JPH01247515A - Method for pre-reducing fine ore and out-of-furnace circulating type fluidized bed reduction furnace - Google Patents

Abstract

PURPOSE:To prevent raising of blowing pressure of reducing gas and to stabilize furnace condition by opening middle size grain discharging tube at upper part higher than reducing gas blowing header in a riser and discharging the middle size grain when the pressure loss in the riser becomes much. CONSTITUTION:The middle size grain discharging tube 13 is opened at upper position of the reducing gas header 8 opened in the riser 1. One side of detecting terminal 15 is set at the upper part 3 of the riser 1, and by a differential pressure gage 17 arranging the other detecting terminal 16 in inner part of the reducing gas header 8, the difference between the blowing pressure of the reducing gas and pressure in the furnace at the upper part 3 of the riser 1 is detected. The detected differential pressure is inputted to a differential pressure control device 18 and in the case of exceeding the setting value, the signal is outputted to a flow rate control valve 19, to control the flow rate of carrier gas. Further, the middle size grain ore is discharged to out of the system from pneumatic feeder 14 through the middle size grain discharging tube 13 in accordance with pressure loss in the riser 1. By this method, the thickness of dense fluidized bed 12 formed in the riser 1 is kept to the fixed range, to execute fluidization of the fine ore.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for pre-reducing fine ore to be charged into a smelting reduction furnace with a reducing gas in a fluidized bed furnace, and an external circulation fluidized bed furnace.

[Conventional technology]

The smelting reduction method is attracting attention as an alternative to the conventional hot metal production technology using a blast furnace. The smelting reduction furnace used in this method was developed for the purpose of producing molten iron-based alloys using smaller-scale equipment without being restricted by the raw materials used. Furthermore, in order to effectively utilize the reducing power and heat of the exhaust gas generated in the smelting reduction furnace, a method has been developed in which raw ore is preheated and pre-reduced in a fluidized bed furnace as a fluidizing gas.

In addition, fluidizing gas is blown into the furnace at a high superficial velocity,
BACKGROUND ART An external circulation type fluidized bed furnace is known that performs preheating, preliminary reduction, etc. of fine ore at high speed. In this case, as the superficial velocity of the fluidizing gas increases, the proportion of fine ore scattered outside the riser that constitutes the fluidized bed furnace also increases. Therefore, the scattered fine ore is separated from the exhaust gas by a cyclone installed in the external circulation path, captured, and returned to the riser via the downcomer.

The present inventors have developed an external circulation 11-type fluidized bed reduction furnace of this type, in which the bottom of the downcomer is a slanted hearth, and a carrier gas inlet is opened to form a bubble flow region there. was developed and filed as Japanese Patent Application No. 62-269286. A coarse grain outlet is provided at the lower side of the inclined hearth, and a medium grain outlet is provided at the lower part of the riser, to appropriately take out fine ore having a particle size that is not fluidized by the fluidizing gas.

[Problem to be solved by the invention]

In the fluidized bed reduction furnace introduced in the above-mentioned Japanese Patent Application No. 62-269286, the medium grain discharge port is provided below the reducing gas injection header. However, medium-grained fine ore,
Since it does not reach the top of the riser, it does not flow into the downcomer and is maintained in a fluid state in a small region of the live bottom.

Therefore, the medium-grained fine ore is not extracted from the riser and gradually accumulates at the bottom of the riser.

Then, a region in which medium-grain fine ore is heavily suspended is formed in and above the reducing gas injection header. As the reducing gas rises in the riser through this rich region, the pressure drop gradually increases.

In addition, because the medium-grained fine ore floating in the small area above the reducing gas injection header comes into preferential contact with the reducing gas, which has a large reducing power, the reduction reaction of the medium-grained fine ore progresses excessively. . Moreover, since this medium-grained fine ore circulates in a dense state in a small region below the riser, sticking is likely to occur due to excessive progress of the reduction reaction. When this sticking occurs, not only does the furnace condition become unstable, but the injected reducing gas does not come into contact with the fine ore efficiently, and is likely to be discharged from the furnace without being used.

Therefore, the present invention aims to reduce the reducing gas injection pressure by taking out the medium particle fine ore floating there from the medium particle discharge pipe opened above the reducing gas injection header based on the pressure drop fluctuation in the furnace. In addition to preventing the temperature from becoming excessively high,
The purpose is to operate a fluidized bed reduction furnace under stable furnace conditions without the occurrence of sticking, etc.

[Means to solve the problem]

In order to achieve the purpose of the preliminary reduction method of the present invention, when preliminary reduction is carried out while circulating and fluidizing fine ore with a reducing gas between a riser and a downcomer, when the pressure drop in the riser becomes large, The medium grains are taken out from a medium grain discharge pipe opened inside the riser at a position above the reducing gas blowing header into which the reducing gas is blown.

In addition, the external circulation fluidized bed reduction furnace used in this method is
A reducing gas blowing header provided at the bottom of the riser, a medium grain discharge pipe opening into the riser at a position above the reducing gas blowing header, a discharge device provided in the medium grain discharge pipe, and a riser. It is equipped with a differential pressure gauge that detects the difference between the internal pressure of the furnace in the upper part and the pressure of the reducing gas flowing through the reducing gas header, and a control device that opens, closes, or adjusts the discharge device based on the detected differential pressure.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 is a schematic diagram showing a fluidized bed reduction furnace of the present invention.

This fluidized bed reduction furnace has a riser 1 that constitutes the fluidized bed body.
and a downcomer 2 attached to this riser l. The upper part 3 of the riser 1 is connected to a cyclone 5 provided on the downcomer 2 via a lead-out pipe 4. On the other hand, the lower part of the downcomer 2 is connected to the lower part of the riser 1 via an introduction pipe 6. The fine ore fed into the riser 1 from the charging pipe 7 is fluidized inside the riser 1 by the reducing gas blown from the reducing gas header 8. Here, as the reducing gas, exhaust gas generated in the melting reduction furnace can be used directly or after being reformed.

The fine ore is pre-reduced by contact with the reducing gas. Then, a part of the fine ore is sent to the cyclone 5 via the outlet pipe 4 along with the flow of the reducing gas. In the cyclone 5, the fine ore is separated from the exhaust gas and then moves down the downcomer 2.

A fine grain extraction port 9 is provided in the middle of the downcomer 2, and fine ore is taken out continuously or intermittently depending on the operational status of the smelting reduction furnace.

The remaining fine ore is fed into the riser (2) again via the inlet pipe 6. At this time, in order to smoothly feed the fine ore from the introduction pipe 6 to the lower part of the riser 1, a part of the reducing gas can be branched from the reducing gas header 8 and blown in as the carrier gas 10. In this way, the fine ore charged from the charging pipe 7 is transferred from the riser 1 to the outlet pipe 4.
→ Cyclone 5 - Downcomer 2 = Introducing pipe 6 → The fine particles are reduced while circulating through the riser 1 and cut out from the fine particle outlet 9 as appropriate.

The fluidized state of the fine ore fed into the riser 1 differs depending on its particle size. For example, although it depends on the blowing pressure of the reducing gas, coarse particles with a particle size of 5111 m or more are rarely fluidized and deposited at the bottom of the riser 1. This coarse powder ore is transported through a coarse grain extraction pipe 11 opened at the bottom of the riser 1.
taken from. However, medium particles with a particle size of 1 to 5 mm do not reach the upper part 3 of the riser 1, although they are slightly suspended by the reducing gas. As a result, the medium-grained ore is not sent out from the riser 1 through the outlet pipe 4 to the cyclone 5, nor is it discharged from the coarse-grain take-out pipe 11, but as a dense fluidized bed 12 in the upper and lower vicinity of the reducing gas header 8. increase in small areas over the area.

Since the dense fluidized bed 12 is formed above and below the vicinity of the reducing gas header 8, the reducing gas blown from the reducing gas header 8 is subjected to large resistance. That is, in order to raise the fine ore to the upper part 3 of the riser 1, the blowing pressure of the reducing gas must be increased. Also, a
The region where the thick fluidized bed 12 is formed is where the reducing power of the injected reducing gas is greatest. Therefore, the fine ore floating in the dense fluidized bed 12 centered on the reducing gas header 8 is excessively reduced and tends to cause sticking.

Therefore, in the present invention, in order to take out the medium grain fine ore floating in the a-thick fluidized bed 12, a medium grain take-out pipe 13 is opened above the reducing gas header 8. and,
By opening and closing the discharge device provided in the medium grain removal pipe 13, an excessive amount of medium grain powder ore is prevented from floating in the dense fluidized bed 12. Here, since the medium particle removal pipe 13 is provided at a higher position than the reducing gas header 8, the dense fluidized bed 12 formed above the reducing gas header 8 is efficiently removed and is blown from the reducing gas header 8. This prevents the gas from acting as a resistance to the reduced reducing gas.

In the illustrated case, a two-kneematic feeder 14, which operates based on the pressure loss within the riser 1, is provided in the medium grain removal pipe 13 as a discharge device. That is, the upper part 3 of riser 1
A differential pressure gauge 17 having one detection terminal 15 disposed inside the reducing gas header 8 and the other detection terminal 16 provided inside the reducing gas header 8 measures the blowing pressure of the reducing gas from the reducing gas header 8 and the furnace at the upper part 3 of the riser 1. Detects the difference with internal pressure. The detected differential pressure is input to the differential pressure control device 18. A set value is manually entered in the differential pressure control device 18 in advance, and the detected differential pressure is compared with this set value.

When the detected value exceeds the set value, a control signal is output to the flow rate adjustment valve 19 to control the flow rate of the carrier gas blown into the pneumatic feeder 14 from the carrier gas blowing pipe 20. When the detected value becomes smaller than the set value, the differential pressure control device 18 outputs a signal to the flow rate regulating valve 19 to stop the supply of the carrier gas that has already been blown. Note that, in place of the flow rate adjustment valve 19, it is also possible to provide an on-off valve that turns on and off the operation of discharging the medium-sized powder ore from the pneumatic feeder 14.

Therefore, depending on the pressure drop within the riser 1, medium grain powder ore is discharged from the pneumatic ivy feeder 14 to the outside of the system via the medium grain extraction pipe 13. As a result, the dense fluidized bed 1
2, especially the amount of medium-grained ore suspended above the reducing gas header 8, prevents an increase in pressure drop caused by the dense fluidized bed 12, and allows the reducing gas to be pumped into the riser at a constant blowing pressure. can be blown to maintain a predetermined fluidity state.

Further, since medium-grained ore having a high degree of reduction is taken out, there is no possibility of sticking occurring near the reducing gas header 8. Further, medium-sized fine ore, which is slightly fluidized by the reducing gas but does not reach the upper part 3 of the riser 1, is separated from coarse-grained ore taken out from the bottom of the riser 1 and taken out. Here, reducing gas header 8
Since the medium grain removal pipe 13 is provided above the medium grain ore, the separation accuracy between the medium grain powder ore and the coarse grain powder ore is excellent.

〔Effect of the invention〕

As explained above, in the present invention, the medium grain removal pipe is opened inside the riser at a position above the reducing gas header, and when the pressure drop exceeds a set value, the medium grain removal pipe is opened through the medium grain removal pipe. Granular powder ore is being extracted. Therefore,
The thickness of the dense fluidized bed formed inside the riser can be maintained within a certain range, and fine ore can be fluidized without increasing the blowing pressure. Furthermore, since the dense fluidized bed that undergoes the most active reduction reaction is efficiently taken out, sticking will not occur near the reducing gas header. Moreover, since this medium-grain powder ore is separated from the coarse-grain powder ore with good separation accuracy, it can be easily processed as a raw material in the subsequent melt-reduction process. In this way, according to the present invention, it is possible to produce reduced ore of constant quality under stable furnace conditions.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a fluidized bed reduction furnace of the present invention. 1: Riser - 2: Downcomer 3: Upper part of riser 4: Outlet pipe 5: Cyclone 6: Inlet pipe 7: Charge pipe 8: Reducing gas header 9: Fine particle outlet 10: Carrier gas 1: Coarse particle outlet pipe 12: Dense fluidized bed 13; Medium grain removal tube 14-Nicomatic feeder 15.16: Detection terminal 17
:Differential pressure gauge 18:Differential pressure control device 19:Flow rate adjustment valve 20
: Carrier gas injection pipe patent applicant Nippon Steel Corporation Representative
Masu Kobori (and 2 others) Figure 1

Claims (1)

[Claims] 1. When pre-reducing fine ore while circulating and fluidizing it with reducing gas between the riser and the downcomer, when the pressure drop in the riser becomes large, the reducing gas is blown into the reducing gas. A method for preliminary reduction of fine ore, comprising taking out medium grains from a medium grain discharge pipe opened inside the riser at a position above the blowing header. 2. In a fluidized bed reduction furnace in which fine ore flows and circulates between a riser and a downcomer, there is a reducing gas blowing header installed at the bottom of the riser, and a reducing gas blowing header installed at a position above the reducing gas blowing header above the riser. a medium grain discharge pipe opening into the inside, a discharge device provided on the medium grain discharge pipe, a differential pressure gauge that detects the difference between the furnace internal pressure at the upper part of the riser and the pressure of the reducing gas flowing through the reducing gas header; An extra-furnace circulation type fluidized bed reduction furnace, comprising: a control device that opens, closes, or adjusts the discharge device based on the detected pressure difference.