US2435218A

US2435218A - Apparatus and method for drying wood

Info

Publication number: US2435218A
Application number: US579851A
Authority: US
Inventors: Monie S Hudson
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-02-26
Filing date: 1945-02-26
Publication date: 1948-02-03
Anticipated expiration: 1965-02-03

Description

Feb. 3, 1948. M. s. HuDsoN APPARATUS AND METHOD FOR DRYIHG WOOD Filed Feb. 26, 1945 3 SheetsShest 1 .n ik

Feb. 3, 1948.

Filed Feb. 26, 1945 3 Sheets-Sheet 2 :inventor Gitorneg Feb. 3, 1948. M. s. HUDSON APPARATUS AND METHOD FOR DRYING WOOD 3 Sheets-Sheet 3 Filed Feb. 26, 1945 w h n# V a- 9 f a jm.

zz wn o- 6 mm .fix nl u Al raf umm scf 0| mw 4 :an nf o :am 31 psa, UNM ro 01M wwe o mw 2l Nn NE um www mmmwmwwd W a0 (Iltorneg Patented Feb. 3, 1948 APPARATUS AND m01) FOB DBYING WOD Monia S. Hudson. Spartanburg. 8. C. Application February 20, 1945, Serial No. 579.851 Claims. (Cl. 34-32) This application is a continuation-impart of my co-pending, allowed application Serial No. 431,177, filed February 16, 1942, which was abandoned after transfer of the subject matter to the present application and which was in turn a continuation-in-part of my application Serial No. 324,893, filed March 19, 1940, now Patent No. 2,273,039. The present application covers the subject matter oi' the apparatus originally disclosed in the above application Serial No. 324,893 and the subject matter o! the continuing application Serial No. 431,177, and certain improvements in the apparatus and methods thereof, as described hereafter.

In accordance with my invention I have provided a method and apparatus for drying green or wet wood in a substantially more rapid and emcient manner than heretofore obtainable. Also. this result is obtained without the usual adverse eil'ects on the wood. such as charring, checking, bursting, warping. The element of the required time or duration of the drying treatment is a very important one. The usual yard drying of lumber or other wood requires several months time; and even kiln drying with steam involves at least several days, and often a week or more. In marked contrast to these prior practices. the method and apparatus oi' my invention satisfactorily dries wet wood in less than a days time and in many cases in a few hours time.

My method comprises generally the treatment of the wet wood in a closed space with a highly heated vapor of an organic material that is inert to the wood and permeates the wood so as to ilash-oif the moisture as vapor. The liberated moisture vapor and spent organic vapor are com ducted away from the drying space and are condensed and separated; the moisture condensate being discharged to waste and the organic vapor condensate being recycled through the system and reused in the drying operation. The drying operation may be carried out at normal pressures or under vacuum, as described hereafter.

In accordance with my above original application Serial No. 324,893, the drying process contemplates the use oi a substantially saturated organic vapor as the drying medium throughout the drying operation. This requires continuously feeding a relatively large amount of anhydrous organic drying vapor into the drying chamber at all times, so that the liberated moisture vapor is immediately swept out of the drying chamber and the fresh, hot, organic vapor is continuously brought into contact with the wet wood for liberating the moisture therefrom. The volume oi' 2 organic material required for this type of operation is considerable, and, although it provides the most rapid form of drying. it is desirable in i some cases to utilize an economic balance between the rate of drying and the cost of handling the organic material. In such cases, I have found that it is possible to obtain the beneilts of my invention from the standpoint of satisfactorily drying the wood without adverse eifects thereon, at a somewhat slower rate by permitting the organic drying vapor to be diluted to a dennitely limited extent with liberated moisture vapor. In other words, if the organic vapor is fed into the drying chamber in a less amount or at a slower rate than that required for a saturated atmosphere. the drying medium will contain some of the moisture vapor dashed olf from the wet wood, and the presence oi this moisture vapor will not impair the effectiveness of the drying operation it certain well defined limits with respect to concentration, which will be described hereafter, are observed.

One important feature of one embodiment of my drying method and equipment is the fractional condensation. in a dephlegmator or high temperature, partial condenser, of the liberated moisture vapor and used organic vapor at a sumciently high temperature to condense the organic vapor but not the moisture vapor; the moisture vapor and some entrained organic vapor then being condensed in a low temperature, complete condenser. The high temperature partial condenser eects separation of much of the organic vapor in vapor phase without cooling it appreciably, so that it may be recovered and returned to the evaporator with its sensible heat substantially undissipated and thus conserve heat in the system.

Another important feature is the collecting and dehydrating. in a heated condensate return vessel, of the condensed organic vapor to remove traces oi' moisture before the organic vapor condensate is recycled for reuse in the drying operation.

| T'he term wood as used in the specification and claims herein is used in a generic sense to include any and all types of green or wet wood or partially seasoned wood. from which it is desired to remove all or part of the moisture content. The method and apparatus of my invention have proven particularly useful in the drying of lumber or similar massive forms oi' wood, such as telephone and telegraph poles. railroad ties. piles. bridge stringers. etc., which commonly contain as much as 50% to 100% of water on a dry weight basis. ABU. wood chills. Pulp flour, etc. may be dried. Elective drying of the wood to low moisture content with hot organic vapor in the system of my invention renders them especially suitable for and receptive to impregnation with preservative materials such as creosote. The system of my invention is especially adapted for the treatment of massive pieces, and utilizing therefor evaporators. drying chambers, condansers, separators and other equipment of industrial size and design, and operable at atmospheric pressure or at somewhat less than atmospheric, but nevertheless practical for large scale industrial use. The drying operation does not require the use of extremely 1118i! vacu. um, such as is used for degasiiication and dehydration of electrical and other specialized products having normally only a iew percent moisture content.

For effecting dehydration of the wood in accordance with mv invention. I may use any suitable organic material which can be vaporlzed and which vapor will permeate wet wood and flash off the moisture content thereof without deleteriously aiecting the wood. This involves simply a selection of a suitable material as above indicated, of which there are numerous and practically unlimited examples. Representative but non-limiting classes and specific examples of satisfactory materials which may be vaporised and used effectively for drying wood in accordance with my invention are as follows:

Organic compounds. whether saturated or unsaturated, chain or cyclic, and any of their homo logues that might be suitable for this procedure. such as alcohols, others, amines, acids, aldehydes, ketones, esters. halides, cyanides, sulphides, polyhydric alcohols. anhydrldes such as phthalic and nitro compounds; of which the following are examples:

n-Decanolc acids n-Decyl ketoncs n-Decyl aldehydes n-Decane n-Decyl alcohols n-Decyl others n-Decyi airlines n-Decyl cyanides n-Decyl esters n-Decyl sulphides n-Decyl halides Preferred examples of suitable organic drying mediums are creosote, petroleum distillates, coal tarl wood tar or wood distillates, and the followins:

Mono, di. and trl-cthanolamines Pyridines Quinolines High boiling esters:

Butyl acetate Amyl acetate Butyl lactate Dibutylphthalate Diamylphthalate GLvcol monoethyl ether acetate isopropyl lactate octyl ecetate Diglyooloieate Glycol stearato High boiling ethers:

Diamyl ether Diethylene glycol monoethyl ether Halides:

Chlorobensenes chlorinated phenois Nitrochlorohenzenes ortho-Dichlorcbenzenes ortho-Nitrochlorobenzenes para-Dichlorobenseneg Nitro compounds: Nitrobensene ortho-Nitrotoluenes Hydrocarbons:

Benzenes Toluenes Mesitylenes Cumenes Naphthalenes Diphenyl Ketones:

Benaophenone For a further and more detailed discussion of the method and apparatus of my invention and the particular operation thereof for drying wood, reference is made to the accompanying drawing, in which:

Fig. l is a diagrammatic representation of one complete drying system of my invention;

Fig. 2 is a modification of the drying system wherein the usual type of creosoting plant has been modlied for operation according to my lnvention, and the high temperature, partial condenser is omitted; and

Fig. 3 is a graph illustrating the variation in eective drying with variations in drying medium concentration in the drying chamber.

The general system and method of carrying out the drying operations of my inventionl with reference at ilrst to Fig. l of the drawing, comprises placing the material to be dried, such as wooden poles, or debarked logs, Il, containing a high percentage of moisture. commonly 50% or higher, in a drying chamber Il and supplying the highly heated organic vapor used for dehydrating the poles III from a vaporizer or evaporator Il. The mixture of water vapor liberated from the poles and the spent organic vapor is fractionally condensed in a dephlegmator or high temperature. partial condenser I3, mentioned hereinabove, that condenses a substantial fraction of the organic vapor; the unoondensed water vapor and any steam distilled organic vapor being conducted over to a low temperature, complete condenser Il for condensation and subsequent separation in a separatory funnel or separator Il of the orgnic and water condensates. The partial condenser II eifects condensation and recovery of a substantial fraction of the organic vapor free of water and accordingly it lightens the normal load on the complete condenser Il and permits more rapid Operation of the system. However, when the moisture content of the wood is low or where somewhat slower drying is economically permissible, as is often the case in plant sise operation. the partial condenser I3 may be omitted and the complete condenser I I used for ioint condensation of all oi' the organic vapor and water vapor.

The high temperature organic condensate from partial condenser I3 and the low temperature condensate returned from the complete condenser I4 through separator IB are collected and pooled in a condensate return tank I., as mentioned hereinabove. Small amounts of water contained in the above mentioned low temperature condensate would cause excessive foaming and pressure surges in the system if this condensate were returned directly to the highly heated supply of organic material used for drying. 'I'his difnculty is avoided in my improved system by pooling the high temperature organic condensate and the low temperature condensate in the return tank I I, the temperature of which is maintained above the boiling point of water so that the small water content of the collected condensate is flashed-off leaving behind the dehydrated organic condensate which is then safely returnable to the vaporizer I2. The heat necessary for vaporizing the water in the condensate return vessel is supplied principally by the high temperature organic condensate rmllected there. However. this heat may be supplemented by additional heating means if desired, and when the system is operated without a partial condenser, auch additional heating means is principally relied upon. The dewatered organic condensate collected in the return tank Il is returned as needed to the vaporizer I2 for vaporization and reuse in the drying operation.

Instead of using a separate evaporator for evaporating the organic material used for drying the wood in accordance with my invention, I may employ the arrangement disclosed in my prior Patent No. 2,273,039, issued February i7, 1942. In that arrangement, the organic drying material is fed into the bottom of the drying chamber and evaporated from there by suitable heating means so that the organic vapor produced is brought directly into contact with the wood to be dried. My original arrangement also avoids the necessity of using a condensate return tank. such as shown in Figures l and 2 in the present drawings, and instead returns the organic condensate directly to the drying chamber.

With this original arrangement, the water vapor liberated from the wood and the spent organic vapor may be subjected to vapor phase or liquid phase separation. In the vapor phase separation, the major portion oi' the organic vapor is condensed at a relatively high temperature and returned directly to the drying chamber: and a lesser portion of uncondensed, steamdistilled organic vapor is condensed along with the eiiluent water vapor, and the resulting condensate `is then separated so that the water is discharged to waste and the remaining organic condensate is returned to the drying chamber. In the liquid phase separation, all of the organic vapor and water vapor is condensed together and the combined condensate run through a separator having one line discharging the water to waste and another line conducting the entire organic condensate to the drying chamber.

Any small amounts of entrained moisture in the organic condensate which is returned to the drying chamber in this arrangement would be flashed-oil' quickly by the heat applied to the drying chamber, and the latter would thereby serve the purpose of the condensate return tank.

While this original arrangement avoids the use of a separate evaporator and also a separate condensate return tank, I have found it advantaseous in most practical applications of my drying process to employ these separate pieces of equipment and their operations. Use of a Separate evaporator increases the drying capacity of the drying chamber and avoids possible contamination of the wood with the liquid organic material. Use of the condensate return tank avoids returning small amounts of water to the heated drying system. which in some cases, as heretofore mentioned, would produce foaming and pressure surges.

Using apparatus of the type shown in Fig. l, the poles I 0 are subjected to the dehydrating treatment for a few hours', such as for example 4 to l2 hours, until the desired low moisture content or complete freedom from moisture is obtained. as desired. The poles are then ready for removal or for subsequent preservative treatment.

Referring now more in detail to the apparatus shown in Fig. l, and beginning with all valves closed, the apparatus and method of operation may be described in terms of a typical drying cycle as follows.

Valves I l, Il, Il and 20 are opened, thus bringing the evaporator I2 to atmospheric pressure through lines 2|, 22 and 23, which lead to the partial condenser Il. lines 2l and 2S connecting partial condenser Il with complete condenser Il, and line 2B leading to the separator IJ, which may be opened to the atmosphere through valve 2l mentioned above. Valve 2l is then opened admitting organic drying medium from storage (not shown) through line 28 to pump 29, which is driven by motor 30, and, after opening valves SI and I2, pump 29 ls started and the evaporator I2 is filled through line ll with organic material to the desired level, usually several inches above the heat transfer coils Il. After filling the evaporator, pump 2B is stopped and valves 2l, II and l2 are closed.

The circulation of heat transfer medium is then started through coils I4 to bring the evaporator I2 up to operating temperature. 'Ihe heat transfer medium may be any suitable material, such as a heat transfer oil or diphenyl oxide, and circulation is eil'ected from a heat absorber Jl through line Il to coils ll and then back through return line l1 which includes expansion tank 2l and circulating pump II powered by motor lll.

Heat input to the evaporator I2 is regulated by a thermostatic control 4I arranged on the heat absorber 3l and actuated by a temperature-sensitive element 42 exposed in the drying chamber `j II By this means, the temperature in the drying ber I I may be maintained In correspondence with any desired degree of concentration of organic drying medium, in accordance with considerations to be explained hereafter, by setting the control device Il at the temperature corresponding to this concentration. The evaporator I2 is also appropriately provided with a safety valve indicated at l2.

Where temperature requirements can be met by steam, the coils 3l may be supplied with steam instead of the special liquids mentioned above. In such cases, it is also possible to lead the steam condensate from the coils 34 to a heat exchanger which may be used to supply the heat requirements of condensate return tank I6. An arrangement of this sort is illustrated in Fig. 2 and will be discussed further in that connection. The customary types of process steam boilers, however,

arelimitedtoasteam pressureofnotmorctban about 200 pounds per square inch, which corresponds to a temperature ol about 390 F. The temperature required in the vaporiaer or evaporator I2 depends upon the boiling point oi the drying medium, which may range from about 260 F. to 450 F, Where temperatures above 350 F. are used. the evaporator is most satisfactorily heated by circulating hot oil.

As the evaporator I 2 heats up. the vapors formed pass over through valve I1 to partial condenser I3 which is maintained at condensing temperature by means described below. The resulting condensate may be returned to the evaporator by opening valve Il in line ll which branches oil of the condensate return line ll from partial condenser Il. It may also be desirable during this period to allow moderate drainage from evaporator I2 to condensate return tank Il and eilect recirculation of the drained material by pumping from tank Il to th'e evaporator, in order to preclude layering or stratiiication of any water which may be present in the drying medium as supplied to the evaporator from storage and which might thus be trapped at the bottom oi the evaporator. This may be done by additionally opening valve a so that drying medium will drain from evaporator I2 through line and, together with condensate from partial condenser Il, through line Il to return tank Il. The drying 'medium may be returned from tank Il to evaporator I2 by opening the tank through valve Il to pump 20, and then starting the pump to recirculate the drying medium through line 3l. which includes valve Il, and through valve 82 opened into line Il, which, as described below, discharges into evaporator I2 through spray nozzle Il. Reference is made to the description of Fig. 2 for a disclosure of a further arrangement by which such drainage and recirculation may be effected.

When the temperature in evaporator I2 has reached the level at which the wood is to be processed. valves I1, Il and Il are closed. and the organic vapor is allowed to enter drying chamber II (in which the wood to be processed has been placed) by opening valve Il which connects line 2| to a vapor manifold Il from which the vapor is fed to chamber Il through inlet ports ll. The ports 49 may be equipped with conventional valve-like dampers (not shown) to insure a uniform rate o! flow to all parts of the drying chamber II. and chamber II may be further provided internally with conventional perforated licor plates (not shown) for further dispersing the vapor. Chamber II also has a hinged door il for introducing and removing the poles I (or other material to be processed) which may be supported by means such as tram II riding rails l2.

The arrangement described above by which the evaporator I2 may be connected directly to the partial condenser Il allows the drying chamber II to be lay-passed so that while the evaporator is being brought up to temperature, or at other times when the evaporator is at operating temperature, the drying chamber may be opened to introduce or remove the material being processed without having to shut the evaporator down or walt for it to heat up. By thus being able to bring the evaporator I2 up to temperature before connecting it to drying chamber Il, it is possible to shorten appreciably the time required to bring chamber Il up to operating temperature, This time may be further shortened by lirst building up pressure in evaporator I2 to store additional heat 8 which is then delivered quickly to chamber il when valve 41 is opened.

Only a short period, usually about 30 minutes, is required to bring the temperature in chamber Il up to that of evaporator I2. Material cmdensing in chamber II during this start-up period is drained to condensate return tank Il by opening valve 53 to line 54 which includes a check valve 06 and is connected to tank l. through branching line IB. If this material contains substantial amounts of water it can be pumped to separator I5 by additionally opening valve i1 in line Il, which will allow the condensate to ilow to pump supply line 2l through connector Il. starting pump 29, and opening valves il and Il so that the discharge to the pump will be led to separator Il through line 33 to branch line II and in turn through line Ii2 which branches from line II.

As the drying chamber II is being brought up to operating temperature, and after it has been charged with the material to be p valve I3 in line 25 is opened to allow the vapors formed. to escape from chamber II through outlet ports Il into outlet vapor manifold 65. from which they pass on through line 23 to line 25, and completely expel air from the system through complete condenser Il and separator I5 at valve 2l. The system is then operated on complete condenser Il (which is cooled by means described below) with the partial condenser I3 by-passed; the by-passing being continued until the vapor entering the condenser il has reached a temperature sumciently above the boiling point of water (at least 240 F. to 260 F.) to make it possible to pass the vapor through the partial condenser I2 and cause sufficient lowering of the temperature to condense most of the drying medium without condensing water. This temperature will be reached in about one hour after introduction of vapo'r to the chainber li is begun, and within a short time thereafter a level approximately equal to the temperature in chamber II is reached. Under this steady condition the partial condenser can be operated satisfactorily. Valve 03 is accordingly closed and valves 66 and I0 are opened. and fractional condensation of organic vapor in partial condenser I3 is begun. Valve 20 may then be cloud if it is desired to place the system under liquid seal (not shown) A condensing temperature. above the boiling point of water but below the boiling point of the organic material, is maintained in partial condenser I3 by tube section 01 through which cooling water from supply line 6I may be circulated by opening valve 69. Tube `section l1 controis the temperature of the vapor passing up through partial condenser I3 so that the greater part ci the organic component is condensed and may be' returned to condensate return tank Ii through line IB by opening valve lia. The uncondensed water vapor and any steam distilled. organic vapor fraction ellluent from the partial condenser I3 pass over through line 2l and valve Il into line 25, which leads to complete condenser I4.

Partial condenser I3 is further equipped with a temperature-sensitive element 10. situated in the vapor space above tube section Il and connected wit-h a thermostatically operated valve Il on the discharge side of tube section 61. This arrangement allows the rate of ilow oi cooling water to be regulated in relation to the temperature which it is `desired to maintain in partial condenser I3. A desirable range of temperature in this respect is from about 220 l". to 260 F. so

that the water vapor passing over to the complete condenser Il will be very close ,to the boiling temperature of water.

Condenser I3 is also equipped with a layer of Raschig" rings 12, or similar column packing, which is supported between perforated plates 13. The Raschig rings 12 are conventional, numerous, small, ceramic pieces in the form of short, tubular sections or rings, and provide a large surface area for condensation of the organic vapors.

The bottom section of partial condenser I3 in which the water-free organic condensate collects. holds sufficient liquid to allow any entrained water vapor to break away from the surface. A sight glass 13a is also arranged on partial condenser I3 for gauging the liquid level in this bottom section. Photo-electric controls similar to the arrangement described below in connection with Fig. 2, for automatic pumping from the condensate return tank, may, if desired, be provided on sight glass 13a to actuate a valve (not shown) in line 46, in relation to the liquid level in the bottom section of partial condenser I3, and thus effect automatic drainage from condenser I3.

The above mentioned uncondensed water vapor and steam distilled organic vapor fraction efliuent from the partial condenser I3 are condensed in low temperature, complete condenser I4, and the resulting condensate is drained through line 26 to separator I where separation of water and organic material layers is effected. The condensing temperature in condenser Il (which should of course be below the boiling point of water, about 180 F., for example) is maintained by a tube section 1I similar to the tube section on condenser I3 and fed from the same circulating water supply line 66 through branch line 15 which includes valve 16.

Complete condenser Il has a condensate receiving portion 11 which acts as a reservoir when batch separations of water and organic drying medium are being made in the associated separator I5. This reservoir arrangement is completed by valve I9 in line 26 which connects condenser Il and separator I5. A sight glass 16 is situated on the condensate receiving portion 11 so that the condensate level may be observed and prevented from rising high enough to flood tube section 14.

The separator or separatory funnel I5, of which many modifications are possible, is constructedin the presently described embodiment of my invention as a cylindrical tank 19 having a cone-shaped bottom portion 8U. Arranged on opposite sides of the bottom portion Bl) are glass windows 8| through which the interface in separator I5 may be observed as drying media and water are separated.

Separator l5 is operated by allowing condensate (drying medium and water), drained from condenser I4 through line 26, to collect in the separator in a sufiicient amount, which may be gauged by a sight glass 82, and then shutting oil' line 26 by closing valve I9 and permitting the condensate to stand until a separation into layers occurs.

The procedure followed after satisfactory layer formation is obtained, will depend on whether the organic drying medium being used is lighter or heavier than water. As the drying medium will usually be lighter than water. the operation of separator I5 is described below on the assumption that such a condition obtains. It will be understood, however, that when the drying medium is in fact heavier than water it will only 10 be necessary to reverse the sequence in which the discharge valves are manipulated.

When the condensate has separated satisfactorily into layers, valve Il, which is a three-way valve situated at the apex of cone portion 80, is opened to line 8| and the lower water layer in separator I5 is drained to waste. the discharge to waste being measured by meter B5 in line 84 as an indication of the progress of the drying operation being conducted in chamber Il. As the interface approaches the apex of cone portion Bil, its position is observed through the glass windows 8| and a final sharp cut of the interface is obtained by observing it through bullseye 86. Valve 83 is then opened to line 8.1 and the re maining substantially water-free condensate is passed through three-way valve 8B to line 89 which leads to condensate return tank I6.

Separator l5 is also connected so that it may be isolated on the circulating system from pump 29 through line Il, valve 59, line 6I, branch line 62 and valve 6II, and then back through valve 82, line B1, valve BB, line Il. connector 58 and line 28. This connection makes it possible, when the organic material from storage contains water, to conduct the organic material in batches to separator I5 for separation of the water before delivering it to the evaporator. Also, this connection permits recirculation of condensate from return tank I6 in cases where more than usual amounts of water are collected in tank I 6 as might occur during the start-up periods.

Separator I5 may, if desired. be further equipped with a steam coil SII in order to heat the condensate in cases where separation Ls not as rapid as desired. By this means, liquids which possess different density-temperature gradients from that of water may be made `to separate more rapidly.

When creosote or petroleum fractions, for example, are being vaporlzed in evaporator I2, it is desirable to return condensates as quickly as possible from both the separator I5 and the condensate return tank I6 to the evaporator I2. If the lower fractions of these materials which vaporize first in evaporator I2, and are condensed in the partial condenser Il and complete condenser II, are allowed to accumulate in condensate return tank Il and separator I5, it becomes difncult to maintain the temperature in the evaporator I2 constant, since removal of the lower fractions has a tendency to increase the boiling point of the drying medium remaining. Thus, if the condensate is not returned to the evaporator I2 rapidly under these conditions, the temperature of the vapor entering the drying chamber I I cannot be maintained at a uniform level. For further insuring uniform operating temperature, separator I5 may be modiiled to effect continuous separation, and condensate return tank I6 may be equipped with controls for automatic return of organic condensate to the evaporator. Arrangements of this sort are illustrated and will be de scribed in connection with Fig. 2.

In view of the high temperature maintained in return tank I6 by hot organic condensate from partial condenser Il,sma1l amounts of water contained in the organic condensate returned from separator I5 are dashed-oil' in return tank I6 and the resulting vapor may be removed through line 9i by opening valve l2. In cases where the temperature in return tank I6 is not suiilcient to boil off the water returned with the organic condensate from separator II, the supply to evaporator I2 may be introduced through spray nozzle 93 sans by opening line l through valve 02 oi! ot supply line 03 from pump 20. The organic material will then be forced into the vapor space above the liquid in evaporator I2 where the water will be immediately flashed-off and Dass on through the drying chamber I| to the partial condenser Il. Alternatively. as previously pointed out. a suitable temperature may be maintained in return tank I 0 by heat supplied. entirely or in supplementary amounts, from auxiliary heating coils indicated in Fig. l at Ila.

Return of condensate from condensate return tank I0 to evaporator |2 is accomplished by opening valves 51, 3| and three-way valve 32 to lines 33 or 94, and starting pump 20. After steady operating conditions are established, the condensate being thus returned to evaporator |2 can be protably diverted to absorb heat from the vapor entering high temperature, partial condenser Il by opening valves B0 and 0l. rather than valve 3|, so that the condensate is circulated by line 0| through a lower tube section 0B situated to receive heat from the hot vapor introduced in condenser I3 through line 20.

Through-put of condensed material to evaporator I2 (which is an indirect measure of the amount being vaporizedl is determined by meter 01 in line 0I or meter 00 in line l0, or both: check valves (00 and |00. respectively) being included in each line beyond the meter. It is important to have a readily available measure of the through-put, such as meters 01 and 00 provide, in order to regulate properly the heat input to evaporator I2 so that the minimum amount oi' boil-up required for the processing of material in drying chamber I is delivered.

When the desired amount of moisture has been removed from the wood in chamber |I of which a measure is provided by the amount of water discharged to waste through line 0l es recorded by meter 0l, valves 01 and 00 are closed to shut oi! chamber II. Valve |`l is then opened and valve I8 is closed. and evaporator I2 is allowed to idle on partial condenser I0 while the processed wood is removed from chamber and preparations are made ior a succeeding treatment.

Before the processed wood is removed from chamber II. however. it is usually desirable to subject the wood to a suitable vacuum period in order to recover some of the organic material that has distilled into the wood and thus leave it free of excess chemical in the cuter layers. and also to lower the temperature in chamber II so that the processed wood can be conveniently handled. For this Purpose. any convenient means for establishing vacuum may be employed, such as vacuum pump |0| which is connected to complete condenser Il through line |02 and valve |00. 'I'he vacuum is impressed on chamber through complete condenser |I by opening valve 03 in line 20. Vapor is thus drawn from chamber to complete condenser Il where it is condensed and collected in bottom portion After the vacuum has been impressed for a period sutlicient to obtain satisfactory results under the particular circumstances. the collected condensate is drained to separator I5 and separated according to the methods employed during normal operation. If it is desired to continue vacuum for a longer period than can be accommodated in this manner, intermittent separations may be made by equalizing separator il with condenser Il through line IM, which includes valve |00, to allow condensates to enter separator I0 through line 20. and then closing valve I0 and opening separator I0 to the atmosphere through valve 20 so that the separation may be made. Intermittent separations might also be made by employim a conventional vacuum trapping means (not shown) between complete condenser Il and separator I5.

During this period oi' vacuum treatment. partial condenser Il may be vented to the atmosphere through valve 24a on line 20, so that evaporator I2 can be brought up to temperature and otherwise prepared for processing the next charge of wood while the vacuum period is being applied.

The embodiment of my invention illustrated in Fig. 2 operates in substantially the same manner as the apparatus shown in Fig. i, the major points of di'erence being that Fig 2 illustrates an adaption of the usual type of creosoting plant for operation according to my invention, and the high temperature. partial condenser has been omitted i'rom the drying system in this instance.

As illustrated. the apparatus in Fig. 2 comprises a drying chamber |01 oi' suilicient size to accommodate massive wood pieces, such as telephone poles and the like, and an associated evaporator |00, condenser |09, separator Ill, and condensate return tank I I I, all oi corresponding size and capacity.

Starting with all valves closed, with the drying chamber |01 charged with the material to be dried, and with the evaporator |08 filled to a proper level with organic drying medium (admitted from storage-not shown-through line ||2 and valve I Il to line I Il which leads to motorpump set Ill, and pump discharge line I I6 which includes check valve Illa and valve Ill), the present embodiment of my invention is operated to dry wood as follows:

Evaporator |00 is opened to condenser |00 through valve III in line ||0 which joins line |20; valve |2I on drain line |22, and valve |20 on drain header |24 which also includes check valve |25, are opened to condensate return tank III; valve |20 in line |21 running from condenser |00 to separator ||0 is opened; and equalizer line |28 is opened between condensate return tank III and condenser |00 at valve |20a, and to separator I I0 at valve |20, and to the atmosphere at valve I 30. The system is thus opened to the atmosphere with the drying chamber |01 by-passed. Heat is then supplied at a maximum rate to bring evaporator |00 up to operating temperature. For this purpose, the evaporator is provided with a tube section indicated at |8| which is iltted with a header |32 having suitable inlet and outlet connections Illand |30. respectively, i'or circulating steam supplied at a pressure of about lb./sq. in. The tube section |0| is adapted for an operating temperature of 275 1*.-300 F.

When the temperature in evaporator |00 reaches about 200 F., circulation of cooling water through line Il! to a conventional tube section (not shown) in condenser I 00 is started in order to condense water vapor passing over from the evaporator. Also, drain line |00 from evaporator |00 to condensate return tank III is opened through valve |31 at this time in order to allow moderate drainage and tlrus prevent any stratiilcation of water at the bottom of the evaporator; and return tank I|| is opened at valve |00 through line Ill to pump |ll, pump discharge line ||0 is opened at valve III, and pump III is startedtorecirculatethedryingmediumthatis drained from the evaporator in this manner.

The water condensate formed in condenser |00, together with any steam distilled organic vapoi emuent from evaporator |00, drains to separator through line |21. After the evaporator temperature reaches about 230 F., all of th Y i atei vapor will have passed over to condenser |00, so that when water condensate stops collecting in separator ||0 and a satisfactory layer formation occurs, the water may be drained to waste by opening three-way valve |39 to line |40, after which valve may be opened to line |4| to drain any organic condensate to condensate return tank Drain line |30 from evaporator |05 is then closed, and, when return tank I has been emptied, pump ||5 is stopped and lines ||4 and ||0 are closed. As soon thereafter as the evaporator temperature reaches the boiling point oi the organic drying medium and organic condensate begins to collect in separator H0, the drying operation may be started.

To start the drying treatment, valve ||0 is closed, and valves |42 are opened to introduce organic drying medium from evaporator |00 to drying chamber |01 through vapor intake lines |40. Outlet valves |44 are also opened into the vapor header |45 situated over drying chamber |01, and the vapor header is in turn opened through valves into lines |20 and |41 running to condenser |05; and drain line |45 (which also includes check valve |40) is opened at valve |50 to condensate return tank and line |5| connecting vapor header with drain line |00, is opened at valve |52.

As the drying chamber |07 is cold when the organic drying medium is first admitted, some of the drying medium condenses and drains through line |40 to condensate return tank The steam discharge from evaporator tube section |3| is accordingly diverted at this time through line to heat exchanger coils |54 in return tank to heat the organic condensate collecting there. While the condensate in return tank is heating up, the liquid level, as gauged by a sight glass |55, is maintained just above the top of heat exchanger |54 by opening valve |38, as required, to drain organic condensate through line ||4 to pump 5 which may be started to return the condensate through line |I5 and valve ||1 to evaporator |00. When the temperature in return tank reaches about 230 F., photoelectric cells |50 and |51 adjustably arranged on sight glass |55 may be operated to pump the organic condensate automatically. That is. when the liquid in return tank reaches an upper level that will be indicated in sight glass |55 where the upper photoelectric cell |55 is located, an electrical circuit (not shown) to the motor-pump set ||5 is energized and the pump is operated until the liquid in tank falls to a level that will be indicated in sight glass |55 where the lower photoelectric cell |51 is located, whereupon the motor-pump circuit de-energizes and the pump stops operating. When the liquid in tank again reaches the above mentioned upper level, the operation cycle is repeated. By adjusting the photoelectrlc controls for automatic pumping between narrow level limits, the composition of the drying medium in the evaporator is maintained more nearly unlform with a consequent improvement in the uniformity of the evaporator temperature and operation, especially when, as previously mentioned, drying media having fairly wide boiling ranges, such as creosote and petroleum fractions, are used.

As the drying chamber |01 is brought up to operating temperature and substantial amounts of liberated water vapor mixed with spent organic vapor begin to pass over to condenser |09 form- Y fing oonlicnsate which collects in separator I0,

autllnatlc separations may also be made. For this purpose, separator I0 is equipped with an auxiliary. electrically controlled, valve |50 controlling the iiow in a line |50 running from near the top oi' the cone portion |00 of the separator to line |40 which carries the separated water to waste. A second valve |0| of the same type is situated on a line |02 tapping the lower portion of the body of the separator and running to the organic condensate line |4| to condensate return tank As previously pointed out, separator ||0 receives mixed water and organic condensate from condenser |00 through line |21. For batch operation, the layers which form as each batch is allowed to stand are selectively drained to the appropriate discharge line by manipulating valve |00 in accordance with observations of the interface in windows |00 and nnally in bullseye |04,

For automatic operation. valve |30 is closed and the auxiliary valves |50 and |0| are used to allow the separator to be drained continuously. To operate the separator in this manner. valve |50 is arranged in a normally closed position and valve |0| in a normally open position, each of these valves having actuating circuits running to a pair o! electrodes |05 and |00, respectively. These electrodes are disposed inside the separator ||0 and are designed to complete the circuit to their respective valves when immersed in the water layer being separated. the water acting as a conductor between the electrodes. The mixed water and organic condensate is accordingly allowed to drain continuously from condenser I00. Baille plates |01, comprising perforated partitions or other baille means spaced laterally in separator I0, slow the flow of entering condensate so that channeling is prevented and layer formation is substantially effected by the time cone portion |00 is reached; the tortuous flow imposed by the baille plates |01 spaced beyond the cone portion |00 further insuring that only substantially water-free organic condensate reaches the outlet to line |02 through auxiliary valve |0|. As a result, an interface is malntained at a substantial level in cone portion |00, and, as auxiliary valve |0| is disposed in open position, continuous discharge from the organic condensate layer is eiected through lines |02 and |4| to condensate return tank and water is intermittently drained through line |59 and line |40 to waste by actuation of valve |50.

The efliciency of the continuous separation is maintained. despite variations of the interface level due to the difference in amounts of water vapor liberated at diil'erent stages of the drying process and other fluctuations in operating conditions. by actuating the auxiliary valves |58 and 0| through electrode pairs |55 and |50 in relation to the interface level. Thus. electrode pair |05 actuating valve |50 is disposed in cone portion |00 at a level slightly above that of the inlet to line |50 through valve |50. As long as the interface level remains below the level of electrode pair |05, operation continues as described above and valve |50 remains closed. If the interface rises above the level of electrode pair |05, the circuit to valve |50 is energized so that this valve opens and allows additional discharge o1' water through line |59. Usually this additional discharge will cause the interface to return gradually to a point below the electrode pair |05, whereupon valve |50 returns to closed position. However, at certain times the, relative proportion of water in the condensate flow to separator H may be large enough to cause the interface to continue to rise. To prevent the water layer from flooding the inlet to line |82 under these conditions, the second electrode pair IBI is positioned at about the level o! the bottom oi' the body portion of separator Illl in order to close auxiliary valve I Si when the interface rises to this level. Only water will then be discharged from the separator until the interface level i'alls below electrode pair |68 and allows valve lll to return to its normally open position so that organic condensate may again be drained to condensate return tank III.

Automatic operation of separator |I|l in this manner, together with the automatic condensate pumping controls available on condensate return tank III allow a very rapid and eilicient handling of the organic drying medium in the liquid phase. The condensate collected in return tank III is conditioned for return to evaporator |02 by heat exchanger I which maintains a. temperature in tank III above the boiling point of water so that small amounts oi' water drained of! with the organic condensate from separator H0 are immediately vaporized in tank and pass oil' through line |28 and valve |2la to line I" and are thus returned to condenser |09.

Besides being arranged for return of organic condensate to evaporator IDI, the discharge line III from pump IIS has two branches, one oi' which--line IBB-runs through valve I to separator I I0. and the other-line ITD-doubles back through valve I`|| to supply line I |2 so that return tank III may be emptied to storage when desired.

Provision for measurement of through-put to evaporator |00 is made by situating a. meter |12 in line IIB, and a second meter |12 is arranged in line |40 to measure the water discharged to waste as an indication of the progress of the drying operation.

After the wood being processed in chamber IIII has been dried to the degree desired, a suitable vacuum period, such as heretofore described in connection with Fig. 1, may be imposed to recover organic material from the outer layers of the wood and to lower the temperature oi' chamber |01 so that the processed wood can be conveniently handled. For this purpose, the heat to evaporator |08 is cut oir; the photoelectric controls |58 and |51 are disconnected. and condensate return tank II is pumped empty; the vapor intake lines |43 are closed at valves |42; and the drain header |24 from vapor intake lines |42 is closed at valves |2| and |22, and line |28 is closed at valve I2Ba. 'I'he equalizer line I2! between separator I|0 and condensate return tank |I| is then closed to the atmosphere at valve |30 and opened to a means for establishing vacuum i not shown) at valve |14. When the system has thus been subjected to a vacuum for a suitable period, the vacuum is broken, the dried wood is removed from chamber III'I and preparations are made for a subsequent treatment.

Using an apparatus of the type described herein, I have found it possible to dry wood pieces up to 5 inches in diameter completely in about 2 hours, and pieces as large as l2 inches in dialneter in about 8 hours; in each case between 20 and 3D pounds of water per cubic i'oot are removed, in the time stated, from initially stump green wood.

In carrying out the drying operation. the atmosphere in the drying chamber should be limited to a moisture vapor content of not more than about 50% of the total vapor in the chamber. The critical nature of this moisture vapor limit is illustrated by Fig. 3 of the drawing, which is a curve showing the relative moisture removals at varying concentrations of the drying medium in the atmosphere in the drying chamber. This curve was derived from data obtained from actual tests conducted with six foot sections cut from forty-live foot Southern pine poles having a diameter of about 9 inches. The initial moisture content of the pole on which the tests designated in Fig. 3 as series 1 were run was about 83%, and that oi' the pole for the series 2 tests about 53%. The pole sections were each dried for six hour periods at a particular drying medium concentration in the drying chamber atmosphere, as indicated in Fig. 3. The moisture removal data obtained in this manner were then extrapolated to a drying medium concentration of 100%. and expressed as a percent of the indicated moisture removal at 100% concentration. The resulting values are shown plotted in Fig. 3.

The rapid decrease in the eiectiveness of the drying operation at the moisture vapor limit of 50% is approximated is strikingly illustrated in Fig. 3. While it is possible to operate at a maximum moisture vapor content approaching 50%, such operation falls at the point of steep descent in terms of relative moisture removal, and consequently close control must be exercised in regulating the drying chamber atmosphere in order to obtain eilfective drying operation. In usual practice it ls desirable to operate below the critical concentration of 50% moisture vapor. A commercially advantageous concentration of drying medium is about 65%, corresponding to a moisture vapor content of about 35%.

The advantage of a concentration of about 65% is further indicated by noting from the curve in Fig. 3 that the relative amounts of water removed when operating at 50% and 75% drying medium in the drying chamber atmosphere are about 20% and 85%, respectively, and that above a drying medium concentration of the increase in water removal is much lower. A concentration of 65% is thus about the point of most economic use of drying medium. The concentration may be further increased to advantage when the rapidity of drying is important in the particular drying operation being undertaken, but unless this factor is of particular importance, it is advisable from the point of view oi' economic operation not to exceed a concentration of about In connection with the regulation of the atmosphere in the drying chamber according to the considerations stated above, I have found that the water vapor in the critical proportions stated behaves as a fixed gas in the chamber, since the atmosphere in the chamber is maintained at a temperature above the boiling point of water throughout the drying period, after the start-up period, thus precluding the presence of water as liquid in the chamber; that the organic vapors, when mixed in the drying chamber with water vapor in the critical proportions recited above, substantially obey Dalton's law in the range of temperatures which will give a concentration oi organic vapor in excess of substantially 50% by weight in the atmosphere surrounding the material being dried when water vapor in a corresponding proportion is the B component of the system (in the case of polar substances whose molecules associate with those of water in the vapor phase, obviously Daltons law does not obtain. However, it is possible to determine empirically the temperatures which will insure a percentage of such organic drying medium in the vapor in excess of substantially 50%); and that the water vapor, when present in concentrations of not more than substantially 50% by weight, behaves as an inert material with respect to hydrolyzing action on the wood when it is in the presence of vapor-ized organic substances constituting not less than substantially 50% of the total weight of vapor in the system.

When the atmosphere in the drying chamber is controlled in accordance with the critical ccnditions described above, the drying operation is characterized by absence of hydrolytic effects; the wood and wood products are effectively dried in a satisfactorily rapid time period. e. g., less than l hours in the case of green poles of 12" diameter and in shorter periods for less severe examples; the fuel costs. at a drying medium concentration of about 65%. are reduced to about 50% of that involved where the process is operated using percentages oi organic drying material in the vapor phase of substantially 100% by Weight, and the heat input is also materially decreased which in turn decreases the amount of organic material in the vapor and reduces the amount of organic condensate which must be handled.

In analyzing data from operations using my process on runs utilizing various percentages of organic material to water vapor (evolved from the wood), I have found that there is a logarithmic relation between the amount of water remaining in the wood at any given instant and the drying time. For example, a graph of the drying operation will yield a straight line if the logarithm of the concentration of water in the wood. expressed as the amount or percentage of Water per unit volume or unit Weight of wood, is plotted against time. For various percentages of organic materials in the vapor phase, which corresponds to various temperatures, the slopes of these straight lines differ. 'I'he slope constants of these lines indicate the rate of drying. This relation between Water removal and drying time may be used to predict the drying eiect obtainable after any given period of drying.

To regulate the drying process according to the considerations described above, vapor-pressuretemperature relations of the organic material to be used in the process are determined from samples, and a. graph is made up based on Daltons law calculations showing the relation of percentage by weight of organic material in the vapor phase (water being the B component) to temperature. The drying chamber temperature necessary to maintain a given concentration of organic drying medium in the drying chamber may then be selected by nding the temperature on the chart corresponding to the desired. concentration. By thermostatically controlling the heat input to the evaporator as previously mentioned by means of a temperature-sensitive element exposed in the drying chamber. as at 42 in Fig. 1, which is set to maintain the temperature selected as above, the desired concentration of organic drying medium in the atmosphere in the drying chamber is obtained and maintained.

As a further illustration of the materials and procedure used in drying wood according to my invention, the following non-limiting examples are given:

18 A. Typical analyses oi' organic drying media that have been employed successfully in carrying out the vapor drying process of my invention:

Cou. TAR FnAc'rIoNs Example I.C'rude light coal tar solvent Color Straw Specic gravity 38/38 C .868 Condition at 60 C Liquid Initial boiling point 91 C.

Dlstillation: Per cent distilling To C 2.4 100 to 110 C 14.7 to 120 C 29.3 to 130 C 23.2 to 140 C 21.1 140 to 150 C 5.9 Residue above 150 C 3.4

Example II.-Crude :rylol Color Medium straw Specic gravity 38/38 C .852 Condition at 60 C Liquid Initial boiling point 121 C.

Distillation: Per cent distilllng To 130 C 6.0 130 to 135 C 19.3 to 140 C 19.9 to 145 C 22.5 to 150 C 14.5 to 155 C 9.0 Residue above C 8.8

Example IIL-Solvent miphtha Color Water White Specic gravity 38/38" C .831 Condition at 60 C Liquid Initial boiling point- 134 C.

Distillation: Per cent distilling To 140 C 2.8 140 to 145 C 25.8 145 to 150 C 32.3 150 to 155 C 17.6 155 to 160 C 9.5 to 170 C 9.9 Residue above C 2.1

Example IV.-Crude heavy coal tar solvent Color Dark amber Specific gravity 38/38 C .952 Condition at 60 C Liquid Initial boiling point 137 C.

Distillation: Per cent distilling To 150 C .8 150 to 160 C 2.4 160 to 170 C 18.8 170 to 175 C 30.3 to 180 C 28.1 to 190 C 15.5 Residue above C 4.1

Example V.-Svecial coal tar distillate (180 to 210 C.)

Color Dark amber Specic gravity 38/38 C .976 Condition at 60 C Liquid Initial boiling point 178 C.

Distillation: Per cent distilling To 180 C .7 180 to 190 C 38.2 190 to 200 C 36.0 200 to 210 C 15.2 Residue above 210 C 9.9

19 Example VI.-Neutral oil o! coal tar Color Dark brown Specific gravity 38/30" C 1.008 Condition at 60 C Liquid Initial boiling point 189 C.

Distillation: l Per cent distilling To 190 C 1.5 190 to 200 C 5.5 200 to 210 C 21.3 210 to 220 C 25.8 220 to 230 C 20.1 230 to 240 C 13.2 240 to 250 C 5.8 Residue above 250 C 6.8

Pl'rnorm menons Example VIL- Light naphtha Color Water white Specific gravity 30/38 C .742 Condition at 60 C Liquid Initial boiling point 104 C.

Distillation: Per cent distilling To 110 C 1.7 110 to 115 C 10.3 115 to 120 C 22.1 120 to 125 C 20.1 125 to 130 C 15.9 130 to 140 C 21.4 Residue above 140 C 8.5

Example WIL-Medium naphtha Color Water white Speciic gravity 38/38 C .777 Condition at 60 C Liquid Initial boiling point ..1 166 C.

Distillation: Per cent distilling To 170 C 11.7 170 to 175 C 54.0 175 to 180C 20.5 Residue above 180 C 18.8

Example Iii-Light distillate Color Straw Speciic gravity 38/38 C .795 Condition at 60 C Liquid Initial boiling point 166 C.

Distillation: Per cent distilling To 210 C 15.9 210 to 235 C .32.7 235 to 250 C 26.2 250 to 270 C 17.2 270 to 285 C 7.9 Residue above 285 C .1

B. Examples o1 the vapor drying process of my invention:

Example )L -Vapor drying of red calc crossties Using apparatus arranged as described above. nine successive changes oi eighteen red oak crossties taken from green stock were dried according to my invention. Moisture determinations indi cated an average initial moisture content o! about 70%. 'I'he drying medium used was a, coal tar distillate of the type identiiled in Example IV above. The temperature of the drying chamber was brought up to the boiling point of the drying medium in about an hour and a half after the rst introduction oi vapor. This temperature was maintained for a period of 12 hours. Introduction of vapor was then stopped, and vacuum corresponding to about 25 inches oi mercury was applied to the drying chamber for 2% hours.

'heretofore available.

The final moisture content o! the crossties after this treatment was about 28%.

Example JIL-Vapor drying of black gum crossties 'I'he procedure outlined in Example X was repeated in drying two charges of black gum crossties having en initial moisture content of about 59%. The iinal moisture content after the drying treatment was 27%.

Example JUL-Vapor drying 0f mixed hardwood The drying operation was carried out with five charges each consisting of twenty crossties selected from newly cut, mixed hardwood stock. I'he drying medium used was a coal tar distillate of the type identiiled in Example IV above. The operating conditions and moisture removal obtained are indicated below:

Heating Vacuum ve e Ave e Charge I"Inlti t I,Fina t Inch of er om or con 1'. Hrs. Hrs. Mm Moisture Moisture l2 2. 5 25 04. l 24. 5 6 2 2li 08. 0 42. l l2 2 M B0. 2 32. 7 8 2 25 ill. 8 61. 1 6 2 25. 5 94. 6B. l

Example XUL-Vapor drying under vacuum The procedure oi' Example XII was repeated with three similar charges from the same stock, except that the vapor drying was carried out under vacuum in order to lower the operating temperature by lowering the boiling point ot the drying medium. The drying medium was heated at atmospheric pressure to a temperature corresponding to the boiling point of the drying medium at the vacuum to be used. The drying chamber was then brought up to temperature under vacuum, and the vacuum was maintained for the periods indicated, alter which the introduction of vapor was stopped and the drying chamber was subjected to a iinal vacuum period. The operating conditions and moisture removal obtained are indicated below:

In each case the crossties treated in the manner illustrated in the foregoing examples were markedly free from the adverse effects, such as checking, loss o! fiber strength due to hydrolysis, case hardening, and warping, usually attendant upon the drying of wood. It will also be noted from the examples that wood may be conditioned according to the present invention with great facility for subsequent preservative treatment, for which a moisture content ol 30% is generally considered optimum.

By means of the apparatus and method described and illustrated above. I have found it possible to dry wood products rapidly and eiliciently and without the obiectional irnperfections which have resulted from the processes Although it has been found that equipment similar to that described is the most suitable for the operation. it should be understood that variations may be employed which do not depart substantially from the invention herein disclosed and which will give substantially the same results. The equipment may also be adapted to drying kilns, or similar drying apparatus, in a manner which will greatly reduce operating time and increase the effectiveness of operation.

It will be noted that in the above disclosure, the methods employed are for the handling of organic drying media which are immiscible with water. In using the apparatus in conjunction with drying media which are miscible with water, it would of course be necessary to eliminate the liquid phase separator and substitute a receiving tank which would be employed as a distillation unit in conjunction with suitable fractionating columns. Also, it is apparent that the organic drying medium used in the arrangement shown should exist as a liquid at temperatures below the boiling point of water, to obviate any difficulties due to solidication of the drying medium in the separator or the condensers. To prevent the occurrence of this undesirable condition, a margin of safety between the temperature at which the drying medium begins to deposit solids and the temperature of the boiling point oi water should be maintained at all times. Where it is desirable to use an organic drying medium which has a melting point above that of the boiling point of water, it is possible to establish the proper temperature characteristics for the organic material by employing it incorporated in a suitable solution. All of the organic drying media referred to above are inert to wood and wood products, that is, they have no deleterious ecct on the wood. Any reactions which take place between the drying medium and the wood are of a beneficial nature.

I claim:

l. An apparatus for preserving and drying wood comprising a drying chamber, means therein for supporting the wood, an evaporator for supplying a drying medium in vapor phase to said chamber, a high temperature partial condenser for receiving water vapor and drying medium in vapor phase from said chamber and for condensing the vaporous drying medium to liquid phase, a condensate return chamber, a line leading from said partial condenser to said return chamber for returning condensed drying medium thereto. another line leading from the partial condenser to the evaporator, and a line leading from the return chamber to the evaporator for supplying condensate thereto, a low temperature complete condenser, a separator associated with said complete condenser, a. 'line leading from the partial condenser to the complete condenser to deliver thereto uncondensed vapors of the drying medium, and Water vapor, separate lines leading from said separator to said evaporator and to said return chamber respectively for returning condensed drying medium thereto, and a line leading from said return chamber to the line leading from the partial condenser to the complete condenser for delivering vapors from the return chamber to said complete condenser.

2. An apparatus for preserving and drying wood comprising a drying chamber, means therein for supporting the wood, an evaporator for supplying a drying medium in vapor phase to said chamber, a high temperature partial condenser having a high temperature tube section, and said condenser being adapted for receiving lil) water vapor and drying medium in vapor phase from said chamber and for condensing the vaporous drying medium to liquid phase, a condensate return chamber, a line leading from said partial condenser to said return chamber for returning condensed drying medium to the return chamber, a line leading from the partial condenser to the evaporator for returning condensed drying medium to the evaporator, a line leading from the return chamber to the evaporator for supplying condensate to the evaporator, a line leading from the return chamber to said tube section of said partial condenser for delivering condensate to said tube section, and a line re- 'turning from said tube section to said evaporator to deliver the condensate to the evaporator.

3. An apparatus for drying and preserving wood, comprising a closed receptacle defining a treating chamber having means therein for supporting the wood for dehydration and impregnation, an evaporator in which a liquid drying medium is vaporized, a conductive connection through which the vapor is taken from the evaporator into the treating chamber at a temperature higher than that of the vaporization point of the moisture content of the wood, and interconnected means for progressively removing from said treating chamber the spent treating vapor commlngled with the moisture vapor liberated from the wood during its treatment under the surrounding and permeating influence of the supplied vapor in the chamber, said interconnected means including a high temperature partial condenser cooperatively communicable with said treating chamber Aand said evaporator for condensation of said treating vapor only. and a low temperature complete condenser cooperatively communicable with said treating chamber, said high temperature partial c-ondenser, and said evaporator for condensation of both treating vapor and moisture vapor.

4. An apparatus for drying and preserving wood, comprising a treating chamber in which the wood is placed and confined for dehydration and impregnation, means within said chamber for supporting the wood, an evaporator in which a liquid drying medium is vaporized, a conductive connection through which the vapor is taken from the evaporator into the treating chamber at a temperature higher than that of the vaporization point of the moisture content of the wood, means for progressively removing from said treating chamber the spent treating vapor commingled with the moisture vapor liberated from the wood during its treatment under the surrounding and permeating influence of the supplied vapor in the chamber, and means for separating from the removed moisture vapor the spent treating vapor taken therewith from the treating chamber and returning a condensate of such spent treating vapor to said evaporator for reuse, said last named means comprising a condensate return chamber connected to said evaporator, a high temperature partial condenser connected to said treating chamber, said evaporator cycled for reuse in the system. comprising a drying chamber having means for housing and supporting the wood therein, an evaporator connected to said chamber for vaporizing the organic drying medium and supplying the hot vapor to said chamber, a high-temperature, partial condenser connected with said drying chamber for receiving the moisture vapor liberated trom said wood together with the used organic drying vapor, means for maintaining the operating temperature o1 said partial condenser sumciently high to prevent condensation oi' said moisture vapor but sufficiently low to eiect condensation of said organic vapor, means for conducting the uncondensed moisture vapor away from said partial condenser, a receiver connected with said partial condenser for receiving said condensed organic drying material only, and means for recycling the organic condensate from said receiver to said evaporator for reuse therein.

6. A closed system adapted for drying green or wet wood with a heated organic drying vapor, in which the drying medium is condensed and recycled for reuse in the system, comprising a drying chamber for housing the wood and having means therein for supporting the wood, an evaporator connected to said chamber for vaporizing the organic drying medium and supplying the hot organic vapor to said chamber, a high-temperature. partial condenser connected with said drying chamber for receiving the moisture vapor liberated from said wood together with the used organic drying vapor, means for maintaining said partial condenser at suihciently high temperature to prevent condensation oi' said moisture vapor but sufficiently low to eiect condensation of said organic vapor, a low-temperature, complete condenser connected with said partial condenser for receiving the uncondensed eiliuent therefrom and for condensing the moisture vapor and residual organic vapor, and means for separating the water and organic liquid components of this condensate, a return vessel connected with said partial condenser and with the organic condensate delivery portion of said separating means whereby to receive only condensed organic drying medium, and means for recycling the organic condensate from said return vessel to said evaporator.

7. A closed system adapted for drying green or wet wood with a heated organic drying vapor, in which the drying medium is condensed and recycled for reuse in the system, comprising a drying chamber for housing the wood and having means therein for supporting the wood, an evaporator connected to said chamber for vaporizing the organic drying medium, a high-temperature, partial condenser connected with said drying chamber for receiving at least some of the moisture vapor liberated from said wood together with some of the used organic drying vapor, means for maintaining said partial condenser at sufllciently high temperature to prevent condensation of said moisture vapor but suiilciently low to effect condensation of said organic vapor, a low-temperature, complete condenser connected with said drying chamber and with said partial condenser for receiving therefrom the uncondensed organic vapor and moisture vapor and condensing the same, a separator connected to said complete condenser for receiving and separating the water and organic liquid condensates, a return vessel connected with said drying chamber, and with said partial condenser and with the organic condensate delivery portion of the sepa- 24 rator whereby to receive only condensed organic drying medium, and means for continuously recycling the organic condensate from said return vessel to said evaporator 8. The system as set forth in claim 5, and in which the operating temperature of said partial condenser and said organic condensate return vessel is approximately 230 F. to 260 F, whereby moisture vapor is prevented from condensing and organic vapor is condensed in said partial condenser and receiving vessel.

9. An apparatus for preserving and drying wood comprising a drying chamber, means for supporting the wood in said chamber for direct contact of a drying medium with the wood, an evaporator for supplying a drying medium in vapor phase to said chamber, a high temperature partial condenser for receiving both water vapor and drying medium in vapor phase from said chamber, means for cooling said partial condenser sumciently to condense only the vaporous drying medium to liquid phase, a condensate return chamber, a line leading from said partial condenser to said return chamber for returning condensed drying medium to said return chamber, another line leading from the partial condenser to the evaporator for returning condensed drying medium directly to the evaporator, a line leading from the return chamber to the evaporator for supplying condensate from said chamber to the evaporator, a low temperature complete condenser. a separator associated with said complete condenser, a line leading from the partial condenser to the complete condenser to deliver to said complete condenser uncondensed vapors of the drying medium and water vapor, and lines leading from said separator to said evaporator and to said return chamber for returning only condensed drying medium to the evaporator and to the return chamber, respectively.

10. A rapid, high temperature method oi' dehydrating wood in a closed space, which is characterized by substantially complete drying of the wood in a matter of several hours instead of days, comprising providing and maintaining in said space a saturated atmosphere of a nonaqueous, inert, organic vapor that does not deleteriously affect the wood and which permeates the wood to effect rapid removal of the moisture therefrom, the vapor being maintained at a high temperature substantially above the vaporization temperature of the moisture in the wood so that the moisture is ilashed ofi', immediately and progressively removing the liberated moisture vapor during the drying operation until the desired degree of dryness of the wood is obtained, fractionally condensing said liberated moisture vapor and used organic vapor to effect condensation of the organic vapor only, separating said moisture vapor from the condensed organic vapor and condensing and discharging said moisture vapor condensate from said closed space, conducting said organic condensate to a receiving vessel and recycling it therefrom for reuse in the drying of the wood.

l1. A rapid method oi dehydrating wood in a closed space by means of an organic vapor and requiring less than one days time for completion. comprising surrounding and permeating the wood with an inert vapor of an organic compound heated to a temperature within the range of substantially above 212 F. up to about 450 F. so that the organic vapor at said high temperature causes the moisture in the wood to be flashed ofi', immediately removing said liberated moisture vapor from the dehydrating operation so that condensation oi' said moisture vapor into liquid water and hydrolysis of the wood are avoided, maintaining throughout the drying operation the temperature of the organic vapor substantially above the condensation temperature of the moisture liberated from the wood, iractionally condensing said liberated moisture vapor and used organic vapor to eiect condensation of the organic vapor free of moisture, separating said moisture vapor from the condensed organic vapor and condensing and discharging said moisture vapor condensate from said closed space, conducting the resulting, dewatered, organic condensate away from the closed space, and recycling said organic condensate for reuse in the drying of the wood.

12. The method of dehydrating wood which comprises subjecting the wood in a closed space to the rapid drying action of an inert organic vapor of a hydrocarbon having a boiling temperature in said space substantially higher than that of water, maintaining said organic vapor at a temperature substantially above 260 F. such that water vapor liberated from the wood is not permitted to condense to form liquid water in said closed drying space, continuing the introduction of fresh, heated organic vapor to remove the liberated water vapor from the drying space, continuously removing during the drying operation the liberated moisture vapor and the used organic vapor as a vapor mixture, passing said mixture through a relatively high temperature zone which causes condensation of said organic vapor but not of the water vapor, separating said moisture vapor from the condensed organic vapor and condensing and discharging said moisture vapor condensate from said closed space, and re cycling the resulting organic condensate free of water for reuse in the drying operation.

13. A method of drying and preserving wood and wood products which comprises placing the same in a chamber, continuously introducing into said chamber an atmosphere oi a drying medium having a boiling point above the boiling point of water. continuously removing water vapors evolved from the Wood and wood products and the drying medium in vapor phase from said chamber, condensing at least a substantial part of the drying medium, pre-heating the condensate of the drying medium by passing the same in heat exchange relation to the vapors o! the drying medium being condensed, returning the preheated condensate to the drying medium supply, condensing any remaining drying medium vapor for recovery, and condensing the water vapor and discharging the condensate thereof to waste.

14. A system adapted for drying green or wet wood with a heated organic drying vapor comprising a drying chamber for housing the wood, means for supporting the wood in the drying chamber for contact with the organic drying vapor, means communicably connected with said chamber for producing and supplying to said chamber the organic drying vapor, a condenser connected with said drying chamber for receiving and condensing the moisture vapor liberated from the wood together with the used drying vapor, a separator connected with said condenser for separating substantially the water from the condensed drying vapor, means for removing from the separator and from the system said water condensate, a receiving vessel communicably connected with said drying chamber for receiving therefrom hot organic drying vapor condensate which heats the receiving vessel, this latter condensate being at a temperature higher than the boiling point of water and having a boiling point higher than that of water, said vessel also being communicably connected with said separator for receiving therefrom relatively cool organic drying vapor condensate containing some water, which water is then heated in said receiving vessel by said hot organic vapor condensate suillciently to vaporize said water, a conduit connecting the top of said receiving vessel with said condenser for conducting said water vapor back through said condenser and disposal therefrom as aqueous liquid condensate, and said receiving vessel also being connected with said organic vapor producing means for supplying thereto the dewatered, organic liquid condensate.

15. A rapid, high temperature method of dehydrating wood confined in a closed space ,comprising introducing into said space and in contact with the wood, an atmosphere of an inert, organic vapor that does not deleteriously aiect the wood but permeates the wood to eiect rapid removal of the moisture therefrom, the vapor being maintained at a high temperature substantially above the vaporization temperature of the moisture in the wood, continually removing the liberated moisture vapor during the drying operation until the desired degree of dryness of the wood is obtained, condensing said liberated moisture vapor and used organic vapor, substantially separating the water vapor condensate from said organic vapor condensate and discharging said water vapor condensate to waste, conducting ofi and collecting in another space the hot organic vapor condensate that forms in the closed, wood-drying space, also collecting in this second space the relatively cool, aforesaid, used, organic condensate and which contains an amount of water not removed in the aforesaid separation, this water content then being heated and vaporized in said second space by said hot organic vapor condensate, which has a higher boiling point than Water and its temperature in said second space being higher than the boiling point of water, the water vapor produced in this second space being conducted directly to said rst mentioned condensing operation and there condensed and discharged to waste, and recycling the resulting dewatered organic condensate from said second space for reuse in the drying operation.

16. A rapid, high temperature method of dehydrating wood in a closed space, comprising providing in said space an atmosphere of highly heated, inert, organic vapor that does not deleteriously aiect the wood and which permeates the wood to eiect rapid removal of the moisture therefrom. the vapor being maintained at a high temperature substantially above the vaporization temperature of the moisture in the wood so that the moisture is flashed oi, removing the liberated moisture vapor during the drying operation sutilciently to limit the amount of moisture vapor present in the drying chamber to an amount not exceeding approximately 35% of the total amount 0f vapor in the drying chamber and thereby preventing degradation of the wood being dried, fractionally condensing the liberated and renamed moisture vapor and used organic vapor to effect condensation of the organic vapor only, separating the uncondensed moisture vapor from the organic vapor condensate, condensing the water vapor and discharging the resulting condensate from said closed space, conducting said organic 27 condensate to a receiving vessel and recycling it therefrom for reuse in the drying oi the wood.

17. An apparatus for drying green or wet wood with a heated organic drying vapor, in which the drying medium is condensed and recycled for reuse, comprising a drying chamber for housing the Wood and having means therein for supporting the wood, an evaporator connected to said drying chamber for vaporizing the organic drying medium and supplying the hot organic vapor to said chamber, means for progressively removing the moisture vapor liberated from said wood together with the used organic drying vapor from said drying chamber, means for recovering the used organic vapor including a. condenser and associated means for separating the water and organic liquid components of the condensate formed in said condenser and means for discharging the water component to waste, a, return vessel connected to receive the recovered organic condensate and associated means for maintaining the condensate in said return vessel at a temperature above the boiling point of water to vaporize any water entrained with the recovered organic vapor condensate, means for conducting oir water vapor from said return vessel back to said condenser for discharge to waste, and means for recycling the 4organic condensate from said return vessel to said evaporator.

18. An apparatus for drying green or wet wood with a heated organic drying vapor, in which the drying medium is condensed and recycled for reuse, comprising a drying chamber for housing the wood and having means therein for supporting the wood, an evaporator provided with a heat exchange unit and means for passing heated iiuid through said heat exchange unit for vaporlzing the organic drying medium, said evaporator being connected with said drying chamber for supplying the hot organic vapor to said chamber, a condenser connected with said drying chamber for receiving the moisture vapor liberated from said Wood together with the used organic drying vapor and for condensing the moisture vapor and organic vapor, means for separating the water and organic liquid components of the resulting condensate and discharging the water to waste. a return vessel connected to receive the organic condensate from said separating means and provided with a second heat exchange unit and means for passing the heated duid supplied to said iirst mentioned heat exchange unit, through said second heat exchange unit whereby the condensate received in said return vessel may be maintained at a temperature above the boiling point of water to vaporize any Water entrained in the organic condensate received from said separating means, means for conducting of! water vapor from said return vessel. and means for recycling the organic condensate from said return vessel to said evaporator.

19. An apparatus for drying green or wet wood with a heated organic drying vapor in which the drying medium is condensed and recycled for reuse, comprising a drying chamber for housing the wood and having means therein for supporting the wood, means for vaporizing the organic drying medium and supplying the hot organic vapor to the wood to be dried, means for progressively removing the moisture vapor liberated from the wood together with the used organic drying vapor from said drying chamber, means for condensing the major portion of the used organic vapor and means for returning the resulting condensate for revaporization and use in the drying chamber, means for condensing the remaining lesser portion of the organic vapor and the water vapor to form a mixed condensate, means for separating the two condensates. means for discharging the separated water condensate to waste. and means for recycling the remaining organic condensate for reuse in the drying chamber.

20. The process of drying wood with vapors of a heated organic drying medium which comprises subjecting the wood in a, closed drying space, having exhaust and supply ports, to an atmosphere of the vapors of said organic drying medium. supplying the vapors of said organic drying medium to said closed drying space at a temperature sufiicient to vaporize and liberate the moisture in the wood and maintain the liberated water vapor in vapor phase in said closed drying space, and removing the liberated Water vapor and spent organic vapor from said closed drying space throughout the drying process by supplying additional organic vapor through said supply port and thereby displacing the liberated water vapor and spent organic vapor from said drying space through said exhaust port, said additional organic vapor being supplied at a rate that provides in said closed drying space a concentration of organic vapor of at least 50% by weight but less than that of a saturated atmosphere of said organic vapor.

21. The process of drying wood with vapors of a heated organic drying medium which comprises subjecting the wood in a closed drying space, having exhaust and supply ports, to an atmosphere of the vapors of said organic drying medium, supplying the vapors of said organic drying medium to said closed drying space at a temperature sufficient to vaporize and liberate the moisture in the wood and maintain the liberated water vapor in vapor phase in said closed drying space, and removing the liberated water vapor and spent organic vapor from said closed drying space throughout the drying process by supplying additional organic vapor through said supply port and thereby displacing the liberated water vapor and spent organic vapor from said drying space through said exhaust port, said additional organic vapor being supplied at a rate that provides in said closed drying space a concentration of organic vapor of at least 65% by weight but less than that of a saturated atmosphere of said organic vapor.

22. The process of drying wood with vapors of a heated organic drying medium which comprises subjecting the wood in a, closed drying space, having exhaust and supply ports, to an atmosphere of the vapors of said organic drying medium, supplying the vapors of said organic drying medium to said closed drying space at a temperature sufficient to vaporize and liberate the moisture in the wood and maintain the liberated water vapor in vapor phase in said closed drying space, and removing the liberated water vapor andspent organic vapor from said closed drying space throughout the drying process by supplying additional organic vapor through said supply port and thereby displacing the liberated water vapor and spent organic vapor from said drying space through said exhaust port, said additional organic vapor being supplied at a rate that provides in said closed drying space a concentration of organic vapor from about 65% to 90% by weight of the total mixed organic vapor and liberated water vapor.

23. A rapid, high temperature method of dehydrating green or wet wood. in a. closed space,

29 the wood commonly containing 50% to 100% moisture on a dry weight basis and the drying being effected without adversely aiecting the strength and other desired properties o! the wood. comprising vaporizing in a heated vaporizer an organic drying medium that does not deleteriously affect the wood, subjecting said wood to an atmosphere of the vapor of said organic drying medium in said closed space, the vapor of said organic drying medium being maintained in said closed space at a temperature substantially above the boiling point of water and thereby causes the moisture in the Wood to be ashed oi, immediately and progressively removing the liberated moisture vapor and spent organic vapor during the drying operation, condensing said vapors and separating the predominant portion of the moisture condensate and discharging same to waste, collecting the organic vapor condensate in a heated space and boiling ofi therein any remaining water condensate entrained in said organic condensate so as to dehydrate substantially completely said organic condensate, carrying oi the resulting moisture vapor for reconden- 30 sation and discharge to waste and recycling said dehydrated organic condensate to said vaporizer for reuse in the drying operation.

24. A method as defined in claim 23 and in which the atmosphere of drying vapor used is a substantially saturated organic vapor atmosphere.

25. A method as defined in claim 23 and in which the organic vapor is obtained by heating an organic compound selected from the class consisting of creosote. petroleum distillates, coal tar, Wood tar and wood distillates.

MONIE S. HUDSON.

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

UNITED STATES PATENTS Number Name Date 1,059,820 Besemfelder Apr. 22, 1913 2,273,039 Hudson Feb. 17, 1942 2,293,453 Clark Aug. 18, 1942 Certificate of Correction Patent No. 2,435,218.

February 3, 1948.

MONIE S. HUDSON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 16, line 25, for operation at read operation als; column i9, distilling for .32.7

these corrections therein that the same may con Patent Uce.

read 32.7; and that the said Letters form to the record of the case in the line 52, Example IX, under the heading Per cent Patent should bc read with Signed and sealed this 6th day of April, A. D. i948.

[SEAL] THOMAS F. MURPHY,

Assistant Uommissioner of Patents.

MONIE S. HUDSON.

February 3, 1948.

these corrections therein that the same may con Patent Uce.

[SEAL] THOMAS F. MURPHY,

Assistant Uommissioner of Patents.