US2548403A - Lumber kiln - Google Patents

Description

E. V. SMITH LUMBER KILN April 10, 195i 3 Sheets-Sheet 1 Filed Nov. 1, 1944 INSULATION law Elicia V. :Sl/Zii/Q.

E.- v. SMITH LUMBER KILN April 10, 1951 3 Sheets-Sheet 2 Filed Nov. 1, 1944 NH l I" ZOE-(4:07:

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E. V. SMITH LUMBER KILN Aprii w, 1953 3 Sheets-sheaf 5 Filed Nov. 1, 1944 QWN @ f W9 9 w@ m@ M w P OWN Patented Apr.10, 1951 r 2,548,403

UNITED- STATES *PATENTY OFFICE v LUMBER KILN Elton V. Smith, Hot Springs, Ark. 1 Application November 1, 1944, Serial No. 561,402 '7 2 Claims. (01. 34-491) This invention relates to lumber kilns and methods of drying lumber, and more particularly to a novel arrangement employing the use of wet steam as the conditioning medium and dry steam as the drying medium, together with the complete recovery of Joy-products, such as turpentine and wood oils from the exhaust steam. U

Wet steam may be defined as steam witha relative abundance of Water vapor co-mingled with the steam while dry steam may be defined as superheated steam in which there is little or no water vapor co-mingled with the steam. I

Various arrangements have heretofore been proposed for the drying of lumber and in certain of these, the use of steam has been resorted to, in order to reduce the moisture content of the lumber to a value acceptable to industry. In prior devices of this character, however, it has been found that an exceptional amount of steam has been required to eifect a drying to the minimum moisture requirements so that such installations resulted in high operating costs as well as a relatively low efficiency. Attempts have also been'made to effect a recovery of the wood oils resulting from the treatment of the lumber, but as far as at present known, the results have not been satisfactory, due to the lack of appreciation of all the problems involved.

It is accordingly one of the objects of the present invention to provide a novel method and arrangement for the conditionin and drying of for use with wet steam as the conditioning medium and superheated steam as a drying medium, and which may easily and quickly be filled to maximum capacity with lumber to be treated, thus resulting in a highly efficient plant. I

A further object resides in the utilization of a novel series of steps in conditioning the lumber and including the use of wet steam and superheated or dry steam in a selected manner and time cycle, in order to achieve a thorough seasoning of the lumber in a short time and at minimum expense of operation.

Still another object comprehends a novel method of stacking the lumber prior to treatment including the use of spacer members or stickers of such nature and size that a consider:

variation in volume thereof due to shrinkage dur- 7 in the drying process. 7

Another object is to provide a novel method of treating lumber which includes the use of wet steam and superheated steam in alternate cycles for selected time periods in order to effect a high-' ly efficient drying of the lumber without causing it to check or crack.

Still another object resides in the employment of steam as the drying medium in an all-metal kiln, thuseliminating fire hazards. Other objects and novel features .of the invention will appear more fully hereinafter from the following description whentaken in connection with the accompanying drawings whereinone embodiment of the invention is illustrated. It 'is, to be expressly understood, however, that the drawings are employed for purposes of illustration only, and are not designed as a definition of the limits, of the invention, reference being had for this purpose to the appended claims. I

In the drawings wherein similar reference characters refer to similar parts throughout the several views; g

Fig. 1 is a transverse. sectional ,view of a kiln constructed in accordance with the present in; vention and illustrates one phase of thefoperae tion thereof, with a stack, of lumber positioned therein for treatment;

Fig. 2 is a side view, partly in section, of the kiln of Fig. 1; Y v

Fig. 3 is an enlarged sectional view ofa, portion of a kiln car and illustratesthe sprin construction which cooperates: with the lumber bands;

Fig. 4 is a sectional view taken on line 4 4 of Fig. 3, with the spring removed; d

Fig. 5 is a diagrammatic View of a timer construction andthe piping layout of the complete system, and Fig. 6 is a sectional view of a contact block of the timer, taken substantially along lines 6-6 of Fig. 5. p a

Referring more particularly to Figs. 1 and. 2, a lumber kiln 8 embodying the principles of the present invention is illustrated therein as including a cylindrical steel shell Ill having front and rear doors l2 and M respectively, the entire assembly being heat insulated, as by means of Alfol insulating panels l6, and being securely mounted on concrete piers or supports l8 so that a plurality of loaded kiln cars may be transferred from tracks 64, into the kiln for treatment, and thereafter removed from the kiln by way of the rear door l4, and suitable tracks, not shown. It is desired to particularly emphasize that the kiln of the present invention is a pressure-tight retort device capable of being fabricated from relatively light-gauge steel, while the use of insulation, in panels or otherwise, serves to materially conserve the heat within the kiln during per= tion.

One of the features of the present invention resides in a novel method of treating a, stack of lumber within the kiln 8, by the use of wet steam and superheated or dry steam, and recovering from the exhaust, a maximum amount of turpentine and wood oils, abstracted from the lumber during the drying process. In order to provide a construction for alternately subjecting a lumber stack 20 to the action of the steam a plurality of pipes 22, 24 and 26 are positioned along one side of the interior wall of thekiln and each pipe is provided at spaced intervals with suitable spray jets 28, in the form of petcocks, through which the steam issues at high velocity, directed upon the adjacent side of the stack 20. A similar set of pipes 30, 32 and 34 are positioned along the opposite side of the wall of the kiln, and these are likewise provided with similar jets 28 for directing steam toward the opposite side of the stack 20. The group of pi es 22, 24 and 26 are connected to a header 36 while pipes 30, 32 and 34 communicate with a header 38, steam being supplied to these headers alternately, in a manner which will appear more fully hereinafter, so that opposite sides of the stack 20 will besubjected to periodic steam flow in opposite directions.

In order to maintain the temperature within the kiln at a selected value and also to impart to the steam issuing from jets 2B suilicient heat to compensate for the heat loss in expansion through the jets, a steam heating coil 4!! is positioned on either side of the stack 20, between the latter and the respective groups. of jets 2B. As shown, each coil comprises headers 42, arranged at each end of the kiln, and a plurality of pipes 44 extending the entire length thereof, all of these pipes being preferably provided with fins 46 as indicated in Fig; 2, in order to increase the effective heat radiation, and being supported along the kiln wall as by means of a plurality of spaced standards 48. As shown in Fig. 5, one end of eachcoil is provided with an expansion loop 50, of well-known construction, and these are connected to a common return line 52. It is desired to point out that since the maintenance of a steam-tightatmosphere within the kiln is one of the features of the invention, all openings in the wall forthe passage of pipes and other fittings, are securely welded. Moreover both the front and rear doors are tightly sealed when closed, and. may include any suitable construction for this purpose, such as a plurality of bolts 54 on the kiln, adapted to be received within openings 56 in the door l2, and thereafter sealed in wellknown manner.

While the steam issuing from the opposite sets of jets 28 is automatically cycled to secure an alternate flow, additional heat is provided by the heating coils 40 charged with steam! D 1? to this feature, the interior of the kiln is automatically maintained at a uniform temperature regardless of which jets are in operation. Preferably, the steam flow to the coils 40 is governed in accordance with the kiln temperature desired so that a constant temperature is secured throughout the entire conditioning cycle.

Means are provided for supporting the lumber so that it may be readily moved along the track 64 and into the kiln, and as shown such means include a plurality of cars 58, each having a base 60 for supporting the lumber, and a plu- "rality of wheels 62 cooperating with tracks 64.

As illustrated in Fig. 2, the cars are arranged in tandem and constitute an eflicient mobile support for the heavy weight of the lumber stack.

A novel construction is provided by the present invention for insuring that the steamfrom the sets of jets 28 will pass through the lumber stack rather than over or under the same. Such an arrangement is one of the major factors contributing to the high efficiency resulting from the use of this invention, inasmuch as all the steam from the jets is used to condition and dry the lumber stack rather than to merely flow around the exterior of the stack. .As shown, such construction includes a baffie 66, preferably of thin, spring metal, extending along the top of the kiln from one end to the other and supported by a bracket 68 also extending from end to end of the kiln The ends of the baiile are formed to receive longitudinally extending rods 10 which are of sufhcient weight as to cause the two arms of the bafile to contact the top of the stack 20, the construction thus preventing steam flow over the top of the stack.

In order to prevent any substantial flow of steam beneath the stack 20, the kiln is provided with a pair of bottom baflles 12 cooperating with opposite sides of the kiln cars. Since both of these baffles are of similar construction, it is believed only necessary to describe one in detail. As shown, the baflle 12 comprises a spring arm 14, bent into U-shaped form and embracing the side edge of the base 60 of each kiln car, and bein interposed between flat strips 13 and T 5, the arm and strips extending from one end of the kiln to the other. Strip 15 is preferably welded to the kiln wall and spaced-apart brackets 16 serve to strengthen the baffle assembly. With this arrangement, passage of steam through the lumber stack is assured.

In stacking lumber for kiln-drying purposes, it is quite common in practice to employ wooden strips or stickers between each layer, in order to separate adjacent layers so that the drying medium may more effectively flow around the lumber. Stickers heretofore used, however, have been of substantial thickness for giving the re quired separation to insure adequate circulation of the slow-moving drying medium, and hence occupy considerable space in the kiln. By the present invention, due to the high velocity of the steam used for the drying medium, the space between layers may be considerably reduced at the same time that the open, vertical flues up through the stack may be completely eliminated. A further important feature resides in the use of stickers 18 made of rust-resistant metal and of a thickness of the order to &5 inch, for separating adjacent layers. Thus, a considerably saving in space is effected, so that a greater amount of lumber may be processed. At the same time, the stickers are indestructible and are moreover not subject to warping, twisting, bending or sion the latter.

breaking as in the case of wooden type heretofore utilized.

'It is desired to'po-int out here, that by an ar rangement which will be referred to more in detail hereinafter, the pressure within the kiln is maintained at a value slightly above atmospheric, as for example up to about two pounds maximum per square inch. During the treatment of the lumber, the wood oils will vaporize and the kiln exhaust is conducted from the kiln as steam, holding'liquid vapors in suspension by exhaust pipes 80 and 82, opening into the interior of the kiln adjacent the sides thereof, Fig. 1, and adapted to be opened in the same timed sequence as the sets of jets 28. Preferably the arrangement is such that when the left hand set of jets is in operation, the right hand exhaust line 82 is open and when this time cycle is completed, the right hand set of jets and the exhaust line 80 come into operation. In this manner the flow of steam is periodically reversed through the lumber stack and thence to exhaust, resulting in a highly efiicient operation.

Means are provided for insuring that the lumber stack will'be bound securely together as a unit for resisting tendencies of certain pieces to twist or warp during drying, and as shown, such means comprising a relatively thin metal band 84 which passes completely around the stack and beneath each kiln car. The ends of the band may be provided with any suitable type of quick-detachable connection, or crimped seal. The arrangement provided, also insures that substantially the same tension will be secured in the bands when the stack shrinks .during the drying process. This desirable advantage is achieved by utilizing one or more springs 86 interposed between the band 84 and the base of each kiln car, Fig. 3, the spring serving to move the band 84 from its full line position, when the lumber is green, to its dotted line position, when the lumber is dried, thus exerting a substantially constant force on the band to ten- More particularly, the car 58 is provided. with a centrally-disposed depending housing 88 for receiving the spring, one end of the latter being secured to the base 60 at 90, and the opposite end being attached at 92 to a suitable plate, Fig. 3. mounted in the housing in such a manner as to move longitudinally thereof, this result being secured by providing the interior of the housing with a plurality of spaced ribs 94 received within notches 96 in the periphery of the'plate. The housing 88 is provided with cutaway portions 98 for reception of the band 84. It will be understood that the side edges of each base 60 of the kiln cars, are provided with openings through which the bands 84 may be passed in assembling the stack of lumber. Preferably, each base 60 is provided with a pair of longitudinally extending spaced ribs I00 to position a bottom sticker of Wood. The bases are moreover provided with a plurality of openings I02 in order to decrease Weight.

' Referring more particularly to Fig. 5, a flow diagram is shown therein which is illustrative of the preferred form of piping arrangement which may be employed. As shown therein, a boiler I02 is connected to the high pressure jet headers 36 and 38 by way of a pipe I04 which includes a manual'valve I06, solenoid valves I08, H0 and H2, a strainer II4 of any suitable type being inserted at a convenient point in the line I04. A pipe II6 serves to by-pass the steam around the valve I08 and through a solenoid valve H8 and kiln may be maintained constant throughout the cycle of operation. As shown a thermostat I28, responsive to kiln temperature is adapted to control the valve I26 through an electrical connection I30.

In order to recover the turpentine and wood oils from the exhaust steam issuing from the ports positioned in the sides of the kiln and which communicate with the exhaust pipes 80 and 82, the latter are connected through solenoid valves I32 and I34, pressure regulating valve I86, and pipe I38, with a condenser I40, the latter being connected to a suitable apparatus I42 for collecting the crude turpentine and wood oils after separation from the water in the gravity separator I43.

, Water from the latter retains considerable heat The latter is non-rotatably and this is preferably abstracted by passing the Water through a preheater or heat exchanger I44, in thermal conducting relation with the incoming water passing from the source I46 to the boiler I02, following which the spent water is exhausted to waste. In this manner, incoming water is preheated prior to its entry into' the boiler and this feature contributes greatly to the high efficiency of the system. It will be understood that strainers and traps 'of well-known construction may be utilized at various points in the system where their use is found to be desirable, and it has hence not been considered necessary to illustrate all of these elements. Also, an air vent is preferably utilized at the top'of the kiln to exhaust the air, and a pressure relief valve is associated with one side of the kiln to prevent a vacuum within the kiln, when starting up. All of these elements are so constituted, however, that the kiln is steam-tight and maintains a pressure within the kiln at about 2 pounds per square inch, as determined by the setting of the pressure regulating valve I 36.

Referring to Figs. 5 and 6, there is-disclosed therein, a novel timing arrangement for controlling the various operations of the kiln in an automatic manner. This timer is so arranged that it may be quickly and easily adjusted to secure the desired method of operation, once the cycling periods have been determined from a consideration of the various characteristics of the lumber to beprocessed. As shown the arrangement comprises a timer I48'having a plurality of contact-supportingbus bars I50, I52, I54 and I56 carried by a suitable standard I58 and adapted to receive metallic elements I60 thereon, the latter carrying a contact face I62 or an insulating face I64. A contact-carrying block I66 is arranged to; cooperate with the elements I60 and carries a plurality of contacts I68, I'I0, I'IZ'and H4. The block is made of two parts ofinsulating material; and is moved along the timer as by means of a threaded shaft I16 driven by a synchronous motor- I18, the latter being energized by an electric clock I80. As shown, the block I66 rides between upper and lower-grooved guides I82 and I84 respectively, this arrangement: insuring longitudinal m0vement; of the block over the elements I50 in accordance with time. The surface of the upper uide I82 is provided with a time scale I85, numbered in hours and subdivided into fifteen minute intervals as shown. It will be understood that the elements I80 are assembled on the bus bars to secure any desired sequence of energization of the said bars and that the contacts I08, I10, I12 and IIfi are all connected to a suitable source of electrical supply I85 through a lead I83 and switch I89. Preferably, opposite ends of the bus bars I50, I52, I54 and I56 are provided with end caps I90 for holding the elements I50 thereon in assembled relation, and opposite ends of the threaded shaft I'IB are provided with smooth portions I92 so that the split block I56 may be assembled and manually moved to the initial position to engage the threads, and may be disassembled and removed from the opposite end of the shaft following the completion of the operation. As shown, the switch I89 is connected to the clock I80 by lead I04 and to the thermostat I28 by lead I96, the bus bars I50, I52, I54 and I56 being respectively connected as by leads I98, 200, 202 and 204, to the solenoid valves H2 and I32, the solenoid valves I I and I34, the solenoid valve I I8 and the solenoid valve I08. It is to be pointed out that for purposes of simplification of illustration the electric wiring employed is shown in dotted lines and comprises a single wire system with ground return, although a two Wire system may be used if desired. Also all solenoid valves utilized are of the type which are springclosed and only open, when electrically energized. Thus, any failure in the electrical system will result in the valves automatically closing, this materially improving the safety characteristics of the apparatus.

In operation, it will be assumed that a stack of cold or relatively dry thick lumber has been placed in the kiln for processing and that the timer I48 has been adjusted by so arranging the elements I60 on the bus bars I50, I52, I54 and I55 as to give the cycling desired for the particular lumber. With the boiler I0 2 in operation so as to provide a source of dry superheated steam of the order of 150 pounds per square inch absolute at a temperature in the neighborhood of 358 F., and the pressure regulating valve I36 set to 2 pounds per square inch gage pressure, the switch I89 is closed to energize the clock I80, the motor I18, the movable contacts I08, I10, I12 and I'M, the thermostat I28 and the steam valve I25. The block IE6 is then moved to the position shown whereby it is moved by the threaded shaft I16 over the contacts and insulating portions I62 and IE4 in accordance with time. Energization of bus bar I54 will open solenoid valve H8 to convey the dry superheated steam past the steam pans I20, it being understood that the steam will be wetted as soon as any condensate returns by line 52. Inasmuch as the elements I60 on the bus bars I50 and I52 are so arranged as to alternately energize these bars every fifteen minutes it will be manifest that the solenoid valves H2 and I32 on the one hand, and valves i In and I34 on the other will be periodically energized and opened. Such operation will alternately supply wet steam to each set of jets 28, it being understood that opposite exhaust lines 80 and 82 will be likewise periodically opened, to convey exhaust steam and wood oil vapors to the condenser I40 through the pipe I38. As shown in Fig. this operation continues for 3 hours and during this time the entire the heating coils 40, to a temperature of abm tv 230 F. and the thermostat I28, pre-set to this temperature, has just about closed valve I26. This preliminary step of heating and condition,- ing the lumber with wet steam has been found to be highly desirable, not only for the more complete reclamation of the natural oils, but also for the more rapid and complete drying of thelumber. During this step, a liberal amount of hot water of condensation is deposited on the cold lumber, and since heat travels much faster through water by convection than through cellulose-by conduction, it will be seen that the stack is rapidly brought up to a relatively high temperature. The lumber may absorb some of this water so that the internal free and inbibed moisture, including the wood oils, more readily travels to the surface for removal and subsequent treatment. During this initial step, little or no drying is effected. Howerer, the lumber is thoroughly conditioned for subsequent treatment by the dry superheated steam which is cycled through the jets in precisely the same manner as soon as the bus bar IE4 is ole-energized and bus bar I58 energized. When this occurs, valve I It will close and valve I08 will be opened and thus the superheated steam from the boiler will pass directly to the jets 28, rather than through the by-pass H6. During this stage of the operation, which continues to the end of the run as determined before-hand, the lumber is gradually dried by the action of the dry superheated steam, and a maximum amount of raw turpentine and woods oils is recovered by the treatment of the exhaust. While the foregoing explanation is based upon the use of a selected time period for the conditioning or initial step when using wet steam, and the periodic alternation of the jets every fifteen minutes, it will be understood that the preliminary step may be varied as to time period In accordance with the characteristics of the lumber to be treated, and that the reversal of jet action may be likewise altered. This may readily be effected by using contact elements of different lengths, in assembling them on the bus bars I50, I52, I54 and I56.

This ease and rapidity with which the timing cycle may be varied, with the present invention, gives the apparatus great flexibility in the conditioning of both soft and hard woods. In any 01' the foregoing, it will be understood that a final treatment of dry superheated steam may be utilized, if desired, to secure a thorough final drying of the lumber undergoing treatment. Such an arrangement, as above outlined, is effective to produce an entirely new process of drying and conditioning lumber which is termed breathing, and is especially desirable in conditioning woods for certain purposes, such as for use in the manufacture of furniture. In this latter industry, lumber which has been air dried for a long number of years, and subjected to wet and dry seasonal atmospheric changes to the extent that it has acquired a permanent set, is in great demand. With the present process 'of breathing, a continuing method is provided which closely simulates the alternate swelling and shrinking of prolonged air drying, and yields a product which is sub stantially free from any further dimensional changes due to varying moisture conditions encountered in normal uses.

There is thus provided by the present invention a novel lumbe drying apparatus together with a novel method of conditioning lumber.

which is so constituted as to not only more efficiently dry the lumber, but also to secure a maximum recovery of crude turpentin and wood oils from the wood. These novel and advantageous results flow from the many features heretofore described, among which is the novel retort type of insulated kiln which is so arranged as to be steam-tight, and heat-tight, the novel use of wet steam and dry superheated steam, the baffle and sticker constructions resulting in maximum use of the steam for conditioning, and maximum cubical content Of the lumber stack, the flexible timer construction, the process of simulating prolonged air drying by breathing the lumber, and others.

While the invention has been described herein with considerable particularity, it will be understood that the same is not limited thereto, but is capable of variety of expressions without departing from the spirit of the invention, as will be understood by those skilled in the art. Reference will therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In combination with a dry kiln having a plurality of lumber-supporting cars therein arranged in tandem from one end of the kiln to the other, means positioned along the side walls of the kiln for alternately subjecting opposite sides of the lumber to the action of a drying medium, and bafile means for preventing the flow of said medium between the side edges of the cars and the kiln wall comprising elongated metal members supported by the kiln and. bent into substantially U-shaped form for embracing the opposite side edges of all of said cars.

2. Apparatus of the type set forth in claim 1 which includes in addition, a weighted baflle carried at the top of the kiln and extending from one end thereof to the other and contacting the top of the lumber supported by said cars.

ELTON V. SMITH.

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

UNITED STATES PATENTS Number Name Date 208,649 I'ripler Oct. 1, 1878 637,308 Wendling Nov. 21, 1899 783,868 Jarratt Feb. 28, 1905 825,819 Geibel July 10, 1906 918,335 Lain Apr. 13, 1909 1,054,597 Moore Feb. 25, 1913 1,086,716 Jacobus Feb. 10, 1914 1,147,601 Boss July 20, 1915 1,212,583 Tanner Jan. 16, 1917 1,219,406 Banks Mar. 13, 1917 1,268,180 Tiemann June 4, 1918 1,299,470 Hope Apr. 8, 1919 1,328,655 Fish, Jr Jan. 20, 1920 1,515,214 Kelleher Nov. 11, 1924 1,577,044 Mason Mar. 16, 1926 1,693,395 Lawton Nov. 27, 1928 1,778,586 Cobb Oct. 14, 1930 1,829,139 Henderson Oct. 27, 1931 2,081,098 Steel May 18, 1937 OTHER REFERENCES Drying Lumber by Means of superheated Steam, etc., Report No. 702 of Forest Products LaboratoryRevised, August 15, 1931, pages 14a- 18.

Steaming Black Walnut Lumber to Darken the sapwood, Report No. R1673 of Forest Products Laboratory, April 1947.

Properties of Saturated Steam, Handbook of Chemistry by Norbert Adolf Lange, 1937, page 1216.

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