JPS6096707A - Direct reduction of iron ore - Google Patents

Abstract

PURPOSE:To reduce hydrocarbon content in the exhaust gas in a smelting reducing furnace by a method in which the operating pressure of a prereducing furnace is set higher than that of the smelting reducing furnace, and by supplying the exhaust gas of the former to the latter, the high-grade hydrocarbon group in the said gas is pyrolyzed. CONSTITUTION:In the smelting reducing process of iron ore, the operating pressure in a prereducing furnace is set higher than that of a smelting reducing furnace. The exhaust gas containing the hydrocarbon group generated in the prereducing furnace is fed to the smelting reducing furnace using the pressure inclination and is used for the reduction of molten iron, and is made to pyrolyze the high-grade hydrocarbon group of tar, etc. in the exhaust gas by means of intense heat of the smelting reducing furnace. By this system, the prereducing efficiency is improved, so that the iron ore prereduced can be charged to the smelting reducing furnace in the intense heat condition. Furthermore, the transport system for the prereduced ore can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a process for producing molten iron that directly reduces iron ore without using a blast furnace, and more specifically, a process using a pre-reduction furnace and a converter-type smelting reduction furnace (hereinafter referred to as In the converter-type melting process), the pressure inside each furnace is controlled to improve thermoeconomic efficiency, and the content of higher hydrocarbon components such as tars in reducing exhaust gas is reduced as much as possible. It is about the method.

New iron manufacturing methods to replace the blast furnace method are being researched in various fields, but processes that can improve the resource situation and use steam coal are attracting attention. Krup'p method, KR method, converter type melting method, etc. have been developed.

However, each method has its advantages and disadvantages; for example, I NRED
In this method, the preliminary reduction furnace and smelting reduction furnace are directly connected to create an almost integrated appearance, and are designed to minimize energy consumption, and the exhaust gas energy is used to operate a steam turbine to generate the electricity required for the electric furnace. Although there are various advantages in that it is possible to cover the following conditions, it is extremely difficult to manage operations because the reaction is based on seconds, and coal is mixed with 02 and simultaneously injected to ensure complete combustion. Therefore, there is little hope for the usefulness of the exhaust gas from a component standpoint, and it cannot be evaluated at all from the perspective of producing valuable gas.

Next, since the ELRED method uses an electric furnace to produce molten iron, a high capacity of electric power is required, and the cost of power generation equipment becomes extremely large. In addition, in this process, the reaction proceeds at a temperature of 900°C or less in the pre-reduction furnace, so the tar content in the exhaust gas remains undecomposed, making it necessary to add a tar treatment step during the exhaust gas treatment process. This also causes an increase in equipment costs and is also a drawback in terms of operation. Moreover, depending on the type of tar treatment equipment, there is a risk of causing pollution problems, and there are many difficulties in adopting water submergence. The PLASMA method also uses Plasma-3m, which generates a plasma arc in a coke-filled shaft furnace.
There are two methods: the ELT method and the Plas+WA-RED method, in which coal and coke are gasified using a plasma arc and the gas is led to a shaft furnace to reduce iron ore, but the plasma arc requires a large amount of electricity to generate, making it difficult to use the blast furnace method. There is no advantage to replace it.

On the other hand, in the converter type melting method, iron ore is pre-reduced in a shaft furnace or fluidized bed, and then it is introduced into a smelting reduction furnace for iron production and coal gasification in a bottom-blowing converter method. It is seen as a promising alternative to the blast furnace method due to its relatively low cost and the ability to obtain valuable gas. This method has drawbacks such as poor operability since it is necessary to provide a large number of raw material charging ports at the bottom of the melting reduction furnace.

The present invention was made under these circumstances, and as a result of comparing and examining the advantages and disadvantages of each process and searching for room for improvement, it was discovered that there is a promising method for the converter type melting method. After further various studies, the present invention was completed. In other words, the present invention has the ability to use air instead of a large amount of oxygen, and it is also possible to reduce the loading of raw materials into the smelting reduction furnace, and further to reduce the amount of tar in the pre-reduction furnace exhaust gas. The purpose of the present invention is to provide a new converter-type melting process that can efficiently process such materials.

Therefore, the improved converter-type melting process according to the present invention involves pre-reducing iron ore with coal or coke in a pre-reduction furnace that forms a fluidized bed, and then leading it to a smelting-reduction furnace to reduce it to molten iron. The main point is to make the operating pressure in the preliminary reduction furnace higher than that in the smelting reduction furnace, and the exhaust gas generated in the preliminary reduction furnace is charged into the smelting reduction furnace and reduced to molten iron. The gist of the system is to provide a high-temperature reactor and to thermally decompose higher hydrocarbons (hereinafter referred to as tars) in the exhaust gas using the high heat of a smelting reduction furnace.

That is, in the present invention, the hydrocarbon-containing exhaust gas generated in the preliminary reduction furnace is sent to the melting reduction furnace using a pressure gradient, and the tars are thermally decomposed by the heat of the reduction furnace. Therefore, the operating pressure of the pre-reduction furnace is made higher than the operating pressure of the smelting reduction furnace.In addition to the above, the effects of increasing the operating pressure of the pre-reduction furnace are that the pre-reduction furnace can be made more compact, and the pre-reduction furnace can be made more compact. Examples include improved efficiency, the ability to charge the pre-reduced iron ore into the smelting reduction furnace in a high-temperature state, and the simplification of the transportation system for the pre-reduced iron ore.

The configuration and effects of the present invention will be clarified by comparing and explaining the conventional converter type melting process and the converter type melting process of the present invention.

Figure S1 is a typical flow diagram showing a conventional converter type melting process, and a process with a modified flow as shown by the solid line is also known. That is, raw iron ore is made into powder, lumps, or pellets and charged into a preliminary reduction furnace from line A, and is partially reduced (usually about 70%) by reducing gas (H2 rich) at around 900°C supplied from line M. C) receive a preliminary return. The pre-reduced hot iron ore enters the cooler along line B, and the refrigerant circulating in line c, c' force direction (
1 is a cooler), the temperature is lowered slightly by the cooler, and the air is blown to the line D.
The melting material is charged into the main furnace along the following lines. A slag-forming agent is charged into the recess from line E, powdered coal (or coke) is charged from line H together with gear scum (N2 or reducing scum), and O2 and nozzle cooling are charged from line I. The melting reduction progresses due to the mixed gas of the waste. The produced molten iron is discharged through line G, the molten slag is discharged through line F, and the smelting reduction furnace exhaust gas (usually about 1600 to 1700'C) containing cobalt and N20 as main components is discharged from line J. And this exhaust gas is sent to cooler 3
After being cooled, it passes through a venturi type dust remover and is further cooled. Next, it is pressurized by a compressor and enters the CO2 remover 6 through the line. On the other hand, the preliminary reduction furnace gas is separated from line O into lines P and R, and the latter is cooled by cooler 2, then pressurized by a compressor, and flows from line S to line ''. That is, since unreacted reducing gas (N2 + GO) remains in the exhaust gas of the preliminary reduction furnace, the purpose is to recycle this gas. After the merging, the residue enters the aforementioned CO2 remover 6, where CO2 is removed by a dry or wet method, and the exhaust gas with increased capacity is heated by the pre-reducing furnace exhaust gas supplied from the line P. After being restored to about 900'C by exchange, it is blown into the preliminary reduction furnace along line M. Incidentally, the waste that enters the heat exchanger from line P is discharged in the direction of line Q, undergoes appropriate exhaust gas purification treatment, and is then effectively used as boiler raw material gas in a subsequent process. The CO2 gas discharged from the CO2 remover 6 in the direction of line T is either released into the atmosphere or effectively utilized as inert gas.

Although the flow of the dashed line route indicated by lines J', S', T', T'' and U is simplified as a process, it is essentially the same as the flow of the solid line route described above.

Now, looking at the flow of waste in the conventional route shown in Figure 1, the retained heat of the exhaust gas generated on the high temperature side (smelting reduction furnace) is used in the low temperature # (pre-reduction furnace), and the waste generated on the low temperature side is Some of the waste waste is recycled considering its composition, but
The remainder is used as a heat medium on the high-temperature side of the heat exchanger, and then
It has a structure in which it is sent outside and used for other purposes, and can be said to be an extremely conventional method when viewed as a general tJl Atari River system. However, if you carefully examine this process, you will find that it contains various problems. The first point is that raw coal is charged from the bottom of the furnace, which increases the number of pores at the bottom of the furnace, making it easy for local blockages to occur.
This means that stable driving is difficult. Two points are that it is difficult to operate without using butyric gas as an oxidizing gas, and a large amount of butyric is required, which increases the manufacturing cost and causes an increase in costs. The third point is that a large amount of coal is decomposed in a small reactor, so
Tar-like hydrocarbons inevitably remain in the outlet gas,
This adheres to the inner surfaces of piping or various types of equipment during the subsequent exhaust gas treatment process. This phenomenon poses extremely important problems for equipment maintenance. The fourth point is the exhaust gas from the smelting reduction furnace, but if you look at the process from line J to line M, in the case of a solid line flow, it goes through a cycle of cooling → heating → cooling → warming, and thermoeconomically It must be said that this is an extremely lossy method.

That is, 1600-1700'c of smelting reduction furnace exhaust gas! It cannot be said that the energy of high heat, which can reach up to 100,000 yen, is being fully utilized.

FIG. 2 is a flow diagram showing an example of the process of the present invention, and in each line in the diagram, the same symbols are added to those having the same meaning as in FIG. 1.

In the preliminary reduction furnace, powdered ore is charged along line A and pulverized coal (or pulverized coke) is charged along line A', and at the same time, fluorine gas is introduced into room temperature air supplied from line N. It is added, further compressed and heated, and then blown along line N. The first advantage of this process is that the coking coal is produced in two stages: the pre-reduction furnace and the smelting reduction furnace.
Since the coking coal is charged from two places, the amount of coking coal charged from the bottom of the smelting reduction furnace is about half, and the number of coals at the bottom is therefore significantly reduced, which is extremely advantageous in terms of equipment design.

Y'Uti';a type of main furnace injects ore and pulverized coal from the lower part to partially harden the pulverized coal, gasify the pulverized coal, and produce reducing gas to extract 50 to 80% of the ore powder. As the reduction progresses, the particle size of the reduced fine ore becomes larger, and it moves along line D along the line D, along with the partially coked carbonaceous material, toward the smelting reduction furnace.

A second advantage is the use of air instead of oxygen as the oxidizing gas used in the pre-reduction furnace. By using air, the power cost for oxygen production is reduced only for the smelting reduction furnace, and it is significantly reduced.
Since the expensive oxygen production equipment is downsized, the process becomes simpler in terms of equipment.

The third advantage is that, unlike the normal direct reduction ironmaking process, the exhaust gas from the preliminary reduction furnace is charged into the smelting reduction furnace (in normal processes, it is the opposite), and while it is partially used for reduction, the exhaust gas in the exhaust gas is The point is that it is designed to completely decompose the tar content and supply reducing scum with no tar content to the outside. To take advantage of this advantage, the pre-reduction furnace is operated at a higher pressure than the smelting reduction furnace. However, if the pre-reduction furnace is made to have too high a pressure, the advantage of converting oxygen to air will be lost, so the operating pressure is preferably 2 to 5 kg/cm2G (the power cost for the oxygen production equipment is mainly for converting air to 5 kg/cm2G). (This is the power cost to compress air to a pressure below this pressure, so it is more advantageous to use air if it is compressed below this pressure.)

On the other hand, the melting reduction furnace has a simpler structure than the one shown in FIG. 1, and is normally operated at normal pressure and high temperature. Therefore, partial reduction progresses in the preliminary reduction furnace,
When free iron is generated and fusion begins to occur, the iron ore raw material whose particle size has grown due to fusion begins to fall from the bottom of the pre-reduction furnace and moves along line D toward the smelting reduction furnace. do. If necessary, it is possible to install a storage container on this transfer route and add a quantitative cut-out device to control the charging of raw materials into the smelting reduction furnace, or in any case, from the high pressure side to the normal pressure side. Since the transportation is for the destination, it is possible to create an extremely simple transportation system.

Also, since the pre-reduced fine ore itself has a high temperature,
Since it has a tendency to be re-oxidized when exposed to outside air, the route of the transport system described above must be such that re-oxidation is inhibited. However, in the converter type melting method of the present invention, the reducing exhaust gas discharged from the preliminary reduction furnace can be obtained in a high pressure state. It is also possible to adopt a sealing method that uses high pressure, and in this aspect as well, it can be evaluated as an extremely rational method.

On the other hand, it is also impractical to operate the smelting reduction furnace under slight pressure.
Although it is not an effective feature, (1) running costs do not decrease significantly even if high-pressure operation is performed in the molten iron manufacturing process, and (2) the pressure difference with the preliminary reduction furnace decreases, reducing each of the above-mentioned effects. (3) 1500-1800℃
The pressure-resistant structure of a high-temperature operating furnace is not recommended due to design and manufacturing difficulties.

By the way, the exhaust gas generated from the pre-WI reduction furnace contains tars as mentioned above, and when the temperature drops to near room temperature, these tars become sticky liquid substances and are used in the cooler (including the cooler shown). , compressor, CO2 remover,
Alternatively, the blower 1 or even the pipes may become clogged, creating a major obstacle to continuous operation. However, in the process of the present invention, the exhaust gas from the pre-reduction furnace (usually containing 1 to 2% tar) is passed through the simplest and shortest possible route (in other words, the shortest pipe possible). Since the exhaust gas is charged into the high-temperature smelting-reduction furnace through the smelting-reduction furnace (through the line and while maintaining the temperature as high as possible), the above exhaust gas is heated to an even higher temperature in the smelting-reduction furnace and remains there for a short time. almost completely thermally decomposed. Therefore, equipment costs and maintenance costs are significantly reduced compared to the conventional process, which requires the installation of a special tar processing equipment in order to discharge most of the pre-reduction furnace exhaust gas.
The fear of pollution caused by tar has disappeared.

The experimental results are shown below.

(+) Test on T4JFI reduction furnace Test using a small experimental fluidized bed (3000 mm (1 x 100 mmφ) under the following conditions, iron ore with a preliminary reduction rate of 70% was obtained, and coke was found in it. to 2
The composition of the column and the preliminary reduction furnace exhaust gas was as shown in Table 1, and it was confirmed that it contained about 2% tar.

Preliminary reduction furnace test conditions 1) Coal supply @: : 400 g/Kg-Fe2) Air supply amount: 9901/Kg-Fe3Ni dynamic gas supply i: 970 sentences/Kg・Fe4) Fluid gas composition: GO=67%, C02 =18%.

H2=13%, N20=1%.

N2 = 1% 5) Pre-reduction furnace temperature (average value): 900°C Table 1 Pre-reduction furnace test conditions (2) Test for tar removal The test equipment as shown in Figure 3 was used for the test shown in Figure 3. A test was conducted to decompose tar in the preliminary reduction furnace exhaust gas (Table 1) generated from the equipment.

Melting reduction furnace (100+smφX 1000m+*”)
The test conditions are as shown below.

1) Coal injection rHj: 630g/Kg-Fe2)
Y'gu 11 reduced ore (70%) injection amount: 1200g /
KgIIFe 3)02 Injection amount: 4501/Kg ・Fe4) Stone j<: 120g/Kg*Fe At this time, the composition and stars of the generated exhaust gas were as follows.

1) 1m gas capital: 1200~12501/Kg
11Fe2) Hu gas composition: C0=59%, C02=14%.

H2 = 13%, N20 = 13 N2 = 1% 3) Exhaust gas temperature = 1650-1700°C Charge the preliminary reduction furnace exhaust gas into the smelting reduction furnace shown in Figure 3 while adjusting the amount and temperature, and As a result of measuring the temperature T and the relationship between the outlet temperature T1 and the tar removal rate, the following data were obtained.

Table 2 Note) The residence time of gas in the furnace is Adjusted to about 1 second.

Judging from the above results, the melting reduction furnace outlet gas is
By heating the temperature to 00° C. or higher, tars in the pre-reduction furnace exhaust gas can be almost completely removed, making handling of the smelting reduction furnace exhaust gas extremely easy.

In the above explanation, the configuration and experiment were described in which all the exhaust gas from the preliminary reduction furnace is supplied to the smelting reduction furnace.
As shown in the figure, after cooling and removing dust, a part of it is recompressed and returned to the bottom of the pre-reduction furnace (circulation), or, although not shown, it is simply circulated without performing any of these processes to generate a reserve. It is also possible to adopt a method of returning the material to the reduction furnace. When charging all or part of the preliminary reduction furnace exhaust gas to the smelting reduction furnace, it is not limited to the case where it is blown in from the bottom of the same part as shown by line O, but also when it is blown into the smelting reduction furnace as shown by the dashed line 0. It is also a recommended measure to efficiently thermally decompose the tars in the exhaust gas using a heat exchanger 11 that is charged in the upper part of the furnace and provided in the circulation section. In addition, if you want to effectively recover the tar, after discharging it out of the system via route W,
Needless to say, there are also conventional methods for recovering tar.

In addition to the above-mentioned effects, the effects of employing the process of the present invention include the utilization of smelting reduction furnace exhaust gas. That is, since the discharged gas in the present invention is a smelting reduction furnace exhaust gas which is at a high temperature and does not contain tars, etc., compared to a pre-reduction furnace exhaust gas which is relatively low temperature and contains tars,
Its range of use is extremely wide, and there is no risk of environmental pollution. Heat exchange can be mentioned as a form of utilization of high-temperature energy, but it should be noted that it has a chemical composition rich in CO and H2, and it can be used as a fuel (for example, fuel for general boilers or fuel for gas turbines, etc.). This is recommended as a solution. Note that line J in Figure 2
, W route is an example of this, but when a part of line W is extracted in the line Considering that the temperature is quite low at the line J, it is recommended to heat (heat exchange) with the exhaust gas partially taken out from the line J to the inner V. However, a more effective use is to use it as a fuel for fuel cells, focusing on the fact that it contains H2 and CO, and taking advantage of the fact that it contains almost no tars.

In other words, since the above exhaust gas contains H2 and CO,
Although it has inherent utility value as a hydrogen/oxygen type or carbon monoxide/oxygen type fuel for fuel cells, it is necessary to increase the interfacial area between the electrode and electrolyte in order to increase the efficiency of conversion into electrical energy. , porous materials such as honeycomb structures or sintered bodies must be used. However, if a large number of tars are present in the supplied gas, they will adhere to and accumulate on the surface of the porous structure, reducing the contact area between the electrolyte and the supplied gas, and having a serious adverse effect on the conversion efficiency.

Therefore, the supply gas is originally required to be a clean gas that does not contain tar, etc., but the smelting reduction furnace exhaust gas obtained by the present invention fully satisfies this condition, and is more effective than simply using waste heat. It can be applied to extremely useful applications. In addition, it is easy to understand from the chemical composition in -h that it can also be used as a raw material for C1 chemistry, and the present invention should not be positioned as a mere iron manufacturing method, but as a coal gasification technology. It also has aspects.

Since the present invention is configured as described above, the calorific value and components of the exhaust gas generated in the pre-reduction furnace are almost completely utilized in the smelting reduction furnace, which is extremely effective compared to the conventional use only for heat exchange. In addition, since the tars in the exhaust gas are almost completely thermally decomposed, maintenance of equipment becomes easier, there is no need to install special equipment to remove tars, and there is no problem of environmental pollution. Almost completely resolved. In addition, the exhaust gas from the smelting reduction furnace has high heat and does not contain tar, etc., so it can be used not only directly as heat or as various fuels, but also as fuel cell gas and C1.
It is now possible to use it as a raw material gas for chemicals.

[Brief explanation of drawings]

FIG. 1 is a flow diagram showing a conventional process, FIG. 2 is a flow diagram showing a process of the present invention, and FIG. 3 is a flow explanatory diagram showing a test apparatus according to the present invention. Applicant Kobe Steel, Ltd.

Claims (1)

[Claims] (1) Iron ore is prepared by pre-reducing iron ore with coal or coke in a pre-reduction furnace that forms a fluidized bed, and leading the pre-reduced iron ore to a smelting reduction furnace to reduce it to molten iron. This is a direct reduction method, in which the inside of the preliminary reduction furnace is operated at a higher pressure than the inside of the smelting reduction furnace, and the exhaust gas generated in the preliminary reduction furnace is charged into the smelting reduction furnace to be reduced to molten iron. A method for direct reduction of iron ore, which is characterized by reducing the amount of hydrocarbons in exhaust gas from a smelting reduction furnace as much as possible by thermally decomposing higher hydrocarbons in the exhaust gas. (2. Claim 1, 7. A heat exchanger is provided at the top of the smelting reduction furnace, and a part of the preliminary reduction furnace exhaust gas is guided to the heat exchanger to thermally decompose hydrocarbons in the exhaust gas. Direct reduction method for iron ore. (3) A method for direct reduction of iron ore according to claim 1 or 2, in which power generation is performed by a fuel cell using exhaust gas from a smelting reduction furnace.