CA1279477C - Method of preparing fine-particle high-loaded coal-water slurry and equipment for preparing the same - Google Patents
Method of preparing fine-particle high-loaded coal-water slurry and equipment for preparing the sameInfo
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- CA1279477C CA1279477C CA000523028A CA523028A CA1279477C CA 1279477 C CA1279477 C CA 1279477C CA 000523028 A CA000523028 A CA 000523028A CA 523028 A CA523028 A CA 523028A CA 1279477 C CA1279477 C CA 1279477C
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- mill
- coal
- classifier
- slurry
- preparing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23K—FEEDING FUEL TO COMBUSTION APPARATUS
- F23K1/00—Preparation of lump or pulverulent fuel in readiness for delivery to combustion apparatus
- F23K1/02—Mixing solid fuel with a liquid, e.g. preparing slurries
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Liquid Carbonaceous Fuels (AREA)
- Crushing And Grinding (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A method of preparing fine-particle high loaded coal-water slurry and equipment for preparing the same. Slurry flowing out from a first stage mill is supplied to a second stage mill so as to be ground therein after almost all coarse particles have been substantially removed therefrom.
A method of preparing fine-particle high loaded coal-water slurry and equipment for preparing the same. Slurry flowing out from a first stage mill is supplied to a second stage mill so as to be ground therein after almost all coarse particles have been substantially removed therefrom.
Description
DETAILED DESCRIPTION OF l'HE INVENTIOM:
[Field of the Invention]
The present invention relates to a method of preparing fine-particle high-loaded coal-water slurry which contains extremely small amount of coarse particles and equipment ~or preparing the same.
[Description of the Prior Art]
High-loaded coal-water slurry is a fluid rnixture of solid coal suspended in water, which is prepared in order not only to facilitate the transportation and storage thereof but also to allow the direct combustion thereof to be performed like oil. Further, since this fluidification of coal makes it possible to incorporate an ash removing process into the preparing procedure, ~uel having low ash and sulfur concentration can be obtained.
As methods of preparing this high-loaded coal-water slurry, a wet method, a dry method, a method which is a combination of wet and dry methods, etc. are known.
The wet method includes such methods as a method and a lower coal concentration higher coal concentration method.
In the higher coal concentration method, wet grinding is conducted by utilizing a ball mill or the like while supplying crushed coal, water, and a dispersion t~ ~
1 ag~nt comprising surfactant, thereby producing high-loaded coal-water slurry having the coal con-tent of not less than 60~ by weight~ I~ required, a stabilization agent may also be added.
When high-loaded coal-water slurry is burnt in combustion equipment such as a boiler, the requirPd combustion period is determined in accordance with the coal fuel ratio, the ash content, the particle size of the coal, the oxygen concentration, the combustion la temperature, etc. There~ore, when the period during which ~he slurry stays within the combus~ion equipment is insufficient to allow for the required combustion period, the combustion residue comprising fly ash, etc.
which is discharged together with the combustion gases will contain unburnt carbon, thus resulting in a calorific loss. In addition, when the air ratio is reduced and the combustion temperature is also lowered to a certain extent with the intention of reducing the generation of NOx in the exhaust gases as a result of the combustion, the combustion period will have to be increased.
In particular, when burning high-loaded coal-water slurry containing relatively large amount of coarse particles, an increase in the amount of unburnt carbon in the residue comprising fly ash etc., or the emission of NOx due to an increase in the air ratio, are noticeable consequences.
Accordingly, the method of preparing high-loaded coal-water slurry and equipment for preparing 1 the same are required ~o be capable of preparing high loaded coal-water slurry in which coarse parkicles are minimized.
It is also required that this method is economically feasible.
Fig. 3 shows a conventional method of preparing fine-particle high-loaded coal-water slurry and conventional equipment for preparing the same. In Fig. 3, coal 1, which has been crushed previously, is supplied by a weighing feeder to a mill 3, for example a ball mill, together with wa~er 4 and dispersion agent 5. The coal 1 is then ground and mixed into slurry within the mill 3 and flows out as fine-particle high loaded coal-water slurry 7, which is then transferred by means of a pump 6. The mill 3 has a length which is large compared to its diameter, the ratio of the length to the diameter being usually 4 to 8. The ratio of the length to the diameter of a mill employed in an ordinary method of preparing high-loaded coal-water 2~ slurry and ordinary equipment for preparing the same is 2 to 3. Increasing the ratio o~ length to diameter of the same makes it possible to increase the residence time of ~he coal-water mixture in the mill, thus promot-ing the grinding operation performed by the grinding medium, and thereby producing fine-particle high loaded coal-water slurry with fine particles.
Fig. 4 shows another conventional method of preparing fine-particle high loaded coal-water slurry ~q~7~
1 and another type of conventional equipment for preparing the same. In Fig. 4, reference numbers 3a, 3b, and 9 respectively designate ~he first mill, the second mill, ~nd a classifier. Re~erence numbers 1, 2, 4, and 5 respectively designate elements corresponding to those shown in Fig. 3. Slurry 8 from the first mill 3a is classified by the classifier 9, and most of the slurry 8 is made to flow as a lower flow 9a, while an upper flow 9b formed by the remaining part of ~he slurry is led to the second mill 3b wherein it is ground to form slurry 10. If required, ash in these parts of the slurry is removed by the coal cleaning device 11. Reference number 12 designates tailings. The slurry 9a and the slurry 10 thus introduced into a coal cleaning device 11 are low coal concentration slurry, each having a coal content o~
not more than 30% by weight.
Slurry 13 from the coal cleaner 11 is introduced into a dehydrating device 14 which removes water 15 therefrom, and the resulting slurry is made into cake 2Q having a coal content of not less than 60% by weight~
Subsequently, the cake is made into a fluid in a device 16. In this way, fine-particle high loaded coal-water slurry 7 is produced and i8 transferred by means of the pump 6.
However, both of the above conventional methods of preparing ine-particle high loaded coal-water slurry and equipment for preparing the same are not satisfactory in terms of simplicity in process and equipm~nt, and 1 reduction of coarse particles. To be specific, when use is made of a long mill which is so dimensioned that the ratio of length to diameter thereof is 4 to 8, fine-particle high loaded coal-water slurry may be prepared by its promoted grinding operation. With this arranyement, however, part o~ insufficiently ground coal are discharged from the mill before being su~jected to an adequate amount of grinding action, thus resulting in the production of a slurry in which coarse particles still remain, even though it is relatively reduced compared to that of a shorter mill. Particularly in the preparing procedure of high loaded coal water slurry having a coal content of not less than 60% ~y weight, this (coarse particles remaining) pro~lem is aggravated, since the 13 viscosity of the mixture rises as the grinding process proceeds.
In the another conventional case, where two mills are used, most of the slurry from the first mill is sent directly to the subse~uent process and only the remain-ing part is sent to the second mill. Since both grindingoperations are performed in a condition of diluted slurry, and a dehydrating device, a conditioning device, etc. are required for producing high loaded coal-water slurry, this arrangement suffers from the problem ~hat the equipment and operation manner are unavoidably complexed.
SUMMARY OF THE INVENTION
The present invention has succeeded in solving ~7~7~
l the problems encountered ~y the prior arts, and an object of the present invention is to provide a method of preparing fine-particle hiyh loaded coal-water slurry and equipment for preparing the same are excellent in the respect that they are capable of preparing high loaded coal-wa~er slurry having minimal coarse par~icles, and thus the unburnt carbon amount in the combustion residue and the NOx concentration in the exhaust gases are reduced substantially, when the slurry is supplied to combustion equipment to be burnt therein.
In order to achieve the above object, according to the present invention, slurry flowing out from a first stage mill is supplied to a second stage mill after considerable amount of coarse particles contained in the slurry have baen removed therefrom. Further according to the present invention, a first stage mill to which coal, water, and a dispersion agent are supplied, a classifier which removes coarser particles contained in slurry flowing out from the first stage mill, and a second 2Q stage mill to which the resulting slurry having been thus considerably removed o the coarse particles is supplied are arranged in series.
A ~all mill which i5 SO dimensioned that the rat;o of length to diameter is 2 to 4 is used for ~he first and second stage mills. As the classifier, a vi~rating screen, cylinder-shaped classifier, horizontal disc-shaped classifi~r, or horizontally movable classifier may be used.
~2~7~
DETAILED DF~SCRIPTION OF PREFERRED EMBODIMENTS:
Preferr~d embodiments of the present invention will be described below with reference to the accompany-ing drawings.
Fig. 1 is the flow sheet of a method of preparing fine-particle high loaded coal-wa~er slurry in accordance with the embodiment of the present invention;
Fig. 2 is a diagram used to explain the particle size distribution obtained in accordance with the method of the invention and that of the prior arts; Figs. 3 and 4 are flow shee~s of conventional methods of preparing fine-particle high loaded coal-water slurry.
Fig. 1 shows the embodiment of the present invention. A first stage mill 3a i5 supplied with coal 1, water 4, and a dispersion agent 5 under the operation o a weighing feeder 2 in such a manner that slurry having a predetermined coal content can be obtained.
The coal 1 is ground within the first stage mill 3a and the mixture flows out as slurry 8. The slurry 8 is then led to a classifier 9 wherein coarser particles 9b contained in the slurry 8 are removed from the mixture.
A lower flow 9a is directly supplied to a second stage mill 3b wherein it is successi~ely ground, flows out from the second stage mill 3b as fine-particle high loaded coal-water slurry 7 containing minimal coarse particles, and then is transf~rred by means of a pump 6.
The coarser particles 9b may be sent back to the first stage mill 3a through suitable means and may be . .
~q~ 7~
l ground together with coal l, ~ater 4, and a dispersion agent 5.
The slurry 8, the lower flow 9a, and the fine-particle high loaded coal-water slurry 7 have practically the same coal content which is not less than 60% by weight.
Although at the first stage mill 3a, part of the coal which has been insufficiently ground is made to flow out from ~he first stage mîll 3a as slurry containing coarse particles which has not been subjected to a sufficient degree of grinding action, the lower flow 9a containing lesser amount of coarse particles is supplied to the mill 3b where it is ground again.
Therefore, since the coarse particles are substantially low in this stage of grinding, the coal particlas can be adequately ~ubjec~ed to grinding action without any disturbance~ thus promoting the grinding operation and thereby producing fine-particle high loaded coal-water slurry 7 which contains minimal coarse particles.
In each of the first stage mill 3a and the second stage mill 3b, a ball mill which is so dimensioned that the ratio of length to diameter is 2 to 4 is used.
Thereore, within the first stage and second stage mills 3a and 3b, grinding can so procead in the state of high loaded coal-water slurry with adequately long residence time to prepare fine-particle high loaded coal-water slurry having a ~specified~ particle size distribution.
This arrangement achieves a remarkably finer particle .
` .
~q~ 7 1 size distxi~ution or arrangemen-t in comparison to that of the case of a single mill having the length to diameter ratio of approximately 3.
If mills having various improvements with respect to the structure and operating parameters are used as the first and second stage mills, ~his will enable realiza~ion of a method of preparing fine-particle high loaded coal-water slurry and equipment for preparing the same which exhibit excellent grinding efficiency lQ (reduced power consumption~ and the grindability.
As for the classifier, a vibration screen having a screening surface, a structure employing cylindrical classifying members having slits, a struc~ure employing rotatable horizontal disc classifying members having screening surfaces, a structure employing horizontally movable classifying members having screening surfaces which are movable in a continuous manner, or the like may be used. Classification is defined here as an operation of removing such partîcle from the original 2Q slurry that degrade grinding. In this emhodiment of the invention, coarser particles contained in the slurry from the first stage mill are removed for the purpose of facilitating the gr;nding in the second stage mill.
Conse~uently, the aperture si2e of the classiier 9 can ~e made much larger than the mean particle size of the fine-particle high loaded coal-water slurry 7, and this arrangement allow~ the slurry 8 to pass through the classifïer 9 witA ease even though the slurry 8 may have _ g _ 1 a high degree of vi~cosity. Therefore~ the capability of the classifier 9 can be increased, and furthermore, even when preparing a large volume of fine-par-ticle high loaded coal-water slurry, it is possible to handle the slurry without employing a classifier having an unreasonably large size~
Experiments conducted in accordance with the above embodiment will be described below. The coal used in the experiments had the following properties:
= BRAND COAL A
PROPERTIES
WATER % 4.3 H ASH ~ 13.2 VOh~TI~E COMPONENTS % 32.8 FIXED CARBON % 49.7 .. ~
C~LORIFIC VALUE Kcal/kg 6,630 FUEL RATIO 1.52 1~ Fig. 2 shows the particle size of fine-particle high loaded coal-water slurry obtained in accordance with the above embodiment, as compared to the particle size o~ slurry in the prior arts. In Fig. 2, a curve group a indicates the particle size obtained by the present invention, a curve group b indicates that obtained by a conventional mill having the length to diameter l ratio of 5, and a curve c indicates that obtained by a conven~ional mill having the length to diameter ratio of 3. The abscissa axis indicates the cumulative weight perc~ntage under the size of 74 ~m, which is an index of suitable particle size for combustion of fine-particle high loaded coal-wa~er slurry, while the ordinate axis indicates t~e cumulative weight percentage over the size of 150 ym, which is an index of unsuitable parti~le si~e. Each of ~he curve groups collectively indicates the data values of a num~er of experiments. As will ~e clearly seen from Fig~ 2, ordinate value ~cumulative oversize of 150 ~m) corresponding to a abscissa value 85~ ~cumulative undersize of 74 ym~ is much lower in curve group a ~he present invention~ than in curve groups b and c ~prior artsl.
In addition, the combustion properties of fine-particle high-loaded coal and water slurry were found to ~e as follows. Bituminous coal was used as raw coal, and the combustion equipment used had an electrical output of 60Q MW.
_ _ METHOD OF THE MET~IOD OF THE
INVENTION PRIOR ART
_ PARTICLE -74 Ym % 85 85 SIZE ~150 ym % l.l 2.9 _ . . _ PERCENTAGE OF TWO STAGE % 30 30 COMBUSTION
UNBURNT CARBON CONTENT % 2~0 4.0 NOx ppm 180 200 ~q~ 3~
1 As a resul~, it is clear that the present invention makes it possible to prepare fine-particle high loaded coal-water slurry containing minim~l coarse particles, and also possible, when the slurry is supplied to combustion equipment to be burned therein, to reduce the amount of the unburnt carbon in the combus-tion residue, and to lower the NOx concentration in the exhaust gases.
Incidentally, the arrangement of the mills and the classifier of the present invention is not limited to what has heen described in the above embodiment.
As described above in relation to the embodi-ments, according to the present invention, because the second stage mill is supplied with slurry from the first stage mill after coarser particles have been removed from the slurry by means of the classifier, and the slurry is then ground in the second stage mill, and also because the grinding is perfo~ned for an adequate period, fine-particle high loaded coal-water slurry containing minimal coarse particles can be prepared by relatively simple method and equipment with-out any complicated equipment or operation, and in addition, when the slurry is supplied to combustion equipment to be burnt therein, the amount of unburnt carbon in the combustion residue can be reduced and also the NOx concentration in the exhaust gases can be lowered. Further, according to the present invention, since the capability of the classifier can be increased, ~Y~7~
1 various advantages are attainable, such as the pos-sibility of mass production of fine-particle high loaded coal-water slurry, and the possibility of excel-lent grinding efficiency (reduced power consumption~ and grindability.
-. .' "' ', .
[Field of the Invention]
The present invention relates to a method of preparing fine-particle high-loaded coal-water slurry which contains extremely small amount of coarse particles and equipment ~or preparing the same.
[Description of the Prior Art]
High-loaded coal-water slurry is a fluid rnixture of solid coal suspended in water, which is prepared in order not only to facilitate the transportation and storage thereof but also to allow the direct combustion thereof to be performed like oil. Further, since this fluidification of coal makes it possible to incorporate an ash removing process into the preparing procedure, ~uel having low ash and sulfur concentration can be obtained.
As methods of preparing this high-loaded coal-water slurry, a wet method, a dry method, a method which is a combination of wet and dry methods, etc. are known.
The wet method includes such methods as a method and a lower coal concentration higher coal concentration method.
In the higher coal concentration method, wet grinding is conducted by utilizing a ball mill or the like while supplying crushed coal, water, and a dispersion t~ ~
1 ag~nt comprising surfactant, thereby producing high-loaded coal-water slurry having the coal con-tent of not less than 60~ by weight~ I~ required, a stabilization agent may also be added.
When high-loaded coal-water slurry is burnt in combustion equipment such as a boiler, the requirPd combustion period is determined in accordance with the coal fuel ratio, the ash content, the particle size of the coal, the oxygen concentration, the combustion la temperature, etc. There~ore, when the period during which ~he slurry stays within the combus~ion equipment is insufficient to allow for the required combustion period, the combustion residue comprising fly ash, etc.
which is discharged together with the combustion gases will contain unburnt carbon, thus resulting in a calorific loss. In addition, when the air ratio is reduced and the combustion temperature is also lowered to a certain extent with the intention of reducing the generation of NOx in the exhaust gases as a result of the combustion, the combustion period will have to be increased.
In particular, when burning high-loaded coal-water slurry containing relatively large amount of coarse particles, an increase in the amount of unburnt carbon in the residue comprising fly ash etc., or the emission of NOx due to an increase in the air ratio, are noticeable consequences.
Accordingly, the method of preparing high-loaded coal-water slurry and equipment for preparing 1 the same are required ~o be capable of preparing high loaded coal-water slurry in which coarse parkicles are minimized.
It is also required that this method is economically feasible.
Fig. 3 shows a conventional method of preparing fine-particle high-loaded coal-water slurry and conventional equipment for preparing the same. In Fig. 3, coal 1, which has been crushed previously, is supplied by a weighing feeder to a mill 3, for example a ball mill, together with wa~er 4 and dispersion agent 5. The coal 1 is then ground and mixed into slurry within the mill 3 and flows out as fine-particle high loaded coal-water slurry 7, which is then transferred by means of a pump 6. The mill 3 has a length which is large compared to its diameter, the ratio of the length to the diameter being usually 4 to 8. The ratio of the length to the diameter of a mill employed in an ordinary method of preparing high-loaded coal-water 2~ slurry and ordinary equipment for preparing the same is 2 to 3. Increasing the ratio o~ length to diameter of the same makes it possible to increase the residence time of ~he coal-water mixture in the mill, thus promot-ing the grinding operation performed by the grinding medium, and thereby producing fine-particle high loaded coal-water slurry with fine particles.
Fig. 4 shows another conventional method of preparing fine-particle high loaded coal-water slurry ~q~7~
1 and another type of conventional equipment for preparing the same. In Fig. 4, reference numbers 3a, 3b, and 9 respectively designate ~he first mill, the second mill, ~nd a classifier. Re~erence numbers 1, 2, 4, and 5 respectively designate elements corresponding to those shown in Fig. 3. Slurry 8 from the first mill 3a is classified by the classifier 9, and most of the slurry 8 is made to flow as a lower flow 9a, while an upper flow 9b formed by the remaining part of ~he slurry is led to the second mill 3b wherein it is ground to form slurry 10. If required, ash in these parts of the slurry is removed by the coal cleaning device 11. Reference number 12 designates tailings. The slurry 9a and the slurry 10 thus introduced into a coal cleaning device 11 are low coal concentration slurry, each having a coal content o~
not more than 30% by weight.
Slurry 13 from the coal cleaner 11 is introduced into a dehydrating device 14 which removes water 15 therefrom, and the resulting slurry is made into cake 2Q having a coal content of not less than 60% by weight~
Subsequently, the cake is made into a fluid in a device 16. In this way, fine-particle high loaded coal-water slurry 7 is produced and i8 transferred by means of the pump 6.
However, both of the above conventional methods of preparing ine-particle high loaded coal-water slurry and equipment for preparing the same are not satisfactory in terms of simplicity in process and equipm~nt, and 1 reduction of coarse particles. To be specific, when use is made of a long mill which is so dimensioned that the ratio of length to diameter thereof is 4 to 8, fine-particle high loaded coal-water slurry may be prepared by its promoted grinding operation. With this arranyement, however, part o~ insufficiently ground coal are discharged from the mill before being su~jected to an adequate amount of grinding action, thus resulting in the production of a slurry in which coarse particles still remain, even though it is relatively reduced compared to that of a shorter mill. Particularly in the preparing procedure of high loaded coal water slurry having a coal content of not less than 60% ~y weight, this (coarse particles remaining) pro~lem is aggravated, since the 13 viscosity of the mixture rises as the grinding process proceeds.
In the another conventional case, where two mills are used, most of the slurry from the first mill is sent directly to the subse~uent process and only the remain-ing part is sent to the second mill. Since both grindingoperations are performed in a condition of diluted slurry, and a dehydrating device, a conditioning device, etc. are required for producing high loaded coal-water slurry, this arrangement suffers from the problem ~hat the equipment and operation manner are unavoidably complexed.
SUMMARY OF THE INVENTION
The present invention has succeeded in solving ~7~7~
l the problems encountered ~y the prior arts, and an object of the present invention is to provide a method of preparing fine-particle hiyh loaded coal-water slurry and equipment for preparing the same are excellent in the respect that they are capable of preparing high loaded coal-wa~er slurry having minimal coarse par~icles, and thus the unburnt carbon amount in the combustion residue and the NOx concentration in the exhaust gases are reduced substantially, when the slurry is supplied to combustion equipment to be burnt therein.
In order to achieve the above object, according to the present invention, slurry flowing out from a first stage mill is supplied to a second stage mill after considerable amount of coarse particles contained in the slurry have baen removed therefrom. Further according to the present invention, a first stage mill to which coal, water, and a dispersion agent are supplied, a classifier which removes coarser particles contained in slurry flowing out from the first stage mill, and a second 2Q stage mill to which the resulting slurry having been thus considerably removed o the coarse particles is supplied are arranged in series.
A ~all mill which i5 SO dimensioned that the rat;o of length to diameter is 2 to 4 is used for ~he first and second stage mills. As the classifier, a vi~rating screen, cylinder-shaped classifier, horizontal disc-shaped classifi~r, or horizontally movable classifier may be used.
~2~7~
DETAILED DF~SCRIPTION OF PREFERRED EMBODIMENTS:
Preferr~d embodiments of the present invention will be described below with reference to the accompany-ing drawings.
Fig. 1 is the flow sheet of a method of preparing fine-particle high loaded coal-wa~er slurry in accordance with the embodiment of the present invention;
Fig. 2 is a diagram used to explain the particle size distribution obtained in accordance with the method of the invention and that of the prior arts; Figs. 3 and 4 are flow shee~s of conventional methods of preparing fine-particle high loaded coal-water slurry.
Fig. 1 shows the embodiment of the present invention. A first stage mill 3a i5 supplied with coal 1, water 4, and a dispersion agent 5 under the operation o a weighing feeder 2 in such a manner that slurry having a predetermined coal content can be obtained.
The coal 1 is ground within the first stage mill 3a and the mixture flows out as slurry 8. The slurry 8 is then led to a classifier 9 wherein coarser particles 9b contained in the slurry 8 are removed from the mixture.
A lower flow 9a is directly supplied to a second stage mill 3b wherein it is successi~ely ground, flows out from the second stage mill 3b as fine-particle high loaded coal-water slurry 7 containing minimal coarse particles, and then is transf~rred by means of a pump 6.
The coarser particles 9b may be sent back to the first stage mill 3a through suitable means and may be . .
~q~ 7~
l ground together with coal l, ~ater 4, and a dispersion agent 5.
The slurry 8, the lower flow 9a, and the fine-particle high loaded coal-water slurry 7 have practically the same coal content which is not less than 60% by weight.
Although at the first stage mill 3a, part of the coal which has been insufficiently ground is made to flow out from ~he first stage mîll 3a as slurry containing coarse particles which has not been subjected to a sufficient degree of grinding action, the lower flow 9a containing lesser amount of coarse particles is supplied to the mill 3b where it is ground again.
Therefore, since the coarse particles are substantially low in this stage of grinding, the coal particlas can be adequately ~ubjec~ed to grinding action without any disturbance~ thus promoting the grinding operation and thereby producing fine-particle high loaded coal-water slurry 7 which contains minimal coarse particles.
In each of the first stage mill 3a and the second stage mill 3b, a ball mill which is so dimensioned that the ratio of length to diameter is 2 to 4 is used.
Thereore, within the first stage and second stage mills 3a and 3b, grinding can so procead in the state of high loaded coal-water slurry with adequately long residence time to prepare fine-particle high loaded coal-water slurry having a ~specified~ particle size distribution.
This arrangement achieves a remarkably finer particle .
` .
~q~ 7 1 size distxi~ution or arrangemen-t in comparison to that of the case of a single mill having the length to diameter ratio of approximately 3.
If mills having various improvements with respect to the structure and operating parameters are used as the first and second stage mills, ~his will enable realiza~ion of a method of preparing fine-particle high loaded coal-water slurry and equipment for preparing the same which exhibit excellent grinding efficiency lQ (reduced power consumption~ and the grindability.
As for the classifier, a vibration screen having a screening surface, a structure employing cylindrical classifying members having slits, a struc~ure employing rotatable horizontal disc classifying members having screening surfaces, a structure employing horizontally movable classifying members having screening surfaces which are movable in a continuous manner, or the like may be used. Classification is defined here as an operation of removing such partîcle from the original 2Q slurry that degrade grinding. In this emhodiment of the invention, coarser particles contained in the slurry from the first stage mill are removed for the purpose of facilitating the gr;nding in the second stage mill.
Conse~uently, the aperture si2e of the classiier 9 can ~e made much larger than the mean particle size of the fine-particle high loaded coal-water slurry 7, and this arrangement allow~ the slurry 8 to pass through the classifïer 9 witA ease even though the slurry 8 may have _ g _ 1 a high degree of vi~cosity. Therefore~ the capability of the classifier 9 can be increased, and furthermore, even when preparing a large volume of fine-par-ticle high loaded coal-water slurry, it is possible to handle the slurry without employing a classifier having an unreasonably large size~
Experiments conducted in accordance with the above embodiment will be described below. The coal used in the experiments had the following properties:
= BRAND COAL A
PROPERTIES
WATER % 4.3 H ASH ~ 13.2 VOh~TI~E COMPONENTS % 32.8 FIXED CARBON % 49.7 .. ~
C~LORIFIC VALUE Kcal/kg 6,630 FUEL RATIO 1.52 1~ Fig. 2 shows the particle size of fine-particle high loaded coal-water slurry obtained in accordance with the above embodiment, as compared to the particle size o~ slurry in the prior arts. In Fig. 2, a curve group a indicates the particle size obtained by the present invention, a curve group b indicates that obtained by a conventional mill having the length to diameter l ratio of 5, and a curve c indicates that obtained by a conven~ional mill having the length to diameter ratio of 3. The abscissa axis indicates the cumulative weight perc~ntage under the size of 74 ~m, which is an index of suitable particle size for combustion of fine-particle high loaded coal-wa~er slurry, while the ordinate axis indicates t~e cumulative weight percentage over the size of 150 ym, which is an index of unsuitable parti~le si~e. Each of ~he curve groups collectively indicates the data values of a num~er of experiments. As will ~e clearly seen from Fig~ 2, ordinate value ~cumulative oversize of 150 ~m) corresponding to a abscissa value 85~ ~cumulative undersize of 74 ym~ is much lower in curve group a ~he present invention~ than in curve groups b and c ~prior artsl.
In addition, the combustion properties of fine-particle high-loaded coal and water slurry were found to ~e as follows. Bituminous coal was used as raw coal, and the combustion equipment used had an electrical output of 60Q MW.
_ _ METHOD OF THE MET~IOD OF THE
INVENTION PRIOR ART
_ PARTICLE -74 Ym % 85 85 SIZE ~150 ym % l.l 2.9 _ . . _ PERCENTAGE OF TWO STAGE % 30 30 COMBUSTION
UNBURNT CARBON CONTENT % 2~0 4.0 NOx ppm 180 200 ~q~ 3~
1 As a resul~, it is clear that the present invention makes it possible to prepare fine-particle high loaded coal-water slurry containing minim~l coarse particles, and also possible, when the slurry is supplied to combustion equipment to be burned therein, to reduce the amount of the unburnt carbon in the combus-tion residue, and to lower the NOx concentration in the exhaust gases.
Incidentally, the arrangement of the mills and the classifier of the present invention is not limited to what has heen described in the above embodiment.
As described above in relation to the embodi-ments, according to the present invention, because the second stage mill is supplied with slurry from the first stage mill after coarser particles have been removed from the slurry by means of the classifier, and the slurry is then ground in the second stage mill, and also because the grinding is perfo~ned for an adequate period, fine-particle high loaded coal-water slurry containing minimal coarse particles can be prepared by relatively simple method and equipment with-out any complicated equipment or operation, and in addition, when the slurry is supplied to combustion equipment to be burnt therein, the amount of unburnt carbon in the combustion residue can be reduced and also the NOx concentration in the exhaust gases can be lowered. Further, according to the present invention, since the capability of the classifier can be increased, ~Y~7~
1 various advantages are attainable, such as the pos-sibility of mass production of fine-particle high loaded coal-water slurry, and the possibility of excel-lent grinding efficiency (reduced power consumption~ and grindability.
-. .' "' ', .
Claims (15)
1, A method for preparing a high loaded coal-water slurry containing not less than 60% by weight of coal having fine particles, comprising the steps of:
supplying coal, water, and a dispersing agent to a first mill, the weight percent of the coal in the mixture so supplied being not less than 60% of the total, and grinding the mixture;
removing a substantial portion of the coarser particles contained in the slurry proceeding from said first mill;
returning said coarser particles to said first mill for further grinding; and supplying the resultant slurry substantially depleted of said coarser particles to a second mill and grinding the same therein, thereby reducing the particle size still further and obtaining a slurry containing a substantial amount of fine particles.
supplying coal, water, and a dispersing agent to a first mill, the weight percent of the coal in the mixture so supplied being not less than 60% of the total, and grinding the mixture;
removing a substantial portion of the coarser particles contained in the slurry proceeding from said first mill;
returning said coarser particles to said first mill for further grinding; and supplying the resultant slurry substantially depleted of said coarser particles to a second mill and grinding the same therein, thereby reducing the particle size still further and obtaining a slurry containing a substantial amount of fine particles.
2. Apparatus for preparing a high loaded coal-water slurry containing not less than 60% by weight of coal having fine particles, comprising in series:
a) a first mill for grinding a mixture of coal, water and a dispersing agent in which mixture the weight percentage of coal supplied is not less than 60% of the total weight;
b) a classifier for removing coarser particles contained in the slurry proceeding from said first mill;
c) recycling means for returning said coarser particles removed by said classifier to said first mill;
and d) a second mill to receive the slurry substantially depleted of said coarser particles, for grinding same and thereby reducing particle size still further to produce a high loaded coal-water slurry containing a substantial amount of fine particles.
a) a first mill for grinding a mixture of coal, water and a dispersing agent in which mixture the weight percentage of coal supplied is not less than 60% of the total weight;
b) a classifier for removing coarser particles contained in the slurry proceeding from said first mill;
c) recycling means for returning said coarser particles removed by said classifier to said first mill;
and d) a second mill to receive the slurry substantially depleted of said coarser particles, for grinding same and thereby reducing particle size still further to produce a high loaded coal-water slurry containing a substantial amount of fine particles.
3. A method for preparing a high loaded coal-water slurry containing not less than 60% by weight of fine particle coal having particles substantially less than 74 microns in size, comprising the steps of:
supplying coal, water and a dispersing agent to a first mill and grinding the mixture therein to produce a first stage slurry;
removing a substantial portion of the coarser particles contained in said first stage slurry and returning said coarser particles to said first mill for further grinding;
and supplying the resulting slurry substantially depleted of coarser particles to a second mill and grinding the same therein, thereby reducing the particle size to less than 150 microns, with a substantial amount of fine particles of size less than 74 microns therein.
supplying coal, water and a dispersing agent to a first mill and grinding the mixture therein to produce a first stage slurry;
removing a substantial portion of the coarser particles contained in said first stage slurry and returning said coarser particles to said first mill for further grinding;
and supplying the resulting slurry substantially depleted of coarser particles to a second mill and grinding the same therein, thereby reducing the particle size to less than 150 microns, with a substantial amount of fine particles of size less than 74 microns therein.
4. Apparatus for preparing a high loaded coal-water slurry containing not less than 60 percent by weight of fine particle coal having fine particles of substantially less than 74 microns, comprising in series:
a) a first mill to which coal, water, and a dispersing agent are supplied for grinding;
b) a classifier for removing the coarser particles contained in a first-stage slurry proceeding from said first mill;
c) recycling means for returning the coarser particles removed by said classifier from said first-stage slurry to said first mill; and d) a second mill to which a slurry substantially depleted of said coarser particles is supplied, for grinding the same to reduce particle size to less than 150 microns and obtain a substantial amount of fine particles of less than 74 microns.
a) a first mill to which coal, water, and a dispersing agent are supplied for grinding;
b) a classifier for removing the coarser particles contained in a first-stage slurry proceeding from said first mill;
c) recycling means for returning the coarser particles removed by said classifier from said first-stage slurry to said first mill; and d) a second mill to which a slurry substantially depleted of said coarser particles is supplied, for grinding the same to reduce particle size to less than 150 microns and obtain a substantial amount of fine particles of less than 74 microns.
5. Apparatus as defined in claim 4, wherein each of said first mill and said second mill comprises a ball mill so dimensioned that the ratio of length to diameter thereof is 2 to 4.
6. Apparatus as defined in claim 4, wherein said classifier is a vibrating screen.
7. Apparatus as defined in claim 4, wherein said classifier is a cylinder-shaped classifier.
8. Apparatus as defined in claim 2, wherein said classifier is a horizontal disc-shaped classifier.
9. Apparatus as defined in claim 4, wherein said classifier is a horizontally movable disc-shaped classifier.
10. The method as defined in claim 3, wherein the percentage by weight of particles having particle sizes greater than 150 microns is no more than about 1.3% and the percentage of particles having a particle size less than 74 microns is at least 85%.
11. The method as defined in claim 10, wherein the percentage by weight of particles having particle sizes greater than 150 microns is no more than about 1.1%.
12. A method for preparing a high loaded coal-water slurry as defined in claim 3, wherein the substantial proportion of coarser particles removed from the slurry proceeding from the first mill are removed by a classifier, said classifier being the sole classifier employed in said method.
13. A method for preparing a high loaded coal-water slurry as defined in claim 1, wherein the substantial proportion of coarser particles removed from the slurry proceeding from the first mill are removed by a classifier, said classifier being the sole classifier employed in said method.
14. Apparatus for preparing a high loaded coal-water slurry as defined in claim 4, wherein said classifier is the sole classifier used in said apparatus.
15. Apparatus for preparing a high loaded coal-water slurry as defined in claim 2, wherein said classifier is the sole classifier used in said apparatus.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP256900/85 | 1985-11-16 | ||
| JP25690085A JPS62116692A (en) | 1985-11-16 | 1985-11-16 | Method and device for production of finely particulate, high-concentration coal-water slurry |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1279477C true CA1279477C (en) | 1991-01-29 |
Family
ID=17298951
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000523028A Expired - Lifetime CA1279477C (en) | 1985-11-16 | 1986-11-14 | Method of preparing fine-particle high-loaded coal-water slurry and equipment for preparing the same |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0223573B1 (en) |
| JP (1) | JPS62116692A (en) |
| AU (1) | AU572410B2 (en) |
| CA (1) | CA1279477C (en) |
| DE (1) | DE3681123D1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU612127B2 (en) * | 1986-12-26 | 1991-07-04 | Ube Industries, Ltd. | Solid fuel-water slurry composition and process for the preparation of the same |
| DE3718568C1 (en) * | 1987-06-03 | 1988-06-30 | Steinmueller Gmbh L & C | Process for producing a coal-water mixture for combustion in a fluidized bed furnace and device for carrying out the process |
| JP2001190974A (en) * | 2000-01-07 | 2001-07-17 | Masumi Kusunoki | Cracking filter device for powder dispersing machine |
| CN103965981B (en) | 2013-01-31 | 2016-05-25 | 通用电气公司 | The apparatus and method of preparation water-coal-slurry |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4391702A (en) * | 1977-10-07 | 1983-07-05 | Nippon Steel Corporation | Method for classification of coals for coke production |
| DE2919914A1 (en) * | 1979-05-17 | 1980-11-20 | Stotz Ag A | Vibrating sieve grid with trough-like lower part - is designed to tip up for easy emptying of residue |
| AU545527B2 (en) * | 1981-12-03 | 1985-07-18 | Electric Power Development Co. Ltd. | Production of high concentration of coal |
| US4477259A (en) * | 1982-05-05 | 1984-10-16 | Alfred University Research Foundation, Inc. | Grinding mixture and process for preparing a slurry therefrom |
| US4477260A (en) * | 1982-05-05 | 1984-10-16 | Alfred University Research Foundation, Inc. | Process for preparing a carbonaceous slurry |
| GB2121819B (en) * | 1982-06-14 | 1985-03-27 | Smidth & Co As F L | Method of manufacturing a pumpable coal/liquid mixture |
-
1985
- 1985-11-16 JP JP25690085A patent/JPS62116692A/en active Granted
-
1986
- 1986-11-13 AU AU65106/86A patent/AU572410B2/en not_active Ceased
- 1986-11-14 EP EP19860308894 patent/EP0223573B1/en not_active Expired
- 1986-11-14 DE DE8686308894T patent/DE3681123D1/en not_active Expired - Lifetime
- 1986-11-14 CA CA000523028A patent/CA1279477C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0223573B1 (en) | 1991-08-28 |
| EP0223573A3 (en) | 1988-09-21 |
| AU572410B2 (en) | 1988-05-05 |
| EP0223573A2 (en) | 1987-05-27 |
| AU6510686A (en) | 1987-05-21 |
| JPS62116692A (en) | 1987-05-28 |
| JPH0329275B2 (en) | 1991-04-23 |
| DE3681123D1 (en) | 1991-10-02 |
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