JPH0213015B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a fluidized bed reduction method for powdery ores such as ferroalloys and non-ferrous metals. [Prior art] Reducing iron ore in its solid state to produce products and semi-finished products has been carried out for a long time as preliminary reduction in the direct iron manufacturing process and as coarse reduced powder in the production of iron powder. . Among the manufacturing methods, a fluidized bed pre-reduction method that applies fluidized bed technology, which is widely used for catalytic reactions and solid reactions in fields such as the chemical industry, has been attempted for a long time. H-Iron Act of 1958, FIQR Act of 1965,
The HIB method of 1972 and other methods are all fluidized bed preliminary reduction methods. The advantage of the fluidized bed reduction method is that the powder can be treated like a fluid, making it easy to carry out continuous production and providing good reaction control. However, on the other hand, it also has a disadvantage: the exhaust gas leaving the fluidized bed usually has the same reaction temperature, and unless the effective use of that heat is considered, the thermal efficiency will not be as good as in a shaft furnace. In order to improve this thermal efficiency, the cement industry has traditionally used a method in which the high-temperature exhaust gas emitted from the rotary kiln is passed through an air-solid counterflow heat exchanger called a suspension preheater, which is a series of cyclones connected before feeding raw materials to the rotary kiln. A method is used to preheat the raw materials. This method can also be applied to the fluidized bed reduction method, and can be said to be one solution to the above problems. Another point is that in the fluidized bed reduction method, the supply of heat corresponding to the latent heat of reaction necessary for reduction, ore heating, and heat dissipation from the furnace body is determined by the sensible heat of the reducing gas, that is, the difference between the preheating temperature of the reducing gas and the reaction temperature. If we try to supply the product of Or, if the amount of reducing gas is kept modest, the required preheating temperature of the reducing gas must be increased, and if the iron ore is placed in the fluidized bed as it is, the iron ore will sinter in the fluidized bed and will no longer maintain its fluidized state. It becomes impossible to do so. [Problems to be Solved by the Invention] The present invention aims to solve the drawbacks of the preliminary reduction of powdery ore using a fluidized bed, and to provide a method for improving thermal efficiency and preventing sintering in the fluidized bed. This is the purpose. [Means for Solving the Problems] As a method to overcome the drawbacks of the fluidized bed reduction method, the present inventors have provided a gas blowing nozzle in the gas inlet flue of a solid-gas heat exchange device, such as a suspension preheater. , some amount of gas containing oxygen is introduced,
A part of the reducing gas discharged from the fluidized bed is combusted to produce high-temperature exhaust gas higher than the reaction temperature, and the exhaust gas is subjected to solid-gas heat exchange with the raw material powder ore to heat the ore to a temperature higher than the reaction temperature. By directly introducing the ore heated above the temperature into the fluidized bed, part of the amount of heat commensurate with reduction reaction heat (endothermic reaction), heat dissipation outside the furnace, etc. is compensated for, and the flow rate of the preheated reducing gas introduced into the fluidized bed is increased. Alternatively, we devised a method to reduce the preheating temperature of the reducing gas. In this case, it is important to note that the reducing gas itself, rather than the exhaust gas from the reducing furnace, is introduced into the solid-gas heat exchange device, and by blowing in oxygen, a part of it is combusted and the ore is heated. It has become clear through extensive research by the present inventors that this is not possible. In other words, the reducing ability of the exhaust gas after reducing the ore is extremely low, so if oxygen is added and some of it is combusted, the reducing ability is almost completely lost, and the gas temperature is close to the melting point of the ore. This is because the present inventors discovered that ore can be preheated without causing sintering trouble even if the temperature rises to . Further, the high exhaust gas temperature of the fluidized bed reduction exhaust gas, which is also a drawback thereof, makes the method of the present invention, that is, the direct solid-gas heat exchange of the fluidized bed reduction exhaust gas with the raw material powder ore, advantageous. This is the technical concept of fluidized bed reduction in which the exhaust gas of the fluidized bed reduction method is directly subjected to solid gas heat exchange with the raw material powder ore, and O ₂ is added thereto to preheat the ore to a temperature higher than the reaction temperature. Not until then. In this case, of course, it is also possible to blow air instead of oxygen. Also, CO and H ₂ are effective reducing gases. [Operation] Before the fluidized bed reduced exhaust gas is subjected to solid-gas heat exchange with the raw material powder ore, a small amount of gas containing O ₂ is injected to burn a part of the fluidized bed outlet exhaust gas and heat the ore above the fluidized bed reaction temperature. , supplying it to a fluidized bed has the effect of reducing the amount of reducing gas or lowering the reducing gas preheating temperature. If the amount of reducing gas can be reduced, the duct diameter, reduction furnace capacity, ore preheating furnace, and calculation equipment as a whole can be reduced, leading to a reduction in equipment costs.
Further, lowering the reducing gas preheating temperature is very effective not only in reducing the amount of fuel required for preheating but also in preventing ore sintering in the fluidized bed. 800℃ in ore reduction technology using fluidized bed
When operating at a reaction temperature of 1,200°C, when high-temperature gas is introduced into the fluidized bed through the dispersion plate, the temperature at the point where it exits the dispersion plate nozzle in the fluidized bed is still close to 1,200°C, so a partial Sintering of the reduced ore is very likely to occur. Therefore, in the ore reduction method using a fluidized bed, it is important to select a reaction temperature that does not cause sintering and to be able to supply gas at a reducing gas temperature as close as possible to the reaction temperature for stable operation. As described above, it is necessary to heat the ore above the reaction temperature in order to compensate for the amount of heat commensurate with the latent heat of the reduction reaction and heat dissipation outside the furnace. On the other hand, in order to prevent sintering of the reduced ore, it is necessary to keep the temperature below 1350°C. [Example] An example of the present invention carried out using the apparatus shown in FIG. 1 will be described. The main parts of the apparatus for carrying out the high temperature reaction, including the reduction furnace 1 and the suspension preheater 3, are protected by a refractory heat insulating material 10 in order to minimize heat loss. Reducing gas supplied from reducing gas supply device 9
H ₂ is heated to a predetermined temperature in the preheating device 8 and introduced into the fluidized bed via the gas distribution plate 7 . The raw material iron ore used in the experiment was sized and dried in advance, and was introduced into the suspension preheater 3 from the ore supply device 2, and while exchanging heat with the fluidized bed outlet exhaust gas, it was passed through the ore supply port 11 attached at the bottom of the fluidized bed. It enters the fluidized bed and is reduced at a predetermined temperature. The suspension preheater 3 is provided with an oxygen blowing nozzle 4 at the fluidized bed outlet exhaust gas introduction section so that the present invention can be carried out. There is a discharge port 6 at the bottom of the fluidized bed that allows continuous discharge of ore. In an operational experiment to clarify the effects of the present invention, the ore supply amount was kept constant at 28.4 kg/h, and the reduced iron ore discharge amount was kept at 19.4 kg/h.
Kg/H constant, reduction furnace reaction temperature constant 800-810℃,
The brand of iron ore used and the particle size of Mount Newman ore of 2 mm or less were constant, and other operating conditions and results are shown in Table 1. The operation is as follows: When iron ore is charged directly into the fluidized bed without using a suspension preheater (comparative example) When a normal suspension preheater is operated to preheat the iron ore using only the exhaust gas at the outlet of the fluidized bed (comparative example) ) Burning a part of the fluidized bed outlet exhaust gas of the present invention,
An example (example) that clearly shows the effect of reducing the reducing gas preheating temperature when the iron ore temperature is raised above the reaction temperature, and in that case, the same amount of reducing gas as above is used. In an operation in which a part of the fluidized bed outlet exhaust gas of the present invention is twisted and fired and the iron ore temperature is raised above the reaction temperature, the required amount of reducing gas can be reduced if the operation is performed at the same reducing gas preheating temperature. This is an example (example) that clearly shows the effect. In this case, as the iron ore preheating temperature, the temperature measured with the thermometer 13 when the damper 12 for adjusting the ore supply amount was closed was taken as a representative value for comparison of the iron ore preheating temperature.
The stirring mechanism 15 was used only when the fluidization state became poor. As is clear from the examples in Table 1, a small amount of O ₂ is injected before the suspension preheater 3 to burn part of the fluidized bed outlet exhaust gas, heat the iron ore above the fluidized bed reduction reaction temperature, and This had the effect of reducing the amount of reducing gas or lowering the reducing gas preheating temperature, making it possible to achieve more stable and economical fluidized bed reduction. Furthermore, it has been confirmed through experiments that the present invention is similarly effective on other ores such as chromium ore.

〔Effect of the invention〕

By the method of the present invention, powdered ore preheated to a temperature higher than the reaction temperature is subjected to a reduction reaction in a fluidized bed, so the temperature of the reducing gas is lowered and the amount thereof is suppressed, thereby achieving stable, economical and efficient fluidized bed reduction. It is possible,
The drawbacks of the conventional fluidized bed furnace could be improved.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an example of an apparatus used for carrying out the present invention. 1... Reduction furnace, 2... Ore supply device, 3... Suspension preheater, 4... Oxygen blowing nozzle, 5...
Reducing gas inlet, 6...Reduced iron outlet, 7...Gas distribution plate, 8...Reducing gas preheating device, 9...Reducing gas supply device, 10...Refractory insulation material, 11...Ore supply port, 12
...Damper for ore supply amount adjustment, 13...Thermocouple for measuring ore temperature, 14...Thermocouple for measuring furnace temperature, 15...
Stirring mechanism.

Claims (1)

[Claims] 1. In the fluidized bed reduction method for powdered ore in which powdered ore is fluidized and reduced with high-temperature reducing gas, oxygen is blown into the fluidized bed exit exhaust gas to burn a part of it, and the exhaust gas is combined with the raw material powdered ore. A fluidized bed reduction method for powdery ore, characterized by heating the powdery ore through solid-air heat exchange and introducing the powdery ore into a fluidized bed.