US2162973A

US2162973A - Rotary drier

Info

Publication number: US2162973A
Application number: US156761A
Authority: US
Inventors: Harold F Roland
Original assignee: Hiram Walker and Sons Inc
Current assignee: Hiram Walker and Sons Inc
Priority date: 1937-07-31
Filing date: 1937-07-31
Publication date: 1939-06-20
Anticipated expiration: 1956-06-20

Description

- June 20, 1939. H F Q A D 2,162,973

ROTARY DRIER Filed July 51, 1937 INVENTOR HAROLD F. ROLAND ATTORNEY B \m N. 2 n v =W mm d! I II I I F r/ Mm 2 NN g m mm I ll q U s l. a v m FHHE Patented June 20, 1939 PATENT OFFICE 2,162,873 no'rAnr DRIER Harold F. Roland, Peoria, 111., assignor to Hiram Walker & Sons Inc., Peoria, 111.

Application July 31, 1937, Serial No. 156,761 6 Claims. (CL- 34-6 This invention relates to rotary driers and more particularly to rotary driers of the type which are adapted to the drying of materials such vide improved means for introducing a stream of air into the drier whereby the lowest velocity of air is in the part of; the drier where the mate rial is the driest, thus minimizing chances of dust loss by entrainment of material particles in the air stream.

Another important object. of the invention is to providemeans for introducing and circulating the air stream in such a waythat cool or cold air enters at the discharge end of the drier, thus cooling the dried material somewhat before it, leaves the drier.

A further object of the invention is to provideair-circulating means for a drier of the characcomparatively cool air at or near the discharge end of the drier and the gradual warming of this air as it travels toward the stack or air vent,

' thus minimizing the possibility of the drier atmosphere reaching its dew point,

A still/further object of the invention is to provide in a drier. of the type specified, means for increasing the drying efliciency through the introduction of two different streams of air which are circulated through the drying compartment in a manner designed to take full advantage of the changing drying characteristics of the materd'ial during thecourse of its travel through the rier. v

,Other objects and advantages 'of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawing wherein I have shown the preferred form in which'I have thus far contemplated applying the principles of the invention.

Referring to the drawing:

Fig. 1 is a side elevationalview, partly in. section, of a rotary drier embodying the improvements of my invention;

F g. 2 15a transverse section through the taken on line'2--2 of Fig. l, and v Fig. 3 is a similar transverse section taken on line 3-3 of Fig. 1. p 3

Considering the drawing in detail, I have, shown therein only such'portions ofa typical redrier iug connected through a pipe 18 with the header ter referred to which permits of the entry of by the shell 4.

' the feed to the discharge end as is usual in rotary passes through thedrier.

. rangement the air-enters turn current rotary drier as are-necessary to give a clear understanding of the improvements constituting the present' invention. The cylindrical shell of the drier is indicated at I, and this is closed at the discharge end by an end 5 wall 5. The opposite end of the shell, that is, the feedend, connects with a stack 6, and the material, such as distillers spent grain, isintroduced into the drier through the feeder 'l. A heated double-walled mandrel 8 extends axially W the full length of the shell, being supported at one end by the wall 5 and at the other end by its stationary extension 9. A plurality of heat-- ing tubes H extend lengthwise of the drier near the shell 4, said tubes connecting at the discharge end of the drier with a header i4 and at the feed end of the drier with a similar header l5. Steam for the mandrel 8 and tubes H issupplied from a pipe [2 which connects through a hollow trunnion 13 with the space between the 20 double walls of mandrel 8, the latter in turn belli. The unit is rotated by a suitable motor (not shown) being supported for rotation by rollers H which engage circumferential t es |8.carried 25 The drier is inclined downwardly slightly from driers of this-general type. The wet material entering the feed end from feeder I is stirred and tumbled between the mandrel 8 and'the shell 4 as it gravitates along the drier until it reaches the discharge chute l9 into which it passes through a series of circumferential openings 2! formed in the lower end of the drier shell 4. 35 Blades or fins 22 on the mandrel 8, and similar blades 23 projecting inwardly from the shell '4, serve to lift thematerial and tumble it back and forth between the shell and the mandrel as it,

The material is thus 40 effectively contacted with the heated tubes ll and'the heated mandrel 8 as it gravitates from the feed to the discharge end of the drier.

The usual method of introducing air into this general type of drier is through the tubular man- 3 drel 8 and its'stationary extension 9, using natural draft,induced draft, hot air or cold air, or any combination of these. With such an. ar-

the stationary end of the mandrel, as at 24, and leaves the mandrel by 50 ports 25, being deflected toward stack 6 by an annular cup-shapewbaflie plate 26.. As stated, this is the usual system employed, and with it all of the air travels the whole length of the drier. 5

Considering now the drying characteristics of the material to be treated it will be observed that for a material such as cereal grain, for example, the rate of evaporation from the point of entry from the feeder I up to an intermediate point, say up to about the point indicated by the numeral 21, (Fig. 1),is constant, or at least substantially so, because all the particles present totally wetted surfaces and the water'is available for evaporation as fast as the air stream will carry it away. Therefore, forthis zone, the rate of evaporation will be higher under the following conditions: (a) large partial pressure difference between the water on material particles and the air stream 1. e. hot dry air and hot particles; and (b) high air velocities to change air often and provide a rapid sweeping away of' moisture.

Beginning at about the point indicated by the numeral 21 and extending on to the discharge end of the drier we have the falling rate period of evaporation, wherein evaporation changes from totally wetted surface particles to particles with partially wetted surfaces, and thence to par- 7 ticles of completely dry surfaces. Over this zone -or portion of the drier diffusion from within the particles to the surfaces at whichevaporation is taking place is the controlling factor in the rate of evaporation, rather than the rate at which this moisture is being removed. Therefore the velocity of the air, thetemperature of the air, and

the partial pressure differences between the water at the'surface of evaporation and the air stream, have very little effect on the rate of drying. So it. is possible and desirable to use in this section of the drier an air stream of low velocity and low temperature,

In order that air may be supplied to the drier to satisfy the foregoing desirable conditions I have, in accordance with my invention, developed an improved duct systemwhich will now be described.

First, in order to provide for the supply of a large volume of hot air to that part of the drier in which evaporation is taking place at a constant rate, a passage 28 is provided by placing a duct 29 within mandrel extension 9 and a duct 3| within mandrel 8. The. duct 29 is stationary, and the duct 3|, which forms a continuation thereof, rotates with mandrel 8, the inner end of said duct 3! being supported by a partitioning wall or plate 32' carried by mandrel 8, and the outer end thereof engaging over the reduced inner end 33 of duct 29. Hot air which is forced into passage 28 at the feed 'end of the drier is directed into the drier shell through a plurality of small stacks 34 which are mounted in and extend through both walls of the double walled mandrel 8, as clearly shown in Figs. 1 and 3. The

stacks 34 are shaped to direct this. stream of hot air toward the main stack 8, and during this course of travel this air passes over the wet material which enters through feeder I. In order to obtain uniform distribution of this stream of hot air, the stacks. 34 are positionedcompletely around mandrel 8, and are also spaced lengthwise of the mandrel over the full distance from the feed end of the drier to wall 32.

Secondly, ducts 29 and II, and ports 25, are used to directa smaller volume of cold air to that part of the drier in which the rate of evaporation is variable due to the diffusion of moisture from the interior of the material particles to the partially or wholly dried surfaces. In practice. coolair or air of room temperature is forced into duct 25, passes through duct II into the tubulu' 28 formed by

ducts

29, 3|, plate 32 and mandrel 8; and the chamber 35 formed by plates 32 and 5 and mandrel I.

To summarize briefly the operating advantages obtainable through the use of this improved duct system:

(a) It will be observed that the air entering at cool or room temperature through ports 25 via

ducts

29 and 3| is subject to a temperature rise as it travels over the material in the drier toward stack 6, and thus the possibility of this air reaching its dew point is minimized.

(b) If hot air were admitted through ports 25 in suflicient volume to take full advantage of the drying conditions in the zone extending from the feed end upto the point 21, such volume would be more than required in the zone extending from the point 21 to the discharge end. The air velocity would, therefore, be excessive in the portion of the drier where the material is the driest, and dust loss would be substantial. Introduction of a separate stream of heated air through stacks 34 cuts down the amount of cool air it is necessary to introduce through ports 25, with the result that in the improved system the lowest velocity of the air is in the part of the drier where the material is the driest, consequently there is far less chance of dust loss by entrainment of the particles in the air stream. a

(c) The cool or cold air entering, as it does, in

the discharge endof the drier cools the material somewhat just before it leaves the drier.

(d) The heat content of the hot air introduced into the drier through stacks 14 has the same effect as an increased heating service within the drier itself and consequently gives the improved drier greater capacity than one of the same size but Of conventional design.

In practice I have found that when operating on distillers spent grains the evaporative effect of my improved drier isfrom twenty to thirty percent-greater than for a conventional rotary 4 with a rotary shell having material feed means at one end thereof and a'discharge passage at the other end, of ,means for-introducing from diiferent sources separate streams of air into thedrier comprising inner and outer ducts disposed axially of the shell and rotatable therewith, and

means providing separate communication between eaeh' of said ducts and the interior of the drier shell, including means for directing air introduced through the inner duct through the walls of the outer duct into the shell at the'dis- 'charge end thereof and additional means for di-. reeting air introduced through the outer duct the walls the latter into the shell at,

a point intermediate the feed end of the drier and the point of entry into the shell of air introduced through the inner duct.

2. In a return current drier, the combination shell, means for introducing into the mandrel at the feed end of the drier a separate stream of air from'a tsource independent of the source of the first mentioned stream, and means for directing the second stream of air from within the mandrel into the drier at a point between the point of entry of said first mentioned air stream and-the feed end of the drier.

3. In a return current drier, the combination with a rotary shell having material feed means at one end thereof and a discharge passage at the other end, of duct means for introducing from different sources separate streams of air into the drying compartment comprising a hollow mandrel extending longitudinally of the shell from the feed to the discharge ends of the shell, said mandrel. being open at the discharge end of the shell to allow passage of a stream of air therefrom into the shell, a transverse partitioning wall mounted within the mandrel intermediate the ends thereof, a plurality of vent tubes extending through the wall of the mandrel at points.-

between said partitioning wall and the feed end of the shell, and an inner duct extending axially of the mandrel from the feed end of the shell through said partitioning wall.

4. In a return current drier, the combination with arotary shell having material feed means at one end thereof and a discharge passage at the other end, of duct means for introducing from different sources separate streams of air into the drying compartment comprising a hollow mandrel extending longitudinally of the shell from the feed to the discharge ends thereof, said mandrel being open at the discharge end of the shell to allow passage of a stream of air therefrom into the shell, a baiiie disposed adjacent s'aid open end of the mandrel for returning air toward the feed end of the shell, a transverse partitioning wall mounted within the mandrel intermediate the ends thereof, a plurality of vent tubes extending through the wall of the mandrel at points between said partitioning wall and the feed end of the shell, said tubes being spaced both longitudinally and circumferentially of the mandrel and the extremities thereof being shaped to direct air passing therefrom toward the feed end of the shell, andan inner duct extending axially of the mandrel from the feed end of the shell through said partitioning wall.

5. In a drier for cereal grains and the like, the

combination of a rotary shell having feed means and a stack at one end thereof, the opposite end being closed except for a discharge passage, a tubular mandrel disposed axially of said shell, and rotatable therewith, means for directing a stream of air into said mandrel at the feed end of the drier, said mandrelhaving openings at-the discharge end of the shell through which a stream of air may pass from the mandrel into contact with material particles whose surfaces are comparatively dry, means for introducing into ,cereal grains and the like, the combination of a rotary steam heated shellhaving feed means and an exhaust stack at one end thereof, a tubular steam heated mandrel disposed axially of said shell, and rotatable therewith, said mandrel having openings at the discharge end of the shell through which a stream of air at predetermined temperature introduced therein at'the feed end may pass from the mandrel into the drying chamber and duct means for introducing a separate stream of air of a predetermined and different temperature from that of said first stream from the mandrel into the drying chamber at a point intermediate the feed end and the point of admission of said first stream.

HAROLD F. ROLAND.