JPS5933179B2 - Method for producing raw material pellets for producing reduced iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing raw material pellets for producing reduced iron by directly reducing iron ore. The present invention relates to a method for manufacturing internal pellets.

It is well known that the blast furnace-converter method is currently widely used as a steel manufacturing method, but although the blast furnace-converter method is considered to be a complete technology, there are still problems. It's not that there aren't any.

In other words, in the blast furnace-converter method, when producing iron by removing (reducing) oxygen from iron ore (iron oxide), pig iron containing excess carbon is first obtained in a blast furnace, and then excess carbon is entrained in a converter. Since steel is produced by oxidizing and removing silicon, phosphorus, etc., it is in principle inefficient.

Moreover, there is also the problem that the supply of strongly coking coal as a raw material for blast furnace coke is becoming insufficient worldwide.

On the other hand, a method was developed in which iron ore is brought into contact with a reducing agent in a solid state, generally reduced to a reduction rate of 85 or higher to obtain reduced iron, which is then further melted and refined in an electric furnace to produce steel. has been done.

Compared to the above-mentioned blast furnace-converter method, this method does not have the waste of so-called excessive reduction-oxidation of carbon, accompanying silicon, phosphorus, etc., and strongly caking coal, which is a raw material for coke for blast furnaces, can be used. It has the advantage of not having to be decorated.

Industrial tests have also been conducted to use reduced pellets with a reduction rate of 70 to 90 as a raw material for blast furnaces to save fuel coke and improve productivity.

The reason why these methods are not popular worldwide is because of the reducing agent used in the production of reduced iron and the raw materials for the reducing agent, such as coal,
This is because areas with natural gas, other carbon, H2, and (a) gaffes are unevenly distributed on the earth, and there are only a limited number of areas where they can be economically advantageous.

The manufacturing method of reduced iron is classified into (a) rotary kiln method, shaft furnace method, fixed bed furnace method, and fluidized bed furnace method depending on the type of reducing furnace, and (b) solid reducing agent method and depending on the type of reducing agent. It is classified as a gas reducing agent method.

→The rotary kiln method is used in the solid reducing agent method,
The remaining three methods are intended to be used in the gas reductant method.

The present invention relates to a method for producing raw material pellets used in the above-mentioned solid reducing agent method, and aims to provide a method in which carbonaceous material used as a reducing agent can be supplied in a coexistence state that is convenient for reducing raw material iron ore. It is for one purpose.

On the other hand, looking at the current state of oil resources, as they are depleted, it is becoming increasingly difficult to obtain high-quality light crude oil, and the trend is for crude oil, including Chinese crude oil, to become heavier.

In order to extract more light oils such as gasoline and diesel oil, which are more commonly used than such heavy oils, attempts have been made to lighten heavy oils by catalytic cracking, hydrogen cracking, etc. When fractionating oil, vacuum distillation is used to extract a large amount of light oil.

Attempts to extract more light fractions in this way will, on the one hand, make the residual oil heavier and worse, creating a new problem in how to effectively utilize the residual oil. are doing.

Thus, in view of the current situation, the present invention provides a new effective use of the poor residual oil by using the poor residual oil as a binder in producing the raw material pellets for producing reduced iron. It has one purpose.

However, the feature of the present invention, which is suitable for each of the above-mentioned purposes, is that 5 to 2 carbonaceous materials are added to iron ore powder as a reducing agent.
0 wt % and 2 to 10 wt % of distillation residue oil of crude oil as a binder, this mixture is kneaded while maintaining the temperature 100 to 150° C. higher than the softening point of the binder, and then the mixed wire is mixed. A method of manufacturing pellets by supplying a material to a pelletizer heated to a temperature 100 to 150°C higher than the softening point of the binder, and in the above method, a contaminant in the pelletizer is further heated to a temperature of 100 to 150°C higher than the softening point of the binder. The method involves producing pellets while spraying a fluidized binder heated to a high temperature to all raw materials at a rate of 11 or less.

Hereinafter, specific embodiments of the method of the present invention will be explained in detail.

That is, in the pellet manufacturing process of the present invention, firstly, iron ore powder and carbonaceous material that have been crushed to an appropriate particle size are prepared, and then charged into a mixer according to a predetermined mixing ratio, and distilled from crude oil as a binder. Residual oil (Distillation R
e5ide (hereinafter abbreviated as DR) was added and kneaded.

In this case, since DR is a solid and highly viscous substance at room temperature, it is difficult to sufficiently mix DR even if the addition and mixing operation is performed at room temperature.

Therefore, it is necessary to heat the DR to an appropriate temperature above the softening point of the DR and add it in a molten state, and to perform the kneading operation by heating the inside of the mixer to the same temperature.

Furthermore, even though DR is in a molten state, it has an extremely high viscosity and a high surface tension, so simply performing a mixing operation will not allow enough DR to act as a binder between each powder particle of iron ore and carbonaceous material. Since the solid particles do not penetrate and therefore do not function as a bonding material for each solid particle, the kneading operation is performed while applying compressive force to the mixture using a roller or the like.
It is necessary to allow DR to sufficiently penetrate between each particle so that the surface of each particle is substantially covered with DR.

The raw material mixture heated and kneaded in this manner is sent to a pelletizer while being heated, and is formed into pellets of a predetermined particle size to become green pellets.

These raw pellets are further fired to become fired pellets for producing reduced iron, or they are used as raw material pellets for producing reduced iron, but in the former case, in the firing process,
In the latter case, the raw pellets are heated above the thermal decomposition temperature of the DR in the preheating step before being sent to the reduction furnace, so the DR is thermally decomposed by the catalytic action of the iron ore particles and becomes light. Therefore, if the amount of added DR is large, the thermal decomposition products can be recovered in these steps and separated by rectification to obtain light oil and cracked gas.

In addition, when the amount of DR is relatively small, the thermal decomposition product can be used as a fuel as it is.

On the other hand, for the thermal decomposition of heavy oil, the fluid catalytic cracking method (FCC method) has been used for a long time, in which heavy oil is catalytically decomposed in a fluid state in the presence of catalyst particles such as silica or alumina. It is known that in this FCC method, carbon (coke) produced as a by-product during thermal decomposition of heavy oil is deposited on catalyst particles.

Therefore, in this FCC method, by replacing the catalyst particles with silica, alumina, etc. and using iron ore particles, it is possible to simultaneously thermally decompose heavy oil and obtain iron ore particles with by-product oil coke attached. .

In the present invention, by using coke-adhered iron ore particles obtained by the FCC method using these iron ore particles as a raw material, carbonaceous material-incorporated pellets are produced in which the surface of the iron ore particles is ideally coated with carbonaceous material as a reducing agent. Be able to manufacture.

Note that the amount of coke attached to iron ore particles by this FCC method varies depending on the residence time and pyrolysis temperature of the iron ore particles in the fluidized bed pyrolysis furnace, as well as the type of heavy oil, and does not necessarily depend on the amount of coke attached to the iron ore particles for the desired lightening. The thermal decomposition conditions and the thermal decomposition conditions for depositing the amount of carbonaceous material necessary for reducing the iron ore on the surface of the iron ore particles do not always match, and the amount of carbonaceous material deposited generally varies by several to ten coefficients. Therefore, if the deposited carbon material is insufficient for iron ore reduction, it is necessary to replenish the shortage with a suitable carbon material such as coke powder during the kneading process.

The above is an overview of the present invention.Next, specific conditions will be explained in more detail based on experimental data.

(A') Influence of DR blending ratio One superimposed hardness in the present invention is the DR blending ratio.

Therefore, various ratios of DR were mixed with iron ore, and problems in pellet production were investigated, and the properties of the obtained pellets were studied.

The blending conditions are as follows: 10% oil coke as a carbonaceous material.
%, and the blending amount of iron ore was varied depending on the blending level of DR.

The pellet manufacturing conditions are as follows: -325 Metsujiuro 0 iron ore powder and oil coke are each preheated to 150°C, then charged into a mixed machine that is kept at the same temperature, and heated to the same temperature at the same time as mixing starts. A predetermined amount of the prepared DR is supplied and mixed for 3 to 10 minutes while applying compressive force.

The kneaded raw materials are charged into the hopper of the quantitative feeder, and while heated, they are fed from the Syntron feeder at a rotation speed of 19.
r pm, an inclination angle of 48 degrees, an inner diameter of 60071!7M, and a pan-shaped pelletizer with a side height of 130 mm to pelletize, and the obtained raw pellets were 11.1 to 12.7 mm.
I sifted it with

The pan-type pelletizer is also kept at 150°C, and if the DR addition amount exceeds 10%, half of the total amount is sprayed into the raw material inside the pelletizer after being heated and melted at 150°C. Pelletizing operation was carried out.

The vacuum residue used as a raw material is a low-pressure oil with a softening point of 40°C of the vacuum distillation equipment currently used in commercial production, and the crude oil is a 70:30 mixture of Daqing and Minas crude oils.

Iron ore from the Rio Doce (Brazil) mine was ground in a ball mill, coarse particles were removed, and the iron ore was heated and dried at 150°C before use.

Oil coke is a product from a dilate coker of Sumatra and Te'L-IJi mixed oils.

These raw materials were also used in the following experiments of the present invention.

FIG. 1 shows the results of investigating the crushing strength (kg/pellet) of the obtained raw pellets.

Here, to measure the crushing strength in the present invention, a Shimadzu R82 type universal strength testing machine is used, a compressive load is applied to one pellet at a specified pressurizing speed, and the applied load at the moment when the pellet breaks is the load applied to the pellet. The crushing strength value of 20 granules was broken and the average value thereof was expressed.

As is clear from Figure 1, the total DR addition amount is in the range of 2 to 20% in order to obtain a strength of 7 to 8 kg/pellet or more, which is the ideal strength of raw pellets, and the preferred range in terms of strength is It can be said that it is about 5 to 13%, but an increase in the amount of DR added will cause the pellets to fuse together, especially forming agglomerates in the reduction furnace, so the amount of DR added should be between 2 and 10%. is preferable.

In addition, when adding a large amount of DR, it is possible to add and mix the entire amount in the kneading process before palletizing, but since it becomes agglomerated during mixing of raw materials and becomes unsuitable as a granulation raw material, this example is not used. It is preferable to spray add DR in a heated and molten state during palletizing, and the total amount added should not exceed 20%. If the amount is too large compared to , the pellets will adhere to each other during granulation, resulting in deformed pellets or agglomerated pellets, so the spray amount needs to be kept below 11 inches, preferably below 5 times.

On the other hand, the position of the cross-wire raw material supply to the pan-type pelletizer and the DR spray position inside the pelletizer is a serious forgery in order to make good pellets. The movement is shown by a solid line vortex, and the raw material supply position and DR spray position are shown by dotted arrows. When general powder is pelletized by water spray, C in the diagram indicates that the raw material is supplied to position D. However, it is said that it is better to spray water at position B, or in the case of the raw material of the present invention, if the raw material is supplied to position C or D, DR
A large number of small particles called nuclei were generated regardless of the presence or absence of spray, and either no particle growth was observed, or good pellets were obtained only when the raw material supply position and spray position were set near A at the center of the vortex. .

From this, it was found that in the case of the present invention, it is necessary to supply the raw material and DR near the center of the transfer vortex.

CB') Effect of heating temperature of raw material mixture A mixture of iron ore and oil coke as a carbon material is heated and mixed while adding DR, and the mixed material is fed to a pan-type pelletizer at the same temperature, and Pellets were formed while spraying DR heated and melted at a certain temperature, and the effect of this heating temperature on the properties of the raw pellets was investigated.

The heating temperature was set at three levels: 100°C, 150'C, and 1180°C.

The particle size of the iron ore was -325mesh 60%, the amount of DR added was 7.5%, the amount of oil coke added was 10%, and the pellet molding conditions were the same as [A].

FIG. 3 shows the relationship between raw material heating temperature and crushing strength of raw pellets produced under the above conditions.

As is clear from Figure 3, the higher the heating temperature, the slightly higher the strength of the green pellets, especially at heating temperature 140.
Since the strength of the green pellets is improved at temperatures above 140°C, the heating temperature is preferably 140°C or above.

Note that since the softening point of DR used in this test is 40°C, this indicates that it is necessary to heat the material to a temperature 100°C or more higher than the softening point of DR.

On the other hand, the heating temperature is 190℃ or higher (15℃ higher than the softening point of DR).
If the temperature is higher than 0° C.), volatile matter from the DR will increase and the quality of the DR will change, so it is necessary to knead at the same temperature or lower.

Incidentally, at low temperatures of 80 DEG C. to 130 DEG C., not only does it take a long time to knead, but there is a strong tendency to form pellets or lumps, making beretizing virtually impossible.

From the above facts, it can be said that the heating temperature during raw material kneading is preferably in the range of +100°C to +150°C, the softening point of DR.

(C) Effect of the amount of carbon material blended In order to investigate the relationship between the amount of internal carbon material and the properties of the pellets, tests were conducted with various amounts of oil coke blended as the carbon material.

The DR as a binder was 7.5 parts, and 2.5 parts was sprayed into 5 parts during kneading.

Other conditions were the same as in (A).

The relationship between the oil coke content and pellet properties is shown in Figure 4.

As the amount of internal carbon material increases, the crushing strength of the pellet tends to decrease, and the porosity tends to increase, but the crushing strength becomes approximately constant at a coefficient of 20 or more.

The porosity was calculated from the true specific gravity and the missed specific gravity using the following formula.

P=(S 5A) Preheat while supplying, then raise the temperature to 1135 ° C in 60 minutes,
Reduction experiments were carried out by holding the temperature for 60 minutes.

The results are shown in FIG. 5 as a relationship between treatment time and weight loss in the reduction step.

The product reduction rate was the best for those containing oil coke of 15% and 20%, showing values of 94 to 95%, and for oil coke of 10%, 5%, and 3%, it was 78φ and 5%, respectively.
The values are 5th and 50th.

On the other hand, the amount of residual carbonaceous material is higher as the amount of oil coke is increased, and in the case of a 15% ratio carbonaceous material remains.

In the case of oil coke with 10% and 5th ratio, most of the carbonaceous material is consumed, especially in the case of 5% and 3rd stage combination, the 5th stage
As is clear from the figure, the weight loss stagnates from the early stage of the reduction process, and it can be seen that the amount of internal carbon material is insufficient in terms of stoichiometry to obtain a high reduction rate.

From the above results, the amount of carbonaceous material added is sufficient as a reducing agent at 15 parts, or at most 20 parts, and adding more than that is not hard, and on the other hand, there is a relationship with the reduction rate.

However, if the amount of DR added is increased, the carbon in DR also contributes to the reduction reaction, so the amount of carbon material added must be at least 5%, and Since it is necessary to add 5 parts or more from the viewpoint of the porosity of the pellets, the amount of carbon material added needs to be in the range of 5 to 20 parts, preferably 10 to 15 parts.

CD) Pyrolysis experiment Fresh pellets were fed at a rate of 40 kg/hr into a grate-type pyrolysis furnace that had been maintained at a predetermined pyrolysis temperature, and a pyrolysis experiment was carried out while supplying steam at a rate of 4 to 5 kg/hr. I did this.

The supplied green pellets are carried on a grate and moved through the furnace, during which time the green pellets are fired, and DR as a binder is thermally decomposed to generate cracked gas and cracked oil.

The fired granules go into the fired product receiving tank, the cracked gas and cracked oil go out of the furnace along with the superheated steam in the grate furnace atmosphere, and the cracked oil and steam are condensed in the condenser and collected in the oil receiving tank. did.

The pyrolysis temperature was carried out at various temperatures, but the temperature was 600°C, which is close to the preheating temperature when charging raw pellets to the reduction furnace.
and shows the thermal decomposition results at 630°C.

Note 1) Gas yield and oil yield are values based on the amount of DR in fed raw pellets. 2) Yield of fired product is a value based on the amount of raw pellets charged. From the table above, 600°C Then, the DR amount of 51.1 is 63
It can be seen that at 0°C, 83.9% can be recovered as gas and cracked oil, respectively.

Note that the remaining DR amount remains in the fired pellets as undecomposed residual oil and carbon.

On the other hand, the components of the effluent gas are mainly Ct, q gas, H2, and CO2, and the components of the cracked oil are at 600℃.
Gasoline is 30%, kerosene is 18%, diesel oil is 12%, residual oil is 40%, and at 630°C, gasoline is 20%.

Kerosene14. %, diesel oil 11%, and residual oil 54%.

[E] Consideration of the type of binder One of the features of the present invention is to use DR as described above as a binder, but water glass and PVA are also conventionally used as binders for forming raw materials for reduced iron production. Since these methods have been proposed, a comparison was made between these and the DR in the present invention.

Of the binders used, water glass was a 8-layer aqueous solution,
PVA is a dihydric aqueous solution, the blending conditions are DR, iron ore 85 parts oil coke 10 parts except for the binder, binder '-5%, granulation temperature is room temperature except OR/'r, and other test conditions. The highest conditions determined from the experiment described above were adopted.

FIG. 6 shows the relationship between one type of binder and green pellet strength.

This result shows that DR is significantly superior in terms of strength compared to other binders.

In addition, in the above test, iron ore grain size of 1325 Metjuro 0 was used for all iron ore grains. This is because as iron ore grain size becomes coarser, pellet strength decreases and the rate of pulverization in the aerobic reduction process or calcination process increases. Judging from these conditions comprehensively, it is preferable to use a raw material iron ore powder having a particle size of -325 mm or more.

The present invention is clear from the above explanation and various experimental results, and the following effects can be expected by the method of the present invention.

(1) In producing raw material pellets for reduced iron production,
Since petroleum distillation residue (DR) is used as the binder, P
Not only is the strength of green pellets higher than that of VA, water glass, etc., but it also provides new uses for DR, which had limited uses. c, this is an extremely significant technology.

(2) By firing the raw pellets containing DR produced by the method of the present invention, the DR in the raw pellets is thermally decomposed during firing to produce cracked oil and cracked gas such as gasoline, diesel oil, and kerosene. By collecting and separating it, useful light oil and gas can be obtained, which is the same as the above-mentioned D.
This not only makes effective use of R, but also has the secondary but significant effect of creating products with higher added value.

(3) Even when the raw pellets of the present invention are subjected to the reduction process without being calcined, the raw pellets are preheated before being charged into the reduction furnace for efficient operation of the reduction furnace. This means that thermal decomposition of DR as a binder will occur, and therefore, if the thermal decomposition products are recovered, the same effect as in (2) above can be expected.

(4) When iron ore powder is supplied as a catalyst into a fluidized bed pyrolysis furnace using the FCC method, which has been used for a long time as a pyrolysis technology for heavy oil, and the heavy oil is pyrolyzed, iron ore particles Since by-product carbon is deposited on the surface, if these carbon-adhered iron ore particles are taken out of the pyrolysis furnace and used as the raw material iron ore powder and carbon material in the present invention, this will not be the biggest problem from the perspective of the FCC method. The problems of carbon precipitation and catalyst deterioration caused by this are completely eliminated, and from the viewpoint of a raw material for producing reduced iron, it can be said that it is an ideal raw material with carbon as a reducing agent uniformly attached to the surface of iron ore particles, so it is truly possible to kill two birds with one stone. Say it.

(5) By blending iron ore powder, carbonaceous material, and DR in a predetermined ratio and heating and kneading this to produce pellets, high-quality reduction with high crushing strength and low powdering rate can be achieved. Pellets can be obtained as a raw material for iron production.

[Brief explanation of the drawings] Figure 1 is a graph showing the relationship between the blending amount of distillation residue (DR) of crude oil and the strength of green pellets, and Figure 2 is a graph showing the flow of raw materials in the pan-shaped pelletizer and the raw material supply. Fig. 3 is a graph showing the relationship between raw material heating temperature and green pellet strength, Fig. 4 is a graph showing the relationship between carbon material content and green pellet properties, and Fig. 5 is a graph showing the relationship between raw material heating temperature and green pellet strength. FIG. 6 is a graph showing changes in reduction reaction depending on various contents of carbonaceous material, and FIG. 6 is a graph showing changes in pellet properties depending on the type of binder.

Claims (1)

[Scope of Claims] 1. A method for producing raw material pellets for producing reduced iron comprising a mixture containing iron ore powder and a reducing agent as main components, wherein iron ore is used as the mixture containing iron ore powder and a reducing agent as the main components. When heavy oil is pyrolyzed in a fluidized bed pyrolysis furnace in which stones are kept in a fluidized state, oil coke, which is produced as a by-product, is attached to the surface of the coke-adhered iron ore particles. The mixture is adjusted to 5 to 20 wt% and is blended to contain 2 to 10 wt% of distillation residue oil of crude oil as a binder, and this mixture is kneaded while maintaining the temperature at 100 to 150 ° C. higher than the softening point of the binder. A method for producing raw material pellets for producing reduced iron, which comprises supplying a hindlimb kneaded material to a pelletizer and pelletizing it. 2. A method for producing raw material pellets for producing reduced iron according to claim 1, wherein the raw material mixture is kneaded while applying compressive force. 3. When a raw material mixed substance is supplied to a pan-shaped pelletizer, the mixed material is supplied near the center of a transfer vortex of the raw material mixed substance formed in the pelletizer. A method for producing pellets, a raw material for producing reduced iron. 4. The method for producing raw material pellets for producing reduced iron according to any one of claims 1 to 3, wherein the iron ore powder is a powder having a mesh of 1325 or more at 6 wt% or more. 5 A method for producing raw material pellets for producing reduced iron consisting of a mixture whose main components are iron ore powder and a reducing agent, in which heavy oil is heated in a fluidized bed pyrolysis furnace in which iron ore is kept in a fluidized state. The carbonaceous material deficiency is added to coke-adhered iron ore particles obtained by adhering oil coke, a by-product during decomposition, to the surface to adjust the total amount of carbonaceous material to 10 to 20 wt%, and the distillation residue of crude oil is used as a binder. A mixture is prepared by blending oil to contain 2 to 10 wt%, and this mixture is kneaded while maintaining the temperature 100 to 150 ° C. higher than the softening point of the binder. After that, the mixed material is fed to a pelletizer, and The reduced iron is pelletized by further spraying a fluidized binder maintained at a temperature 100 to 150° C. higher than the softening point of the mixed material in the pelletizer in an amount of 11 wt% or less based on the total raw material. A method for producing raw material pellets for production. 6. The method for producing raw material pellets for producing reduced iron according to claim 5, wherein the raw material mixture is kneaded while applying compressive force. 7. When supplying the raw material kneaded material to the pan-type pelletizer, the kneaded material is supplied near the center of the transfer vortex of the raw material kneaded material formed in the pelletizer, and the binder is transferred to the center of the vortex in the pelletizer. A method for producing raw material pellets for producing reduced iron according to claim 5 or 6, in which pellets are sprayed nearby. 8 Pellets obtained with a pelletizer are heated to a temperature higher than the thermal decomposition temperature of the distillation residue oil of crude oil, which is the binder, and the thermal decomposition gas generated by thermally decomposing the binder is recovered as light oil and cracked gas, and carbon A method for producing raw material pellets for producing reduced iron as set forth in each of claims 5 to 7, wherein the iron is left in the pellet as a reducing agent and a binder.