JPH0138436B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing ash from coal. In recent years, coal has been reconsidered as a fuel to replace oil. Another disadvantage of coal is its lack of fluidity, which is the inconvenience of transporting and handling fixed coal compared to liquid petroleum.
Various countermeasures have also been considered and implemented to address the problem of nonflammable components, especially ash, which are contained in a higher proportion than petroleum. For example, to solve the problem of fluidity, techniques have been developed to liquefy or gasify coal, or to make it into fine powder and then into a water-based or oil/water-based slurry.
On the other hand, various methods have been developed to remove the latter ash content. Among those ash removal methods,
The foam flotation method, wet granulation method, and dissolved gas flotation method have relatively high ash removal rates, but each has various drawbacks and is not practical as a method for removing ash from fine-grained pulverized coal. This cannot be said to be a completely satisfactory method. In other words, the foam flotation method mainly uses particles with a particle size of 0.5 mm.
The following method is used to sort pulverized coal and remove ash, but if the target pulverized coal has fine particles, such as 200 mesh or less, the purpose of pulverized coal separation and ash removal cannot be achieved sufficiently. However, there are drawbacks such as a reduction in the recovery rate of pulverized coal. On the other hand, wet granulation is a method that takes advantage of the lipophilic nature of coal, and by treating pulverized coal with a mixture of hydrocarbon oil and water, only the coal content is aggregated through the hydrocarbon oil. The granules are separated and recovered from the aqueous phase to which the ash has migrated using a sieve. This wet granulation method is an excellent method that allows the separation of pulverized coal down to several microns, and the recovery rate of coal content reaches 95-98%. However, it cannot be said that this method is necessarily a satisfactory method for removing ash for the following reasons. In other words, the ash content of coal is determined based on its origins: (1) Inorganic content (usually said to be less than 1%) that was included as a component of plants that were transformed into coal; (2) Infiltration of groundwater into the coal seam. (3) Mineral substances that entered the coal seam from outside during the coalification process; What happens is
This is the ash content of (2) and (3). These ash particles exist in coal with a size of several microns, and moreover, these ash particles are composed of quartz or clay minerals, and most of them are aggregates of fine particles of several microns or smaller. Scattered throughout the coal. The ash content that can be removed by the wet granulation method also belongs to (2) and (3).Theoretically, the ash content can be almost completely removed by grinding the coal very finely and increasing the surface area of the coal particles. It is thought that it is possible to remove it. However, currently developed wet granulation methods have the following drawbacks, and the ash removal rate is also at a low level. (1) When coal is pulverized from a few microns to several tens of microns (ultra-fine powder state), the surface area of the coal increases, making it possible to separate pulverized coal made of such fine particles using a sieve. In order to form aggregates (granules) of such size, it is necessary to increase the amount of hydrocarbon oil added.
Therefore, it is usually necessary to use 15 to 30 parts by weight of hydrocarbon oil per 100 parts by weight of coal. (2) Since the amount of hydrocarbon oil is large and the diameter of the granules is large, ash is entangled in the granules, which reduces the ash removal rate. (3) When separating granules using a sieve, ash adheres to the granules on the sieve. This attached ash is difficult to remove even by washing with water, so the amount of water required for sufficient washing is extremely large. (4) Since granulation from ultrafine powder requires a large amount of mechanical energy, it is disadvantageous as an industrial processing method, and it either restricts the particle size distribution or requires cyclic processing of the granulated material. becomes. Attempts have been made to improve the conventional wet granulation method described above, but all of these methods are based on separation of aggregates (granules) using a sieve, making operations complicated. However, there is a problem that a sufficiently satisfactory effect cannot be obtained. In addition, the dissolved gas flotation method involves dissolving gas such as air under pressure in water containing pulverized coal, and the coal aggregates are floated by the floating force of the bubbles generated when the pressure is released. The principle is to separate the water from the aqueous phase. This method has the advantage of providing adequate air bubbles to the agglomerate. However, since the adhesion of microbubbles to coal aggregates is weak, the bubbles tend to detach during the washing operation, and the coal particles tend not to float when washed with water, so it is difficult to wash thoroughly with water, and dissolved gas It requires a high-pressure device for manufacturing, and has drawbacks such as being particularly susceptible to restrictions on increasing the size of the device. The present invention provides a method for removing ash from coal, which is based on the same principle as the conventional wet granulation method described above, but which can achieve a high ash removal rate without using a sieve for coal aggregates. . The present invention uses 100 parts by weight of pulverized coal with an average particle size of 50 microns or less, 500 to 1000 parts by weight of water, and
Surfactant in amount of 50-4000ppm, 50 for coal
An alkali metal salt in an amount of ~5000 ppm and 1 to 10 parts by weight of a hydrocarbon oil are mixed under vigorous stirring sufficient for deashing and gas-liquid contact from pulverized coal, then the coal floats while retaining air bubbles. While stirring slowly so as not to disperse the aggregates of water and hydrocarbon oil,
An organic phase and an aqueous phase containing aggregates of coal and hydrocarbon oil are prepared by adding and mixing 0.1 to 5% by weight of alkaline earth metal chlorides or hydroxides to the coal as an ash treatment agent. The present invention also relates to a method for removing ash from coal, which comprises forming an ash precipitate phase and then separating and recovering an organic phase. The present invention differs from the conventional wet granulation method in that coal is made into pulverized coal, which is treated with water and hydrocarbon oil to form aggregates (granules) of coal and hydrocarbon oil. However, the method of forming aggregates is fundamentally different. In the present invention, when forming an organic phase containing aggregates, the average particle size is
Pulverized coal that has been pulverized to 50 microns or less, a surfactant, an alkali metal salt, and hydrocarbon oil are stirred slowly to maintain air bubbles and prevent the floating aggregates of coal and hydrocarbon oil from dispersing. It is important to mix with stirring, and then add and mix ash treatment agents such as alkaline earth metal chlorides and hydroxides.These treatments easily remove the ash scattered on the surface of the pulverized coal particles. It is dispersed in water to increase the hydrophobicity of the particle surface, and the floc-like aggregates of coal and hydrocarbon oil with relatively low specific gravity and high buoyancy that retain fine air bubbles that are difficult to detach. It is formed and neatly separated into three phases: an organic phase containing aggregates of coal fraction with low ash content and hydrocarbon oil, an aqueous phase, and an ash precipitated phase. Therefore, this organic phase can be easily separated and recovered by, for example, a liquid separation method. According to the present invention, due to these effects, all of the above-mentioned problems (1) to (4) of deashing treatment using the conventional wet granulation method can be improved by the method of the present invention. Become. In addition, the recovery rate of coal content in the ash removal method of the present invention is 95% or more, reaching a level equivalent to the high recovery rate of conventional wet granulation methods. In addition, in the ash removal method of the present invention, there is no need to increase the size of the aggregates to the extent necessary for the separation operation using a sieve, and therefore it is possible to use pulverized coal in an ultra-fine powder state as a raw material, and moreover, it is possible to use coal particles as a raw material. It is also possible to relatively reduce the amount of hydrocarbon oil added by improving the surface hydrophobization. Next, the present invention will be explained in more detail. The ash removal method of the present invention uses coal powder that is more finely ground than the pulverized coal used in conventional wet granulation methods. In other words, the average particle size of pulverized coal needs to be 50 microns or less. If the particle size is coarse, not only will the ash removal rate decrease, but the floatability of aggregates will also be poor, and the separation of the organic phase and aqueous phase will be impaired. It becomes difficult. A more preferable average particle size of the pulverized coal is 30 microns or less. By setting the particle size of pulverized coal within this range, the surface area per unit weight can be increased,
The ash content from the surface of the pulverized coal particles is easily dispersed into water, and the floatability of aggregates and the separation property of the organic phase are also improved, making the ash removal method of the present invention extremely effective. In preparing pulverized coal, it is preferable to use a wet pulverization method, and when pulverized coal prepared by this method is used, a particularly high ash removal rate can be achieved. The hydrocarbon oil used in the present invention can be arbitrarily selected from various hydrocarbon oils obtained from petroleum, shale oil, tar sand, and coal, similar to the hydrocarbon oils used in conventional wet granulation methods. Can be done.
Examples of preferred hydrocarbon oils include heavy refined petroleum fractions, heavy gasified oils, kerosene, residual oils, and coal tar. Particularly preferred are heavy oils, which are easy to handle and inexpensive. The amount of hydrocarbon oil used is 1 part by weight for 100 parts by weight of pulverized coal.
~10 parts by weight. The effects of the surfactant and alkali metal salt used in the present invention are considered as follows. (a) It helps the dispersion of pulverized coal particles into water, and also helps the dispersion of ash into water, thereby promoting the removal of coal particle surface components. (b) Assist in the dispersion of hydrocarbon oils into water. (c) Facilitates homogeneous contact between pulverized coal particles and hydrocarbon oil, promoting the formation of homogeneous aggregates. (d) Aggregates of pulverized coal particles and hydrocarbon oil (coal content/
It makes it easier to entrain air into the inside of hydrocarbon oil aggregates), promotes phase separation between the organic phase and the aqueous phase,
Accelerates the floating of coal/hydrocarbon oil aggregates. As the surfactant having the above-mentioned effects, one having dispersibility or permeability is selected.
Preferred surfactants include anionic or nonionic surfactants with an HLB of 9-17 that promote dispersibility and permeability; specific examples include alkylbenzene sulfonates and polyoxyethylene. Sodium alkyl ether sulfate, sodium lauryl sulfate, ammonium lauryl sulfate, polyoxyethylene stearate, polyoxyethylene sorbitan monostearate, polyoxyethylene lauryl alcohol, polyoxyethylene nonyl phenol ether, polyoxyethylene lauryl ether, etc. Can be done. It is also possible to use only one kind of surfactant, and it is also possible to use two or more kinds in combination. In the present invention, the surfactant is 50%
It is added in an amount of ~4000ppm, preferably 80~2000ppm. If the amount is less than 50ppm, the effect of adding surfactant will not be apparent, and if the amount is less than 4000ppm,
An amount exceeding this amount is not only economically undesirable, but in some cases, the surface tension of water may be severely reduced, preventing the formation of aggregates, and the solubilization of hydrocarbon oil in the aqueous phase may become significant. This may interfere with the decalcification operation. Alkali metal salts are used to enhance the effect of surfactant addition and to enhance the cleaning and separation effect of ash from the surface of coal particles. The alkali metal salt is preferably water-soluble and alkaline, and the amount used is 50 to 5000 ppm based on coal.
is the amount of Coal/hydrocarbon oil aggregates are difficult to form at a pH of 6 or lower, and stable aggregates are easily obtained at a pH of 7 or higher. Therefore, by using a water-soluble alkali metal salt exhibiting alkalinity together with a surfactant, it is possible to improve not only the ash removal rate but also the ability to separate aggregates. Examples of preferred alkali metal salts include phosphates such as sodium tripolyphosphate, sodium pyrophosphate, and sodium hexametaphosphate; carbonates such as sodium carbonate and sodium bicarbonate;
Mention may be made of silicates such as sodium orthosilicate, sodium metasilicate; and alkaline salts such as the sodium salt of CMC. Also,
Neutral salts such as sodium chloride and sodium sulfate can also be used alone or in combination with the above-mentioned alkaline salts. Particularly preferred alkali metal salts are phosphates. In the present invention, pulverized coal, water, surfactant, alkali metal salt, and hydrocarbon oil may be mixed in any order, but pulverized coal, surfactant, and alkali metal salt are mixed with water first. Then, it is preferable to mix a hydrocarbon oil because the ash removal effect can be enhanced. Further, in the present invention, it is an important requirement that the above-mentioned components be mixed under vigorous stirring. This makes it possible to efficiently remove ash from pulverized coal, as well as retain it in fine aggregates that are difficult to desorb, promoting the separation of the organic phase and Phase separation and recovery operations also become easier. After mixing pulverized coal, water, surfactant, alkali metal salt, and hydrocarbon oil with vigorous stirring, in the present invention, an ash treatment agent that can selectively precipitate only ash is added while retaining air bubbles. Add and mix slowly while stirring so as not to disperse aggregates of coal and hydrocarbon oil that have floated to the surface. When the ash dispersed in water is precipitated by adding and mixing an ash treatment agent, an organic phase containing coal/hydrocarbon oil aggregates, an aqueous phase, and an ash precipitated phase are formed. Ash treatment agents include calcium chloride, magnesium chloride, barium chloride, calcium hydroxide,
Alkaline earth metal chlorides and hydroxides such as magnesium hydroxide can be used, but alkaline earth metal chlorides are particularly preferred. The amount of the ash treatment agent added is 0.1 to 5% by weight, preferably 0.5 to 3% by weight based on the coal. If the amount added is too small, the addition effect will not be sufficient, and if it is too large, it will cause inhibition of the formation of the organic phase. In addition, when precipitating the ash content, it is possible to use a flocculant such as a polymer flocculant, aluminum sulfate, etc., but these are unsuitable because they have the disadvantage that they also precipitate the coal content. An example of the ash removal method of the present invention will be described in detail below according to the operating procedure. In the present invention, a predetermined amount of pulverized coal, a surfactant,
A coal slurry consisting of alkali metal salt and water is prepared and placed under stirring, to which a predetermined amount of hydrocarbon oil is added and stirring is continued. It is also possible to introduce air bubbles from the bottom of the container at this stage, but with this method, the rising air bubbles cause the coal and oil to float upwards, making it impossible to perform sufficient agitation. It concentrates at the interface, making it difficult to even form aggregates. Also,
It is also possible to stop stirring at this point and leave the mixture to stand still so that the organic phase containing most of the generated coal/hydrocarbon oil aggregates and the aqueous phase containing a large amount of ash are phase separated. The phase contains a large amount of water in addition to coal and hydrocarbon oil aggregates, and ash is dispersed and suspended in this water. Therefore, by repeating the steps of adding water to the organic phase after phase separation, stirring, separating the organic phase and aqueous phase again, and recovering the organic phase, ultimately the ash in the water mixed into the organic phase can be removed. It could be close to zero. However, this method requires a large amount of water and is also complicated to operate. In addition, many of the ash particles dispersed and suspended in the aqueous phase are several microns or smaller, and therefore do not easily settle by natural sedimentation methods. Therefore, in the present invention, an ash treatment agent such as alkaline earth metal chloride or hydroxide is added without introducing air bubbles from the bottom of the container or immediately stopping stirring to recover the organic phase. By adding a predetermined amount and leaving it to stand after stopping stirring, it is separated into three phases: an organic phase in the upper part, a supernatant water phase in the middle, and an ash sedimentation phase in the lower part, and then the organic phase is separated and recovered. Note that the ash content of the coal contained in the organic phase is significantly lower than that of raw pulverized coal, so it may be dried as is and used for various coal purposes.
It can also be used as a raw material for coal-oil-water slurry by mechanically dehydrating it and adding appropriate additives. Next, Examples and Comparative Examples of the present invention will be shown. [Properties of Coal] The properties of Hunter Valley coal and Wallara coal used in the Examples and Comparative Examples are as shown in Table 1. [Sample Preparation] (1) Sample A Hunter Valley charcoal was dry crushed to a particle size of 500μ.
m powder, and then ball milled to a particle size of 74 μm.
Wet pulverization was performed until the following (passed through 200 meshes) amounted to 95% by weight or more to obtain a coal slurry with a concentration of 45.5% by weight. (2) Sample B Hunter Valley coal is made into a powder with a particle size of 3 mm to 500 μm, which is separated by heavy liquid with a specific gravity liquid of 1.35.The clean coal is then ball milled to obtain 95% by weight or more of particles with a particle size of 74 μm or less. wet grinding until
A coal slurry with a concentration of 50.0% by weight was obtained. (3) Sample C: Warara coal is pulverized in a large rotisserie mill for normal pulverized coal combustion to produce particles with a particle size of 177 μm or less.
Wet grind until the concentration is 98% by weight or more.
A coal slurry of 47.0% by weight was obtained. [Demineralization operation] Collect 300g of sample uniformly, with an inner diameter of 130mm and a height of
A 150 mm cylindrical container with a capacity of 2 and a stopcock at the bottom is placed in a stirring tank equipped with a four-blade stirring rod with a blade length of 30 mm and a height of 25 mm. 900g of water was added to the coal, and a surfactant and alkali metal salt were added to the coal.
After stirring for 5 minutes, 4% by weight of coal was added to heavy oil C as a hydrocarbon oil, and the mixture was vigorously stirred at a rotational speed of 900 rpm for 5 minutes while dispersing the air in the gas phase as fine bubbles in the liquid phase. . The liquid temperature in the stirring tank was about 25°C. Next, the rotational speed was reduced to 120 r.pm, and the coal that had floated to the surface while retaining fine air bubbles was slowly stirred so as not to disperse the aggregates with the hydrocarbon oil.
Adding an ash treatment agent or flocculant to coal,
After stirring for about 2 minutes, the mixture was allowed to stand for 2 to 3 minutes. After standing still, the organic phase containing coal/hydrocarbon oil aggregates formed in the upper part was separated and recovered by opening a stopcock at the bottom of the stirring tank and drawing out the lower ash precipitated phase and the middle aqueous phase. Next, a part of the aggregate was collected and dried at 107°C for 3 hours, and the oil content of the aggregate was measured by n-hexane extraction method to calculate the oil adhesion rate, and after the oil was removed, it was measured according to JIS8812. The ash content was defined as aggregate coal ash content. Next, the coal fraction recovery rate and deashing rate were calculated using the following formulas. Coal recovery rate (%) = (agglomerate weight x (1-oil adhesion rate) x (1-moisture content)
× (1-Agglomerate coal ash content) × 100) / Sample coal weight ×
(1 - ash content in sample coal) Deashing rate (%) = (1 - ash content in aggregate coal / ash content in sample coal) x 100 Examples 1 to 3 and Comparative Examples 1 to 3 Examples 1 to 3 The processing conditions and processing results are shown in Table 2, and the processing conditions and processing results of Comparative Examples 1 to 3 are shown in Table 3. In Examples 1 to 3, it was clearly separated into three phases: an organic phase containing coal and hydrocarbon oil aggregates in the upper part, a transparent aqueous phase in the middle, and an ash precipitate phase in the lower part. In Comparative Examples 1 and 2, although it was confirmed that the coal separated into three phases, the separability was insufficient and the coal fraction recovery rate was significantly reduced. Moreover, in the case of Comparative Example 3, there was no separation into three phases. The organic phase obtained in Examples 1 to 3 above was
It consisted of coal/hydrocarbon oil aggregates with air bubbles attached to them, and water contained between them.
In order to remove this water, the organic phase was filtered using filter paper, and after being dehydrated to some extent, it was further dried at 107° C. for 3 hours to sufficiently remove water. The dried agglomerate consisted of coal fraction and hydrocarbon oil.

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[Table] Used.

Claims (1)

[Claims] 1. Pulverized coal with an average particle size of 50 microns or less
100 parts by weight, 500-1000 parts by weight of water, 50 parts by weight for coal
Surfactant in amount of ~4000ppm, 50~ for coal
Alkali metal salts and hydrocarbon oil in an amount of 5000 ppm 1
~10 parts by weight are mixed under vigorous agitation sufficient for deashing from the pulverized coal and for gas-liquid contact, and then mixed to retain air bubbles to prevent floating aggregates of coal and hydrocarbon oil from dispersing. While stirring slowly, add and mix 0.1 to 5% by weight of alkaline earth metal chloride or hydroxide to the coal as an ash treatment agent to remove aggregates of coal and hydrocarbon oil. A method for removing ash from coal, which comprises forming a containing organic phase, an aqueous phase, and an ash precipitated phase, and then separating and recovering the organic phase.