JPS5834114A - Manufacture of reduced iron - Google Patents

Abstract

PURPOSE:To expand width of utilized hydrocarbon, to manufacture reduced gas at a low cost and easily, and to realize high temperature reduction, by placing in series a spare reducing furnace of a fluid layer system, a gas reforming furnace and a reducing furnace, and making iron ore grains and hydrocarbon flow through in order. CONSTITUTION:Iron ore grains are heated by a heater 1, and after that, are fed to a spare reducing furnace 2, and are brought into contact with hydrocarbon preheated to such an extent as it is not decomposed, by a preheater 5, and circulating gas containing oxidizing gas such as CO2, H2O, etc., which has passed through a heater 21 from a line 12. Subsequently, a part of the hydrocarbon is decomposed and becomes reduced gas, and a part by-produces C and sticks onto the surface of iron ore grains, and the iron ore grains are prereduced. The C stuck grains are fed to a gas reforming furnace 3 together with decomposed gas which has passed through a purifying device 18, and a part of reduced iron of a reducing furnace 4, and the decomposed gas is reformed to reduced gas mainly consisting of CO, H2, etc. This reduced gas is made to pass through a heater 22, also iron ore and the reduced iron which has been partially oxidized are fed to the furnace 4 from the furnace 3 and are made to contact with each other, and reduced iron is generated, and its waste gas is fed to the furnace 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a fluidized bed direct iron manufacturing method in which iron ore particles are kept in a fluidized state and brought into contact with a high temperature reducing gas to reduce the particles to produce reduced iron.

In recent years, there has been a remarkable development and increase in demand for direct steelmaking as a steelmaking technology that does not rely on blast furnaces, among which methods that use so-called gas reducing agents, such as the shaft furnace method, fixed bed method, or fluidized bed method. The development of has been remarkable.

In these gas reduction methods, natural gas (CH
4) as a reducing gas source, the natural gas and H20,C
This is a method for reducing iron ore (iron oxide) using CO+1-12 gas obtained by contacting an oxidizing gas such as O2 at high temperature in the presence of a catalyst as a reducing agent. In this method, most of the oxygen contained in iron ore is removed through a gas-solid crude reaction, and reduced iron is taken out of the reduction furnace in a solid state. In these methods, the reducing gas source is currently limited to natural gas, so these steel plants are limited to regions with abundant natural gas, and a wide variety of hydrocarbons can be used as the reducing gas source. It is hoped that a process will emerge.

In addition, in terms of equipment, the reducing gas production equipment for reforming natural gas to obtain CO+H2 gas requires a large amount of expensive former tubes and Ni-based catalysts to be filled in the tubes. A considerable portion of the plant construction cost must be allocated to these reducing gas production facilities, and as the amount of gas to be processed increases, the amount of reformer tubes and catalysts will also increase proportionately, so there is no economy of scale. was small, and no benefit could be expected from making it larger.

Furthermore, the higher the temperature of the reducing gas and iron ore, the faster the reaction rate, increasing productivity and energy efficiency; however, rapid reduction and reduction due to high temperature By activating the iron surface, reduced iron particles stick to each other in the case of a fluidized bed, and in a fixed bed or shaft furnace method, reduced iron particles in the form of pellets or lumps stick together in the furnace, resulting in stable production. There is a drawback that it makes it impossible to perform the work. For this reason, conventionally (
D In these gas reduction methods, it is necessary to lower the temperature to a range where stable operation is possible, even if it means sacrificing productivity and energy efficiency to a certain extent. On the other hand, in the gas reduction method, 90
The temperature is quite low, around 0°C.

In view of the current situation, the present invention solves the problems of conventional gas reduction methods and provides a method for producing reduced iron through a simple process. The 21st/! : The purpose is to provide a process that can inexpensively and easily produce reducing gas without using expensive former tube-based reducing gas production equipment, and thirdly, even if high temperature reduction is performed, reduced iron particles will not be produced. There is no mutual adhesion between the two, thus providing a highly energy efficient process.

Therefore, if it were possible to reduce iron ore or produce reducing gas by bringing hydrocarbons into direct contact with iron ore particles without reforming them into reducing gas in advance, the reduced iron production process would be extremely simple, and at the same time energy efficient. Since the efficiency can also be greatly improved, the present inventors conducted the following experiments based on the above viewpoint.

[Experiment 1] Iron ore particles (Fe20a) were charged into a reduction furnace and heated to 860°C with CO: 36%, H2: 55%, CO2:
When a mixed gas consisting of 5% CH4 and 4% CH4 is supplied (
Case A) and 950'C''?? CH4: 40%, H2
When a mixed gas of 20% N2 and 40% N2 was supplied (Case B), changes in reduction time and reduction rate were measured, and the results shown in FIG. 1 were obtained. As is clear from Figure 1, in Case A, which uses a normal reducing gas mainly composed of Co and H2, the reduction of iron ore progresses over time, but in Case B, which contains 40% CH4. In Case of,
The reduction progresses to about 70 to 80%, but after that it decreases with time. The vertical axis in Figure 1 shows the weight reduction rate due to reduction, so in case B, after the reduction has progressed to about 70-80%, the weight increases. It shows. So case B
When the iron ore was taken out of the reduction furnace and examined, as shown in the micrograph (150x magnification) submitted as a reference photograph.
It was confirmed that carbon was attached to the surface of partially reduced iron ore particles.

From this experiment, we found that when hydrocarbons are brought into direct contact with iron ore particles without being reformed into reducing gas in advance, the iron ore is partially reduced, and at the same time, the hydrocarbons are decomposed as CH4→C+2H2. It can be seen that the generated carbon adheres to coat the iron ore particles.

[Experiment 2] Iron oxide and reduced iron in various oxidation states were heated at 950°C.
c of CH4 by contacting it with a mixed gas consisting of CH4: 25%, H2O: 25%, and N2: 50% at SV: 500/hr.

When the degree of modification to H2 was investigated, the results shown in FIG. 2 were obtained. Note that the vertical axis in FIG. 2 indicates the conversion rate of CH4 to Co and H2. As is clear from the figure, Fe2O3,
Both Fe3O4 and FeO have poor catalytic ability for the decomposition of CH4, but reduced iron has extremely high catalytic ability.

This experiment shows that hydrocarbons can be reformed into reduced gas using reduced iron produced in the reduction process as a catalyst, without using an expensive Ni catalyst like in the past.

Based on the above experimental facts, the present invention provides a rational reduced iron manufacturing process that achieves the above objectives, and its feature lies in the combination of the following steps.

■ Hydrocarbons are supplied to a fluidized bed pre-reduction furnace that maintains iron ore particles in a fluidized state, and part of the hydrocarbons is decomposed and gasified, while the iron ore particles are partially reduced, and at the same time, the carbon by-product of the decomposition is removed. Step of adhering to the iron ore particles ■ #rI The carbon-adhered iron ore particles, cracked gas, and a portion of the reduced iron from the fluidized bed reduction furnace described later are supplied to a fluidized bed gas reforming furnace, and the iron ore particles and Step O of reforming the decomposed gas into a reducing gas containing CO and H2 as main components while maintaining the reduced iron in a fluidized state I8. A step of producing reduced iron by supplying the partially oxidized reduced iron to a fluidized bed reduction furnace and bringing it into contact with the reducing gas generated in step (1) above while maintaining the partially oxidized reduced iron in a fluidized bed. The gas to be
The steps of the present invention will be explained based on the 70-sheet shown in FIG. 3. In the figure, [+] is a fluidized bed type ore heater; From line (8), iron ore particles with an average particle size of 10 to 200μ are supplied to the heater (+), heated to 1000°C or more, and then sent from line (9) to a fluidized bed pre-reduction furnace ( 2). This reduction furnace has 700 to 100
It is operated at 0'C, and in this case, the line 03) is heated to 400 to 500°C without being decomposed in the preheater (5). 12) to 100 through the heater origin
Circulating gas containing oxidizing gases such as CO2 and H2O, which is heated to around 0''C and supplied, comes into contact with iron ore particles that are heated and maintained in a fluidized state, and one of the hydrocarbons is removed by the following reaction. part becomes reducing gas.

At the same time, iron ore is pre-reduced by these reducing gases through the following reaction.

Fe2Q3 + H2-2FeO+H2OFe2O3
+Co-2FeO+CO2)"'■Furthermore, some of the hydrocarbons produce carbon as a by-product through the following reaction, and the by-product carbon adheres to the surface of the iron ore particles as described above.

Since these reactions of formulas (1) to (2) are all endothermic reactions, it is necessary to supply thermal energy to the preliminary reduction P (2), so that the gas from the line (12) is heated to a temperature above the furnace temperature. At the same time, most of the carbon-attached iron ore particles generated in the pre-reduction furnace (2) are returned to the ore heating furnace f1) from the line (1o), and the iron ore particles are heated sufficiently and supplied.
) A portion of the adhering carbon and elements are combusted by the supplied air and used as a heat source for heating the ore. Alternatively, the heat source can be supplemented by supplying iron ore particles together with high-temperature steam from the line (8).

Next, the carbon-adhered iron ore particles generated in the preliminary reduction furnace (2) are transferred to the fluidized bed type gas reforming section +3 through the line (11).
K is supplied and maintained in a fluidized state together with reduced iron produced in a fluidized bed reduction furnace (4) to be described later and returned through line 04). On the other hand, the cracked gas containing a large amount of hydrocarbon gas discharged from the preliminary reduction furnace (2) enters the gas purification equipment (country) through the line (7), and the H
Among sulfides such as 2S and CO5, and CO2 and H2O,
After removing excess components for reforming the hydrocarbon gas, it passes through the line (20) and is heated in the preheater (6) to a temperature of 400 to 500°C, at a temperature that does not decompose the hydrocarbons, and then to the gas reforming furnace (3).
) 1c is supplied. As mentioned above, reduced iron, which has a high reforming catalytic ability for hydrocarbon gas to reducing gas, and iron oxide, which has a conversion ability of around 10%, are kept in a fluid state, so they are carbonized by the reaction of equation 0. Most of the hydrogen is H2
, Co, and becomes a reducing gas mainly composed of H2+CO, which is sufficiently heated in the heater (2) through the line θ6) and supplied to the fluidized bed reduction furnace +41.

In addition, the gas that is supplied from the line (20) to the gas reforming furnace (4) contains low oxidizing hydrocarbon gas (C02+
The oxidizing gas contains H20), CO, and H2, and is an essential component for reforming hydrocarbons, but if the amount is large, some of the reduced iron will be oxidized in the next reaction. That will happen.

This reaction is an exothermic reaction, whereas the reduction gas generation reaction in Equation 0 is an endothermic reaction, so it serves as a heat replenisher for the reaction in the gas reforming furnace and as an auxiliary reaction for reducing gas generation. do.

Gas reforming furnace containing iron oxide produced by the reaction of type 0 (3
) and the carbon-attached iron ore particles supplied from the line (11) are supplied to the fluidized bed reduction furnace (4) through the line (15). Here, these iron ore particles are kept in a fluidized state and come into contact with the high-temperature reducing gas supplied from the aforementioned line (16), and become reduced iron through the reaction of the following formula.

In the case of a conventional fluidized bed reduction furnace, the reduced iron particles generated by the above reaction cause a sintering phenomenon, so the temperature inside the furnace cannot be made too high, and the temperature is 100.

Although reduction at a temperature exceeding 100°C was impossible, in the present invention, iron ore particles are coated with carbon, so such shishitaring phenomenon does not occur.
High-temperature reduction at a temperature of C or higher becomes possible. Therefore, the reduction temperature can be selected within a wide range of 700 to 1200°C, taking into account the operating temperatures of the preceding and preceding steps.

A portion of the reduced iron produced in the reduction furnace (4) is transferred to the line (14)
The iron is supplied to the gas reforming furnace (3) described above, and a portion is recovered as product reduced iron through line 09).

The typical process of the present invention shown in FIG. 3 has been explained above. are all endothermic reactions, so the amount of heat is mainly absorbed by the ore heater (
1), heater 01) (a) is required, and in particular, the reduction temperature in the reduction furnace (4) must be maintained by the gas 5. If you want to raise the reaction temperature higher than the reaction temperature of the reformer (3), connect the line (through the country) to the gas reformer (
Since the temperature of the carbon-coated iron ore particles and partially oxidized reduced iron supplied from 3) is lower than the temperature of the reduction furnace (4), the reducing gas supplied to the reduction furnace (4) is supplied to the reduction furnace (4) using the heater (a). It is necessary to heat it sufficiently to compensate for the heat. In addition, in order to supply a sufficient amount of heat to the gas reforming furnace (3), the line shown by the dotted line in the figure should be used to raise the temperature at or above the operating temperature of the gas reforming furnace (3) in the ore heater +lj. It is preferable to supply the heated carbon-coated iron ore particles to the gas reforming furnace (3). In this case, all the carbon-attached iron ore particles generated in the preliminary reduction furnace (2) are transferred to the ore heating furnace (t+) VC
From the line (8), new iron ore particles are supplied in an amount equivalent to the amount of carbon-attached iron ore particles sent from the line (8), but this new supply amount remains in the heating furnace +11. The amount of particles that are not coated with carbon in the iron ore that is supplied from the line to the reforming furnace (3) is negligible because the amount of particles that are not coated with carbon is small compared to the large amount of carbon-coated iron ore particles that are coated with carbon. Therefore, in the present invention, there is not only no problem in adopting such a method, but also it has an important meaning as a main heat supply source to the gas reforming furnace (3).

In addition, in order to replenish heat to the gas reforming furnace (3), the gas purification device 08) removes sulfides such as H2S and CO5 and excess 002, and also completely removes H2O. It is also possible to supply the H2O necessary for the reaction of formula 0 in (3) as steam heated to about 1000°C from line (c) at the same time as heat replenishment. be.

On the other hand, the hydrocarbons to be supplied to the preliminary reduction furnace (2) are as follows:
In addition to commonly used natural gas, heavy oils such as ordinary hydrocarbon oils, distillation residue oil of crude oil, and coal liquefied oil may also be used. At the same time, the amount of carbon adhering to the surface of iron ore particles is larger than that of natural gas, so the amount of adhering carbon burned in the ore heater f1) is This reduces the need for an externally supplied heat source and allows operation at higher temperatures.

However, the gas purification device (18) does not necessarily have to be installed between the pre-reduction furnace (2) and the gas reformer (3); 3)
and a gas circulation line (7) connecting the reduction furnace (4) (
It goes without saying that it is sufficient to provide one of 2 (to) (+6) (+2).

In addition, since the residence time of the iron ore particles supplied from the gas reforming furnace (3) to the reduction furnace (4) in the reduction furnace is not constant,
A part of the iron ore particles supplied from the line (15) as FeO is taken out as a product from the line (19), so it is preferable to arrange two reduction furnaces in series in order to improve the quality of the product. In this case, the reduction furnace (4) is used as the first reduction furnace, and as shown by the dotted line in the figure, the reduced iron containing some FeO discharged from the first reduction furnace (4) passes through the line Of. is supplied to a fluidized bed-type second reduction furnace, where it is reduced by contacting with high-temperature reducing gas supplied from the line (I6i!) after being heated by a heater.
c) Produced as higher purity reduced iron. On the other hand, the reducing gas passes through the second reducing furnace, is supplied to the first reducing furnace (4) from line (e), and is further supplied to the preliminary reducing furnace (2) via line (12).

As detailed above, the method of the present invention reduces iron ore and produces reducing gas by arranging a fluidized bed type reducing furnace and a gas reforming furnace in series and sequentially circulating iron ore particles and hydrocarbons. The following remarkable effects are expected.

fl) In a fluidized bed type pre-reduction furnace (2), iron ore particles and hydrocarbons are brought into direct contact to partially reduce the iron ore particles, and at the same time partially decompose the hydrocarbons to produce carbon as a by-product; By-product carbon is attached to the surface of iron ore particles, and the carbon-adhered iron ore particles are fed to the fluidized bed reduction furnace (4)K, so reduced iron does not aggregate due to shishitaring in the fluidized bed reduction furnace. Since there is no heat, high-temperature reduction becomes possible, the reaction rate becomes faster, both thermal efficiency and productivity are improved, and the reduction furnace can be made smaller.

(2) In the fluidized bed gas reforming furnace (3), the reforming reaction to hydrocarbon gas is carried out using reduced iron produced in the reduction process as a catalyst, so it is not necessary to use expensive former tubes as in the past. This eliminates the need for a Ni catalyst, greatly reducing plant costs, and also eliminates the need to replace the Ni catalyst during operation, making maintenance easier.

Also, when increasing the size of the equipment, with the conventional glue former tube method, the number of tubes increases in proportion to the amount of gas processed, so it is difficult to expect school merit, but the fluidized bed gas reformer of the present invention Since economies of scale can be expected, it will be possible to increase the size of the reduced iron plant.

(3) The hydrocarbon gas supplied to the fluidized bed gas reforming furnace can be sent to the product gas that has been decomposed and gasified in the preliminary reduction furnace, so conventionally only natural gas could be used as a reducing gas source. However, heavy oil, which generates a large amount of by-product carbon, can also be used, which widens the range of reducing gas source selections and greatly increases the degree of freedom in plant design. Not only does this make construction possible, but by-product carbon can also be used effectively as mentioned above.

(4) The fluidized bed gas reforming furnace (3) is supplied not only with reduced iron, which has a strong catalytic effect, but also with pre-reduced deaf iron ore particles. The heat capacity of iron ore increases, making it easier to supply heat to the reforming reaction (endothermic reaction) of hydrocarbons, and iron ore particles, as a non-supply source, can reduce the amount of heat supplied by changing the supply temperature and amount. You will be able to adjust it freely.

[Brief explanation of the drawing]

Figure 1 is a graph showing the ability to reduce iron ore by reducing gas and methane, Figure 2 is a graph showing the catalytic ability of various iron oxides to convert hydrocarbons into reducing gas, and Figure 3 is an example of the method of the present invention. This is a flow sheet showing the following. +1)...Ore heater, (2)...Fluidized bed preliminary reduction furnace, (3)...Fluidized bed gas reforming furnace, 14)@...Fluidized bed reduction furnace, +5) +6)・・Preheater, (
Country... Gas purification equipment, e21) (a)... Heater, 6th 111 1 Gen Haruma (way) t112Il1 Tanmaru-Kan ('η')

Claims (1)

[Scope of Claims] 1. A method for producing reduced iron by reducing iron ore particles by contacting them with a high-temperature reducing gas while maintaining them in a fluidized state, the method comprising the following steps (1) to (G). A method for producing reduced iron characterized by: ■ Fluidized bed pre-reduction furnace that holds iron ore particles in a fluidized state + 2) K hydrocarbons are supplied, part of the hydrocarbons is decomposed and gasified, and iron ore particles are partially reduced, and at the same time, by-products of the decomposition are Step of attaching carbon to the iron ore particles @ Supplying the carbon-attached iron ore particles, cracked gas, and a portion of reduced iron from the fluidized bed reduction furnace (4) to be described later to the fluidized bed gas reforming furnace (3). , a step of holding the iron ore particles and reduced iron in a fluidized state and reforming the decomposed gas into a reducing gas containing CO and H2 as main components. Step 0 of producing reduced iron by supplying iron ore particles and partially oxidized reduced iron to a fluidized bed reduction furnace, keeping them in a fluidized state, and bringing them into contact with the reducing gas produced in step 0 above. The gas discharged from the fluidized bed reduction furnace is
2. The method for producing reduced iron according to claim 1, wherein the hydrocarbon supplied to the fluidized bed pre-reduction furnace (2) in step 2 and step (2) is natural gas. 3. The method for producing reduced iron according to claim 1, wherein the hydrocarbon supplied to the fluidized bed pre-reduction furnace in step (2) is heavy oil. 4. The iron ore particles to be supplied to the fluidized bed pre-reduction furnace in step (2) are preheated in the ore heater (1), and the carbon-attached iron ore particles taken out from the fluidized bed pre-reduction furnace (2). The method for producing reduced iron according to any one of claims 1 to 3, wherein a part of the iron is returned to an ore heater and reheated. 5. The fM production method for reduced iron according to claim 4, wherein air is supplied to the magnetic heater to burn part of the carbon attached to the iron ore particles and utilize it for heating. 6. The method for producing reduced iron according to claim 4 or 5, wherein the ore heater is a fluidized bed heater that heats the iron ore particles while maintaining them in a fluidized state. When supplying the exhaust gas from the fluidized bed preliminary reduction furnace to the fluidized bed gas reforming furnace in step 7.0, the exhaust gas is passed through the gas purification device (I8) to remove excess unnecessary components, and then the gas reformer is A method for producing reduced iron according to any one of claims 1 to 6, which is supplied to a quality furnace. In the process of &@, the carbon-attached iron ore particles discharged from the fluidized bed pre-reduction furnace (2) are supplied to the fluidized 1 gas reforming furnace (3) according to any one of claims 1 to 7. The method for producing reduced iron described. In step 9.0, the carbon-attached iron ore particles heated in the ore heater fl) are supplied to the fluidized bed gas reforming furnace (3) according to any one of claims 4 to 7. Method for producing reduced iron 0 10, the fluidized bed reduction furnace includes a first reduction furnace (4) and a second reduction furnace,
The carbon-adhered iron ore particles and partially oxidized reduced iron discharged from the fluidized bed gas reforming furnace (3) are supplied to the first reduction furnace (4), and the first reduction furnace (4) The reduced iron discharged from the furnace is supplied to the second reduction furnace for final reduction, and
The reducing gas from the gas reforming furnace (3) is transferred to a second reducing furnace,'
The method for producing reduced iron according to any one of claims 1 to 9, wherein the reduced iron is supplied to the first reduction furnace (4) after being supplied to the furnace. 11. Temperature inside the fluidized bed pre-reduction furnace is 700-1000'C
. The method for producing reduced iron according to any one of claims 1 to 10, wherein the temperature inside the fluidized bed reduction furnace is 700 to 1200°C, and the temperature inside the fluidized bed gas reforming furnace is 800 to 1000°C. .