MXPA97008409A - Process for melting metal raw materials in a c oven - Google Patents

Abstract

The invention relates to a process for melting substances of metallic materials in a shaft furnace. During the process, the coke is burned with superheated air and substantially clean oxygen, and the combustion gases heat the metal charge counterflow. The foundry is overheated and carburized in the coke bed, air is injected from a fixed portion of the oxygen in the coke bed at a very high rate and as much as possible to improve the passage of gas through the coke bed, and air is injected from a second variable amount of oxygen into the circular duct of the ai

Description

PROCESS TO FUND METAL RAW MATERIALS IN AN OVEN OF CUBA DESCRIPTION OF THE INVENTION The invention relates to a process for melting metal raw materials in a shaft furnace, in which coke is burned with preheated air and very pure oxygen and the combustion gases heat the metal charge in countercurrent, and in which the melt It is superheated and carburized in the coke bed. The metallic and non-metallic materials, such as iron and non-ferrous metals, basalt and green stone, are still melted in vat furnaces heated by coke despite the development of electric and flame-heated casting processes. In this way, approximately 60% of all iron materials are still produced in cupolas to this day. The reason for this high market that shares the cupola is the continuous additional development, with the development of hot air cupola and the use of oxygen among the large number of known process modifications that are of importance.

In this way, for example, the disadvantages of process machining and the metallurgical disadvantages of the hot air cupola, such as - low iron temperatures - high silicon burns - low carburization - high consumption of coke - high absorption of sulfur - high Refractory wear has been greatly compensated for by the development of the hot air cupola. Similar improvements are achieved by the use of oxygen, the oxygen that is blown in the cupola either by enriching the cupola air to a maximum of 25% or by direct injection at a subsonic speed. Due to the high operating costs, however, only oxygen is discontinued discontinuously, for example for quick start of furnace cooling or to raise the iron temperature for a limited period. The possibility of increasing the output, that is, the continuous use of oxygen, is exploited only in exceptional cases. Despite the introduction of these modifications to the process, it is still possible to - the casting outlet - the iron temperature - the coke load varies only within a very narrow range at the optimum operating point. The relationship between the melt outlet and the air velocity, as well as the oxygen addition ratio is described by the known Jungbluth equation. This equation results from a generation of mass and energy, with the coke charge and the combustion ratio that are determined empirically for each cupola. By joining the active parameters, ie the air velocity, the coke charge and the combustion ratio, to the objective parameters produces the casting output diagram, Figure 1, with equal coke load curves and equal air velocities. The casting exit diagram, known as the Jungbluth diagram, must be determined empirically for each cupola. A transfer to other cupolas is not possible, since the operating behavior changes immediately when the conditions are altered such as tendency of coke to form lumps, coke reactivity, charge composition, air velocity, oven pressure, temperature etc. . Heat losses are decreased by a maximum temperature. At excessively high air velocities, that is, at a high flow rate, the furnace is blown out. At excessively small air velocities, that is, excessively low flow velocity, the furnace has a reduced blow. In both cases, the combustion temperature decreases, since, on the other hand, the coke shell with additional N2 must also be heated and, on the other hand, the heat is eliminated by the additional formation of CO. Additionally, the elements that accompany the iron are oxidized more completely in the supershoot. Using oxygen up to, say, 24% by volume in the air, the net line is diverted to the upper right, that is, at high temperatures and higher iron yields. The maximum temperature decreases, and the oven becomes insensitive for reduced blowing or overwrapping. A reduction in the coke load is not possible in constant iron yields and reduced air velocities even with continuous additions of oxygen, since the iron temperature drops and additional machining and metallurgical problems arise, such as - decreased carburization - increase in the burning of Si - increase in the FeO content in the slags - the wall that channels in the furnace due to a reduction in air velocity The cupola produces iron which can not be cast.

Since, from the point of view of the combustion technology, a large excess of coke is present, a reduction in the amount of coke in the output of constant casting is of great interest for economic reasons, since the costs of manufacturing Cast iron is essentially affected by the costs of recast and the costs of raw materials. Additionally, it has been known for a long time that, especially in the case of cupolas having large diameters of structure, the so-called "anchoring mass" still remains in the center of the furnace despite the oxygen enrichment of the air and / or injection Direct oxygen at a subsonic speed. The reaction between the blown oxygen and the carbon takes place only within a restricted region in the vicinity of the air nozzle, that is, the furnace operates with wall ducting. The coke present in the center of the furnace does not contribute to the reaction, since, due to the low momentum, the combustion air can not penetrate the bed located in the front part. The reaction zone is located in the immediate vicinity of the air nozzle (Figure 2a). The depth of penetration is not substantially increased by the known enrichment of the furnace air or by blowing oxygen at a subsonic speed. Due to the high availability of oxygen, the reaction zone expands upwards due to the pressure conditions (Figure 2b).

As a precondition for the desired reduction in the amount of combustion coke, the objective should be uniform combustion between the cross-section of the furnace, that is, the uniform distribution of available oxygen. For this purpose, the momentum, that is, the velocity of the air or the oxygen jets, must be increased beyond the objective values to be described as hitherto in the state of the art. Patent application GB 2,018,295 describes a system by means of which oxygen is blown by means of Laval nozzles incorporated centrally in the air nozzles, that is, at a supersonic speed, in order to minimize wear or the refractory liner . It is not possible to reduce the coke load. In contrast, tests with supersonic nozzles incorporated in the air nozzles have shown, surprisingly, that the combustion coke can be reduced by 20 to 30 kg / t of Fe, without an adverse effect on the operation of the furnace and the metallurgy of iron, if at the same time the air velocity of the specific furnace is reduced from 500 to 600 m3 (iD) / t of Fe from 400 to 480 m3 (iN) / t of Fe and additional oxygen is blown as a function of the diameter of the oven (Figure 3). The specific demand for oxygen must be changed according to Figure 3. In the case of a hot air cupola (500 to 600 ° C hot air temperature) and a furnace diameter of 1 m, approximately 15 to 22 m3 (iN) of oxygen per ton of iron are required, and 40 to 61 m3 (iN) of oxygen per tonne of iron are required in an oven diameter of 4 m. A Mach number of oxygen jets of 1 .1 < M < 3 at the outlet of the nozzle should be set as a function of the diameter of the furnace. Contrary to the theory of cupola so far known, the temperature of the intake is at the same time increased by up to 30 ° C. As a result, the burning of silicon by 10% is reduced and carburization by 0.2% is improved. The best results are obtained with respect to the saving of coke if a fixed part of the oxygen velocity is introduced into the cupola by supersonic injection, since it then applies a more uniform oxygen distribution between the transverse section of the cupola. The proportion of oxygen remaining in a controlled manner is mixed with the air in the air ring (Figure 4). These measurements make analytical constant control possible. The oxygen enrichment in the air blast is controlled and regulated via the CO, CO2 and O2 components in the air oven gas. The reaction zone; which has advanced in the form of a tongue to the center of the cupola as a result of the supersonic injection (Figure 2c), is amplified upwards and becomes more uniform, since, due to the suction power of the supersonic jet, additionally conveys the combustion air enriched with O2 in the center of the furnace (Figure 2d).

Due to the reduction in the oven air, the oven pressure is reduced and the air oven gas ratio decreases by 20%. Due to the decreased flow velocity in the furnace, the amount of powder is further reduced proportionally to the gas ratio of the air furnace. The temperature of the hot air increases by up to 30 ° C, since the recuperator has less to do due to the reduced air ratio. The following principles apply to the division of the oxygen addition in each case to the air ring and to the nozzles. The basic quantities can be selected from the diagram of OCI1 .XL5. The absolute ratio of the oxygen addition is determined by the desired iron temperature. The iron temperature increases when the temperature in the coke bed increases. The temperature in the coke bed increases when the cooling effect of the nitrogen that accompanies the oxygen is absent. The amount of oxygen to be added supersonicly through the lances increases with the size of the furnace. The optimal ratio between the ratio of oxygen added through the spears = 01 and the ratio of oxygen added as enrichment to air = 02 is sought at the beginning for the iron temperature measurement and is then present on the controller.

The optimum ratio of the volume fractions of CO and CO2 in the gas of the air furnace is determined from the sum of the resulting operating costs. A more powerful reducing atmosphere with high CO contents provides savings in silicon and high costs for coke. The optimal fixation therefore also depends on the prices of the particular market of the raw materials. There are times and countries where a more oxidative operating procedure is economical. Therefore, the most advantageous CO / CO2 ratio should be checked from time to time, and the proper oxygen ratio should be set. The optimal CO / CO2 fixation destined fluctuates, since this is caused by the variation in the coal / iron charge quantities. These low-term fluctuations can be compensated by adapting the addition of oxygen. The Boudouard reaction is rapid, since the temperature of the coke bed rises very rapidly when oxygen is added. The feed of the total oxygen ratio to 01 and to 02 is therefore controlled in such a way that the CO / CO2 ratio is maintained at a more economical value. With this operating procedure, the smallest variation in the analysis is then also achieved.

Claims (5)

1 . A process for melting metallic raw materials in a vat furnace, in which coke is burned with preheated air and very pure oxygen and the combustion gases heat the metallic charge in countercurrent, and in which the melt is superheated and carburized in the Coke bed, characterized in that it comprises, for an improved gas penetration in the coke bed, to inject a fixed part relation of oxygen as large as possible in the coke bed at a very high speed and to inject a second variable ratio of oxygen in the air ring.

2. The process, according to claim 1, characterized in that the fixed part ratio is selected in such a way that the highest possible iron temperature is established.

3. The process, according to claim 1, characterized in that the CO / CO2 content of the air furnace gas can be adjusted optimally by the furnace losses. I I

4. The process, according to claim 1 and 2, characterized in that the optimum temperature of the iron is kept constant by means of a control circuit.

5. The process, according to claim 1 and 3, characterized in that an optimum atmosphere of the furnace can be kept constant by means of a control circuit. SUMMARY OF THE INVENTION The invention relates to a process for melting substances of metallic materials in a shaft furnace. During the process, the coke is burned with preheated air and substantially clean oxygen, and the combustion gases heat the metal charge in a counterflow. The foundry is overheated and carburized in the coke bed, air is injected from a fixed portion of the oxygen in the coke bed at a very high rate and as much as possible to improve the passage of gas through the coke bed, and air of a second variable amount of oxygen is injected into the circular air duct. Amendments to the Figures Figure 1 Iron temperature in ° C Air ratio m3 / m2 minute (3% additional O2) C availability in% with O 2 at 3% C availability in% Without O2 Air ratio m3 / m2 minute (without O2 at 3%) Cast iron output in t / m2h) Figure 3 Oxygen (m / t) Supersonic injection Air enrichment Oven diameter Figure 4 Air oven air