JPH08199214A - Method for preventing reoxidation and sticking of fluidized/reduced ore - Google Patents

Abstract

PURPOSE: To prevent reoxidation and sticking of reduced powder ore by specifying the partial pressure of carbon mono-oxide of a carrying gas used for discharging when powder ore is reduced in fluidized layer and is discharged. CONSTITUTION: A fine iron ore is charged from a raw material supply port of fluidizing/reducing device to a riser 1, a reducing gas 9 is introduced from a nozzle of bottom of the riser 1 to form a fluidized layer, and reduction of fine rion ore is executed. The reduced iron ore is sent from the top part of riser 1 to a primary cyclone 2 together with discharge gas, and a caught iron ore is circulated from a primary downcomer 4 to the riser 1. At this time, the gas 23 for powder a part of iron ore is drawn to a bubble fluidized type pneumatic feeder 20 through a reduced ore-drawing tube 25 and a powder- carrying gas 23 including CO of which the partial pressure satisfies the equation (wherein P1: CO partial pressure (atm), P2: CO partial pressure (atm), T: temp. of reduced ore transfer device) is introduced, and the reduced iron ore 21 discharged from a discharge tube 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing reoxidation and sticking of reduced ore obtained by reducing fine iron ore in a fluidized bed.

[0002]

2. Description of the Related Art A fluidized bed for reducing powdered ore is used as a preliminary reduction device for powdered ore in the production of pig iron by smelting reduction, as disclosed in, for example, JP-A-1-111807. . This fluidized bed is of a type called a circulating fluidized bed, and comprises a riser having a powdery ore charging section at the top and a reducing gas introducing section at the bottom, a cyclone provided outside the riser, and a powdery ore collected by the cyclone. It consists of a downcomer for returning to the riser.

Since reduced iron ore having a reduction rate of 30% or more has metallic iron deposited thereon, it is easily reoxidized in the atmosphere and the reduction rate is lowered if left unattended, and the oxidation reaction is an exothermic reaction. Sticking may occur due to mutual contact. Here, sticking refers to a phenomenon in which powders of reduced iron are combined with each other to form a lump,
Sometimes called sintering. Prevention of reoxidation and sticking is an important issue because handling of the product becomes difficult and the quality of the product deteriorates. Generally, a gas is used for transporting the high temperature powder, but an oxygen-free inert gas is usually used for transporting the reduced ore from the viewpoint of preventing reoxidation and sticking.

The applicant of the present invention has previously disclosed the Japanese Patent Laid-Open No. 6-145748.
In order to prevent abnormal flow due to sticking of highly reduced powdered ore in the circulating fluidized-bed reduction device, CO and / or CnHm-rich additive gas is injected into the flow path as a circulating gas for reduced particles, It has been proposed to deposit C on the reduced particles.

Further, the applicant of the present invention, in JP-A-6-48150, conveys the reduced ore reduced in the fluidized bed by a gas containing 25 to 100% of hydrocarbons without oxygen to prevent reoxidation and sticking. Suggested a way to do.

[0006]

However, the method disclosed in Japanese Patent Laid-Open No. 6-145748 has a certain effect in preventing sticking in a fluidized-bed reduction apparatus, particularly in a downcomer, but it is a riser in which a reduction reaction proceeds. It is assumed that the particles will be returned inside. After the particles return to the riser, they are exposed to a high-temperature reducing atmosphere, so that the precipitated C reacts with CO ₂ and H ₂ O to become CO gas and is consumed. Therefore, C, which is sufficient to prevent the sticking of the reduced ore discharged as a product from the furnace, does not remain in the discharged ore, and cannot be a measure to prevent the reoxidation of the product.

The present invention has been made by paying attention to these points, and is not a gas for circulating particles for returning particles to the riser, but a carrier for reducing ore after being extracted from the furnace as a product. It is intended to provide a method for stably and easily discharging reduced ore with respect to a carrier gas.
In addition to this, although hydrocarbons are essential in the method of Japanese Patent Laid-Open No. 6-48150, the present invention reoxidizes and sticks a reduced ore obtained by a fluidized reduction method using a gas that is more easily and cheaply available. To provide a method of preventing

[0008]

The present invention provides a fluidized reduction method of reducing powdered ore in a fluidized bed to obtain reduced ore, when the reduced ore reduced in the fluidized bed is carried out of the furnace. Is discharged by using a carbon monoxide-containing powder-conveying gas that satisfies the condition of formula (1), to prevent reoxidation and sticking of fluidized ore. Is.

P1> {P2 / exp (20400 / T-20.8)} ^0.5 (1) P1: Partial pressure of carbon monoxide (atm) P2: Partial pressure of carbon dioxide (atm) T: Transport of reduced ore Device temperature (K) Further, according to the present invention, the exhaust gas after reducing the powder ore in the fluidized bed is used as the powder-conveying gas satisfying the expression (1). It is a method of preventing oxidation and sticking.

[0010]

The present invention will be described below with reference to FIG.

From the raw material supply port of the fluidized reduction apparatus to the riser 1
The powdered iron ore is charged into, and the reducing gas 9 is introduced from the reducing gas blowing nozzle at the bottom of the riser 1 to form a fluidized bed, and the powdered ore is reduced by a solid gas reaction. The ore thus reduced is sent from the top of the riser together with the exhaust gas to the primary cyclone 2, and the ore collected there is circulated from the primary downcomer 4 to the riser 1. A part thereof is extracted through the reduced ore extracting pipe 25. The product withdrawal rate is usually controlled by the amount of gas added to the pneumatic feeder, and in FIG. 1 is controlled by the amount of carbon monoxide-containing gas 23 added to the bubble fluidized bed type pneumatic feeder 20.

The pneumatic feeder is also called a pneumatic valve. It utilizes the sealing property of powder and the transport property by gas with respect to a mechanical valve. The shape of the seal and the blowing portion of the gas is L valve, U valve.
There are valves and bubbling fluidized beds. Although FIG. 1 shows a system using a bubbling fluidized bed for a pneumatic valve,
The present invention can be applied to other types as long as the amount of powder is controlled by gas or the start and stop of the powder are controlled. In the pneumatic valve, the particle cutting is stopped by stopping the powder carrying gas, and the particle cutting amount increases as the carrying gas amount increases.

Normally, an inert gas such as nitrogen containing no oxygen is used as the carrier gas in order not to oxidize the reduced ore. In the present invention, a gas containing carbon monoxide is used as a carrier gas. The carrier gas containing carbon monoxide acts as follows. Metallic iron in the reduced ore serves as a catalyst to deposit C and accelerate the iron-carbide conversion reaction of metallic iron.
That is, the following reactions proceed.

2CO → C + CO ₂ (2) C + 3Fe → Fe ₃ C (3) 2CO + 3Fe → Fe ₃ C + CO ₂ (4) C generated by the equation (2) is soot-like and should adhere to the metal surface. Prevents sticking. Also,
Fe ₃ C produced by the formula (3) or (4) is much more stable than metallic iron and is not reoxidized in the atmosphere. Further, since iron contains carbon, the carbon can be utilized as energy when melting in the next step.

There are restrictions on temperature and partial pressure in order to smoothly proceed the reactions of equations (2) to (4). That is, if the temperature is too high, the reaction of the formula (2) proceeds in the opposite direction, and the deposited carbon is consumed and returns to carbon monoxide. In addition, CO ₂
If the amount is too large, the same reverse reaction will proceed and the reaction will not occur as desired. As a result of examining the conditions for smoothly proceeding the reaction of the formula (2) from the equilibrium theory, the conditions shown in the formula (1) were obtained. That is, assuming that the reaction temperature is T (K), the carbon monoxide partial pressure is P1 (atm), and the carbon dioxide partial pressure is P2 (atm), if the temperature and the partial pressure satisfy the relationship of equation (1), (2) The reaction of the formula) proceeds.

P1> {P2 / exp (20400 / T-20.8)} ^0.5 (1) For example, if P2 is 0.2 atm and the temperature is 750 ° C., if P1 is 0.69 atm or more (2 ) ~ (4)
The reaction of the formula will proceed. When the carbon monoxide partial pressure is less than this, even if iron carbide or carbon is generated, it immediately returns to metallic iron or carbon monoxide and the sticking prevention effect is lost. Further, at a temperature below this or a partial pressure of carbon dioxide, the consumption reaction of the precipitated iron carbide and carbon does not proceed, and the effect as a sticking preventing material continues to be exhibited.

In the present invention, as the powder-carrying gas for preventing sticking, a carbon-containing fuel such as coal, petroleum, natural gas, converter gas, and coke oven gas is burned or left as it is, if necessary. It can be used by adjusting the temperature of heating and cooling and adjusting the components by mixing gas so as to satisfy the condition of the formula (1). Further, more simply, it is also possible to adjust the temperature of the gas discharged from the fluidized bed for reducing the ore and use it in a state satisfying the expression (1).

[0018]

[Examples] Iron ore was reduced under the conditions of a reduction temperature of 800 to 910 ° C and a gas flow rate in the riser of 8 m / s. The components of the reducing gas used are shown in Table 1.

[0019]

[Table 1]

In Example 1, a normal-temperature converter gas having the composition shown in Table 2 was used as the carrier gas.

[0021]

[Table 2]

The temperature of the pneumatic feeder is 6
Atmospheric pressure was applied at 50 ° C. When this condition is applied to the formula (1), the partial pressure of carbon monoxide may be 0.24 atm or more, and Example 1 satisfies this condition. In order to evaluate the degree of progress of reoxidation, changes in the reduction rate of the product when left in the atmosphere at room temperature were investigated together with comparative examples. In the comparative example, nitrogen containing no carbon monoxide was used as the carrier gas.
Further, in order to evaluate the degree of progress of sticking, the weight ratio of +10 mm of the product when left in the atmosphere at room temperature was investigated together with the comparative example. The results are shown in Figure 2. When the present invention is applied, it is clear that reoxidation is prevented, the reduction rate of the product is hardly reduced even if it is left in the air, and the weight ratio of +10 mm does not increase, and it is also effective in preventing sticking of the product. is there.

In Example 2, the exhaust gas of the iron ore reducing furnace having the composition shown in Table 3 was used as the carrier gas. Here, as a comparative example, blast furnace gas containing about 20 mol% of CO ₂ and about 20 mol% of CO was used as a carrier gas. The temperature of the pneumatic feeder was 700 ° C. and atmospheric pressure. The carbon monoxide partial pressure required in Example 2 is 0.21 atm, and the condition of Example 2 satisfies the formula (1), but the carbon monoxide partial pressure of 0.41 atm or more is required in the comparative example. Therefore, the formula (1) is not satisfied.

[0024]

[Table 3]

A comparison similar to that of Example 1 is shown in FIG. Even in the case of this example, the effect of preventing reoxidation and sticking is apparent by the application of the present invention.

[0026]

Industrial Applicability According to the present invention, it is possible to prevent reoxidation and sticking of reduced ore obtained by a fluidized reduction method, facilitate storage and transportation of reduced powder ore, and
Quality can be maintained for a long time.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a flow reduction apparatus flow based on the method of the present invention.

FIG. 2 is a diagram showing the effects of preventing reoxidation and suppressing sticking in Example 1.

FIG. 3 is a diagram showing the effects of preventing reoxidation and suppressing sticking in Example 2.

[Explanation of symbols]

1 ... Riser 2 ... Primary cyclone 3 ... Secondary cyclone 4 ... Primary downcomer 5 ... Secondary downcomer 6 ... Circulating particles 7 ... Fine powder particles 8 ... Reducing gas blowing nozzle 9 ... Reducing gas 10 ... Riser fluidizing gas 11 ... Particle circulation gas 12 ... Fine particle circulation gas 13 ... Inclined tube 14 ... Reservoir 15 ... Dispersion plate 20 ... Bubbling fluidized bed type pneumatic feeder 21 ... Reduced ore 22 ... Product discharge pipe 23 ... Carbon monoxide gas 24 ... Ore-reducing fluidized bed exhaust gas 25 ... Reducing ore extracting pipe 26 ... Pneumatic feeder exhaust gas

Claims (2)

[Claims] 1. In a fluidized reduction method of reducing powdered ore in a fluidized bed to obtain reduced ore, when the reduced ore reduced in the fluidized bed is carried out of the furnace, the reduced ore is subjected to partial pressure of carbon monoxide. Is discharged by using a powder-carrying gas containing carbon monoxide that satisfies the condition of formula (1), and a method for preventing reoxidation and sticking of fluidized ore P1> {P2 / exp (20400 /T-20.8)} ^0.5 (1) P1: Partial pressure of carbon monoxide (atm) P2: Partial pressure of carbon dioxide (atm) T: Temperature of reduced ore carrier unit (K) 2. The method for preventing reoxidation and sticking of fluidized ore according to claim 1, wherein the exhaust gas after reducing the powdered ore in the fluidized bed is used as the powder conveying gas.