JP5286635B2 - Method for producing pulverized coal - Google Patents

Description

  The present invention relates to a pulverized coal production facility and method, and more particularly to pulverized coal suitable for blowing as a reducing material from a blast furnace tuyere.

  In blast furnace operation, coke is used as a reducing material for iron ore. As an auxiliary reducing material that partially replaces this coke, pulverized coal is used, and pulverized coal injection operation is performed in which pulverized coal is injected from a blast furnace tuyere. The operation of injecting pulverized coal into the blast furnace provides a significant cost reduction effect because pulverized coal is less expensive than blast furnace coke. In addition, by increasing the amount of pulverized coal injected into the blast furnace, it is possible to reduce the load on the coke oven, which is a blast furnace coke manufacturing facility, and contribute to the extension of the life of the coke oven. There is also a problem of depletion of high-quality coking coal, which is a raw material for coke for blast furnace, and a large amount of pulverized coal is blown in blast furnace operation, which greatly contributes to rationalization in hot metal production.

  In such a pulverized coal injection into the blast furnace, usually, the pulverized coal is air-flowed to the pulverized coal injecting device provided on the blast furnace side through the piping system from the pulverized coal production facility by the carrier gas, Next, gas is transported from the pulverized coal blowing device to the vicinity of the tuyere provided on the blast furnace lower furnace wall, pulverized coal is injected into the hot air stream and blown from the tuyere into the blast furnace furnace under appropriate blowing conditions, Burn.

  As the particle size of the pulverized coal increases, the combustibility in the tuyere deteriorates. On the other hand, if the particle size is too small, the transportability up to blowing deteriorates and piping clogging occurs. For example, if the particle size of pulverized coal is 90 mass% or more when the particle size is 44 μm or less, the transportability deteriorates. Therefore, it is necessary to control the pulverized coal used for blowing so as to have an appropriate particle size distribution. Normally, the target particle size is set to 75 to 80 mass% for 74 μm or less, and the pulverized coal particle size is changed by changing the pressing force during pulverization with a pulverizer such as a roller mill according to the hardness of the raw coal. To have a particle size distribution of

  On the other hand, various brands with different properties exist in coal, and each brand has a different hardness. In normal operations, pulverized coal is produced by mixing multiple brands of coal, but only brands of coal in a range where the target particle size can be obtained with the pulverizer used are used. A brand having the same degree of hardness is used.

However, in recent years, it has been difficult to use only the same brand of coal for a long period of time due to the balance of supply and demand due to the increase in global coal consumption. It is desirable to be able to produce pulverized coal using various brands of coal. As a method that can be used even when multiple types of coal with different properties are used, the coal grindability is used as a parameter to adjust the grinding force when grinding the coal and to control the particle size distribution of the pulverized coal blown into the furnace A method for producing pulverized coal is known (see, for example, Patent Document 1). As the grindability, a hard glove grindability index (HGI) can be used. HGI represents the hardness of coal, and the larger the value, the softer.
JP 2002-194408 A

  The method described in Patent Document 1 is a method in which optimum pulverization is performed for each brand, and when a plurality of brands are used, a product pulverized for each brand is mixed after pulverization. Although it is desirable to pulverize by brand of coal, one brand may be insufficient for the amount of pulverization at one time, and if the brand of coal is changed frequently, productivity will decrease. . In addition, in order to average the properties of the pulverized coal to be blown, it is preferable to use a mixture of multiple brands of coal. However, in order to mix them efficiently after pulverization, a large number of pulverizers are necessary and costly. It is.

  On the other hand, if coal having greatly different hardnesses is pulverized at the same time, there is a problem that a target particle size distribution cannot be obtained. As shown in FIG. 3, the particle size distribution when two brands of coal having greatly different hardnesses are simultaneously pulverized has a wider particle size distribution than that of a single brand, and the transportability is deteriorated. This is because, when mixing hard and soft coal and crushing, if the pressing force of the crushing roller is set according to the hard coal, the soft coal will be over-pulverized, and the pressing force of the crushing roller will be adjusted according to the soft coal This is because hard coal is not sufficiently pulverized. If the soft coal is over-pulverized, the fluidity of the pulverized coal is deteriorated, and if the hard coal is not sufficiently pulverized, the combustibility of the pulverized coal at the tuyere is deteriorated. Therefore, it is difficult to produce pulverized coal for blast furnace injection by simultaneously pulverizing coals having greatly different hardnesses.

  Therefore, the object of the present invention is to solve such problems of the prior art and to produce pulverized coal that can produce pulverized coal having a particle size distribution suitable for blast furnace blowing even when pulverizing different hardness coals simultaneously. It is to provide equipment and a manufacturing method.

As a result of repeated experiments and studies to solve the above problems, the present inventors have found the following surprising facts. That is, in the past, it was difficult to obtain an appropriate particle size distribution for target blowing even when coals having different hardnesses were pulverized by the same pulverizer, but the coals having different hardnesses were sufficiently mixed in advance. By setting appropriate pulverization conditions, it is possible to obtain a target particle size distribution. The present invention has been made based on such findings, and the features thereof are as follows.
(1) From a plurality of coal hoppers, a belt conveyor that conveys coal discharged from the coal hopper, a first blending hopper that stores coal transported by the belt conveyor, and the first blending hopper Using a facility having a second blending hopper for storing discharged coal and a pulverizer for pulverizing the coal discharged from the second blending hopper, a plurality of brands of different hardness are mixed. And pulverizing after mixing so that the time fluctuation of the HGI of the mixed coal is within ± 5%.
(2) The method for producing pulverized coal according to (1), wherein pulverization is performed with a pulverization force set according to an average HGI determined as a mass average according to a mixing ratio of the plural brands of coal.
(3) The fine powder according to (1) or (2) , wherein a second belt conveyor for conveying coal is installed between the first blending hopper and the second blending hopper. Charcoal manufacturing method.

  According to the present invention, even if pulverized coals having different hardnesses are pulverized by the same pulverizer, pulverized coal having an appropriate particle size distribution for target blast furnace blowing can be obtained. For this reason, it becomes possible to use the coal of the hardness which was difficult to use conventionally as a pulverized coal raw material. Moreover, it is possible to produce pulverized coal in which plural brands of coal are mixed at low cost. Moreover, since it is not necessary to mix pulverized coal after manufacture, the risk of ignition is reduced and pulverized coal can be manufactured safely.

  First, a conventional pulverized coal production facility will be described with reference to FIG. A conventional pulverized coal production facility includes a plurality of coal hoppers 2, a belt conveyor 4 that conveys coal cut out from the coal hopper 2, a blending hopper 5 that stores coal transported by the belt conveyor 4, and the blending hopper 5 And a pulverizer 8 for pulverizing the coal cut out from the coal. In the manufacture of pulverized coal, the coal stocked in the yard 1 is stored in the coal hopper 2, the coal stored in the plurality of coal hoppers 2 is cut out on the common belt conveyor 4 by the feeder 3, The coal is stored and supplied from the blended hopper 5 to a pulverizer for pulverization.

  By classifying the coal hopper 2 according to the brand of coal (coal type), supplying and mixing each brand of coal at a predetermined ratio and pulverizing, the particle size distribution of the pulverized coal after pulverization can be adjusted. When using different coal, it is difficult to make it within a predetermined particle size distribution range (for example, 74 μm or less is 75 to 80 mass%). In the present invention, a blending hopper is added to the conventional equipment in order to sufficiently mix the coal before pulverization. One embodiment of the pulverized coal production facility of the present invention is shown in FIG. Since the pulverized coal production facility is smaller than the blast furnace charging raw material production facility, the facility can be easily changed and the cost is relatively low, so the present invention can be carried out relatively easily. it can.

  In FIG. 1, the pulverized coal production facility includes a plurality of coal hoppers 2, a belt conveyor 4 that conveys coal cut out from the coal hopper 2, and a first blending hopper 5 that stores coal conveyed by the belt conveyor 4. And a second blending hopper 7 installed on the downstream side of the first blending hopper 5 and a pulverizer 8 for pulverizing the coal cut out from the second blending hopper 7. It is preferable to install the 2nd belt conveyor 6 which conveys coal between the 1st mixing | blending hopper 5 and the 2nd mixing | blending hopper 7. As shown in FIG.

  A method for producing pulverized coal using the equipment shown in FIG. 1 will be described. Coal stocked in the yard 1 is stored in the coal hopper 2 according to brands, and the coal stored in the plurality of coal hoppers 2 is cut out at a predetermined rate on the common belt conveyor 4 by the feeder 3 and discharged repeatedly. A multilayer structure of different kinds of coal is formed on the belt conveyor 4. When this coal is charged into the first blending hopper 5, the coal is still segregated by brand in the hopper. The coal stored in the first blending hopper 5 is mixed to some extent when it is cut out. Coal cut out from the first blending hopper 5 is conveyed by the belt conveyor 6 and charged into the second blending hopper 7. The coal is further mixed when discharged from the second blending hopper 7 and supplied to the pulverizer 8 in a sufficiently mixed state to be pulverized.

  As described above, by providing two or more hoppers that store a plurality of brands (varieties) of coal in a mixed state until the pulverization step, different brands of coal can be sufficiently mixed automatically. When conventional equipment is used, coal is not sufficiently mixed, and the average hardness (HGI) of the coal to be pulverized fluctuates with time. When the coal is sufficiently mixed using the pulverized coal production facility of the present invention, it becomes possible to treat coal as an average brand using the average HGI mass-averaged at the blending ratio of each brand of coal, and the average By performing pulverization using pulverization conditions suitable for specific hardness, pulverized coal having a particle size distribution suitable for target blast furnace blowing can be produced. As pulverization conditions, the pressure applied during pulverization may be adjusted as in the conventional case.

  It is preferable to mix the coal before pulverization until the average HGI time fluctuation is within ± 5%. When the hopper before the coal pulverization process is a single stage, the average HGI time fluctuation was about ± 15%, and mixing was not sufficient, but by providing two or more hoppers, the average The time variation of HGI can be reduced to within ± 5%.

  The pulverized coal produced using the pulverized coal production facility and production method of the present invention may be blown into the blast furnace using the same method as usual. In FIG. 1, the produced pulverized coal is conveyed by gas through a main pipe 10 to a pulverized coal blowing device 11. The pulverized coal conveyed to the pulverized coal blowing device 11 is supplied to the distributor 12 by air feeding, and further distributed to the many tuyere 15 parts below the blast furnace 14 from the distributor 12 through a plurality of branch pipes 13. Pulverized coal is injected from the nozzle 19 into the hot air 18 supplied from the hot air furnace 16 to the blow pipe 17 at each tuyere 15 part, and pulverized coal is blown from each tuyere 15 together with the hot air and burned. The pulverized coal adjusted to a predetermined particle size is blown from the tuyere without causing clogging in piping or the like, and has good combustibility.

  Using the same equipment as shown in FIG. 4, pulverized coal was produced. The pulverization was performed using a roller mill that presses a plurality of rollers against a horizontally rotating table and finely pulverizes the raw material by compressive force or shear force. Roller with 50% HGI as raw material coal (low HGI charcoal) and 70% by mass of 75% HGI coal (high HGI charcoal) and calculated from average HGI A pulverized coal was produced by pulverizing the pressing force of the mill roller at 2.5 MPa, and the fluidity was measured to obtain a comparative example. The fluidity was evaluated by the transport time of a specific section when transporting gas (nitrogen) to the pulverized coal blowing apparatus.

  The particle size distribution in the case of the comparative example is the average particle size of 20 to 30 μm, and the difference between the particle size at the position where the cumulative volume ratio is 10% and the particle size at the position of 90% is divided by the particle size at the position of 50%. The index (hereinafter referred to as “index S”) was 3.7 to 4.0. The index S is an index indicating the spread of the particle size distribution, and the larger the value, the wider the particle size distribution.

  Next, pulverized coal was produced using the same equipment as shown in FIG. The roller mill is of the same type as above, and has the same composition as the coal described above (high HGI coal blending ratio is 70% by mass), and pulverization conditions (coal feed amount: 50 t / h, roller mill pressure) : 2.5 MPa) was pulverized in the same manner, and the particle size distribution and fluidity were evaluated to obtain an example of the present invention.

  The particle size distribution of the pulverized coal of the present invention example had an average particle size of 20 to 30 μm, but the value of the index S indicating the distribution spread was 2.1 to 2.3, and the spread of the distribution was suppressed.

  The fluidity measurement results of the inventive example and the comparative example are also shown in FIG. As shown in FIG. 2, in the example of this invention, it turns out that the transport time of pulverized coal becomes short and fluidity | liquidity is improved.

1 is a schematic view of pulverized coal production equipment and blowing equipment showing an embodiment of the present invention. The graph which shows the change of the fluidity | liquidity of pulverized coal. The graph which shows the comparison of the particle size distribution at the time of single brand and two brand mixed grinding. Schematic of conventional pulverized coal production equipment and blowing equipment.

Explanation of symbols

1 Yard 2 Coal Hopper 3 Feeder 4 Belt Conveyor 5 (First) Compounding Hopper 6 Second Belt Conveyor 7 Second Compounding Hopper 8 Crusher 10 Main Pipe 11 Pulverized Coal Injector 12 Distributor 13 Branch Pipe 14 Blast Furnace 15 Tuyere 16 hot blast furnace 17 blow pipe 18 hot blast 19 blow nozzle

Claims (3)

Multiple coal hoppers,
A belt conveyor for conveying coal discharged from the coal hopper;
A first blending hopper for storing coal conveyed by the belt conveyor;
A second blending hopper for storing coal discharged from the first blending hopper;
Using the facilities having a pulverizer for pulverizing the coal discharged from said second compounding hopper, a,
Multiple brands of coal with different hardness are stored in each of multiple coal hoppers by brand,
From the plurality of coal hoppers, the plurality of brands of coal are cut out on the belt conveyor to form a multilayer structure of different kinds of coal on the belt conveyor,
The coal conveyed by the belt conveyor is fed to the first blending hopper, mixed by discharging from the first blending hopper, and the mixed coal is fed to the second blending hopper. further mixed by discharging from the second compounding hopper, as time variation of HGI of mixed together coal is within 5% ±,
Next, the mixed coal is supplied to the pulverizer and pulverized to pulverize the coal. The method for producing pulverized coal according to claim 1, wherein the pulverized coal is pulverized with a pulverization force set according to an average HGI determined as a mass average according to a mixing ratio of the plural brands of coal. The method for producing pulverized coal according to claim 1 or 2, wherein a second belt conveyor for conveying coal is installed between the first blending hopper and the second blending hopper.

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