US3517628A - Process for the treatment of crude coal slurry for fuel purposes - Google Patents

Description

June 30, 19.70 H. o. HARNISCH ETAL ,PRQCESS FOR THE TREATMENT OF CRUDE COAL SLURRY FOR FUEL PURPOSES Filed June 12. 1968 s mlwn e r 5 61 a m m Mw a w m Mr? f 1.4 1. w a N z- 5% M 2 mhfimw 0 8 a R a un W United States Patent 3,517,628 PROCESS FOR THE TREATMENT OF CRUDE COAL SLURRY FOR FUEL PURPOSES Heinz Harnisch, Heinz Friedrich Ottiny, and Rudolf V.d. Gathen, Dortmund, Hermann Hennecke, Mulheim- Saarn, Werner Heitmuller, Bielefeld, and Heinz Jochims, Moers, Germany, assignors to Deutsche Babcock & Wilcox-Dampfkellel-Werke-Aktien-Gesellschaft, a corporation of Germany Filed June 12, 1968, Ser. No. 736,381 Int. Cl. F23k 1/02 U. S. Cl. 110--101 15 Claims ABSTRACT OF THE DISCLOSURE This invention provides for hydro-mechanically produced coal a coal handling and firing system. In this system a slurry of fine coal granules is separated from a stream of larger coal pieces and then thickened upto the limit of its pumpability. Means are provided for pumping the thickened slurry to a reservoir. The thickened slurry is taken from the reservoir by a circulating pumping system and continuously circulated through a closed circuit and returned to the reservoir. By means of a burner system having an inlet into the circulating system, at least a portion of the thickened slurry is pumped at high pressure through a furnace burner.

BACKGROUND OF THE INVENTIOIN In the mechanical production and transportation of coal, part of the coal comes inevitably in the form of superfine granules in the size of less than 0.5 mm. Generally, part of the superfine granules are separated out in sitters, and the other part goes into the washing water at a later separation.

The increasing mechanization of the coal mining industry leads to a constant increase in the percentage of superfine granules in the raw coal. At the same time, the regulations for bonding the dust by means of water, for the sake of safety and health protection, are becoming stricter. Also, water is used in certain production methods. Thus, the water content of the raw coal has increased. It also follows that the percentage of the dust is reduced that can be sifted out by means of an air stream, while the slurry portion has increased.

In contrast to the mechanical production of coal, all of the superfine granules in a hydro-mechanically produced coal system are turned into a slurry. This slurry, which can be called a raw slurry, is separated by conventional settling installations and dehydrated according to known methods of flotation and filtration. In use, the slurry has been added to the coking coal. However, it is noted that this admixture of slurries is limited by the maximum admissible water content.

Accordingly, there have been various systems and processes developed to utilize these surplus slurries resulting from the mechanization and the hydro-mechanical method of coal production. [In one process, the raw slurries of coal are fired in the form of a coal/water suspension. However, in this process, the solids in the raw slurry must be ground to a fineness considerably below their natural initial state. Also, this wet grinding requires the use of expensive machinery which increases the costs of the entire operation.

It is, accordingly, an object of the present invention to provide a system for firing raw coal slurries with the coal in its natural granule composition and in a wide range of granule sizes.

3,517,628 Patented June 30, 1970 SUMMARY OF THE INVENTION The present invention relates to a system for handling and firing hydro-mechanically produced coal. The system includes a means for delivering a slurry of line coal granules from a stream of larger coal pieces and a means for thickening the slurry up to the limit of its pumpability. Pumping means are provided for pumping the thickened slurry to a reservoir for storage thereof. The thickened slurry is taken from the reservoir by a ciculating pumping system and continuously ciculated in a closed circuit and back to the reservoir. A burner system is provided having an inlet into the circulating pumping system and is arranged to pump at least a portion of the thickened slurry at a high pressure through a furnace burner. In the preferred embodiment of the pesent system, there is a density measuring device in th first portion of the circulating system to control the density of the thickened slurry.

An important advantage of the present system for handling and firing hydro-mechanically produced coal is that the slurry of fine coal granules is thickened up to the limit of its pumpability and to its ability to pass through the nozzle of a furnace burner. In practice, this means that the percentage of water in the slurry is only sufficient as a carrier for the coal granules and is kept as low as possible.

Another advantage of the present system is that the costly wet-grinding of coal granules to produce a suspension is not required; thus, the over-all system is simplified as well as being inexpensive.

The various features, aspects, and objects of the present invention will be more fully understood when considering the following detailed description in conjunction with the drawing. The drawing illustrates a coal handling and firing system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Refering to the drawing, hydro-mechanically produced coal is fed in a stream A into a wet sorting device or initial separator 1. The stream A consists of granules of coal of sizes varying from O to 50 mm., and 27% water. The superfine granules, i.e.'less than 0.5 mm., make up approximately 25% of the total amount of granules. The remaining portion consists of granules of 0.5 to 2.0 mm. (about 25% granules of 2. mm. to 10 mm. (about 35%), and granules larger than 10 mm. (about 15%). It is noted that these sizes are given only for purposes of illustrating generally the sizes of granules and the percentage they compose of a stream of hydro-mechanically produced coal.

From the separator 1, a primary slurry B- is separated, which is about 15% of the hydro-mechanically produced coal fed to the separator. The primary slurry B is composed of a comparatively large percentage of superfine granules below the size of 0.5 mm., as compared to the amount of 2 mm. granules of coal.

The primary slurry B, by means of gravity, is delivered directly to a blending or thickener tank 2. In the thickener tank 2, the thickening takes place through sedimentation. In this thickening operation, a certain concentration of solids accumulates in the lower part of the thickener tank 2 while the clear water remains on the top.

From the initial separating device 1, the other portion of the hydro-mechanically produced coal travels to a settling tank 3, in which the separation of the saleable coal C from the medium quality coal D (ranging in sizes from 2 to 50 mm.) and the tailings E takes place. As illustrated in the drawing, in this operation more slurry is produced, a secondary slurry F which is also fed into the thickener tank 2.

The secondary slurry F, as does the primary slurry B, consists of a comparatively large percentage of superfine granules, i.e. less than 0.5 mm. granules. The primary slurry B and the secondary slurry F undergo, by means of the abovementioned sedimentation process, a thickening of about 60% solids to 40% water.

A pump 4 is provided, beneath the thickener tank 2, which sucks the thickened slurry G out of the thickener tank 2 and feeds it to a storage tank 6 by way of a foreign matter separator 5. In the tube through which the slurry G is transported, a device 7 is mounted for measuring the density, e.g. an isotope density measuring device. The device 7 controls the performance of the pump 4 in such a manner that the solids content in the slurry stream G remains constant.

The separator 5 is of importance in that it insures that the granules of coal in the slurry furnished from the storage tank 6 are not of a larger size than the diameter of the nozzles of the burners of the furnaces described hereinbelow. In other words, the separator 5 insures, at the firing of the coal slurry, that no solid particles are of a size larger than the diameter of the nozzles of the furnace burners.

As shown in the drawing, the thickened coal slurry enters the lower cone-shaped part of the separator 5. The separator 5 has a centrifugal force such that the through velocity causes an upwardly directed spiral in which the larger foreign particles go downwardly through a valve 9 at the bottom of the separtor 5 to a collection point, and are entirely separated from the coal slurry. The action of the separator 5 is based on the fact that the entering velocity is a multiple of the through flow velocity.

In order to hold back floating foreign matter of more than a certain size from the storage tank 6, a perforated plate 8 is provided in the separator 5. The progressive clogging of the perforated plate 8 causes the pressure loss of the separator to increase. After a predetermined presusre loss is reached, the separator is emptied. For this purpose, the slurry stream is cut off, and the valve 9 at the bottom of the separator 5 is opened. The contents of the separator can then flow out through the conduit to the collection point.

A circulating system is provided for taking the thickened slurry from the storage tank 6. The circulating system includes a pump 10 installed under the reservoir storage tank 6 in a line 11. The line 11, with a return line 14, forms a closed circuit through which the thickened slurry is continuously circulated and returned to the reservoir storage tank 6. At spaced positions along line 11, there are conduits 17 connected for feeding the coal slurry to individual furnaces 12 of steam generators 13. Portions of the coal slurry are pumped by burner pumps 18 at a high pressure through the burners of the furnaces 12.

The surplus quantities of the slurry not fed to the furnaces '12 are returned to the reservoir 6 by means of the return line 14. With this arrangement, breakdowns and clogging of the nozzles of the furnace burners by the surplus slurry are prevented. Also, the continuous circulation of the thickened slurry causes a continuous turbulence which insures a stable suspension. Accordingly, velocity conditions can be provided in the closed circit, i.e. lines 11 and 14, so that there are no deposits occurring therein.

In order to insure a satisfactory, trouble-free operation, quantity measuring devices 15 are mounted in both lines 11 and 14 for adjusting exactly the quantity ratio of the slurry pumped to the furnace burners and returned to the storage tank 6. Another device 16 for measuring the density by means of isotopes is provided in line 11. This serves for an exact control of the density required for the optimum thing of the coat slurry.

When the pumps 18 are started up, the burners are, by means of a pneumatic device 19, automatically run into operating position with a certain time delay. In case of any difiiculty, the system is arranged to be automatically 4 turned off. For this purpose, a pump pressure measuring device 20 with sequenced control is provided. The pres sure measuring device 20 will cause any particular burner to be run back, away from the radiant heat zone of the firing, when a maximum pressure is reached whereby the burner pump 18 is simultaneously turned off.

A wash water conduit 21 is provided to further insure that the nozzles of the furnace burners are not clogged with deposits of solids of the coal slurry. After the furnaces 12 have been switched off, additional water by means of the conduit 21 is led through the burner pumps 18 and the nozzles of the furnace burners to flush out any deposit of solids therein.

Accordingly, when the furnaces 12 are switched off, the solids in line 11 must also be flushed out. For this purpose, a second wash water conduit 22 is provided under the storage tank 6, which leads into line 14. The deposits of the coal slurry contained in line 11 are accordingly pumped to the storage tank 6. This flushing process is continuous until the water is practically clear which flows out of the return line 14.

From the foregoing, it will be understod that the coal handling and firing system described above is well suited to provide the advantages and new and improved features set forth, and since various embodiments may be made of the features of this invention without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth and shown in the accompanying drawing is to be interpreted as illustrative, and not in a limiting sense, and that in certain instances some of the features of the invention may be used without a corresponding use of other features, all without departing from the scope of the invention as defined by the fol lowing claims.

What is claimed is:

1. A coal firing system in which the coal is in a slurry form thickened up to the limit of its pumpability, said system comprising:

(a) a circulating firing supply system in which said thickened slurry of fine coal granules is pumped at a first pressure from a reservoir and continuously circulated through a closed circuit back to said reservoir;

(b) a burner system having an inlet into said circulating firing supply system and arranged to pump at least a portion of said thickened slurry at a second and higher pressure through a furnace burner; and

(c) a coal delivery system to said circulating firing supply system in which a slurry of fine coal granules is separated from a larger stream of coal and thickened to the limit of pumpability, after which it is pumped into said circulating system to make up for the coal passing into said burner system.

2. A coal firing system as set forth in claim 1, wherein the slurry of fine coal granules is thickened to a residual water content of about 40% by weight.

3. A coal firing system as set forth in claim 1, wherein said burner system includes pneumatic control means for automatically operating said furnace burner when said slurry of coal is being pumped into said burner system.

4. A coal firing system as set forth in claim 1, wherein a density measuring device is placed in the first portion of said circulating system.

5. A coal firing system as set forth in claim 1, which includes a flushing system for flushing said closed circuit with water upon cessation of circulation of said thickened slurry to remove old granules therefrom and return the same to said reservoir.

6. A coal firing system as set forth in claim 1, wherein quantity measuring devices are placed in the first and second portions of the circulating system for adjusting the quantity ratio of said thickened slurry entering into said burner system and returning to said reservoir.

7. A method of firing coal from a stream of hydromechanically produced coal comprising:

(a) initially separating a slurry of fine coal granules from a stream of larger pieces of coal;

(b) thickening the slurry of fine coal granules up to the limit of its pumpability;

(c) pumping said thickened slurry to a reservoir station;

(d) subjecting said thickened slurry to a centrifugal force such that the through flow of velocity causes an upwardly directed spiral in which the :larger formed particles move downwardly to a collection point for the elimination from said slurry;

(e) effecting a continuous circulation of said thickened slurry from said reservoir station through a closed circuit back to said station; a

(f) pumpably removing at least a portion of said circulated thickened slurry at high pressure through a furnace burner; and

(g) upon cessation of circulation of said thickened slurry flushing said closed circuit with waterto remove old coal granules and return the same to the storage station.

8. A method of firing coal as set forth in claim7, wherein the slurry of fine coal granules is thickened to a residual water content of about 40% by weight.

9. A coal firing system as set forth in claim 1, wherein said coal delivery system includes a foreign particle separator having a centrifugal force such that the through flow velocity causes an upwardly directed spiral in which the larger foreign particles go downwardly to a collection point for elimination from the stream.

10. A coal firing system as set forth in claim 9, wherein a perforated plate is mounted in said separator to insure the separation of the larger foreign particles from the slurry of fine coal granules.

11. A coal firing system as recited in claim 1 wherein a density measuring device is placed in said coal delivery system.

12. A transporting system for a hydro-mechanically produced coal system comprising:

(a) a separator for separating a slurry of fine coal granules from a stream of larger coal pieces;

(b) means for thickening said slurry of fine coal granules up to the limit of its pumpability;

(c) a foreign particle separator having a centrifugal force such that the through flow velocity causes an upwardly directed spiral in which the larger foreign particles go downward to a collection point for elimination from the stream;

((1) a reservoir for receiving said thickened slurry of fine coal granules for storage thereof; and

(e) means for delivering said thickened slurry of fine coal granules from said separator to said reservoir.

v13. A transporting system as set forth in claim 12,

wherein a perforated plate is mounted in said separator to insure the separation of the larger foreign particles from the slurry of fine coal granules.

14. A method of firing coal comprising:

(a) circulating continuously a slurry of fine coal granules thickened to the limit of its pumpability;

(b) drawing from said circulating slurry at selected points portions of said slurry;

(c) pumping said portions of said slurry at a high pressure through furnace burners; and

(d) providing to said circulatory slurry a make-up stream of a slurry of fine coal granules thickened up to the limit of its pumpability.

15. A method of firing coal as set forth in claim 14,

wherein the slurry of fine coal granules is thickened to a residual water content of about 40% by weight.

References Cited UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner US. Cl. X.R. 302-66

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