US2328568A - Process for dedusting comminuted soap - Google Patents

Description

Sept. 7, 1943. B. MAXWELL lar AL inocEss FOR DEDUSTING oMMINuTED sQAP Filed Ag. 15, 1940 Il 'By L'lrarles Z'Hhwad INVEN'roR S award L'. han# Patented Sept. 7, 1943 PROCESS FOR DEDSUSTING COMIMJINUTED Bernard L. Maxwell, Reading, and Charles T. Atwood. Belmont, Mass., assignors to Lever Brothers Company, Cambridge, Mass., a corporation of Maine Application August 15, 1940, SerialI No. 352,738

3 Claims.

This invention relates to classiication of finely comminuted materials, and has particular reference to an improved method for separating excessively fine soap particles from comminuted soaps, and the improved soap product.

In general, the forming of comminuted soaps is accomplished by spray drying the liquid soap stock to obtain particles in characteristic granule form. The dried soap particles are classified Within designated limits of particle size by a screening opera-tion, and packaged. Commercial grades of comminuted soap ordinarily range in particle size between those 'particles passing a 20 mesh screen and retained by an 80 mesh screen, the oversized particles and fines being returned to the manufacturing system for reprocessing. However, with screening methods presently in use, soap fines and dust occur in the packaged product in amounts varying between 5% and 30% of the total pack.

The presence of soap iines and dust in the comminuted product is objectionable for several reasons. The ne particles have an irritating eiect on the nasal passages. Such a dust irritating eiect may become apparent in several ways. For example, the user of a comminuted soap of undesirably high dust content may sneeze and cough on opening a package of such soap or in pouring it out for use. is also particularly apparent in the comminuted soap manufacturing process. Objectionably large amounts of dust are formed during the manufac- This undesirable effect ture of comminuted soap and the problem is dificult to overcome in view of the pulverulent properties of the soap particles.

Soap dust extracting methods heretofore employed in comminuted soap manufacture have been, in most cases, entirely inadequate, land in many cases the use of dust masks by workmen associated with the screening and packaging rooms is necessary.

Moreover, the wastage of soap between the spray drying and screening operations by excessive sifting or filtration from apparatus and entrainment of fine particles in the air, is considerable. amounts of fines in bulk comminuted soaps causes undesirable variance in'bulk-weight proportions of the packaged granules. I

The forming of small amounts of nes in comminuted soaps during screening and packaging is unavoidable, due to agitation of the particles inherent in these operations. However, the accumulation of large amounts of fines in bulk comminuted soaps during manufacture and prior to It has been found that the presence of large screening leads directly to air pollution through excessive dusting, and enhances the ineillciency of the screening operation as an accurate method of lparticle classification, due to clogging of the screen mesh.

It has been discovered that a comminuted soap containing in the bulk only those particles 'retained by a mesh screen is not objectionable from the point of view of causing the nasal irritation often indicated by excessive coughing or sneezing. Removal and collection of soap dust Aof such neness is not satisfactorily accomplished during the screening operation due to the tendency of the bulk soap to retain a portion of the dust, and the tendency of microscopic particles to entrain in air upon agitation, the eiect of gravity thereon being negligible. Similarly, apparatus presently available for classication and dedusting of relatively hard materials such as case hardened soap drops and the like, are not adaptable to the relining of bulk comminuted soaps, due to the fragile nature of the soap particle and the tendency to crumble with excessive agitation, reducing the percentage of packageable dedusted product. 1

It is an object of the present invention to provide an improved method of separating excessively fine soap particles from bulk comminuted soaps, without undue loss of packageable soap by powdering, under excessive agitation.

A further object is to provide a method of controlling dust accumulation and ltration in comminuted soaps to produce a comminuted product having a very lowfdust content.

A still further object is to provide a bulk comminuted soap product having a low content, preferable less than 1%, of objectionable fines and soap dust, upon packaging.

Other objects and advantages will appear from the following description and drawing, wherein:

Figure 1 is a view in verticalsection of the soap particles classifying and dedusting apparatus of the invention; y

Figure 2 is a similar view of a modiiied form apparatus of the present invention; and

Figure 3 is a}view in top section along the line 3-3 of Figure 2 and looking in the direction of the arrows. l l

Referring to Figure 1 of the drawing, the numera1 lll indicates a tower preferably rectangular in cross-section, having a top wall I I and bottom plates l2 converging to a particle discharge outlet i3. A hopper I4 discharges into a tortuous chamber I5 enclosed by a series of ramps I6 positioned to form inclined falls throughout the soap particles into containers.

tower. The chamber I5 at its lower portion connects with the outlet I3, which discharges to a conveyor 24 or other device suitable to divert the A suction pump I1 adapted to draw a ilo'w of gaseous medium such as air through an air inlet I8 into the chamber I5 at its lowerportion exhausts spent gaseous mediultimate exhaustion through the hood I9 is avoided. By proper adjustment of the dampers um through an aperture in the upper wall II by means of a hood I9 and a conduit 20. A damper 2i at the upper portion of the chamber I5 proiary conduits 22 opening into the chamber I5 at points adjacent the sequences of the ramps I6. The conduits 22 permit the carrier air to be drawn oil.' at intermediate zones in the tower. Dampers 23 in each of the conduits 22 permit of controlof the rate of exhaustion of gaseous medium through each. There is also a control damper 23 in the draw-off conduit 20. Y

In operation, the pump I1 is operated to provide an airilow in chamber I5. This airflow has preferably a iixed velocity determined in accordance with the degree of particle separatory action desired. The comminuted soap product is continuously introduced into the chamber I5 through the hopper'll, falling by gravity over the inclined .ramps I6 to ultimate discharge through the outlet I3. The slope of the ramps I6 is selected to permit of free gravitational fall of the particles ofsoap which are subjected to a series of winnowing actions as they pass over the ends of the ramp sequences and fall by gravity through the upowing air to the surface of the ramp next below. It is essential that the rate of feed and the slope of the ramps I8 be correlated to obtain a particle flow characterized by minimum agitation, in order to preserve the particle form of the packable soap and avoid pulverization. The air, traveling counter to the particle fall, entrains and carries the excessively iine particles of soap dust through the hood I9 and conduit 20 to suitable particle recovery means, not shown, such as a cyclone separator, or a dust bag for example. 'I'he degree of particle separation eiiected will depend upon the velocity of the flow of air in the tortuous chamber I5, which velocity may be varied as desired by proper manipulation of the damper 2l. For example, if it is desired to separate only those dust particles passing through a 140 mesh screen from the bulk soap, a moderate counter-ilow velocity may be Provided by opening the damper 2|. If it is desired to effect removal of all soap ilnes and dust passing through, for instance, an

80 mesh screen, the velocity 0f the counterilow may be duly increased by closing the damper 2| to exert the full effect of the suction generated by the pump I1 on the counterflow in the chamber I5.

In the modication shown in Figure 2 of the drawing, comminuted soap is introduced into the chamber I5 and a suitable gaseous counterflowu generated therein, as described. By means of the 23 and 23', the rate of withdrawal of portions of the airilow in the chamber I5'may be controlled inaccordance with previously determined condi'- tions of dust concentration in the soap bulk, and the airflow velocity desired at designated points along the' length of the chamber I5.- If desired, additional air may be bled into the chamber at points intermediate the ends thereof to replace the dust-laden air withdrawn through conduits 22, thus avoiding operating at ldecreasing linear velocities from the bottom to the top ofthe chamber. For instance, as the maximum concentration of dust in the comminuted soap bulk will occur lupon initial introduction of the soap par--` ticles into the chamber I5, it may be desirable to introduce additional air and, to operate the top auxiliary conduit 22 with the damper 23 in position to restrict the ilow therein and thus main-A tain a maximum velocity'of the counterilow at the nrst ramp sequence. The number of auxiliary conduits 22 may be varied ,as desired.

The angle of incline of the ramps I5 may be determined in accordance with the relationship of the ramp slope to the desired rate of travel of the particles thereover. The rate .of travel is also dependent upon the size and density of the soap particles and the velocity of the upward iiow of ai/r. By reducing the area. between the ramps at points along the lengthy of the tower III, the velocity of the airflow will be `proportionately increased at those points. It has been noted, for example, ina test unit having a capacity of 200 ounces per minute of astandard spray dried soap screen through 20 mh and with 6 ramps or falls at an angle of 45 degreesthat a spacing of eleven inches was desirable between the inclined ramps. 'I'he air volume was about 450 cubic feet per minute and the velocity of iiow about 500 feet per minute. A screen analysis of the soap originally and after treatment gives the following data:

By simple experimentation with ramp positioning, airiiow velocity and volume and positioning of the damper 2|, in accordance with the principles indicated and taking the aforementioned factors of particle size, density and rate of feed into consideration, operation 'of the novel particle separating and dedusting apparatus of the invention may be maintained at peak emciency to obtain a dedusted bulk comminuted soap product having a percentage content of objection-able iines and soap dust considerably under 1.0% of the total bulk. For a given rate of feed of soap particles, which rate has an optimum value for any given size of the apparatus there will be a critical volume of airflow determined by the setting of the damper 2I, and a critical velocity of airflow, determined by the spacing between the ramps I6 and the setting of damper 2i, at which adjustment a maximum eiliciency of dust separation both from the mass of soap particles as they pass from the surface of the ramps and from the particle screen as the' particles. pass across the upflowing air. This, furthermore, as a result of our` invention, may be amplified Without undue loss of packable soap.

granules as a result of the separation. l Desirable results, we have found, may be obtained commercially by utilizing an air volume of about 6000 cubic feet per minute and an air velocity of about 600 feet per minute. When operating under these conditions ofI air velocityand volume, the width of the unit preferably is aboutl feet and the spacing between the inclined ramps preferably is about twelve inches. Obviously, for commercial purposes, a greater capacity may be obtained by utilizing multiple towers. `For example, a battery of three towers operating under the above conditions of air volume and velocity will have a capacity of about 40,000 lbs. of soap per hour. With this rate of feed, a material containing 3 to 4% of nes through 140 mesh is reduced in lines content to less than 1%. l

While it is preferred to carry out the method of the invention in a comminuted soap manufacturing system prior to screening or otherwise classifying the soap vparticles for packaging, in order to expedite classification, the dedusting operation may be carried out with equally successful results subsequent to screening, or at any other point in the manufacturing process subsequent to spray drying of the soap particles.'

By incorporating rthe method of the present invention into presently used processes for manu-- facturing comminuted soap, operatinginelciencies incurred through air pollution and waste of product through dust ltration are eliminated. The method of the invention provides a bulk comminuted soap product with an effectively standardized bulk-weight proportion, and having a soap dust content of less than 1% prior to packaging.

While the invention has been described herein with reference to specific structure, these references are made by way of illustration. It is intended to include all equivalents within the scope of the invention, which is to be limited only as dened in the appended claims.

We claim:

1. A method of dedustlng bulk comminuted soaps comprising particles of varying sizes and including substantially in excess of 1% of particles passing through a mesh sieve, comprising conducting the bulk soap in a continuously ilowing thinly dispersed particle layer over a tortuous path with minimum distintegration of the particles, providing successive intervals of free gravitational fall of the said particle layer at each successive change in direction of the tortuous path to form successive curtains of falling particles, passing a gaseous carrier medium counter tothe iiow of the curtains of falling particles and at an angle thereto, and at a velocity to provide a series of successive winnowing actions on the soap particles at each of said successive changes in direction of the tortuous path to entrain the soap dust content of the particle layer to an extent that the particles so treated will have less than 1% passing through a 140 mesh sieve, and separating the gaseous carrier medium with the entrained dust from the soap particles.

v2. A method of treating 'a pre-formed comminuted soap product having particles of varying sizes and containing substantially in excess of 1% of ine particles passing through a 140 mesh sieve, which comprises forming a plurality` of vertically falling curtains of said particles, passing a gaseous mediumV through said curtains of particles at an angle to the vertically falling particles and at a velocity such as to entrain a major portion of the fine particles in the gaseous medium so that the particles falling through said gaseous medium will contain less than 1% of particles passing through a 140 mesh sieve.

3. A method of treating a pre-formed comminuted soap product having particles of various sizes and including substantially in excess of 1% of particles passing a 140 mesh Sieve, which BERNARD L. MAXWEIL. CHARLES T. ATWOOD.

Images