US2361922A - Method of pulverizing - Google Patents

Description

Patented Nov. 7, 1944 2,301,922 METHOD or rupvamzmc Norwood H. Andrews, Moorestown, N. 1., asslgnor to International .Pulvel'izlng Corporation, Moorestown, N. J., a corporation of New Jersey No Drawing. Application June 17, 1942, Serial No. 447,437

2 Claims.

This invention relates to an improved method for pulverizing fibrous or other dimcultly frangible materials, and in particular concerns a method whereby such materials may be reduced to an extremelyflne state of subdivision.

This invention is particularly concerned with reducing materials such as plant leaves and stems containing active principle, natural berries, wood flours, and other fibrous substances, to particle sizes predominantly below about forty microns.

Among the various known methods for carrying out pulverizing operations, that commonly referred to as jet-pulverizaticn is generally considered to be one of the simplest and more' efllcient, particularly where the desired particle size is within the sub-sieve range (below 400 mesh). Such method is described in detail in United States Letters Patent 2,032,827 and consists essentially in introducing the material to be ground into an inwardly spiraling gaseous vortex which is formed and maintained by a multiplicity of concentrically arranged and tangentially d rected high velocity jets of an inert gaseous fluid such as air-or steam. The tam gential direction and the high velocity gradients of the fluid jets cause the mass of material to rotate at high speed and the individual particles thereof to be subjected to violent directional changes and impaction. The pulverizing action i thus primarily due to particle 'impact and shattering rather than to attrition by abrasion. Because of its high rotational speed, the mass of material undergoing pulverizaticn is also sub-.

jected to an intense centrifugal classification, with the result that the lighter, more finely divided material is carried to the center of the vortex where it. is withdrawn, and the heavier particles are thrown outward to the periphery of the vortex where they undergo further pulverization.

While this method of grinding has proved to be applicable with great efllciency to the widest variety of materials, there are certain materials, particularly those of vegetable origin. such as wood and similar substances, seeds, shells, etc., which, because of their fibrous nature, must be either subjected to such pulverizing treatment over extended periods of time with the consumption of large amounts of energy in order to be reduced to the desired state of fine subdivision, or, cannot be satisfactorily ground.

It is accordingly-an object of this invention to provide a method whereby fibrous and other types of difficultly frangible materials may be readily reduced to an extremely fine powder.

Another object is to provide a method whereby such materials may be obtained in sub-sieve particle sizes without undue expenditure of time vide an improved method of preparing comminuted food products by pulverizing fibrous or other dimcultly frangible edible materials to an extremely fine state of subdivision so that it is not necessary to extract the active principle from the fiber before use.-

Other objects will be apparent from the following detailed description of the invention.

In general, my method for the reduction of difilcultly frangible material of vegetable origin to finely divided particles, particularly in the sub-sieve size ranges includes introducing said material and an impact-disintegrating agent into the open zone of an inclosed chamber. These materials maybe roughly comminuted be-. fore feeding, say to about 40-100 mesh. The said agent may be somewhat larger in size than the material to be ground, although not necessarily so, and, both'materials may be up to at least 8 mesh, in most cases. a gas under pressure at high velocity is introduced to suspend such materials. The said gas is preferably chemically inert to the material to be reduced and to the impact-disintegrating .agent employed. Air, steam, carbon dioxide,

nitrogen, helium, and other gases may be used, according to the nature of the material being ground. The gas is introduced at a plurality of points around said chamber and directed into the chamber at an acute angle to the periphery thereof n such a manner as to create a reentrant circulatory path for solid particles larger than predetermined size ranges. The action of the gas streams causes the added, hard, impactdisintegrating agent to strike the fibrous vegetable material and shear such material. The gas flow is adjusted so that particles of fibrous material smaller than predetermined sized ranges are entrained n the gas exhausted from said chamber. while the particles above said size ranges are retained by centrifugal force near the eriphery of the chamber.

The re-entrant circulatory path for solid particles larger than predetermined size ranges can Into said chamber be created and maintained in various forms of jet pulverization apparatus such as that described in United States Letters Patent 2,032,827. Another iorm of apparatus which may be employed in carrying out the present invention is that described in United States Letters Patent 2,191,095 or 2,219,011. In either of these forms of jet pulverization apparatus a reentrant circulatory path for particle travel is created and maintained by the introduction of high velocity jets of gas. The term re-entrant circulatory path as herein employed, is used to describe the line of flow of solid particles travelling in an inclosed zone or chamber in which solid particles above predetermined size ranges are retained in said zone by centrifugal force and are subjected to the action of high velocity jets of gas and in which the solid particles below predetermined size ranges may be continuously exhausted from the zone by entrainment in gas leaving the same.

The term impact-disintegrating agent as herein used, means a substance diiferent from the material to be reduced in particle size and relatively harder and generally denser than the substance to be reduced. It is preferably crystalline in nature.

During the pulverizing treatment, such agent is dispersed uniformly throughout the mass of material being treated and, because of its harder, denser nature, serves to intensify the impact action within the mass, thereby securing more efficient grinding action. While suitable impactdisintegrating agents are usually of the class of materials known as abrasives, their action during jet pulverization is primarily one of impact intensification rather than an abrading or smoothing action.

The particular impact-disintegrating agent employed in carrying out the method of the invention depends upon the material being ground as well as upon the use to which the pulverized product is to be put. Thus, for example, in grinding nut shells for use as an insecticidal diluent, sand hasbeen foundto be a satisfactory agent since it promotes rapid grinding and does not detract from the desirable properties of the pulverized product. In certain other cases such materials as carborundum, alundum, pumice, and talc have proved to be the most satisfactory. When grinding materials having a volatile active principle, for example pyrethrum flowers and the like, it may be desirable to employ an impact-disintegrating agent having absorptive properties, such as bentonite, certain types of activated charcoal, etc., in order to reduce the loss of the active principle by volatilization during grinding. In the preparation of comminuted food products, the impactdisintegrating agent is preferably edible in nature and sugar is the agent commonly employed since it forms a desired constituent in the final product. The sugar also serves to absorb or adsorb the essential oil from edible beans, berries, and the like, and prevent its loss.

The impact-disintegrating agent is usually employed in a proportion representing approximately 1 to 15, preferably from 5 .to 10, per cent by weight of the material to be ground, although the most suitable proportions also depend somewhat upon the particular material being ground and the use to which the pulverized product is to be put. In some instances, for example in grinding vanilla beans with sugar as the impact agent, it is necessary to use proportions as high as 90 per cent of the total weight of the feed.

The grinding operation itself is carried out by the general process of jet pulverization hereinbefore explained at ordinary or elevated temperatures, In grinding specific materials, the particular operating conditions, i. e. rate of feed of material, temperature, velocity or the gaseous fluid jets, relative dimensions of.the chamber in which the operation is carried out, etc., vary somewhat with the material being ground as well as with the particle size desired, but will readily be apparent or easily determined by those familiar with the process of jet pulverization, after a study of the following examples. These examples are illustrative of practice in accordance with the invention, but are not to be construed as limiting the same.

Example 1 Approximately 99 pounds of rotenone (100 mesh) together with 1 pound of ordinary quartz sand of 16 mesh is fed into a commercial jet pulverizer of the type known as a Micronizer," at a uniform rate over a period of 15 minutes. The pulverizer consists essentially ofa shallow circular grinding chamber around the periphery of which are located eight jets directed into the chamber tangential to a theoretical circle within of about two-thirds the diameter of the chamber. The jets had a diameter or a: inch and were supplied with air at pounds gauge pressure. The material to be ground was fed into the chamber through an opening at the top located near its periphery. The exhaust air is led out through an opening in the top of the chamber at its center, and the pulverized product is collected in a conical chamber leading from the bottom of the grinding chamber at its center. The product withdrawn from the collector had an average particle size of 5 microns, and contained less than one per cent of material above 30 microns in size.

Example 2 An insecticidal composition consisting of 207 pounds of 100 mesh tobacco dust, 75 pounds of 75 mesh pyrethrum flowers, and 1.5 pounds of Aresket (a wetting agent) is mixed with 16.5 pounds of 16 mesh quartz sand and fed into a Micronizer at a rate of 450 pounds per hour. The Micronizer employed is similar to that described in Example 1 and has a 20-inch circular grinding chamber, around the periphery of which are located eight n inch jets supplied with air under pressure. The product withdrawn from the collecting chamber has an average particle size of 5 microns and an extremely small percentage above 15 microns.

Example 3 Example 4 This example illustrates the use of an impactdisintegrating agent which absorbs or adsorbs the active principle of the fibrous material being reduced. A composition consisting of 10 pounds of vanilla bean powder passing a mesh screen and 90 pounds of about 100 mesh cane sugar, fairly uniformly mixed, was fed into a pet pulverizer at a rate of 50 pounds per hour. The

pulverizer consisted essentially of a shallow circular grinding chamber 12 inches in diameter around the periphery of which were located 6 jet nozzles having a diameter of a: inch. The jets were evenly distributed and tangentially directed to a concentric theoretical circle within said chamber having a diameter of 6 inches. Air at 100 pounds gauge pressure was supplied to the jets. The pulverized product was collected in a conical chamber leading from the bottomof the crinding chamber at its center and the exhaust air was led out through an opening in the top of the chamber at its center. The product withdrawn from the collector had an average particle size of about -10 microns.

The roasted seed of the cacao tree can be readily pulverized with the aid of sugar to yield a chocolate flour giving an exceptionally smooth base for candy-coatings and dispersing into water with greater ease than ordinary cholocate powder,

In addition to providing a way for reducing to an extremely fine state of subdivision fibrous difficultly frangible material, my invention has the particular advantage of enabling far greater recovery of the active or desired principle of materials such as the vanilla bean. For example, when operating according to the procedure outlined in Example 1, the essential oil of vanilla is not destroyed chemically or by the physical action of the grinding operation, and the over-all recovery of the oil in the bean is increased by about 50 per cent over that recovered by ordinary methods.

While I have described the operation of the method in connection with vortex created by gaseous jets injected into an open zone tangential to a theoretical circle within said zone, as morepartlcularly shown in said Patent 2,032,827, it is equally applicable for use in vortiginous gases travelling in other shaped paths in open or confined zones, as shown in said Patents 2,191,095 or 2,219,011. The gas streams are to be directed into the zone at an acute angle from the periphery thereof, as more fully shown in said patents.

This application is a continuation-in-part of my prior application Serial 327,659, filed April 3, 1940, and of my prior application Serial 327,658, filed April 3, 1940.

I claim:

1. The method which includes; introducing a diflicultly frangible, fibrous material of vegetable origin containing a desired active principle and particles of a relatively harder, different material capable of adsorbing or absorbing said principle into the open zone of an inclosed chamber; in-

troducing a gas chemically inert at least to said active principle into said chamber from a plurality of points on, and at an acute angle to, the periphery thereof, under suificient pressure to suspend said material in the gas and to create a re -entrant circulatory path for particles larger than about forty microns in size; and, exhausting from said chamber gas having entrained therein substantially only those particles which are below about forty microns in size.

2. The method which comprises introducing a comminuted dificultly frangible fibrous material of vegetable origin containing a volatile active ingredient and added fine granular particles of a relatively harder and denser inert absorbent impact disintegrating agent into an endless circulating stream formed. and maintained by a multiplicity of high velocity streams of a gas directed into an open zone of a substantially closed chamber at an acute angle from the periphery whereby the said materials are subjected to violent directional changes and the fibrous material is struck by particles of said disintegrating agent.

NORWOOD H. ANDREWS.