JPH0372012A - Circulating fluidized bed pre-reduction furnace - Google Patents

Abstract

PURPOSE:To suppress flow velocity of a reduction gas to slow and to prevent the pulverization of an ore by arranging a coarse grain discharging tube at the outer circumference of a reduction furnace and feeding the grains retaining a furnace to a downcomer through a conveying tube from a lower discharging hole in the coarse grain discharging tube. CONSTITUTION:The concentric circular type-coarse grain discharging tube 2 is arranged at the outer circumference of reduction furnace 1 for forming a fluidized bed to constitute a circulating fluidized bed pre-reduction furnace. The fluidized bed part providing a lower discharging hole 12 at a lower end part of the coarse grain discharging tube 2 is formed. The grains, which is likely to retain in the reduction furnace 1, come into between the reduction furnace 1 and the coarse grain discharging tube 2 and are fed into a downcomer 7 connectedly arranged with a granular collector 6 with a screw feeder 8 from the lower discharging hole 12 through the conveying tube 9. The retained grains in the fluidized bed are efficiently discharged. By this method, the pre-reduction can be efficiently executed to iron ore over the wide range of grain diameters.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to improving productivity,
Improving the reduction rate of products and reducing the basic unit of refractories in smelting reduction furnaces,
This invention relates to an iron ore circulating fluidized bed pre-reduction furnace (hereinafter abbreviated as pre-OI reduction furnace) that can achieve a reduction in carbon material consumption per unit.

<Prior Art> In order to obtain good particle circulation in a fluidized bed, it is important to make the reducing gas flow rate higher than the terminal velocity of the particles (the gas flow rate at which the particles fly out of the fluidized bed). In order to pre-reduce fine ore with a wide particle size range in a pre-reduction furnace, it is necessary to maintain the gas flow rate above the terminal velocity of the largest particle. However, as the gas flow rate increases, the efficiency of collecting fine ore in collectors such as cyclones decreases (wrinkles), which reduces the yield of ore and requires reinforcement of collectors to maintain collection efficiency. Tonari Set @
On the other hand, when pre-reducing fine ore in a pre-reducing furnace, thermal cracking due to rapid heating, collision, cracking due to abrasion, etc.
Powdering of the ore occurs due to cracking caused by the change in m, leading to a decrease in the charging yield to the smelting reduction furnace and productivity, but an increase in the gas flow rate promotes the pulverization of the ore. Therefore, in order to prevent pulverization of the ore and obtain the desired productivity and reduction rate, it is desirable that the gas flow rate be as slow as possible.

However, if the gas flow velocity is lower than the terminal velocity of the largest particle,
Particles whose terminal velocity is higher than the actual gas flow rate remain permanently in the fluidized bed, making particle circulation unstable or, in the worst case, stopping particle circulation, making operation impossible.

Therefore, in the case of preliminary reduction under such provision f',
It is necessary to selectively and efficiently discharge only the coarse particles that remain permanently inside the pre-reduction furnace to the outside of the furnace. In order to solve this problem, the inventors of the present invention proposed in Japanese Patent Application No. 63117328 and No. 63-241499 that they provided a plurality of ore extraction ports in the height direction of the preliminary reduction furnace to reduce the amount of ore accumulated in the furnace. They reported that pre-reduction of ores with a wide range of particle sizes could be achieved through adjustment, and in Japanese Patent Application No. 63-247500, a partition plate extending in the axial direction was installed inside the pre-reduction furnace to divide the inside of the furnace into multiple sections. death,
We reported a technology that can simultaneously process fine ore with different particle sizes by introducing reducing gas at different flow rates in each compartment.

Further, Japanese Patent Publication No. 55-9048 discloses a method in which coarse particles are selectively taken out from the material retained in the fluidized bed and fine particles are returned to the fluidized bed to continue granulation.

Furthermore, in JP-A No. 63-11609, a plurality of preliminary reduction furnaces are installed, and a path is provided to guide the ore discharged from one reduction furnace to the other reduction furnace, thereby separating coarse and fine ore. A method for efficient pre-OI reduction in each pre-reduction furnace is disclosed, and Japanese Patent Application Laid-Open No. 11610/1983 discloses that after preheating fine ore in a fluidized bed preheating furnace, fine particles are converted to coarse particles in the middle of an external circulation path. A method is disclosed for efficiently pre-reducing fine ore having a wide particle size range by introducing and reducing the fine ore from the bottom of the pre-heating furnace into separate pre-(lIl reduction furnaces).

<Problem that the invention seeks to solve> Problems with the above-mentioned conventional technology are shown below.

Patent Application No. 117328/1983, Patent Application No. 24749/1983
The technology reported in No. 9 is an appropriate technology for discharging particles that are permanently retained in the riser, and can pre-reduce fine ore with a wide range of particle sizes, but the efficiency of extracting the accumulated particles is low, so There was still room for improvement in the efficiency of reduction. In addition, the technology shown in Japanese Patent Application No. 63-247500 can pre-reduce fine ore with a wide range of particle sizes, but the gas flow rate in the fluidized bed on the side that processes fine particles must be made higher than that on the fine particle side. Therefore, it is impossible to prevent ore pulverization. In addition, the technology disclosed in Japanese Patent Publication No. 55-9048 has the same problems as the technology of Japanese Patent Application Publication No. 63417328 mentioned above, and furthermore, it requires a classification device in addition to a preliminary reduction furnace, and the height of the equipment is high. Therefore, it is not preferable from the point of view of equipment cost.
The technique disclosed in Japanese Patent No. 610 requires a plurality of preliminary reduction furnaces, which is disadvantageous in terms of equipment.

The present invention solves the above-mentioned problems and further suppresses the flow rate of the reducing gas that forms the fluidized bed to a low level, thereby preventing iron ore from being pulverized as much as possible, while efficiently processing iron ore in a wide range of particle sizes at once. This was done in order to provide a pre-reduction furnace capable of pre-reduction.

Means for Solving the Problems> The present inventors have made the following findings as a result of intensive research to solve the above problems. The behavior of permanently retained particles in a fluidized bed is due to internal circulation within the bed, and is formed from rising particles at the center of the bed and descending particles near the bed wall. The positional relationship with the particle supply pipe is not constant but fluctuates, and the position where the descending particle flow is generated changes depending on the amount of ore retained in the furnace, gas flow rate, particle circulation rate, etc. Based on these findings, we came up with the invention of a pre-reduction furnace with a double-tube structure in which the entire periphery of the fluidized bed serves as a discharge port so that particles permanently resident in the bed can be efficiently discharged. Ta.

The present invention has a fluidized bed section in which powder and granules are brought into a NfL fluidized bed dynamic state by reducing gas, and a powder and granules discharged from the upper part of the fluidized bed section.
This is a W4 ring fluidized bed pre-reduction furnace consisting of a collector for collecting particles and a diagonal pipe for returning the collected powder to the fluidized bed section. It consists of a longer concentric coarse particle discharge pipe, and a fluidized bed section with a lower discharge port at the bottom end of the coarse particle discharge pipe, and a fluidized bed section that collects the powder discharged from the upper part of the fluidized bed section. This is a circulating fluidized bed pre-reduction furnace, which is composed of a collector and a downcomer connected to each other, and the lower discharge port and the downcomer are connected via a transport pipe.

<Operation> An example of the preliminary reduction furnace according to the present invention is shown in FIG. The main part includes a coarse particle discharge pipe 2 arranged concentrically around the inner cylinder of a reduction furnace 1 for forming a fluidized bed. The behavior of particles in the fluidized bed is schematically shown in Figure 2. The descending particles flow along the bed wall along the descending particle flow 15, and the position of the descending particle flow is determined by the amount of ore retention and the gas As mentioned above, the inventors' research has shown that it changes depending on the flow rate, etc.
ζ has been found. Particles that tend to remain permanently in the reduction furnace tend to descend along the layered wall of the reduction furnace, get between the surrounding coarse grains 1 and the outlet pipe, and flow through the transport pipe 9 from the lower discharge port 12. It is sent to the downcomer 7 by the screw feeder 8 via the screw feeder 8. Therefore, according to the device according to the present invention, permanently resident particles in the fluidized bed can be efficiently discharged. Slowing down the gas flow rate in the fluidized bed improves the collection rate with cyclones, etc., but some of the fine particles whose final velocity is slower than the gas flow rate also enter the phase particle discharge pipe, increasing the amount of fine ore as a whole. Although it is regrettable that the reduction rate of the reactor will be low, there is no problem because it is circulated to the reduction furnace 1 via the transport pipe 9 and the inclined pipe 4.

<Example> Preliminary reduction of Australian ore having a particle size of -5+n was carried out using the apparatus according to the present invention shown in FIG. The implementation conditions are shown in Table 1, and FIG. 4 shows the device used in the comparative example. The dimensions of the device in the comparative example are the same as the device in FIG. Furthermore, other conditions were also the same as in the examples of the present invention.

Ore replenishment and discharge to the circulating fluidized bed pre-reduction furnace is carried out via a granular ore supply pipe and a granular ore discharge pipe that are independently connected to any position in the circulation path except for the collector.
Due to the principle of a circulating fluidized bed, the connection positions of these pipes have the same effect at any point in the circulation path for granular ore, excluding the collector; It is necessary to prevent it from being discharged as is.

Specifically, the powder ore supply pipe is located at the bottom of the reduction furnace.

It is connected to the top of the reduction furnace or the top of the downcomer, and the discharge pipe is often connected to the bottom of the reduction furnace or the bottom of the downcomer. In the embodiment described later, the case is described in which the supply pipe is connected to the upper part of the downcomer and the discharge pipe is connected to the lower part of the downcomer, but the effect of the device of the present invention is the same even if it is connected to other parts as described above. be.

Table 2 shows the amount of particles retained in the fluidized bed, the particle Va ring velocity, the average reduction rate of extracted particles, and the product discharge rate for Examples and Comparative Examples. operation, but the particle circulation rate and the average reduction rate of the discharged product are reduced. That is, in the case of Comparative Example 1, it was found that the extraction speed of coarse particles having a terminal velocity equal to or higher than the actual gas flow velocity was lower than that of the example, so that the particle WJ ring velocity became small, resulting in poor productivity.

Furthermore, as Comparative Example 2, the device according to the present invention was operated at a high gas flow rate using the device shown in FIG. FIG. 3 shows the particle size structure of the product in this case, and the particle size structure of the product when the apparatus shown in FIG. 4 is operated at a high gas flow rate, together with the particle size structure of the raw ore.

If the device of FIG. 4 is operated at a high gas flow rate, it is possible to obtain productivity comparable to that of the device according to the present invention, but as shown in FIG. Remarkably,
Furthermore, the oil collection efficiency in the cyclone has also decreased. In this embodiment, the ore is fed to the screw feeder 8,
It was returned to the downcomer 7 through the transport pipe 9 and circulated,
It may be processed separately without being circulated. 2 shown in Figure 3
Different types of pre-reduced ores (treated ores of Examples and treated ores of Comparative Examples) were added from the furnace mouth of a nominally 100 t iron bath type smelting reduction furnace at a charging rate of IL/win. Table 3 shows the addition yields of both with the same iron bath temperature, acid delivery rate, lance hide, etc., but it is clear that the pre-reduced ore with a larger average diameter treated with the apparatus according to the present invention has a higher yield. The addition yield was high, and the effect of the apparatus according to the present invention was recognized.

Table 1 <Effects of the Invention> According to the present invention, iron ore having a wide particle size range can be efficiently pre-reduced while reducing the reducing gas flow rate to a low level and preventing the iron ore from being powdered as much as possible.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus according to the present invention, FIG. 2 is a schematic diagram of the behavior of particles in the fluidized bed, and FIG. 3 is a characteristic diagram showing the particle size structure of the treated ore in the treatment method. FIG. 4 is a schematic diagram of an apparatus implemented as a comparative example. 1... Reduction furnace, 2... Coarse particle discharge pipe, 3...
Constant W1 supply device, 4... Oblique pipe, 5... Discharge pipe,
6...Oil collection 2L7...Downcomer, 8...
Screw feeder 9...transport pipe, IO...
・Fine ore supply pipe, 11...Fine ore discharge pipe, 12...
Lower discharge port, 13...Gas, 14...Ore, 15...Downward particle flow, 16...Upward particle flow, 1
7...Particle conjunctive tube.

Claims (1)

[Claims] A fluidized bed section that turns the powder into a fluidized bed using reducing gas, a collector that collects the powder discharged from the top of the fluidized bed, and a diagonal pipe that returns the collected powder to the fluidized bed. A circulating fluidized bed pre-reduction furnace consisting of a cylindrical reduction furnace forming a fluidized bed and a longer concentric coarse particle discharge pipe arranged around the outer circumference of the cylindrical reduction furnace. It consists of a fluidized bed section with a lower discharge port at the lower end, and a downcomer connected to a collector that collects powder and granules discharged from the upper part of the fluidized bed section, and the lower discharge port and downcomer are A circulating fluidized bed pre-reduction furnace connected via a transport pipe.