JPS6259757B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a chemical deashing method for removing ash contained in coal. In recent years, due to uncertain oil supply prospects and soaring prices, energy diversification has been recognized, and there is a growing momentum around the world to reconsider coal, and effective ways to use it are being considered. Coal has traditionally been used as a major energy source, but it has the disadvantages of being solid and containing a large amount of ash, which has little utility value compared to petroleum. That is, coal contains several percent to several tens of percent of inorganic substances as ash, and therefore, when coal is used as a fuel, a large amount of these ash is discharged. Coal also contains sulfur compounds, and these sulfur compounds produce sulfur oxides when burned, causing air pollution. Furthermore, since coal is solid, there is a problem in that it is troublesome and expensive to handle during transportation and cargo handling. In order to solve these problems, various methods for deashing coal have been studied, and these methods are broadly classified into physical deashing methods and chemical deashing methods. Here, the physical deashing methods include methods such as heavy liquid beneficiation, flotation, magnetic beneficiation, and oil agglomeration, but the deashing efficiency by these methods is generally low. On the other hand, a deashing method using chemical treatment of coal involves reacting an inorganic substance as ash contained in coal with a chemical to separate and remove it from the coal. Here, the composition of ash in coal varies depending on the type of coal, but is generally as follows. SiO ₂ : 40-60 wt% Al ₂ O ₃ : 25-35 wt% Fe ₂ O ₃ : 5-25 wt% CaO: 1-15 wt% MgO: 0.5-4 wt% Na ₂ O, K ₂ O, _SO3 : 1 to 4% by weight The above ash composition is after combustion. Therefore, in actual coal, iron etc. is FeS ₂
It often takes the form of There are four conventional methods for chemically deashing coal. (1) Dissolution by acid. (2) Dissolution by alkali (under high temperature and pressure conditions). (3) After oxidation treatment with air, nitrogen dioxide, etc., dissolution with acid or alkali. (4) Treatment with hydrofluoric acid or hydrogen fluoride gas. These methods include a method for removing ash from coal or coke (see Japanese Patent Publication No. 17-466), a method for desulfurization and deashing from coal (see Japanese Patent Publication No. 23711-1983), and a method for deashing coal (see Japanese Patent Publication No. 1982-23711). 55-133487)). Here, the acid or alkali treatment in methods (1) and (2) above is usually carried out under pressurized and heated conditions, and deashing is performed by dissolving metal components. Therefore, under mild conditions, virtually no demineralization effect is observed, making it unsuitable as a demineralization method. In addition, method (3) above, which involves oxidation treatment and then acid or alkali treatment, is the same in principle as methods (1) and (2) above.
This is an attempt to dissolve FeS ₂ components, which are difficult to dissolve through oxidation treatment, after oxidizing them in advance. In the treatment method using hydrofluoric acid or hydrogen fluoride gas in (4) above, since SiO ₂ does not dissolve easily in acids or alkalis, coal is treated with hydrogen fluoride gas and Si is separated as gaseous SiF _4. and obtains a demineralizing effect. However, since these hydrofluoric acid or hydrogen fluoride are extremely toxic and corrosive, there are many practical problems in their use. As described above, although the coal deashing method is an extremely important technology for the effective utilization of coal, there is no truly effective and practical method. As a result of extensive research in view of the above points, the inventors found that the ash content in coal could be reduced by using a combination of citric acid and acidic ammonium fluoride (ammonium hydrogen fluoride: NH ₄ HF ₂ ). We have discovered a method that can remove these substances very effectively, and have completed this invention. That is, the method for chemically deashing coal of the present invention involves pulverizing coal containing ash to produce pulverized coal;
This pulverized coal containing ash is immersed in an aqueous solution containing citric acid and acidic ammonium fluoride to cause the ash to react with the citric acid and acidic ammonium fluoride, and then the pulverized coal from which the ash has been removed from the aqueous solution is It is characterized by being able to be taken out. In the above, the coal containing ash has an average particle size of 35 meshes or less (i.e., an average particle size of 500 μm or less), preferably an average particle size of 100 meshes or less (i.e., an average particle size of 500 μm or less).
149μm or less) into pulverized coal. As is easily understood, the purpose of pulverizing the coal is to increase the contact area with the immersion liquid, speed up the dissolution rate, and relatively increase the efficiency of liquid penetration into the inside of the coal. be. However, it is not necessary to pulverize the coal to an extreme degree, and if the size is as described above, the deashing rate will not change significantly. Further, the above treatment liquid contains 1.0 to 10.0% by weight of citric acid, preferably 2.0 to 10.0% by weight, and 1.0 to 10% by weight of acidic ammonium fluoride (NH ₄ HF ₂ ), preferably
Contains 2.0-10% by weight. Here, if the amount of citric acid is less than 1.0% by weight and the amount of acidic ammonium fluoride is less than 1.0% by weight, a sufficient deashing rate cannot be obtained. Furthermore, if citric acid is 4.0% by weight or more and acidic ammonium fluoride is 5.0% by weight or more, the deashing rate will be almost constant. It is desirable to use less than %. In addition, acidic ammonium fluoride is
It reacts with metal compounds such as SiO ₂ , Fe ₂ O ₃ , Al ₂ O ₃ and even sulfur, thereby producing soluble salts, so its use depends on the ash content in the coal. It is necessary to increase or decrease the amount. Furthermore, since the coal deashing treatment described above is based on a chemical reaction, the reaction temperature naturally affects the deashing rate. If the deashing treatment time is constant, the higher the reaction temperature, the higher the decarburization rate.
It was found that the deashing reaction progressed even at room temperature (approximately 25°C), and that a practical deashing rate could be obtained by increasing the treatment time. In addition, the reaction time is regulated by the concentration of citric acid and acidic ammonium fluoride in the reaction solution and especially by the reaction temperature. The demineralization rate was . Lowering the reaction temperature will extend the time. Next, examples of the present invention will be described together with comparative examples. Example 1 Daido charcoal was crushed into 100 pieces (mesh size).
The pulverized coal was sieved using a 149 μm sieve to obtain 100 mesh sieve-sized pulverized coal, which was used as sample charcoal. The ash content of this sample charcoal was 10.3% on a dry basis. In addition,
The ash content was measured as follows (JIS M8815). First, an appropriate amount of sample charcoal is collected in a porcelain crucible of W ₀ g, dried in a dryer at 105±5°C for 2 hours, and then weighed (W ₁ g). Next, this was heated in an electric furnace from room temperature to 500℃ over 1 hour, and then
Heat to 815℃ for 1 hour. Then, the ashing process is continued while occasionally stirring the sample charcoal to completely ash it. After incineration, the container was cooled and weighed (W ₂ g). Then, the ash content percentage on a dry basis was determined using the following formula. Dry standard ash content=W ₂ -W ₀ /W ₁ -W ₀ ×100 (%) Next, deashing treatment was performed as follows. That is, 200 ml of an aqueous solution containing citric acid and acidic ammonium fluoride in a predetermined ratio is placed in a Teflon beaker, 20 g of sample charcoal is added and suspended, and heated to a predetermined temperature while stirring with a magnetic stirrer equipped with a heater. It was processed for a predetermined time. After the ash reaction, the sample charcoal was separated by filtration and washed with water. In addition, in this water washing operation, check the pH value of the washing liquid using PH test paper.
This was repeated until it showed 7. Then, the ash content of this deashed coal was measured as described above, and the deashing rate was calculated using the following formula. Deashing rate = Ash content of sample coal (%) - Ash content of deashing coal (%) / Ash content of sample coal (%) x 100 (%) The results obtained from the above deashing treatment are summarized in the table () below. Ta.

[Table] In the table () above, the first stage (Experiment No. 1~
In the experiment 4), the citric acid concentration was varied. In the experiments of the second stage (experiments Nos. 5 to 7), the concentration of acidic ammonium fluoride was varied. Furthermore, the experiments in the third stage (experiments Nos. 8 and 9) show the results of varying the treatment temperature and treatment time, respectively. First, in the first stage, it can be seen that by allowing citric acid to coexist with acidic ammonium fluoride, the deashing rate can be increased to a practical level. however,
The demineralization rate also slightly depends on the citric acid concentration, and the demineralization rate is lower at 1.0% citric acid concentration than others. The results are shown graphically in FIG. As can be seen from the figure, at citric acid concentrations of 5.0% or higher, the demineralization rate is approximately
It has come to show an almost constant value of 80%. Next, it can be seen that in the second stage, an excellent deashing rate can be obtained by using a coexisting solution of citric acid and acidic ammonium fluoride. The results are shown graphically in FIG. In addition, Figure 2 shows an experiment under the same conditions.
The results of No. 2 are also shown. As is clear from Figure 2, the influence of the acidic ammonium fluoride concentration is extremely large, and the demineralization rate has already reached 75% at a concentration of about 1.25%. For reference, the results of experiments in which temperature and time were varied are shown in FIGS. 3 and 4. As is clear from FIG. 3, the influence of temperature is relatively large, and the higher the temperature, the higher the demineralization rate. Furthermore, as is clear from Fig. 4, a constant demineralization rate of 80% was reached in approximately 3 hours of treatment time. Example 2 Daido coal was crushed using an ultra-fine crusher, and the average particle size was
Ultrafinely pulverized sample charcoal (No. 10) of 3.16 μm was prepared.
The ash content of this sample charcoal was 11.7%. On the other hand, sample charcoal (No. 11) of 28 mesh to 48 mesh (average particle size 444 μm) was prepared by crushing the same Daido charcoal. The ash content of this sample charcoal was 10.5%. Both sample coals were subjected to deashing treatment under the following conditions, and the deashing rate was measured. Sample charcoal amount: 20g, treatment liquid amount: 200ml treatment temperature: 80℃, treatment time: 3 hours treatment liquid composition: 3% citric acid, 2.5% acidic ammonium fluoride solution. As a result, the ultra-finely pulverized sample coal (No. 10) had a deashing rate of 67.6%, whereas the sample coal with a relatively large particle size (No. 11) had a deashing rate of 54.3%. In this way, the results of sample coal (No. 10) are the same as those of Example 1 above.
Since it is almost the same as in the case of , it can be seen that there is no need to grind the coal very finely. However, the deashing rate decreased with sample coal (No. 11), which had a large particle size. Here, it is difficult to determine the degree of pulverization of coal in the coal deashing treatment due to the relationship with other deashing treatment conditions, but it is preferable to crush the coal to approximately 100 mesh or less. Example 3 A sample charcoal (No. 12) was prepared by pulverizing Liddale charcoal from Australia and sieving it into 70 to 200 meshes (average particle size 142 μm). The ash content of this sample charcoal was 8.28%. When 13 g of this sample coal was deashed under the same conditions as in Example 2, the deashing rate was 70.9%. As described above, according to the method of the present invention, an excellent deashing rate can be obtained even when the types of coal are different. Comparative Example 1 For comparison, the sample charcoal of Example 1 was deashed using water and various acid or alkali aqueous solutions. The results obtained are shown in the table () below. The amount of treatment liquid was kept constant at 200 ml.

[Table] As is clear from the above table (), some amount of ash can be removed even by washing with water. However, in treatments using aqueous solutions of various acids, the deashing efficiency is only about 20 to 30%, which is a low value, even though the concentrations of these acids are quite high. Furthermore, the deashing rate of treatment with aqueous caustic soda solution is also low. Furthermore, the treatment with a 3% citric acid solution was similar to the water washing treatment, and almost no deashing effect was observed. Comparative Example 2 For comparison, the sample charcoal of Example 1 was deashed using an aqueous solution containing various fluorine compounds. The processing conditions are as follows. Sample coal amount: 20g, treatment liquid amount: 200ml, treatment temperature: 80℃, treatment time: 3 hours. The results obtained are shown in the following table ().

[Table] As is clear from the above table (), with the aqueous solutions of acidic potassium fluoride and acidic ammonium fluoride, a deashing rate of approximately 50 to 60% was obtained. This is probably due to the influence of the hydrogen ion concentration (PH value) in these aqueous solutions. In other words, although the mechanism of coal deashing is not clear at present, it is thought that the dissolving action of acid plays an important role. Hydrofluoric acid and hydrogen fluoride are highly reactive with silica, so they can be expected to be effective as deashing agents, but they are highly toxic and corrosive, and hydrogen fluoride is gaseous. Therefore, it is actually very difficult to handle. Comparative Example 3 A predetermined amount of citric acid was added to each of the various fluorine compounds of Comparative Example 2, and sample charcoal was deashed under the same conditions as Comparative Example 2 using a coexisting solution of the fluorine compound and citric acid. The results obtained are shown in Table () below.

[Table] As is clear from the above table (), a considerably high deashing rate can be obtained by using a coexisting solution of acidic potassium fluoride and citric acid; This is approximately the same level as in the case of an aqueous solution. As described above, the method of the present invention can deash coal much more efficiently than conventional coal deashing methods, and is also extremely safe. Furthermore, all treatment steps can be carried out in an aqueous solution under atmospheric pressure, which is practical and highly economical. In this invention, citric acid is used, and since this citric acid is an organic acid, it disappears by combustion. Therefore, even if citric acid remains in the coal after deashing, it disappears through combustion, so there is no chance of it remaining in the ash, and there is no risk of air pollution or equipment corrosion. No problems arise at all. For example, when mineral acids such as hydrochloric acid and sulfuric acid are used, there is a problem of environmental pollution due to chlorine and sulfur content, and therefore, it is troublesome that these mineral acids must be sufficiently removed after deashing. In addition, since citric acid is used, the burden on corrosion prevention when selecting the material for the deashing treatment equipment is reduced, and equipment costs are extremely low. Further, in this invention, acidic ammonium fluoride is used together with citric acid, which is solid at room temperature and therefore easy to handle.
This acidic ammonium fluoride is easily soluble in water,
There is almost no partial pressure of hydrogen fluoride in aqueous solution. Furthermore, since it is an ammonium salt, even if this salt remains in the coal after deashing, it will not remain in the ash after combustion, unlike the case with other metal salts. There is an advantage.

[Brief explanation of the drawing]

FIGS. 1 to 4 are curve diagrams showing the measurement results of the deashing rate in experimental examples of the method of the present invention.

Claims (1)

[Claims] 1. Make pulverized coal by crushing lime containing ash,
This pulverized coal containing ash is mixed with 1-10% by weight of citric acid and 1-10% by weight of acidic ammonium fluoride (NH ₄ HF ₂ ).
A method for chemically deashing coal, which comprises immersing coal in an aqueous solution containing pulverized coal to react the ash with citric acid and acidic ammonium fluoride, and then extracting pulverized coal from which ash has been removed from the aqueous solution.