JPH0337595B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to aqueous coal suspensions. More particularly, the present invention relates to highly concentrated aqueous coal suspensions that are utilized to facilitate the transportation of coal or used directly as fuel. According to known technology, various methods have been proposed for preparing this aqueous coal suspension. US Pat. No. 3,762,887 discloses a suspension of coal particles with a particle size of 4 to 325 mesh (Tyler standard sieve), in which the coal concentration reaches up to 69% by volume. In the suspension of this US patent, the majority of the coal particles are between 4 and 28
It has a particle size of mesh (Tyler standard sieve), which means it corresponds to a size of 4 mm or more. The suspension of the above US patent has essentially two drawbacks. One is that many of the coal particles have a fairly large size;
Another reason is that the coal concentration is relatively low. These 2
Two drawbacks (particularly the first one) mean that they can only be used directly as fuel in special equipment, such as cyclone burners, and therefore cannot be used in common combustion equipment. Furthermore, even when using special combustion equipment, i.e. equipment with long downtimes of the type mentioned above, there is always the disadvantage that during malfunctions for some reason unburned coal is discharged together with smoke and/or ash. It existed. West German Patent Application No. 2823568 states that the particle size
Aqueous suspensions of coal particles less than 100 μm are disclosed. However, the method for preparing this suspension is complicated. That is, the coal contains 10 wt. The coal suspension must be dispersed in water at a concentration that does not exceed that of the inert particles, and therefore the coal suspension must be concentrated after separation of the inert particles, and the small size of the coal particles leads to low filter efficiency and separation costs. It has the disadvantage of being high. The inventors have discovered that the drawbacks of the conventional method as described above can be solved by selecting two different size ranges of coal particles and adding to the suspension a polyelectrolyte selected from compounds with a special chemical structure. The inventors have found that the problem can be easily solved by doing so, and have arrived at the present invention. The coal suspension according to the invention contains particles of a first group with an average size of 210 to 60 μm (with a maximum size not exceeding 300 μm) and an average of 1/6 to 1/20 of the average particle size of the first group. a second group of particles having a size. Note that the "average particle size" of each group is the size corresponding to 50% of the heterogeneous mass distribution of that group. the first group of particles is at least 40% by weight of the total particles;
Preferably it is present at about 60% by weight. Because the cumulative particle size distribution curve represents two fractions (i.e., two different groups of coal particles), when plotted on a log-log graph, there is a flattening between the values representing the average size of the component fractions. It must indicate the area. This flat area means that the derivative when calculated on a log-log graph is less than 0.4, preferably less than 0.1, particularly preferably 0. Therefore, the cumulative particle size distribution has two particle sizes d ₁ between the mean diameters of the two fractions.
and d ₂ , and the numerical value expressed by the following formula is smaller than 0.4, preferably 0.1 or less, and particularly preferably 0. log (% CM ₁ ) − log (% CM ₂ )/log d ₁ − log d ₂ where (% CM ₁ ) and (% CM ₂ ) are the fraction of particles with sizes smaller than d ₁ and d ₂ ( %). The numerical value in this formula is the unit of particle size (μm
or mm). In addition to coal of the above-mentioned size, the coal suspension according to the invention contains a non-surface-active anionic polyelectrolyte, in particular containing alkyl-substituted polynuclear aromatic groups, with a molecular weight of more than 500, preferably from 800 to 3000. Contains giblets). In particular, monovalent cationic salts of polymerized alkylnaphthalene sulfonic acids with a molecular weight of approximately 2000 were selected, among which DAXAD15 and
DAXAD19 (trade name, WRGrace) and
Reoplast203 (trade name, Fratelli Lamberti SP
There is a compound commercially available as A.). The amount of polyelectrolyte in the suspension is generally from 0.1 to 1% by weight, preferably from 0.3 to 0.5%, particularly preferably about 0.4% by weight of the total suspension. The polyelectrolyte is also preferably added in the form of a concentrated aqueous solution. The polyelectrolyte solution is added to the water before dispersing both groups of coal particles, or
Alternatively, it is added to the aqueous suspension of coal particles of the second group, for example when prepared by wet milling, prior to adding the particles of the first group. The suspension according to the invention contains a stabilizer selected from organic gel types, preferably polysaccharides, such as the substance known under the name Kelzan (Kelco). The stabilizer is added in an amount of 0.01 to 0.03%, preferably 0.02% by weight of the total suspension, either simultaneously with the polyelectrolyte or after its addition. Stabilizers are only used if the coal suspension is to be used after a long period of time. This depends on the properties of the coal, and for example, this period may be about one month. The aqueous coal suspension according to the invention may contain inert substances associated with the coal. In this case, the method for preparing the coal suspension according to the invention differs from other methods, which require the separation of inert substances beforehand; in the latter method, the coal-water suspension is only carried out after the separation operation. A suspension is prepared. In this way, inert substances do not constitute an obstacle in the preparation of highly concentrated stable suspensions. If the concentration of the suspension is set to a very high value, e.g. coal 80
% by weight or more. As for the type of water used to prepare the coal suspension according to the invention, it can be of any type, plain fresh water or demineralized water or containing 40 g/or more of dissolved salts. water, especially seawater, can be used. The method for preparing a coal suspension according to the present invention consists of the following steps. (1) A process of grinding coal into two particle size levels. This grinding process is carried out either dry or wet (in the presence of water), in the case of dry grinding two groups of coal particles are obtained and in the case of wet grinding two groups of coal particles are obtained. A soft mass is obtained. However, in order to obtain large-sized particles, it is preferable to carry out dry grinding, and in order to obtain small-sized particles, it is preferable to carry out wet grinding. Polyelectrolytes may be present in the case of wet milling. (2) A step of mixing the two groups of coal particles in appropriate proportions if both were prepared dry or wet. (3) Adding the polymer electrolyte to water or, if only small-sized coal particles are wet-prepared, to an aqueous suspension of small-sized coal particles. (4) Adding the two mixed groups of coal particles to an aqueous polyelectrolyte solution, or adding larger sized coal particles to an aqueous suspension of smaller sized coal particles containing a polyelectrolyte. (5) Adding the stabilizer with the polyelectrolyte or after adding the polyelectrolyte and before adding the two mixed groups of coal particles or large size coal particles, or adding the two groups of coal particles to water. The process of adding after adding to. Examples of coal suspensions prepared according to the invention are shown in Table 2, but these specific examples are intended to further illustrate the invention and are not intended to limit the invention. Table 1 shows the characteristics of each coal tested.

【table】

【table】

TABLES Figures 1 and 2 are graphs showing the shape of the cumulative proportion curve versus particle size plotted on log-log coordinates. The vertical axis shows %CM, and the horizontal axis shows diameter (μm). From Figure 1, the average particle size of the first group is 83μm.
, the particle size of the second group is 11 μm, and d ₁
It can be seen that is 44 μm, _d2 is 25 μm, %CM ₁ is 40, and %CM ₂ is 40 (Example
twenty three). From Figure 2, the average particle size of the first group is 82μm.
, the particle size of the second group is 7.2 μm, and d ₁
is 50μm, _d2 is 20μm, and % _CM1 is 69.6
It can be seen that %CM ₂ is 63.6 (Example 10).

[Brief explanation of the drawing]

FIGS. 1 and 2 are log-log graphs plotting cumulative fraction versus particle size.

Claims (1)

[Scope of Claims] 1. A stable, transportable, directly combustible aqueous coal suspension containing a polyelectrolyte and, if necessary, a stabilizer, in which the particles of coal are
It has a maximum particle size not exceeding 300 μm and is divided into two different particle size groups, the first of these two particle size groups accounting for at least 40% by weight of the total coal particles, with an average particle size of 60 to 210 μm. The second group has an average particle size of 1/6 to 1/20 of the average particle size of the first group (here, "average particle size" refers to the cumulative mass of the group). (the size corresponding to 50% of the distribution), the cumulative particle size distribution curve plotted on a log-log graph shows a flat area between the mean diameters of the two particle size groups, and the particle sizes of the two groups d ₁ and d ₂ is the formula (a) log(%CM ₁ )−log(%CM ₂ )/logd ₁ −logd ₂ <0.4 (where (%CM ₁ ) and (%CM ₂ ) are each d ₁
and _d2 ), characterized in that the polyelectrolyte is a non-surface-active anionic substance. 2. In what is stated in claim 1,
the amount of coal particles in the first group is about 60% by weight;
Aqueous coal suspension. 3 In what is stated in claim 1,
An aqueous coal suspension having a value of the above formula (a) of 0.1 or less. 4 In what is stated in claim 3,
An aqueous coal suspension in which the value of the formula (a) is 0. 5 In what is stated in claim 1,
An aqueous coal suspension, wherein the non-surfactant anionic polyelectrolyte has an alkyl-substituted polynuclear aromatic group. 6 In what is stated in claim 5,
Aqueous coal suspension, wherein the polyelectrolyte has a molecular weight of more than 500, preferably from 800 to 3000. 7. In the claim 1, 5, or 6, the polymer electrolyte is selected from monovalent cationic salts of alkylnaltalene sulfonic acid polymers having a molecular weight of about 2000. There are things that can be done,
Aqueous coal suspension. 8. The invention according to claim 1, 5, 6 or 7, wherein the amount of polyelectrolyte is from 0.1 to 1% by weight, preferably from 0.3 to 0.5% by weight of the total suspension. %, aqueous coal suspension. 9 In what is stated in claim 8,
Aqueous coal suspension, wherein the amount of polyelectrolyte is 0.4% by weight of the total suspension. 10. An aqueous coal suspension according to claim 1, wherein the stabilizer is present in an amount of 0.01 to 0.03% by weight of the total suspension. 11. The aqueous coal suspension of claim 10, wherein the stabilizer is present in an amount of 0.02% by weight of the total suspension. 12 Claims 1, 10, or 1
Aqueous coal suspension according to claim 1, wherein the stabilizer is an organic gel, preferably a polysaccharide. 13. The aqueous coal suspension according to claim 1, wherein the water is salt water. 14. The aqueous coal suspension according to claim 13, wherein the brine is seawater.