JPH0366365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a method for direct reduction of iron ore, in particular, which can minimize the problems of sintering and agglomeration of iron ore particles.
It relates to an optimization method that is operable at higher reduction temperatures. A further object of the present invention is to provide a method for the direct reduction of iron ore, which allows the required dimensions of the reducing gas generator to be reduced.

[Conventional technology and its problems]

Moving bed reactor reduction methods are well known in the art. Generally, the device is constructed with two zones, the first of which is a so-called reduction zone in the upper part of the reactor, where the iron ore is fluidized by gravity and flows upwards. It contacts the flow of high-temperature reducing gas countercurrently, and in this case the reducing gas is mostly H ₂ and
It is a gas mixture consisting of CO. In this zone, the iron ore is preheated and reduced.

The second zone is the so-called cooling zone at the bottom of the reactor, where the descending heat, reduced iron ore particles are in countercurrent contact with an upward flow of cooling gas.
The reduced iron ore particles are cooled before being discharged into the atmosphere. This cooling is necessary to avoid reoxidation of the reduced particles by the oxygen present in the air.

The productivity of the reduction zone is determined by the time required to reduce the iron ore particles. That is, the shorter the residence time, the greater the output achieved by the same reduction zone.

It is known that the higher the temperature of the reducing gas at the inlet of the reduction zone, the shorter the residence time of the solids in this zone. This means that _H2 and CO
This is because the kinetics of the iron ore reduction method is strongly dependent on temperature. The higher the temperature, the faster the reaction rate and the higher the productivity of the process.

Direct reduction methods usually involve
It operates at temperatures ranging from 750 to 900°C.

The main obstacle to increasing this temperature further is the tendency of most highly reduced iron ores to sinter and agglomerate when temperatures exceed 900°C.

This problem is particularly pronounced when processing iron-rich iron ore particles, especially in the form of pellets. This is because pellets exhibit high iron content and low gangue content.

It is currently preferred to use pellets with high iron content as feedstock for direct reduction processes. The main reason for this is that pellets are generally more easily reduced than lump ores. This property is useful in obtaining highly metallized products. Furthermore, pellets are more resistant to mechanical disintegration during the reduction process, and for this reason they produce smaller fines than lump ores.
It is also possible to vary the chemical composition of the gangue within certain limits to optimize the use of the reducing material as an arc furnace feedstock.

Recently, there has been a trend in the steel industry to use pellets with an iron content of over 67%. This fact increases the problem of clumping. This is because increasing the iron content is known to increase the problem of pellet sintering and agglomeration.

When solids agglomeration occurs in a moving bed reactor, serious problems with solids flow and gas flow distribution are encountered. This results in losses in process control and variable product characteristics.

Several solutions have been proposed to solve the problem of agglomeration in moving bed reactors for direct reduction of iron ore. The most obvious one is to use an agglomerate breaking mechanism, but this is not an optimal solution. This is because these mechanisms are usually placed in the path of the solids flow, thereby disrupting the flow and increasing the problem. Additionally, these mechanisms are subjected to harsh conditions of friction and high temperatures. These mechanisms are complex and expensive.

Other known methods of solving the problem of pellet agglomeration when operated at high temperatures include filling the reactor with pellets and agglomerates or with pellets and amorphous inert material. In both cases, shape effects are observed, which are useful in minimizing agglomerate problems.

In the case of lump ores, the disadvantage is that lumps are generally more difficult to reduce than pellets and also produce more fines. Furthermore, there is only a small amount of bulk ore available for direct reaction in the world. For this reason, it is not always convenient to plan to operate a direct reduction plant on the basis of using a mixture of pellets and agglomerates.

The disadvantage of using a mixture of inert material and pellets is the need to separate the inert material from the product and the reduction in reactor productivity.

Due to the advantages of using pellets, such as high reducibility, low gangue content, and less fines production, operations have been reduced to 900% using 100% pellets with a high iron content of over 67%. There is a need for a direct reduction process that can be performed harmoniously at reduction temperatures above 0.degree. C. without sintering and agglomeration problems.

US Pat. No. 4,268,303 discloses a direct reduction process that can be operated at high temperatures without agglomeration problems. The process disclosed in this patent has no cooling zone and is based on a moving bed reactor with two reduction zones.

In the first zone, reduction occurs using gases with high methane content (15-40%) at temperatures on the order of 950-1200°C.

According to the teachings of this patent, the first reduction stage (30-80%) can be carried out at elevated temperatures and when the methane content is high. This is because the reduction reaction of methane is a significant endothermic reaction.

In the second zone, the reduction is carried out using a gas with a lower methane content (2-7%) at temperatures ranging from 750 to 950°C.

The main limitation of this method is the extreme level at which the temperature of the methane-rich gas must be raised to effect the reduction. On the one hand, the materials that require heating equipment to operate at temperatures of the order of 1200 °C are very special and expensive, and on the other hand, at these temperatures the thermal decomposition of methane is favored (this resulting in problems of high carbon deposition, which translates into operational problems in the reactor).

The high agglomeration tendency of high iron content pellets is not mentioned in this patent, nor is any method disclosed for solving this problem.

[Means and actions for solving problems]

The present invention discloses a process based on a moving bed reactor having three zones: a reduction zone in the upper part of the reactor, a cooling zone in the lower part of the reactor, and an intermediate zone for separating each of the aforementioned zones.

In the reduction zone, reduction is carried out using a gas containing 4-10% methane, 60-70% hydrogen and 2-15% carbon monoxide at temperatures on the order of 950°C.

A product cooling zone is provided at the bottom of the reactor. Cooling takes place in a closed loop comprising the lower part of the reactor, a quencher and a compressor. A stream of natural gas, consisting primarily of methane, serves as replenishment to this loop. Since there is no gas outlet external to the reactor in this cooling loop, the methane blown into this loop will cause the methane to flow itself from there through the intermediate zone to the reduction zone.

In the intermediate zone, the methane traveling from the cooling zone is mixed with a portion of the thermally reducing gas blown into the reduction zone.

The cooling gas flowing from the cooling zone is 400 to 600
It has a temperature of ℃. In the intermediate zone, contact of the cooling gas with the oxidant element present in the thermally reducing gas promotes a significant endothermic regeneration reaction of methane. These reactions cause the temperature of the solid to decrease rapidly. This is because the heat of reaction is supplied by the falling mass of solids. By virtue of such heat exchange, the rapid cooling of the solids avoids agglomeration of the highly metallized pellets and particles. This is because the pellets and particles remain at high temperatures for a very short time.

By this method, agglomeration of highly metallized pellet particles can be avoided, which means a high methane content in the reducing gas, which means a reduction zone at very high temperatures (1200 °C). It is not necessary to have the following.

In the present invention, the reduction is carried out in a single step with a mixture of hydrogen and carbon monoxide;
And this mixture has a faster reduction rate than methane.

Regeneration that occurs in the intermediate zone avoids the formation of agglomerates and allows a reduction in the capacity of the natural gas regenerator. U.S. Patent No. 4,046,557 and
No. 4,049,440 discloses blowing natural gas into the cooling loop of a moving bed reactor reduction process. Nevertheless, the blowing of natural gas is always carried out with an auxiliary blowing of recirculated cooling reducing gas. The main objective of the above patent is to utilize the recirculated gas from the reduction loop as cooling gas, without being influenced by said reduction loop. Natural gas is blown to regenerate the reduction potential of the recycle gas by reforming the natural gas in the cooling loop, and then flows a portion of this gas upward to the reduction loop. In US Pat. Nos. 4,046,557 and 4,049,440, the amount of methane that is blown into the cooling zone and then regenerated in the reactor does not contribute to reducing the capacity of the regenerator. This is because the amount of thermal regeneration gas flowing from the regenerator is fixed by the temperature requirement at the reduction zone inlet. This temperature is fixed by a mixture of thermal reducing gas and cooling zone gas. It is not possible to significantly reduce the hot gas flow coming from the regenerator without reducing the temperature at the reduction zone inlet. That is, in order to maintain the temperature at the inlet of the reduction zone at the reduction temperature, the amount of thermal regeneration gas must be maintained at a constant amount. Therefore, it is not possible to make the natural gas blown into the cooling loop a useful material for reducing the capacity of the regenerator. In the process according to the invention, the regenerated gas is injected cold into the reduction loop as make-up, and the make-up mixture is heated together with the re-reduced gas prior to its injection into the reduction zone of the reactor. In this case, blowing natural gas helps to reduce the size of the regenerator.

As stated above, it is an object of the present invention to provide a method for operating pellets with a high iron content of more than 67% at temperatures of 900 DEG to 960 DEG C. without agglomeration. To achieve this objective, the present application promotes regeneration in the intermediate zone with a portion of the thermal reducing gas stream circulating through the reduction zone and methane proceeding from the cooling zone present at the bottom of the reactor, and By rapidly cooling the descending reduced ore endothermically, agglomeration of the pellets at the high temperature is avoided.

Another object of the present invention is to provide a method for reducing the corresponding dimensions of a reduction reactor and associated regenerator. This is important because the regenerator is the most expensive equipment in a direct reduction plant. In order to achieve these other objectives, the present application supplies a portion of the natural gas fed to the regenerator for producing reducing gas to a cooling loop located at the bottom of the reactor, and in the cooling zone produces reducing gas and its Moreover, because the reducing gas generated in the regenerator and the circulating gas circulating in the reduction zone are mixed, and the temperature drop of the mixed gas is increased by the heater,
The mixing ratio with circulating gas can be made relatively low, thereby suppressing the gas flow rate of regeneration gas,
Therefore, the capacity of an expensive regenerator can be reduced.

〔Example〕

FIG. 1 shows the effect of temperature on productivity in a direct reduction plant of the type in which the method according to the invention can be utilized. As shown in this graph, the reduction temperature is 850 to 960℃
An increase in the range increases plant productivity by 17% and reduces the amount of regeneration gas used.
It therefore becomes desirable to operate at high reduction temperatures. The main problem when operating at high temperatures with pellets exhibiting high iron contents of over 67% is their agglomeration when the pellets are metallized. The presence of agglomerates causes turbulence in the solids and gas flows within the moving bed reaction bed used in the direct reduction of iron ore pellets. These disturbances result in low blunt utilization (i.e., loss of productivity) and losses in product quality control (due to nonuniform mass flow due to nonuniform processing, resulting in nonuniform product). This creates an operational problem in that it leads to

Figure 2 shows the so-called agglomerate index Ia defined below: Ia = lnWa/lnWb where: Ia = agglomerate index Wa = agglomerate weight in operation Wb = problems in plant availability and product quality control Figure 2 shows the effect of the iron-containing quality of the filler material on the formation of agglomerates based on the agglomerate weight during operation resulting in .

According to this definition, it is desirable that Ia always be less than 1.0, which is the maximum value acceptable for safe operation of the plant without causing problems with solids and gas flow.

Three curves are shown in Figure 2, and the method represented by the two continuous solid line curves is performed at temperatures of 900°C and 960°C, respectively, without blowing in natural gas.
The process according to the invention is operated at 960° C. with natural gas blowing, while the process represented by the dotted curve is a process according to the invention operated at 960° C. with natural gas blowing.

According to this information, the iron content in the pellets must be 66.6°C in order to operate the plant at 960°C without injecting natural gas and without further operational problems.
% or less than 67% iron content
If it is desired to operate with pellets exceeding
The temperature must be less than 900℃.

In contrast, when utilizing the method according to the invention, 960
It is possible to operate at ℃. By using a fill material consisting of pellets with a high iron content as opposed to the use of non-pelletized lump ores, the present invention results in high metallization and low fines formation, as well as high plant productivity and excellent product quality. It is something to do.

According to Figure 2, without blowing natural gas,
To operate with pellets having an iron content of 67.4%, the temperature would have to be reduced to the order of 900°C, resulting in a 10% productivity loss.

When natural gas is injected into the cooling zone, the Ia: T at 960°C is
The curve can be conveniently moved to the right. This quenching is primarily caused by an upward flow of methane injected into the closed cooling loop, in particular by the regeneration of the methane by the oxidant elemental component of the gas coming from the reduction loop. A portion is mixed in an intermediate zone within the reactor, promoting the endothermic reaction of regeneration: CH ₄ +H ₂ O→CO+3H ₃ …(1) CH ₄ +CO ₂ →2CO+2H ₃ …(2) Thermal reduction proceeding to the reduction loop. The gas has a carbon dioxide content of 2 to 15% and a water content of 1 to 4.
%. These oxidant elements are used for the regeneration that occurs in the intermediate zone.

FIG. 3 shows the effect of temperature and natural gas injection on the capacity of the regenerator of the reduction plant. For an operating temperature of 960°C, the natural gas blowing process requires about 15% less regeneration equipment than the process without natural gas blowing.

In natural gas-based direct reduction processes, natural gas typically has two uses. A portion of the natural gas is fed to a catalytic regenerator to convert the hydrocarbons into a mixture of hydrogen and carbon monoxide that is used as the reducing element in the direct reduction of iron ore.
Another portion of the natural gas is used as a fuel to generate the heat necessary to carry out the endothermic reaction of regeneration and is also used to heat the reducing gas prior to its injection into the reduction reactor. .

Generally, natural gas used as a fuel has a low reducing power but can still be used as a fuel. Mix with the purged gas stream from the method. This second natural gas gas stream is utilized to improve the purging of the process gas used as fuel for the heating and regenerators of the method.

In the method according to the invention, a portion of the natural gas is blown into the cooling loop. In this loop,
Natural gas enhances the cooling of the product due to its high heating capacity, so that cooling occurs more quickly and more effectively.

Since the cooling loop is closed loop, the injected natural gas flows upward through the reactor and reaches the intermediate zone where the natural gas is converted into a thermally reducing gas which facilitates the regeneration of some of this natural gas, as described above. come into contact with some of the

When regenerating methane within the reactor, a reducing element component is produced that is used in the reduction zone to make the reduction more efficient (and to reduce regenerator capacity requirements).

The unregenerated methane in the intermediate zone flows to the reduction zone and serves as a heat carrier element that contributes to the heating of the iron oxide that takes place within the reduction zone.

Eventually, this methane (mixed with hydrogen, carbon monoxide, carbon dioxide, and moisture) leaves the reactor, and a portion of this mixture is used as a purge gas in the system of the method to be used as fuel. leave from

In summary, methane blown into the cooling loop provides a series of advantages in the present process. These include improved cooling of the product in the cooling zone, rapid endothermic cooling in the intermediate zone to avoid pellet agglomeration, and regeneration performed in the intermediate zone to reduce regenerator capacity requirements; in which it acts as a heat carrier and ultimately enriches the purge gas mixture used as fuel in the regenerator and heater burners.

It is important to point out here that all these advantages are achieved only in the method according to the invention. This is because the process of the invention has a regenerator and a heating device for the reduction inlet gas proceeding to the reduction zone outside the reduction loop.

A stoichiometric regenerator is provided, while no heating device is provided for the recycle gas stream. In methods such as those disclosed in the aforementioned patents, it is not possible to have the advantage of reducing the size of the required regenerator by blowing natural gas into the cooling loop. Because it is impossible to reduce the flow of hot gas from the regenerator without reducing the temperature at the inlet of the reduction zone,
As a result, the productivity of the plant will be reduced.

If the regenerator is placed in the reduction loop, the methane blown into the cooling loop will eventually reach the regenerator, so in this case the advantage of reducing the capacity of the regenerator cannot be achieved.

The present invention has the advantage of reducing the capacity of the regenerator from which the ore is derived, whether it is pelleted or lumpy ore.
It is clear that whether it is a mixture of the two is an issue independent of the shape of the filling material for the reactor.

FIG. 4 shows a preferred embodiment of the method for achieving the objects of the invention.

The reduction of iron ore takes place in a moving bed reactor, designated by the reference numeral 1, which comprises three zones: a reduction zone 2, an intermediate zone 3 and a cooling zone 4. It is preferred to operate at slightly above atmospheric pressure, typically 5 Kg/cm ² . Iron ore is continuously charged into the reactor 1 via the feed duct 5 and the ore flows by gravity into the three zones of the reactor. The rate of solids flow is controlled by a rotary valve 6 located at the bottom of the reactor. By controlling solids flow, this valve also controls solids residence time and reactor production.

In the lower part of the reduction zone 2, a stream of reducing gas 7 is blown in at a temperature of 900°C to 960°C. This stream flows upwardly via reduction zone 2, where it comes into contact with the descending solids. When the hot gas comes into contact with the iron ore, reduction of said material takes place.

The reducing gas leaves the top of the reactor via pipe 8. This reducing gas is cooled in a quenching device 9, where moisture generated by the reduction reaction with hydrogen is removed by condensation. With this method,
The reducing power of the gaseous effluent from the reactor is increased.
The gaseous effluent from the quenching device 9 is divided into two streams 10 and 13. One of them 10
(corresponding to the first thermal reducing gas described in the claims section) is recirculated by the compressor 11 via the heating device 12 at a point where the thermal reducing gas is blown into the lower part of the reduction zone 2. Ru.

The other stream 13 is connected to a heating device 12 described below.
and is sent to the fuel header for use as fuel in the burner of the regenerator 14. Recirculating gas stream 1
0 passes through the regenerator 1 before passing through the heating device 12.
It is mixed with the cold regeneration gas proceeding from 4.
In regenerator 14, catalytic conversion of natural gas and steam occurs to produce a gaseous mixture consisting primarily of hydrogen and carbon monoxide. A stream of natural gas 15 and a stream of steam 16 are fed to the regenerator to effect the catalytic conversion. Regenerator 14 is typical and uses a nickel catalyst to facilitate the regeneration of methane contained in natural gas. In order to protect the catalyst of the regenerator 14 from excessive carbon deposition, such devices are generally operated with an excess of water vapor relative to the amount stoichiometrically required to carry out the regeneration reaction. Since this water vapor is a desirable element in the make-up reducing gas for the reducing system, unreacted water vapor must be removed from the gaseous effluent of the regenerator 14. For this purpose, a quenching device 17 is used, which provides a stream 18 that is substantially free of water and has a high content of hydrogen and carbon monoxide. Stream 18 is mixed with recycle gas 10 and fed to heating device 12 where its temperature is increased prior to blowing into reduction zone 2.

In the lower part of the cooling zone 4, a cold gas stream is blown in and flows countercurrently to the descending solids. This cooling gas (corresponding to the second cooling gas in the claims) leaves the reactor via a pipe 20 located at the top of the cooling zone 4. Next, this gas is cooled in a quenching device 21. This cold gas is then recycled to the lower part of the cooling zone 4 by the compressor 22 in a closed loop.

A cold natural gas stream 23 (which corresponds to the third gas stream in the claims section) is injected as make-up to the cooling loop and forms stream 19 with the recirculated cooling gas, which in turn passes through the cooling zone. It is blown into 4.

Since the cooling loop is closed, a portion of stream 19 flows inwardly from cooling zone 4 to intermediate zone 3 as indicated by arrow 24 (corresponding to the fourth gas flow in the claims section). ). In the intermediate zone 3, the methane rising from the cooling zone 4 comes into contact with the oxidizing elements present in the thermally reducing gas stream 7.
Facilitate the regeneration of some of the injected methane.

It is important to point out that stream 23 must be small compared to stream 7 in order not to over-cool the reducing gas and not to adversely affect the reduction reaction in reduction zone 2. It is. In the method according to the invention, the flow rate of stream 23 has a value of 1 to 2% of the flow rate of stream 7.
In addition to natural gas streams 15 and 23 (both used in the process, one stream of which is blown into the regenerator 14 and the other stream into the closed loop of reactor 1), another natural gas stream is blown into the closed loop of reactor 1. There is a gas stream 25, which is used as fuel. Said stream 25 is mixed with the purge gas stream 13. This mixture is used to supply the necessary heat to the burner 26 of the heating device 12 and the burner 27 of the regenerator 14 .

It will be apparent to those skilled in the art that there are variations to the preferred embodiment that do not depart from the spirit of the invention. Variations such as including a CO ₂ absorption device for cleaning CO ₂ from stream 10 and further utilizing a portion of stream 18 as a minor portion of the replenishment to the cooling loop are within the spirit of the invention due to its broad nature. It is thought that it is inside. It should also be considered within the spirit of the invention to heat only stream 10 and mix it with the thermal reducing gas proceeding from the regenerator.

〔Effect of the invention〕

A preferred embodiment of the invention includes a moving bed reactor configured to include three zones. In the upper zone, the reduction of iron is carried out by a reducing gas with a low methane gas content of 4-10% and a high content of reducing components, i.e. 75-90% hydrogen and carbon monoxide, at a reduction temperature of 900-960°C. Performed at °C. This reducing gas flow is in a closed loop with make-up reducing gas supplied from another regenerator.
The lower zone of the reactor is a cooling zone, which is connected in a closed cooling loop with a quench and a compressor. Preferably, the gas composition of the make-up gas to the cooling loop comprises a cooling gas having a methane content of at least 75%. A natural gas stream is typically useful as a supplement to this loop. The amount of this natural gas make-up is 1 to 2% of the amount of reducing gas stream (at the inlet of the reduction zone).
It is.

Between the reduction zone and the cooling zone there is an intermediate zone in which mixing occurs under controlled conditions between a portion of the thermal reducing gas proceeding from the reduction zone and the methane proceeding from the cooling zone. promoted. In this intermediate zone, methane regeneration takes place by absorbing considerable heat, which rapidly cools the solids and thus avoids agglomeration of the pellets with high metallic iron content.

By regenerating the methane blown into the cooling zone within the reactor, the size of the regenerator required as a reduced body generator is reduced.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the productivity of a direct reduction plant and the operating temperature; Figure 2 is a schematic diagram showing the effect of iron content in the pellets on the agglomeration index; Figure 3 is for two different cases. a graph showing the effect of operating temperature on the required dimensions of the reducing gas generator, one with natural gas blowing into the cooling loop and the other without this main blow;
The figure is a schematic representation of a preferred embodiment of the method according to the invention. Explanation of symbols 1... Moving bed reactor, 2... Reduction zone, 3... Intermediate zone, 4... Cooling zone, 7... Reducing gas, 9, 17, 21... Rapid cooling device, 10, 13, 1
8, 19...flow, 11, 22...compressor,
12... Heating device, 14... Regeneration device, 15, 23,
25...natural gas, 16...steam.

Claims (1)

Claims: 1. A transfer having three zones: a reduction zone located in the upper part of the reactor, a cooling zone in the lower part of the reactor, and an intermediate zone located between said reduction zone and the cooling zone. A method for the direct reduction of iron ore to produce sponge iron from iron ore in the form of pellets, lumps or a mixture of both in a bed reactor, in which pellets with an iron content of more than 67% by weight are placed in the upper part of said reactor. iron ore, mainly composed of hydrogen and carbon monoxide,
A first thermal reducing gas stream, further containing trace amounts of oxidant elements in the form of water and carbon dioxide, is blown into the reduction zone at a temperature of 900 to 960°C;
circulating a second cooling gas consisting primarily of methane in a reduction loop comprising a quench zone, a compressor, and a heating device for said reducing gas; supplying a third gas stream having a methane content of at least 75% to said cooling loop, thereby causing said second gas stream to flow upwardly within the reactor; forming a fourth gas stream, mixing a portion of the first gas stream with the fourth gas stream, thereby converting methane present in the fourth gas stream to the first gas stream; characterized in that the reduced iron ore is regenerated by the oxidant element component and endothermically cooled reducing iron ore entering the intermediate zone, and the cooled reduced iron ore is discharged via the lower part of the reactor. Direct reduction method for iron ore. 2. The method of claim 1, wherein the methane content of the first gas stream is between 4 and 10% by volume. 3. The method of claim 2, wherein the first gas stream has a moisture content of 1 to 4% and a carbon monoxide content of 2 to 15%. 4. A method according to claim 3, wherein the flow rate of said third gas stream, in terms of its methane content, is 1 to 2% by volume of the preceding flow rate of said first gas stream. 5. The method of claim 4, wherein said first gas stream is a mixture of recycle gas from said reduction zone and make-up gas from a catalytic regenerator. 6. A method for direct reduction of iron ore according to claim 5, wherein the recycled reducing gas is heated and then mixed with the thermal reducing gas stream proceeding from the regenerator. 7. A method for the direct reduction of iron ore according to claim 6, wherein carbon dioxide is purified from the recycled gas stream.