JPH0422963B2

JPH0422963B2 -

Info

Publication number: JPH0422963B2
Application number: JP19998986A
Authority: JP
Inventors: Kazuya Kunitomo; Yoichi Hayashi
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1986-08-28
Filing date: 1986-08-28
Publication date: 1992-04-21
Also published as: JPS6357709A

Description

[Brief explanation of drawings]

第１図は本発明を実施する装置の一例を示す説
明図、第２図乃至第５図は本発明における制御条
件と成品還元率との関係を示す説明図である。 FIG. 1 is an explanatory diagram showing an example of an apparatus for implementing the present invention, and FIGS. 2 to 5 are explanatory diagrams showing the relationship between control conditions and product return rate in the present invention.

Claims

[Scope of Claims] 1. In a circulating flow reduction method for ores, in which ores accompanying exhaust gas discharged from a reaction tower are recovered and charged into the reaction tower again via a descending connecting pipe for reaction, The reduction rate, the reducing gas composition at the inlet and outlet, and the pressure at the inlet and outlet of the reaction tower are measured, and the product extraction rate, ore circulation flow rate, reducing gas supply amount, and reducing gas inlet are adjusted to correct the difference from the predetermined target value of the product reduction rate. 1. A method for circulating fluid reduction of ores, characterized by controlling at least one condition of degree of oxidation. *Theory (industrial application field) The present invention relates to a method for reducing ore, particularly iron ore, using a fluidized bed reactor. (Prior Art) As a method of reducing iron ore to obtain molten iron, the most widely used process is a method using a blast furnace. However, in order to maintain stable operations in the blast furnace steelmaking process, high-quality agglomerate ore and coke are required, and problems have been pointed out such as increased costs for producing these and restrictions on raw material selection. . As one means of solving these issues,
Research and development has been conducted on a smelting reduction process in which iron ore is reduced while being heated and melted using the heat of partial oxidation of coal. For example, in Japanese Patent Application No. 59-184056, iron ore, coal, and oxygen-containing gas are charged into a fluidized bed reactor, and the reaction is allowed to proceed to obtain iron ore and chir. , a steelmaking process characterized in that briquettes obtained by mixing and agglomerating coal supplied from another system are charged into a top-bottom blowing converter type reactor, and the pre-reduced ore is melted and reduced. The law is shown. Regarding the preliminary reduction process, for example, in Belgian Patent No. 826521, carbonaceous material is gasified by a partial combustion reaction with oxygen using a circulating fluidized bed, and a part of the carbon material is turned into a char. A process for reducing iron ore with gas is disclosed. Furthermore, Japanese Patent Application Laid-Open No. 51-99671 discloses a method of suppressing reoxidation of 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 Progress6, 58−63
(1971) and Japanese Patent Application Laid-Open No. 51-99671, the gas flow rate is determined solely from the viewpoint of transporting particles, and the gas and carbon substances introduced into the reaction tower are generated by the reaction with O ₂ . The efficiency with which this gas is utilized for reduction is not necessarily guaranteed. Originally, a fluidized bed reaction tower reacts reactants in a dilute bed, and therefore has the drawbacks of lower productivity per volume and poor gas utilization efficiency compared to a packed bed type reaction tower. In particular, the circulating fluidized bed has a large amount of gas passing through it, and this tendency is remarkable. For this reason, in a circulating fluidized bed, it is important to ensure productivity and produce products with a stable reduction rate, and establishing an operating method for this purpose is an issue. (Problems to be Solved by the Invention) The present invention takes the above-mentioned problems into consideration and provides a control method that can stably obtain a product with a target reduction rate in a circulating fluidized bed. be. (Means for Solving the Problems) The present invention provides ore circulation in which the ores accompanying the exhaust gas discharged from the reaction tower are recovered and charged into the reaction tower again through a descending connecting pipe for reaction. In the fluidized reduction method, the product reduction rate, the reducing gas composition at the inlet and outlet, and the pressure at the inlet and outlet of the reaction tower are measured, and the product extraction rate, ore circulation flow rate, and reducing gas are adjusted to correct the difference from the predetermined target value of the product reduction rate. supply amount,
This method is characterized by controlling at least one condition of the degree of oxidation at the inlet of the reducing gas. The present invention will be explained below with reference to the drawings. FIG. 1 is an explanatory diagram showing an example of an apparatus for implementing the present invention, in which ore 1 supplied to a reaction tower 2 is transported upward from the bottom of the reaction tower together with the ore in the reaction tower. The ore is blown upward while being reduced by the reducing gas 7 which has a sufficient velocity to reduce the ore, and only the ore is collected by the cyclone 3 and sent to the hopper 4, descending connecting pipe 5, and pneumatic valve 6.
After that, it returns to the reaction tower again. Semi-reduced ore can be extracted steadily by extracting the product 10 at a rate commensurate with the reducing capacity, and generally, the circulation mass rate of ore is in the range of 10 to 100 times the extraction mass rate of the product. It is driven by At the lower and upper parts of the reaction tower, pressure gauges 11a, b,
The gas analyzers 12a and 12b measure each value to understand the situation inside the furnace. In other words, the pressure value and its fluctuations are indicators of whether upward transport of particles is being carried out stably within the furnace. According to the research results obtained by the present inventor, the pressure difference ΔP between the pressure gauge 11a and the pressure gauge 11b needs to be controlled to be equal to or less than ΔPmax determined by equation (1). ΔPmax＝0.15・ρs・L×10 ^-4 (1) ΔPmax: Allowable maximum differential pressure (Kg/cm ² ) ρs: Ore density (Kg/m ³ ) L: Reaction tower height (m) When ΔP is greater than ΔPmax value, the particle layer becomes too thick and stable circulating flow cannot be obtained;
Therefore, it is not possible to control the concentration of the particle layer as described below. In addition, if the pressure value shows a fluctuation of 0.2 kg/cm ² or more within 5 seconds, it is assumed that coarse particles have accumulated at the bottom of the column, and it is necessary to increase the gas flow rate or extract coarse particles intensively. There is. On the other hand, gas analysis values are effective in understanding the progress of the reaction, and are particularly important because the control method differs depending on whether the reduction reaction has reached equilibrium. For example, iron ore Fe ₂ O ₃ is converted into Fe with CO gas or
When reducing with H ₂ gas, the equilibrium shown in equations (2) and (3) can be the rate-determining step. FeO＋CO←→Fe＋CO ₂ (2) FeO＋H ₂ ←→Fe＋H ₂ O (3) For example, in reduction at 900℃, CO:CO 2 ≒7:3 in CO gas reduction, and CO:CO ₂ ≒7:3 in H ₂ gas reduction.
CO ₂ or H ₂ O in a ratio of H ₂ :H ₂ O≒3:2 or more
It is known that the reaction that increases the amount does not proceed and the reduction reaction virtually ends. Therefore, if the outlet gas composition has not reached equilibrium, measures must be taken to bring it closer to equilibrium, and if equilibrium has been reached, measures must be taken to control the reduction rate even if the outlet gas utilization rate is constant. Next, we will discuss the relationship between operating conditions and product return rate control. The product extraction rate can change the reduction rate of the product without affecting the amount of particles in the reaction tower, the flow rate of reducing gas, etc. Through research on various ores, it has been found that the relationship between product extraction rate and product reduction rate can be expressed by an upwardly convex graph as shown in FIG. As is clear from this, effective control is possible in a relatively high production range, but it must be noted that the effect of reduction rate control becomes less at low production rates. Note that when operating in a steady state, the extraction rate of finished products and the supply rate of ore are equal, and the supply rate is changed in accordance with the extraction rate. The circulating flow rate of ore is effective in controlling particle hold-up in the reaction tower, and increasing the circulating flow rate
Since the slip rate between gas and particles is approximately constant, the void fraction is reduced and the amount of particles in the reaction column can be increased. This control is effective when the degree of oxidation of the gas at the top of the column has not reached equilibrium;
As shown in the figure, the reduction rate of the product can be increased by increasing the circulation speed. Note that when the number of circulation pipes is increased, the hold-up increases and the pressure loss within the column increases, so effective control is possible only when the pressure loss is less than ΔPmax shown in equation (1). Although the effect of changing the reducing gas supply amount is somewhat complicated, the following facts were found as a result of analysis. That is, when the degree of oxidation of the gas at the top of the furnace has reached an equilibrium composition, the product reduction rate can be increased by increasing the gas flow rate. This is nothing but adding an absolute amount of reducing gas while the degree of oxidation of the furnace top gas is constant, and reduction is promoted. On the other hand, when the degree of oxidation of the gas at the top of the furnace has not reached the average level, the increase in gas flow rate has the effect of diluting the particle layer, resulting in poor reducibility.
On the contrary, the return rate for finished products will decrease. This situation is shown in FIG. Changing the oxidation degree of the reducing gas inlet is a change in the reducing ability of the supply gas itself, and has a large effect, but the oxidation degree of the supply gas is normally operated at a considerably lower level using CO ₂ and H ₂ O removal equipment. Therefore, the control range is not necessarily large in many cases. However, in relation to the cost involved in removing CO ₂ and removing H ₂ O, it can be an effective control, and even if the outlet gas composition reaches equilibrium, it is an effective control means. The effect is as shown in Figure 5. As described above, the reducing gas composition and pressure at the inlet and outlet are detected, and at least one of the following conditions is selected depending on each situation: product extraction rate, ore circulation flow rate, reducing gas supply amount, and degree of oxidation at the reducing gas inlet.
By controlling one or more of these factors, the return rate of the finished product can be brought closer to the target value. (Example) An example in which the control method described above is applied to an actual circulating ore reduction fluidized bed will be described. Standard operating conditions are a target reduction rate of 60% and iron content.
10t/ ^m2hr of 68% iron ore was charged into the furnace, and the gas composition and temperature at the inlet were _H2 : 15.0%, CO: 82.5%,
Under the conditions of _H2O : 0.5%, _CO2 : 2.0%, 900℃,
Gas is injected at 10.500Nm ³ /m ² hr. As an operating index at this time, Table 1 shows an example of a method for determining the control means to be adopted when the return rate is lower than the target value. The product return rate was measured once every 10 minutes, and when the difference from the target value was 3% or more and remained 20% or more, the necessary action was determined based on Table 1 and the operating conditions were changed. The change width is 10% of the standard value,
A change action of up to 30% was taken. As a result, 92% of the finished products fell within the target reduction rate of ±5%, and good controllability was obtained. In Table 1, the circulation speed and gas flow rate actions, which have relatively little impact on cost and productivity, are prioritized over changes in the product withdrawal speed and the oxidation degree of the inlet gas.
Basically, only one condition is changed at a time, but the priority of actions may be changed depending on the situation, and the number of conditions that can be changed at a time is not limited to one. do not have. [Table] [Table] - indicates that comparison is not necessary.
(Effects of the Invention) As explained above, according to the present invention, in the circulating flow reduction of ore, the reduction rate of the product can always be controlled to a value within the target range, and therefore the product of stable quality can always be produced. Obtainable.