JP2010137118A - Grinding aid for coal and method for using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grinding aid for coal, which can allow the grinding efficiency of coal to be improved drastically and can contribute to further improvement of the combustion efficiency of a pulverized coal-fired boiler and to provide a method for using the grinding aid. <P>SOLUTION: The grinding aid contains fine silica (SiO<SB>2</SB>) having 4 nm to 20 μm average particle diameter, is preferably colloidal silica containing 1-50 mass% silica having 4-200 nm average particle diameter or is further preferably the colloidal silica which contains 1-50 mass% silica having 4-200 nm average particle diameter and to which a Li compound or the like is added. When coal is pulverized, the grinding aid is added to be 0.1-2.0 mass% in terms of SiO<SB>2</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technology for pulverizing coal supplied to a pulverized coal combustion boiler, and improves coal pulverization, improves the fineness of coal powder supplied to the boiler, and improves the combustion efficiency of the boiler. The present invention relates to coal pulverization aids that can be used and methods of using such pulverization aids.

Coal is now the main fuel for thermal power generation because of its large reserves and stable supply.
Currently, most coal-fired power generation facilities are pulverized coal fired boilers. In this pulverized coal combustion boiler, lump coal is pulverized into fine powder and burned by injecting it into a high-temperature boiler, which has good load compatibility, high combustion efficiency, and a wide range of coal types. It has become mainstream.

  However, since coal has a large amount of ash and contains sulfur, environmental measures such as NOx suppression measures and smoke treatment are required. Such environmental measures must be improved in terms of handling and pulverization of coal.

The above-mentioned pulverized coal combustion boiler is usually provided with a pulverized coal machine for pulverizing coal having a diameter of several centimeters into fine powder, and the coal pulverized by this pulverized coal machine has 200 mesh (aperture 75 μm). The content rate of the fine powder to pass will be about 80%.
In pulverized coal combustion boilers, it is known that the particle size of pulverized coal has a large effect on the combustion state, and generally, the smaller the particle size, the faster the burning out, and the lower the amount of NOx generated and the unburned content.

Therefore, conventionally, carbon black, higher fatty acids such as palmitic acid and stearic acid and their metal salts are added to and mixed with coal as a grinding aid to improve the coal grinding efficiency and increase the proportion of fine powder. Has been proposed (see Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 1-127057 Japanese Unexamined Patent Publication No. 1-127058

  However, none of the conventional pulverization aids described above necessarily have sufficient pulverization efficiency, and the coal is further pulverized to further increase the combustion efficiency of the pulverized coal combustion boiler. In order to further reduce the particle size, it has been desired to develop an auxiliary agent that can further improve the grinding efficiency.

  The present invention has been made in view of the above-mentioned problems in conventional coal pulverization technology, and the object of the present invention is to greatly improve the coal pulverization efficiency as compared with the prior art, and pulverized coal combustion. An object of the present invention is to provide a coal grinding aid that can contribute to further improvement in the combustion efficiency of a boiler, and a method of using such a grinding aid.

As a result of intensive investigations aimed at achieving the above object, the present inventors have found that silica having an average particle size of 4 nm to 20 μm has an effect of improving coal pulverization efficiency, and further uniformly distributes fine particle silica on coal. In order to obtain an effective effect when added, it has been found that a water dispersion is excellent. Among these aqueous dispersions of silica, the present inventors have found an excellent effect of improving coal pulverization efficiency particularly on colloidal silica containing silica (SiO ₂ ) particles having an average particle diameter of 4 to 200 nm, thereby completing the present invention. .

That is, the present invention is based on the above knowledge, and the coal pulverization aid of the present invention is a pulverization aid used for pulverization of coal having a particle size of 100 mm or less, and a powder having an average particle size of 4 nm to 20 μm. It is characterized by being silica. Moreover, it is the grinding | pulverization adjuvant used for the same coal, Comprising: It is the colloidal silica which preferably contains the water dispersion containing the silica with an average particle diameter of 4-200 nm, Preferably the said silica is 1-50%.
Furthermore, in the method of using the grinding aid of the present invention, when adding the grinding aid to coal, the auxiliary agent is added to the coal in a mass ratio of 0.1 to 2.0% in terms of SiO _2. It is characterized by adding so that.

  Since the coal grinding aid of the present invention contains very fine silica, such as colloidal silica, the coal grinding efficiency can be improved by adding and mixing this to the coal, The combustion efficiency of a pulverized coal combustion boiler using such finely pulverized coal can be improved.

Below, the grinding | pulverization adjuvant of the coal of this invention and the usage method of the said grinding | pulverization adjuvant are demonstrated further in detail and concretely.
In the present specification, “%” means mass percentage unless otherwise specified.

As mentioned above, pulverized coal combustion boilers pulverize lump coal into fine powders and inject them into a high-temperature boiler for combustion. It has become.
Bunkers are transported and stored as small pebbles from silos or yards. The coal is sent from the bunker to a coal feeder and weighed, and a certain amount of pulverized coal (mill) is attached to the boiler. ).

In a vertical mill generally used as a pulverized coal machine, coal is supplied onto a rotating table and is pulverized by being caught between pulverizing rollers. The pulverized coal is pumped by primary air to a pulverized coal burner. Combustion is pulverized coal combustion, in which fine powder is injected into a high-temperature field, and particles are combusted by ambient radiant heat.
In pulverized coal combustion of coal with improved fineness, that is, coal with an increased content of fine powder, the reaction with air (O ₂ ) becomes active and combustion efficiency is improved. Then, the boiler outlet O ₂ by improving the combustion efficiency is reduced and the combustion promoting effect is also reduced unburned fly ash is obtained.

In addition, the improvement of the fineness speeds up char burning out, which reduces the reducing atmosphere of the furnace and suppresses the apparent decrease in the clinker (coal ash) melting point that occurs in the reducing atmosphere.
Such a change in the atmosphere of the combustion field has an effect similar to load fluctuation and change of coal type (cleaning coal) on the clinker adhering to the furnace wall, and brings about a physical clinker peeling action.

In addition to this, the amount of SiO _{2 in} the coal is increased by using the grinding aid of the present invention. As a result, the silica percent of the coal increases and the B / A ratio (basicity), which is an index of slagging, decreases, so that the coal ash is reformed to a low clinker property.
B: Base alkaline component (Fe ₂ O ₃ + CaO + MgO + Na ₂ O + K ₂ O)
A: Acid acidic component (SiO ₂ + Al ₂ O ₃ + TiO ₂ )

  In the present invention, when pulverizing massive coal into fine powder, silica having an average particle diameter of 4 nm to 20 μm is used as a grinding aid. Coal pulverized using such a pulverization aid has improved fineness, and in a boiler that burns such pulverized coal, the effects of improving combustion efficiency and reducing unburned content as described above can be obtained. Furthermore, the effect of clinker peeling action can be obtained.

In the present invention, the silica fine particles adhere to the surface of the massive coal, thereby forming slight irregularities and exhibiting an anti-slip effect. Since coal contains oil, the resistance at the time of pulverization becomes small and it is difficult to pulverize, but the resistance is generated by silica and is easily pulverized.
As the coal is further pulverized into fine powder, the resistance value and vibration of the pulverized coal machine are reduced.

  The method for adding the silica particles is not particularly limited. For example, the coal before being pulverized in the particle state alone or mixed with other particles (for example, coal powder or a conventionally known auxiliary agent). Or can be added during grinding. Moreover, it can spray to coal beforehand in the state disperse | distributed in water or another solvent, or can be sprayed in the middle of the conveyance path to a pulverized coal machine.

The size of the silica particles used in the grinding aid of the present invention is in the range of 4 nm to 20 μm. That is, particles having an average particle size of less than 4 nm are difficult to obtain, while if it exceeds 20 μm, the particles are too coarse and resistance to crushing may increase.
In the present invention, the size (particle size) of the silica particles means an effective diameter measured by a laser diffraction scattering method.

In the pulverization aid of the present invention, further fine colloidal silica can be used as the silica (SiO ₂ ) particles, and the colloidal silica containing 1 to 50% by mass of silica having an average particle diameter of 4 to 200 nm is used as it is. It can be used as a grinding aid.
Since colloidal silica is fine particles, it tends to settle on coal after drying. Moreover, if the concentration is high, the number of particles increases and the anti-slip effect is excellent.

In addition, since the silica particle contained in colloidal silica is very fine, although the upper limit of the average particle diameter was 200 nm, since the number of particles increases, the finer one is desirable.
In addition, if the silica particle concentration of the colloidal silica is low, it is necessary to increase the amount of colloidal silica added to give the target amount of silica, and the amount of water transferred into the coal increases, and the time required for drying. Since energy is wasted, it should be 1% or more. On the other hand, 50% of the upper limit value is close to the limit value for producing colloidal silica.

In the grinding aid of the present invention, it is desirable that one or both of Na and K be contained in a mass ratio of 0.01 to 1% as the total amount of Na ₂ O and K ₂ O.
These alkali metals contribute to stable dispersion of the silica particles in the high-concentration colloidal silica, and are also expected to have an effect of improving the clinker suppressing action of the silica particles by being burned in the furnace together with the silica particles. However, when the content in the auxiliary agent is less than 0.1%, the effect of addition is not sufficiently observed. Conversely, when the content exceeds 1%, the amount of clinker adhesion may be increased instead. .

In general, colloidal silica contains about 0.3% of Na as an impurity in production, which contributes to the improvement of the dispersibility of silica particles. In order to further secure this effect. Alternatively, in order to improve the clinker suppressing action, Na and K can be added within a range not exceeding the upper limit.
In addition, it has been confirmed that there is almost no influence of alkali metals on the anti-slip action by the colloidal silica, that is, the action of improving the grindability of coal, and even if colloidal silica containing no Na is used, it has the same performance as a grinding aid. It is thought that it shows.

Also, by adding Li, it is possible to obtain the same effect as the Na or K, likewise, it may be added in a range of 0.01% to 1% as a Li ₂ O. It should be noted that Li can obtain a stabilizing effect in a slightly smaller amount than Na.
These alkali metals, Li, Na, and Ka can be added in the form of carbonate, hydroxide, or silicate.

When using the grinding aid of the present invention, it is desirable to add the aid so as to be 0.1 to 2.0% with respect to coal in terms of SiO ₂ contained therein.
That is, when the addition rate of SiO _{2 to} coal is less than 0.1%, the effect of improving the pulverization efficiency by adding the pulverization aid is hardly exhibited, and conversely even if added exceeding 2.0%, This is because the effect is saturated and no further efficiency improvement effect can be obtained.

By using the grinding aid of the present invention, the pulverization of coal is promoted, and the clinker stripping action is obtained as an incidental effect due to the increase of SiO _{2 in} coal ash. As described in.
Fig. 1 shows the results of an investigation of the characteristics of the coal used and the clinker adhesion in the boiler by visual observation by an experienced worker in a pulverized coal combustion boiler with an evaporation amount of 600 tons / h and a coal consumption of 60 tons / h. It is illustrated.

In other words, taking the SiO ₂ percent in coal on the horizontal axis and the total content (ppm) of Fe ₂ O ₃ and CaO on the vertical axis, “▲” indicates a large amount of clinker adhesion, and “●” indicates a small amount of clinker adhesion. As a result of plotting, it is understood that the amount of clinker adhesion is divided at a boundary between 8000 and 12000 ppm of (Fe ₂ O ₃ + CaO) in the coal, and it can be evaluated that coal of 8000 ppm or more can be evaluated as a poor coal with strong slagging properties. It was.
Incidentally, CaO and _Fe 2 _{O 3} content in the coal are those determined by the following equation.
CaO (ppm) = coal ash (%) x CaO in ash (%) x 100
Fe ₂ O ₃ (ppm) = Coal ash (%) × Fe ₂ O ₃ (%) in ash × 100
Further, the silica percent of abscissa is the percentage of the content of SiO ₂ with respect to _{SiO 2,} Fe ₂ O 3, CaO and the total content of MgO in the coal ash.
Silica percentage: SiO ₂ × 100 ÷ (SiO ₂ + Fe ₂ O ₃ + CaO + MgO)

For such coal with remarkable clinker adhesion, that is, coal having a total content of CaO and Fe ₂ O ₃ of 8000 ppm or more, the addition amount of the grinding aid of the present invention is increased, and the SiO ₂ equivalent is 0.00. It is effective to add to 4 to 2.0%, and in addition to improving the pulverization efficiency, it is possible to prevent and reduce clinker adhesion even in poor coal with strong slagging properties. It was found.

  Hereinafter, the present invention will be specifically described based on examples. Needless to say, the present invention is not limited to these examples.

(Example 1: grinding aid 1)
2% of silica powder with an average particle size of 10 μm was mixed with Australian charcoal sieved to a size of 1 to 4 mm, and then ground by a vibration mill and a crusher. After pulverization, a sample that became pulverized coal was taken out, and the particle size distribution was measured by sieving. The results are shown in Table 1 and FIG. 2 for the vibration mill and in Table 2 and FIG. 3 for the crusher, respectively.
The time required for grinding by the vibration mill and the grinder was 1 minute and 10 minutes, respectively.

(Example 2: grinding aid 2)
After mixing the aqueous dispersion containing silica having an average particle diameter of 10 μm to the Australian coal screened as described above so as to be 2.0% in terms of SiO ₂ , similarly using a vibration mill and a crusher. The particle size distribution of the pulverized coal obtained after pulverization was measured by the same method. The results are shown in Tables 1 and 2 and FIGS.

(Example 3: grinding aid 3)
The Australian coal screened as described above contains 40% silica with an average particle diameter of 18 nm, and colloidal silica containing 0.3% sodium as Na ₂ O is 0.4% in terms of SiO _2. Sprayed and dried at 105 ° C. This was similarly pulverized using a vibration mill and a crusher, and the particle size distribution of the obtained pulverized coal was measured by the same method. The results are shown in Tables 1 and 2 and FIGS.

(Example 4: grinding aid 4)
Grinding used in this example by adding lithium to 0.3% as LiO ₂ to colloidal silica containing 40% silica with an average particle size of 18 nm and 0.3% sodium as Na ₂ O An auxiliary was obtained.
And the Li containing colloidal silica adjusted in this way was sprayed evenly on the above Australian coal so that it might become 0.4% in terms of SiO ₂ and dried at 105 ° C. This was ground in the same manner using a vibration mill and a crusher, and the particle size distribution of the obtained pulverized coal was measured in the same manner. The results are shown in Tables 1 and 2 and FIGS.

(Example 5: grinding aid 5)
The colloidal silica containing 40% of silica having an average particle diameter of 18 nm and 0.3% of sodium as Na ₂ O is added so that potassium becomes 0.5% as K ₂ O, and pulverized for use in the examples. An auxiliary was used.
And the Ka containing colloidal silica adjusted in this way was sprayed evenly to the above-mentioned Australian coal so that it might become 0.4% in terms of SiO ₂ , and similarly dried at 105 ° C. This was similarly pulverized by a vibration mill and a crusher, and the particle size distribution of the obtained pulverized coal was measured by the same method. The results are shown in Tables 1 and 2 and FIGS.

(Comparative Example 1)
The Australian coal sieved to 1 to 4 mm was crushed in the same manner using a vibration mill and a crusher without any treatment, and the particle size distribution of the pulverized coal was measured in the same manner. The results are shown in Tables 1 and 2 and FIGS.

(Comparative Example 2)
After mixing 1% of No. 7 silica sand with an average particle size of about 0.1mm to the above-listed Australian coal, it was pulverized in the same way with a vibration mill and a crusher, and the particle size distribution of the pulverized coal after pulverization was measured in the same way. did. The results are shown in Tables 1 and 2 and FIGS.

  As apparent from Table 1 and FIG. 2, in the pulverization by the vibration mill, fine powders of 75 μm or less account for nearly 90%. However, in Examples 1 to 5 of the present invention in which fine powder silica, an aqueous dispersion of silica, colloidal silica, and further added Li or K as an auxiliary agent were pulverized without any treatment. It was confirmed that the amount of fine powder of 45 μm or less was significantly increased as compared with Comparative Example 1 and Comparative Example 2 using coarse silica sand. And among these, it was confirmed that the form of the aqueous dispersion and the colloidal silica can obtain better results as a grinding aid than the case where silica is used as a powder.

  Moreover, although the grinding | pulverization result inferior to a vibration mill in the grinding | pulverization result shown in Table 2 and FIG. 3 compared with a vibration mill, the Example of this invention using silica powder, the aqueous dispersion of silica, and colloidal silica In 1-5, the fine powder of 75 micrometers or less exceeded 70%, and the fine powder of 150 micrometers or less occupied about 90%. Among these, silica was better in the aqueous dispersion and colloidal silica than the powder. On the other hand, in Comparative Examples 1 and 2, the occupancy ratios were about 50% and 60%, respectively.

(Example 6: Grinding aid 6)
Grinding used in the examples by adding lithium to 0.3% as LiO ₂ to colloidal silica containing 20% silica with an average particle size of 10 nm and 0.3% sodium as Na ₂ O An auxiliary was obtained.
Then, the Australian coal was sieved this Li-containing colloidal silica to the size of 1 to 4 mm, evenly sprayed so that 0.4% in terms of SiO _2, and dried at 105 ° C.. This was similarly pulverized using a crusher, and the particle size distribution of the obtained pulverized coal was measured in the same manner. The results are shown in Table 3 and FIG. In these tables and figures, the data of Example 3 (grinding aid 3: silica particle size 18 nm) and Comparative Examples 1 and 2 are also shown for comparison.

(Example 7: grinding aid 7)
The particle size distribution of pulverized coal obtained by repeating the same operation as in Example 6 was measured in the same manner except that colloidal silica containing 40% of silica having an average particle size of 50 nm was used. The results are also shown in Table 3 and FIG.

(Example 8: Grinding aid 8)
The particle size distribution of pulverized coal obtained by repeating the same operation as in Example 6 was measured in the same manner except that colloidal silica containing 40% of silica having an average particle size of 100 nm was used. The results are also shown in Table 3 and FIG.

  As a result, when the average particle diameter of the silica becomes coarse, the occupancy ratio of the fine powder does not tend to be slightly lower, but compared with Comparative Example 1 that does not use an auxiliary agent and Comparative Example 2 that uses coarse silica sand. It was confirmed that the fineness was greatly improved.

Example 9
The pulverizing coal of the present invention is added to the pulverized coal machine of the pulverized coal combustion boiler that is operating without using the pulverizing aid together with the coal. From the measured data of the current value and vibration width of the pulverized coal machine during the charging time, The effect of grinding aid on the charcoal machine was investigated.
That is, to the pulverized coal machine of the pulverized coal combustion boiler with the evaporation amount of 70 ton / h and the coal use amount of 6.5 ton / h, the same colloidal silica as in Example 3 (grinding aid 3: silica average particle size 18 nm, silica 40% content and 0.3% Na ₂ O equivalent content) were added together with the coal. The input amount of colloidal silica at this time was set to 0.4% in terms of the SiO ₂ conversion mass ratio with respect to coal.

As a result, in the charging time zone of the pulverization aid, the current value of the pulverized coal machine is reduced from 21A before being charged to 20.5A, and the vibration width of the pulverized coal machine is also reduced from 29 μm to 25 μm. It was confirmed that the load during the operation of the pulverized coal machine was reduced by the addition of the grinding aid.
Regarding the fineness of the coal powder after being pulverized by the pulverized coal machine, the proportion of fine powder passing through the opening of 45 μm is increased from 42% before introduction to 60% during the introduction time of the grinding aid. Was confirmed.

(Example 10)
The pulverizing coal of the present invention is charged together with the coal into the pulverized coal machine of the operating pulverized coal combustion boiler without using the pulverizing aid, the outlet oxygen concentration of the boiler before and after the charging is measured, and the pulverization given to the combustion status of the boiler The effect of auxiliaries was investigated.
That is, the same pulverized coal machine of a pulverized coal combustion boiler with an evaporation amount of 600 ton / h and a coal use amount of 60 ton / h is used as a pulverization aid with the same colloidal silica (pulverization aid 3) as in Example 3 together with coal. The SiO ₂ ratio was added.

As a result, the oxygen concentration at the boiler outlet decreased from 3.0% to 1.2% with the introduction of the grinding aid. In the boiler, the system was controlled so that the outlet oxygen concentration was 3.0%, and thus increased to 3.0% over time. However, when the charging of the grinding aid was stopped, the outlet oxygen concentration was increased. The concentration rose to around 4.0%.
At this time, for the pulverized stone coal, the proportion of fine powder passing through the opening of 45 μm increased from 55% before the addition to 68% by the addition of the pulverization aid, and the fineness was increased by the pulverization aid of the present invention. As a result, it is considered that pulverized coal combustion was promoted and oxygen was consumed much.

  For comparison, the same amount of water as the above colloidal silica was added together with the coal, and the same investigation was conducted, but some changes were observed in the particle size composition of the pulverized coal and the oxygen concentration at the boiler outlet. I couldn't.

(Example 11)
The total content of CaO and Fe ₂ O ₃ using the above-mentioned grinding aids 3 and 4 by a pulverized coal machine attached to a pulverized coal combustion boiler with an evaporation amount of 600 ton / h and a coal consumption of 60 ton / h, respectively. Were pulverized four types of coal, respectively 6000 ppm, 8000 ppm, 12000 ppm, and 16000 ppm, and compared with the fineness when pulverized by adding only the same amount of water. Table 4 shows the results of the fineness of the pulverized coal powder as the ratio of fine powder that passed through a 45 μm opening.

In addition, the addition amount of colloidal silica at this time is 1% with respect to coal, respectively, and becomes 0.4% in SiO ₂ conversion mass ratio.

  From the results of Table 4, in any coal powder, the fineness is improved by using the grinding aids 3 and 4 of the present invention compared to the case where the grinding aid is not used (only water). It was confirmed.

  Next, each of the above coals is put into operation in the above-mentioned pulverized coal combustion boiler without using a pulverization aid, and each coal powder pulverized with each pulverization aid is injected and burned. Changes in clinker adhesion status were investigated by visual inspection of experienced workers. The results are shown in Table 5.

As shown in Table 5, by using a grinding aid of the present invention, as compared with the case of not using the grinding aid, the amount of deposition of clinker is reduced, especially adhesion of clinker marked CaO and Fe ₂ It was confirmed that a reduction effect by the grinding aid can be obtained in coal having a large O ₃ content.
That is, in coal with a total content of CaO and Fe ₂ O ₃ of 6000 ppm, as shown above (see FIG. 1), the slugging property is low, so even if the grinding aid of the present invention is used, it is used. Compared to before, there was not much change in the clinker adhesion.

On the other hand, in the coal having a CaO + Fe ₂ O ₃ content of 8000 ppm, the adhesion of clinker is recognized, and in particular, in the coal containing 12000 ppm or more of CaO + Fe ₂ O ₃ , a large amount of clinker adheres in the furnace to 16000 ppm or more. Then, the enlarged clinker was attached.
When a pulverization aid was used for such coal, the amount of clinker attached was reduced and slagging was suppressed in coal with CaO + Fe ₂ O ₃ of 8000 ppm due to the effect of improving pulverization. In addition, it was confirmed that the amount of clinker attached in the entire furnace decreased when the coal burned with 12,000 ppm of CaO + Fe ₂ O _{3, which} had a large amount of clinker attached in the furnace. In coal with 16,000 ppm of CaO + Fe ₂ O ₃ in which adhesion of enlarged clinker was observed, the use of a grinding aid gradually peels off the fist-sized lump from the surface of the enlarged clinker, and the clinker becomes smaller The situation was confirmed.

  Further, the grinding aid obtained by adding Li to colloidal silica has a clinker-inhibiting action similar to that of colloidal silica alone, and further, an action of promoting the clinker peeling effect was observed.

Is a graph showing the effect of _Fe 2 _O 3 + CaO content on the clinker deposition amount in the boiler. It is a graph which shows the particle size distribution of the coal grind | pulverized by the vibration mill using the grinding aids 1-5 by this invention compared with the case where coarse grained silica sand is used when an adjuvant is not used. It is a graph which shows the particle size distribution of the coal grind | pulverized by the crusher using the grinding | pulverization adjuvants 1-5 by this invention compared with the case where coarse grained sand is used when an adjuvant is not used. It is a graph which shows the particle size distribution of the coal grind | pulverized with the crusher using the grinding | pulverization auxiliary | assistance 4 and 6-8 by this invention compared with the case where coarse grained sand is used when an adjuvant is not used.

Claims (7)

  A coal pulverization aid used for pulverization of coal having a particle size of 100 mm or less, which is silica of powder having an average particle size of 4 nm to 20 μm.   A coal pulverization aid used for pulverization of coal having a particle size of 100 mm or less, wherein the coal pulverization aid is an aqueous dispersion containing silica having an average particle size of 4 nm to 20 µm.   A coal pulverization aid used for pulverization of coal having a particle size of 100 mm or less, which is colloidal silica containing 1 to 50% by mass of silica having an average particle size of 4 to 200 nm. . Grinding aid according to claim 2 or 3, characterized in that the Na and / or K containing 0.01% to 1% by total weight ratio of Na ₂ O and _{K 2} O. The pulverization aid according to any one of claims 2 to 4, wherein Li is contained as Li ₂ O in a mass ratio of 0.01 to 1%. When the grinding aid according to any one of claims 1 to 5 is added to coal, the aid becomes a mass ratio of 0.1 to 2.0% in terms of SiO _{2 with} respect to coal. A method of using a grinding aid characterized by being added as described above. When the total content of CaO and Fe ₂ O _{3 in} coal is 8000 ppm or more, the grinding aid is made to have a mass ratio of 0.4 to 2.0% in terms of SiO _{2 with} respect to coal. The method for using a grinding aid according to claim 6, wherein the grinding aid is added.

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