JPS6245282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an apparatus for producing molten metal by pre-reducing powdery ore containing metal oxides and then melting and reducing the ore, in which the pre-reduced ore is transferred from a pre-reduction furnace to a smelting-reduction furnace. The present invention relates to a method for preventing blow-through in a gravity transfer path when a gravity transfer path is carried out.

In recent years, ore raw materials containing various metal oxides have decreased in the form of lumpy ores and have become more powdery or small-grained ores, and the proportion of powdery ores will continue to increase in the future. Conventionally, binders and carbonaceous materials were added to powdery ore to process it into pellets and sintered ore and use it as agglomerates, but this not only required extra resources and energy for agglomeration. However, when firing is required, there is a drawback that the cost for treating NOx, SOx, dust, etc. in the gas discharged from the firing furnace is large.

Furthermore, when smelting is carried out in an electric furnace, such as in the production of ferrochrome by smelting chromium ore, the electricity consumption rate reaches several thousand KWH/t, making the cost extremely high in areas where electricity is expensive.

In view of the above circumstances, the present inventors have developed a method for producing molten metal by directly using powder ore without agglomerating it and producing molten metal without using electricity. We have developed and proposed a method in which the pre-reduced material is blown into a vertical melting reduction furnace together with high-temperature air through the tuyere, and then melted and reduced (Japanese Patent Application No. 1983-63294).

The present invention relates to a method for preventing blow-through of a transfer path for transferring powdery pre-reduced ore from the pre-reduction furnace to the smelting-reduction furnace in a smelting-reduction apparatus comprising a pre-reduction furnace and a smelting-reduction furnace. Transfer of pre-reduced ore in smelting reduction needs to satisfy the following conditions compared to normal powder transfer.

(1) Pre-reduction ore is discharged from the pre-reduction furnace at a high temperature, so this must be dealt with.

(2) It is necessary to branch from the pre-reduction furnace to the many tuyeres of the smelting reduction furnace and distribute it evenly.

(3) The amount of pre-reduced ore injected into each tuyere can be controlled.

(4) By diluting the pre-reduced ore in the transfer pipe, it is possible to prevent accidents in which the tuyere blast gas blows through the transfer pipe.

The present invention enables the smooth transfer of pre-reduced ore even under the above special conditions, and prevents the tuyere blast gas of the melting reduction furnace from blowing through the transfer path of the pre-reduced ore. The purpose is to provide an effective method that can be used.

In the present invention, an atrium prediction box having a cross-sectional area 10 to 50 times the cross-sectional area of this transfer path is interposed in the middle of a gravity transfer path for powdery pre-reduced ore discharged from a pre-reduction furnace. It is characterized in that a change in the position of the boundary surface of the difference in packing density of the pre-reduced ore in the prediction box is constantly detected, and when a sign of blow-through occurrence is detected, the shutoff valve of the transfer path is closed.

A system showing one embodiment of a melt reduction apparatus for carrying out the method of the present invention will be described with reference to FIG.

The pre-reduction furnace 2 is supplied with ore containing powdery metal oxides by the supply device 1 . Part or all of the high-temperature reducing gas discharged from the smelting reduction furnace 3 is introduced into the preliminary reduction furnace 2, and powdery flux, solid reducing material, reducing gas, etc. are supplied from the supply port 4 as necessary. Ru. The granular ore is dried, heated, and pre-reduced in the pre-reduction furnace 2 in a fluidized bed format. The pre-reduced ore is discharged from the discharge port 5 along with flux etc., falls by gravity in the gravity transfer path 6, and is then transported by gas through the introduction pipe 9 provided at the lower end of the gravity transfer path 6. According to this method, the air is blown into the tuyere blower branch pipe 8, and is blown into the melting reduction furnace 3 together with the high temperature air in the tuyere blower branch pipe 8. The pre-reduced ore described in the present invention may be accompanied by the above-mentioned granular flux and solid reducing agent, and these are collectively referred to as pre-reduced ore.

Inside the melting reduction furnace 3, a packed bed is formed of a lumpy carbon-based reducing agent supplied by a supply device. The pre-reduced ore blown into the smelting reduction furnace 3 is melted inside the smelting reduction furnace 3 and reduced while dripping down the lower part of the smelting reduction furnace to generate molten metal and molten slag, which are then discharged from the discharge port 13. It is discharged from the furnace in a timely manner.

The present invention relates to a method for preventing blow-through of tuyere blown gas in the method for transferring pre-reduced ore described above. The length of the gravity transfer path is designed so that the resistance of the powdered pre-reduced ore filling the transfer path is greater than the difference between the tuyere blow gas pressure and the pressure in the pre-reduction furnace, so it is usually Blow-through of the tuyere blast gas should not occur. However, as a result of the inventors' experimental study of the blow-through phenomenon using an experimental device that allows direct observation, we found that in the following cases, the powder in the gravity transfer path is diluted and the packing density decreases, and the powder When the resistance becomes smaller than the difference between the pressure at the tuyere and the pressure at the pre-reduced ore discharge port of the pre-reducing furnace, it becomes clear that the tuyere pressure is higher and the tuyere blast gas blows through to the pre-reducing furnace. Ta.

When a large amount of the carrier gas for transporting powder that is blown into the introduction pipe installed at the lower end of the gravity transfer path flows back into the preliminary reduction furnace.

When powder becomes clogged due to agglomeration (sintering) in the gravity transfer path or at the outlet of the pre-reduction furnace and cannot flow smoothly.

When the tuyere blow gas blows through the pre-reduced ore transfer path, the following problems occur.

(a) The inside of the fluidized bed pre-reduction reactor is a high temperature and flammable atmosphere containing CO, and there is a risk of explosion if tuyere blast gas containing oxygen enters the pre-reduction reactor.

(b) reoxidizing the pre-reduced ore in the pre-reducing furnace;
In addition, the furnace top may be damaged due to temperature rise due to reoxidation reaction.

(c) It takes time to recover, reducing productivity.

Therefore, from the standpoint of ensuring operational safety and improving productivity, it is important to prevent the tuyere blast gas from flowing into the pre-reduction furnace.

FIG. 2 is a longitudinal cross-sectional view of a gravity transfer path for pre-reduced ore, illustrating the blow-through prevention method according to the present invention.

7 indicates a blow-through prediction box, and 15 indicates a shutoff valve. The blow-through prediction box 7 is interposed in the middle of the gravity transfer path 6 and has a larger cross-sectional area than the gravity transfer path 6.

The behavior of the pre-reduced ore in this transfer system shows the following phenomenon when it approaches the blow-through limit.

When the flow rate of the carrier gas backflow increases, which is one of the causes of the above-mentioned blow-through, the carrier gas obstructs the gravity fall of the pre-reduced ore and causes some of it to flow back into the pre-reduction furnace, so the pre-reduced ore in the transfer path 6 is diluted. On the other hand, the dilution rate of the pre-reduced ore in the blow-through prediction box 7 becomes smaller due to the decrease in the flow rate of the reverse gas, so the packing density of the two pre-reduced ores is clearly different. The boundary surface 17 between the layers having different packing densities descends within the blow-through prediction box. When no blow-through prediction box is installed, no boundary surface descent phenomenon is observed in the gravity transfer path.

Even if the pre-reduced ore does not flow smoothly due to blockage, which is another cause of blow-through, if the blockage position is on the side of the pre-reduction furnace from the blow-through prediction box, the boundary surface in the blow-through prediction box 7 will be 17 gradually descends.

The present invention provides a sensor 16 that can relatively detect the difference in packing density at two locations in the upper and lower parts of the atrium prediction box 7.
By inserting
7 is constantly detected, and when the boundary surface 17 begins to move down inside the prediction box and the detected value changes greatly, it is a sign of blow-through, so the shutoff valve 15 is closed to prevent blow-through.

According to the experimental results, it is optimal to set the cross-sectional area of the atrium prediction box to the range shown below.

10≦S ₁ /S ₂ ≦50 where S ₁ : Cross-sectional area of the blow-through prediction box S ₂ : Cross-sectional area of the transfer path If the cross-sectional area of the blow-through prediction box is less than 10 times the cross-sectional area of the transfer path, the packing density The difference no longer appears clearly. If it exceeds 50 times, the falling speed of the pre-reduced ore in the blow-through prediction box during normal transfer will be significantly reduced, which will easily cause problems such as agglomeration of the pre-reduced ore and a drop in temperature.

It is appropriate to install the blow-through prediction box near the lower end of the transfer path. The reason for this is that this prediction box is ineffective against powder blockage from the blow-through prediction box to the smelting reduction furnace side.

As the sensor 16 for detecting the powder bed boundary surface 17 with a difference in packing density, a sensor for detecting an electrical resistance difference, a sensor for detecting a pressure difference, a temperature difference sensor, a sensor for measuring a difference in attenuation due to gamma rays, etc. can be used. can. Sequence control for opening and closing the cutoff valve 15 based on the detected values of these sensors can be performed using a known method.

It is also possible to install a plurality of prediction boxes depending on the purpose.

The effects of the present invention are as follows.

When transferring powdered pre-reduced ore from the pre-reduction furnace to the smelting-reduction furnace in a smelting-reduction device consisting of a pre-reduction furnace and a smelting-reduction furnace, there is a transfer path using gravity and a blowing device using a carrier gas provided at the lower end of the transfer path. According to this, it is preferable because it can be transferred with good controllability. In this case, there is a risk that a large amount of the carrier gas will flow back, or that the pre-reduced ore in the gravity transfer path will become clogged due to agglomeration, etc., preventing smooth transfer, resulting in blow-through. The present invention can reliably detect this blow-through and prevent the blow-through, so that explosions, re-oxidation, productivity inhibition, etc. caused by the blow-through can be completely prevented.

Example (1) Melting reduction furnace inner diameter 1.2m (2) Pre-reduction furnace inner diameter 1.1m (3) Air blowing tuyeres 4 upper tiers (also serves as powder injection) 4 lower tiers (4) Air flow rate 1200Nm ³ /hr (5) Powder transfer pipe: Inner diameter 25mm Introductory pipe Inner diameter 25mm (6) Blow-through prediction box inner diameter 100mm (7) Powder carrier gas N ₂ Using the above test furnace, powdered chromium ore (average particle size 0.2mm) ferrochrome smelting operation from powdered iron ore (average particle size 0.37 mm) and pig iron smelting operation from powdered iron ore (average particle size 0.37 mm). We created the cause of blow-through by mixing coarse particles to block the transfer path, and investigated the effectiveness of the blow-through prediction box, and as a result, we confirmed that it works well.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of the melting reduction apparatus, and FIG. 2 is a vertical sectional view of a gravity transfer path for explaining the method of the present invention. 1...Powdered ore supply port, 2...Preliminary reduction furnace, 3...
Melting reduction furnace, 4... Supply port for powdery flux, solid reducing material, reducing gas, etc., 5... Preliminary reduced ore discharge port, 6... Gravity transfer path, 7... Atrium prediction box, 8... Tuyere blower branch pipe, 9... Inlet pipe, 10... Carrier gas supply pipe, 11... Raceway, 12... Solid carbon-based reducing agent supply device, 13... Discharge port for molten metal and molten slag, 14... Air blowing main pipe, 15... Shutoff valve, 16... Filling Density difference detection sensor, 17... Boundary surface of packing density difference of pre-reduced ore.

Claims (1)

[Claims] 1. In the middle of the gravity transfer path of the powdered pre-reduced ore of the smelting reduction equipment consisting of a pre-reduction furnace and a smelting reduction furnace,
A blow-through prediction box having a cross-sectional area of 10 times or more and 50 times or less than the cross-sectional area of the transfer path is interposed, and changes in the position of the boundary surface of the difference in packing density of pre-reduced ore in the blow-through prediction box are constantly detected. . A method for preventing blow-through in a gravity transfer path for powdered pre-reduced ore, comprising: closing a cutoff valve of the transfer path when a sign of blow-by occurrence is detected.