US2675070A - Desiccating apparatus - Google Patents

Description

April 13, 1954 D. D. PEEBLES DESICCATING APPARATUS 2 Sheets-Sheet l Filed Nov. 14. 1949 Q ZW'J ATTORNEYS April 13, 1954 D. D. PEEBLES 2,675,070

DESICCATING APPARATUS Filed Nov. 14, 1949 2 Sheets-Sheet 2 INVENTOR Dav/'0 0. eeb/es ATTORNEYS Patented Apr. 13, 1954 DE SICCATING APPARATUS David D. Peebles, Hillsborough, Calif., assignor to Western Condensing Company, San Francisco, Calif., a corporation of California Application November 14, 1949, Serial N 0. 127,221

This invention relates generally to desiccating apparatus of the spray drier type, and to methods for the spray drying of liquid or semiliquid materials to form dry powdered products.

It is well known by those familiar with the operation of desiccating apparatus of the spray drier type, that a given spray drier may operate satisfactorily with some materials, whereas with other materials the equipment may be unsatisfactory or completely inoperative. While various factors may be involved when a particular piece of equipment fails to operate satisfactorily on certain materials, it has been found that in many instances unsatisfactory operation is due to a build-up of material upon the inner Walls of the desiccating chamber. Thus When spray drying a material like concentrated liquid whey, to form a dry powdered product containing from say 8 to 14% total moisture, a substantial part of the atomized particles are not maintained in suspension in the swirling drying gas, but are propelled outwardly from the atomizer to impact and adhere to the peripheral walls of the drying chamber. This results in a general build-up of the material upon th walls of the chamber. Although some of this material may slough oif from time to time to merge with the remaining dried material, in general the build-up tends to increase to the point of making it necessary to shut down the equipment. Excessive buildup of material upon the walls of the drying chamber is also deemed objectionable because it frequently results in burning or overheating, with resulting discoloration or other injury to the final product. While various contributing factors may be involved in this build-up of material, it can be attributed largely to particles which are not swept into the main part of the desiccating chamber in entrainment with the drying gas, but instead are discharged outwardly with relatively high radial velocity components to impact the surrounding walls of the chamber. Such particles are generally semidry when they strike the chamber walls, and therefore they adhere and build-up as previously described.

2 Claims. (Cl. 159-4) It is an object of the present invention to provide a desiccating apparatus and method which will serve to minimize objectionable build-up of material upon the inner walls of the desiccatlIlg chamber.

Another object of the invention is to provide an apparatus and method of the above character which will make use of auxiliary dryin means for adherence and drying of semidry particles 2 such as would otherwise impact and adhere to the side walls of th drying chamber.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawing.

Referrin to the drawing:

Figure 1 is a plan view illustrating desiccating apparatus incorporating the present invention.

Figure 2 is a side elevational view in section i1- lustrating the apparatus of Figure 1.

Figure 3 is an enlarged detail in section illustrating the manner in which the drying rolls are operated.

Figure 4 is a cross-sectional detail illustrating a modification in which the supplemental drying roll is separately heated.

Figure 5 is a side elevational view in section like Figure 2 but illustrating another embodiment of the invention.

Figure 6 is a detail partly in section illustrating another embodiment in which the supplemental drying roll is provided with means for removing material from the same.

Figure 7 is a cross-sectional detail showing the arrangement of Figure 6 in plan.

In Figures 1 and 2 of the drawing I have shown desiccating apparatus of the spray drier type comprising a desiccating chamber H], which in this instance is constructed with an upper cylindrical portion Mia and a lower conical shaped portion Nib. In order to maintain an atmosphere of hot drying gas within the desiccatin chamber, hot air conduits I I are shown communicating with the side walls of the chamber portion lfla, and gas is continuously removed through the exhaust conduit l2. An atomizing device I3 is located concentric with the central vertical axis H of the desiccating chamber, and is preferably of the centrifugal type. It is mounted upon the rotatable shaft 15, through which the liquid or semiliquid material to be atomized can be introduced.

It is desirable to introduce some additional drying air into a region closely surrounding the atomizing-device l3. Thus a chamber l B is shown mounted upon the top wall ll of the main desiccating chamber, and is connected to the hot air supply pipe [8. The lower portion of the chamher. It is convergent whereby hot drying air is introduced through the annular zone I9 in a region which closely surrounds the atomizing de- In the-arrangement illustrated the exhaust stantially as illustrated in Figure 3.

conduit i2 has been extended upwardly (portion lie) into the lower part of the desiccating chamber, in alignment with the axis I4. Centrifugal separating action therefore takes place in the region 2! surrounding the inner portion 12a of the exhaust conduit, whereby dry powder tends to collect in the lower end portion 22 of the chamber, for removal through conduit 23.

Positioned in the upper part of the desiccating chamber and in a region generally surrounding the atomizing device it, I provide a plurality of auxiliary drying rolls 24. These rollers are preferably mounted on vertical axes, or axes parallel to the vertical axis 14 of the main desiccating chamber, and during operation of the machine they are continuously rotated at a slow speed. Thus each roller 24 is mounted upon an individual shaft 26 which extends through the top wall l? and is carried by the journal 23. A sprocket 28 is attached to each shaft and suitable means such as an extended endless chain 29, engages with all of the sprockets to rotate them simultaneously at a predetermined rate.

The individual rollers canbe constructed sub- The cylindrical wall 3! should have a relatively smooth exterior finish, free of obstructions or indentations. Suitable means such as the motor-driven sprocket 32 can be used for driving the chain 25 at a predetermined rate. The speed of rotation of the drums selected for use will be dependent somewhat upon the operating characteristics of the equipment, the temperature employed and the type of material being desiccated. When desiccating whey concentrate to produce material containing from say 8 to 14% total moisture, good results have been secured by using a speed of rotation of 2 R. P. M.

With the arrangement of conduits l l, and rolls 24 illustrated in Figures 1 and 2 the hot gas discharged from conduits H initially passes through the space 3!] and thereafter spreads into the main part of the chamber with swirling movement about the axis I 4. Swirling movement of gas is also induced in the region between the rolls and the atomizer l3.

Normally in the operation of the desiccator, the centrifugal atomizing device 13 operates at a relatively high speed, and the liquid or semiliquid material supplied to this atomizer is discharged in the form of atomized particles. The major proportion of these particles are entrained with the swirling currents of drying air and find their way into the main part of the desiccating chamber, to be finally deposited in the lower portion 22 of the chamber. Some of the particles discharging from the atomizing device impact the surfaces of the rollers 24. These particles retain considerable moisture, or in other words they are semidry material, and upon impact with the surfaces of the rollers, they adhere thereto.

By virtue of their conductive relation to hot drying gas in the desiccating chamber, the rolls are heated to an elevated temperature, and thus iaterial plastered upon their exterior surfaces is dried to such an extent that the material tends to lose its adherent qualities, and to slough off from the surface of the roll.

It will be understood from the above that as the desiccator is in operation, there is a continual plastering or adherence of semidried material upon the surfaces of the rolls 24, and as this material is carried around it is dried in con tact with the rollers, finally to drop off in the form of friable cakes into the lower part of the desiccating chamber.

The semidry particles which impact the rolls have spiral paths of flight, due to the action of the swirling drying gas. Therefore substantial- 1y all of such particles strike the rolls, although the rolls may be spaced apart as illustrated.

Although in many instances the walls of the rollers can be heated by virtue oi their heat transfer relationship with the hot gases within the desiccating chamber, it is possible to provide supplemental heating means such as illustrated in Figure 4. Thus in this instance roll 35 is carried by the hollow shaft 3'5, and is formed to provide fiow passages which connect with the pipes 38 and 39. A coupling cl serves to connect the pipe passages with the exterior stationary pipes 42 and 43. Pipe can connect to a source of steam under pressure, whereby steam is introduced into the interior of the drum through the pipe 38. Pipes as and :33 can conmeet to an evacuating means for the removal of condensate or wet steam. If desired, passages or coils can be provided within the drum 3%, in order to secure better distribution of heat.

Auxiliary rolls as described above can be incorporated with various types of spray driers. it is possible to utilize an arrangement such as illustrated for example in Figure '5. In instance the spray drying chamber 55 has an upper cylin drical shaped portion 46a and a lower conical shaped portion 4%. The auxiliary drying rolls 41 are mounted in the upper chamber portion 45a, and are distributed to generally surround the centrifugal atomizing device ta. Hot drying air is introduced into the manifold it, and is discharged into the upper part of the drying chamber through the inclined louvres 5E, which deliver the hot air with both downward and rotary velocity components. some additional hot drying air can be supplied through conduit 52, to be delivered downwardly about the atomizing device 48 through the annular region With the arrangement illustrated in Figure it will be evident that the auxiliary rollers ii can be evenly distributed about the drying chamher, and that the hot air from the manifold is all delivered into an annular region outwardly of the rolls. In toad of g pneumatic separation within the chamber, the spent drying gas together with the dried powdered material is shown being removed through the conduit 5t.

Certain types of material being treated with my apparatus and method may not freely slough off from the surfaces of the rollers. In such event it is possible to positively remove the dried material means of a suitable scraper. Thus as shown in Figures 6 and 7, the auxiliary drying roller 56 cooperates with a scraping blade which is suitably mounted on the adjacent wall portion of the desiccating chamber. The scraper is positioned in such a manner that material is removed'from the surface of the roll immediately before that surface is again exposed to material discharged outwardly by the atciniaing vice.

The apparatus and method described above is particularly applicable to the drying of lacteal products containing a substantial amount of milk sugar, such as concentrated liquid whey (i. e. commercial whey concentrated by evaporation to say 30 to 60% solids) to form a stable powdered product having sufiicient residual moisture to satisfy water of crystallization of the lactose present. When operating a conventional spray drier upon concentrated liquid whey, the centrifugal atomizing device tends to plaster the inner walls of the spray drier with semiolried ma terial, in the manner previously described.

When using my apparatus and method, semidried particles of whey concentrate impact and adhere to the surfaces of the auxiliary drying rollers, where the material remains until a sub stantial amount of moisture has been removed. Thus assuming that it is desired to remove the dried whey product from the desiccator with about total moisture, the semidried whey impacting and adhering to the surfaces of the rollers may initially contain as much as moisture. After the material remains upon the rollers for a suflioient period of time to reduce the moisture content to say about from 10 to 12%, this material sloughs off and merges with the powdered material in the lower part of the desiocating chamber. After the material has been removed from the desiccating chamber it can be readily crushed as by passing it through an ordinary blower to pulverize the friable cakes which have sloughed from the auxiliary drying roll. After or prior to such crushing, the mate rial can be subjected to secondary drying to reduce the total moisture content to say 8%.

By utilizing my apparatus and method for the spray drying of liquid whey concentrate serious build-up of semidried material upon the inner walls of the desiccating chamber is avoided, and detrimental eifects of such build-up, such as over-heating, burning, necessity for frequent shut downs and the like, are likewise obviated.

I claim:

1. In desiccating apparatus of the spray drier type, a drying chamber, means for maintaining an atmosphere of hot drying gas in the chamber, atomizing means for introducing an atomized spray of liquid material into a central region of the chamber and into the drying gas, said last means imparting outwardly directed radial velocity components to the atomized particles for free flight of the particles in the drying gas, whereby the particles are flash dried while suspended in the gas, a plurality of auxiliary drying drums disposed in the chamber and in an annular region generally surrounding and spaced lat erally from the atomizing means, means serving to mount said drums for rotation about their individual axes, and drive means for continuously rotating said drums, the exterior of said drums forming drying surfaces for temporary adherence of semi-dried material lodging upon the same after free flight from the atomizing means.

2. In desiccating apparatus of the spray drier type, a drying chamber having a central vertical axis, means for maintaining an atmosphere of hot drying gas in the chamber, atomizing means for introducing an atomized spray of liquid material into the chamber in a region located adjacent said central axis, said last means: imparting outwardly and horizontally directed radial velocity components to the atomized particles for free flight of the particles in the drying gas, whereby said particles are subjected to flash drying while suspended in the gas, a plurality of drums disposed within said chamber in an annular region spaced horizontally from and generally surrounding the atomizing means, said drums being spaced circumferentially and forming peripheral surfaces against which semi-dried atomized particles are caused to impact and temporarily adhere after free flight from the atomizing means, means for mounting said drums on individual axes which are substantially parallel to the axis of the drying chamber, and means for continuously rotating said drums.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 758,065 Hall Apr. 26, 1904 927,169 Roch July 6, 1909 1,634,640 Zizinia July 5, 1927 1,845,163 MacLachlan Feb. 16, 1932 1,846,288 Varnau et a1 Feb. 23, 1932 1,958,702 Johnston, Jr., et a1. May 15, 1934 2,087,788 Thai July 20, 1937 2,304,221 Walsh Dec. 8, 1942 2,314,159 Peebles Mar. 16, 1943 2,390,167 Patrick Dec. 4, 1945 2,396,689 Davis Mar. '19, 1946

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