JP4996211B2 - Method for determining particle size of granulated raw material when producing iron ore pellets - Google Patents

Description

  The present invention relates to a technology for producing iron ore pellets by a great kiln system for producing iron ore pellets used for blast furnace raw materials and the like.

  In order to respond to the recent high blast furnace operation in blast furnaces, for the pellet kiln production facility using the Great Kiln method for producing iron ore pellets (hereinafter also simply called “pellets”), which is one of the main raw materials of blast furnaces. There is also a demand for increased production.

  Conventionally, as shown in FIG. 1, a pellet kiln manufacturing facility using a great kiln system is known, and this facility comprises a granulating facility and a firing facility. The granulation facility includes a granulator 21 and a roller feeder 22, and the firing facility includes a great furnace 1, a preheating chamber burner 8 as a kiln combustion exhaust gas temperature raising means, and a rotary kiln (hereinafter also simply referred to as “kiln”). 9 and the annunculus 11.

  The powdered granulated raw material M obtained by mixing auxiliary raw materials with iron ore as necessary is granulated into raw pellets GP by the granulator 21, and the powder is removed by the roller feeder 22. Supplied.

  The great furnace 1 is composed of a raw pellet GP laid on a pallet of the Great 2 by an endless traveling great (hereinafter simply referred to as “Great”) 2, a drying chamber 3, a water separation chamber 4, and a preheating chamber 5. While being moved in the longitudinal direction of each chamber in this order, drying and preheating are performed by downward ventilation of the heating gas described later. The water separation chamber 4 is installed when the iron ore contains crystal water.

  Reference numeral 6 denotes a preheating chamber wind box group. The space below Great 2 is partitioned into a plurality of rooms along the pellet movement direction, and these rooms are called wind boxes. In other words, the preheating chamber windbox group 6 is composed of a plurality of windboxes, and nine windboxes, for example, are arranged in a row along the longitudinal direction (pellet movement direction) with respect to the preheating chamber 5. ing. Reference numeral 7 denotes a preheating chamber suction fan, which has a fan damper (not shown) for adjusting the suction air volume (downward air flow), and is used for the high temperature kiln combustion exhaust gas used for pellet firing from the rotary kiln 9 described later. The heating gas is introduced into the preheating chamber 5, and the heating gas is sucked downward through the pellet layer on the pallet of the great 2 and the wind box group 6 and sent out into the next water separation chamber 4.

  The rotary kiln 9 is directly connected to the great furnace 1 and is a cylindrical rotary furnace with a gradient. The rotary kiln 9 is charged from the preheating chamber 5 of the great furnace 1 by combustion by the kiln burner 10 disposed on the outlet side. The dried and preheated pellets (hereinafter referred to as “preheated pellets”) are fired, and the high-temperature combustion exhaust gas used for firing the pellets is fed into the preheating chamber 5 as a heating gas. Fuel such as pulverized coal and coke oven gas is blown into the rotary kiln 9 by the kiln burner 10 and burned together with combustion air.

  The preheating chamber 5 is provided with a preheating chamber burner 8 as a kiln combustion exhaust gas temperature raising means for raising the temperature of the kiln combustion exhaust gas from the rotary kiln 9.

  A fuel such as pulverized coal or coke oven gas is used as the fuel for the preheating chamber burner 8, and the kiln combustion exhaust gas is heated by burning the fuel with residual oxygen in the kiln combustion exhaust gas in the preheating chamber 5. Yes. By doing so, the strength of the preheated pellets can be increased, and the occurrence of kiln rings in the rotary kiln 9 that causes unstable operation (the pelletized powder adhered to the brick wall surface of the kiln inner wall) is prevented. (See Patent Documents 1 to 3).

  Recently, a burner (water separation chamber burner) has also been installed in the water separation chamber 4 in order to promote the removal of crystal water from the raw pellet GP.

  Here, in order to increase the production of pellets, in the great furnace 1, the moving speed of the great 2 (hereinafter referred to as “the great speed”) is increased, or the height of the raw pellet GP stacked on the great 2 ( Hereinafter, it is necessary to increase the thickness (referred to as “pellet layer thickness”) (see, for example, Patent Document 4). However, when trying to increase production by increasing the pellet layer thickness, the pressure loss of the gas passing through the pellet layer increases. If it becomes stable, the load of the preheating chamber suction fan 7 etc. increases and the power consumption increases, or if the suction capacity of the fan 7 is insufficient, the suction capacity of the fan 7 needs to be increased. There is a problem that it takes extra. For this reason, the production rate is usually increased by increasing the great speed.

  However, if the great speed is simply increased for the purpose of increasing production (productivity improvement), the time for the raw pellet GP to pass through the drying chamber 3 and the water separation chamber 4 is shortened, so that the removal of crystal water from the raw pellet GP is insufficient. Thus, bursting occurs in the preheating chamber 5 and the air permeability in the pellet layer is deteriorated, the strength (crushing strength) of the preheated pellet is reduced and the powder rate is increased (see the result of the pot great test in FIG. 5). Therefore, it is necessary to take operational measures such as reducing the thickness of the pellet layer, and as a result, the purpose of improving productivity cannot be achieved.

  Therefore, in order to ensure the residence time of the raw pellet GP in the drying chamber 3 and the water separation chamber 4, a large facility modification such as extension of the length of the great furnace 1 is required, and the cost burden is large. Furthermore, such a large facility remodeling also has a problem that it is difficult to flexibly respond to changes in the raw material situation in the future, such as a tendency to further crystallize raw iron ore.

Further, as a means for compensating for insufficient removal of crystal water from the raw pellet GP when the great speed is increased, a means for increasing the gas temperature by increasing the capacity of the burner (water separation chamber burner) installed in the water separation chamber 4 can be considered. If the gas temperature is raised so that the crystal water can be sufficiently removed up to the raw pellet GP at the bottom of the pellet layer, the raw pellet GP at the top of the pellet layer is excessively heated, causing bursting in the water separation chamber 4. There was a problem such as.
Japanese Examined Patent Publication No. 7-116528 (page 2) JP 11-325740 A (paragraphs [0015] to [0019]) JP 2005-60762 A (paragraphs [0013] to [0018]) JP-A-62-20832 (page 4, line 5 from the bottom left column to line 4 from the top right column)

Accordingly, an object of the present invention is to provide stable productivity while suppressing or preventing the occurrence of bursting in the Great Furnace without requiring significant equipment modification in the Great Kiln type iron ore pellet manufacturing method. It is providing the particle size determination method of the granulation raw material at the time of manufacturing the iron ore pellet which can be improved.

  The present inventors considered that it is possible to increase the production of pellets without improving the facility by improving the air permeability of the pellet layer in the great furnace, and conducted the following examination.

  That is, the pressure loss ΔP of the pellet layer in the great furnace is expressed by the following Kozeny-Carman equation.

ΔP = (3C _f ) · [1 / (Φ · d _p )] · [(1−ε) / ε ³ ] · L · ρ · u ²

In the above formula, controllable factors that can reduce the pressure loss ΔP are the pellet average particle size d _p , the porosity ε of the pellet layer, and the pellet layer thickness L, but increasing the pellet average particle size d _p is a blast furnace. Since the standard is defined on the side, it is virtually impossible to change, and when the pellet layer thickness L is reduced, the productivity of the pellet is also reduced, so that the change is difficult. Therefore, the aim was to reduce the pressure loss ΔP of the pellet layer in the great furnace by increasing the porosity ε of the pellet layer. Specifically, by suppressing or preventing the mixing of powder into the pellet layer, the porosity ε of the pellet layer is increased, the pressure loss ΔP of the pellet layer is reduced, and the air permeability of the pellet layer is improved. Therefore, the problem of the present invention can be solved.

  Therefore, first, using a pot grate test apparatus (inner diameter: 300 mm, pellet layer thickness: 200 mm) simulating an actual great furnace, the raw pellets having an average particle diameter of 11.2 mm are averaged at a constant gas temperature and a constant suction pressure. The powder in the pellet layer affects the preheating pellet production time (time required to preheat to the lowest layer of the pellet layer) by conducting a preheating pellet production test on the powder having a particle size of 3 mm added with the addition amount being sequentially changed. The effect of rate is shown in FIG. As is clear from the figure, it can be seen that by reducing the powder rate in the pellet layer, the preheating pellet manufacturing time can be shortened, and the pellet productivity can be improved.

  The powder contained in the pellet layer in the actual great furnace was (1) pulverized in the conveying process until granulation and charging into the great furnace, and (2) pulverized by bursting in the great furnace. There are two main types.

  The amount of these two types of powder generated is closely related to the density of the raw pellets. The high density raw pellets are excellent in cold strength and less pulverized in the conveying process, but the amount of pores in the raw pellets Therefore, water vapor generated inside the raw pellets during the preheating process of the great furnace is difficult to escape to the outside, and bursting is likely to occur. On the other hand, raw pellets with low density have low strength in the cold, and pulverization in the conveying process increases, but since the amount of pores in the raw pellets is large, water vapor generated inside the raw pellets in the preheating process of the great furnace is Easy to pull out and less likely to burst.

  And it is known that the density of raw pellets can be controlled by the particle size of the granulated raw material. Therefore, in the actual pellet manufacturing equipment, the result of granulating raw pellets with different densities by changing the Blaine specific surface area (JIS R5201), which is usually used as an index of the particle size of the granulated raw material, and operating the great furnace Is shown in FIG.

As shown in FIG. 5A, when the specific surface area of the granulated raw material is gradually reduced from 3000 cm ² / g (that is, when the granulated raw material is coarsened), the pressure in the preheating chamber is increased. The loss (hereinafter abbreviated as “preheating chamber pressure loss”) decreases almost linearly at first, but shows a minimum value at a Blaine specific surface area of about 2750 cm ² / g, and then increases again almost linearly. It is done.

Further, as shown in FIG. 4B, when the specific surface area of the granulated raw material is gradually reduced from 3000 cm ² / g (that is, when the granulated raw material is coarsened), It can be seen that the drop resistance decreases almost linearly.

  Here, the drop resistance means that each of the 12 raw pellets randomly sampled from the granulated raw pellets is naturally dropped onto the iron plate from a position of 50 cm in height, and this is repeated until it breaks. This is defined by the average value (times / piece) of 10 raw pellets excluding those showing the maximum and minimum values.

In FIG. 2A, when the Blaine specific surface area of the granulated raw material is decreased from the larger side, the initial preheating chamber pressure loss is reduced because the granulated raw material becomes coarse and the density of the raw pellets is reduced. It is considered that the bursting in the Great Furnace was suppressed, and the preheating chamber pressure loss showed a minimum value and then increased again. The granulated raw material became too coarse and the density of the raw pellets decreased. As shown in the figure (b), it is considered that the drop resistance (strength) of the raw pellets decreased and the amount of pulverization increased in the transporting process to the great furnace.

  From the above results, it is possible to operate the great furnace in the vicinity where the preheating chamber pressure loss shows a minimum value by adjusting the particle size (brane specific surface area) of the granulated raw material. As a result, the pellet layer in the great furnace It is assumed that air permeability is improved and productivity is improved.

  As a result of further investigation based on the above findings, the present inventors have completed the following invention.

The invention according to claim 1 is a method in which raw pellets obtained by granulating a granulation raw material are charged into a great furnace and moved in a traveling great, heated in a drying chamber and a preheating chamber, and then the kiln burner is In the method for producing iron ore pellets of the great kiln method that is fired in the rotary kiln provided, the raw pellets charged into the great furnace, among the raw pellets obtained by granulating the granulated raw material, the average particle diameter In this case, the value of the pressure loss in the preheating chamber showing a minimum value (hereinafter referred to as “optimal brain specific surface area”) is preliminarily determined for the grain specific surface area of the granulated raw material. JP determined advance, in subsequent operations, as Blaine specific surface area of the granulated material is in the range of 0.95 to 1.05 times the optimum Blaine specific surface area, to determine the particle size of the granulated material A granulation particle size determination method of the raw material in the production of iron ore pellets to.

  According to the present invention, by adjusting the brane specific surface area of the granulated raw material so that the pressure loss in the preheating chamber is almost minimal (minimum), the bar in the great furnace can be increased even if the great speed is increased. The strength of the preheated pellets can be secured while suppressing or preventing the occurrence of sting, and the productivity of the pellets can be stably improved without the need for equipment modification.

  Hereinafter, an embodiment of the present invention will be described with reference to an example in which iron ore pellets are manufactured using the pellet manufacturing facility having the configuration shown in FIG.

  In the present embodiment, as the granulated raw material M, for example, a raw material A after pulverization obtained by pulverizing a coarse raw material a (including secondary raw materials such as limestone and dolomite in addition to iron ore) and originally fine granules. However, the case where a plurality of pellet feed brands (for example, three brands of B, C, and D) having different particle sizes (brain specific surface areas) are mixed and used will be described.

  The specific surface area of the granulated raw material M is that the degree of pulverization of the coarse raw material a, that is, changing the specific surface area of the raw material A after pulverization, and changing the blending ratio of the raw materials A to D, It can be easily adjusted by either alone or by appropriately combining the two. In addition, the Blaine specific surface area of the granulated raw material M can be calculated by a weighted average from the Blaine specific surface area of each raw material A to D and the blending ratio.

  And it operates using the granulation raw material M which changed the brain specific surface area variously by the said means beforehand, measured the preheating chamber pressure loss on each condition, and the granulation raw material as shown in FIG. The relationship between the B specific surface area of M and the preheating chamber pressure loss is determined.

  Next, an optimum brane specific surface area, which is the brane specific surface area of the granulated raw material M having a minimum value of the preheating chamber pressure loss, is obtained from the relationship between the specific surface area of the granulated raw material M and the preheating chamber pressure loss.

  In the subsequent operation, the granulated raw material M is operated by adjusting the particle size of the granulated raw material M so that the specific surface area of the granulated raw material M is in the vicinity of the optimal brane specific surface area.

  The vicinity of the optimum brain specific surface area is recommended to be in the range of 0.95 to 1.05 times the optimum brain specific surface area. If it is less than 0.95 times, the granulated raw material is too coarse and the density of the raw pellets is reduced, so that the bursting in the preheating chamber is suppressed, but the strength (drop resistance) of the raw pellets is reduced to the great furnace. It is because it becomes easy to be pulverized in the transporting process, the powder is brought into the great furnace 1, the porosity of the pellet layer is reduced, and the preheating chamber pressure loss is increased. On the other hand, if it exceeds 1.05 times, the density of raw pellets is increased because the granulated raw material is too fine, but the strength (drop resistance) of the raw pellets is increased and pulverization in the conveying step is suppressed, This is because powder tends to be generated by bursting in the preheating chamber, the porosity of the pellet layer is lowered, and the pressure loss in the preheating chamber is increased. A further recommended range in the vicinity of the optimum brain specific surface area is a range of 0.97 to 1.03 times, particularly 0.98 to 1.02 times the optimum brain surface area.

  As described above, in the subsequent operation, by adjusting the particle size of the granulated raw material M so that the brane specific surface area of the granulated raw material M is close to the optimum brane specific surface area, Both pulverization and pulverization by bursting in the preheating chamber 5 are suppressed, the void of the pellet layer in the preheating chamber 5 is secured, and the pressure loss in the preheating chamber is maintained almost minimal (minimum). High productivity operations.

[Modification]
In the said embodiment, although the example which adjusts only the Blaine specific surface area of the granulation raw material M was shown, 0.7 times the average particle diameter among the raw pellets GP obtained by granulating the granulation raw material M In the following, it is also possible to charge the great furnace 1 after removing the 0.75 times or less. Thereby, since the small particle | grains or powder which generate | occur | produced at the said conveyance process are reliably removed before charging into the great furnace 1, the fall of the porosity of the pellet layer in the great furnace 1 can further be suppressed, and this invention The effect of can be obtained more reliably. The raw pellet GP obtained by granulating the granulation raw material M can be easily removed by adjusting the roll gap of the roller feeder 22 installed immediately before the great furnace 1. It can be carried out.

  Moreover, although the said embodiment illustrated the case where the raw material A after the grinding | pulverization which grind | pulverized the coarse-grain raw material a with the grinder as a granulated raw material M, and mix | blends and uses a several fine-grain pellet feed brand name, pellet feed is illustrated. Is not necessarily limited to the case of using a plurality of brands, and can naturally be applied to the case of using only one brand, or the case of using only the raw material A after pulverization without using any pellet feed. Furthermore, the present invention can naturally be applied to the case of using only a plurality of pellet feed brands without using the raw material A after pulverization.

  As granulated raw materials, coarse raw materials (including secondary raw materials such as limestone and dolomite in addition to iron ore) are pulverized raw material A, and originally fine particles but grain size (Brain specific surface area) For the case of blending and using pellet feed 3 brands B, C, and D having different sizes, means for adjusting the Blaine specific surface area of the granulated raw material were studied.

Table 1 shows the results of adjusting the particle size (Brain specific surface area) of the granulated raw material by blending the above raw materials A to D. In the same table, with respect to the base conditions of case (a), cases (b) and (c) are cases where only the mixing ratio of raw materials A to D is changed, and case (d) is only the pulverized particle size of raw material A after pulverization Cases (e) and (f) were prepared by adjusting the pulverized particle size of the raw material A after pulverization and changing the blending ratio of the raw materials A to D. From the results shown in the same table, the specific surface area of the granulated raw material M is determined by adjusting (changing) the degree of pulverization of the coarse raw material a, that is, the specific surface area of the raw material A after pulverization, and It was confirmed that changing the blending ratio of D can be easily adjusted either alone or by appropriately combining the two (cases (c) to (e)).

  Therefore, in the pellet manufacturing facility having the configuration shown in FIG. 1, in order to increase the production from the conventional level, the results of operation with various adjustments of the granulation raw material particle size (Brain specific surface area) by the above means are shown in Table 2 and FIG. Shown in

In the table and the figure, in order to increase the level of productivity from about 11000 to 11500 t / day in periods 1 and 2 (conventional example) to about 12000 t / day, first, in period 3 (comparative example), the level of Blaine specific surface area of the particle material on changing from conventional about 3000 cm ² / g to about 2900 cm ² / g, tried to increase production by increasing the Great speed. However, during this period, the preheating chamber pressure loss increased remarkably, the preheating fan pre-temperature decreased significantly, and the operation became unstable. It is assumed that since the granulation raw material was not sufficiently coarsened, bursting occurred in the preheating chamber and the pressure loss in the preheating chamber was significantly increased. In addition, the temperature of the gas introduced into the water separation chamber decreases due to the decrease in the temperature before the preheating fan, and the removal of crystal water from the raw pellets in the water separation chamber becomes insufficient, and the raw pellets remain while the crystal moisture remains inside. As a result of being brought into the preheating chamber, it is assumed that bursting is further promoted, and that the amount of extra heat is required to dissociate the crystal moisture remaining in the raw pellets in the preheating chamber, resulting in a decrease in pre-heating fan temperature. Is done.

Therefore, in period 4 (invention example), the level of the Blaine specific surface area of the granulated raw material was further reduced to about 2800 cm ² / g to increase production. As a result, the pressure loss in the preheating chamber decreased and recovered to the level of the prior art (period 1), and the temperature before the preheating fan also increased and recovered to the level of the prior art (period 1), thereby stabilizing the operation. It is considered that the bursting in the preheating chamber was sufficiently suppressed by adjusting the Blaine specific surface area of the granulated raw material to be close to the optimum Blaine specific surface area (about 2750 cm ² / g).

Although the drop resistance (strength) of the raw pellets tends to be reduced by reducing the Blaine specific surface area of the granulated raw material, the roll gap of the roller feeder 22 installed just before the great furnace 1 is conventionally used. The removal efficiency of small pellets and powder generated in the transport process by changing from 8 mm (0.67 times the average particle size of raw pellets of 12 mm) to 9 mm (0.75 times the average particle size of raw pellets of 12 mm) It is considered that the effect of suppressing the bursting was sufficiently exhibited.

It is a flowchart which shows the outline of the pellet manufacturing equipment which concerns on embodiment. (A) is a graph which shows the relationship between the brane specific surface area of a granulated raw material, and a preheating chamber pressure loss, and (b) is a graph which shows the relationship between the brane specific surface area of a granulated raw material, and raw pellet fall resistance, respectively. It is a graph which shows transition of the operation result before and after application of this invention in a pellet manufacturing facility. It is a graph which shows the relationship between the powder rate in a pellet layer, and preheating pellet manufacturing time. It is a graph which shows the mode of the change of the crushing strength of a preheating pellet and the powder rate at the time of the production increase only by a great speed increase.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Great furnace 2 ... Traveling great 3 ... Drying room 4 ... Dewatering room 5 ... Preheating room 6 ... Preheating room wind box group 7 ... Preheating room suction fan 8 ... Preheating room burner 9 ... Rotary kiln 10 ... Kiln burner 11 ... Annula Laura 21 ... Granulator 22 ... Roller feeder a ... Coarse raw material A ... Raw material B, C, D after grinding ... Pellet feed M ... Granulated raw material GP ... Raw pellet

Claims (1)

A great kiln in which raw pellets obtained by granulating granulation raw materials are charged into a great furnace , moved in a traveling grate, heated in a drying chamber and a preheating chamber, and then fired in a rotary kiln equipped with a kiln burner. In the method of manufacturing iron ore pellets,
The raw pellets charged in the Great furnace, from among the raw pellets obtained by granulating the granulation raw material, those having an average particle size of 0.7 times or less removed,
In advance , the value of the pressure loss in the preheating chamber showing the minimum value (hereinafter referred to as “optimum brain specific surface area”) is obtained for the specific surface area of the granulated raw material.
The iron ore pellets characterized by determining the particle size of the granulated raw material so that the granulated raw material has a brane specific surface area in the range of 0.95 to 1.05 times the optimum brane specific surface area in subsequent operations. The particle size determination method of the granulation raw material at the time of manufacturing .

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