JPS6018585A - Preparation of coal slurry - Google Patents

Abstract

PURPOSE:To obtain coal slurry having such viscosity that it can be transported by pipeline, by blending coal particles adjusted to particle diameters in a specific range with a liquid to give slurry having a specific concentration. CONSTITUTION:Coal particles having 5-95wt% cumulative weight ratio, having a particle size distribution adjusted in such a way that it obeys the formula [D is coal particle diameter(mum); D50 is coal particle diameter(mum)(5-500mum) at 50wt% cumulative weight ratio; F is cumulative weight ratio(wt%) of coal particle finer than coal particle diameter D; a is 2-5 in >=D50 particle diameter range, and 1-3 in <=D50 range particle diameter range] is blended with a liquid such as water, petroleum oil, methanol, etc. and the coal concentration is adjusted to >=55wt%, to give the desired slurry.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides pulverized coal that has been pulverized and then subjected to particle size distribution adjustment, and is mixed with a solvent to obtain a viscosity that is suitable for pipe transportation. The present invention relates to a method for producing coal slurry.

[Background of the invention]

Powder slurry transportation technology has been studied for a long time as a method for transporting solid powder as a fluid that is easy to handle. In recent years, the above-mentioned slurry transportation technology has been applied to the transportation of coal, which is safe without problems such as spontaneous combustion or dust scattering, and is easy to handle because it can be transported through pipes, which improves transportation efficiency. Various types have been developed.

These methods include COM (heavy oil-coal mixture), C
There are methods using coal slurries such as WH (water-coal mixture) and CMM (methanol-coal mixture).

In such a coal slurry, it is important to increase the coal content as much as possible in order to improve coal transportation efficiency. However, if the content of coal is increased, the viscosity of the slurry produced becomes high and the fluidity of the slurry is lost, making it impossible to transport the slurry through pipes. Therefore, there is naturally an upper limit to the coal content in the coal slurry, and for a slurry that has a viscosity that is suitable for practical use, the limit value is 50 to 55% by weight.

On the other hand, research on the viscosity of slurry, which is a mixture of powder and liquid, has been conducted for a long time using spherical particles, which are an ideal powder shape, and the following general conclusions have been obtained so far.

(1) The viscosity of a slurry is related to the proportion of interparticle void space that exists when the powder contained therein is packed with light. The smaller the void space in the powder slurry, the lower -1(n, R
oscoe, J3rit, J, Appl, pi
]ys,.

3.267 (1952), Rin J, par hS
+ Tran S, S”.

Rheology, 12.281 (1968), Mori Yoshibe, Chemical Engineering + 201488 (1956) +
J., v., Robson, J.

ph)rs, & Co11oid Chem, 53.
1042 (1949) ) (2) The interparticle void space during close-packed optical fibers becomes smaller when the particles have a plurality of different particle sizes rather than a single particle size. (A, E, R, ~
vestma”+ J, Am, Ceram, Soc,
, 13, 767 (1938), K. McQeary
, J. Am, Ceram, Soc., 44
．． 513 (1961) eF, D, Andereg
gl Ifld, Eng, C11eln, , 23
．． 1058 (1931)) In other words, in the study of (2) above, as shown in Figure 1, in a powder mixture of particles with different particle sizes, small-diameter particles filled the void space between the large-diameter particles. Therefore, the larger the particle size width (width from the maximum particle size to the minimum particle size) of the particles, the smaller the void space of the powder at the time of close-packed light, and the more densely filled it becomes. states. Therefore, when making a slurry by adding a liquid to a powder that is densely packed with particles with different particle sizes, the larger the particle size range and the more densely packed the powder is, the more fluid it is necessary to give the slurry fluidity. It can be assumed that a small amount of liquid is sufficient.

Therefore, in the research on (1) above, when making a fluid slurry by mixing powder and liquid,
It is stated that at the same concentration, the wider the particle size range of the powder particles, the higher the fluidity, that is, the lower the viscosity of the slurry can be produced.

Two methods of adjusting the particle size so that the interparticle void space is as small as possible during close-packed light emitting are two methods: one is to mix multiple powders with different particle sizes, and the other is to continuously distribute the particles over a wide range of particle sizes. There is a known method of pulverizing it. Research has been conducted for a long time on the connected particle size distribution that reduces the interparticle void space during close-packed light emitting, and the Andreasen formula (% formula (1930)) is known. The Andreasen equation, which is a typical one among these methods, is expressed as the following equation.

Here, D is the particle size (μm), F is the cumulative polymerization ratio (wt%) of particles that are smaller than the particle size, DL is the maximum particle size of the particles, n
is a constant having a value of 0.2 to 0.7. Figure 2 shows the AND777 formula, DL=300μm, n=0.46
This is the particle size distribution curve when

By producing a cis slurry using particles having such a distribution curve, it is possible to produce a highly concentrated slurry.

However, the above particle size distribution equation that gives the smuggling ratio applies only when the powder is composed of ideal spherical particles, and cannot be applied to particles such as pulverized coal whose particle shape is not spherical but irregular. do not have. Therefore, even if the particle size of coal is adjusted to match the above particle size distribution, it does not necessarily give the most densely packed coal, and it is also possible to produce cis slurry by mixing the coal adjusted in this way with a liquid. However, it does not necessarily provide low viscosity. For this reason, it has been difficult to produce a low-viscosity, high-concentration coal slurry that can be transported through pipes.

[Purpose of the invention]

An object of the present invention is to provide a method for producing a highly concentrated coal slurry having a viscosity that allows pipe transportation.

[Summary of the invention]

The present inventors prepared a highly concentrated slurry using coal particles pulverized into various particle size distributions and investigated its viscosity. At the same time, the inventors determined the optimum slurry for υ coal by measuring the porosity of these pulverized coals. The present invention was arrived at as a result of searching for particle size distribution. When a powder containing a mixture of particles with different particle sizes is packed in a close-packed manner by applying a vibrating metal or under centrifugal force, as shown in Fig. Since small particles are sequentially bombarded with light, particles of a single particle size can be filled with high density. It is necessary to add the necessary amount of liquid to impart properties. FIG. 3 schematically shows the filling state of particles in a fluid slurry, and in FIG.
1 is a liquid that fills the interparticle void space (interstitial liquid), 2 is a liquid that acts as a fluidizing medium (liquid film), and 3 is a coal particle.

According to research by the present inventors, the amount of liquid that acts as a fluid medium necessary to produce a slurry with fluidity suitable for pipe transportation is approximately 1 to 5% of the volume of powder in the slurry. This is clear from the results.

Therefore, when the specific gravity of coal is 1.3 and the amount of fluidizing medium required to produce a slurry with fluidity suitable for pipe transportation is 5 cm of the volume of coal in the slurry, the densest light of coal Percentage of interparticle void space at time (hereinafter referred to as porosity)
Figure 4 shows the diameter between the coal weight concentration of the slurry and the coal weight concentration of the slurry. Fourth
The previous limit was 50 to 5.
In order to produce a slurry with a coal concentration of 75% by weight or higher, which is higher than 5% by weight, the porosity of the coal must be about 28 or less. However, coal is a porous substance, and when coal and a solvent are mixed, some of the solvent is absorbed into the coal particles, so the porosity actually differs depending on the type of coal, so the above values are It varies somewhat.

From the above points, the present inventors believe that in order to obtain a coal slurry with a fluidity suitable for pipe transportation and with a still high concentration, the present inventors applied a close-packed optical fiber to conventionally known ideal spherical particles. It has been found that an optimum particle size distribution unique to pulverized coal is required, which is different from the particle size distribution that gives pulverized coal, and non-spherical irregular particles are formed.

The present invention provides the optimum particle size distribution of such coal particles as follows:
When the cumulative weight percentage is between 5 and 95%, the particle size distribution of coal is substantially expressed by the following formula: % () Dso: Coal particle size (μm) at a cumulative weight percentage of 50%
(5 to 500 μm) F: Cumulative weight percentage (weight %) of coal particles with finer coal particle diameter a Two constants (2 to 5 in the particle size range of Dso or more, I) go
The following particle size range is 1 to 3), and the pulverized coal having the particle size distribution is dispersed in a liquid.

In the present invention, there is an advantage that the power required for pulverizing the coal can be reduced by making the coal particles have a maximum particle size within the range of the above formula (1). However, it is not a good idea to make the coal particle size too large because the particles in the slurry settle due to the action of gravity during transportation and storage. The sedimentation of coal particles in slurry is not affected by the particle size, but also by the specific gravity and viscosity of the solvent used, but in view of the above circumstances, the coal used for slurry production has particles in which more than 95% are 1000 μm or less. It is desirable to crush it so that it has a diameter.

In the present invention, the particle size distribution of coal particles as shown in the above equation (1) can be obtained by, for example, sieving pulverized coal, separating coal particles with a small particle size, and -10,000 large coal particles with a large particle size. This can be achieved by wet-pulverizing with a ball mill or the like, dividing the wet-pulverizing time into several stages to prepare several types of coal particle groups with different particle size ranges, and mixing these coal particle groups.

The liquid mixed with coal particles having a predetermined particle size distribution is
Any of the solvents used in COM, CWM, and CMM coal slurries, ie, water, petroleum oil, and methanol, can be used.

FIG. 5 shows the particle size distribution of coal obtained by pulverizing and adjusting the particle size. The curve 1 in Fig. 5 is given by equation (1),
= 38 μm% I) a-3,0, D in the particle size range of go or more
,. The particle size distribution is shown when 8 = 2.5 in the following particle size range.The curve 2 in Figure 5 shows that the cumulative weight ratio changes almost continuously within the particle size range of 1 to 300 μm. The particle size was adjusted to
It has a narrow particle size distribution of ~90 μm and is close to a single particle size.

Figure 6 shows that coal adjusted to the particle size distribution shown in Figure 5 1 to 3 is placed in a cylindrical container, and the container is tapped until the volume of the coal-filled bed no longer decreases. This shows the porosity of the coal porosity layer when 1 to 3 in FIG. 6 correspond to the particle size distributions 1 to 3 in FIG. 5, respectively. As can be seen from FIG. 6, the porosity (1) of coal having a particle size distribution according to equation (1) according to the present invention is significantly smaller than that of coal having other particle size distributions, and ( It can be seen that the particle size distribution of formula 1) is effective in reducing the porosity of pulverized coal at the closest density.

When adjusting the particle size of the coal shown in FIG. 5, the particle size distribution was measured as follows. Particle size 37μm (400 mesh)
The above particle sizes were determined by wet classification using water using the criteria specified by JIS, and the particle size distribution was measured. Particles with a particle size of 37 μtn or less were measured by a light transmission method using sedimentation in a centrifugal force field. Moreover, water was used as a solvent.

In addition to the above-mentioned light transmission method, there are methods to measure the particle size distribution of fine particles with a particle size of 37 μm or less, such as the call counter method and the light scattering method, but the measurement results of the particle size distribution of microparticles are used. It is known that there are some differences depending on the measurement method and equipment. The particle size distribution according to the present invention is based on particle size distribution measurement using the above-mentioned light transmission method.

The viscosity of not only coal slurry but also slurry obtained by mixing powder and liquid varies greatly depending on the degree of aggregation of powder particles in the slurry. This is because the particle size distribution of the powder in the cis slurry appears to be of higher quality due to aggregation of the particles. In addition, when multiple particles aggregate to form an aggregate, the solvent is completely absorbed into the aggregate, resulting in the amount of solvent that contributes to the flow of the slurry (indicated by 2 in Figure 3). will decrease.

FIG. 7 schematically shows this situation. 7th
In the figure, an agglomerate-internal liquid 4 is present in an agglomerate 5. The cohesiveness of particles is greater as their surfaces are more lyophobic to the slurry solvent. In order to prevent such agglomeration of coal particles and create a coal slurry with higher concentration and lower viscosity,
It is desirable to further add a surfactant to the coal slurry to make the surface of the coal particles sticky with respect to the slurry solvent.

Addition of a surfactant is particularly effective for coal slurries that use water as a solvent; anionic surfactants or nonionic surfactants can be used as the surfactant.

[Embodiments of the invention]

Example After pulverizing coal A using a screen mill, the mesh size was 2.
Classified through a 97 μm (48 mesh) sieve, particle size 2
Coal particles of 97 μm or less were separated.

This coal particle is referred to as t-I. Coal particles having a particle size of 297 μm or more were wet-pulverized using a ball mill.

Wet pulverization was carried out for 10 minutes, 2 hours, and 12 hours, respectively, to prepare pulverized charcoal groups with different particle sizes.

The pulverized charcoal group wet-pulverized for 10 minutes is ■; the pulverized charcoal group wet-pulverized 2 hours is ■; the pulverized charcoal group subjected to 12-hour pulverization is ■.
shall be. By mixing the four types of pulverized coals 1 to 2 with different particle sizes produced in this way, the particle sizes were adjusted so that the particle size distribution was as shown in 1.2 of FIG. 5.

However, the coal having the particle size distribution shown in 3 in FIG. 5 was prepared by classifying the above-mentioned pulverized coal A using a sieve with an opening of 88 μm (x7o mesh).

A slurry was prepared using the three types of particle size-adjusted charcoal thus prepared. In this example, a coal-water slurry was prepared by using a highly ionic surfactant and water as a solvent. The slurry was prepared according to the following procedure. 100 g of dried particle size-adjusted charcoal and 42.9 g of water in which 0.5 g of anionic surfactant was dissolved were mixed and stirred.

The slurry thus prepared is a high IJ [coal water slurry] containing 7ON of coal. The viscosity of these slurries was measured using a rotating cylindrical viscometer at a temperature of 20 C and a shear rate of 18 s. 1 of Fig. 5 according to the present invention
The viscosity of slurry prepared with coal having a particle size distribution of approximately 1
The viscosity of the slurry prepared with coal having a particle size distribution of 000 cp and 2 in Figure 5 was approximately 1700 cI). On the other hand, the slurry prepared using coal having a particle size distribution of 3 in FIG. 5 showed no fluidity, and it was impossible to measure its viscosity.

Coal A used in this example has a relatively large pore volume;
Because it has high hydrophilicity, it has a great property of absorbing water, which is a slurry solvent. Incidentally, when Coal A is immersed in water, it absorbs 10 parts of water based on its dry weight (hereinafter referred to as 10% water absorption). As mentioned above, coal with a high water absorption absorbs water as a solvent into its particles, so the amount of solvent N that contributes to the flow of the slurry is reduced. Therefore, the maximum coal concentration (hereinafter referred to as critical concentration) of a slurry with a viscosity suitable for pipe transportation is lowered by the amount of solvent absorbed into the coal particles. In the case of coal A adjusted to particle size distribution 1 in Figure 5, the viscosity of the slurry adjusted to various concentrations using the above method is approximately 2000 CI.
) Therefore, it is considered that the coal-water slurry using Coal A can be sufficiently transported through pipes even if the coal concentration is about 72% by weight.

Example 2 In this example, coal A and Coal A also had a small water absorption rate (absorption rate 2-7
%), a coal slurry was prepared in the same manner as in Example 1, and its viscosity and processing limit were examined. As in Example 1, coal Bf whose particle size was adjusted to the particle size distribution shown in 1 to 3 in FIG. 5: Coal concentration 74
When we prepared a slurry with a weight of F% and measured its viscosity, it was found that the slurry prepared with coal having a particle size distribution of 1 in Figure 5 was approximately 1200 cp, and the slurry prepared with coal having a particle size distribution of 2 in Figure 5 was approximately 1200 cp. The resulting slurry was approximately j4oocp. Furthermore, the slurry prepared using coal having a particle size distribution of 3 in FIG. 5 did not exhibit fluidity as in Example 1, and it was impossible to measure the viscosity. A slurry with a coal concentration of 75% by weight was prepared using coal Bk having the particle size distribution shown in FIG. 1, and its viscosity [f was measured and found to be about 2500 cp. From this, it is considered that the upper limit of the coal concentration in the coal slurry having the particle size distribution of the present invention is about 75% by weight.

〔Effect of the invention〕

After adjusting the pulverized coal particles to have a predetermined particle size distribution, by mixing them with a liquid, it is possible to obtain a high concentration and low viscosity that does not interfere with pipe transportation, which improves coal transportation efficiency. It is possible to improve ξ.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the filling state of mixed powder with particles of different particle sizes, Figure 2 is a graph showing an example of Andreasen's particle size distribution, and Figure 3 is a diagram showing the filling state of particles in slurry. Schematic diagram, Figure 4 is a diagram showing the relationship between the porosity of pulverized coal during close packing and the coal weight concentration in a slurry made with coal having this porosity, and Figure 5 is a graph of coal after particle size adjustment. Figure 6 is a diagram showing the particle size distribution of each grain size distribution shown in Figure 5.
The figure shows the state of agglomerates of particles in a slurry in a schematic % formula % $1 Figure $2 Factor 1 Strange (,11*) 'f73 Figure 7

Claims (1)

[Claims] 1. When the cumulative weight ratio is between 5 and 95 inches, the particle size distribution is substantially expressed by the following formula (1). : Cumulative weight ratio 5 (coal particle size (μm) in l
(5 to 500 μm) F: Coal particle size DJ:, 9 Cumulative weight percentage of fine coal particles (weight i%) a Two constants (2 to 5 in the particle size range of Dso or more, I) go
A method for producing a coal slurry, which comprises mixing coal particles whose particle size has been adjusted to comply with the following particle size range 1 to 3) with a liquid to obtain a coal concentration of at least 55% by weight. 2. A method for producing a coal slurry according to claim 1, characterized in that the coal is pulverized so that the particle size of 1000 μm or less becomes 95 or more, and then the particle size distribution is expressed by the formula (1) above. . 3. The method for producing coal slurry according to claim 1, wherein the liquid is water, petroleum oil, or methanol. 4. The method for producing coal slurry according to claim 1, wherein the liquid is water, and a surfactant is added to the water.