AU656184B2 - Production method of high-concentration coal-water slurry - Google Patents

Description

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AUSTRALIA

Patents Act 1990 656184

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: PRODUCTION METHOD OF HIGH-CONCENTRATION COAL-WATER SLURRY.

The following statement is a full description of this invention, including the best method of performing it known to me:- C C kC C C

SPECIFICATION

Title of the Invention Production Method of High-Concentration Coal-Water Slurry Field of the Invention This invention relates to a production method of a high-concentration coal-water slurry comprising crushed coal dispersed in water.

Description of the Prior Art o o In order to improve the transportability, storage adaptability, and ease to handle of coal, it is conducted that coal is pulverized into a fine powder and dispersed in water in the form of a slurry. This coal-water slurry is a relf-combustible fuel that burns without assistant fuels.

0 And it is required to have a high concentration in view of the combustion efficiency and have a low viscosity in view of ease to transport and handle. In order to meet the physically contradictory requirements of any higher concentration and any lower viscosity, various methods have heretofore been studied.

As wet production methods of high-concentration coalwater slurry, there have been known a hi,gh-concentration pulverization method, in which relatively large amounts ofj L

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i crushed coal, a relatively small quantity of water, and a dispersant are pulverized by a ball mill and then size classified to remove relatively coarse particles, producing a coal-water slurry with a high coal concentration of over by weight, and a low-concentration pulverization method, in which relatively small amounts of crushed coal and a relatively large amount of water are pulverized by a ball mill to produce a low-concentration coal-water slurry with a coal concentration of below 60% by weight, -the slurry is dehydrated to form a dehydrated cake, and the dehydrated do..a'0 cake is dispersed in water to yield a high-concentration coal-water slurry.

o0000 In the past, the low-concentration pulverization method has been predominantly used for its ease to remove coarse .dehydrated by way of a dehydrator to obtain a dehydrated particles by classification. For example, coal and watera are supplied to a first ball ia ll to produce at lowwith water and screened to remove coarse particles,i d Sidehydrated by way of a dehydrator to obtain a dehydrated icake, and the cake is fed along with water and a dispersant to a second ball mill to yield a high-concntration coalwater slurry (Japanese Patent Publication Laid-open 63- 15893/1988), or crushed coal and water are treated by way of a tube mill to produce a low-concentration slurry, the slurry is divided into two parts, one part is classified to 4C col-aersury particle dehydrated cake, the other part is treated by way of a wet ultra-fine pulverization mill, and then mixed with the above dehydrated cake to yield a high-concentration coal-water slurry (Japanese Patent Publication Laid-open 63-51493/1988). However, these methods have been defective in that it is difficult to obtain satisfactory products in terms of high concentration and low viscosity, they involve a complex operation, and require larger amounts of power for 96 0 a dehydrator and the like.

With the aim of providing an efficient method of lower o 0 power requirements to produce a high-concentration, stable, low-viscosity coal-water slurry of close-packed particles, the inventors have developed a production method of highconcentration coal-water slurry (Japanese Patent Application 2-418028/1990), in which raw coal is crushed by a crusher, 0 00 the crushed coal is mixed with water and a dispersant and pulverized by a mill to obtain a high-concentration coalwater slurry, part of the high-concentration coal-water 00o000 slurry is pulverized by a tower mill to obtain an ultra-fine, high-concentration coal-water slurry, and the ultra-fine, high-concentration coal-water slurry and the above remaining high-concentration coal-water slurry are mixed in the presence of a shearing force to yield a' high-concentration coal-water slurry with a reduced porosity ratio.

3 t 4 Object of the Invention Since, in the above-described production method of a highconcentration coal-water slurry, ultra-fine pulverisation in the tower mill is carried out at high concentration and high viscosity, the process is still insufficient in terms of reduction in power requirement and ease to handle the resulting ultra-fine particle slurry. It is a primary object of the present invention to provide an efficient method of producing a stable, easier-to-handle, highconcentration, low-viscosity coal-water slurry of closepacked particles with a low power requirement, by improving the above method so as to carry out pulverisation at low concentration and viscosity.

o Summary of the Invention 15 In accordance with the present invention, there is provided a method of producing a high-concentration coal-water 0 slurry comprising pulverising in a mill crushed coal having an average particle diameter of from 300 to 800 pm and a ilow-concentration finely pulverised coal-water slurry having an average particle diameter of 3 to 15 pn and a coal concentration of from 40 to 65%, followed by kneading to form the high-concentration coal-water slurry, wherein I; the said low-concentration finely pulverised coal-water slurry is obtained by mixing water and part of said high- 25 concentration coal-water slurry obtained in the pulverising c t c C step in the mill and finely pulverising the mixture so formed by a fine pulveriser.

stafl/irid/keep/pa16195.92 9.11 rN 1 The present invention will now be described in detail with reference to the drawings. In Fig.1, numeral I indicates a, hopper for storing crushed coal, numeral 2 indicates a pulverizer for pulverizing coal at high concentration, numeral 3 indicates a kneader for kneading, numeral 4 indicates a fine pulverizer for pulverization at low concentration, and numeral 5 indicates a product tank o for storing the high-concentration coal-water slurry.

I Numerals 6 and 7 indicate water and a dispercant, :o s 0respectively, to be added during pulverization, and numerals *00 8 and 9 indicate waler and a dispersant, respectively, to be added during fine pulverization.

F. First, crushed coal with an average particle diameter of 300 to 800 1 um is supplied from the hopper 1 to the pulverizer 2. The crusher 2 is separately supplied with the low-concentration finely pulverized coal-water slurry, water 6, and a dispersant (for example, an anionic surfactant) 7, o' Average diameter of coal fine particles of the lowconcentration finely pulverized coal-water slurry is 3 to The pulverizer is a ball mill or rod mill. A highconcentration coal-water slurry with an average particle diameter of 15 to 50/m and a concentration of 65 to 80% is obtained by the pulverization. The resulting high-

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concentration coal-water slurry is divided into two parts, I 1 1 1 1 1 1 1 1 1 1 1 1 l l l l one part is kneaded by the kneader 3 to obtain a product, which is stored in the product tank 6. The kneader is preferably of a type which provides kneading in the presence of a high shearing rate.

The other part of the high-concentration coal-water slurry is transferred to the fine pulverizer 4, where it is mixed and finely pulverized with water 8 and a dispersant 9.

For the fine pulverization, it is preferable to use a tower mill (for example, TOWER MILL (tradename)). In the present invention, the fine pulverization is carried out with additional water and at a. low concentration, thereby reducing the power requirement. Furthermore, the resulting low-concentration finely pulverized coal-water slurry has an average particle diameter of 3 to 15/im, but is easy to e4 U o, handle because of its low concentration. The slurry is returned to the pulverizer 2 to be used for the production of the high-concentration coal-water slurry.

As described above, in the present invention the low- 6" concentration finely pulverized coal-water slurry is added in the pulverization of crushed coal. With this method, coal particles are pulverized very efficiently compared to pulverization of the crushed coal alone, because finely pulverized coal particles of the low-concentration finely pulverizedcoal-water slurry come into gaps between crushed coal particles, enabling pulverization at low viscosity due -6- 6 I ,*I ALY--1 to a reduction in porosity.

When coarse crushed coal particles and finely pulverized coal particles with smaller particle diameters are mixed and pulverized by a pulverizer, the coarse coal particles and the finely pulverized coal particles with smaller diameters are pulverized independently of each other. As a result, control over the particle size distribution of the coalwater slurry for high concentration at the outlet of the pulverizer can be achieved by controlling the particle size distribution of coal particles at the inlet of the o pulverizer. In the present invention, the particle size distribution of coal particles at the pulverizer inlet can be flexibly adjusted by controlling the particle diameter and amount of the finely pulverized coal-water slurry oe>. supplied from the tower mill.

As described above, the present invention has an 0 advantage that the coal particle size distribution at the pulverizer outlet can be easily controlled. This is .u achieved by using the recirculation system in which part of the high-concentration coal-water slurry pulverized by the pulverizer 2 is further finely pulverized into fine particles by the fine pulverizer 4 and returned to the pulverizer 2, an effect which cannot be obtained by using a recirculation system in 'which part of the high-concentration coal-water slurry pulverized by the pulverizer 2 is simply -7- 2.

1 returned to the pulverizer 2.

Furthermore, since, in the Pulverization of crushed coal in -the present invention, coal particles can be pulverized in the state in which finely Pulverized coal particles of -the low-concentration finely pulverized coal-water slurry come in-to gaps between crushed coal particles -to redutce the gaps, that is, in a low-viscosity state due to a reduced porosity ratio, pulverization can be carried out at even higher concentration. Therefore, 'the amount of water to be added at -the pulverization can be reduced, and a process can 0 a be selected in which 'the reduction amount of water can be added at kneading.

Fig. 2 is a flow chart of the process. The amount of water 6 added -to the pulverizer 2 is reduced and the reduction amount of water is added as water 10 at kneading.

Thus, by -the addition of water at kneading, the viscosity can be reduced and -the resulting slurry can be stabilized by very simple kneading. For example, when a slurry of a tt t pulverization concentration of 69% is used to obtain a 69% coal-water Slurry, the slurry must be -thoroughly kneaded to obtain the desired viscosity reduction. On the other hand, when -tle pulverization concentration is 72%, the slurry can be mixed with 3% water to reduce 'the concentration to 69%, and in association with this, -the viscosity can be reduced to a value below -that of after kneading, obtained with -8- V~k 1V almost no substantial kneading, -thereby obtaining a stable slurry. Therefore, with -this method, kneading can sometimes be eliminated, or -the kneading power can be considerably reduced, -thereby obtaining a low-viscosity, stable, highconcentration coal-water slurry.

In the present invention, a- dispersant is added -to enhance and stabilize -the fluidity of -the slurry. It is preferable -to add the dispersant at pulverization, or it may alternatively be added at both pulverization and fine pulverization.

Brief Description o~f the Drawings Fig. I is a process flow chart of an embodiment of the production method according to -the present invention.

4I~rFig. 2 .is a process f low chart of another embodiment of the production method according -to the present invention.

Fig. 3 is a graph showing results of Embodiment I of present invention.

4 Description of the Preferred Embodiments A Preferred embodiments of the present' invention will now be described.

Embodiment 1 Raw coal was crushed by a crusher Into an average particle diame-ter of 600gim. 69 kg of the crushed coal, -9- I" 26.5 kg of water, and 34.5 kg of a low-concentration finely pulverized coal-water slurry obtained using the following procedure were supplied to a ball mill and pulverized to obtain 130 kg of a high-concentration coal-water slurry having a coal concentration of 69%. 100 kg of the slurry was kneaded by a kneader to yield a product. The product had a viscosity of 920 cp (at 250C) with good stability.

The low-concentration finely pulverized coal-water slurry was prepared as follows. 30 kg of the above remaining high-concentration coal-water slurry, 4.5 kg of water, and an appropriate amount of a dispersant were finely tr pulverized by a tower mill. As a result, 34.5 kg of a lowconcentration finely pulverized coal-water slurry having an average particle diameter of 5gm and a concentration of Sit was obtained. The low-concentration finely pulverized S t* t coal-water slurry was supplied to the above ball mill and pulverized.

Recirculation ratio of the amount of the low- K' concentration finely pulverized coal-water slurry to the pulverization amount was varied to investigate the relationship between the recirculation ratio and the Sattained concentration (attained concentration at a viscosity of 900 cp) and the porosity ratio of the product,.

The results are shown in Fig. 3. The attained concentration of the product is the highest and the porosity ratio is the 10 a~i~aaeas~ VtW 1. .i i I' I- o oc o 43 04 a *43 43443444 NO a o ec o j 6s 0 r ft r a 434 r434 434*4344 43 a34 4 1 f 434 t I *(t 43 C lowest at a recirculation ratio of approximately Embodiment 2 Raw coal was crushed by a crusher into an average particle diameter of 600uim. 69 kg of the crushed coal, 21 kg of water, and 34.6 kg of a low-concentration finely pulverized coal-water slurry obtained using the following procedure were supplied to a ball iill and pulverized to obtain 124.6 kg of a high-concentration coal-water slurry having a coal concentration of 72%. 95.8 kg of the slurry was mixed with 4.2 kg of water and kneaded by a kneader to obtain a high-concentration coal-water slurry having a coal concentration of 69%. The product had a viscosity of 620 cp (at 250C).

The low-concentration finely pulverized coal-water slurry was prepared as follows. 28.8 kg of the above remaining high-concentration coal-water slurry, 5.8 kg of water, and an appropriate amount of a dispersant were finely pulverized by a tower mill. As a result, 34.6 kg of a lowconcentration finely pulverized coal-water slurry having an average particle diameter of 5um and a concentration of was obtained. The low-concentration finely pulverized coal-water slurry was pu'veri7ed by the above ball mill.

In Embodiment 2, the amount of water at pulverization was reduced, and water of the amount corresponding the 11 -g ii I:ic F-i~i i.

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t 1 /I 12reduction was added at kneading. Viscosity, reduction effect of the addition of water at kneading is shown in Table 1.

Table 1 pulverizer outlet Water added M% Coal cone. M% of product Kneading (5,000 rpm, 6 min.) Product viscosity (cp) Viscosity reduction by water addition (cp) Viscosity reduction by kneading (cp) 69 0 69 None Kneaded 1,720 920 72 3 69 None Kneaded 0 00 0 4 0 00) 0000 0 40 0 00e~,0 0 00 0 0 0000 000900 O 6 9 00 0 00 OOE,0 0 00 00 0 *6 000 0 0060 0 0 0000 06 0 0 60 0 0 760 960 620 800 Particle diameter (00 lI g11 5.6 6.9 l Ottin 32.6 33.8 74ttm 84.5 81.4 o 21.5 21.1 As can be seen from Table 1, even when -the concentrations of -the final products are -the same as 69%, for the case in which the pulverizer outlet concentration is 69%, viscosities before and after kneading (requiring a power of approx. 10 kWH per ton of coal-water slurry) are 1,720 cp and 920 cp, respectively. On the other hand, for -the case in which -the pulverizer outlet concentration is 72%, the viscosity can be reduced to 760 cp by adding only 3% of water. Thus, when the amount of water at 12 4 J) cy 1/

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concentration to 72%, the power for kneading can be eliminated and the viscosity reduced by further 160 cp (920 760 160).

As described above, in the present invention, crushed coal and a low-concentration finely pulverized coal-water slurry are pulverized to produce a high-concentration coalwater slurry, which is divided into two part, one part of the slurry with water and a dispersant is finely pulverized S by a fine pulverizer, and returned to the pulverizer. Thus, 4 't additional water is mixed in the fine pulverizer to allow fine pulverization at low concentration and viscosity, thereby reducing the power required for fine pulverization and allowing easy handling of the finely pulverized coalwater slurry at the fine pulverizer outlet. Furthermore, by 9 t returning the finely pulverized slurry to the pulverizer, 'adjustment of particle size distribution of the high- 44 t concentration coal-water slurry as a product becomes easy and the porosity ratio of the coal-water slurry can be reduced, thereby providing efficient pulverization by the pulverizer due to a reduction in viscosity of the slurry.

Furthermore, since -the viscosity at pulverization can be reduced by returning the finely pulverized slurry to the pulverizer, the amount of water at pulverization can be reduced, and viscosity reduction achieved without kneading S13 6 1 r I puvrzrdet rdcini icsiyo h lry

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by adding the reduction amount of water at kneading, thereby reducing power required for kneading. Therefore, with the present invention, a low-viscosity coal-water slurry can be produced by a. simple process and operation with reduced power requirement.

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Claims (12)

1. A method of producing a high-concentration coal- water slurry comprising pulverising in a mill crushed coal having an average particle diameter of from 300 to 800 pmn and a low-concentration finely pulverised coal-water slurry having an average particle diameter of 3 to 15 pm and a coal concentration of from 40 to 65%, followed by kneading to form the high-concentration coal-water slurry, wherein the said low-concentration finely pulverised coal-water slurry is obtained by mixing water and part of said high- concentration coal-water slurry obtained in the pulverising step in the mill and finely pulverising the mixture so formed by a fine pulveriser.

2. The method of claim 1 in which water is added to 15 the mill in which the crushed coal and low-concentration finely pulverised coal-water slurry are pulverised.

3. The method of claim 1 or 2 in which a dispersing agent is added to the mill in which the crushed coal and low-concentration finely pulverised coal-water slurry are 20 pulverised.

4. The method of any preceding claim in which a dispersing agent is added to the mixture in the fine pulveriser to form the low-concentration finely pulverised coal-water slurry.

5. The method of any preceding claim in which the crushed coal has an average particle diameter of 600 pm.

6. The method of any preceding claim in which the finely pulverised coal-water slurry has an average particle diameter of 5 pm. stafl/irid/keeppat16195.92 9.11 i i) 2- 16

7. The method of any preceding claim in which the high-concentration coal-water slurry has a coal concentration of 69%.

8. The method of any preceding claim in which the finely pulverised coal-water slurry has a coal concentration of

9. The method of any one of claims 2 to 8 wherein the amount of water added at the pulverisation step is reduced and water is further added at the kneading step.

10. The method of any one of claims 3 to 9 wherein a dispersing agent is added to the fine pulverisation step or at both the fine pulverisation and pulverisation steps.

11. A method of producing a high-concentration coal- water slurry substantially as hereinbefore described with reference to the accompanying drawings.

12. A method of producing a high-concentration coal- water slurry substantially as hereinbefore described with reference to any one of the foregoing examples. C Dated this 9th day of November, 1994 20 JAPAN COM CO., LTD. By Its Patent Attorney GRIFFITH HACK CO Fellows Institute of Patent Attorneys of Australia staff/irid/keep/pat/l61 95.92 9.11 0Y 3 -Y& U -S T, f Abstract of the Disclosure A production method of a high-concentration, low- viscosity coal-water slurry of close-packed particles with a low power requirement, in which crushed coal with an average particle diameter of 300 to 800t/m and a low-concentration finely pulverized coal-water slurry with an average particle diameter of 3 to 15/,m and a concentration of 40 to 65% are pulverized to obtain a high-concentration coal-water slurry, which is divided into two parts, and one part of the slurry is kneaded by a kneader to yield a product which is stored in a product tank. The other part of the high-concentration coal-water slurry is mixed with water and a dispersant and finely pulverized by a fine pulverizer into a low- concentration finely pulverized coal-water slurry, which is returned to the pulverizer. 6 0 0 tea 0 044 0 60 0 a t t t r I S t Sr t (5 t I *1 4