JPS6259759B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chemical deashing treatment apparatus for coal that is applied to produce deashed coal that can be transported or burned smoothly.

As is well known, in recent years there has been concern about the outlook for oil supply,
Due to the soaring prices of coal, the necessity of diversifying energy sources has been advocated, and coal has been chosen as the first candidate for its replacement, and efforts are being made to promote its effective use. Coal has been used as a major energy source since ancient times, but was replaced by the advent of oil. The main reason for this is that petroleum has become cheap and available in large quantities, but it also stems from the fact that coal is solid and contains ash, which has little utility value. That is, since it is a solid, it is very difficult to transport, and transportation costs are high. The presence of ash in coal reduces its energy density, which alone makes it a less efficient energy source than oil without ash. Furthermore, since ash is directly emitted when coal is burned, it costs a lot of money to dispose of it at thermal power plants, which have recently become larger. Although it is not strictly limited to inorganic substances, there is also the problem of sulfur content. That is,
These sulfur components generate sulfur oxides upon combustion, and are of great concern from the viewpoint of environmental pollution. Currently, Japan relies on foreign coal for a considerable amount of its coal demand, but the ash content in coal ranges from a few percent to several tens of percent, usually 10 to 20 percent, and this ash content is not being used effectively. In the end, 10 to 20% of transportation costs are wasted. As described above, the problem of the ash content of coal is extremely important for the effective use of coal, and if the ash content of coal can be effectively removed, the economic effects will be immeasurable.

In addition, as coal is solid as mentioned above, it costs a lot of money to transport it, but in order to reduce costs, there are ways to reduce the cost by pulverizing coal and transporting it pneumatically, or by making it into water slurry or oil slurry. A method of transporting it as a fluid is being considered. Furthermore, when it comes to large-scale coal combustion boilers, pulverized coal combustion boilers are almost always used, and such boilers generally use coal that has been pulverized to about 80% less than 200 mesh.

Now, regarding the conventional method of removing ash from coal, that is, the deashing method, it must be said that although this is being considered, there is currently no truly effective method. The ultimate technology for deashing would be coal liquefaction technology, but this is still considered a technology of the future. A relatively effective method is oil agglomeration, in which pulverized coal is suspended and stirred in a mixture of water and oil, only the coal particles are agglomerated in an oil layer, and the ash is separated into a water layer. There is also an old method of treating coal with alkali at high temperature and pressure. Also, very recently, a method of treatment with hydrogen fluoride gas has been proposed (Unexamined Japanese Patent Publication No.
55-133487), but none of them can be said to be completely practical. In other words, an effective deashing method has not yet appeared in the world.

Prior to filing this patent application, the present inventors proposed a chemical method for treating coal with a solution of fluoride added to hydrochloric acid or citric acid aqueous solution as a deashing method (Japanese Unexamined Patent Publication No. 151698/1983). and JP-A-57-
(See Publication No. 162791). As the fluoride, acidic ammonium fluoride, ammonium fluoride, acidic sodium fluoride, sodium fluoride, acidic potassium fluoride, and potassium fluoride are effective, and acidic ammonium fluoride is particularly effective. When using acidic ammonium fluoride as the fluoride, 1 to 10% by weight of hydrochloric acid and 1.25 to 10% by weight of acidic ammonium fluoride (NH ₄ HF ₂ ), as described in the previously proposed application specification; or 1-10% by weight of citric acid and 1-10% by weight of acidic ammonium fluoride
Using an aqueous solution containing % by weight. The previously proposed method is a so-called wet method based on an aqueous solution reaction, does not generate harmful hydrogen fluoride gas, and has a deashing effect even at room temperature.

Here, we will discuss the pulverization method.As is well known, there are an infinite number of pulverization methods. That is, there are various types of mills, from crushers that are coarse crushers to various types of mills that are fine crushers, and these crushers are currently used depending on the purpose. There are various cases in the case of pneumatic transportation as described above, transportation as a pseudo fluid such as water slurry or oil slurry, but the coal particles are about 100 mesh or less, and in the case of combustion, they cannot be contained. In general, the boiler is 80% less than 200 mesh.
Fairly pulverized coal is used.

Now, regarding the conventional method of removing ash from coal, that is, the deashing method, it must be said that although this is being considered, there is currently no truly effective method. The ultimate technology for deashing would be coal liquefaction technology, but this is still considered a technology of the future. A relatively effective method is oil agglomeration, in which pulverized coal is suspended and stirred in a mixture of water and oil, only the coal particles are agglomerated in an oil layer, and the ash is separated into a water layer. There is also an old method of treating coal with alkali at high temperature and pressure. Also, very recently, a method of treatment with hydrogen fluoride gas has been proposed (Unexamined Japanese Patent Publication No.
55-133487), but none of them can be said to be completely practical. In other words, an effective deashing method has not yet appeared in the world.

Prior to filing this patent application, the present inventors proposed a chemical method for treating coal with a solution of fluoride added to hydrochloric acid or citric acid aqueous solution as a deashing method (Japanese Unexamined Patent Publication No. 151698/1983). and JP-A-57-
(See Publication No. 162791). As the fluoride, acidic ammonium fluoride, ammonium fluoride, acidic sodium fluoride, sodium fluoride, acidic potassium fluoride, and potassium fluoride are effective, and acidic ammonium fluoride is particularly effective. When using acidic ammonium fluoride as the fluoride, 1 to 10% by weight of hydrochloric acid and 1.25 to 10% by weight of acidic ammonium fluoride (NH ₄ HF ₂ ), as described in the previously proposed application specification; or 1-10% by weight of citric acid and 1-10% by weight of acidic ammonium fluoride
Using an aqueous solution containing % by weight. The previously proposed method is a so-called wet method based on an aqueous solution reaction, does not generate harmful hydrogen fluoride gas, and has a deashing effect even at room temperature.

Here, we will discuss the pulverization method. As is well known, there are an infinite number of pulverization methods. That is, there are various types of mills, from crushers that are coarse crushers to various types of mills that are fine crushers, and these crushers are currently used depending on the purpose. There are various cases in the case of pneumatic transportation as described above, transportation as a pseudo fluid such as water slurry or oil slurry, but the coal particles are about 100 mesh or less, and in the case of combustion, it is smaller than that. Often. Mills are often used as this type of pulverizer. Mills can be roughly divided into dry and wet types, but from a pure efficiency standpoint, wet types are considered better. That is, in the case of a dry type, fine particles adhere to the walls, balls, etc. of the pulverizer, and the efficiency decreases due to the buffering effect of the particles. On the other hand, in the case of a wet method, fine powder flows out, so this phenomenon does not occur and efficiency is high.

In view of the above points, the present inventors focused on the efficiency and function of a wet pulverizer, as well as the characteristics of the chemical wet deashing method described above, and developed an apparatus that can simultaneously pulverize and deash coal. He discovered this and completed this invention. According to the deashing treatment apparatus according to the present invention, it is possible to obtain the optimum deashing coal to be supplied to pneumatic transportation, water slurry, oil slurry, etc.

This invention will be explained below based on embodiments shown in the drawings.

It should be noted that the Examples show one specific example of the present invention, and the present invention is not limited to such Examples.

In the drawing, raw coal to be pulverized is put into a mixing tank 1, where the raw coal and a deashing agent aqueous solution are mixed at a predetermined ratio. The mixture of raw coal and deashing agent aqueous solution is introduced into the next wet crusher 2. Here, the crusher 2 is not particularly limited, and wet-type crushers such as a ball mill, tube mill, rod mill, and attrition mill are used. In this pulverizer 2, the raw coal is pulverized and at the same time, the pulverized coal and the deashing agent aqueous solution are brought into contact. In this case, a heating device is not particularly necessary;
The pulverization and deashing reactions are carried out under normal pressure.

Here, the deashing agent aqueous solution is a hydrochloric acid or citric acid aqueous solution containing a corrosion inhibitor to which fluoride is added. The corrosion inhibitor is used to protect equipment, piping, etc. from the corrosive properties of hydrochloric acid or citric acid aqueous solutions, and commercially available ones can be used. That is, as this type of corrosion inhibitor, those used when pickling boiler tubes and plant piping can be used. Hydrochloric acid and citric acid are effective in dissolving ash in coal, especially iron-based compounds, and fluoride is effective in dissolving silica-based compounds. However, both these acids and fluorides have a synergistic effect, and the greatest demineralization effect can be obtained when both are present in the same solution. The fluoride used herein is selected from the group consisting of acidic ammonium fluoride, ammonium fluoride, acidic sodium fluoride, sodium fluoride, acidic potassium fluoride, and potassium fluoride. Among these fluorides, acidic ammonium fluoride is the most effective for demineralization. This not only has a strong deashing effect, but also has the effect of not increasing the amount of sludge during subsequent wastewater treatment because it can be decomposed, unlike the case of sodium salts and potassium salts.

Incidentally, the ash content in coal is divided into two types: one that exists as an impurity in the coal, and the other that exists within the coal's structure.
The former is what is mixed in from outside during the coal production process, such as mud or stones. This ash appears on the surface of the coal particles by crushing by the wet crusher 2. Therefore, the ash comes into contact with the chemical solution very efficiently, and the ash is quickly dissolved. The ash present in the coal tissue was introduced during the genesis of the coal's original plant, and it is extremely difficult to remove it.

In addition, chemical solutions consisting of hydrochloric acid or citric acid aqueous solutions containing fluorides have strong penetrating power and penetrate into the ash, so they play the role of loosening the binding force between coal and ash, making the coal itself more likely to crack. Overall, it produces good results that increase the crushing efficiency. The dissolution of ash is affected by the contact efficiency between the ash and the chemical solution, and it can be said that the situation inside the wet crusher 2 has ideal conditions from the viewpoint of this contact efficiency.

The slurry exiting the wet crusher 2 is then introduced into a classifier 3. Although there are no particular restrictions on the classifier 3, for example, a rake classifier or the like can be used. The coarse coal separated in the classifier 3 is supplied to the mixing tank 1 again. The granulated coal and the chemical liquid that have reached a predetermined size are introduced into a dehydrator 4, where they are separated into coal and the chemical liquid. Here, as the dehydrator 4, a centrifugal separator, a filtration machine, or the like can be used. Most of the chemical solution is then transferred to the chemical solution preparation tank 8 again.
A part of it is extracted, and the metal ions such as Si, Al, Fe, etc. dissolved in the chemical solution are removed as sludge in the wastewater treatment equipment 7, and the treated solution is returned to the chemical solution preparation tank 8. and used in circulation.

On the other hand, since hydrochloric acid or citric acid and fluoride are attached to the coal dehydrated by the dehydrator 4, this coal is introduced into the cleaning tank 5. Then, the chemical solution adhering to the coal is cleaned in the cleaning tank 5 while circulating the cleaning water. Note that a plurality of cleaning tanks 5 may be installed as necessary. The thoroughly washed coal is extracted from the washing tank 5 and guided to a dehydrator 6. Note that the amount of water replenished into the cleaning tank 5 corresponds to the amount of water taken out together with the sludge and product coal. Also, conventional techniques are used for such washing.

Next, the dehydrated coal in the dehydrator 6 undergoes a drying process if necessary, and then becomes product coal. The water separated by the dehydrator 6 is returned to the chemical solution preparation tank 8 again. The chemical liquid preparation tank 8 also has the function of a decanter. In this preparation tank 8, the drug is replenished so that the drug solution has a predetermined concentration. The prepared deashing agent solution is supplied to the mixing tank 1 again.

In this invention, as described above, raw coal is pulverized in the wet pulverizer 2, and at the same time, deashing is performed using a chemical solution made by adding a specific fluoride to hydrochloric acid or citric acid. The efficiency of coal pulverization is improved, and the pulverized coal and the chemical solution are sufficiently stirred to ensure sufficient contact between the two, resulting in a high deashing rate. In addition, since the coal pulverization and deashing operations are performed simultaneously and under normal pressure without the need for heating equipment, the various equipment necessary for the deashing operation as well as the stirring power for the deashing reaction tank are required. etc. are no longer necessary, resulting in a very economical effect.

[Brief explanation of the drawing]

The drawing is a flow sheet showing an embodiment of the invention. 1... Mixing tank, 2... Wet crusher, 3... Classifier, 4... Dehydrator, 5... Washing tank, 6... Dehydrator, 7... Wastewater treatment equipment, 8... Chemical solution preparation tank .

Claims (1)

[Claims] 1. A fluoride selected from the group consisting of acidic ammonium fluoride, ammonium fluoride, acidic sodium fluoride, sodium fluoride, acidic potassium fluoride, and potassium fluoride is added to an aqueous solution of hydrochloric acid or citric acid. Mixing tank 1 for mixing the deashing chemical and coal
and a wet crusher 2 that crushes coal in a chemical solution.
, a classifier 3 that separates coarse coal from the pulverized coal in a chemical solution, a dehydrator 4 that separates the fine coal from the chemical solution from a mixed solution containing the deashed granule coal and the chemical solution, and a deashing machine. It is equipped with a wastewater treatment device 7 that processes a part of the chemical solution after treatment, and a chemical solution preparation tank 8.
Raw coal and a chemical solution are mixed in the mixing tank 1, and this mixture is introduced into a wet pulverizer 2, where the coal is pulverized in the chemical solution and, at the same time, the ash content in the coal is removed by the chemical solution. The mixture of the pulverized coal and the chemical solution is led to the classifier 3, where coarse coal is separated, and this is returned to the mixing tank 1, where it is separated from the deashed fine coal taken out by the classifier 3. The mixed solution containing the chemical solution is sent to the dehydrator 4.
is introduced into the chemical solution preparation tank 8, where it is separated into deashed pulverized coal and the chemical solution, and most of the chemical solution after the deashing process is transferred to the chemical solution preparation tank 8.
A part of the chemical solution is sent to the wastewater treatment equipment 7 for sludge removal and then sent to the preparation tank 8, from which the chemical solution is circulated and supplied to the mixing tank 1. Coal chemical deashing treatment equipment.