SU679784A1 - Charge pre-heating plant - Google Patents

Description

The invention relates to metallurgy, in particular to steelmaking in electric furnaces and converters, where. loading of metal charge with baskets is used. A device for preheating a mixture of oxygen converters 1 is known, which is a rotating drum with a refractory base mounted on inclined sectors or another device that allows the drum to be tilted. One end of the drum is connected to the exhaust tract of the converter, and the other end is connected with a portion of the exhaust tract in close proximity to the converter. At this end there is a lance, through which oxide is blown into the drum. While the metal is being purged in the converter, the portion of solid charge is preheated. the drum is due to the heat of the exhaust gases, and the CO in the exhaust gases is burned by feeding the oxidant through a lance. After the melting is released, the drum is tilted and the heated mixture is loaded into the converter, and then another portion of the charge is fed into the drum and the melting is started in the converter. The disadvantage of the known device. This is the possibility of significant oxidation of the charge during the heating process. This is explained by the fact that the charge is heated in a stream of complete oxidation products having a temperature in excess of 1500 ° C. In this case, when heating scrap of ferrous metals to a temperature above 800 ° C, its oxidation is inevitable, which leads to a decrease in the yield of a suitable metal. Metal oxidation could be avoided by limiting the temperature of the exhaust gases due to suction of ambient air into the drum to supply excess oxidant through the lance. However, this increases heat loss due to an increase in the volume of waste gases and reduces the heating efficiency. A device for preheating the charge is also known, which includes an incineration chamber, an umbrella for gas extraction, a heat exchanger and a gas afterburning chamber with a grate, equipped with a .11 Batch, in the lower part of which an annular channel is connected to the nozzles of the combustion chamber. A nozzle is installed between the annular channel and the combustion chamber. connected to the gas supply path. The nozzles at the top are covered with visors, and the number of nozzles depends on the diameter of the tank 2. The disadvantage of this installation is the impossibility of heating the charge over the products of complete combustion, as this causes metal oxidation and a decrease in the yield. The installation provides for heating with incomplete combustion products (which removes restrictions on the heating temperature of the charge) with the afterburning of these products outside the batch in a special chamber and the subsequent use of the body obtained here to heat the air in recuperate. This installation option has the following disadvantages; installation design is complicated (afterburner and recuperator required); the degree of heat utilization decreases as additional heat losses are inevitable in both the afterburning chamber and the recuperator. The aim of the invention is to improve the use of heat from waste gases, increase productivity, simplify the design and operating conditions. The goal is achieved by the fact that the nozzles are placed in two or more Russ on the height of the tub within 1 / 4-2 / 3. Such an arrangement of the nozzles allows the gases to be burned directly in the layer at the charge temperature below. In this case, the limitation on the heating temperature of the scrap of the products of complete combustion of fuel is removed, and when heated with products of incomplete combustion, the thermal efficiency of the device is increased due to the refusal to install the heat exchanger and the afterburner. At the same time, the design of the device is simplified and reduces the cost of its manufacture. The drawing shows the scheme of the described device. The device contains a loading bucket 1 with a drop-down bottom 2. The upper part of the bucket is covered with a lid 3 with an opening. Bottom 2 ba dyi match with. smoke box 4, which is connected with smoke duct b by duct 5, in the side wall of the bucket 1 there are several channels of openings with nozzles that are closed from inside with protective visors 8. The upper shaft is set at a distance of 2/3 of the tub height and the bottom is distance 1/4 of this height. The rest of the ru are distributed evenly between the top and bottom, and their number is not limited (in principle, the more Russ, the better). The device works the next time. Waste gas from a steel-smelting furnace, for example, from an electric arc furnace, flows through a hole in the lid of the tub to the surface of the scrap metal placed in it. The temperature and composition of the gases depend on the melting period in the smelting furnace. The gas temperature is 800-1700 ° C, and the carbon monoxide content is 0-80%. In this case, the following regularity is always observed: the higher the temperature of the gases, the greater the content of carbon monoxide in them. This allows supplying gases to the surface of the heated scrap, without first limiting their temperature, since the presence of CO in them does not lead to the oxidation of scrap when it is heated above 800 ° C. The post-combustion of carbon monoxide contained in the gas is produced in the scrap layer by feeding an oxidant through nozzles installed in the side wall of the tub. The angle of inclination of the nozzles to the axis of the tub, depending on various conditions, can vary from 90 to 10 °. Begin to deliver the oxidizer to the upper rus of the nozzles until the scrap temperature at the level of the specified Rus reaches bOO-800s. The magnitude of this temperature is determined by the type of scrap being heated. Although thermodynamically noticeable oxidation of scrap begins after heating above 800 ° C, experiments show that scrap with a developed surface (for example, chips) begins to oxidize earlier. Thus, for very fine chips, the onset temperature is about 600 ° C, which is explained by the catalytic action of some oxides present on its surface. Experiments also show that it makes no sense to place the top nozzles above 2/3 of the tub height, since when scrap is heated, the average mass is up to 500 ° C (this guarantees a high degree of heat utilization and the absence of metal oxidation) during the heating cycle The level of the upper rusa manages to reach the required temperature without after-burning CO. After the temperature at the level of the upper russia reaches 600,800 ° C, the oxidant in the lower rus is located next to be blown in until the indicated temperature is reached at its level. In the same sequence, the oxidizer is fed through all the other Russ of the nozzles (ending with a low brown). It is not recommended to place the nozzle lower nozzles below 1/4 of the height of the tub, since otherwise overheating of the opening bottom is observed with the possibility of its destruction. The device works in the same way, if instead of exhaust gases from a steel-smelting furnace, products of incomplete combustion of fuel are used. To compare the performance of the proposed and known devices, in a laboratory installation, scrap metal from carbon steel or a tub of a cylindrical form, is heated in which 640 kg of scrap is placed. The dimensions of the tub are as follows: a height of 1000 m is a diameter of 800 mm. The tub has a bottom with holes for pumping gases. Example. Heating in the proposed device. A gas-air burner is installed in the lid of the tub, to which 14 gas is supplied to natural gas (methane). In order to prevent the oxidation of the upper layer of the breakage into the tank, the combustion of gas with air is carried out at a flow coefficient d O, Ci. At the entrance to the layer, the parameters of the combustion products are as follows: composition,%: CO 9.1; CO2 3.7; 11 HjO 14.2; Nj- the rest; temperature 1287 ° C. The afterburning of gases is carried out in a layer, for which, in the side wall of the tub, 9 nozzles are installed in three tiers — three in the tusk, through which air is blown. The nozzles of the upper tier are located at a height of 700 mm; medium - at a height of 500 mm; bottom - at a height of 250 mm. Jets of air are directed to the axis of the tub at an angle of BO. The amount of air is calculated from the composition of the gas at ot 1.1. The supply to the nozzles of the upper Russ starts simultaneously with the supply of natural gas to the burner located on the lid of the tub. After 14 minutes at the level of the nozzles of this trough, the scrap temperature is equal to 750 ° C, after which the switch to air supply through the middle trestle nozzles, on which in 10 minutes so the temperature reaches 750 ° C. 4 After this, air is supplied to the nozzles of the lower rus. After 8 minutes, upon reaching a temperature of 700 ° C, the flow of air into the nozzles of the lower rus is stopped. The temperature of the scrap in the lower part of the tub is 380C. Total heating time 32 minutes; the average mass temperature of scrap is 730 ° C; oxidation (waste) of scrap determined by weighing, 0.10%. Thermal efficiency of 62.4%, Example 2. Heating in a known device. Tub equipped with nozzles at the bottom, afterburner and recuperator. Natural gas also in the amount of 14 m W / h is burned with air in the burner in three modes: G., Incomplete combustion, with a value of 0.60; II. Full burning with СХ.1,10; 111. Complete combustion with i 1.72. Modes I and 1H guarantee the absence of scrap oxidation, since the first produces a reducing flame, and the third limits the temperature of the gases entering the heating to. In all cases, the combustion products enter through the pipeline to the nozzles in the lower part of the tub and are sucked from the bottom upwards through the scrap layer, and then sent to the afterburner and recuperator. I do not use the afterburner and heat exchanger in modes H and Sch, since there is nothing to burn in gases, and the temperature of gases leaving the bed is low. In mode I, the afterburner is working, and in the recuperator, the air is heated to 400 ° C and is subsequently used to burn natural gas. In all cases, heating is stopped when the temperature of the upper layer (by 1 min. Temperature along the height of the layer) reaches 380 ° C. The results of the experiments are presented in the table.

Heating time, min

Average scrap temperature, ° С

Minimum scrap temperature, C

Oxidation (waste),% Thermal efficiency,% Performance,%

From the table it follows that the heating in the proposed device has significant advantages over heating in the known device with

34

37

685

730

720

380

380

380

4.4

0.12.

0.10 42.6. 58 52.5

59.3

86.5

94

bom version: whether it is heated by the products of complete or incomplete combustion of natural gas. The proposed 65 device always guarantees the practical