JPH06172764A - Method for improving low-rank coal and production of coal-water mixture using the same - Google Patents

Abstract

PURPOSE:To decrease the equilibrium moisture of a low-rank coal by thermally treating it at the critical temp. of water or lower in the presence of water and CO. CONSTITUTION:A pressure vessel, such as an autoclave, is charged with water and a low-rank coal having a carbon content of 75wt.% or lower and an equilibrium moisture of 15wt.% or higher in a wt. ratio of water to coal of (0.3:1.0) to (3.0:1.0). After the introduction of CO at normal temp. under 0.5-5MPa (gauge pressure) into the vessel, the coal and water are thermally treated under stirring at the critical temp. of water or lower (523-647.3K) for 0.2-6hr to give a slurry, which is separated by filtration into a liq. phase and an improved coal having a carbon content of 75wt.% or lower and an equilibrium moisture of 10wt.% or lower. The slurry is mixed with a surfactant (e.g. a condensate of sodium naphthalenesulfonate with formalin) and adjusted in the water content, giving a slurry (CWM) which is stable, has a good flowability, and contains 30-35wt.% water, 65-75wt.% coal, 0.2-0.7wt.% surfactant, and, if necessary, a filler.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for reforming low-coal-grade coal which enables safe and high-efficiency transportation of low-coal-grade coal having high water content, and coal using the reformed product. -It relates to a method for producing a water mixture.

[0002]

2. Description of the Related Art Low coal-grade coal having a carbon content of 60 to 75% by weight (anhydrous ashless standard) is generally manufactured by Japanese Industrial Standard JIS.
Moisture (specific moisture) specified in M8812 is 20 to 3
Many of them are as high as 0%, and depending on the type of coal, the water content (equilibrium water content) at room temperature and 98% relative temperature is 60
Some can reach ~ 70%. It is uneconomical to transport such coal with high water content, and it is inefficient when used for fuel or other purposes. In order to reduce the water content of coal, even if it is dried using a method such as hot air drying or natural drying, the obtained dry coal reabsorbs water during storage or transportation, and in the process of further absorbing water. There is a risk of coal fragmentation and spontaneous combustion. Due to such problems, the field of application of low-rank coal is limited,
In order to expand utilization, there has been a demand for a method of reforming low-rank coal to reduce the water content.

In the transportation of low-rank coal, it is extremely convenient in handling if it can be transported as a mixed slurry of coal and water (hereinafter referred to as CWM) which can be used as a fuel as it is. Much research has already been done on the preparation of CWM, and many factors that control the properties of CWM have been pointed out, but the most important factor among these is the amount of water stored by coal. That is, in order to produce a CWM having a high coal concentration, it is desirable that the amount of water that is stored in the pores of the coal particles and reduces the calories of the CWM, but does not contribute to the improvement of fluidity is as small as possible. . Here, the amount of water stored in the pores of the coal particles is considered to be approximately proportional to the equilibrium water content in an atmosphere having a relative humidity of 98% or more at room temperature. It can be a measure of manufacturing difficulty. Also, C
The properties of WM (coal concentration, viscosity, stability, etc.) are largely governed by the amount of water existing outside the coal particles, and are determined only by a 2-3% change relative to coal. Often have a negative impact. From this point of view, regarding the effective utilization of low-coal-grade coal, reforming for reducing equilibrium water content of low-coal-grade coal in order to transport it safely and with high efficiency or to produce CWM having good properties. Various methods have been tried. For example, as a method for reforming low-rank coal, a temperature of 473 to 573K and a pressure of 1.5 to
Fleissner method (TG Rozgony) of reducing water content in coal by using saturated steam of 8.5 MPa
i and I. Z. Szigeti, Interna
regional J. Mining Eng. 2 , 157
1984) or a mixture of coal and water at a temperature of 473-6.
Hydrothermal treatment method (TA Potas, RE Sear) for reforming in pressurized water at 03 K and a pressure of 1.5 to 17 MPa.
S.D. J. Maas, G .; G. Baker and
W. G. Willson, Chem. Eng. Comm
un. 44 , 133 1986) are known. However, in these methods, although the effect of reforming the low-rank coal and reducing the water content is recognized, the equilibrium water content is about 11 to 20%. Although there is a tendency for the degree of reforming to be enhanced by increasing the treatment temperature and lengthening the treatment time, industrially, low temperature treatment in a short time is desired, and the treatment temperature also increases the saturated steam pressure. Therefore, a high pressure device is required in terms of equipment, which is not preferable in terms of cost. From this point of view, it is the current situation that the conventional method has a limit of reforming up to about 11% of the equilibrium water content. This degree of reforming is not sufficient from the perspective of expanding the use of low-coal coal.

On the other hand, a method of treating coal using water and carbon monoxide is known, although the technical field is different from the present invention. As such a technique, a critical temperature of water (647.
Coal and its related substances are heated at a temperature of 3 K) or more (that is, in the absence of water as a liquid), and a water-gas equilibrium reaction between water and carbon monoxide (CO + H ₂ O → CO ₂ +
An attempt to liquefy coal under a specific catalyst by using nascent hydrogen generated by H ₂ (Yokoyama et al.
57 , 182 (1977)), which is an attempt to decompose and liquefy coal, and is essentially different from that for reducing the stored water content of coal.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to an improved method for reforming coal by utilizing a hydrothermal reaction, in which low-rank coal having a temperature below the critical temperature of water is used. ,
It reforms in the presence of water as a liquid (that is, in the state where water and steam coexist), lowers the equilibrium water content of coal to less than about 11%, which is the limit of the prior art, and also improves the safety of coal. An object of the present invention is to provide a method for reforming a low-coalized coal which can contribute to a highly efficient transportation method, and a method for producing a coal-water mixture using the reformed coal obtained by this method.

[0006]

[Means for Solving the Problems] The present inventors diligently studied a method of reforming low-coal-rank coal, which has been difficult to transport due to its large water content, to lower the equilibrium water content. As a result, by treating the coal under a specific condition, it is possible to obtain a coal having a low equilibrium water content, which was difficult to reach by the conventional reforming method, and the reformed coal obtained by this reforming method. The present invention has been completed by finding that a CWM having a high coal content and good properties can be produced by using the same.

[0007] That is, the present invention is a method for reforming low-coal-rank coal, which comprises heat-treating low-coal-rank coal in the presence of water and carbon monoxide at a temperature below the critical temperature of water. A method for producing a coal / water mixture, characterized in that a surfactant is added to a reformed product obtained by this reforming method to adjust the content of water and mixed. In the prior art, the hydrothermal reaction generally means a reaction using high temperature / high pressure water,
The reaction in the present invention can be said to be in the category of this reaction, but since it can be processed even with a water / coal weight ratio of 0.3 as described later, it is called hydrothermal treatment rather than hydrothermal treatment.

The present invention can be implemented by the following method, for example. That is, after charging water and coal in a pressure vessel such as an autoclave, carbon monoxide (CO) is injected under pressure,
Coal having a low equilibrium water content can be obtained by maintaining the reaction temperature of 523K to 647.3K (critical temperature of water) and causing the reaction. In addition, the liquid phase of the treated product (slurry) recovered from the pressure vessel after the heat treatment contains a large amount of organic carboxylic acid, which is generally called humic acid produced by the reaction, and acts as a surfactant. Therefore, when the CWM is directly prepared from the slurry after the heat treatment, the amount of the surfactant added can be reduced.

In the present invention, the low-rank coal has a carbon content of 75% or less on a dry ashless basis (daf basis), J
Moisture (specific moisture) specified in IS M8812 is 10
% Or more, or at room temperature, the coal (equilibrium moisture) at a relative temperature of 98% corresponds to any condition of 15% or more, but does not exclude the implementation of coal that does not meet the above conditions. Also, the type of coal is not particularly limited.

As a device used for heat treatment, a pressure vessel is preferably used because it is operated at a pressure exceeding normal pressure. For example, a batch type or a flow type autoclave and the like can be preferably used. The container is not particularly limited.

The ratio of water to coal charged in the pressure vessel may be an appropriate ratio depending on the type of pressure vessel used, the difference in the process after the heat treatment, and the like. It is sufficient if the amount is sufficient to make contact. That is, it may be approximately in the range of 0.3 to 3.0 (water / coal weight ratio), and in the case of use as a CWM, the amount of water is made relatively large to form a slurry, and the water to be treated is drained before use. When doing so, it is advantageous to make it relatively small. The viscosity of coal is, for example, about 200 mesh or less when the modified coal is directed to CWM production, and about 8 to 20 mesh when the modified coal is used after being drained or used as it is. However, the particle size may be appropriately adjusted depending on the application.

Further, in order to generate hydrogen by a water-gas equilibrium reaction between water and carbon monoxide, it suffices to increase the partial pressure of carbon monoxide. However, if the partial pressure of carbon monoxide is increased, the pressure of the reaction system will increase. Since it becomes large and causes industrial and economic problems in industrial implementation, high-purity carbon monoxide gas is used, and the amount is 1 at the room temperature partial pressure display of carbon monoxide in the reaction system. It is preferably in the range of 5 MPa (gauge pressure). The partial pressure range of the carbon monoxide is
It is a preferable range in consideration of practicality, and implementation outside this range is not excluded.

The reaction temperature is preferably 523K to 647.3K (critical temperature of water). At a reaction temperature of 523 K or less, the reaction rate is small and not practical, and the critical temperature of water is 64
At a temperature of 7.3 K or higher, the coal to be treated is thermally decomposed, which is not preferable.

The partial pressure of carbon monoxide and the reaction temperature are set so that the partial pressure of carbon monoxide is lowered to lower the reaction pressure in the reaction system when the reaction temperature needs to be raised particularly depending on the type of coal to be treated. Adjustments such as suppressing the total pressure may be made.

The reaction time varies depending on the type of coal to be treated, the type of pressure vessel used for heat treatment, etc., but it may be appropriately set according to these options, but it is approximately 0.2 to 6
Can be processed in reaction time of time. If the reaction time is short, the reforming effect is not sufficient. On the other hand, if the reaction time is long, the equilibrium water content is lowered, but if it is too long, no further effect is observed.

The chemical oxygen consumption (COD) of the liquid phase in the coal-water mixture recovered from the pressure vessel after the heat treatment is determined by the conventional heat treatment method (TA Potas etc.) and the method of the present invention. Although the higher the value is, the larger the tendency tends to be, the method of the present invention in which carbon monoxide is added and the heat treatment is more remarkable, and the COD value is about twice the value of the conventional method. Also, there is no direct effect on the reforming of coal,
_The COD value is further increased by adding ₂ CO ₃ and heat treatment. The components in the liquid phase are mainly organic carboxylic acids generally called humic acid, which acts as a surfactant, so when CWM is prepared as a means of transporting coal, the amount of surfactant added is reduced. It has the effect of being able to.

By the way, the water-gas equilibrium reaction is essentially CO 2.
And H ₂ O are industrially carried out to produce H ₂ , which is a reaction represented by CO + H ₂ O → H ₂ + CO ₂ . Since this reaction is an exothermic reaction, the equilibrium is more advantageous for the production of H ₂ at lower temperatures, but it is generally carried out using a catalyst at a temperature of 720K or higher because of its low reaction rate. Although the water-gas equilibrium reaction in the present invention has not been completely clarified, it is completely different from the above reaction in that a catalyst is not used and the temperature is lower than the temperature used in the water-gas equilibrium reaction. There is. Certainly CO + H ₂ O →
Although nascent H (reaction rate is low) generated by the reaction of H ₂ + CO ₂ is used, it has never been considered or was known that it is effective for reforming coal. I can say. The reason why the equilibrium water content of the low coal-grade coal can be reduced by the method of the present invention is that nascent hydrogen (H) produced by the water-gas equilibrium reaction between water and carbon monoxide acts on the coal to contain it in the coal. By reducing the oxygen functional groups, the pore walls in the coal become hydrophobic, and the cross-linking due to hydrogen bonds involving these functional groups is eliminated and the coal matrix becomes dense, resulting in an equilibrium moisture content of the reformed coal. Is expected to decrease. This is because when the heat treatment is performed using hydrogen (H ₂ ) instead of using carbon monoxide (CO), the coal reforming effect is hardly improved as compared with the conventional heat treatment. Is also guessed.

Therefore, by using the reforming method of the present invention, the pore wall in coal becomes hydrophobic and the coal matrix becomes dense, so that the carbon content is 75% or less, usually 20 to 30%. It is possible to reduce the equilibrium water content of the low-rank coal having the above degree to about 10% or less, and it is possible to obtain a reformed coal with less water re-adsorption. The reformed carbon obtained by the reforming method of the present invention can be used for fuel and other applications after being dried if necessary, and is particularly suitable for directing to CWM production in a slurry state after the reforming treatment. ing.

The CWM can be manufactured by the following method, for example. That is, the water content of the slurry obtained by treating the low-rank coal with the above-mentioned reforming method may be adjusted, and a surfactant for imparting stability and fluidity as CWM may be added and mixed. The surfactant used here is not particularly limited, but in order to increase the coal content of CWM, for example, a surfactant having a sodium naphthalene sulfonate formalin condensate having a water reducing effect, a dispersing effect, etc. Is preferably used. In addition, depending on the type of surfactant used, in order to exert its effect, CW
The hydrogen ion concentration (pH) of the liquid phase in the M slurry may be adjusted. Here, since the slurry obtained by heat-treating the low-rank coal using the method of the present invention contains a component having the action of a surfactant, the addition amount of the surfactant to be newly added. Is less. The general composition of CWM is as follows: water content 30-35%, coal 65-70
%, 0.2 to 0.7% of an added surfactant, and a small amount of filler such as kaolinite, if necessary, are generally contained, but it may be appropriately adjusted depending on the application. Also,
The viscosity of coal is preferably about 80% by weight through 200 mesh.

According to the method of the present invention, the carbon content is 75.
A CWM having a high coal concentration, a stable and good fluidity, and easy long-distance transportation can be easily produced from a coal with a low coalification degree of not more than%. In addition, in the preparation of CWM, it is convenient and preferable in terms of processing operation to use the processed product obtained by the modification method of the present invention as it is.
CWM may be newly prepared after obtaining the modified carbon.

Hereinafter, the present invention will be described more specifically with reference to Examples.

[0022]

[Example] Prior to the reforming treatment, the coal shown in Table 1
A sample was prepared by adjusting the particle size so that the particle size was 60 mesh. In addition, in Table 1, elemental analysis values are expressed by% ashless standard, and industrial analysis values are Japanese Industrial Standard (JIS) M.
It is a value analyzed based on 8812.

In the examples and comparative examples, the pressure vessel used was an electromagnetic stirring type autoclave (made by SUS) having an internal volume of 50 cm ³ .

(Examples 1 to 8 and Comparative Examples 1 to 10) Using the coals A, B and C shown in Table 1 as raw material coals, for each coal, 10 g of coal (dry coal standard) and 20 g of pure water were used.
Were charged into the autoclave, carbon monoxide of 0.5 to 5 MPa (gauge pressure) was added at room temperature under the conditions shown in Table 2, and then 553 K, 573 K with electromagnetic stirring.
The heat treatment was carried out by holding the reaction temperature of 593 K for 6 hours.
The slurry after the heat treatment was filtered to separate it into coal (reformed coal) and a liquid phase. For the obtained reformed coal, the yield (the ratio of the amount of reformed coal to the amount of raw coal) on the basis of dry coal, the elemental composition, and the relative moisture at room temperature of 75% and 100% equilibrium moisture were measured. As for the liquid phase, the slurry immediately after being recovered from the autoclave was filtered and fractionated, and the chemical oxygen consumption (COD) was immediately measured according to JIS K0101. In addition, as an example in the case where carbon monoxide is not used, coal 10
g and pure water of 30 g were used, and the heat treatment was performed according to the conditions of the example. The results of these measurements are also shown in Table 2. In addition, Comparative Examples 1, 4 and 8 are coals (untreated) used as raw materials shown in Table 1. From the results in Table 2, it is found that it is extremely difficult to reduce the equilibrium water content to about 11% or less at 100% relative humidity (RH) by the hydrothermal treatment without using carbon monoxide shown in the comparative example. . On the other hand, according to the method of adding carbon monoxide of the present invention, 6 to 8
It can be seen that the equilibrium water content can be reduced to 10%, and even in the case of coal A, which is particularly difficult to reform, it can be reduced to 10%.

[0025]

[Table 1]

[0026]

[Table 2] (Example 9, Comparative Examples 11 to 12) Using coal C, as Example 9, heat treatment by the method of the present invention, and Comparative Example 11
~ 12, instead of carbon monoxide (CO), hydrogen (H
₂ ) using carbon monoxide (CO), hydrogen (H)
Heat treatment was performed in a system that did not use ₂ ). The treatment conditions were a reaction temperature of 553 K, a reaction time of 6 hours, in both Examples and Comparative Examples.
The addition amount of carbon monoxide or hydrogen was 5 MPa in gauge pressure. Table 3 shows the equilibrium water content of the obtained reformed carbon and the gas composition after the reaction. From the results of Table 3, in Comparative Example 11 in which hydrogen was used instead of carbon monoxide, coal reformation was somewhat advanced as compared with the case where Comparative Example 12 did not use carbon monoxide, but in Example 9 It can be seen that the effect is extremely small as compared with the case of using carbon monoxide. Further, as for COD, as shown in the examples of Table 2, a high COD value (COD value when treated with 20 ml of water for 10 g of coal) was obtained by the heat treatment with addition of carbon monoxide. In Comparative Example 11 using hydrogen, the amount was 1450 ppm, which is a conventional heat treatment (Comparative Example shown in Table 2 (10 g of coal and 30 m of water).
There is no big difference with the value of COD value when treated with l.
Further, the COD value when heat-treated using K ₂ CO ₃ under the conditions of Example 9 was as large as 7070 ppm, and it exists as a potassium salt of humic acid in the liquid phase after the heat-treatment. K ₂ CO ₃ has no effect on the reforming of coal, but it is convenient for preparing CWM because of the large amount of the potassium salt of humic acid as a surfactant.

[0027]

[Table 3] (Example 10, Comparative Example 13) Example 8 as Example 10
CWM was prepared using the modified coal obtained in 1. and untreated Coal C as Comparative Example 13. In addition, reformed coal,
The particle size of coal was adjusted to 80% through 200 mesh. In the case of Comparative Example 13, in order to prepare a stable and fluid CWM, it is necessary to add a surfactant containing sodium naphthalenesulfonate formalin condensate as a main component to the dry coal in an amount of 1%. C at that time
The maximum coal concentration of WM (dry coal weight / water weight) is 42%
Met. On the other hand, in the case of Example 10, 3N-NaOH solution was added to the liquid obtained by filtering and separating the slurry after the heat treatment to adjust the pH value to about 12, and the surfactant was added to the dry coal amount. By using 0.5% added as a liquid component, a CWM having a maximum coal concentration of 65% and stable and good fluidity could be produced.
Thus, by utilizing the method of the present invention as a pretreatment for the preparation of CWM, C
It is understood that the coal concentration of WM can be extremely increased.

[0028]

[Effects of the Invention] When reforming low-coal-coal having a high water content by heat treatment, by adding carbon monoxide and heat-treating at a temperature below the critical temperature of water, the method of the present invention is used to obtain pores in coal. Since the walls are made hydrophobic and the coal matrix is densified, the equilibrium water content of the reformed coal after heat treatment can be reduced. Due to this, when preparing CWM, which is said to be useful as a long-distance transportation means for coal,
By utilizing the method of the present invention as a pretreatment for the preparation of CWM, a CWM having a high coal concentration, a stable and good fluidity can be obtained by adding less surfactant.

Claims (2)

[Claims] 1. A method for reforming low-coal-grade coal, which comprises heat-treating the low-coal-grade coal at a temperature not higher than the critical temperature of water in the presence of water and carbon monoxide. 2. A surfactant is added to a reformed product obtained by heat-treating a low-coal-rank coal in the presence of water and carbon monoxide at a temperature not higher than the critical temperature of water to increase the content of water. A method for producing a coal-water mixture, which comprises adjusting and mixing.