US2499157A - Apparatus and method for drying solid material - Google Patents

Description

J.. E. PEIRCE APPARATUS ND METHOD FOR DRYING SOLID MATERIAL Feb. 28g 3950 Filed July 14, 1945 NTI \ bnn/UV INVENTOR. a//fvfP/R Patented Feb. 28, 1950 y I 2,499,157

UNITED STATES PATENT APPARATUS AND ME'EHOEB FOR DRYNG SOLID M'EERAL John E. Peirce, Arlington, N. Ji., assigner to titled Chemicai c Dye Corporation a corporation et' New York Application .Fully M, 11945, Serial No. 605,142

3 Claims. (m. 3dB-1137) i f E This invention relates to apparatus and method and the rotary drum. Principally because of apfor treating solid material with a gas, at least preciable eccentric and axial movementl of the some of which material exists as dust when in rotary drum, resulting from wear and tear land the treated condition. maladjustinent of the rotary drum on its sup- The present improvements may be exemplified 5 porting rollers and driving gears, it is dilcult in connection with construction and operation of and often impossible to provide a gas and dusta rotary drum used to eect the final drying of tight joint between the rotary drum and the xed salts such as anhydrous bisuliite of soda, trisogas inlet. Hence, to avoid dusting at this joint dium phosphate, sodium hyposulte, and sodium it has been the practice to operate the apparabiuoride. In several processes in the chemical tus as a whole in such a way as to maintain a industry, materials of the nature indicated are slight negative gas pressure at the material out'- preliminarily dried, e. g. dewatered or separated let-gas inlet end of the dryer. Such a. procedure from the mother liquor as by a centrifuge, and requires the use not only of a blower to supply there results a salt containing say 3-10% moisgas to the gas inlet end of the dryer but also an ture which must be removed before the material additional suction fan in the tail gas line of the is ready for packaging. Final drying is commondryer, the operation of which fan must be carely eiected by means of a rotary drum and a suitfully adjusted in order to maintain the desired able drying gas. In the operation of apparatus negative pressure at the material discharge-gas of this type, the material to be dried is fed into inlet end of the dryer. Often, it is necessary to one end of the drum arranged so that the maeffect drying by means 0f an inert gas to avoid terial passes thru the drum to the opposite or oxidation of the material being dried. In this material outlet end. A drying gas such as heated situation, when Operating in accordance with the and nltered air or a heated inert gas such as carprior practice, i. e. maintaining a negative presbon dioxide, depending upon the particular nasure at the material outlet end of the drum, it ture of the operation at hand, is charged into the 5 is not possible to avoid drawing in atmospheric material outlet end of the drum and iiowed thru air thru the joint between the rotary drum and the drum countercurrent to movement of the mathe fixed gas inlet. Further, the atmosphere in terial. Because of their damp condition as fed many chemical plants contains impurities which into the drum, such materials present no particuare sucked into the dryer and cause contaminalar dusting problem in that portion of the drying tion of .the product being dried. zone at and near the material inlet-gas outlet This invention aims to provide a. system by end of the dryer. However, as theV material is means of which the foregoing 'difficulties are gradually dried, dusting proportionately ineliminated. The invention, its further objects creases, and in the immediate vicinity of the maand advantages may be understood from the folteria] discharge end, a substantial amount of the lowing description .taken in connection with the material exists in dust form. Because of dustaccompanying drawing, in which Fig, 1 is 8,1011..

ing. depending largely 'upon the diameter of the gitudinal vertical section of the improved apdryer, it is necessary to supply the treating eas paratus, and Fig. 2 is a transverse section on the thereto in such a way that the gas stream pass- 1in@ 2 2 of Fig 1 ing thru the dryer has a velocity insucient to to Referring to une drawing, it indicates a horientlaiin an apprECia'ble dust lOad, require-1 Zgnta] cylindrical drum providing an elongated ment being imposed so as to avoid sweeping dust, drying chamber H, The drum is mounted for constituting an appreciable portion of the dry mtaticn on rollers g2 and tracks g3, and is D'dlt, 0u? 0f the dryer along Wlth the Spent equipped with suitable driving gear not shown gaSffOllS dlylng agem- Thus for dryer 0f glYen 45 associated with a source of power. Damp matedeslgn the v eloclty 0f the treatmg gas Passmg rial to be dried may be fed continuously by a star thru the dI-Vmg Chamber musf be held below or feeder i5 into a chamber i6 having at the botat not more than @gwen maxmumtom a ribbon conveyor il. Introduction of ma- In the constructmn. of dryers of the kind un- ,terial into chamber i@ may be Such that the del Consideration, the treating 0I' drying gas is 50 level of material is maintained at about or beusually fed into the drum from a gas bustle 01 low the axis of the conveyor i'i so as to provide vestibule communicating with the source of gasa, free space thru which spent drying gas enters ecus drying agent. As previously stated, the atchamber it forv discharge from the apparatus mosphere' at the solid material diScharge-drythru outlet 2i.v The drum is pitched slightly toing gas inlet end of the dryer is substantially ward the gas inlet end which pitch in conjuncdust-laden. Because of this condition, and the tion with longitudinal nights 22 serves to move fact that the dryer proper is rotary and the gas the material thru chamber it. vestibule is fixed, in the prior practice it has been A source of gaseous drying medium 23 is concustongary to attempt to provide gas-tight joints nected .to the suction side of a blower 2d which at. the connection between the xedgas bustle forces the gas successively thru a suitable purifier 26 and a heater 21, the discharge pipe 28 of which` is provided with a valve 29 and opens into the fixed gas inlet chamber or vestibule indicated generally by 30.

According to the present invention, it is not necessary to attempt to provide a gas and dusttight joint at the connection between the fixed gas chamber 30 and the rotary drum I0. The construction and operation afforded are such, notwithstanding the requirement of maintaining in the drying chamber I I a relatively low gas velocity, as to prevent the presence of dust at the gas inlet opening of the drum and at the conlnection between the drum and the fixed gas inlet chamber. On the side adjacent the rotary drum, chamber 30 is provided with aA circular cut-out 32 having a diameter appreciably greater than the outside diameter of the drum neck 33 which projects into chamber 30 and forms a gas inlet opening 34 for the drum. If desired neck 33 maybe provided with an outwardly projecting flange 35. As shown on the drawing, the relation of drum neck 33 and flange 35 on the one hand and circular cut-out 32 on the other is such as to permit appreciable eccentric and axial movement of the drum neck without a metal-tometal contact and thus affords a non-gas-tight joint connection between the drum and the gas chamber.

In accordance with the invention, the area of the gas inlet opening 34 of the drum is chosen, relative to the cross-sectional area of drying chamber II and a maximum permissible gas velocity thru the latter, so that there is created in the gas stream passing thru inlet opening 34 a gas velocity high enough to prevent the presence of dust in the immediate vicinity of neck 34 and the connection thereof with the gas chamber. For this purpose, the material outlet end of the drum is provided with a section 38 connecting the end of the drum to the drum neck 33. While section 33 may be cylindrical and coextensive with neck 33, in which case section 38 connects with the vertical end wall 39 of the drum at a right angle, preferably section 38 is conical and approximately of the configuration shown on the drawing. The conical design of section 3B along with the restricted cross-sectional area of drum throat 33 provide a Venturi tube effect which facilitates maintenance at the gas inlet end of the drum of a relatively high gas velocity. It has been found that, in order to create in the gas stream entering the drum a gas velocity high enough to prevent the presence of dust in that vicinity, the vcross-sectional area of the drum throat 33 should not be more than about one third the cross-sectional area of drying chamber II. Further, when using a conical connecting section 38, to create the most desirable Venturi tube effect and secure the best results, it has been found that the area of the circle formed by the intersection of connectionv 38 and drum wall 39 should be not more than half the cross-sectional area of chamber Il, and that the axial length of section 38 should be equal to at least half the diameter of opening 34.

Another'feature of the invention provides for removal of the dry material from the drum in such a way that the material being discharged is out of contact with the gas stream entering thru opening 34. This objective is-accomplished by a conveyor the tube of which is .supported in the position shown on the drawing by a suitable bracket 46 and the end wall 41 of gas chamber 30. Tube 45 houses a screw 49 driven by a motor 50 and opens at the discharge end into an elevator conduit 5I or other receptacle. The closed portion of the tube 45 extends into drying chamber II far enough so that material being discharged by conveyor 49 is out of contact with gas in the zone of high gas velocity. The inner end of tube 45 is provided with an open top trough 54, the design of such trough and of flights 22 being such that, during normal rotation of the drum, those portions of flights 22 adjacent the solid material outlet end of the drum keep trough 54 filled with dry material.

Assuming use of air as the drying agent, operation is as follows: Air is drawn into the system by blower 24 and passed successively thru a suitable filter or purifier 26 and a heater 21 in which the air is heated to the desired drying temperature. Valve 29 in pipe 2B is adjusted so as to maintain heated air in the gas inlet chamber 30 under such a positive pressure that the velocity of the gas stream passing thru drying chamber Il does not exceed or is less than the maximum permissible value, specific velocity being dependent upon the cross-sectional area of chamber I I and the nature of the material being dried. By the construction described, there is thus created in the vicinity of the drum throat and of the connection between the same and the fixed gas chamber 30, a gas velocity which is high enough to keep dust back in the drying chamber and well away from the gas inlet zone formed by the conical section 38, drum throat 33 and the non-gas-tight connection between the throat and gas inlet chamber 30. The positive pressure existing in chamber 30 maintains a small outflow of gas at the connection lbetwen the rotary drum and the 'fixed gas chamber and prevents ingress of atmospheric air.

Following is an example of operation in which the material dried was anhydrous bisuliite of soda containing about 5% by Weight of water as fed into the rotary drum. 'I'he length of the cylindrical portion of the drum was 40 feet. The axial length of section 38 was 18 in., and the inside diameter of drum throat 33 was 24 inches. The cross-sectional areas of drying chamber II, of the circle of intersection of end wall 39 and conical connection 38, and of gas inlet opening 34 were 19.6, 7, and 3.1 square feet respectively. Air was cleaned in purifier 26 by passing thru glass wool and cloth lter, and heated in heater 21 to an initial drying temperature of 95 C. Blower 24 and-valve 29 were adjusted so as to maintain the gas in chamber 30 at a positive pressure of 0.2 in. (water). This pressure created an average gas velocity in the cylindrical section of drying chamber I I of about feet per minute, which gas velocity was low enough to avoid substantial entrainment of dust in the spent gas discharged from the dryer. Under these conditions, the solid material was dried at a rate of 1.5 tons per hour, and there was no discernabie leakage of dust at the non-gas-tight connection between the drum and the fixed gas chamber 30.

I claim:

1. Apparatus for treating solid material at least some of which exists as dust when in the treated condition, which apparatus comprises a rotary drum forming a treating chamber and having-a material inlet-gas outlet end and an; oppositely disposed material dicharge-gas inlet.

end, means for introducing solid material to be treated into said material inlet end of said chamber. means for moving the material thru said chamber to said gas inlet end, an annular wall xed at its outer periphery to said gas-inlet end of said drum, a frusto-conical section of substantial axial length having open ends one of which is larger than the other, the large end of said section being fixed to the inner periphery of said wall, and the small open end of said section having a cross-sectional area not more than onethird that of said chamber, said section forming a gas inlet chamber for said treating chamber, a gas reservoir chamber communicating with the small end of said section and associated therewith by a non-gas-tight eccentric-motion-permitting joint, means for supplying treating gas to said reservoir chamber under positive pressure to thereby supply gas under positive pressure to said gas inlet chamber and to said treating chamber, and means for discharging treated material from said treating chamber thru said gas inlet chamber While out of contact with a gas stream passing thru such inlet chamber.

2. Apparatus for treating solid material at least some of which exists as dust when in the treated condition, which apparatus comprises a rotary drum forming a treating chamber and having a material inlet-gas outlet end and an oppositely disposed material discharge-gas inlet end. means for introducing solid material to be treated linto said material inlet end of said chamber, means for moving the material thru said chamber to said gas inlet end, an annular wall fixed at its outer periphery to said gas-inlet end of said drum, a frusto-conical section having open ends one of which is larger than the other, the large end of said section being ilxed to the inner periphery of said wall and having a crosssectional area not more than half that of said chamber, and the small open end of said section Y having a cross-sectional area not more than onethird that of said chambensaid section having an axial length equal to at least half the diameter of said small end and forming a gas inlet chamber for said treating chamber, a gas reservoir chamber communicating with the small end of said section and associated therewith by a non-gas-tight eccentric-motion-permitting joint, means for supplying treating gas to said reservoir chamber under positive pressure to thereby sup- Iply gas under positive pressure to said gas inlet chamber and to said treating chamber, and means for discharging treated material from said treating chamber thru said gas inlet chamber while out of contact with a gas stream passing thru such inlet chamber.

3. Apparatus for treating solid material` at least some of which exists as dust when in the treated condition, which apparatus comprises a rotary drum forming a treating chamber and having a material inlet-gas outlet end and an oppositely disposed material discharge-gas inlet end, means for introducing solid material to be treated into said material inlet end of said chamber, means for moving the material through said chamber to said gas inlet end, an annular wall fixed at its outer periphery to said gas-inlet end of said drum, said wall having a frusto-conical section of substantial axial length having open ends one of which is larger thanthe other, the large end of said section being relatively adjacent said gas inlet end of said drum and the small end of said section being relatively remote from said gas inlet end of said drum, the small open end of said section having a cross-sectional area not more than one-third that of said chamber, said section forming a gas inlet chamber for said treating chamber, a gas reservoir chamber communicating with the small end of said section and associated therewith by a non-gas-tight eccentric-motion-permitting joint, means for supf plying treating gas to said reservoir chamber under positive pressure to thereby supply gas under positive pressure to said gas inlet chamber and to said treating chamber. and means for discharging treated material from said treating chamber while out of contact with a gas stream passing through such inlet chamber.

JOHN E. PEIRCE.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS OTHER, REFERENCES The Link-Belt Roto-Louvre Dryer, Book No. 1911. Copyright 1941 by Link-Belt Company. Pages 4,5, 14 and 15.

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