US 2568400 A
Description (OCR text may contain errors)
Patented Sept. 18, 1951 PROCESS FOR SUBDIVIDING SOLID PARTICLES Kenneth K. Kearby, Cranl'ord, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application September 1a, 1946, Serial No. 697,810
The present invention is concerned with'an improved process for subdividing solid particles. The invention more particularly relates to an improved process for finely dividing or pulverizing carbonaceous solid particles, as for example coal, which pulverized particles are subsequently handled to produce gaseous products, as for example gaseous fuels, feed gases suitable for hydrocarbon synthesis reactions, and the like. In accordance with my invention, I employ a standpipe arrangement which is of sufficient height to secure the desired fluid head necessary to inject the particles to be finely divided into a high pressure fluid stream. The fluid stream containing the solid particles to be pulverized is then passed through a jet pulverizing means.
It is known in the art to pulverize or finely divide solid materials, for example, carbonaceous materials, such as coal and the like, by passing a stream of the material through a jet arrangement in which the pressure is reduced resulting in the pulverization of the material. How ver one disadvantage of these processes is that no satisfactory continuous method of introducing the solid particles into the fluid stream such as steam or air, has been obtained. Various suggestions have been made and attempts directed toward overcoming this problem and securing a satisfactory method of continuously introducing the carbonaceous particles into the fluid stream. These efforts have not however been very successful.
I have now discovered a method of incorporating solid material into the fluid stream which is entirely satisfactory and which may be operated in .a continuous manner. In accordance with my invention I employ a fluidized zone of sufllcient height to secure thedesired fluid head. From the bottom of my standpipe arrangement, I introduce suspended fluid solid particles into the fluid stream as for example steam, and then pass this high pressure stream through a jet arrangement in which the pressure is substantially reduced resulting in the pulverization of the solid material.
The process of my invention may be readily understood by reference to the attached drawing illustrating a modification of the same. For the purpose of illustration the operation described with respect to the drawing is assumed to be a coal pulverization process. Referring specifically to the drawing carbonaceous solid material, as for example coal, is introduced into hopper arrangement III by means of conveyor line or equivalent means I. The feed coal falls downwardly in zone It and contacts upflowlng suspending gases which are introduced into zone ID by means of line 2 and distributed throughout the zone by distributing means 3. The velocity of the upflowing gases is sufllcient to maintain the solid particles in a fluid ebullient state, the upper level of which is at point A. The velocity of upfiowing gases is generally in the range from about 0.5 to 2.0 ft./sec. Although the size of the solid particles introduced into zone l0 may vary considerably, for the purpose of illustration, it is assumed that these particles have a, particle size in the range from about 20 to mesh. Additional suspending gases may be introduced if necessary at points i. The suspending gases pass upwardly through zone l0 and are withdrawn by means of line 5 after passing through a cyclone or equivalent separating means '6. Entrained solid. particles separated in cyclone separator t are returned to the bed by means of line I. Larger particles which are not suspended fall past distributing means 3 and are removed from zone I0 by means of line '8. These particles may be passed through mechanical crushing means 9 and recycled to the top of zone it by means of line H. These larger particles may also be withdrawn from the system by means of line l2.
In accordance with my process, I withdraw fluidized particles from zone It through standpipe arrangement it which is shown as a broken conduit to indicate that its length may vary appreciably. The suspended coal particles having a fluid head proportional to the size of th particles, the density of the particles per cubic foot, and the length of the standpipe itself are introduced into line It through which gaseous fluids are passed. For the purpose of illustration, the gaseous fluid passed through line I comprises steam. The steam containing the fluidized coal particles is passed through jet arrangement l5 positioned in pulverizing zone 20. As the gases pass through jet arrangement 15 the pressure on the gases and on the coal is substantially reduced resulting in the pulverization of the coal. The suspending gases and the pulverized coal pass upwardly through cyclone separator or equivalent means l6 positioned in the upper section of zone 20. The steam and the finely divided coal particles are withdrawn from zone 20 by means of line H and may be handled in any manner desirable. Larger particles removed from the suspending gases in cyclone separator [6 are withdrawn by means of line It and preferably recycled to the top of zone In by any suitable conveying means. Larger particles which are not pulverized as they pass through jet arrangement I! are collected in the bottom 01' zone 20 and removed by means of line I 9. These particles are likewise recycled to the top of zone Hi.
My process may be applied to any operation wherein it is desired to flnely divide solid pargreater than the pressure within the line into a which the fluidized solids are being fed. This, as pointed out previously, will depend upon the particular solids being fluidized, the pounds per cubic foot, and the height of the standpipe itself. In a process designed for the pulverizatioh of coal it is preferred that the pressure in the steam line be in the range from about 60 to 100 pounds per sq. inch, and that pressures in the expansion zone after the jet be about atmospheric pressure. Under these conditions the height of the standpipe will be in the range from about l'to 200 it.
If the particles introduced into zone are relatively large it may be necessary to introduce flner particles in order to secure adequate particle size distribution. These finer particles may be secured from an external source and introduced by means of line '21, but are preferably 7 secured by segregating a portion of the particles withdrawn from zone 20 and introducing these pulverized particles into zone I0 by means of line 22.
It is to be understood that the apparatus may be modified. For example, line l3 may be lowered within zone 10 so that coarse material would be allowed to fall downwardly through the bed in zone l0, be withdrawn from the bottom of zone III by means of line l3 and passed through jet arrangement as described. It is also within the concept of my invention to employ a downwardly moving bed in zone In of larger nonfluidized particles with fluidized solid particles interspersing between the interstices of the larger particles. In other words, the bed within zone l0 would comprise nonfiuidized solid particles and fluidized solid particles in which all particles were moving downwardly. The only requirement is that no particles would be too large so that it could not pass through the jet. It is also within the scope of m invention to pass the solids to be pulverized directly to jet means 15.
The process or my invention is not to .be limited by any theory as to mode of operation, but only in and by the iollowing claims in which it is desired to claim all novelty insofar as the prior art permits.
Y I claim:
1. Process for dividing solid particles whic h comprises introducing said particles into a hopper zone, maintaining said particles in said hopper zone in a fluidized state, whereby the larger of said particles segregate at the bottom or said hopper zone, withdrawing said larger particles from the bottom of said hopper zone, mechanically breaking the same and returning the same to an upp r point or said hopper zone, withdrawing fluidized particles from an intermediate point in said hopper zone, introducing said particles into a fluid stream, maintaining said fluid stream under pressure, passing said fluid stream and said introduced solid particles through a jet positioned in a pulverizing zone under conditions to substantially reduce the pressure on said fluid stream whereby said solid particles are subdivided.
2. Process as defined by claim 1 wherein said particles are carbonaceous particles.
3. Process as defined by claim 1 wherein said particles comprise coal particles, and wherein said fluid stream comprises steam.
rcamwrn x. KEARBY.
REFERENCES CITED The following references are 01. record in the file of this patent:
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