulky scrap is extremely undesirable, as it causes rapid cooling of the entire melt).

 Existing refractories cannot ensure a constant bath profile, especially in nodes where metal flows from one zone to another. This leads to a change in the mass of the metal in a separate zone, the depth of the bath, its level. Hence the inability to maintain stable process conditions for heating, the rate of oxidation of impurities and leads to errors in estimating the mass of metal in the unit, which as a result causes errors in calculating the required amount of additives - deoxidizing and alloying.

 The next drawback is the complexity of the transition to the smelting of another steel grade, which significantly differs in chemical composition from the previous one, since an abrupt change in temperature and chemical composition in these processes is impossible without stopping the unit.

 A smooth change in the mentioned parameters requires a special selection of the corresponding steel grades, which will be forced to be released from the unit upon transition from one grade to another.

 Moreover, with an unexpected change in the chemical composition of the metal (for example, accidental contamination of scrap metal or cast iron), timely intervention in the process with the aim of correcting it is practically eliminated.

 All these disadvantages exclude any mass industrial application of continuous steel smelting methods.

 A known method of steel smelting, implemented with a rotary system of converters.

 According to this system, converters move from one workplace to another.

 At a particular workplace, a specific operation is performed, for example scrap filling. After that, the "pear" of the converter is moved with the help of a transfer car to the place of cast iron pouring, and then to the place of purging. At the end of the smelting cycle is repeated in a closed curve.

 The disadvantage of this method is that it does not use the heat of the exhaust gases to heat the scrap metal. Moreover, when transporting the converter from one workplace to another, a certain part of the heat is irretrievably lost.

 Delay of any operation leads to the inevitable delay of the whole process and a sharp decrease in productivity. But at the same time, the process, despite the conveyor scheme, is not continuous.

 The closest to the proposed technical essence and the achieved result is a continuous unit. The working space of the unit consists of a common arch and four stationary bathtubs, separated by passes. The unit has a rigid piping, similar to open-hearth furnaces. In the front wall of the unit are working windows. Moving oxygen lances, stationary fuel and oxygen burners, openings for supplying specially selected scrap metal and lime are located in the vault above the bathtubs. Each bath has steel outlets at the bottom of the hearth, and the fourth additionally has an upper hole located at the level of the passes between the baths.

 Cast iron is poured using a special tilting device, scrap metal and lime are fed from the hoppers by vibrodosers.

 Metal flows from the bath to the bath through the passes, and the finished one merges continuously through the upper steel outlet. Additional thermal energy is supplied by stationary gas-oxygen burners.

 The disadvantages of this unit are the same as those given above. Particularly noteworthy is the change in the profile of overflow troughs, where the greatest wear is observed due to the erosive action of metal and slag. If the geometry of the overflow troughs changes over time, it is impossible to maintain stable technological parameters, and this practically makes the unit unsuitable for wide industrial use. In addition, since the unit must be constantly covered by liquid metal, the requirements for its quality exceed the current technical level on an industrial scale.

 The aim of the invention is to increase the productivity of the unit, the efficient use of heat of the exhaust gases, simplifying technological and repair operations, reducing their duration, improving the environmental friendliness of the process, expanding technological capabilities. To this end, the entire sequence of technological operations is performed with isolated volumes of metal, which are sequentially moved in a single working space of the unit.

 The technical means for achieving this goal is an aggregate containing a working space bounded by a vault with oxygen tuyeres installed in it, oxygen-fuel burners, walls with loading and technological windows, made in the form of successively arranged melting baths with a hearth divided into separate technological zones, each of which equal in length to one melting bath, a device for carrying out technological operations, characterized in that it is equipped with devices for the movement of the melting baths along the working space of the unit and their periodic removal from the unit, while the melting baths are made with the possibility of autonomous action when they are sequentially moved from one technological zone to another.

 The main features that make up a significant difference from the known methods are the following.

 The object of the technological process becomes a separate isolated volume of metal. If we consider the process in a separate bath, then from this point of view it can be defined as final, which is not the case in similar continuous ones - there, in each melting bath, the same technological operation is continuously performed, and the metal in the bath changes.

 In the known method there is no important technological detail - a single unit. Therefore, the process is uniquely periodic: interruption of technological operations is inevitable when replacing the "pears" of the converter.

 In the proposed technical solution, the operation of, for example, burners and metal heating are continuous, which makes it possible to qualify the process as continuous. The combination of a continuous unit with a periodic one in this case gives a qualitatively new result, consisting in the possibility of using the heat of the exhaust gases (it is theoretically possible to construct such an unit that will fully use this heat with a sufficient length), as well as the possibility of repair operations to restore the hearth without process shutdowns.

 The issue of filling up scrap metal, including lightweight and bulky, is being solved, since this operation is removed from the unit, therefore it does not affect productivity. The size of the loaded pieces of scrap metal is limited by the dimensions of the bath, and the loading method (scoop, tub, bridge crane) is absolutely reliable due to its primitiveness. In addition, there is a margin of time for organizing filling without compromising productivity. These points in the known continuous units have not been resolved.

Thus, the proposed technical solution combines the advantages of several methods of steel production:
Converter - in terms of performance;
open-hearth furnace - according to the amount of scrap used (50% or more) due to the use of heat from the exhaust gases, and also - according to the flexibility of the ratio of cast iron - scrap;
electric smelting - if necessary, you can install in one (or several) zone electric arc (or plasma) heating;
continuous - according to the stability of the process.

 New opportunities arise - the use of large-sized scrap metal, unburnt limestone, as well as the possibility of introducing baths with an acid lining into the furnace and melting using the appropriate technology without a special unit.

 The proposed method for continuous steelmaking is as follows.

 Before heating, prepared lined bathtubs are introduced into the unit in such a quantity that they form a continuous furnace without gaps, after which heating burner devices are turned on. Flue gases move from the head of the unit to the tail, ie, from a “hotter” zone to a “colder” one. Upon reaching operating temperature, the bath located at the dispensing window is discharged from the unit and covered with a lid. Accordingly, all other bathtubs are moved in the furnace, and another bath is placed on the vacant space in the head of the furnace. At the same time, the issued bath moves to the loading window, the lid is removed from it and moves to the dispensing window to cover the next bath.

 The bath located at the loading window is loaded with scrap metal in the required amount (up to 100% of the metal charge when working with the scrap process), the next bath is issued, and the bath with metal scrap is fed into the loading window. The first few zones may not have burners or other devices for supplying heat. Heating is carried out by heat of exhaust gases. Spatter of metal and slag from the "liquid" baths settles here, which ensures a reduction in the amount of work when cleaning slag and the recovery of heat from the spray.

 Then the bath enters the heating zone (all subsequent baths undergo the same technological operations with “delay” for one operation compared to the previous one). The heating zone is equipped with a fuel-oxygen (or other) burner (s), and there may be several such zones. The next zone (s) is equipped with devices for cast iron filling, slag loading (by tilting the bathtub or otherwise), as well as oxygen purge lances. The subsequent zone (group of zones) is a zone equipped with devices for supplying heat, due to which the metal is heated, as well as devices for introducing slag-forming and other reagents. A purge with oxygen and other reagents (including powder ones) may be provided. The last zone (group of zones) has devices for introducing deoxidizers and alloying and other reagents.

 After the next bath is dispensed, it is covered with a lid and the metal is merged, for example, by tilting the bath through a slide gate or by any other known method, and the metal can be poured into a steel pouring or intermediate ladle or directly into a continuous casting mold or mold (mold). After that, the bath is transferred to the loading platform, the lid is removed, inspection, refueling is performed, and if necessary, the bath is repaired (the repaired is replaced by a backup).

 The criterion of "significant differences" in this case corresponds to a movable sub unit, consisting of separate autonomously operating bathtubs.

 In FIG. 1-3 shows a diagram of the proposed unit.

 The steelmaking unit of continuous operation consists of a roof 1, walls 2, identical autonomous movable trolleys on which a melting bath 3 is installed, their total length is equal to the length of the working space; roller bearings 4, on which the bathtubs-bathtubs move, devices for moving the carts, in this case the pusher 5; fuel-oxygen burners 6, purge lances 7, transfer trolleys 8, with which the trolley returns to its original position at the end of the cycle, the lid 9, which covers the trolley with finished metal coming out of the unit, at the time of release of metal and transportation of the trolley to the next place scrap metal filling; gas exhaust duct 10 (11 - working window). The arrow shows the direction of movement of the carts.

 The unit for implementing the method works as follows.

 Movable cart-baths 3 are placed in the unit, so that the roller (or other) mechanism by which the carts move is closed from high temperature exposure. After that, the unit starts heating with fuel burners 6 and other devices, if provided. The number of bathtub trolleys in this case is five, for convenience they are numbered with numbers from N 1 to N 5, N 6 - the trolley is located outside the unit. After warming up the furnace to operating temperature, it is pushed under one pusher 5 with a pusher (or in another way). In this case, the trolley N 5 is extended from the unit. At the same time, trolley N 6 with the help of transfer trolleys 8 and any known device (roller conveyor, bridge crane, etc.) moves to its initial position (in place of trolley N 1), and the lid with it by a crane (or other device) is fed to trolley N 5. Trolley N 5 moves to the loading place (near the head of the unit), the cover is removed from it and transported to the rear of the unit to cover the next bath trolley leaving the furnace (in this case, N 4).

 The cart-bath N 5 is loaded from the tub (or in another way) with scrap metal, after which the cycle of moving the bathtubs-carts is repeated, and the cart N 5 is inside the working space and the preliminary heating of the scrap metal with exhaust gases begins. After the next cycle, cart No. 5 is in place of cart No. 2, where the scrap metal is heated by an oxy-fuel burner.

 The next zone (initial position - trolley N 3) has a chute for casting iron (not shown), an oxygen purge lance 7 and a device for tilting the bath (not shown). A bath with heated scrap metal in this zone is poured with the necessary amount of molten cast iron, purged with oxygen using a lance 7. At this time, primary slag is drained sideways by tilting the bath. In the next zone, further heating and pickup of new slag takes place.

 In the subsequent zone, the metal is finally heated, if necessary, slag is removed, then deoxidized. After this cycle, the bath exits the oven.

 Moreover, in each bath, the metal smelting process is periodic, and the operation of the entire unit as a whole is continuous. This makes it possible to implement an industrial continuous process of steel production with existing technical capabilities.

 Since smelting is carried out in separate bathtubs, all operations are distributed in space, but are combined in time, i.e. in each individual bath, at a certain moment, operations occur that amount to a complete technological cycle. Therefore, the performance of the unit will be determined by the duration of one of the longest operations, and not by the sum of them.

 At the same time, each bath goes through a closed technological cycle, i.e., in succession each operation. Moreover, the process cycle itself can be quite long.

 This circumstance makes it possible to increase the productivity of the unit to a large extent, not by increasing the unit capacity of one bath, but by dividing the process into separate simple operations, i.e. by increasing the number of bathtubs (operations). In other words, an aggregate having 12 baths of 200 tons each can have the same capacity as having 24 baths of 100 tons each.

 PRI me R 1. Steelmaking unit having 12 baths, 200 tons each, is divided into 12 zones in which the following operations are performed.

 Zone 1 - loading, equipped with a loading window and a transfer trolley, on which a bath with scrap metal is fed into the unit. It is used for loading and preheating scrap metal and slag-forming materials.

 Zone 2 - further heating of the mixture; in addition, flue gases are vented through it into a vertical channel.

 Zones 3-5 - charge heating. All three zones do not have special burner devices. Heating is carried out by heat of exhaust gases.

 Zones 6 and 7 are equipped with gas-oxygen burners (vaulted or otherwise). Here is the final heating of the mixture before casting iron.

 Zone 8 - cast iron pouring and the beginning of melting. Equipped with filling devices and blowing lances.

 Zone 9 - the zone in which the final melting and downloading of the primary slag is performed (by tilting the bath or in another known manner). The bath is also purged with oxygen and slag-forming is introduced to introduce new slag (if necessary).

 Zones 10 and 11 - zones of heating to the required temperature by an external heat source, as well as by purging the bath with oxygen.

 Zone 12 - temperature correction, slag downloading (if necessary), metal chemical composition correction, preliminary deoxidation and alloying.

 Change in temperature and sampling of metal and slag is provided in zones 8-12 in order to adjust the technological operations in each subsequent zone.

 The bath is in the same zone for 15 minutes. The total duration of operations: heating 1 h 45 min, cast iron casting + melting 30 min, heating and lapping 45 min.

 The total time spent by the metal in the furnace is 3 hours, the productivity of the process is 800 t / h. Blending 50% scrap metal, 50% liquid cast iron.

 At the end of the smelting, the bath is released from the furnace, covered with a lid and the metal is poured into a steel pouring ladle mounted on a stand or suspended on a crane. At the same time, the final cleavage and alloying are performed, as well as the necessary after-furnace treatment. The metal is drained by tilting the bath. After that, the bathtub moves to the inspection and refueling (shotcrete) platform of the hearth, where the lid is removed and transferred to the heated stand or directly to the newly issued bathtub.

 The inspected bath moves to the loading platform, where it is loaded with metal from the tub (basket). Slag forming feed from the hopper. Scrap preparation and loading of tubs (baskets) is carried out on a specially designated site away from the furnace.

 PRI me R 2 implementation of the proposed technical solution.

 The unit is located in the building of the open-hearth shop, previously equipped with 11 open-hearth furnaces, at the level of the working platform so that a number of columns, between which the furnaces were located earlier, were along the back wall of the unit. The vertical channel, smoke hog and pipe are used from the old open-hearth furnace. The gas treatment and the waste heat boiler are being reconstructed to fit the parameters of the new unit.

 The unit has 12 two-hundred-ton bathtubs-carts (zones) in the working space, while the first six are used to heat scrap and slag-forming materials. Blending - 50% scrap metal, 50% molten iron. Four zones are heated only by the heat of the exhaust gases, two by gas-oxygen burners.

 The bulk of the iron merges in the eighth zone. The ninth has a chute for cast iron casting, but it is used for this only when violent reactions occur and it is impossible to finish casting iron in the 7th zone. Both zones have purging devices, devices for downloading slag and are equipped with slag stands.

The average depth of each bath is 0.5 m, the area is about 64 m ² .

 Zones 9 and 10 have devices for feeding slag-forming (hopper), as well as purge lances and fuel burners.

 Zone 11 is equipped with an oxy-fuel burner and (or) electric arc heating. Here, the metal is heated to the required temperature completely.

 In zone 12, equipped with a device for feeding ferroalloys and for downloading slag, preliminary deoxidation and alloying of the metal is carried out.

 At the output with the help of a filling tap, the bathtub is covered with a lid, and the metal is released through the slide gate.

 After that, with the help of transfer trolleys and a roller conveyor, the bath is transferred to the scrap loading area, the lid is transferred by a tap to another bath, and the bath is loaded with scrap metal using another filling tap.

 Cast iron is also filled with a filling tap.

 There is no complete sealing between the walls and the bogie carts. Partial sealing is achieved by adding refractory powder (e.g. calcined dolomite).

 The roller conveyor (figure 3) is designed so that when leaving the metal roller wiring is not affected. This keeps the unit working even in case of a serious accident.

 The inclination of the concrete base in the direction of the casting span will contribute to the flow of the departed metal into the area of operation of the casting cranes, i.e., the quick elimination of the consequences of the accident.

 The advantage of the proposed method also lies in the fact that it can be implemented in the reconstructed open-hearth shop, and only the steelmaking unit at the work site needs to be reconstructed, and the nozzles of the regenerators and one vertical channel of the furnace are removed.

 All other basic and auxiliary equipment can be used without reconstruction.

 The advantages of the proposed unit is that it can be mounted inside the existing open-hearth shop. At the same time, the existing equipment can also be used without significant reconstruction (bridge cranes, ways to supply cast iron and scrap metal, gas-oxygen fittings, etc.).

The productivity of the furnace will be determined only by the possibilities of its supply (for example, to smel 6 million tons of steel per year, approximately as much as the open-hearth furnace of CherMK smelts, one furnace of this type will be needed with twelve 200 tons of bathtubs with a total length of about 80 m.)
The problem of quick filling of the furnace, including bulk bulk scrap, is solved, since filling buckets can be prepared nearby on a separate site and not affect the performance of the unit itself. The consumption of scrap metal can in principle reach 100%, only in this case a sufficiently long heating zone and powerful gas-oxygen burners should be provided so that the heating of scrap metal is sufficient. It will also use the heat of the exhaust gases.

 There is no need for frequent cleaning of slag, since the bulk of the splash of slag and metal will settle on the "cold" baths.

 Such operations as the release (discharge) of metal, inspection, refueling and repair of the hearth are excluded from the smelting time, since they will occur outside the unit, on special stands where working conditions can be significantly facilitated.

 One such furnace can replace, for example, eleven CherMK open-hearth furnaces, of which two two-shaft furnaces (each 2x300 tons), eight 600 tons open-hearth furnaces and one 300 tons furnace. This will free up more than 50% of the main technological personnel, reduce redistribution costs, reduce liquid iron consumption by 100-150 kg / t, improve working conditions and environmental safety of production.

 In addition, a rhythmic supply of metal to the rolling shops is ensured, which can give an economic effect.

Claims (3)

 METHOD FOR CONTINUOUS SITING OF STEEL AND UNIT FOR ITS IMPLEMENTATION.  1. A method of continuous steelmaking, including the sequential filling of scrap metal and slag-forming materials, heating the mixture, casting iron, heating, downloading slag, purging with oxygen, metal discharge, deoxidation and alloying with the execution of the entire sequence of technological operations simultaneously in a single working space of the unit, characterized in that, in order to increase the capacity of the unit, the efficiency of the use of heat of exhaust gases, simplification of technological and repair operations, reduction of their duration NOSTA, improved environmental friendliness of the process, the expansion of technological capabilities, the entire process sequence produced with insulated metal volumes, are successively moved into a single workspace unit.  2. A unit for continuous steelmaking, containing a working space bounded by a vault with oxygen tuyeres and fuel-oxygen burners installed in it, walls with loading and technological windows, made in the form of successively arranged melting baths with a hearth part divided into separate technological zones, each of which equal in length to one melting bath, a device for carrying out technological operations, characterized in that it is equipped with devices for moving the melting baths along the working space of the unit and their periodic removal from the unit, while the melting baths are made with the possibility of their autonomous action when sequentially moving from one technological zone to another.

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