JPH0297888A - Operation of circulation type fluidized bed preliminary reducing furnace - Google Patents

Abstract

PURPOSE:To permit wide operation without selecting the kind of employing ore by a method wherein powdered ore is extracted out of the side wall of a furnace and is introduced into the inlet side of a cyclone when the amount of ore, stagnating in a fluidized bed preliminary reducing furnace, is increased. CONSTITUTION:When the flow speed of fluidized reducing gas 3, introduced into a preliminary reducing furnace 1, is higher than the terminal speed of powder ore or solvent, the solvent or the powder ore is flown out of the fluidized bed preliminary reducing furnace and is collected by a cyclone 8. The collected powdered ore 7 is descended to the lower part of the cyclone but is returned again into a fluidized bed 4 through a circulating passage 9. Then, the powdered ore 7 is fluidized again by the reducing gas 3 and is ascended through the fluidized bed 4 while being reduced by CO, H2 and CH4 in the reducing gas and, thereafter, is flown out of the furnace. The flying powder bodies are collected again by the cyclone 8 and are returned into the fluidized bed 4 again through the circulating passage 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for operating a circulating fluidized bed pre-reduction furnace for pre-reducing powdered ore.

(Conventional technology) Iron ore and other metal ore resources tend to be less in the form of lumps and more in the form of powder.Currently, methods such as flotation and magnetic separation are being used to improve the quality of low-grade ores. This trend is expected to become even stronger in the future, partly because ore beneficiation is being actively promoted.

In recent years, in response to the increase in the amount of powdered ore used, a so-called smelting reduction method has been developed to directly produce molten metal from powdered ore.

There are various types of smelting reduction methods, but the inventors have been engaged in research and development of smelting reduction methods using vertical smelting reduction furnaces and fluidized bed pre-reduction furnaces for many years, and have has also reported numerous development results.

For example, Special Publication No. 59-18452, No. 59-18453
No. 62-5207, JP-A-59-80703 and JP-A-62-56537.

In the smelting reduction method, high-temperature exhaust gas from the smelting reduction furnace is introduced into a fluidized bed pre-reduction furnace to form a fluidized bed, and powdered ore is pre-reduced using high-temperature wandering gas (fluidized reducing gas) as a system. It is considered advantageous.

In a fluidized bed pre-reduction furnace, the amount of fluidizing reducing gas is limited by the equipment scale, especially the column diameter (inner diameter) of the fluidized bed, the particle size of the powdered ore, and the apparent density, and as a result, the amount of powdered ore processed is limited. Since the reduction rate is limited, if the flow rate of the fluidizing reducing gas can be increased, the throughput of ore and the reduction rate can be increased even with the same equipment scale.

Therefore, the inventors conducted extensive research in order to realize an advantageous increase in the flow rate of the fluidizing reducing gas, and as a result, they found that when the flow rate of the fluidizing reducing gas in the fluidized bed exceeds the terminal velocity, the powdered ore will fly out of the fluidized bed. However, if such ejected particles are collected using a cyclone and the collected powder ore is then returned to the fluidized bed using a circulation device in a closed circuit, the flow rate of the fluidizing reducing gas can be effectively reduced. Based on this knowledge, we previously proposed a circulating fluidized bed pre-reduction furnace in Japanese Patent Application No. 136644/1983.

(Problems to be Solved by the Invention) The above-mentioned circulation of powdered ore is easy for ores with relatively small particle sizes, but the larger the particle size, the less they jump out of the fluidized bed, and the more they accumulate in the furnace. This had the disadvantage of increasing the amount of ore and causing problems in fluidized bed operation. Therefore, when using a circulating fluidized bed pre-reduction furnace, it is necessary to limit the particle size of the raw ore, which means that the circulating fluidized bed pre-reduction furnace cannot be used for pre-reducing relatively large-diameter powdered ores. There remained a problem.

Therefore, the purpose of this invention is to propose a method for operating a circulating fluidized bed pre-reduction furnace that enables a wide range of operations regardless of the ore used.

(Means for Solving the Problems) This invention forms a fluidized bed by introducing high-temperature fluidized reducing gas into a fluidized bed pre-reduction furnace at a faster rate than the ejection speed of powdered ore or pre-reduced ore powder. On the other hand, the pre-reduced ore powder flying out from the top of the fluidized bed is collected by a cyclone, and the collected ore powder is returned to the reduction furnace through the circulation path, thereby circulating and fluidizing the pre-reduced ore powder. A circulating fluidized bed pre-reduction furnace characterized in that during pre-reduction, if the amount of accumulated ore in the fluidized bed pre-reduction furnace increases, powdered ore is extracted from the side wall of the furnace and introduced into the inlet side of a cyclone. This is the operating method.

This invention will be specifically explained below.

FIG. 1 schematically shows a circulating fluidized bed pre-reduction furnace suitable for carrying out the present invention.

In the figure, 1 is a fluidized bed preliminary reduction furnace, 2 is an inlet for the fluidized reducing gas 3 from the smelting reduction furnace, 4 is a fluidized bed by the fluidized reducing gas 3, and 5 is a raw material supply facing the fluidized bed 4. 6 indicates the fluidized reducing gas 3 and powdered ore 7 ejected from the fluidized bed 4.
The discharge port 8 is the powdered ore ejected from the preliminary reduction furnace 1 (
A cyclone 9 collects the powdered ore 7 (including a solvent depending on operating conditions), and a cyclone 9 guides the powdered ore 7 collected by the cyclone 8 again to the circulation supply port 10 of the preliminary reduction furnace l (circulation path, 11
Reference numeral 12 designates a transportation path that leads the pre-reduced powdery ore to the smelting reduction furnace or the outside, and 12 represents an extraction pipe that extracts the accumulated ore from the middle part of the fluidized bed 4 and introduces it into the inlet side of the cyclone 8. Reference numeral 13 shown in FIG. 2 is a retention amount detector for detecting the amount of accumulated ore in the preliminary reduction furnace 1. In addition, circulation route 9
has a function of injecting particle circulation gas such as N2 (not shown).

Now, when the flow velocity of the fluidized reducing gas 3 introduced into the pre-reduction furnace 1 is higher than the terminal velocity of the powdered ore and the solvent, the solvent and the powdered ore fly out of the fluidized bed pre-reduction reactor into the cyclone 8. will be collected. Collected powdered ore 7
falls below the cyclone, but is returned to the fluidized bed 4 through the circulation path 9. Then, it is fluidized again by the reducing gas 3, and the CO, H! , and CH4
It rises in the fluidized bed 4 while being reduced by such methods as above, and flies out of the furnace. The ejected powder is collected again by the cyclone 8 and returned to the fluidized bed 4 via the circulation path 9.

Powdered ore is pre-reduced while repeating the circulation flow as described above, and becomes pre-reduced ore powder with a high pre-reduction rate.
In this invention, this type of pre-reduction furnace is referred to as a circulating fluidized bed pre-reduction furnace.

In this way, the powdered ore and the solvent are reduced or heated while being circulated many times, and especially in the case of limestone, carbon dioxide gas is removed.

Here, the faster the gas flow rate in the preliminary reduction furnace 1, the more coarse the powdered ore and solvent can be processed.

(Function) Circulating flow in the above-mentioned circulating fluidized bed pre-reduction furnace can be easily realized as the particle size of the powdery ore becomes smaller, but since the particle size of the powdery ore is not constant, While it is easy for particles to jump out of the fluidized bed 4, particles with a large size are difficult to jump out of the fluidized bed 4 and may gradually stay in the furnace. When the amount of ore retained in the furnace increases, the pressure on the inlet side of the pre-reduction furnace increases and pressure fluctuations become large, making it impossible to operate the pre-reduction furnace. If the preliminary reduction furnace is operated in conjunction with the smelting reduction furnace, the pressure fluctuations in the pressure furnace of the smelting reduction furnace will increase, and the operation of the smelting reduction furnace may be affected due to the air blower becoming unable to blow air. becomes incapable.

Therefore, in this invention, the amount of accumulated ore in the preliminary reduction furnace 1 is detected by the accumulated amount detector 13, and if the detected amount exceeds a predetermined value, powdered ore is introduced from the extraction pipe 12 into the inlet side of the cyclone 8. In this way, the amount of accumulated ore is reduced, thereby reducing the pressure loss inside the pre-reducing furnace 1. Therefore, since the amount of ore retained in the preliminary reduction furnace can be adjusted, it is possible to control the reduction time of ore and achieve an appropriate reduction rate.

The high-temperature fluidized reducing gas required for the fluidized bed is not only supplied directly from the smelting reduction furnace, but due to the variety of processes, reducing gas generated by the smelting reduction furnace is cooled and stored in a gas tank. It may also be used, in which case increasing the temperature of the reducing gas is made possible by burning part of the reducing gas.

The retention amount detector 13, which detects the amount of retained ore, consists of pressure gauges grounded at multiple locations on the side wall in the height direction of the preliminary reduction furnace l, as shown in Fig. 2, and measures the pressure at each location. Calculate each differential pressure from the measured values.

From the differential pressure, the amount of retained ore in that section (for example, between P and P4) can be calculated using the following formula.

Differential pressure: ΔP (kg/m") = Pl - P4 pre-reducing furnace cross-sectional area: S (m") Retention ore amount: W (kg)・Δpxs Simplified management is based on differential pressure rather than ore weight (kg) do. For example, when the differential pressure between P and P4 is normally 0.15 kg/m'', when the measured value reaches 0.20 kg/l112 and the preliminary reduction furnace is not operating properly, the extraction pipe 12 is temporarily opened. By accelerating the ejecting speed of ore from the preliminary reduction furnace and normalizing the differential pressure between 23 and 21 to 0.15 kg/m'' in a short time, it becomes possible to continue the subsequent operation. .

(Example) The circulating fluidized bed preliminary reduction furnace shown in FIG. 1 was combined with a vertical smelting reduction furnace, and powdered ore was smelted and reduced under the following conditions.

1. Furnace used: Vertical smelting reduction furnace inner diameter Furnace lower part: 1.2 m Furnace upper part: 1.8 m Furnace height: 4 m Tuyere 2 stages Upper tuyeres: 3 lower tuyeres: 3 Fluidized bed pre-reduction furnace Inner diameter: 0.7 m Furnace height: 4.5 m 2. Operating conditions i) Melting reduction section/blow volume (0, concentration 40%): 990 Nm2
/hO generated gas flow 1: 2200 Nm+''/hO generated gas temperature: 1 oos'c - Carbon material (coal)? 905 kg/hii) Fluidized bed preliminary reduction section - Reducing gas flow rate: 2200 Nm'/h - Reducing gas flow rate : 3 m/s Cloudy reducing gas composition: CO: 30% H dew = 21% N!? 38% Others = 11% ・Reducing gas temperature: 970°C ・Pressure: 0.9 kg/cm"G ・Circulating gas Flow rate: 45 Nm”/hI) Iron ore powder (
Average particle size: 30μm and 140#Il) Supply amount: 5
80 kg/h tv) limestone powder (average particle size: 35p and 200p)
) Supply amount: 100 kg/h ■) Silica powder (Average particle size: 35μ and 200μ)
Supply amount: 43 kg/h Melting reduction treatment was performed under the above conditions, and the total retention amount in the pre-reduction furnace during operation was 2100 kg (total differential pressure P of the pre-reduction furnace).
I - Pi became 0.55 kg/cs + "G) and the operation became unstable due to the pressure increase and pressure fluctuation, so the ore was extracted from the extraction pipe and introduced into the inlet side of the cyclone, and the total differential pressure in the preliminary reduction furnace was 0.29 kg/cm''G and the operation normalized, the ore throughput was 400 to 600 kg/h and the reduction rate was 50 to 70%.

For comparison, when the smelting reduction process was continued under similar conditions without extracting the ore midway, the pressure of the blower blowing air into the smelting reduction furnace exceeded the allowable range, making it impossible to continue the operation. .

(Effects of the Invention) According to the present invention, ores having different particle sizes can be pre-reduced simultaneously or in the same furnace, and flexible operation that is not influenced by raw materials can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a circulating type fluidized pre-reduction furnace used to carry out the present invention, and FIG. 2 is a schematic diagram showing the installation of a retention amount detector. 1... Pre-reduction furnace 2... Inlet 3... Fluidized reducing gas 4... Fluidized bed 5... Raw material supply port
6...Discharge lower...Powdered ore 8.
...Cyclone 9...Circulation route 10...
Circulation supply port 11...transport route 12...
Extraction pipe 13...Retention amount detector Fig. 1

Claims (1)

[Claims] 1. High-temperature fluidized reducing gas is introduced into the fluidized bed pre-reduction furnace at a speed higher than the ejecting speed of powdered ore or pre-reduced ore powder to form a fluidized bed. The pre-reduced ore powder that has flown out from the top of the layer is collected by a cyclone, and the collected ore powder is returned to the reduction furnace through the circulation path, thereby circulating and fluidizing the pre-reduced ore powder while pre-reducing it. A method for operating a circulating fluidized bed pre-reduction furnace, characterized in that when the amount of accumulated ore in the fluidized bed pre-reduction furnace increases, powdered ore is extracted from the side wall of the furnace and introduced into the inlet side of a cyclone.