CN1004707B - Oxygen Converter Coal Oxygen Combined Blowing Process - Google Patents

Abstract

The invention is a combined blowing process for an oxygen top-blown converter using bottom-blown coal and oxygen. The entire smelting process is regulated and controlled by means of the top blowing oxygen lance: the bottom coal oxygen lance can inject coal oxygen from beginning to end without affecting the top blowing operation, in order to achieve the functions of thermal compensation and stirring the molten pool. The invention can effectively increase the heat supply in the furnace and increase the scrap steel ratio in the furnace charge. At the same time, even when the carbon content of the molten pool is very low, it can maintain a high decarburization speed, reduce the oxidation of slag, and eliminate the overoxidation of the molten pool. The invention can also improve the desulfurization ability of slag and the recovery rate of manganese.

Description

Coal-oxygen composite converting process of oxygen converter

The invention belongs to a converter steelmaking process. The method is mainly suitable for thermal compensation of the oxygen top-blown converter and improves the capability of the converter for receiving cold raw materials (scrap steel, pig iron, sponge iron and the like).

Conventional converter steelmaking relies on the physicochemical heat of the charge itself to raise the bath temperature and provide heat for heating the molten scrap. Therefore, the addition amount of the scrap steel is strictly limited by the physical chemical heat of the molten iron, and the fluctuation of the scrap steel ratio is 5-25%. This is a major disadvantage of the converter steelmaking process compared to the open hearth process. In recent years, in order to save blast furnace coke and other reasons, the silicon content of steel-making molten iron at home and abroad is reduced, and the chemical heat of the molten iron is reduced. After the existing composite converting technology is adopted, the oxidation loss of iron is reduced, and the capability of melting the converter scrap steel is correspondingly reduced. In order to remedy this problem, metallurgical workers in various countries have proposed various technological schemes to improve the thermal efficiency of the converter. At present, a plurality of new steelmaking processes are developed in succession around the adoption of the converter coal injection technology. The purpose is to increase the addition of the scrap steel of the converter and enhance the adaptability of the converter to the furnace burden.

The converter thermal compensation technology which is successfully developed or is being researched and developed abroad can be divided into a top blowing method and a bottom blowing method.

The bottom blowing method is represented by KMS method (STEELMAKING PROCEEDINGS, 1982, vol65, 287-295) of West Germany Clockner-CRA technology development Co. The process changes a bottom oxygen lance of a bottom blowing converter into a bottom blowing coal oxygen lance. The spray gun adopts a three-layer sleeve structure, coal powder is sprayed from a central tube, oxygen is sprayed from a middle circular seam, and a cooling medium is filled into an outer circular seam. In the middle smelting stage, coal and oxygen are blown at the bottom to provide heat for a molten pool and melt scrap steel. And in the initial stage and the later stage of smelting, the pulverized coal is switched into lime powder for normal smelting. In order to improve the thermal efficiency of the heat exchanger, an oxygen gun is arranged at the top of the bottom blowing converter, and furnace gas is combusted. The bottom blowing oxygen lance protection technology is still adopted, and the bottom coal oxygen lance is protected by natural gas or methane gas. In order to solve the problems of dephosphorization in the earlier stage and slag formation as soon as possible, the thermal efficiency of a molten pool is improved, and a bottom spraying lime powder technology is adopted. The process can melt about 6 kg of scrap steel by one kg of coal dust.

KMS is a thermal compensation process technology suitable for bottom blowing converters. It retains the metallurgical characteristics of bottom blowing converter, unlike top blowing method, and has a great amount of foam slag in the smelting process, so that its heat efficiency is low. The process has the following defects that the natural gas is required to be consumed for cooling the coal oxygen spray gun by each ton of steel by 2.7 standard meters ³ or 3-5 kg of oil, and the distribution coefficient of sulfur among slag steel at the end of smelting is only 8-12.

The top-blowing method is represented by TAPS method (iron-in-steel 1986, no. 15, 71-84) and ALCI method of Luxembourg (STEELMAKING PROEEDINGS, 1985, vol68, 129-136) in Japan. The technology is characterized by taking top-blown coal dust as a characteristic, and combines the coal dust injection technology of the converter with the secondary combustion technology to improve the steel scrap ratio of the top-blown converter. The TAPS method was used for 15 ton converter experiments. And the TAPS oxygen lance is adopted, so that the pulverized coal is sprayed into the solution pool at a higher powder supply speed in the middle smelting period as short as possible. In order to improve the yield of the pulverized coal, a hard blowing process is adopted, the gun position is reduced, and the pulverized coal is sprayed into molten steel. 4 kg of scrap steel can be added for each kg of coal dust. The ALCI method has been tested in 250 ton LBE combined blown converter from Junjin. The process is basically the same as the TAPS method, and one kilogram of coal dust can be used for melting 4-6 kilograms of scrap steel.

The TAPS and ALCI method is suitable for a thermal compensation process of top-blown smelting, and has the main defects that the smelting process is interrupted by adopting a top-blown coal powder technology, the powder spraying amount and the powder spraying time are limited, the thermal efficiency is low, the CO ₂ content in furnace gas is reduced by adopting a hard-blown coal powder technology, the normal operation of a top lance is disturbed, the problems of slag overflow and splashing caused by low-temperature foam slag formed in a furnace after a large amount of scrap steel is added cannot be solved, the desulfurization efficiency is low, and the distribution coefficient of sulfur among slag steel is only 4-6.

Another process, the COIN method, was proposed by the Side Krupp institute. The process is characterized in that pulverized coal and oxygen are sprayed from the bottom of a molten pool, and a pulverized coal protection spray pipe is directly adopted. However, it is known by the company that refining cannot be performed simultaneously by this operation method.

The invention aims to provide a hot compensation steelmaking process technology of a top-blown oxygen converter, which has the advantages of high heat efficiency, high scrap steel ratio (or other cold material ratio), low cost, capability of improving the product quality and good metallurgical effect.

The solution of the invention is as follows:

One or more coal-oxygen spray guns (which are different according to the size of the furnace) are arranged on the bottom of the top-blown oxygen converter. Not only top blowing oxygen, but also bottom blowing coal oxygen. On one hand, the smelting process is regulated and controlled by means of top lance operation, so that the advantages of high slag melting speed and high heat efficiency of the top-blown oxygen converter are maintained, and on the other hand, the characteristics of high metal yield of the bottom-blown coal oxygen, strong stirring of a molten pool, large heat supply and stable blowing are exerted, so that the optimal metallurgical effect is obtained. Meanwhile, coal dust is directly used as a coolant to protect the bottom spray gun, so that the conventional natural gas or light diesel oil is replaced, and the cost is reduced.

In the whole process of coal-oxygen composite converting, the smelting process is controlled by adjusting the lance position and the oxygen flow of the top-blowing oxygen lance. Simultaneously, coal dust and a part of oxygen are sprayed from the bottom all the time, and the characteristic of high-efficiency heat supply is fully exerted. The coal injection amount can be adjusted, and the operation of the top-blown oxygen lance is not interfered.

In order to improve the heating benefit of coal, the top-blown oxygen lance adopts a multi-hole lance (comprising a double-flow-passage lance) so as to strengthen the secondary combustion of furnace gas.

When converting is started, the invention adopts small coal-oxygen ratio (namely, the ratio of the flow of coal powder to the flow of oxygen is smaller) to provide heat for the molten pool, thereby accelerating the temperature rise of the molten pool, and avoiding the phenomena of slag overflow and splashing caused by excessive temperature drop of the molten pool when the amount of scrap steel is large.

In the middle of converting, in order to prevent the strong stirring of bottom blowing coal and oxygen and the tendency of easy return of slag, a top lance adopts the soft blowing operation of 'high lance position, large oxygen pressure and dispersed oxygen supply'. The gun position is adjusted in time to strengthen the emulsification and oxidization of the top oxygen jet flow on the slag, ensure certain FeO content in the slag and promote the dissolution of lime.

At the final stage of smelting, coal oxygen is continuously injected into the molten pool to obtain good metallurgical effect, and the main appearance is that (1) the molten pool still keeps higher decarburization speed at the final stage, but FeO in slag is low to prevent the peroxidation of the molten pool. Practice proves that when low-carbon steel is smelted, the content of FeO in slag and oxygen in steel are the same as those in a bottom blowing method. (2) The desulfurization capability of slag is improved, the distribution coefficient of sulfur among slag steel reaches 10-20, which is higher than that of a bottom blowing converter steelmaking method of bottom spraying lime powder. (3) is also advantageous for dephosphorization. And at the end of converting, properly increasing the bottom blowing oxygen pressure and controlling the coal-oxygen ratio to be less than 1.0.

The solution of the invention can be further illustrated by the following figures.

FIG. 1 is a process flow diagram of the present invention.

FIG. 2 is a graph showing the effect of fixed carbon content on the ability to melt scrap.

FIG. 3 is a graph showing the relationship between the flow rate of pulverized coal and the oxygen supply intensity of a single coal-oxygen lance;

FIG. 4 is the effect of bottom-blown coal-to-oxygen ratio on the combustion of furnace gas;

FIG. 5 is a graph showing the relationship between nitrogen content in steel and bottom blowing oxygen to nitrogen ratio;

FIG. 6 is a graph of critical velocity versus powder to gas ratio;

Figure 7 shows the change of the technological parameters of the bottom coal injection of the six-ton converter.

In the attached figure 1,1 is a hopper, 2 is a vibrating screen, 3 is a powder storage tank, 4 is a powder injection tank, 5 is a bottom blowing coal oxygen lance, 6 is a top blowing oxygen lance, 7 is a nitrogen control system, 8 is a converter, 9 is a discharge valve, 10 is a coal dust conveying pipeline, and 11 is a bottom blowing oxygen pipeline.

Before smelting starts, the powder spraying tank 4 is pressurized by a nitrogen control system 7. After pressurizing, the discharging valve 9 of the powder spraying tank is opened, and coal powder is sprayed into the molten pool in the converter 8 through the coal powder conveying pipeline 10 and the hearth oxygen coal 5. Simultaneously, an oxygen valve is opened to supply oxygen to the molten pool through a coal oxygen gun.

The coal-oxygen lance is of a double-layer sleeve structure: the inner tube conveys oxygen; the external circumferential seam conveys pulverized coal. Coal powder is used as cooling medium to protect the bottom of the furnace from blowing oxygen gun.

After the powder spraying is stable, a small amount of slag is added into the converter 8 from the furnace mouth, and then scrap steel is added. If the steel scrap ratio is high, the addition amount is large, and the steel scrap can be added in two batches. Then adding molten iron. After molten iron is added, the furnace body is rocked, and the top gun is lowered to blow. When blowing, the gun position of the top gun needs to be controlled, and primary slag is quickly changed. And meanwhile, the bottom oxygen blowing pressure is improved, and the full combustion of the sprayed pulverized coal is ensured. 3-5 minutes after blowing, entering a decarburization period, and enabling the C-O reaction to be severe. The top blowing gun position should be improved in time to avoid or reduce the middle-stage slag from being returned to dryness. At this time, the bottom-blown coal oxygen ratio was controlled to about 1.0. After converting for 10-12 minutes, the molten pool tends to be stable. The top gun should be lowered in time to increase the decarburization speed of the molten pool. And pouring the furnace after the carbon flame is received, wherein the carbon fluctuation of the furnace pouring is 0.03-0.10%, and tapping.

The invention has high heat efficiency, and according to practical results, 7-9 kg of scrap steel can be melted by injecting 1 kg of coal dust. As shown in fig. 2. The vertical axis in the figure is the capability of one kilogram of coal powder to melt scrap steel (1 kilogram of scrap steel/kilogram of coal), and the horizontal axis is the fixed carbon content in the coal powder. It can also be seen from the figure that the fixed carbon content of the pulverized coal has a great influence on the thermal efficiency of coal injection. The process has the requirements on pulverized coal that fixed carbon is more than 70%, sulfur content is less than 0.5%, and moisture content is 0.5-1.5% of anthracite pulverized coal. The granularity of the pulverized coal is required to be less than 100 meshes. The pulverized coal can also be replaced by coke powder.

The flow Gs (kg/min) of the pulverized coal injected from the bottom is calculated according to the selected coal type, the secondary combustion intensity and the required increased scrap steel amount W as follows:

Gs=W/6.5 (1+2B) (% C) t (kg/min)

Wherein B is the secondary combustion rate of furnace gas, t is converting time (in minutes) (%C) is the fixed carbon content in coal, and W is the required increased scrap steel amount compared with the case of not spraying coal powder.

P _co and P _co2 are the partial pressures of CO and CO ₂, respectively, in the furnace gas.

The flow rate and oxygen supply intensity of the pulverized coal sprayed by the single coal-oxygen lance and the capability of melting scrap steel are shown in figure 3. In the figure, the vertical axis is the oxygen supply intensity (³/min) of a single spray gun, and the horizontal axis is the pulverized coal flow (kg/min) of the single spray gun. The oxygen supply pressure at the bottom is 6-12 kg/cm ², the oxygen supply intensity is 0.6-1.5 standard meter ³/ton/min, and the oxygen supply at the bottom accounts for 15-30% of the oxygen supply at the top.

FIG. 4 shows the effect of bottom-blown coal-to-oxygen ratio on the combustion of furnace gases. In the figure, the ordinate is P _co2/P_co+P_co2, and the abscissa is the ratio of coal to oxygen (weight ratio). According to the graph, the weight ratio of the bottom coal injection oxygen is controlled within the range of 0.4-1.2, so that the thermal efficiency of coal injection can be improved.

FIG. 5 is a graph showing the relationship between nitrogen content in steel and the volume flow ratio of bottom-blown oxygen to nitrogen. In the figure, the vertical axis represents the nitrogen content (PPm) in steel, and the horizontal axis represents the volume flow ratio of bottom-blown oxygen to nitrogen. According to this figure, the bottom blowing oxygen to nitrogen volumetric flow ratio should be greater than a certain amount (e.g., greater than 5.0) to limit the nitrogen content in the steel.

FIG. 6 is a graph showing the relationship between the pulverized coal outlet velocity Vm and the pulverized coal-gas ratio mu ₂ (the weight ratio of pulverized coal to carrier gas such as nitrogen). From the graph, when the powder-gas ratio mu ₂ of the outlet two-phase flow fluctuates within the range of 5-25, the apparent gas speed of the outlet is correspondingly controlled within the range of 200-80 m/s, so that the purpose of stably conveying the pulverized coal can be achieved.

Fig. 7 shows the variation of the process parameters of the bottom coal injection of the six-ton converter. In the figure, the vertical axis represents each process operation parameter (such as cylinder pressure, powder discharge amount, flow ratio, etc.), and the horizontal axis represents time. By adopting the powder spraying process, the pulverized coal is stably conveyed to a molten pool.

The coal-oxygen composite blowing process of the invention achieves good metallurgical effect, and mainly comprises the following steps:

(1) Improves the stirring condition of a molten pool at the end of smelting and reduces the oxidizing property of slag. In the low carbon area, the iron oxide content in the slag and the oxygen content in the steel are equivalent to those of a bottom blowing method;

(2) The distribution coefficient of manganese among slag steel is reduced, the recovery rate of manganese is improved, and meanwhile, the desulfurization capability of slag is improved, and the distribution ratio of sulfur among slag steel is up to 10-20.

(3) When the volume flow ratio of the bottom blowing oxygen and the nitrogen is controlled to be larger than a certain value, such as larger than 5.0, the nitrogen content in the steel can be controlled to be below 60 PPm.

(4) High heat efficiency. 7-9 kg of scrap steel can be melted by one kg of coal dust. The scrap steel ratio can reach 40-50%, and the process operation and the smelting time are not greatly influenced.

Compared with a bottom blowing coal injection process-KMS method or compared with a top blowing coal injection process-PLCI and TAPS method, the invention has the following advantages:

(1) The coal dust is directly used as a cooling medium to protect the bottom blowing coal-oxygen lance, and the natural gas is saved by 2.7 standard meters ³ per ton of steel or 3-5 kg of oil per ton of steel.

(2) The metallurgical effect is good, the slag desulfurization capability is strong, and the distribution coefficient of sulfur among slag steels reaches 10-20.

(3) The heat efficiency is high, and 7-9 kg of scrap steel can be melted by one kg of coal dust.

(4) Coal injection and molten pool refining are carried out simultaneously, the coal injection time and the coal injection amount are not limited, high scrap ratio operation can be adopted, and the smelting time does not need to be prolonged.

Example 1

An oxygen spraying gun is arranged at the bottom of the six-ton oxygen top-blown converter, and coal dust is used as cooling medium by the oxygen spraying gun. The charging amount of the ingredients is 10 tons, the steel scrap is 2 tons, the molten iron is 8 tons, the using amount of the steel scrap is increased by 1.5 tons, and the steel scrap ratio is 20%.

The molten iron comprises 4.0% of C, 0.6-0.8% of Si,0.06% of P and 0.05% of S. Pulverized coal with 83% of fixed carbon and 0.37% of sulfur content is adopted, 21.4 kg of pulverized coal is consumed by ton of steel, the flow rate of pulverized coal injection is 10 kg/min, the oxygen (weight) ratio of bottom blowing coal is 0.9, the oxygen supply strength of bottom blowing coal is 0.93 standard meter ³/min/ton, and the oxygen supply strength of top blowing coal is 3.2 standard meter ³/min/ton.

Blowing time was 20 minutes. The end tapping temperature is 1710 ℃. The carbon content in the steel is 0.08%, the sulfur content is 0.020%, the P content is 0.010%, and the FeO content in the slag is 11%.

Example two

The apparatus of example one and the same starting materials were used. The addition amount of the scrap steel is 4 tons, the molten iron is 6 tons, the addition amount of the scrap steel is 3.5 tons, and the scrap steel is 40 percent. And the coal consumption per ton of steel is 40 kg. The flow rate of the pulverized coal is 20 kg/min, the top oxygen supply strength is 3.2 standard meter ³/min.ton, the bottom oxygen supply strength is 1.6 standard meter ³/min.ton, and the coal-oxygen (weight) ratio is 1.0.

The final tapping temperature is 1630 ℃, the carbon content in the final steel is 0.03%, the sulfur content is 0.03%, and the FeO in the slag is 12%. Blowing time was 20 minutes.

Claims (6)

1. A top-blown converter steelmaking composite blowing process in which pulverized coal and oxygen are injected into the molten pool via a coal-oxygen injection lance installed at the bottom of the converter. The process is characterized in that pulverized coal and oxygen are injected simultaneously into the molten pool via the lance throughout the entire smelting process. The top-blowing oxygen lance utilizes a multi-hole lance (including a dual-flow channel lance) and adopts a "soft blowing" process with a high lance position, high oxygen pressure, and dispersed oxygen supply. 2. The composite blowing process according to claim 1, wherein the pulverized coal flow rate Gs of the bottom-blown coal oxygen is determined by the following formula: Gs＝W/6.5（1+2B）（%C）t（kg/min） Where t is blowing time, (%C) is the fixed carbon content in coal, W is the amount of scrap steel required to be increased compared to when no pulverized coal is injected, and B is the secondary combustion rate of furnace gas. P _co and P _co2 are the partial pressures of CO and CO ₂ in the furnace gas respectively. 3. The composite blowing process according to claim 1, wherein the amount of bottom blowing oxygen is 15-30% of the amount of top blowing oxygen. 4. The composite blowing process according to claim 1, wherein the weight ratio of the bottom-blown coal to oxygen is controlled within the range of 0.4 to 1.2. 5. The composite blowing process according to claim 1, characterized in that the powder-gas ratio (weight ratio of coal powder to its carrier gas, such as nitrogen) of the two-phase fluid conveyed by the bottom-blowing coal oxygen lance is controlled within the range of 5 to 25, and the superficial flow velocity of the two-phase fluid at the outlet is correspondingly controlled within the range of 200 to 80 m/s. 6. The composite blowing process according to claim 5, characterized in that when nitrogen is used as the carrier gas for carrying pulverized coal, the volume flow ratio of bottom blowing oxygen and nitrogen should be greater than 5.0.

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