Abstract: Wood is preliminary dried until its moisture content is reduced to 20 to 30%, and then treated by radio frequency heating in two stages, i.e., the first stage where the radio frequency heating is carried out at a temperature of 60.degree. to 120.degree. C., and the second stage where the radio frequency heating is carried out at a temperature of not more than 60.degree. C.

Abstract: Oil-borne preservative-impregnated wood is post-treated by:(A) contacting the preservative-impregnated wood in a closed vessel with steam and collecting a water-containing condensate generated in the vessel;(B) applying a vacuum which is sufficient to reflux water condensate to remove at least some surface deposits from the wood and to distill water out of the vessel leaving an oil-preservative solution in the vessel;(C) releasing the vacuum; and(D) recovering the post-treated wood from the vessel.

Abstract: A kiln controller controls the drying of lumber in a kiln by executing a drying schedule and adjusting the drying schedule in response to actual measured conditions in the kiln. A computer within the controller controls heating coils, spray nozzles and vents in the kiln to achieve the conditions prescribed in the drying schedule. The computer first executes a routine whereby the kiln temperature is brought up to a desired initial temperature. Then the computer concurrently executes the drying schedule and a routine wherein it monitors the temperature, vent load and spray nozzle activity, and automatically adjusts the duration of the current step in the drying schedule.

Abstract: An apparatus for a supercritical fluid-solid bed process such as for decaffeinating green coffee beans including an elongated cylindrical vessel having a top and bottom. The solids accumulate to form a fluid-solids bed on the bottom of the vessel which includes a central bottom opening, a valve for periodically allowing flow of the solids through the bottom opening and a frustoconical bottom wall. A flow promoting insert having a lower conical wall is provided circumjacent to but spaced from the frustoconical bottom wall. The lower conical wall is provided with a rougher surface than the adjacent frustoconical bottom wall to promote uniform flow of solids. The fluid initially flows through the solids counter-current to the solid flow and is introduced to the vessell through means located above the flow promoting insert.

Abstract: This invention relates to an improved aggregate drying apparatus and method where the dried aggregate is particularly useful for making hot mix asphalt. In accordance with the system, heat typically lost in exhaust gases and moisture evaporated in a heater is recovered to dry and preheat the aggregate. The invention also relates to novel components used in the system, including an improved aggregate dryer and an improved mass flow apparatus for use in an aggregate dryer or otherwise in aggregate feed bins.

Abstract: A system for conditioning grain in a sealed container through the removal of liquid from a bushel of grain by sequentially evacuating high relative humidity air from the sealed container and thereafter allowing dry environmental air to reenter the sealed container. A sensor in the sealed container detects the relative humidity therein and supplies a controller with a signal to operate a pump which evacuates high relative humidity air from the sealed container. Thereafter, a pressure sensor detects a vacuum in the sealed container and supplies the controller with a signal which terminates the operation of the pump to allow dry environmental air to reenter the sealed container. The replacement of high relative humidity air with dry environmental air continues until the liquid content per bushel of grain is at a desired level.

Abstract: In the vacuum drying of solid wood (2) and other wood-based products, the invention provides a method of achieving a better control of the drying process and a better heat economy than by the traditional methods of vacuum drying. This is achieved by completely evacuating the air from the space around the wood (2), and instead to fill the space (1) around the wood (2) with superheated water vapors (11). By maintaining a uniform pressure and temperature in all parts of the drying chamber (1) during the drying process, and controlling the temperature and the pressure of the superheated water vapors (11) in accordance with directives described in more detail, it is possible to control the dampness (MC) of the wood very precisely, and thereby to avoid damage to the wood (2) during drying.

Abstract: Method and apparatus for effecting treatment needed to regenerate spent hydrocarbon conversion catalyst. The invention may be termed a variable gas flow catalyst bed. Catalyst particles in a vertically-elongated movable bed are contacted with a hot oxygen-containing gas stream in order to remove, by means of combustion, coke which accumulated on the catalyst particles while they were used in a hydrocarbon conversion zone. The catalyst particles are confined in the bed by means of catalyst retention screens. The catalyst retention screens are configured such that gas flow through the bed varies from a maximum at the top of the bed to a minimum at the bottom of the bed. The variation in gas flow is accomplished by varying the size of gas flow apertures in the retention screens from a maximum at the top of the bed to a minimum at the bottom of the bed.

Abstract: A method, apparatus and system for use in drying particulate matter employing a drier comprising a cylindrical upper section, a frustoconical lower section, a rotatable shaft extending substantially the entire length of the interior of the drier, a plurality of axially spaced arrays of circumferentially spaced, radially extending stirring arms appended to the shaft, and at least two perforated frustoconical separators mounted within the drier in fixed, inverse and spaced apart relation to each other, and means for introducing a heated gas into the drier for contacting and drying the particulate matter, the stirring arms and separators cooperating to retard agglomeration of the particulate matter.

Abstract: Parts for a wooden casing, in particular in the form of a telephone apparatus case, are manufactured as follows. A piece of timber is dried inside an oven to a moisture content of about 4-5% with sufficient moisture content being left to avoid cell collapse in the timber. At the end of the drying period the temperature is raised causing the resin in the timber to flow out and seal the pitch fibers of the wood preventing the wood from reabsorbing moisture. A blank is taken from the dried timber and worked into the final shape of a casing. Any weak points in the casing are reinforced with a reinforcing material in the form of wood or some other material. The pores of the wood are then sealed with varnish.

Abstract: Vacuum dryer for sawn timber, in which at least one wall of a pair of opposing walls of the drying chamber for containing the timber is substantially rigid and flat while the opposing wall is sealingly movable towards the rigid wall under the pressure which acts on the exterior when the chamber is evacuated, so as to press the timber forcibly against the flat wall.

Abstract: The invention relates to an improved process for drying and preserving wood products. The improved process comprises the steps of first drying the wood products by submerging them in a naphthalene poor, coal tar based heat transfer medium under conditions of elevated temperature and reduced pressure. The dried wood products then are impregnated with a naphthalene rich, coal tar based wood preservative agent by submerging said dried wood products in said agent under conditions of both elevated temperature and pressure.

Abstract: A process and apparatus are disclosed for accelerating the drying of green and/or partially dried lumber. The lumber is dried at pressures below standard atmospheric pressure to rapidly remove moisture from the lumber without degrading the wood structure. A kiln for performing this function includes a chamber for a charge of lumber, an electrically activated flexible heating blanket to impart heat into the charge of lumber, a device for reducing pressure within the chamber, and a device for removing moisture vapor from the chamber. The process for accelerating the drying of the wood includes the step of heating the wood piece in the chamber to a selected temperature. The pressure in the chamber is reduced to a pressure at least as low as the vapor pressure of water at the selected temperature. The wood is controllably heated to maintain the wood at the selected temperature while the pressure in the chamber is reduced.

Abstract: Method and apparatus for use in drying biomass particles provide a dryer having a chamber for a predetermined volume of biomass particles with apertures distributed throughout one boundary of the chamber enabling hot gas to be introduced and forced through the particles to exit from the opposite boundary. The gas stream to the chamber is so regulated that a layer of particles adjacent the opposite boundary functions as a relatively cool filter bed operable to prevent, to a desired extent, noxious liquids, gaseous, or particulate emissions from exiting from the dryer.

Abstract: A heat exchanger consisting of a housing (1) with integrated caloric surfaces (3) for cooling bulk materials (8)--in particular hot foundry molding sands--comprises a retarder system in the form of a sand cascade which consists of an upper perforated plate (9) with many small individual holes (11), of a lower perforated plate (12) with few individual holes (12), said perforated plates being spaced apart by perforated plates (4,15), the sand flow through the slide system (5,6,14) being controllable and sealable.The passage holes may assume the shapes of triangular, longitudinal or T slots in order to operate such a retarder cooler over a large range of regulation.The perforated spacer plates (4) moreover form a support plate with high static load capacities to absorb the substantial weights of the bulk materials.

Abstract: A gas to solid contacting apparatus comprising a chamber, at least one solid inlet conduit opening into the chamber, at least one gas inlet conduit opening into the chamber, the gas inlet and outlet comprising superimposed conduits.

Abstract: An apparatus and process for drying lumber under vacuum conditions using a drying vessel operationally connected to a sump which collects the extracted moisture. Vaccum conditions are maintained in the vessel and in the sump within the range of 10,000 to 15,000 microns, which reduces the boiling point of water to less than 80.degree. F. The temperature within the vessel is raised to approximately 105.degree. F. by a heating source and this combination of reduced pressure and elevated temperature causes the moisture in the lumber to boil off as vapor. This vapor is condensed inside the vessel by refrigeration coils cooled to a temperature between 36.degree. F. and 42.degree. F., and the liquid condensed on the coils is carried to the sump through a drain pipe where it is pumped to waste disposal through a flow meter.

Abstract: Impregnated wood and other impregnated cellulose based materials are dried in high boiling drying media, drying oil, under reduced pressure. During the treatment the material is withdrawn from direct contact with the drying medium at several times. The absorption of oil in the materials can hereby be controlled. Materials of different qualities and origin can be dried with good results and the oil absorption does not have to be made dependent on the penetration depth of the impregnating solution. An autoclave for drying of wood according to this process preferably has a rectangular inner cross section and is provided with means for lifting and lowering the materials. Preferably a lifting table or frame.

Abstract: A process and apparatus for drying of materials such as wood chips or lacquers. A stream of hot gas is provided, the hot gas passes over the material to be dried, the now waste gas is removed from the material to be dried, the volatile substances are deposited from the waste gas and the deposited substances are moved to a collector location. Dust and similar materials can be also bonded during the depositing step. The deposited volatile substances can be removed by intermittent evaporation and/or sublimation and the volatile substances can be collected at a predetermined collector location, or by continuously washing out the volatile substances, or by compressing before cooling down and expanding after cooling down the volatile substances. Removing of deposited volatile substances may be triggered in response to a certain degree of dirtying or soiling and to passing predetermined threshold values of temperature and/or pressure and in accordance with a predetermined time plan, respectively.

Abstract: A preheating moist fine material, such as pit coal and lignate, peat, wood, oil shale, or even ores or limestone for cement production, and an apparatus for carrying out the method are disclosed. Moist fine material is mixed above a heater with predried and preheated material until the mixture is made fluid. The fluid mixture slides down between and piles up to a level above the heater. A part of the predried and preheated fine material is removed from below the heater in an amount corresponding to another part thereof and is conveyed to above the heater with the moist fine material.

Abstract: A process is described for the modification of wood and wood products by heat treatment in a closed, heatable vessel, wherein the water content of the starting material is controlled to be no higher than 10% by weight.

Abstract: A process for the drying of wood is disclosed. The drying is carried out by heating the wood in an oil and under vacuum with heating being carried out wholly or partly by use of dielectric energy.

Abstract: A sawdust drying apparatus and process wherein sawdust passes downwardly in a sinuous fashion to and through multiple, vertically spaced dryer plates at a temperature and velocity so as to progressively dry the sawdust and render it suitable as a highly combustible wood fiber fuel.

Abstract: A process for the treatment of wood is disclosed wherein the wood is contacted with an oil mixture in order to dry/color the wood. The mixture comprises both low and high boiling oils.

Abstract: Wood is beneficiated by treating the wood with an agent capable of forming a borate ester linkage between hydroxyl groups of the cell wall constituents of the wood, and thereafter treating the wood with an aldehyde to effect aldehyde cross-linking of cell wall structural constituents of the wood. Suitable borate ester forming agents include boric acid, lower polyalkyl borate esters, mono- and di-substituted derivatives of boric acid and/or the borate esters, and compounds capable of forming these agents in situ under the prevailing reaction conditions.

Abstract: The removal of water from wood by the process of the invention is carried out by supplying sufficient quantities of heat to maintain the pressure of the environment in which the wood is disposed above atmospheric pressure, and discharging water vapor from this environment, the heat supply and the discharge of water vapor being regulated so as to maintain a succession of conditions of substantially saturated water vapor in the said environment.

Abstract: A process and apparatus for accelerated drying of green and partially dried lumber at pressures above atmospheric pressure to rapidly remove selected portions of moisture from the wood without degradation of the wood structure. A kiln for performing the method comprises a generally cylindrical kiln chamber to contain a stack of lumber, a by-pass line from the front to the back of the chamber to heat and distribute steam evenly to the lumber surfaces, a pressure-controlled steam vent to regulate kiln temperature, and temperature control to regulate the rate of drying. Conditions of pressure and temperature in the kiln can be regulated by heat added from an external source to equalize and condition the lumber rapidly in steam.

Abstract: A veneer block moisturizing vault which has a single upright openable end which is closeable and exposeable through vertical shifting of a rigid unitary door. The lateral margins of the door are received in confronting channels, which, together with the door's margins, provide an effective lateral moisture barrier inhibiting the escape of steam from the vault when its door is closed. With the door closed, the bottom edge of the same rests snugly upon a specially prepared cement apron--also to effect a steam-capturing moisture barrier. Moisturizing in the vault is accomplished through the controlled blending and injection thereinto of steam and cold water.

Abstract: A method for sealing a dryer against leakage of hot gases from within the dryer through joints between adjacent panels enclosing the interior of the dryer. The method comprises fastening respective elongate enclosing members into abutment with mutually adjacent pairs of panels along the joints between them so as to form respective enclosures between the enclosing members and the panels at such joints. Thereafter, at a temperature less than the operating temperature of the dryer, a heat-resistant, gas-impermeable closed cell foam is injected into the enclosures through spaced perforations in the enclosing members so as to substantially fill the enclosures. Thereafter, when the veneer dryer is operated at its normal elevated operating temperature, the temperature of the closed cell foam is thereby increased so as to expand the foam within the enclosures into tight sealing abutment with the joints to prevent gas leakage therethrough.

Abstract: In a method of drying boards by radio-frequency heating a stack of boards is passed between live and earthed electrodes. The connections to the electrodes are periodically reversed so that each is alternately live and earthed; this increases the uniformity of heating in the stack. Preferably the boards are stacked in short spacer sticks to delay the escape of steam from intermediate boards in the stack and reduce surface checking. The escape of steam from the top and bottom boards of the stack to be dried can be delayed by using top and bottom covering boards treated with a liquid substantially unaffected by radio-frequency heating.

Abstract: A process for drying solid wood, particularly in the form of planks or semifinished products, by means of superheated steam is described.The main feature of the process is to comprise superheating surges for heating the wood above 100.degree. C. alternating with cooling surges for cooling the wood below 100.degree. C., in order to improve the plasticization of the wood during the entire drying process.

Abstract: A method for treating whole logs to prevent them from splitting as they are dried to a desired moisture content. Whole green logs are placed in a pressure vessel which is sealed. Preferably the logs are debarked before they are placed in the vessel, but they may be debarked after their removal therefrom. Steam is thereafter injected into the vessel until the wood throughout the logs has reached a temperature within the range of about 190.degree.-240.degree. F., while condensed water and other fluids from the wood are drained from the vessel. Subsequently the pressure in the vessel is released at a rate slow enough that no significant collapse of the wood within the logs occurs, and when the logs are cool enough to handle they are removed, debarked if necessary, and dried in a room whose relative humidity is maintained not less than about 45% until the logs have reached a predetermined moisture content.

Abstract: Apparatus and process for treating wood and other fibrous materials within a hermetically sealed, heat insulated chamber comprising means for applying a predetermined mechanical pressure to said fibrous materials, means for controlling the conditions within said chamber whereby steam is generated in the center of said fibrous materials, and means for subsequently removing said steam; means are additionally provided for staining, finishing, fireproofing, laminating, forming, shaping, and increasing the density and tensile strength of said fibrous materials.

Abstract: A method of kiln drying timber in a kiln chamber by directing a restricted jet of hot air or gas over timbers in the stack and cyclically varying the direction of the jet in order to play the heated air or gas over the whole of the stack. A kiln for performing the method comprises a generally cylindrical kiln chamber having an elongate nozzle along one wall parallel to the axis of the cylinder and pivotable about an axis parallel to the axis of the cylinder; a group of fans arranged in a row parallel to the axis of the chamber draws gas or air from within the chamber and directs it along conduits one surface of which is a heat exchange surface to the nozzle where it is directed back into the kiln chamber. The heat exchange surface of the conduits may be heated in any known way, by means of heaters or by forming it as one surface of a water jacket.

Abstract: A reaction vessel for regenerating particulate adsorbents has a bottom outlet and top inlets for admission of the adsorbent to be regenerated by being heated to a regeneration temperature, and for a particulate regenerating material at a temperature above the regeneration temperature. The mixture of the adsorbent with the regenerating material forms a bed in the reaction vessel and is continuously withdrawn through the outlet so that the bed descends toward the latter and is replenished from above under the formation of a cone at the upper region of the bed. A plurality of tubular baffles coaxially surrounds the inlets which are also coaxial with one another, each of the tubular baffles penetrating into the bed in the region of the cone and retards the flow of the particles of the mixture down the slope of the cone in that the particles must pass underneath the baffle to flow to the next baffle.

Abstract: The invention provides a chamber, or tank, sealable by closing its cover and in which green lumber, agricultural products and/or earthenware to be dried can be artificially dried to the desired degree, or in which they can be provided with insect-proofing and/or rot-proofing treatment or coloring treatment as well as said drying treatment.The chamber has means for measuring the degree of drying or moisture content of the material to be dried, and means to heat, moisten or dampen the inside of the chamber and to reduce the inside pressure of the chamber.Such processes (drying, moisturizing and pressure reduction) are carried out in several steps, thereby changing the atmospheric conditions in the chamber in phased programs. This control is performed by checking the drying condition of the material as it is in the chamber. Moreover, unmanned operation is thereby easily secured by converting the drying condition to electrical signals and automatically setting the running conditions with those signals as input.

Abstract: Procedure for drying an organic material, most suitably one which is xylogenic (originating from wood), such as veneers for instance, by means of hot circulating air which circulates in the drying space from a blower to a heat exchanger, passes by the organic material, collecting the water vapor released by the material, and further to the blower, whereafter part of the air/water vapor mixture is conducted through a vent, throttled by means of a damper, into the free atmosphere. In the drying space, the temperature and pressure are monitored, and the damper is used to control the vented air quantity in such manner that there is continuously a given, predetermined vacuum in the drying space.

Abstract: A vacuum drying kiln has a drying chamber in which, in use, is placed timber to be dried and around which is a surrounding water jacket through which is circulated a heat exchange fluid which derives its heat by flowing through the secondary circuit of a heat exchanger through the primary circuit of which is pumped a mixture of air and water vapor drawn by a vacuum pump from the interior of the drying chamber. The kiln is operated cyclically through successive heating and evacuation phases and the vacuum pump is one utilizing a secondary fluid to effect pumping, the characteristics of this secondary fluid being that it is immiscible with water and has a low specific heat so that it encourages the condensation of the water vapor in the primary circuit of the heat exchanger by undergoing large temperature variations for small changes in heat content.

Abstract: A method and apparatus for controlling the drying of lumber and the like. During drying, the weight of a lumber charge is continuously monitored to indicate both total weight loss and rate of weight loss. These data are employed, either automatically or manually, to adjust drying action so as to control the moisture-removal rate, and to stop drying action when the desired terminal dryness is reached. Multi-point weight monitoring is used to provide localized moisture-content data. The latter data is used further to adjust drying action so as to promote uniform moisture levels throughout a charge during drying.

Abstract: A method and apparatus are disclosed for drying materials by contact with a drying gas consisting essentially of internally generated superheated drying steam above 212.degree. F., to vaporize the water in the material and remove it to produce the steam used for drying. A minor portion of steam is removed from the drying gas and discarded to maintain pressure equilibrium. The drying steam is produced within the drying chamber from water evaporated from the material being dried and is either heated within the drying zone where it is in contact with the material or removed from the drying zone, heated to form superheated steam, and returned to the drying zone for contact with the material during drying. A wood veneer dryer employing the invention is described as well as an apparatus for drying particulate material.

Abstract: The invention relates to a settling and drying apparatus composed of a settling tank in whose center is immersed a tube of an annular supply tank with central overflow comprising, coaxially, an extractor tube plunging to the bottom of the tank and surmounted by a drying tank.

Abstract: Veneer is dried by passing a veneer sheet by at least one set of spaced orifices or nozzles through which jets of superheated organic solvent vapor are directed against one or both of the bottom and top sides of the sheet. After impinging on the wood surface, the spent solvent vapor plus moisture and other volatile substances from the wood passes to a condenser where the solvent is separated and passed to a vaporizer and superheater for recycle to the process. In an optional variation, a preliminary extraction of the entering veneer by condensing solvent is achieved by adjusting the flow rate or temperature of the solvent vapor in the fore part of the drying apparatus. Apparatus for carrying out the veneer drying process with means for recovering and recycling spent solvent is shown.

Abstract: Systems for drying moisture entrained particulate material include a pressurizable chamber for receiving the material to be dried, and a fluid bed device disposed within the chamber for moving the material from an inlet through the chamber to an outlet. A heat exchanger heats the material to be dried flowing into the chamber. Compressing apparatus in the form of a blower pump draws air from the chamber to remove moisture from the material and for compressing the moisture entrained air for heating it. The heated moisture entrained air is guided from the compressing device to the heat exchanger for supplying heat to it. In one form of the invention, a second heat exchanger disposed near the oulet of the chamber cools the material prior to its leaving the chamber for retaining heat within the system. The air flowing from the second heat exchanger is heated by conduction from the blower pump prior to entering the pressurizable chamber for an even more efficient operation of the system.

Abstract: A method of improving the stability of primarily dry seeds which comprises a step of secondary drying of the seeds at a first temperature of from 50.degree. to 60.degree. C and under a vacuum of at least 100 microns Hg for from 30 minutes to 24 hours wherein the secondary drying is carried out in four or five steps at temperature increments of from 10.degree. to 15.degree. C. increasing successively from an initial temperature of from 50.degree. to 60.degree. C to a final temperature of from 90.degree. to 100.degree. C.

Abstract: A process for drying wood at subatmospheric pressures comprising a phase in which the wood is heated up in a sealed environment, is characterized in the fact that this heating-up phase comprises the operations of:I. introducing into said closed environment an operative fluid which is capable of imparting, moisture to the wood, causing this fluid to cycle repeatedly around a closed circuit in such a way that in every cycle, the fluid passes through a pile formed by the pieces of wood, and then returns without passing through the pile;Ii. supplying thermal energy to the operative fluid in such a way that the thermal content of the fluid increases overall in each cycle at a diminishing rate until the fluid reaches a substantially steady cyclical state in which there is no overall increase in its thermal content in each subsequent cycle.

Abstract: Apparatus and process for curing and/or treating wood items such as logs and cut lumber. In one form of the invention a baffle is medially interposed in a closed chamber, separating such chamber into positive and negative pressure compartments, such baffle clamping to the lumber to be cured. A vacuum pump applies pressure to one compartment within the vessel and vacuum to the remaining compartment of the vessel, for the purpose of aiding with the withdrawal of resin from the wood. A resin solvent or diluent is introduced at the pressure side for rendering less viscous the resin contained in the lumber, to thereby aid in its travel through and withdrawal from such lumber. The return circuit to the vacuum pump includes a resin collector and also a water-moisture trap. Other fluid additives such as fireproofing and anti-rotting fluid materials may be introduced in the pressure side of the vessel.

Abstract: Apparatus and process for treating wood and other fibrous materials within a hermetically sealed, heat insulated chamber comprising means for applying a predetermined mechanical pressure to said fibrous materials, means for controlling the conditions within said chamber whereby steam is generated in the center of said fibrous materials, and means for subsequently removing said steam; means are additionally provided for staining, finishing, fireproofing, laminating, forming, shaping, and increasing the density and tensile strength of said fibrous materials.

Abstract: Wood is impregnated with a solution of a preservative in a vaporizable, water-free, organic solvent and thereafter treated with a warm high-boiling oil composition under subatmospheric pressure conditions effecting evaporation of the solvent used in the impregnation step.

Abstract: Surface accumulation of crystalline treating agents, such as pentachlorophenol, and water insoluble extracted wood resins, developed during solvent removal after pressure impregnation, and readily removed by contacting the so treated wood while still in a heated condition with liquid solvent thereby causing ebullient boiling of the solvent at the surface effecting a cleaning action and dissolution of the removed crystalline agent in the body of the solvent. If the solvent is contacted with the hot surface and removed immediately following cessation of ebullient boiling no additional post treatment is necessary to remove solvent from the surface of the wood. If desired a light (short duration) post steaming, however, may be employed without adverse effect, i.e., bringing more treating agent to the surface which would again permit crystallization of the agent at the surface.

Abstract: A process and an apparatus for decreasing the moisture content in wood which comprises the step of maintaining the wood in a vapor atmosphere made essentialy from sap until the center of the wood has substantially reached the temperature of the vapor, then gradually raising the temperature of the vapor atmosphere to a degree and during a time sufficient to bake the resinous substances inside the wood and reduce the moisture content to a predetermined percentage and subsequently reducing gradually the temperature of the housing to the temperature of the vapor, wherein the vapor is maintained during the process at a pressure slightly above the atmospheric pressure. The wood boards are disposed vertically to form vertical channels and the source of heat is located to obtain a vertical circulation of the vapor through the boards.