JPH0635610B2 - Pig iron manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing pig iron with an improved preliminary reduction step.

(Prior Art) As a pig iron manufacturing method, a gas reduction process using a modified reducing gas has already been industrialized. On the other hand, as a method of using resource-rich steaming coal as a reducing agent, a method using a rotary kiln occupies the mainstream. However, this method leaves room for consideration in terms of equipment costs, thermal efficiency, reduction rate, and the like. Further, it has been considered to form a multi-stage fluidized bed to enhance the reduction efficiency, but many troubles occur in the mechanism for moving the ore particles to the lower stage, and the operation is difficult, and the structure is complicated.

(Technical problem to be solved by the invention) The present invention provides a method for producing pig iron having a thermal reduction and a high reduction rate, capable of reducing the load of the melting furnace, and having a preliminary reduction furnace capable of performing stable operation. To aim.

(Means for Solving the Technical Problem) First, the present invention was made by paying attention to the following knowledge. FIG. 1 schematically shows the change in the fluidized state when the gas flow rate is increased. Fluidization start flow velocity U
At a flow rate slightly exceeding mf, the fluidized bed is uniformly fluidized (Fig. 1 (a)). When the gas flow velocity increases, the surplus gas will pass through the layer as bubbles (Fig. 1 (b)). When the flow velocity is still increased, as shown in Fig. 1 (c),
The state shifts to the slugging state as shown in (d). In this case, if the bed height is smaller than the pipe diameter, the slugging state does not occur.

On the other hand, in the case of a fluidized bed with a bed height larger than the tube diameter, the bubbles generated near the dispersion plate at the bottom of the bed coalesce as they rise, spread to the full tube diameter, and particle layers and voids exist alternately. It becomes such a state. The fluidized bed in such a state is called a slugging fluidized bed. The void is called a slug, and the thickness of the particle layer between the voids is called a slug space. Since the particle layer between each slug moves in a piston flow and the mixing of particles in the particle layer is small, the residence time of the particles as a whole is close to that of a fluidized bed, and although it is a single fluidized bed, it has a multi-stage flow. Has layer-like properties. As a result, it is expected that the reaction rate of particles and the heat transfer efficiency will increase.

The present invention was made by paying attention to this finding, and
Coal is inserted from the bottom of the elongated pre-reduction tower with a diameter of 5 or more, and coal combustion gas is blown to fluidize and burn coal to form char in the carbonization state, and these gases and char are moved upward, and from the top. Inserting ore particles and forming a fluidized bed in the slugging state by the above gas and moving the ore particles to the lower stage one by one, in this state sequentially preheating the ore particles and pre-reducing, and the pre-reduced ore The method for producing pig iron comprises the steps of taking out particles, putting them in a melting furnace, and reducing and melting the particles.

(Example) FIG. 2 shows an apparatus for producing pig iron. This apparatus is constructed by combining a pre-reduction tower 11 and a melting furnace 12. The preliminary reduction tower 11 has a tower height / tower diameter of 5 or more, preferably 5 to
20. At the lower part of the preliminary reduction tower 11, a coal charging pipe 1
3, a furnace top gas blowing pipe 14 and a heated air blowing pipe 15 are attached. A furnace top gas injection pipe 16 is attached to the coal charging pipe 13 via an injection feeder 17,
A coal supply hopper 18 is equipped on the top of this feeder. Further, a powder ore charging pipe 19 is attached to the upper portion of the preliminary reduction tower 11, and a powder ore supply hopper 20 is mounted on the charging pipe 19. Further, a furnace top gas exhaust pipe 21 is attached to the top of the preliminary reduction tower 11. Here, hot cyclones 22 and 23 and a heat exchanger 24 are mounted. The powdered ore collected by the hot cyclone 22 is returned to the upper part of the reduction tower. The heat exchanger 24 heats the air, and the air heated here is heated by the heated air blowing pipe 1
5 is supplied into the reduction tower. A part of the exhaust gas after passing through the heat exchanger is supplied to the injection feeder 17 for injection by the booster 25. Reduction tower 1
A powder ore take-out pipe 26 is attached to the lower part of the unit 1 to supply the pre-reduced powder ore to the melting furnace 12. In the melting furnace 12, oxygen is blown into the supplied powdered ore from the oxygen ejection pipe 27 to dissolve and reduce the ore particles to obtain molten iron and slag. The gas such as CO generated in the melting furnace 12 enters the preliminary reduction tower from the injector 28 together with the exhaust gas from the top of the reduction tower.

However, in the pre-reduction tower, the coal inserted from the lower part is fluidized and burned by the air from the lower part, and the dry char moves upward together with the gas. On the other hand, the ore particles inserted from the upper part form a fluidized bed in the reduction tower by the gas from the lower part. In this case, since the preliminary reduction tower has an elongated shape as described above, a plurality of particle layers 32 are provided through the gas layer 31.
Is formed. The reason why the tower height / tower diameter ratio is limited to 5 or more in the present invention is that if the ratio is less than this, it is not possible to form a plurality of stages of particle layers 32. The solid particles composing the particle layer 32 sequentially move to the lower method while being heated and reduced by the gas from the lower part. And powder ore take-out pipe 26
Is charged into the melting furnace 12. According to this pre-reduction tower 11, since the residence time of particles is close to the moving bed,
Heat exchange with the gas from the lower part of the reduction tower is carried out sequentially, and its efficiency is good. Most of the heat generated by fluidized combustion of coal is given to the reduction zone in the upper part of the reduction tower, and part of the exhaust gas in the reduction zone is blown in the middle of the coal and the residual char causes the proportion of CO and H ₂ in the reduction gas. And the reducing power is regenerated, which is used for ore reduction. As in the embodiment, it is preferable to perform oxygen enrichment and blowing of preheated air for compensating the heat quantity.

In the boundary region between the lower reducing gas generation zone and the upper reducing zone, the reduced ore particles and the char rising from the lower portion are mixed, and this char can prevent the ore particles from adhering. As a result, the temperature of the ore particles can be increased considerably. For example, in the case of reduction in a normal fluidized bed, about 700 to 800 ° C. for particles and 1 for pellets
The upper limit is about 000 ° C, and in the case of a shaft furnace, 90
Although it is about 0 ° C., in this method, it is possible to raise the upper limit temperature by about 100 to 200 ° C. by mixing char.

Further, in the case of a shaft furnace, the operation of cutting out the particles must be performed mechanically and requires some cooling, but in the method of the present invention, the reduced particles are fluidized in the reduction tower, so that the temperature is high. It can be discharged as is. Therefore, the method of the present invention has an advantage that ore particles can be supplied to the melting furnace at a high temperature. Further, in the present invention, the residence time of the ore particles can be kept constant, so that a stable reaction rate can be obtained. The char that is inserted into the melting furnace together with the ore particles is effectively used as fuel in the melting furnace.

Next, an example of calculation of the material and heat balance of the method of the present invention is also shown in FIG.

The ore has an oxidation degree of 1.5 and a gangue content of 200 kg.

Industrial analysis results for coal show that solid oxygen is 40% and volatile matter is 50
%, Ash content 5%, water content 5%, and the elemental analysis results (daf) are C78%, H6%, and O16%.

Basic unit, the air 1130 nm ^3, oxygen 52 nm ^3, a coal 580 kg.

The composition of the furnace top gas is N ₂ 43.8%, CO 18.6%,
CO _{2 is} 18.6%, H _{2 is} 9.5%, and H ₂ O is 9.5%. The amount of heat (heat of combustion) is 800 Kcal / Nm ³ .

In the extraction pipe 26, 95% reduced pig iron 1021 kg, slag 222 kg, and char 70 kg are extracted and supplied to the melting furnace. In the melting furnace, 1000 kg of molten iron can be obtained.

(Effect of the Invention) According to the present invention, the ore in the preliminary reduction tower can be hot-charged at a high reduction rate, so that the load on the melting furnace can be reduced. When coal is put directly into the melting furnace, combustion suddenly occurs and the operation becomes unstable. However, in the present invention, since it enters as char, the operation becomes stable.

[Brief description of drawings]

1 (a) to 1 (d) are explanatory views showing classified fluidized states, and FIG. 2 is an explanatory view showing an example of the method for producing pig iron of the present invention. 11 ... Preliminary reduction tower, 12 ... Melting furnace, 13 ... Coal charging pipe, 14 ... Furnace top gas blowing pipe, 15 ... Heating air blowing pipe, 16 ... Furnace top gas blowing pipe, 17 ... Injection feeder, 18 …… Coal supply hopper, 19 …… Powder ore charging pipe, 20 …… Ore supply hopper, 21 …… Top gas exhaust pipe, 22,23 …… Hot cyclone, 24 ……
Heat exchanger, 25 ... Booster, 26 ... Powder ore take-out pipe, 2
7 ... Oxygen ejection tube, 28 ... Injector

Claims (1)

[Claims] 1. A coal is inserted from the lower part of an elongated pre-reduction tower having a tower height / tower diameter of 5 or more, and coal combustion gas is blown to fluidize and burn coal to obtain char in a carbonization state. Move upward, and insert ore particles from the top, form a fluidized bed in the slugging state with the above gas and move the ore particles sequentially to the lower stage, preheat the ore particles sequentially in this state and pre-reduce A method for producing pig iron, comprising the steps of: going out, and taking out the pre-reduced ore particles, putting them in a melting furnace, and reducing and melting them.