JPH0635614B2 - Fluidized bed reduction method for ores - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for reducing ores, particularly iron ores, by a fluidized bed reactor.

(Prior Art) The most commonly used process for reducing molten iron ore to obtain molten iron is a blast furnace. However, high quality agglomerated ore and coke are required to maintain stable operation in the blast furnace steelmaking process, and problems such as increased costs for producing these and restrictions on raw material selection have been pointed out. .

As one means for solving these problems, a smelting reduction process in which iron ore is reduced by heating and melting by the partial oxidation heat of coal has been researched and developed. For example, in Japanese Patent Application No. 59-184056, iron ore, coal, and an oxygen-containing gas are charged into a fluidized bed reactor and the reaction is allowed to proceed to obtain iron ore and cheers. , An iron-making method characterized in that a briquette obtained by mixing and agglomerating coal supplied from another system is charged into an upper-bottom blow converter reactor and the preliminary reduced ore is melt-reduced. It is shown.

Regarding the pre-reduction step, for example, in Belgian Patent No. 827521, a circulating fluidized bed is used to gasify carbonaceous materials by a partial combustion reaction with oxygen, and a part of them is converted into a char. Discloses a process for reducing iron ore. Further, Japanese Patent Application No. 51-99671 discloses a method of suppressing the reoxidation of already reduced ore particles in the oxidation region by devising the shape of the reactor.

However, regarding the gas flow rate in the reaction tower, Chemical
Engineering Progrecs 67, 58-63 (1971) and JP Sho
In Japanese Patent Laid-Open No. 51-99671, the gas flow rate is determined only from the viewpoint of transporting particles, and is used for the reduction of the gas produced by the reaction of the gas and carbon substances introduced into the reaction tower with O _2. Efficiency is not always guaranteed.

Originally, a fluidized bed reaction tower has a drawback that productivity per unit volume is low and gas utilization efficiency is poor as compared with a packed bed type reaction tower because the reaction substances are reacted in a dilute layer. In particular, the circulating fluidized bed has a large amount of passing gas, and this tendency is remarkable.

(Problems to be Solved by the Invention) In the present invention, in the vertical fluidized bed reduction, the degree of freedom of the reducing gas temperature and composition is increased, the utilization efficiency of the reducing agent is increased, and the volumetric productivity of the reaction tower is improved. It provides an enhanced reduction method.

(Means for Solving Problems) In the present invention, an ore preheated to 1000 ° C. or less and having a particle size of 1 mm or less is combined with an ore separated and collected from a furnace top gas and supplied to the lower part of the furnace for reduction. In the circulation flow reaction method of supplying a reducing gas from the bottom of the furnace, the amount of the reducing gas to be supplied to the bottom of the furnace is regulated to an amount obtained by subtracting the distribution amount from the theoretical total amount, and The reducing gas is supplied by providing at least one position in the height direction of the furnace at which the utilization rate is best and a reducing gas inlet having a distribution rate corresponding to the above-mentioned distribution amount. It is characterized by compensating ability.

In the present invention, iron ore is preferably sized to a particle size of 1 mm or less. Also, the tower is heated below 1000 ° C. One of the problems of the fluidized bed reaction tower (hereinafter referred to as a reaction tower) is that, as described above, in order to carry out the reaction in a dilute bed,
The use efficiency of the reducing gas (hereinafter referred to as gas), and hence the productivity per volume, is lower than other methods. Particularly in the circulating fluidized bed, the porosity in the reaction tower is large, and this tendency is remarkable.

That is, the existence ratio of particles staying in the fluidized bed (1-porosity)
Depends on the linear velocity of the gas, and as the linear velocity of the gas decreases, the particle concentration increases, resulting in higher contact efficiency and higher gas utilization rate. On the other hand, the reducing gas comes into contact with the ore,
When the reaction occurs, the degree of oxidation of the gas increases and the reducing ability is lost.

In the present invention, in consideration of such basic properties of the reaction tower, not all of the gases required for the reaction are supplied from the bottom at once, but the final reduction is performed at a position in the height direction of the reaction tower. A part of the reducing gas is branched and blown with a reduction rate determined in advance according to the particle size of the iron ore, the reactivity, the temperature of the reducing gas, the composition, and the like, and a predetermined ratio.

That is, the gas velocity in the lower part of the reaction tower is kept low,
By increasing the particle concentration, the gas utilization rate is increased, and the shortage of the reducing ability caused by the shortage of the gas amount is compensated by supplying the gas branched earlier to the intermediate portion of the reaction tower. To do.

The present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing the flow of the present invention.

That is, 1 is a circulating fluidized bed reaction tower, and 2 is a cyclone for separating gas and ore particles discharged from 1.
The preheated ore 3 supplied from the lower part of the reaction tower is fluidized by the reducing gas 4 heated to a predetermined reaction temperature together with the circulating ore 6 separated from the furnace top gas 7 by the cyclone 2.

5 is a reducing gas branched from the reducing gas 4 described above, and is blown into the furnace from the middle of the reaction tower. Further, if necessary, the gas is further branched to a plurality of stages 5-2,
Split blowing from 5-3 into the furnace. Further, as will be described later, the gas 5 blown from the middle can be replaced with fossil fuel and high concentration oxygen.

According to the experiment, since the gas amount is small in the lower portion of the reaction tower 1 (A in the figure), the fluidized state is present on the bubble having a relatively high solid concentration, and the gas amount is large in the upper portion of the reaction tower (B in the figure). ,
It can be confirmed that a high-speed fluidized bed with a relatively low solid concentration is obtained, the advantages of both fluidization modes can be combined, and a high gas utilization rate can be obtained.

In particular, when reducing gas production is performed in parallel in the reaction tower by partial oxidation by supplying high-concentration oxygen of fossil fuel instead of branching the gas, the reactor temperature can be adjusted at the same time. The temperature of the part supplied as gas to the tower,
And the composition does not necessarily have to meet all the conditions such as the temperature and composition necessary for the reduction, and can be sufficiently compensated by the carbonaceous material and oxygen that are secondarily supplied, and in the known fluidized bed, Although the temperature decreases in the furnace, the present invention enables temperature compensation and makes effective use of the entire reaction tower.

If the degree of incomplete combustion is further strengthened to generate a cheer,
In high-temperature fluidized reduction, it is possible to avoid sintering troubles between particles that are likely to cause problems. Further, since it has the duality of the bubble type and the high-speed flow type, it can be said that the method is suitable for treating mixed particles having a wide particle size range and different specific gravities.

Fig. 2 shows a circulating fluidized bed reactor with the same cross-sectional area and the same tower height, with the total amount of reducing gas being constant, when the whole amount is blown from the bottom of the tower, and part of it is blown from the middle of the tower. This is a comparison of the effects on changes in the gas concentration in the tower at different times.

In the figure, the solid line is the case where the entire amount of gas is supplied from the furnace bottom.
The reducing gas concentration decreases monotonically as the gas increases.
On the other hand, when the air is blown midway, the amount of gas is small up to the mid-air blow level Zi, and due to the decrease in the gas flow velocity,
Since the abundance ratio of the particles is high, the reducing gas concentration X sharply decreases and reaches X ₁ . After blowing in the middle, the concentration X is again X ₂
However, at higher levels, the amount of gas matches the case without blow-in, so it follows a curve close to the case without blow-in and reaches the top of the tower.

Next, a method of determining the gas branching ratio and the blowing position will be described.

When the reaction amount of one particle per hour is proportional to the difference between the mole fraction X of the reducing gas and the mole fraction X'of the reducing gas in equilibrium with the particle, the gas composition in the height direction Change of dx / dz
Is theoretically expressed by equation (1).

β is a coefficient depending on temperature, pressure, particle size, etc., N is the number of particles per unit volume, and u ₀ is a gas flow velocity.

(1) by integration of equation any height mole fraction X of reducing gas, the mole fraction X of the reducing gas at a certain height Z _{0
If 0} is given, it can be calculated by equation (2).

In the state without branching, the gas concentration distribution in the furnace when the amount of gas was changed was measured, the constant in Eq. (2) was determined, and then the gas injection position and the gas distribution ratio α were used as parameters. In consideration of the increase of N in the low gas flow velocity region below the gas injection level, the influence on the productivity can be simulated.

Generally, when the amount of air blown per hour is W, the reaction amount P per hour when the mole fraction of the reducing gas changes from X ₁ to X ₀ at the inlet and outlet of the reaction tower, with K as a proportional constant. It can be given by equation (3).

P = K · W (X ₁ −X ₀ ) (3) Therefore, in the case of FIG. 2, the reaction amount P ₀ per hour in the case without injection is given by the equation (2).

P ₀ = K · W (X ₀ −X ₄ ) (4) The reaction amount P ₁ per hour in the case with injection is given by the equation (5).

P ₁ = K · αW (X ₀ −X ₁ ) + KW (X ₂ −X ₃ ).
(5) Here, α is the ratio of the total amount of gas blown from the bottom of the furnace.

X ₂ is given by the equation (6), where Xi is the reducing gas mole fraction of the gas blown from the middle of the tower.

WX ₂ = W (αX ₁ + (1-α) Xi) (6) From the above, the relative improvement margin P ₁ / P ₀ of productivity can be obtained by the equation (7).

P ₁ / P ₀ = {α (X ₀ −X ₁ + X ₂ −X ₃ } / (X ₀ −
X ₄ ) (7) Since the relationship between the distribution ratio of the branched gas, the injection position, and the gas utilization rate can be obtained in this way, there are restrictions on equipment and disadvantageous conditions such as heat generated by branching. The branch injection position and the distribution amount can be determined so as to obtain the best gas utilization rate in the reaction column, taking into consideration the increase in loss, the complexity of the apparatus, and the like.

(Example) With a target preliminary reduction rate of 60%, 1470 Kg of iron ore having an iron content of 68% per hour was charged into the furnace, and the composition and temperature of the inlet gas were H ₂ ; 15.0%, CO; 82.5%, H 2 ₂ O; 0.5%, C
O ₂ ； 2240Nm per hour under the condition of 2.0% and 900 ℃
^The solid line shows the gas concentration distribution in the furnace when the gas of No. 3 was blown in all from the bottom without branching.

FIG. 4 shows the result of determining the constant of the equation (2) from this, and performing the simulation with the blowing position and the distribution ratio changed by the above-mentioned calculation method based on this. From this, it can be seen that the relative productivity becomes maximum at point A, that is, at the dimensionless height of 0.3 and the distribution rate α = 0.4.

Further, in FIG. 3, the dotted line shows the gas concentration distribution when the gas amount is branched, although the total gas amount is the same as the case of the solid line.
When the branch gas is blown in, the reducing gas mole fraction at the top of the tower is decreasing, and the amount of the reducing gas is affected by that amount, and the productivity is 8.
It rose by 7%.

In this way, referring to FIG. 4, it is possible to improve the productivity by determining the optimum positions of the branched gas injection position and the distribution ratio. Also, it is clear that it is advantageous to branch into more stages in the same way.

(Effects of the Invention) The present invention specifies, in a vertical fluidized bed reactor, an equivalent amount obtained by subtracting the distribution amount from the theoretical total amount of reducing gas blown from the bottom, and blowing from the bottom to determine the distribution amount equivalent. Since the reducing gas is blown from the position where the utilization rate of the reducing gas is best at the top of the furnace, an extremely efficient fluidized bed reduction reaction is obtained and the industrial effect is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the present invention, FIGS. 2 and 3 are diagrams of reducing gas mole fraction and tower height, and FIG. 4 is a diagram of relative productivity and gas injection position. 1: Reaction tower 2: Cyclone 5: Branch gas injection port

Claims (2)

[Claims] 1. An ore preheated to 1000 ° C. or less and having a particle size of 1 mm or less is combined with an ore separated and collected from the furnace top gas and supplied to the lower part of the furnace, and a reducing gas is supplied from the bottom part of the furnace. In the circulating fluidization reaction method, the amount of the reducing gas supplied to the bottom of the furnace is regulated to the amount obtained by subtracting the distribution amount from the theoretical total amount, and the position where the utilization rate of the reducing gas in the reaction tower becomes the best. A reducing gas inlet having a distribution ratio corresponding to the distribution amount is provided at one or more positions in the height direction of the furnace to supply the reducing gas to compensate the reducing ability in the furnace. Fluidized bed reduction method for ores. 2. The method for reducing a fluidized bed of ores according to claim 1, wherein fossil fuel and oxygen are supplied to a position where the utilization rate of the reducing gas is the best in the reaction tower.