JPS62202007A - Method for reducing iron oxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a method for directly reducing powdered iron ore without calcination or granulation, and supplying it to a melting furnace such as an electric furnace, a converter, or a smelting reduction furnace. This relates to a method for reducing iron oxide, which is used in the process of using it as a raw material for pig iron and steel, or in the process of producing iron powder by fluid reduction of high-purity ore with a low gangue content.

[Prior art] As a conventional method for reducing iron oxide,
Carbonaceous particles are suspended in a reduction furnace as in the 05M publication, and an iron oxide raw material is introduced into the floating layer and passed through it. During this process, the iron oxide raw material is reduced by carbon and CO atmosphere, and the generated CO2 is converted into carbon. A method is known in which CO is produced by reacting with coarse particles, and further reduced iron oxide is reduced to discharge the generated reduced iron out of the furnace from the lower part of the floating layer.

[Problems to be Solved by the Invention] However, such conventional methods have the following problems.

(i) Since the method involves passing the iron oxide particles through a floating layer of carbonaceous particles, it is not possible to provide a large amount of contact time with the gas.

(ii) Due to the presence of carbonaceous particles, sintering can be prevented even if reduction is carried out at temperatures above 900'C;
Even at a high temperature of 100° C., reduction with CO takes time.

(Capital) Carbonaceous particles float and are consumed in the reaction of CO2 + C- + GO, and only the shortage is supplied, so they are atomized and discharged as dust. When exhaust gas is used as circulating gas, the amount of dust recovered is will increase.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the present invention forms an upward flow of heated reducing gas in a reduction furnace, and oxidizes in this upward flow. After feeding iron particles and carbonaceous particles to form a mixed fluidized bed of both particles and reducing the iron oxide particles, the 1"2 molar ratio of the gas discharged outside the reduction furnace was adjusted to 40~40.
While maintaining the molar ratio of 60% and 00 within the range of 45% or less, the mixture was circulated and introduced from the lower part of the reduction furnace.

[Operation] If the particle sizes of the iron oxide particles and carbonaceous particles and the flow rate of the reducing gas are appropriately selected, a mixed fluidized bed is formed, and hydrogen and hydrogen-based gas are generated from the carbonaceous particles to form char, The iron oxide particles are reduced by reducing gas, hydrogen, hydrogen-based gas, etc., and the 1'2o and CO produced by the reduction reaction are
A part of the carbonaceous particles is consumed by the following reaction H2O+C→H2+GO CO2+C→2CO with 2, and the remaining carbonaceous particles are discharged as char to the outside of the reduction furnace together with the reduced iron reduced by the reducing gas etc. .

In the above reduction reaction, by increasing the reducing components H2 and CO in the gas discharged outside the furnace to a predetermined ratio and heating and recirculating the gas, a high reduction rate can be obtained and productivity can be improved.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of iron oxide reduction equipment used in carrying out the method of the present invention, in which 1 is a fluidized bed reduction furnace, 2 is a circulating high temperature reducing gas, 3 is iron oxide particles, 4 is carbonaceous particles, 5 is iron oxide particles in the fluidized bed, 6 is carbonaceous particles in the fluidized bed, 7 is semi-reduced iron or reduced iron, 8 is char, 9 is exhaust gas, 10 is dust, 11 is Clean exhaust gas, 12 is a heater,
13 is an aeration pipe, 14 is a header for the aeration pipe, 15 is a hopper, 16 is a charging device, 17 is a chute, and a cyclone 18 is installed downstream of the exhaust gas duct 25 connected to the top of the reduction furnace 1 to collect the exhaust gas. Separate the dust 10 from the dust 9 and add GO2 remover 19 and H2O remover 2 to the downstream side.
O@ is installed to remove CO2 and H2O from the clean exhaust gas 11, respectively, and the reducing gas containing a large amount of reducing components is passed through the fan 2.
Shun, which is pressurized in step 1 and heated by heater 12, is passed through header 14 for diffuser pipe 13 as high-temperature reducing gas 2.
3 to feed into the reduction furnace 1.

In the figure, 22 is a cooler, 23 is a discharge device, and 24 is a screen.

The heated reducing gas 2 is introduced into the reduction furnace 1 through the header 14 and the diffuser pipe 13 in the reduction furnace 1 to form an upward flow. During this updraft, the hopper 15 is
, the iron oxide particles 3 and the carbonaceous particles 4 are continuously fed through the charging device 16 and the chute 17 to form a fluidized bed with a predetermined height H in the reduction furnace 1. In the fluidized bed, the iron oxide particles 5 are reduced by H2 and CO of the reducing gas 2 introduced into the ring. Furthermore, it is also reduced by H2 and H2-based gas generated from the carbonaceous particles 6, and the generated HzO is reacted with C of the carbonaceous particles 6 to be reduced to H2 and CO. The exhaust gas 9 discharged from the reduction furnace 1 is passed through the cyclone 1
After the dust 10 is removed in Step 8, use CO2 remover 19.
, H2O remover 2O sequentially removes CO2 and H2O, respectively, the pressure is increased by a fan 21, and after being heated by a heater 12, it is circulated into the reduction furnace 1.

On the other hand, the iron oxide particles 5 in the reduction furnace 1 are reduced to become reduced iron 7, and the carbonaceous particles 6 become char 8 as volatile matter is removed. In the reduction furnace 1, iron oxide particles 5 and carbonaceous particles 6 remain in an amount equal to the pressure drop of the fluidized bed height H, but normally the supply and discharge are carried out while keeping this pressure drop constant. Let's do it. Residence time is controlled by varying the rate of discharge or by varying the pressure drop with these. The discharged reduced iron 7 and char 8 are cooled in a cooler 22 and then passed through a discharge device 23 and discharged to the outside of the furnace. Then, the particles are separated by, for example, a screen 24 that utilizes a difference in particle size or by magnetic separation.

By the way, in the reduction by the fluidized bed method, the residence time of the iron oxide particles 5 in the reduction furnace 1 is short, and in this case, reduction by 1''2 is more effective than by CO.

Therefore, in order to accelerate the reduction rate and increase productivity, 1" 2
It is desirable to receive a refund by

On the other hand, CO is more efficient in terms of the cost of the reducing gas, and CO reduction is also more advantageous in terms of heat compensation of the endothermic valve due to the reduction reaction.

In the present invention, carbonaceous granules 4 are used as the reducing gas 2 source, and hydrogen, hydrocarbons, and carbon oxides generated from the carbonaceous granules 4 are used.The amount and residence time of the carbonaceous granules 6 in the furnace are By controlling H2 and CO in the reducing gas in the furnace
The aim is to maintain the value within an optimal range.

In a fluidized bed, the residence time and residence amount in the furnace are A
T: Residence time m1n AP: Fluidized bed internal pressure drop kg/Cm' S: Fluidized bed cross-sectional area cm2 Q: Discharge amount kg/min Further, the retention amount is determined according to the fluidized bed pressure loss and becomes 4P-3. From this formula, for example, if AP is constant and Q is increased, aT will be shortened, so to lengthen AT, either increase AP or Q
All you have to do is reduce it. By the way, when coal is used as the carbonaceous particles 4 to be supplied into the fluidized bed, the volatile content is vaporized in a high-temperature reducing atmosphere, generating hydrogen and hydrocarbon gases, and forming coke (char). Furthermore, a part of the hydrocarbons reacts with H2O or CO2 produced by thermal decomposition or reduction reaction with the iron oxide particles 5 to produce H2 and CO.

Next, char 8 is HzO or CO generated by the reduction reaction.
2 to produce H2 and CO. The reaction at this time can be expressed as follows.

Now, when the reactions of the above formulas (1) and (2) proceed one time, as a result, 3 moles of C are consumed, 1 and 2 remain unchanged, and 3 moles of CO are generated.

Next, when the reactions of formulas (1) and (2) are repeated twice, as a result, 6 moles of C are consumed, H2 remains unchanged, and 6 moles of CO are generated.

In addition, in the case of the reactions of formulas (1) and (2) above, CO increases by the mole of C consumed each time it is repeated.

The actual reaction inside the reduction furnace 1 is based on temperature, pressure and H2O/H2
Although the above equation does not completely follow due to the relationship of CO2/Co partial pressure, etc., the tendency is that as the consumption of C increases, the molar ratio of 82/Go in the reducing gas in the reduction furnace increases as CO increases. Go in the direction you want.

From this, in the early stage of coal supply, H2 from volatile matter is
It can be seen that the H2 molar ratio in the reducing gas increases, and then the CO molar ratio gradually increases with the residence time of Char 8.

By the way, in a mixed fluidized bed of iron oxide particles 5 and char 8, if the volumetric time of char 8 is shortened, the molar ratio of H2 in the reducing gas increases for the above-mentioned reason, but the iron oxide particles 5
Since the residence time of the compound becomes shorter, it may become impossible to achieve the desired return rate, and from this point of view, the residence time is restricted.

From the above, the optimum supply amount of carbonaceous particles from the viewpoint of the reduction rate of iron oxide particles, productivity, and economic efficiency of reducing gas,
Line tests were conducted to confirm residence time and reducing gas composition using the equipment shown in FIG. The results are shown in Table-1.

In addition, Table 2 shows the iron ore used as iron oxide particles 3, Table 3
The components and particle sizes of various coals used as the carbonaceous particles 4 are shown in FIG.

Table-2 Composition and particle size of ore The following findings were obtained from this test.

(1) Reduction temperature 92O℃, pressure [130-250mm A
Q.

H2 in the circulating gas is reduced to 40-60% with a residence time of 20-45 minutes.
%, CO could be maintained within a range of 45% or less, and reduced iron with a metallization rate of 90% was stably obtained.

(2) Fixed carbon (F, C, >, v) depending on the coal type.

Although M was different, the gas composition in (1) above could be maintained by controlling the supply amount of coal type and residence time.

(3) If the composition of the discharged char is the residual F, C and ash, as shown in Table 4, 17.5
~40% is consumed, and 60-82.5% of C1 and ash remain unconsumed.

Table 4 Consumption rate of F and C in coal in the reduction furnace (4) Because of the mixed fluidized bed with carbonaceous particles, high temperature reduction operation at 92O'C can be maintained stably without sintering. .

(5) High metallization rates were obtained for lignite with various hydrogen contents, indicating that reduction is possible even with young grass coal or dry wood.

(6) Ash content 1 in coal does not affect the metallization rate.

The above tests were conducted at a reduction temperature of 92O℃, but from 92O to
Even at 1000'C, it has been confirmed that a metallization rate of 90% or more can be achieved within the range of the above-mentioned circulating gas composition.

Next, the reduction method of the present invention will be examined from the viewpoint of cost.

In the reduction equipment shown in Fig. 1, as shown in Fig. 2, 100% H2 or mixed gas of H2 + N2 at various ratios is supplied as the reducing gas, and the residence time and metals at various coal/ore ratios are The conversion rate was tested. The result is the second
As shown in the figure, at 100% H2, a metallization rate of 90% was obtained with a short residence time. Table 5 shows a comparison between the results and the results of test No. 1.2 of the circulation test in Table 1.

Table-5 100% H2, Circulating Gas Test Various Comparisons From Table-5, a simple cost comparison in terms of unit consumption of reducing gas and coal: H2: 60 yen/Nm3. In the case of 100% H2: H2: 1.43 to 1.46 Nm3/kcl-ore
85.8~87.6 yen Coal: 0.43~0.34ka
/kg-ore 8.6-6.8 yen For circulating gas: Circulating gas: OO Coal: 0.43-0.82kg/kg-ore, 8
．． The cost is 6 to 16.4 yen (the circulating gas source is supplied coal and the material cost is O), and the circulating gas method is significantly cheaper.

Note that the iron oxide reduction method of the present invention is not limited to the above-mentioned embodiments, but may be supplemented with H2, H2O, Co, or hydrocarbons to control the circulating reducing gas composition using carbonaceous particles. By adding gas, oil, etc., the reduction rate may be increased by increasing the 82 molar ratio to 40 to 60%, or the iron oxide may be reduced by increasing the 82 molar ratio to 60% or more, or, for example, A smelting reduction furnace is combined downstream of this method, and the iron oxide particles are pre-reduced by this method, and the semi-reduced iron produced is finally reduced in the smelting reduction furnace, and then melted and refined to produce pig iron and steel. It goes without saying that various modifications may be made without departing from the gist of the present invention.

[Effect of the invention] As explained above, according to the method for reducing iron oxide of the present invention,
It exhibits various excellent effects as described below.

<I> By supplying only carbonaceous particles, it is possible to maintain a reducing gas with a high molar ratio of 82, and moreover, continuous operation with high productivity and metalization rate is possible.

<n> The reducing gas to be circulated can be obtained by simply removing dust, H2O, and CO2 from the reducing furnace exhaust gas, and does not require a separate gas generating furnace or gas reforming furnace.

(Dish) Because the char is mixed and flowing with the iron oxide particles, 90
Even in high-temperature reduction above 0°C, sintering of reduced iron does not occur during the reduction process, allowing stable operation to be maintained.

■ Low-quality coal can be used as the carbonaceous granules as a source of reducing gas, making it economical.

(V) The discharged char can be effectively used within the system, for example, as a heat source for heating the circulating reducing gas. Furthermore, since it does not contain hydrogen or hydrogen-based gases, it is effective as a carbon material for a carbon material melting furnace such as a smelting reduction furnace.

<vp Because of the mixed fluidized bed, the residence times of iron oxide and char match and can be controlled simultaneously.

Since the reducing components of the gas discharged outside the furnace are adjusted to a predetermined ratio and recycled, the BEC is significantly reduced compared to when hydrogen is used.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of iron oxide reduction equipment used to carry out the reduction method of the present invention, and FIG. 2 shows various types of reducing gases to be supplied,
A diagram showing the relationship between average residence time and metallization rate at coal/ore ratio. 1 is a reducing furnace, 2 is a reducing gas, 3 is an iron oxide granule, 4 is a carbonaceous granule, 5 is an iron oxide granule in a fluidized bed, 6 is a carbonaceous granule in a fluidized bed, 7 is a semi-reduced iron or reduced iron, 8 is char, 9
is exhaust gas, 11 is clean exhaust gas, 12 is a heater, 13 is a diffuser pipe, 14 is a header for the diffuser pipe, 15 is a hopper, 1
6 is a charging device, 17 is a chute, 18 is a cyclone, 1
9 is CO2 remover, 2O is H2O remover, 21
22 is a fan, 22 is a cooler, and 23 is a discharge device.

Claims (1)

[Claims] 1) An upward flow of heated reducing gas is formed in a reduction furnace, and iron oxide particles and carbonaceous particles are supplied into this upward flow to form a mixed fluidized bed of both particles. After forming and reducing the iron oxide particles, the H_2 molar ratio of the gas discharged outside the reduction furnace was set to 40 to 6.
A method for reducing iron oxide, characterized in that iron oxide is circulated and introduced from the lower part of a reduction furnace while maintaining a CO molar ratio within a range of 0% and 45% or less. 2) Supplying hydrogen-containing carbonaceous particles as carbonaceous particles,
In addition, without replenishing the hydrogen source other than the carbonaceous particles from outside the system, hydrogen and hydrogen-based gas were volatilized in the fluidized bed and then turned into char, and the H_2O and C produced by the reduction of the iron oxide particles.
By controlling the amount of char consumed in the reaction of O_2 H_2O+C→H_2+CO CO_2+C→2CO,
The method for reducing iron oxide according to claim 1, wherein the reduction is performed while maintaining the range of H_2 and CO molar ratio. 3) The method for reducing iron oxide according to claim 1 or 2, wherein the reduction temperature is 900 to 1000°C.