US1591577A - Drying apparatus - Google Patents

Description

July 6 1926.

R. THELEN DRYING APARATUS Filed Sept. 12, 1924 4 Sheets-Sheet l ooooooo. oooooooooooooo@ IN V EN TOR ROLF THE LE N BY N* A TTORNEYS.

Fieri July 6 1926.

- R, THELEN DRYING APPARATUS Filed Sept. l2. 1924 4 Sheets-Sheet 2 INVENTOR. ROLF THEM-:pl

TORNEYS.

`Iuly 6 1926.

R. TH ELEN DRYING APPARATUS 4 sheets-sheet 5 i Filed Sept. l2 1924 oooooooooooo -4/ gooooo IN V EN TOR. ROLF 'WEKEN l M A TTORNEYS.

July 6 1926.

R. THELEN .DRYING APPARATUS Filed Sept. l2 1994 4 Sheets-Sheet 4 INVENTOR. .A OLI: TIPELEN Mm WTTORNEYS.

Patented July 192%.

UNITE A'strates ROLF THELEN, 0F MADISON, WISCONSIN'l DEDICATED. BY MESNE ASSIGNMENTS, T0 THE GITIZENS 0F THE UNITED STATES OF AMERICA.

DRYING APPARATUS.

Application led September 12. 1924. Serial` No. 737,369.

(GRANTED UNDER THE ACT OF MARCII 3. 1883; 22 STAT. L. 625.)

This application is made under the act of March 3, 1883. chapter 142 (22 Stat. 625) and the invention herein described and claimed may be used by the Government of the United States, its officers and emloyces, and by any person in the United gtates without the payment to me of any royalty thereon. I hereby dedicate the same to the free use of. the Government and the people of the United States.

This invention consists in brief in subjccting the material to be dried to air currents whose path takes a spiral or helical direction in contradistinction to most drying processes in which the path of the drying medium lies more or less in a single plane. This spiral circulation producesa greater uniformity in the drying medium throughout the length ofthe drying chamber than it has been possible to secure heretofore.

It is well known that spiral circulations of certain types have been used heretofore, thus, for instance, Letters lPatent No. 449,170, issued to Phillips on March 31, 1891, discloses a system of drying bricks or other similar material in which the air enters the drying chamber at one end and follows a spiral path through the chamber, finally being discharged'to the atmosphere at the opposite end ofthe drying chamber. This type of circulation, which may be Aclassed as an external circulation because the air is drawn from4 the outside, asses but once through the spiral path wit in the chamber and is then discharged to the outside atmosphere, is designed for and adapted to progressive systems of drying. In these systems the material to be dried'enters the drying chamber at one end and is `periodically or constantly moved toward the opposite end, emerging therefrom at the end of the drying process.

The present invention is limited specifically to compartment systems of drying. In these systems the material to be dried remains continuously in .position in the drying chamber throughout the entire period, the entire charge being loaded into the chamber at one time and likewise removed from the chamber at one time. This invention is further limited to internal circulation of the drying medium. In this type of circulation the principal movement of the drying medium is constantly throughout the same patin the drying medium being recirculated and used repeatedly. It is the common commercial practice at the present time in many compartment systems of drying to employ a circulation of the drying medium which is principally in vertical planes perpendicular to the longitudinal axis of the drying chamber. Exc-e t in so far as it is disturbed by outside in uences, each particle of the drying medium moves continuously in one of these planes. No positive means are provided for producing any longitudinal circulation in the drying processes. It has been found in actual full scale commercial tests that it is not possible with these systems to maintain uniform d Y throughout the length of t e rying chamber. This lack of uniformity is especially pronounced in the case of long chambers in which material of Widely varying moisture contents and Widely varying drying rates is being dried rapidly.

In thoseparts of the dr 'ng chamber in which the material to be dyir'xied has become dry first, the atmosphere becomes drier and hotter than in those portions of the dr 'n l chamber in which the material to be rie dries more slowly. The resulting condition is disadvantageous because it roduces overdrying in certain portions of t e matei'iai to in conditions be dried and under-drying in other portions, ai;

The present invention overcomes these diiiculties by'producing a certain amount oi" longitudinal circulation of the. dryin medium in addition to the normal circu ation which is commonly called cross-circulatron. This longitudinal circulation imposed upon eirthe cross-circulation results in a spira.' culation as will become evident tron detailed description oit trie application oi.

invention to tivo types yot' drying chambers.

The present invention does not limit itself to specified methods of producing either the cross-circulation or the longitudinal eirculatioiusince its purpose can be equally well accomplished whatever .the method of produing the circulation may be. For purposes o't` illustration and to make the operation of this invention clear to those skilled in the art. two typical applications are presented. the first one illustrated in Figures I and II. a ventilated natural draft compartment kiln designed tor the seasoning of lum ber and other wood products, and, second, an internal tan compartment dry kiln, also designed especially for the seasoning of lumber and other Wood products.

Figure I is a cross-sectional elevation of a ventilated natural draft compartment kiln. Figure II is a longitudinal sectional elevation of the same kiln. Figure III is a crosssectional elevation oi an internal fan compartment kiln. Figure '[V is a longitudina'l sectional elevation ot' the same kiln. Correspoi'iding parts on the four figures are correspondingly lettered in so vfar as possible. Letters A to 0, inclusive, apply to all tour figures Letters P. Q. and R apply only on Figures I and II. Letters S to Z. inclusive,

y Zontal.

and Nos. 1 and 2 apply only on Figures III and IV.

Referring to the figures, AA rein-osent piles of lumber to be dried. The individual boards `in the pile are" arranged with the long axis parallel to the longitudinal axis of the kiln and with the board faces hori- Suitable spaces provided between the layers of lumber permit the passage of the drying medium.

. BB represent the walls of the drying chamber.

CC are air inlet ducts.

DD are air inlet duct dampers.

EE are air outlet ducts.`

FF are air outlet duct dempers.

' GG are heating coils.

HH are steam spray lines.

ll are bunks'upon which the lumber rests.

JJ are the rails upon which the piles of lumber are moved into and out of the drying chamber.

KK are rail supports.

L is a motor.

M isy the motor pulley.

N is the belt.

O is the. driven ulley.

P is the blower 1n Figure II'.

Q is the suction duct in Figures I and II.

1t' is the discharge duct in Figures I andII.

S is the line shaft in Figures III and IV.

'ITeire line shai't bearings in Figures III and IV. l

Y'f'."U are disc lans in Figures III and IV.

'VV are cross ducts in Figures III and IV.

' IVIV are plenum chambers in Figures III and lV.

XX are plenum chamber ditfusers in Figures lll and IV.

Y is the suction box in Figure IV.

Z is the pressure box in Figure IV.

1 is the reversing switch in Figure IV.

`L is the longitudinal duet in Figures III and lV.

'lhe general arrangement of the kiln shown in Figures III and IV is similar to that illustrated in my Patent No. 1,466,518, issued on August QS, 1923, with the addition ot' the part required to produce the spiral circulation Which'is the subject of this invention.

-Thc two kilns illustrated in Figures I to lV are intended to use a mixture of air and water vapor, hereinafter referred to as air,

vfor the drying medium. Super-heated steamf can. however, be used as a drying medium with any change indesign.

The kiln illustrated in Figure I and Il Yl'ollows` present commercial practice rather closely, with the exception of the blower P and the mechanism functioning with it. This blower may be of conventional design, the lparticular type to be used to be determined by the individual conditions sur-4 rounding the design. When comparatively high pressures are required a centrifugal blower is indicated. When, on the other hand, the pressures required are very low, disc or propeller fans can be used to ood advantage. The blower illustrated is o the centrifugal type. It is driven from the motor L through the pulleys M and O and the belt N: A suction duct Q extends from one endeof the kiln to the suction side of they blower and a discharge duct R extends from the pressure side of the blower to the other end of the kiln. When the blower is in operation it draws air from one end of the kiln and discharges it to the other end of the kiln, producing a longitudinal circulation.

This circulation, combined with the erosscirculation produced in the usual manner as will be described later, produces a resultant circulation of spiral form.V The specific effeet of this spiral circulation is a continual mixing of the air from end to end of the kiln. This avoids the formation of hot spots and cold spots in the kiln and thus produces more uniform drying. A

The detailed operation of the kiln shown in Figures I and II is as follows:

After the kiln has been loaded and closed, the blower P is put into operation, steam is turned into the heating coil G, the temperature of the kiln is regulated and controlled by the control of the steam supply through the heating coils. This control may be manual or automatic as desired. Control of the humidity ofthe air in the kiln is secured by the manipulation of the air inlet duct Cia dampers and the air outlet duct dampers and by regulation of the supply of steam to the steam spray lines. It is customary to open the dampers sufficiently to maintain the humidity below the desired point under ordinary lumber drying conditions. The atn'iosphere outside oi the kiln contains less moisture per cubic foot than that within thel kiln; therefore, the humidity of the air in the kiln can be reduced by mixing with it the air from the'outside atmosphere. Air may enter the kiln through the air inlet ducts and escape from the kiln through the air outlet ducts. y

Having secured the desired setting of the dampers the humidity of the air of the kiln may be raised by admitting steam to the steam spray lines, which discharge the steam downward as indicated in Figure I.

Control of this steam supply may be manual or automatic as desired. The steam sprays issuing from the steam spray line tend to produce a downward air circulation as indicated by the arrows. This circulation is intensified by the action et the heating coils which tend to make the air rise in the space between the rows of lumber piles and by the cooling eiiect of the e evaporation of moisture from the wood. When the side walls of the kiln are exposed to the outside atmosphere the cooling etfect produced by them also tends to increase the circulation of the air in the kiln. The resultant circulation, commonly termed cross circulation, is in the plane et Figure I and in the general direction indicated by the arrows. The discharge of air from the discharge duct is producing a slight plenum at the end of the kiln opposite the discharge end of the duct and the withdrawal ot' air throughout the suction duct Q produces a slight `vacuum at the other end of the kiln. sult is a movement of air from the plenum toward the vacuum. This longitudinal movement superimposed upon the cross-circulation I have termed the spiral circulation.

It is not anticipated that the resulting eirculation will be true spiral nor. is it necessary, to accomplish the purpose et. the invention, that it be so. The principal purpose oi"A the invention is to produce greater uniformity in the drying medium and this is accomplished satisaetorilyeven when the nath oi'i'the air particles is not a true spiral. i The iriln illustrated in Figures III and IV follows very closely the detailed construction illustrated and described in my Fai/ent No. Lfithl, With the exception et the iongit-udinal duct, the suctionbox and assure box. The detailed construction ian il in Figure IV die the in'essure'l" a che The obvious recated by the arrows. This pressure box communicates with the longitudinal duct, and the air discharged from the fan passes through the longitudinal ducts into the suction box Y from which it is drawn through the disc fan U at the lett hand of the kiln as illustrated in Figure IV. This action, coupled with the cross-circulation normally produced by the fans creates a longitudinal mixing of the air, which I have termed the spiral circulation. When the direction of rotation of the fans is reversed the direction of the air movement in the longitudinal duct is also reversed and the cross-circulation as illustrated by the arrows in Figure III is reversed. The pressure box Z is then under vacuum and the suction box Y under a slight pressure. Likewise, theV plenum chambers WW are under a slight vacuum and the cross ducts V serve to conduct the air` from the fans to the heating coils instead ot from the heating coils tothe fans. The detailed operation is similar to the operation of the kiln illustrated in Figures l and II. Control of temperature and humidity may be had in precisely the same manner. The method of producing the eirculation is different trom the one previously described in that the principal circulation is produced by means of disc fans. This operation is described in detail in my Patent No. 1,466,518, already referred to. When the circulation of the air is as indicated by the arrows in Figure III' all of the fans except the left hand one` Figure IV, draw air from the heating coils through the cross duet. The air passes fromall of the fans except the right hand one, Figure IV, into the plenum chambers through the plenum chamber ditl'users upward between two rows ot lumber piles. laterally outward and downward to the heating coils, as illustrated. The right hand fan, Figure IV. discharges into the longitudinal duct to the pressure box and the lett hand fan, Figure IV, draws air from the longitudinal duct to the suction box. When the direction of rotation of the shaft and the fans is reversed the air movement through the longitudinal duct is from left to right and the direction of the circulation through the lumber is opposite to that illustrated in Figure III.

The longitudinal circulation produced by the action et the end fans as just described has precisely the same etl'ectas thel longitudinal circulation produced by the blower P in the kiln illustrated in Figures I and II. This eect is in brief the longitudinal mixing et the air' in the kiln which results in a greater degree of uniformity of the air than can be obtained without such longitudinai mixing.

Having :uily described this invention and n how it can be appiied in two typical f original:

Ye ii 1. In u drylkiln adapted to compartment Charge duct adapted to withdraw air from operation, means 'for producing :1 spiral cirthe kiln at one end and to discharge Suid culation of air in said kiln` and means for uir into said kiln ut the opposite end, and 10 maintaining aiunilmm temperature and hu means for maintaining a uniform tempera midity throughout the kiln. ture und humidity throughout the kiln.

2. In a dry kiln adapted to Compartment Aug. 1Q, 1924. operation, :1 blower, n suction duct, a dis- ROLF THELEN.

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