JPH03100111A - Operating method of fluidized reduction furnace for powder ore - Google Patents

Abstract

PURPOSE:To improve the reduction efficiency and also to stabilize the condition in a fluidized bed reduction furnace by adjusting gas flowing velocity and circulating flow rate of powdery iron in the fluidized bed and keeping grain vol. fraction ratio in the furnace to a specific value at the time of pre-reducing the powdery iron ore in the fluidized bed reduction furnace. CONSTITUTION:When producing a molten iron from powdery iron ore, with the combination of a pre-reduction furnace and a smelting reduction furnace and without using a blast furnace, a fluidized bed reduction furnace is used as the pre-reduction furnace. The powdery iron ore 4 is charged from lower inlet 3 of an uptake cylinder 1 in the fluidized bed reduction furnace 10, and reducing gas 5 is blown from the bottom part to form the fluidized bed of powder iron ore, and the powdery iron ore is pre- reduced in the solid phase and the ore accompanied with the gas 5 by a cyclone 6 is descended in the downtake tube 2, and the reduced ore is again ascended in the uptake cylinder 1 after taking out a part of the reduced ore from an outlet 7 to form the fluidized bed, and unreducing iron ore is pre-reduced. In this case, by keeping the grain vol. fraction in the furnace within a range of 4-15% in the shown equatation, the reduction efficiency in the fluidized bed reduction furnace is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for maintaining highly efficient operation of a fluidized bed reduction furnace for ores, particularly iron ore.

[Conventional technology]

In recent years, the conventional method of making iron using a blast furnace requires large capital investment,
In addition, a smelting reduction ironmaking process has emerged that eliminates problems such as restrictions on raw material selection, which require high-quality agglomerate ore and coke. The smelting reduction ironmaking process is comprised of two large units: a smelting reduction furnace and a pre-reduction furnace, and a method in which a fluidized bed with a particle circulation device is generally applied to the pre-reduction furnace is generally used.

This fluidized bed reduction furnace basically consists of a fluidized bed reaction tower into which iron ore and reducing gas are charged, and a cyclone to collect the ore discharged from the reaction tower together with the gas, and to separate the gas from solids.
It has a structure consisting of a descending connecting pipe that is reinjected into the lower part of the reaction tower.

However, in such a fluidized-bed reduction furnace, since the reaction is carried out in a dilute fluidized bed in which fine ore is suspended, the efficiency of reducing gas utilization is poor, and the productivity per volume of the reaction tower is low.
Another drawback is that it is difficult to obtain a product with a stable reduction rate.

Therefore, various operating methods have been proposed to ensure productivity in the fluidized bed reduction furnace and to obtain products with a stable reduction rate.

For example, Japanese Patent Application Laid-Open No. 63-57709 discloses a method of controlling the reduction rate by changing the product extraction rate, ore circulation flow rate, reducing gas supply amount, and reducing gas inlet oxidation degree.

Furthermore, Japanese Patent Laid-Open No. 1-115447 discloses a method of stably maintaining a fluid state against fluctuations or changes in operating conditions by controlling the flow rate of circulating gas or particle circulation rate.

These disclosed operating methods make it possible to maintain operating conditions without causing major changes in the reduction rate or fluidity of charged ore.

[Problem to be solved by the invention]

However, such control methods are only aimed at stable operation of the furnace, and do not take into consideration obtaining a highly efficient operating state that fully utilizes the processing capacity of the reduction furnace, resulting in a reduction in operational efficiency. Inferior operations will continue.

The problem to be solved by the present invention is to establish a highly efficient operating method for a circulating fluidized reduction furnace that not only allows stable operation but also makes maximum use of its capacity and the reducing function of the introduced reducing gas.

[Means for Solving the Problems] The present invention makes the most effective use of the reducing gas introduced into the fluidized bed for reducing ore by maintaining the particle volume fraction in the fluidized bed of a fluidized bed reduction furnace within a specific range. This was completed based on the knowledge that productivity can be improved by controlling the gas flow rate of the fluidized bed reduction furnace, the particle circulation flow rate, or both to reduce the particle volume fraction to approximately 4 to 15%. It shall be kept within the range of .

[Effect]

The operational efficiency of the reduction furnace, which is expressed by the utilization rate of the reducing gas introduced into the fluidized bed, exhibits a high value when the volume fraction of ore particles in the reactive fluidized bed is within a specific range.

When the ore particle volume fraction is small, there are few particles in the fluidized bed that react with the reducing gas, so the gas does not react sufficiently and is discharged outside the furnace, resulting in a sharp drop in efficiency. The permissible limit is approximately 4%.

In addition, when the particle volume fraction in the fluidized bed is large, the amount of particles in the fluidized bed is large, but the dispersion of particles becomes poor and particle aggregates are unevenly distributed, and gas blows between them, resulting in solid gas. Due to insufficient contact, the gas is discharged outside the furnace without sufficiently reacting with the iron particles, resulting in a sharp drop in efficiency. The permissible limit is approximately 15%.

The ore particle volume fraction can be maintained within this range by adjusting either the gas flow rate of the fluidized bed reduction furnace, the particle circulation flow rate, or both.

〔Example〕

FIG. 1 is a diagram schematically showing the operation mode of the present invention. The fluidized-bed reduction furnace 10 is composed of an ascending pipe 1 that forms a reaction layer and a descending pipe 2 that forms a route for returning the partially reduced particles to the rising pipe 1 again.

Referring to the same figure, powder ore 4 supplied from raw material supply port 3
is reduced by forming a fluidized bed by the reducing gas 5 supplied from below the riser 1. The reducing gas 5 after the reaction enters the cyclone 6, and the particles entrained in the gas return to the riser pipe 1 via the downcomer pipe 2.

In the process, some of the products are the lower part of the downcomer pipe 2,
Alternatively, it is collected from the product outlet 8 at the bottom of the fluidized bed. The pressures at the lower and upper portions of the riser pipe 1 during operation are detected by pressure detectors 9a and 9b attached to the respective locations.

The particle volume fraction in the fluidized bed in such a fluidized bed reduction reactor is estimated by the following equation.

Particle volume fraction (%) = 100 (PL-P2)/L
/ρs However, Pl: Lower pressure of riser pipe (kg/m″
) P2: Riser upper pressure (kg/m'') L: Distance between pressure detection ends 9a and 9b (m) ρS: Particle density in the fluidized bed (kg/m').

FIG. 2 is a diagram showing the relationship between the volume fraction of ore particles in the fluidized bed of the fluidized reduction furnace shown in FIG. 1 and the gas utilization rate.

The gas utilization rate shown in the figure is determined by the fluidized bed population and the oxidation degree of the reducing gas at the outlet, that is, ((COI + H10) / (CO + CO2 + H* +
LO) ], and can be used as an index of the efficiency with which the reducing gas is effectively used for reduction.

The main operating conditions at this time are the temperature in the fluidized bed of 820~
860℃, oxidation degree of inlet gas 12-18%, product reduction rate 40-50%, particle circulation rate 50-250 kg/m'
/s, gas flow rate 5-9 m/s.

When the particle volume fraction in the fluidized bed is within a specific range A, the gas utilization rate is 13 to 18% and the production rate is 5 to 9 t-F.
e/m'/h was obtained. All of these values were 1.5 times or more outside the specific range A.

The range of particle volume fractions that yield high gas utilization and production rates is within the range of approximately 4% and approximately 15% for any dimension furnace or operation under any conditions. That is, the gas utilization rate when the particle volume fraction is within the specific range A is 1.5 times or more than when it is outside the specific range A, and the production rate is also 2t-F.
e/m'/h or more can be obtained.

On the other hand, the volume fraction of ore particles in the fluidized bed in a fluidized bed reduction furnace has a unique relationship with the gas flow rate in the fluidized bed and the circulating flow rate of ore, respectively. FIG. 3 shows the relationship between the particle volume fraction, the gas flow rate in the fluidized bed, and the ore circulation flow rate. As shown in the figure, the particle volume fraction in the fluidized bed increases as the gas flow rate decreases, and vice versa. Furthermore, as the particle circulation flow rate increases, the particle volume fraction increases.

Therefore, from the relationship shown in Figures 2 and 3, the gas flow rate in the fluidized bed and the circulating flow rate of ore, or both factors, are maintained within the specified range A of the particle volume fraction in order to obtain the above-mentioned high operational efficiency. It can be used as a control factor for

Figure 4 shows an example of the operation of a fluidized bed reduction furnace having the structure shown in Figure 1, and shows the relationship between the circulation flow rate of ore particles, the gas flow rate, the resulting particle volume fraction, ore reduction rate, and production rate. .

As shown in the figure, it is possible to control the particle volume fraction in the fluidized bed by controlling the gas flow rate and the particle circulation flow rate, and in turn, it is possible to control the operating efficiency of the fluidized bed by changing the gas flow rate and particle circulation flow rate. I understand.

〔Effect of the invention〕

The operating method of the fluidized-bed reduction furnace of the present invention can provide the following effects.

(1) Reactions can occur in a region where there is good contact between the reducing gas and the ore. As a result, it becomes possible to operate the reduction furnace by making the most of its efficiency.

(2) Efficient operation can be maintained, making it possible to operate the reduction furnace with high efficiency.

(3) Reduction progresses smoothly and productivity improves.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the operation mode of the present invention. FIG. 2 shows the relationship between the volume fraction of ore particles and the reducing gas utilization rate, and FIG. 3 shows the relationship between the volume fraction of ore particles, gas flow rate, and particle circulation flow rate. FIG. 4 is a diagram showing the operating state of the fluidized bed reduction furnace shown in FIG. 1. 1: Ascending pipe 2: Descending pipe 3: [Paddy supply port 4: Powder ore 5: Reducing gas 6: Cyclone 7.8: Product outlet

Claims (1)

[Claims] 1. Adjust the gas flow rate and ore circulation flow rate in the fluidized bed, or both, to increase the particle volume fraction in the fluidized bed reduction furnace.
A method of operating a fluidized bed reduction furnace for fine ore to maintain the concentration within the range of ~15%.