JPS625478B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a coal-water slurry. Coal/water slurry is attracting attention as a material for transporting granular coal and as a raw material for direct combustion. For use in such applications, there is a need for a method that can produce a slurry with a desired concentration and viscosity, particularly a slurry with high concentration and low viscosity. Although various methods for producing coal slurry have been proposed in the past, no method has yet been proposed that meets these expectations. For example, JP-A-54-16511 discloses a method for producing a slurry containing 60 to 80% by weight of coal particles, but this method does not produce a slurry with low viscosity. The purpose of the present invention is to solve the problems of the prior art and provide a method for producing coal/water slurry that can produce a slurry with a desired concentration and viscosity, and in particular can produce a slurry with high concentration and low viscosity. . The inventors conducted extensive research on the concentration and viscosity of various coal/water slurries, and found that a certain correlation was established between concentration and viscosity, and this correlation is explained by the liquid film model described below. Therefore, it has been found that using this liquid film model, the concentration and viscosity of the slurry can be set to desired values, and that slurries with high concentration and low viscosity can also be produced. The present invention was made based on such knowledge, and was determined experimentally in advance when producing a coal/water slurry by mixing and stirring powdered coal and water. From the relationship between the slurry viscosity η and the liquid film water volume v calculated by equation (1) below, determine the liquid film water volume v ₀ corresponding to the target viscosity η ₀ , and then The above object is achieved by a method for producing a coal/water slurry having a viscosity and concentration matching a target value, which is characterized by adjusting the viscosity of coal so that the amount of water becomes _v0 . v=(V _T /V _C −ρ _C・ν)(1−ε)−ε …(1) where V _T : Water addition amount (cm ³ ) V _C : Coal particle volume (cm ³ ) ρ _C : Coal Bulk density of particles (g/cm ³ ) ν: Volume of water that unit weight of coal absorbs in water (cm ³ /g) ε: Volume ratio of voids between coal particles in air First, let us consider the effect on slurry viscosity. We will explain the concept of liquid film water by using a liquid film model. The liquid film model is shown in Figure 1. First, coal particles 10 are packed in air in contact with each other as shown in FIG. 1a. When water V _T (cm ³ ) is added to slurry the coal particles, the water enters between the coal particles 10, and the coal sticks become separated from each other as shown in FIG. 1b. At this time, the total water V _T added to form a slurry is divided into the following three parts. In other words, the “absorbed moisture” absorbed inside the coal particles
20Vab (cm ³ )”, “liquid film water” surrounding coal particles
30Vf (cm ³ )'' and ``40Vp (cm ³ )'' of pore water existing between the liquid film water.Among these, it is the liquid film water that affects the slurry viscosity.The liquid film here Water is defined as:
The liquid film water was determined by comparing the coal particles in the air shown in Figure 1a with the coal particles in the slurry and the liquid film water around them as shown in Figure 1b. The shapes and sizes of the two are designed to be similar to each other. Considering this, as is clear from comparing Figure 1 a and b, the volume ratio (porosity) ε of the voids between coal particles in the air is the same as the pore water in the slurry. , is equal to the volume ratio to the total volume of the slurry, that is, the sum of pore water Vp, liquid film water Vf, and coal particle volume Vc. Therefore, equation (2) is obtained. ε=Vp/Vp+Vf+Vc (2) On the other hand, since the total moisture V _T in the slurry is equal to the liquid film water Vf, the pore water Vp, and the absorbed moisture Vab, equation (3) is obtained. V _T = Vf + Vp + Vab … (3) Also, if the bulk density of coal particles is ρ _C (g/cm ³ ) and the volume of water absorbed by unit weight of coal in water slurry is γ (cm ³ /g), the absorbed moisture is Vab is expressed by equation (4). Vab/Vc=ρ _C γ (4) When the liquid film water amount v per unit volume of coal is calculated from equations (2) to (4), equation (5) is obtained. v=Vf/Vc=(V _T /V _C −ρ _C γ)(1−ε)
−ε…(5) In the liquid film model, if the amount of liquid film water is large, the
It is thought that the thickness of the liquid film becomes larger and the distance between the coal particles increases, and therefore the viscosity of the slurry decreases. In order to prove the validity of this idea, we actually measured the slurry viscosity of coal particles with different coal types and particle size distributions, and investigated the correlation between the slurry viscosity and the amount of liquid film water per unit volume of coal. The results are shown in FIG. The coals used were Australian Blairsall and Warkworth coals, and domestic Miike coal. There is a good correlation between the slurry viscosity and the liquid film volume per unit volume of coal, as shown in Figure 2, and it is recognized that the slurry viscosity decreases as the liquid film volume per unit volume of coal increases. The validity of the liquid film model is demonstrated. Furthermore, from FIG. 2, it is recognized that the following empirical formula holds true between the viscosity η and the amount of water in the liquid film. Therefore, after the target viscosity and concentration of the slurry are set, first, the value of the target viscosity is substituted into η in equation (6) to find the required value of the liquid film water amount. Next, substitute the required value of this liquid film water amount into equation (5), and further add water amount V _T
(calculated from the target concentration value), water absorption γ (previously measured water absorption of unit weight of coal), ρ _C
(bulk density of coal particles measured in advance), and coal particle volume V _C (slurry concentration and bulk density ρ _C
) is substituted, the porosity ε is calculated. By adjusting the particle size distribution of the coal powder so that the calculated ε is achieved, it becomes possible to produce a coal/water slurry having the desired viscosity and concentration. Examples will be described below. Example 1 Target viscosity 2Pa・S or less, coal concentration 60-80
% by weight slurry is prepared according to the method of the present invention. First, the liquid film water amount is determined, and then the porosity ε is determined from this liquid film water amount. Since the viscosity is 2Pa・S or less, from equation (7), η=8×10 ^-3・(Vf/Vc) ^-2 ≦2 …(8) Therefore, Vf/Vc≧0.06 …(9) becomes. Furthermore, since the coal concentration is 60 to 80%, 0.25≦V _T ρ _W /V _C ρ _C ≦0.67 (10) holds true. (V _T ρ _w is the weight of water in the slurry,
V _C ρ _C is the weight of coal in the slurry, and the coal concentration
For 60% this ratio is 40/60=0.67, for 80%
This is because 20/80=0.25. ) Here, by transforming equation (6), V _T /V _C =1/1-εVf/Vc+ε/1-ε+ρ
_C ν…(11) becomes. Substituting this equation (11) into equation (10), (0.25ρ _c /ρ _w −ρ _C γ) (1−ε)−ε≦Vf/V
c≦(0.67ρ _c /ρ _w −ρ _C γ)(1−ε)−ε (12). Also, from equation (9), Vf/Vc≧0.06 …(9), so from equation (9) and (12), 0.06≦Vf/Vc≦(0.67ρ _c /ρ _w −ρ _C γ) (1 −
ε) − ε…(1 3) Therefore (0.67ρ _c /ρ _w −ρ _C γ)(1−ε)−ε≧0.06…(14
) ε, we get Here, ρ _C and γ are values specific to coal, so
From these, if the particle size of coal particles is adjusted so that the porosity of coal particles in the air satisfies the optimum value determined by equation (14), the desired low viscosity (η≦2Pa) can be achieved for the desired coal type.・S) and high concentration (coal content 60-80% by weight) slurry is produced. Next, a method for determining the optimum value of porosity for various types of coal will be explained. The test coals were Australian Blair sole, which is one of the bituminous coals that absorbs the most moisture among the bituminous coals used as fuel, domestic Miike coal, which is one of the coals that absorbs the least amount of moisture, and the coals that absorb these two coals. This is Australian Warkworth coal with an intermediate moisture content. A highly concentrated water slurry with a glass slurry viscosity of 2 Pa・S or less is produced with the measured values of the bulk density ρ _C of these three coal types and the absorbed water ρ _C γ per unit volume of coal, and the coal weight concentration of 60 to 80%. Table 1 summarizes the optimum porosity of coal particles in air for the following reasons.

[Table] From Table 1, the optimum value of porosity becomes lower as coal absorbs more moisture. Coal that absorbs a lot of moisture is
Since a large amount of water added to form a slurry is absorbed into the particles, water as a medium located outside the coal particles decreases, increasing the viscosity of the slurry. Explaining using a liquid film model, in equation (7), the absorbed water ρ _C γ increases, so the amount of liquid film water Vf / Vc
decreases and the slurry viscosity increases. Therefore, in order to suppress the slurry viscosity, it is sufficient to lower the porosity ε in equation (7). Therefore, the optimum value of porosity becomes lower as coal absorbs more water. The Blairsall coal shown in Table 1 is the coal that absorbs the most moisture among bituminous coals, so the optimum value of the porosity should be the lowest. Therefore, if the particle size of each coal is adjusted to a particle size distribution such that the optimum value ε≦0.324 for the porosity of this Blairsall coal is achieved, a highly concentrated water slurry can be produced for most bituminous coals. Therefore, next we will discuss a method for adjusting the particle size distribution so that ε≦0.324. Figure 3 shows the results of measuring the cumulative weight percentage CPFT and porosity of coals with different particle size ranges produced under different grinding conditions. From FIG. 3, it was found that the wider the particle size range, the lower the porosity. In Figure 3, A, B, C
satisfies ε≦0.324, but the lower ε is, the more highly concentrated and low viscosity slurry can be produced, so a particle size adjustment method for further lowering ε will be explained. In order to lower the porosity, fine particles may be filled between coarse particles. In other words, the particle size range needs to be made wider. Therefore, coal particles were wet-pulverized for 20 hours to produce fine particles of 6 microns or less, which were mixed with coal A in Figure 3 and the porosity was measured. The results are shown in FIG. When the weight blending ratio of particles of 6μ or less is 0 to 10%, the porosity decreases. The particle size distribution at this time is shown in FIG. When 0 to 10% of particles of 6μ or less are mixed, the cumulative weight proportion CPFT (%) of 6μ or less is 0 to 11.3%. As mentioned above, in order to lower the porosity ε, it is necessary to add colloidal particles of several microns by weight to coal containing coarse particles produced by dry grinding.
% to widen the particle size range. Therefore, if finer particles are mixed in to further widen the particle size range, the porosity will decrease and a slurry with higher concentration and lower viscosity can be produced. However, in order to industrially produce large quantities of colloidal particles of several micrometers in size, many wet mills must be operated continuously for long periods of time, which means that a large amount of water is used as a wet milling medium. There is a problem in that the operating cost of the crusher is quite high. Therefore, even if finer particles of colloidal size could be produced and the porosity could be further reduced by particle size adjustment, the produced highly concentrated water slurry would be costly;
As a fuel, it will be as expensive as or even more expensive than COM or CMM, and the characteristics of highly concentrated water slurry will be lost. Therefore, due to cost considerations, there are restrictions on the size of colloidal particles, and this also places a lower limit on the porosity. Next, Blairsall coal is used as a raw material, and based on the above calculation results, the viscosity is 2 Pa・S or less, and the coal concentration is 60 to 80.
% slurry was produced. FIG. 6 is a process diagram. The raw coal 1 is crushed to at least 1 mm or less by a dry crusher 2, and then a part of the coal particles of 1 mm or less is sent to a wet crusher 5, where it is crushed into colloidal particles of about 6μ or less, and then sent to a dryer 6. send. Next, 5% by weight of this pulverized coal of 6μ or less was mixed with 1 mm or less of pulverized coal, and the particle size was adjusted so that the CPFT of 6μ or less was in the range of 0 to 11.3%. After the coal whose particle size has been adjusted is thoroughly mixed in the mixer 3, it is added to the water tank 7.
More water is supplied to form a slurry in the stirring tank 4. The viscosity was measured at a coal weight concentration of 60% to 80% in the slurry. The results are shown in FIG. The viscosity was measured using a double cylindrical measuring device while changing the shear rate, and the results shown in FIG. 7 were obtained. From FIG. 7, it is recognized that the viscosity of each slurry is 2 Pa·S or less. In the same manner, coal powder having a particle size distribution shown in Fig. 8 I to K, all of which are 6 μm or less and a CPFT of 10% or less, was produced, and after adding water so that the coal concentration was 65%, the mixture was stirred. did. For comparison, the CPFT of 6 μm or less is 20% (Fig. 8H),
A slurry containing no fine particles (L in Figure 8) was also produced to obtain a similar slurry. The measured porosity of these powders is shown in Figure 9, and for I, J, and K, ε≦0.324.
However, H and L are larger than 0.35. When the viscosity of these slurries was measured, it was found that
The results shown in Figure 0 were obtained. From Fig. 10, for I, J, and K where ε≦0.324, η≦2Pa・S, but for H, where ε>0.324,
It is recognized that L is η>2Pa·S. The above examples are η≦2Pa・S, coal concentration 60-80
% by weight, but the present invention is applicable to other viscosities,
Concentration products can also be manufactured by controlling the amount of liquid film water in the same manner. When the slurry produced by the method of the present invention is used as a fuel for a pulverized coal combustion boiler, the maximum particle size of the coal particles is preferably 100 to 1000 μm. This is because coarse particles have a low combustion speed and are difficult to burn. Further, in order to produce a low-viscosity slurry by the method of the present invention, it is preferable that the particle size distribution of the coal be as close to a close-packed system as possible. This is because the porosity of coal particles in the air becomes low. For example, in a slurry with a maximum particle size of 100 to 1000 μm, 10% by weight of fine powder with a particle size of 6 μm or less is used.
It is preferable to contain the following. In this range, the porosity becomes small and the viscosity becomes low. When the amount of fine powder of 6 μm or less exceeds 10% by weight, the porosity gradually increases and the viscosity of the slurry also increases. As described above, the present invention produces a slurry having a desired viscosity and concentration by adjusting the amount of liquid film water based on a liquid film model, and produces a slurry having a desired concentration and viscosity. In particular, highly concentrated and low viscosity slurries can also be produced.

[Brief explanation of the drawing]

Figures 1a and b are liquid film models, Figure 2 is a correlation diagram between slurry viscosity and liquid film water content, and Figure 3 is a relationship between porosity and
CPFT correlation diagram, Figure 4 is a correlation diagram between the blending ratio of particles of 6μ or less and porosity, Figure 5 is a correlation diagram of CPFT and porosity when the blending ratio of particles 6μ or less is changed, Figure 6 The figure is a process diagram of an embodiment of the present invention,
FIG. 7 is a correlation diagram between the coal concentration in the slurry and the slurry viscosity for the water slurry prepared according to the present invention.
Figure 8 is a graph showing the particle size distribution of coal powder, Figure 9 is a graph showing the particle size distribution of coal powder.
The figure is a graph showing the porosity of coal powder, and FIG. 10 is a graph showing the viscosity of coal slurry. 1... Raw coal, 2... Dry crusher, 3... Mixer,
4... Stirring tank, 5... Wet grinder, 6... Dryer, 7...
Aquarium.

Claims (1)

[Claims] 1. When producing a coal/water slurry by mixing and stirring powdered coal and water, the viscosity η of the slurry, which has been experimentally determined in advance, is calculated by the following equation (1). From the relationship with the liquid film water volume v, the target viscosity η
₀ , and _{the coal particle size is adjusted so that the liquid film water volume becomes v 0 according} to the target concentration. Method for producing water slurry. v=(V _T /V _C −ρ _C・ν)(1−ε)−ε …(1) where V _T : Water addition amount (cm ³ ) V _C : Coal particle volume (cm ³ ) ρ _C : Coal Bulk density of particles (g/cm ³ ) ν: Volume of water absorbed by unit weight of coal (cm ³ /g) ε: Volume ratio of voids between coal particles in air 2 Target viscosity η ₀ is below 2Pa・S,
The method for producing a coal/water slurry according to claim 1, wherein the slurry has a water content of 40% by weight or less. 3 Powdered coal has a maximum particle size of 100 to 1000 μm, and the content of fine particles of 6 μm or less is 10% by weight.
A method for producing a coal/water slurry according to claim 2, which is as follows.