US2716002A - Plural stage comminution system for wet solid materials - Google Patents

Description

Aug. 23, 1955 o. CRAIG 2,716,002

PLURAL STAGE COMMINUTION SYSTEM FOR WET SOLID MATERIALS Filed Oct. 18, 1950 2 Sheets-Sheet 1 a7 33 25 M 23 5 5 4 j 22 7* A INVENTOR BY W ATTORNEY Aug. 23, 1955 o. CRAIG 2,716,002

PLURAL STAGE COMMINUTION SYSTEM FOR WET SOLID MATERIALS Filed 0C(.. 18, 1950 2 Sheets-Sheet 2 R 52 /4 G O INVENTOR CAL/SON CRH/G BY dxQ/ fw ATTORNEY United States Patent fiFice 2,716,002 PatentedAug. 23, 1955 PLURAL STAGE CONIMINUTION SYSTEM FOR WET SOLID h IATERIALS (Ellison Craig, Worcester, Mass assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts Application October 18, 1950, Serial No. 190,715

3 Claims. (Cl. 24143) This invention relates to the comminution of wet solid material, and more particularly to an improved apparatus arranged to receive solid material having an appreciable quantity of surface moisture associated therewith and to reduce the material to a fine powder.

It has long been recognized that the capacity of a L pulverizer will decrease whenever-surface moisture is associated with the material entering the machine, and that a large percentage of surface moisture in the material may even render it impossible for the machine to operate at all. Various remedies have been suggested, including the provision of a drying apparatus to remove excess moisture from the material before it enters the pulverizer. Another suggestion involves introducing into the pulverizer heated gas, such as air, to aid in drying the material and to carry the fine material out of the machine. A drying apparatus is an expensive piece of equipment, it is often diflicult and complicated to operate, and in many installations it is not economically justified since the excess moisture conditions may be encountered rather infrequently. While the feeding of hot gas to the pulverizer is helpful with some types of pulverizer, there are many machines so constructed that such a procedure has very little effect in increasing the capacity.

It is accordingly one object of the invention to provide an apparatus capable of comminuting wet solid material to a fine powder at a very high rate in proportion to the sizeof the apparatus.

It is a further object of the invention to provide, in combination with a pulverizer of known construction, other apparatus which will greatly increase the capacity of the pulverizer- It is a further object of the invention to provide an apparatus for producing a fine powder from solid material and having a very high capacity in proportion to its size, the construction being such that no appreciable reduction in the capacity will take place even though the moisture content of the material as received may increase greatly.

It is a further object of the invention to provide an apparatus adapted for comminuting coal or similar solid fuel and delivering the fuel as a fine powder to a furnace for combustion, the capacity of the apparatus being affected very little by a considerable increase in the amount of surface moisture in the coarse fuel.

With these and other objects in View, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In accordance with the invention in its preferred form there is provided a pulverizer, which may be of any suitable and known construction. For example, the pulverizer may include a plurality of rolling elements, such as rollers or balls, arranged to pulverize material in a horizontal annular zone from which the fine material is discharged outwardly into a surrounding upwardly flowing current of air. Or the pulverizer may include a hollow drum rotating about a substantially horizontal axis and containing loose grinding bodies which pulverize material delivered to the drum, the fine material being removed by a current of air flowing through the drum. Whatever may be the construction of the pulverizer, there is associated therewith a suitable crusher having revoluble hammers arranged to crush the material and deliver it to the pulverizer. The crusher hammers are preferably revoluble about a substantially horizontal axis, with an arcuate grid located beneath the hammers, the hammers serving to force the crushed material through the grid. Hot gas, such as air, is supplied to the crusher and is intimately mixed with the material by the action of the revolving hammers, so that the surface moisture is very rapidly evaporated from the material before it leaves the crusher. Thus the crushed material entering the pulverizer is comparatively dry and the pulverizer can be operated at its full capacity. Furthermore, because of the very appreciable comminution effected by the crusher, there is less work required of the pulverizer, and the capacity of the pulverizer is correspondingly increased. When the construction of the pulverizer is such that different entrances are required for the air and for the material to be pulverized, a separator is provided between the crusher and the pulverizer, the separator being close-coupled to the crusher. This separator may be of the centrifugal type in which the entering mixture is whirled so that the crushed material will be thrown outwardly from the air and led to the pulverizer by one pipe, while the air travels through another pipe to the air entrance of the pulverizer.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Fig. 1 is a somewhat diagrammatic elevation, partly in section, showing an apparatus for preparing pulverized coal and feeding the same to a steam boiler furnace for combustion therein; and

Fig. 2 is a view similar to Fig. 1 but showing a modification.

The embodiment illustrated in Fig. 1 comprises a steam boiler furnace 10 arranged to be fired with pulverized coal supplied through a pipe 11 leading to a burner 12 at the front of the furnace. The hot gaseous products of combustion flow through a duct 14 to an air heater 15 and thence through a duct 16 to a stack or induced draft fan L (not shown). Air is supplied to the heater 15 by a forced draft fan 18, and the hot air leaves the heater through a duct 19 leading to the burner 12.

The coal to be burned in the furnace 10 is reduced to a fine powder by means of a pulverizer 21 of the general type disclosed in the United States patent to Wood et al. No. 2,237,021 granted April 1, 1941. This machine comprises an upwardly open circular bowl 22 rotatable about a vertical axis and having an annular inner lining 23 which forms a grinding track, or ring. A series of idler rollers 25 cooperate with the track 23 to pulverize material, each roller being urged outwardly toward the track by a spring 26. The bowl 22 is secured to the upper end of a vertical shaft 27 having a worm gear 28 thereon, the gear meshing with a suitably driven worm 29. The coal is delivered to the interior of the bowl by gravity through a pipe 31. The bowl is mounted within a casing 32 shaped to leave an annular space 33 around the outside of the bowl. Air enters the casing through an inlet opening 34 located somewhat below the bowl and flows upwardly through the annular space 33 at suflicient velocity to entrain coal which has spilled outwardly from the bowl.

The air with the entrained coal flows upwardly through.

openings (not shown) into a classifier 36 above the casing 32, the classifier being, adapted to separate the coarser particles of coal from the air stream and to return them to the bowl 22 by gravity through a central opening 37 in the top of the casing. The air stream, with the fine other driving means.

particles of coal entrained therein, flows upwardly from the classifier through a pipe 38 leading to the inlet of a fan 39, the outlet of this fan being connected to the pipe 11 which leads to the burner 12.

Before the coal enters the pulverizer 21, it is subiected to a combined drying and crushing operation. For this purpose there is provided a crusher 41comprisi'ng a casing 42 within which there is mounted a rotor 43 provided with a series of revoluble hammers 44. The rotor 43 is rotated about'a horizontal axis by a suitable motor or An arcuate grid 46 is mounted within the casing 42 directly beneath the hammers 44 and extends concentrically with the rotor 43 throughout approximately 180 degrees. A tramp metal pocket 47 having'an access door 48 is provided at one side of the grid'46 in position to .reecive hard foreign bodies which may enter the crusher with the coal and be thrown outwardly by the hammers 44. Coarse coal isclelivered at a desired rate to the upper portion of the casing 42through a pipe 49'by a suitable feeder. 50 comprising a horizontal Tl pocketed drum 51 located at the bottom of a supply hopper 52. The drum is' rotated at a desired speed by any 7 suitable means, and feeds coal from the hopper 52 to the pipe 49. Hot air from the duct 19 is delivered to the upper portion of the casing .42 through a pipe 53 provided casing 58 also has a central upwardly extending air outlet 60 which is connected by a pipe 61 to the air inlet 34 of the pulverizer21; The casing 58 tapers downwardly to a restricted'coal outlet 62 which is connected to the .upper end of the coal supply pipe 31 of the pulverizer. 'In order to prevent air from flowing downwardly through the coal outlet '62, a pivotally mounted valve plate 63 .is mounted therein to form a trap, this valve plate being a biased upwardly toward its closed position by a counterweight 64. V V

Under'certain conditions it may be desirable to by-pass the crusher 41. For this purpose a pipe66 leads downwardly from the coal feeder G to the air outlet 60 of the separator 57, and a flap valve 67 is pivotally mounted between the upper ends of the pipes 49 and 66 so that the coal fed by the drum 51 can be diverted into either of these pipes as desired. In addition a pipe 68 with a valve 69 therein connects the hot air duct 19 to the pipe 61.

'The operation of this embodiment will now be apparent fromtheabove disclosure. Normally the valve 69 will beclosed, the valve 54 will be open sufficiently to permit hot air from the duct 19 to flow at a desired rate into the crusher 41, and the flap valve 67 will be placed in the position shown so that the coarse wet coal fed downwardly from the hopper 52 by the rotating drum 51 will travel through the pipe 49. into the 'cru'sher41. As the hot air and the wet coal e nter the crusher, they will be very rapidly, violently, andintimately mixed by the action of the revolving hammers 44. These hammers will crush the fuel into relatively small particles and distribute the surface moisture over the greatly increased exposed area of such particles. By reason of such distribution of the moisture over a very large surface area, and the exposure of the moisture to intimate contact with the hot air, the

moisture will evaporate almost instantaneously and the crushed fuel passing through the grid 46 will be comparatively dry. Any tramp iron or other hard foreign matter too large to pass through the grid will be deposited in the pocket 47. The air and the crushed coal will travel 1 through the chamber 55 and the tangential inlet pipe 59 to produce awhirlingrnass within the casing 58 of the separator 57. The air, with some of the finest coal particles entrained therein, will flow upwardly through the outlet pipe 69 and through the pipe 61 and the air inlet opening 34 of the pulverizer 21. Most of the coal will separater from the air by the action of gravity and centrifugal force, and travel downwardly past the trap plate 63 and through the outlet 62 to the coal supply pipe 31, which will discharge the coal into the rotating bowl 22. Centrifugal force will cause the coal to move outwardly to the ring 23, against which the coal will be finely ground 7 deliver this stream through the pipe 11 to the burner 12,

where additional air will be supplied from the duct 19 to maintain combustion in the furnace 10. V

Because of the combined drying and crushing action performed upon the coal as it travels through the crusher 41, it is possible to operate the pulverizer ata'much higher grinding rate than would otherwise be the case. The increase in the grinding capacity is of course more pronounced when the coal supply has a high percentage of surface moisture. When the load on the boiler furnace 10 is low, so that a high grinding rate is not required of the pulverizer, and particularly when the coal supply is comparatively dry, it is feasible to take the crusher 41 out of service. For this purpose the flap valve 67 will be swung over to the position indicated by the broken lines, so that the coal which is fed downwardly by the drum 51 will all pass through the pipe 66 to the pipe 60, past the valve 63 and the separator outlet 62 to the pipe 31 and into the bowl 22 of the pulverizer. At the same time the valve 54 can be closed and the valve 69 opened to admit hot air from the duct 19 through the pipe68 to the pipe 61 and thence to the air entrance 34 of the pulverizer.

In Fig. 2 there is shown a modification of the invention in which the pulverizer 21 of Fig. l is replaced by a pulverizer 71 of the general typedisclosed in the United States patent to Schwartz No. 2,275,595 granted March 10, 1942. This machine comprises a central member'72 secured to a vertical rotatable shaft 73 having a bevel gear 74 mounted on its lower portion. A bevel pinion 75 is mounted on a horizontal shaft 76 driven by any suitable means. The pinion meshes with the gear 74 and thus serves to drive the shaft 73. The outer portion of the member 72 provides'a revoluble ring or track for an 'annular series of balls 78 above which there is located an upper ring or track 79. Several springs 80 (only one of which is shown) force the upper ring 79 downwardly against the balls 78. A rotary classifier 81 is mounted on the top of the member 72. These parts are enclosed within a casing 82 having an air inlet 83 and shaped to provide an annular space 84 through which the air may flow upwardly around the outside of the grinding rings 72,-79 to the classifier 81. The coal to be ground is supplied to the pulverizer 71 by gravity through a pipe 85, which deposits the coal within the upper ring 79 so that the coal will be pulverized by the rolling action of the balls 78 as it travels outwardly between the rings 72-79. The ground coal leaving these rings enters the annular space 84 and is entrained by the air current flowing upwardly therethrough. Theclassifier 81 returns any coarse particles for further grinding, while the air and fine particles continue through a pipe86 to the burner'12.

The air pipe 61 leading from the separator 57 is connected 7 to the inlet of a fan 87 which discharges into the air inlet 83 of the pulverizer 71. Since this arrangement places the interior of the pulverizer under pressure, the .coal outlet 62 .of the separator 57 is preferably provided with a modified form of trap comprisinga star wheel 88 suitably rotated by a motor 89 at a speed sufiicient to transfer coal to the pulverizer supply pipe 85 as fast as it accumulates in the bottom of the separator, while preventing upward flow of air through the pipe 85. r

The operation of the embodiment disclosed in Fig. 2 will be essentially the same as that already described in connection with Fig. 1, except for the slight differences brought about by the change in the type of pulverizer. Thus the coarse wet coal will be supplied by the feeder 50 to the crusher 41, where it will be crushed and mixed with the hot air supplied through the pipe 53, this air serving to dry the coal very rapidly. Any tramp metal present will be deposited in the pocket 47. The crushed coal and air will be separated in the casing 58, the coal traveling downwardly past the star wheel 88 and through the pipe 85 into the interior of the upper ring 79 and thence outwardly into the path of the balls 78. The air will flow outwardly through the pipe 60 to the pipe 61 and the fan 87, and thence at a higher pressure through the pipe 83 into the pulvetizer and upwardly through the space 84, where it will entrain the pulverized coal moving outwardly past the balls 78. The air and coal will flow upwardly past the classifier 81, which will throw back the coarse particles while the air and fine particles continue through the pipe 86 to the burner 12. As in the case of the Fig. 1 embodiment, there will be a very pronounced increase in the grinding capacity of the pulverizer, particularly when wet fuel is encountered.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Apparatus for comminuting wet, raw coal comprising a mill having revoluble crushing hammers and having an arcuate sifting grid situated therebelow, the said mill being of the type which subjects the coal to violent agitation, means to feed the coal into the path of the hammers, means to direct hot gas into the path of the hammers so that the coal will be simultaneously crushed and dried, a separator, close-coupled means to lead the gas and the dry crushed coal substantially by gravity to the separator so that the coal will be separated from the gas, a pulverizer adapted to grind coal to a fine powder, the pulverizer having an entrance for coal to be ground and a separate entrance for gas to entrain the fine powder, the pulverizer being of the type which subjects the coal to very fine comminution, means to lead the crushed coal from the separator to the coal entrance of the pulverizer, means to lead the gas from the separator to the gas entrance of the pulverizer whereby the same gas which passes through the hammers also passes through the pulverizer, and means for applying additional hot gas to the gas in the said last-named means.

2. Apparatus as set forth in claim 1, wherein the said mill coal feed means includes a by-pass means for selectively feeding coal to the mill or directly to the separator.

3. Apparatus for comminuting wet, raw coal comprising a mill having revoluble crushing hammers and having an arcuate sifting grid situated therebelow, the said mill being of the type which subjects the coal to violent agitation, means to feed the coal into the path of the hammers, means to direct hot gas into the path of the hammers so that the coal will be simultaneously crushed and dried, a separator, close-coupled means to lead the gas and the dry crushed coal substantially by gravity to a separator so that the coal will be separated from the gas, a pulverizer adapted to grind coal to a fine powder, the pulverizer having an entrance for coal to be ground and a separate entrance for gas to entrain the fine powder, the pulverizer being of the type which subjects the coal to very fine comminution, means to lead the crushed coal from the separator to the coal entrance of the pulverizer, and means to lead the gas from the separator to the gas entrance of the pulverizer whereby the same gas which passes through the hammers also passes through the pulverizer, and means for applying additional hot gas to the gas in the last-named means, the mill being provided with a pocket arranged to retain tramp metal and other hard, foreign matter thrown outwardly by the revoluble hammers, the dry, crushed material leaving the separator through a passage having a trap therein arranged to prevent the flow of gas through the passage.

References Cited in the file of this patent UNITED STATES PATENTS Re. 17,212 Stockton Feb. 12, 1929 679,046 De Camp July 23, 1901 1,051,887 Hiller Feb. 4, 1913 1,258,969 Williams Mar. 12, 1918 1,513,279 Sawford Oct. 28, 1924 1,560,766 Crites Nov. 10, 1925 1,591,758 Griflin July 6, 1926 1,646,720 Andrews M Oct. 25, 1927 1,719,831 Daniels July 9, 1929 1,729,424 Harshaw Sept. 24, 1929 1,737,800 London Dec. 3, 1929 1,744,927 Sinclair Jan. 28, 1930 1,768,619 Lykken July 1, 1930 1,955,255 Sengstaken Apr. 17, 1934 2,032,402 Colby Mar. 3, 1936 2,071,380 Bailey Feb. 23, 1937 2,075,506 Crites Mar. 30, 1937 2,091,297 Ximinez Aug. 31, 1937 2,148,447 Dundas et a1. Feb. 28, 1939 2,237,021 Wood Apr. 1, 1941 2,274,789 Horesi Mar. 3, 1942 2,275,595 Schwartz Mar. 10, 1942 FOREIGN PATENTS 369,330 Great Britain Mar. 24, 1932

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