JPS6325044B2 - - Google Patents

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, but in particular, the development of methods that use so-called gas reducing agents, such as the shaft furnace method, fixed bed method, and fluidized bed method. There is something remarkable about it.

These gas reduction methods generally use natural gas (CH ₄ ) as a reducing gas source and bring the natural gas into contact with an oxidizing gas such as H ₂ O or CO ₂ at high temperature in the presence of a catalyst. This is a method of reducing iron ore (iron oxide) using the CO + H ₂ gas obtained as a reducing agent, and most of the oxygen contained in the iron ore is removed through a gas-solid phase reaction between the reducing gas and iron oxide. In this method, reduced iron is removed from 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, natural gas is reformed to produce CO + H ₂
As reducing gas production equipment to obtain gas requires large amounts of expensive reformer tubes and Ni-based catalysts filled in the tubes, a considerable portion of the plant construction cost is spent on these reducing gas production equipment. Furthermore, as the amount of gas to be processed increases in this equipment, the amount of reheating tubes and catalysts will also increase proportionally, so the economies of scale are small, and the benefits of making it large-scale are expected. I couldn't do it.

Furthermore, the higher the temperature of the reducing gas, the faster the reaction rate between the reducing gas and iron ore.
It is possible to increase productivity and energy efficiency, but due to rapid reduction and activation of the reduced iron surface due to high temperatures, reduced iron particles stick together in the case of a fluidized bed, and in a fixed bed or shaft furnace. This method has the disadvantage that reduced iron particles in the form of pellets or lumps stick together in the furnace, making it impossible to perform stable work. For this reason, in the conventional 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. In contrast, the gas reduction method achieves a considerably lower temperature of around 900°C.

In view of the current situation, the present invention aims to solve the problems of the conventional gas reduction method and provide a method for producing reduced iron through a simple process. Our goal is to provide a process that can use not only natural gas (CH ₄ ) but also a wide range of hydrocarbons as a reducing gas source. The purpose is to provide a process that can easily produce reducing gas, and thirdly, even if high temperature reduction is performed, reduced iron particles do not stick to each other, and therefore it is a highly energy efficient process. The point is to provide the following.

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 (Fe ₂ O ₃ ) were charged into a reduction furnace, and at 860°C, CO: 36%, H ₂ : 55%, CO ₂ : 5%,
When a mixed gas consisting of CH ₄ : 4% is supplied (case A), CH ₄ : 40%, H ₂ : 20% at 950°C,
_N2 : When 40% mixed gas is supplied (Case B)
When the changes in reduction time and reduction rate were measured, 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 H ₂ , the reduction of iron ore progresses over time, but when the iron ore contains 40% CH ₄ In case B, the reduction progresses to about 70-80%, but then decreases over time. Note that the vertical axis in Figure 1 shows the weight reduction rate due to reduction, so in case B, it is 70 to 80%.
This shows that after the reduction has progressed to a certain extent, the weight increases. The iron ore in Case B was taken out of the reduction furnace and examined, and as shown in the micrograph (150x magnification) provided as a reference photo, carbon was attached to the surface of the partially reduced iron ore particles. was confirmed.

This experiment shows that when hydrocarbons are brought into direct contact with iron ore particles without first being reformed into reducing gas, the iron ore is partially reduced and at the same time the hydrocarbons are also reduced.
It can be seen that the carbon is decomposed as CH ₄ →C+2H ₂ and the generated carbon adheres to coat the iron ore particles.

[Experiment 2] Iron oxide and reduced iron in various oxidation states were contacted at 950°C with a mixed gas consisting of CH ₄ : 25%, H ₂ O: 25%, N ₂ : 50% at SV: 500/hr. Let ch ₄
When the degree of modification to CO and H ₂ was investigated, the results shown in Figure 2 were obtained. In addition, the longevity vertical in Figure 2 is CH ₄ CO,
The conversion rate to _H2 is shown. As is clear from the figure, Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO all have poor catalytic ability for the decomposition of CH ₄ , but reduced iron has extremely high catalytic ability.

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

Based on the above experimental facts, the present invention provides a rational reduced iron production process for achieving the above-mentioned objectives, and its feature lies in the combination of the following steps.

○B Iron ore particles are heated in advance with an ore heater and supplied to a fluidized bed pre-reduction furnace, and hydrocarbons are supplied to the fluidized bed pre-reduction furnace which maintains the iron ore particles in a fluidized state, and one of the hydrocarbons is A step of decomposing and gasifying the iron ore particles, partially reducing the iron ore particles, and simultaneously attaching carbon by-produced by the decomposition to the iron ore particles.

○B 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, while the iron ore particles and reduced iron are maintained in a fluidized state. The cracked gas is converted into CO and _H2
The process of reforming into a reducing gas whose main component is

○C The iron ore particles and partially oxidized reduced iron discharged from the fluidized bed gas reforming furnace of ○B above are supplied to the fluidized bed reduction furnace, and while these are maintained in a fluidized state, the iron ore particles and the partially oxidized reduced iron are produced in ○B above. A process to produce reduced iron by contacting it with reducing gas.

○D A step of supplying the gas discharged from the fluidized bed reduction furnace of ○C to the fluidized bed preliminary reduction furnace 2 of ○B.

Below, the process of the present invention will be explained based on the flow sheet shown in Fig. 3. In the figure, 1 is a fluidized bed type ore heater, and from line 8, an ore heater with an average particle size of 10 to
200μ iron ore particles are fed to the heater 1;
It is heated to 1000° C. or higher and is supplied to a fluidized bed type pre-reduction furnace 2 through a line 9. This reduction furnace is operated at a temperature of 700 to 1000℃, and here, a preheater 5 is connected to line 13 to prevent decomposition.
Hydrocarbons preheated to 400 to 500°C, such as natural gas or hydrocarbon oil, and oxidizing substances such as CO ₂ and H ₂ O, which are heated to around 1000°C and supplied from line 12, which will be described later, via heater 21. The circulating gas containing the gas comes into contact with iron ore particles that are heated and maintained in a fluidized state, and a portion of the hydrocarbons becomes a reducing gas through the following reaction.

CH ₄ +H ₂ O→CO+3H ₂ CH ₄ +CO ₂ →2CO+2H ₂ ... At the same time, iron ore is pre-reduced by these reducing gases through the following reaction.

Fe ₂ O ₃ +H ₂ →2FeO+H ₂ O Fe ₂ O ₃ +CO → 2FeO+CO ₂ ... Furthermore, some of the hydrocarbons produce carbon as a by-product through the following reaction, and as mentioned above, the by-product carbon becomes iron ore particles. will adhere to the surface.

CH ₄ → C + H ₂ 2Fe ₂ O ₃ + CH ₄ → 4FeO + 2H ₂ O + C ... Since all of these reactions in formula ~ are endothermic reactions, it is necessary to supply thermal energy to the preliminary reduction furnace 2, so the line The gas from 12 is sufficiently heated above the furnace temperature and supplied, and most of the carbon-attached iron ore particles produced in the pre-reduction furnace 2 are passed through the line 10 to the ore heating furnace 1.
The deposited carbon is partially combusted by the air supplied from the line 17 and used as a heat source for heating the ore. Alternatively, iron ore particles can be supplied along with high temperature steam from line 8 to replenish the heat source.

Next, the carbon-adhered iron ore particles generated in the preliminary reduction furnace 2 are transferred to a fluidized bed type gas reforming section 3 through a line 11.
and produced in the fluidized bed reduction furnace 4 described later,
It is kept in a fluid state with the reduced iron returned through line 14. On the other hand, the cracked gas containing a large amount of hydrocarbon gas discharged from the preliminary reduction furnace 2 is transferred to the line 7.
After passing through the purifier 18 and removing components surplus to reforming the hydrocarbon gas among sulfides such as H ₂ S and COS and CO ₂ and H ₂ O generated in the preliminary reduction furnace 2, It passes through a line 20 and is heated in a preheater 6 to a temperature of 400 to 500° C., which is enough to prevent hydrocarbons from being decomposed, and then supplied to the gas reforming furnace 3. As mentioned above, reduced iron, which has a high ability to catalyze the reforming of hydrocarbon gas into reducing gas, and iron oxide, which has a conversion ability of around 10%, are kept in a fluid state, so the reaction of the above formula is carried out. Most of the hydrocarbons are converted to H ₂ and CO, and H ₂ +
Line 16 becomes a reducing gas whose main component is CO.
Then, it is sufficiently heated by the heater 22 and supplied to the fluidized bed reduction furnace 4.

In addition, the gas supplied to the gas reforming furnace 4 from the line 20 contains oxidizing gas (CO ₂ + H ₂ O) and CO, H ₂ in addition to hydrocarbon gas, and the oxidizing gas is It is an essential component for hydrocarbon reforming, but if its amount is large, reduced iron will be partially oxidized by the following reaction.

Fe+H ₂ O→FeO+H ₂ Fe+CO ₂ →FeO+CO... This reaction is an exothermic reaction, whereas the reducing gas production reaction in the equation is an endothermic reaction, so it plays the role of replenishing heat for the reaction in the gas reforming furnace, and It serves as an auxiliary reaction for producing reducing gas.

The reduced iron in the gas reforming furnace 3 containing iron oxide produced by the reaction of the formula 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 fluid state and come into contact with the hot reducing gas supplied from the aforementioned line 16.
It becomes reduced iron by the reaction of the following formula.

FeO+H ₂ →Fe+H ₂ O FeO+CO→Fe+CO ₂ ... 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. ,
High-temperature reduction exceeding 1000°C has been impossible, but in the present invention, since the iron ore particles are coated with carbon, such sintering phenomenon does not occur. Refund is possible. Therefore, considering the operating temperature of the previous and previous processes,
The reduction temperature can be selected within a wide range of 700-1200°C.

A part 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 taken out from the line 19 as a reduced iron product.

The typical process of the present invention shown in FIG. 3 has been described above, but in this example, the main reactions in the preliminary reduction furnace 2, reduction furnace 4, and gas reforming furnace 3 are all endothermic reactions. Therefore, these amounts of heat need to be mainly provided by the ore heater 1 and the heaters 21 and 22. In particular, the reduction temperature in the reduction furnace 4 must be covered by the gas reforming furnace 3.
When raising the reaction temperature to a temperature higher than the reaction temperature of It is necessary to sufficiently heat the reducing gas supplied to the furnace 4 to compensate for its heat. In addition, in order to supply a sufficient amount of heat to the gas reforming furnace 3, carbon-coated iron ore heated to the operating temperature of the gas reforming furnace 3 or higher in the ore heater 1 is Preferably, stone particles are fed to the gas reforming furnace 3. In this case, all of the carbon-coated iron ore particles generated in the preliminary reduction furnace 2 are returned to the ore heating furnace 1, and from line 8, an amount equivalent to the amount of carbon-coated iron ore particles sent from line 23 is returned. New iron ore particles are supplied, but since this new supply amount is small compared to the large amount of carbon-adhered iron ore particles retained in the heating furnace 1, it is In the present invention, since the amount of particles not coated with carbon in the iron ore supplied to the iron ore is negligible,
Not only is there no problem with adopting such a method, but it also 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 18 removes sulfides such as H ₂ S and COS and excess CO ₂ , and also completely removes H ₂ O. Required for the reaction of the above formula in the quality furnace 3
H ₂ O can also be supplied from the line 24 as steam heated to about 1000° C. to provide heat supplementation.

On the other hand, the hydrocarbons to be supplied to the preliminary reduction furnace 2 may be ordinary hydrocarbon oils, distillation residue oils of crude oil, heavy oils such as coal liquefied oils, etc., in addition to commonly used natural gas. In the case of , most of the iron ore is thermally decomposed into C ₁ to C ₄ components in the pre-reduction furnace 2, and the amount of carbon attached to the surface of the iron ore particles is also larger than in the case of natural gas. , the amount of adhering carbon burned within the ore heater 1 is increased, reducing the external heat source and enabling operation at higher temperatures.

Furthermore, the gas purification device 18 does not necessarily have to be installed between the pre-reduction furnace 2 and the gas reforming furnace 3;
and gas circulation lines 7, 2 connecting the reduction furnace 4.
Needless to say, it is sufficient to provide it at any one of 0, 16, and 12.

Note that 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 directly transferred from the line 19. Since it is taken out as a product, 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 part discharged from the first reduction furnace 4 is
The reduced iron containing FeO is supplied through line 19' to a fluidized bed type second reduction furnace 27, where it comes into contact with high-temperature reducing gas supplied from line 16' and heated by heater 22'. It is reduced and produced through line 25 as high-purity reduced iron. On the other hand, the reducing gas passes through the second reducing furnace 27 and from the line 26 to the first
It is supplied to the reduction furnace 4 and further supplied to the preliminary reduction furnace 2 via the line 12.

The method of the present invention has been described in detail above, but when reduced iron was actually produced according to the steps A to D above, the results of Experiments 1 and 2 described earlier were confirmed, and various results described below were confirmed. It was recognized that this effect was achieved.

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.

(1) In the fluidized bed pre-reduction furnace 2, iron ore particles are brought into direct contact with hydrocarbons to partially reduce the iron ore particles, and at the same time partially decompose the hydrocarbons to produce carbon as a by-product. Since raw carbon is attached to the surface of iron ore particles and the carbon-adhered iron ore particles are sent to the fluidized bed reduction furnace 4, reduced iron does not aggregate due to sintering in the fluidized bed reduction furnace. Therefore, 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
This eliminates the need for expensive reflow march tubes and Ni catalysts, greatly reducing plant costs, and also eliminates the need to replace Ni catalysts during operation, making maintenance easier.

In addition, when increasing the size of the equipment, it is difficult to expect economies of scale in the conventional re-former tube method because the number of tubes increases in proportion to the amount of gas processed, but the fluidized bed gas reformer of the present invention Since economies of scale can be expected,
It becomes possible to increase the size of reduced iron plants.

(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 pre-reduction furnace, so it is now possible to use natural gas as a source of reducing gas, whereas in the past only natural gas could be used. 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) Since not only reduced iron having a strong catalytic effect but also pre-reduced iron ore particles are supplied into the fluidized bed gas reforming furnace 3, the heat capacity inside the gas reforming furnace is reduced. This makes it easier to supply heat to the hydrocarbon reforming reaction (endothermic reaction), and iron ore particles can be used as a heat supply source to freely adjust the amount of heat supplied by changing the supply temperature and amount. become.

[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,
FIG. 3 is a flow sheet showing an example of the method of the present invention. 1...Ore heater, 2...Fluidized bed preliminary reduction furnace,
3... Fluidized bed gas reforming furnace, 4, 27... Fluidized bed reduction furnace, 5, 6... Preheater, 18... Gas purification device, 21, 22... Heater.

Claims (1)

[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 (a) to (d): A method for producing reduced iron characterized by: (b) Iron ore particles are heated in advance with an ore heater 1 and supplied to a fluidized bed pre-reduction furnace 2, and hydrocarbons are supplied to the fluidized bed pre-reduction furnace 2 which maintains the iron ore particles in a fluidized state; A step of decomposing and gasifying a portion of the hydrocarbons, partially reducing the iron ore particles, and simultaneously attaching carbon by-produced by the decomposition to the iron ore particles. (b) The carbon-adhered iron ore particles, cracked gas, and a portion of the reduced iron from the fluidized bed reduction furnace 4 to be described later are supplied to the fluidized bed gas reformer 3, and the iron ore particles and reduced iron are brought into a fluidized state. While retaining the decomposition gas, CO
The process of reforming the gas into a reducing gas whose main components are H2 and _H2 . (c) The iron ore particles and partially oxidized reduced iron discharged from the fluidized bed gas reforming furnace 3 of (b) above are supplied to the fluidized bed reduction furnace, and while maintaining them in a fluidized state, the iron ore particles and the partially oxidized reduced iron are ) The process of producing reduced iron by contacting it with the reducing gas produced in (d) A step of supplying the gas discharged from the fluidized bed reduction furnace of (c) to the fluidized bed pre-reduction furnace 2 of (a). 2. Claim 1 in which the hydrocarbon supplied to the fluidized bed pre-reduction furnace in the step (a) is natural gas.
The method for producing reduced iron as described in section. 3. The method for producing reduced iron according to claim 1, wherein the hydrocarbon supplied to the fluidized bed preliminary reduction furnace in step (a) is heavy oil. 4. Any one of claims 1 to 3 in which a part of the carbon-attached iron ore particles taken out from the fluidized bed pre-reduction furnace 2 in the step (a) is returned to the ore heater and reheated. The method for producing reduced iron described. 5. The method for producing reduced iron according to claim 4, wherein air is supplied to the ore heater, and a part of the carbon attached to the iron ore particles is combusted and utilized 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. 7. When supplying the exhaust gas from the fluidized bed preliminary reduction furnace to the fluidized bed gas reforming furnace in step (a), the exhaust gas is passed through the gas purification device 18 to remove excess unnecessary components, and then the gas is reformed. A method for producing reduced iron according to any one of claims 1 to 6, which is supplied to a furnace. 8. In the step (b), the carbon-attached iron ore particles discharged from the fluidized bed pre-reduction furnace 2 are supplied to the fluidized bed gas reforming furnace 3 according to any one of claims 1 to 7. Method for producing reduced iron. 9. In the step (b), the reduction according to any one of claims 4 to 7, in which the carbon-attached iron ore particles heated in the ore heater 1 are supplied to the fluidized bed gas reforming furnace 3. Method of manufacturing iron. 10 The fluidized bed reduction furnace consists of a first reduction furnace 4 and a second reduction furnace 27, and carbon-adhered iron ore particles and partially oxidized reduced iron discharged from the fluidized bed gas reformer 3 are transferred to the first reduction furnace. The reduced iron discharged from the first reducing furnace 4 was supplied to the second reducing furnace for final reduction, and the reducing gas from the gas reforming furnace 3 was supplied to the second reducing furnace 27. Claims 1 to 9 are arranged to supply the first reduction furnace 4 after the first reduction furnace.
A method for producing reduced iron according to any one of the paragraphs. 11 The temperature inside the fluidized bed pre-reduction furnace is 700-1000℃,
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.