JPH0119440B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dry deashing method for coal, which makes it possible to separate coal into carbonaceous fine powder and ash (mineral substance) fine powder. Recently, there has been active development of the use of coal as an alternative fuel to petroleum, but coal has a higher ash content than petroleum, which often causes problems when used not only as a fuel but also as a raw material for chemical products. It is necessary to remove mineral substances that turn into ash (hereinafter simply referred to as deashing) in advance. Therefore, conventionally, flotation method, heavy liquid precipitation method, OA
Techniques have been developed to refine coal into fine grains and remove mineral substances by methods such as the oil agglomeration method. However, all of these conventional methods have the following problems. (1) Since coal powder is deashed in water, the water content is high and dewatering is expensive. (2) There is a limit to the demineralization rate, and it is difficult to freely adjust it. (3) Since water used as a medium is a liquid, it has greater fluid resistance than gas, and it takes time for coal particles to move through it, making it inefficient. (4) In order to improve the deashing performance, it is necessary to add chemicals such as additives and oil, and there are many operating conditions for adjusting these, making the operation complicated and requiring advanced technology. The present invention aims to solve the above-mentioned problems, and by combining two types of dry separation means, coking coal can be efficiently separated into carbonaceous fine powder and ash fine powder. The purpose is to provide a method for dry deashing of coal. Therefore, in the method of the present invention, raw coal is pulverized into a mixture of carbonaceous fine powder with a size of several microns to several tens of microns and ash fine powder, and then this mixture is subjected to geometric classification using a sieve or the like. The above-mentioned carbonaceous fine powder is classified into a plurality of particle size stages each within a certain particle range using When separating ash into fine powder and ash, if the minimum particle size at each particle size stage is d ₁ and the maximum particle size is d ₂ , the terminal velocity of ash particles with particle size d ₁ in the force field of the subsequent sorting means is is characterized in that d ₁ and d ₂ are respectively determined so that the particle diameter is faster than that of carbonaceous particles having a particle diameter of d ₂ . When coking coal is pulverized, the fine powder is separated into carbonaceous fine powder and mineral fine powder, that is, ash, but since the two remain in a mixed state, it is necessary to obtain high-quality pulverized coal that does not contain ash. The two must be separated. In general, methods for separating fine particles include geometric classification methods such as sieves that focus on the size of the particles themselves.
and sorting means B that utilize gravity, centrifugal force, and other inertial forces.In the latter separation in particular, sorting is performed not only by the particle diameter itself, but also by the so-called final velocity of the particles, which is the addition of specific gravity. It will be done. When particles fall in a fluid, their falling speed increases at first, but as the speed increases, fluid resistance increases, and when this resistance becomes equal to gravity,
The particles fall at a constant speed without being accelerated any further. This terminal velocity is called the terminal velocity. Therefore, if we compare two particles with the same particle size, the fluid resistance will be the same, so the particle with higher specific gravity and therefore greater gravity will naturally
They have a small specific gravity and a higher terminal velocity than particles with smaller gravity. The method of the present invention is characterized by the above-mentioned two
By utilizing the differences in the separation characteristics of the seed separation means and combining them, fine mineral powder can be removed from the above-mentioned pulverized coal, and high-quality pulverized coal with carbonaceous quality can be collected in a dry state. be. When coking coal is pulverized as it is, the particle size ranges of both carbonaceous fine powder and mineral fine powder generally overlap, although the latter is in a slightly smaller range. Therefore, classification method A
Basically, it is difficult to separate them by using only a single method. Furthermore, even if an attempt is made to separate the two fine powders by focusing on the difference in specific gravity (about 1 for carbonaceous fine powder and about 2 for mineral fine powder) using sorting means B, this method will not allow separation due to the final velocity of the powder. As a result, carbon powder with a large particle size and mineral powder with a small particle size exhibit the same behavior, and it is basically difficult to separate the carbon powder and mineral powder. However, for sorting means B, if the particle diameter is the same, the terminal velocity is determined only by the specific gravity of the fine powder, so first, the raw material fine powder is classified into several particle size stages by classification method A, By applying the sorting means B to each particle size stage, it becomes possible to separate the raw material fine powder into carbonaceous fine powder and mineral fine powder. Figure 1 shows the frequency distribution of the particle diameter of the raw material fine powder.
The shaded area in the figure shows one particle size step of the particle size divided by the classification means A, and the geometric particle size of the raw material fine powder in this range is the difference between d ₁ and d ₂ . between. In order for the raw material fine powder in this range to be separated into carbonaceous fine powder with a low specific gravity and mineral fine powder with a high specific gravity by the sorting means B, the particle size d ₂ is required.
It is sufficient that the terminal velocity of the carbonaceous fine powder at the particle size d1 is lower than the terminal velocity of the carbonaceous fine powder at the particle size _d1 , and if the final velocity of separation by the sorting means B is set to the terminal velocity of this boundary, the two can be separated. It will be possible. That is, as shown in FIG. 3, for the same particle size, the terminal velocity of ash particles is faster than that of carbonaceous particles, and each terminal velocity increases as the particle diameter increases. Now, if the particle size of the ash particles corresponding to the terminal velocity v ₁ is d ₁ and the particle size of the carbonaceous particles is d ₂ , then in the particle size region sandwiched between d ₁ and d ₂ , the ash content is The terminal velocity of all particles is greater than v ₁ , and that of carbonaceous particles is always less than v ₁ . Therefore,
When sorting is performed using the terminal velocity v ₁ , ash particles and carbonaceous particles are completely separated. FIG. 2 shows the separation process of the present invention. In Fig. 2, the raw material end is crushed into a fine powder with a size of several microns to several tens of microns by a crusher 1, and a classifier 2 as a geometric classification means such as a sieve, and gravity, centrifugal force, or inertial force. Separator 3 as a subsequent sorting means using etc.
It is separated by As the crusher 1, a roller mill, bowl mill, ball mill, tube mill, or other fine crusher can be used, and these mills are commercially available and the technology has already been established. Considering the subsequent separation process, the narrower the particle size range, the more economical it is. The raw material fine powder pulverized by the pulverizer 1 is supplied to the classifier 2 along the line shown by the solid line, and is geometrically classified into various stages of particle size. As for the classifier 2, a sieve whose technology has already been established may be used. The raw material fine powder classified into particle size stages by the classifier 2 is further supplied to the separator 3 through a line shown by a solid line. In the separator 3, carbonaceous fine powder and ash (mineral substance) fine powder are separated at each particle size stage based on the difference in specific gravity, and collected as shown by double lines and broken lines, respectively. As the separator 3, a gravity sedimentation type separator, a centrifugal force type separator, etc. can be considered, but the sharper the separation, the more effective it is, so the former uses an upward flow type, and the latter uses a rotating internal counterflow type. Separators are effective. In either case, by using air or other gas as the separation fluid, carbonaceous fine powder can be efficiently collected in a dry state. Next, an embodiment of the coal dry deashing method of the present invention will be described. The terminal velocity of ash particles and carbonaceous particles corresponding to the mesh size of currently commercially available sieves is
As shown in the table.

[Table] From this table, after passing through a sieve of 170 meshes, 200
Particles that do not pass through the mesh sieve will have a diameter of 74-88μ. For particles in this range, the terminal velocity is greater than 75.4 cm/sec for ash and
33.6cm/sec or less, so if a mixture of both particles is thrown into the airflow blowing up from below at a flow rate of 50cm/sec, the carbonaceous particles will be blown upwards and the ash particles will fall downwards. The two can be separated.
This also applies to other sieve mesh areas, and Table 2 shows the flow velocity of the blowing air current for each area.

【table】

[Table] Figure 4 shows the configuration of the classifier 2 that uses a normal multi-stage sieve as a geometric classification means, the mesh number of wire mesh for each stage, and the minimum particle diameter d ₁ of each particle size stage. , indicates the maximum particle diameter d ₂ , particles of 88μ or more and particles of 20μ or less are discarded, and particles with a particle size between them are sent to the separator 3. In addition, in the figure, the code|symbol 21 shows a vibration exciter. FIG. 5 shows a specific example of the separator 3 as a subsequent sorting means based on terminal velocity, and is an example of an upward flow type separator. In this way, one separator 3 is required for each particle size group divided by the above-mentioned geometric classifier 2, and in this figure, an example corresponding to a group of particle sizes ranging from 74 to 88μ is shown. It shows.
That is, the particles that passed through the 170-mesh sieve of the classifier 2 mentioned above but did not pass through the 200-mesh sieve are separated into carbonaceous matter and ash, and the flow rate of the upward air current is 50 cm/sec. In addition, in the figure,
Reference numerals 31 and 32 indicate rotary valves. In this way, according to the method of the present invention, the following effects and advantages can be obtained. (1) Since gas is used as the deashing medium and it is a dry process, there is no need for dehydration, there is little fluid resistance, and deashing is performed quickly. (2) Since deashing is carried out by taking advantage of the difference in separation characteristics between the two types of separation means, already established technology can be used for each separation means, so operation is easy. (3) Since two types of separation means are effectively combined and utilized, a high degree of separation accuracy can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the frequency distribution of particle diameters of raw pulverized coal, Figure 2 is a process block diagram of the dry coal deashing method of the present invention, and Figure 3 shows the principle of sorting based on terminal velocity. FIG. 4 is a schematic diagram of a geometrical classification means used in a coal dry deashing method according to an embodiment of the present invention, and FIG. 5 is a schematic diagram of a subsequent classification means based on terminal velocity. It is a diagram. 1... A crusher, 2... A classifier using a geometric classification means such as a sieve, 3... A separator using a sorting means using gravity, centrifugal force, inertial force, etc., 21...
Vibrator, 31, 32...Rotary valve.

Claims (1)

[Claims] 1. After pulverizing raw coal into a mixture of carbonaceous fine powder with a size of several microns to several tens of microns and fine ash powder, this mixture is divided into a certain particle range by geometric classification means such as a sieve. The particles are classified into a plurality of particle size stages, and each particle size stage is separated into the above-mentioned carbonaceous fine powder and ash fine powder by subsequent sorting means based on terminal velocity using gravity, centrifugal force, inertial force, etc. When the minimum particle size at each particle size stage is d ₁ and the maximum particle size is d ₂ , the terminal velocity of the ash particles with particle size d ₁ in the force field of the subsequent sorting means is carbon with particle size d ₂ A method for dry demineralization of coal, characterized in that d ₁ and d ₂ are determined to be faster than those for coarse particles.