US2884707A

US2884707A - Method for drying wood

Info

Publication number: US2884707A
Application number: US475369A
Authority: US
Inventors: Sandback Jonas
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-01-18
Filing date: 1954-12-15
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

May 5, 1959 sAN Ac 2,884,707

METHOD FOR DRYING woon Filed Dec. 15, 1954 3 Sheets-Sheet 1 28 29 25 Fig.1

May 5, 1959 JfsANbBAcK 2,884,707

METHOD FOR DRYING woon Filed Dec. 15, 1954 3 Sheets-Shet 2 May 5, 1959 J. SANDBACK METHOD FOR DRYING WOOD 3 Sheets-Sheet 3 Filed Dec. 15, 1954 2 ,707. 1 7 METHOD FORDRYING WOOD j Jonas Sandbiick, LjusdaL Sweden I Application' Decemb er ls, 1954, Serial No. 475,369 Claims priority,application Sweden January 18,1954 '4 Claims. or 3436)' The invention relates to a method for drying wood.

, Itis known to dry wooclby means ofa mixture of air and combustion gasesgthe wood being placed in stacks in a. drying chamber, where the gas mixtureis introduced and whirled around by a fan arranged in the chamber. The present invention is based on .the principle of using such a gas mixture as drying mediumandhas for its object an improved method which permits of a more efiective utilization of the heat content of the gases at the same .time as the surface of the wood is preserved. The method comprises passing the wood and a mixture of air and combustion gases in countercurrent through a tunnel-shaped drying chamber, the gas mixture introduced into said chamber being held at'a temperaturebelow 70.- C.

Stacked wood is fed through one end of the tunnel and is successively dischargedat the other end, where the drying gas is preferably introduced. 'As mentioned, the temperature of the incoming gas must not exceed 70? C., as otherwise undesired reactions may. occur. rule itis possible to work with a temperature of 30-40 C. of the incoming drying gas; lower temperatures cause a deteriorationof the dryingetfect. g p

The amount of drying gas and its speed of flow through the tunnel are preferably so-adjusted that the temperature of the gas sinks to the dew point at the tunnel end 'where the wood last introduced is located. Thus, a condensation of steamon .the,cold Wood takes placeat this end, and the wood is warmed'by the heat of condensation freed. Tests have shown that the woodmay even be heated to ,a temperature exceeding the gas temperature prevailing in the cold tunnel zone. I

In this way itis possible to effectively utilizethe, heat content of the drying gas introduced. It is ideal if the gas escaping from the colder zone of the tunnel, while maintaining a good drying effect in .the'warmerzone, has about the same temperature, as'theisurrounding atmosphere. Provided that the drying tunnel is well heat insulated, the heatcontent of the combustion gases is .in such-case almost fully utilized for the drying process,

Besides a good heat economy, however, the method accordingto the invention has the further effect that condensible or soluble substances contained in or added to the gas mixture are absorbed by the layer of condensation water formed on the surface of the still cold wood, which facilitates the penetration of said substances into the outer layer of the wood.

Of course, a great amount of carbon dioxide is always contained inthe combustion gases, and ifthefuel con sists of an oil having a normal sulphur content. also a certainamountof sulphur dioxide is obtained..f,.,IBoth these gases, particularly thesulphur'dioxide, are soluble in water. The ,carbondioxide has .a suffocating effect on most living organismsand retards iidri-asiinilating fungi, while the sulphur dioxide acts disinfecting as well as bleaching. If the h'eatha's been generated bi "combustion of a fuel with little or'no sulphur co'ntentfsuch as wood, sulphur in some suitable rorrnmay be added to the fuel 6i introduced infotlifiame orabunier."

2,884,707 7 Patented May 5, 1959 As the=wood-is slowly moved towards the warmerzone of-the-tunnel, -part of the absorbed carbon-dioxide and a stances either -directly to the hot combustion gases-or to theless hot mixtureo f air and combustion-gases-which is-tobe introduced into the dryingtunnel. For killing insects and larvae for instanee- DDT-preparations may be added'tosaid gas-mixture.

'- A The wood introduced into the drying tunnel is preferably stacked in the customary way, ie the layers of boards are laid on-crossers, so that sufficient spaces are obtained for the passage of the drying gasin the longitudinal d-irectionof thetunneh As t he wo od is usually advanced in its longitudinal direction thepassage area is furtherincreased, if perforated'crossersare used.- In any'case, it lS-l essential that the "space between thesides of the wood stacks and the surrounding tunnel is kept as narrowas possible so thatthe greater part of the drying gas is towed to pass through the stacks.

Asa'

The method accordingto the invention will be described more closely below with reference to the accom panying drawings which show'diflerent embodiments of a dryingplant t Fig l shows adryi ngtunnel with a heating aggregate in horizontal section.

Figs. 2 4 show in cross section different embodiments of drying tunnels. i

Fig. 5 shows, ln'horiz on tal section, a drying plant "with arrangement for pre-heating the drying air.

Fig 6 shows a modification of the' plant in Fig.- 5.-

- Figs. 7 'and 8 show two different, modified embodiments of the drying tunnel in Fig. l. Y

-Fig 9 shows; as seen from above, a view of a plant with arrangement for circulation of'the drying gases.

Fig. 10 shows, as seen from above and partly in-horizontalsection, another plant with'gas circulation, and

Fig. 11 shows a vertical section along the line -Xl- XI in-Eig.-10; I f I The drying tunnel 12 shown in Fig.1 has preferably a rectangular cross section and such a length that it can simultaneously receive a great number of wood stacks l3' introduced after each other. The wood is fed'through the right end of the tunnel (in Fig. l) and is discharged through-the left end. The two ends of the tunnel may be closed byfgates" or

shutters

14, 15. M p I As mentioned above, the space between the wood stacks and-the surrounding walls of the tunnel must not have such a width that the drying gas preferably seeks that way.- On the other hand, said space should he dimensioned to admit a sufficientamount of drying gas to pass wood layers.

for drying the outermost portiorisof the wood. Therefore, it-is suitableto keep the space around the stacks of the same; agnitude'as the space between the different -The-transporting means within the tunnel maybe of many: difierentkinds, and Figs. 2-4 show only some errrbodirnents. According to Fig. 2 the wood "stacks are advanced on rollers 16 rotatably journaled immediately above-thebottom of the tunnel crosswise to its longitudinal' direction According to Fig. 3;th e wood isloaded on a wagon 17,- the wheels ofwhich runon :two rails 18. To prevent an -=undesi-rablepassage of drying gasrunder the Wagonsthe latter are provided with screens 19 which wood is stacked on a suspended wagon 20 carried by rollers 21 which run on rails along the sides of the tunnel immediately below the ceiling. Hinged screens 22 may be suspended from the ceiling to prevent that too great an amount of drying gas passes above the stacks.

An aggregate for producing drying gas is connected to the left end of the tunnel, 'i.e. the discharge end for the wood. A burner 23 for liquid or gaseous fuel, for instance fuel oil or generator gas, is arranged to direct a flame into a combustion chamber 24, the Walls of which are preferably made of heat resistant brickwork and are well heat insulated. The burner may be of a usual type with or without a separate air fan.

The combustion chamber 24 has an air intake 25 provided with a filter or a fine meshed, net at its outer end toprevent the sucking-in of solid objects. A damper 26 is provided for controlling the amount of air. The combustion chamber opens into a mixing chamber 27 having a larger air intake 28 with a filter 29 and a controlling damper 30.

The mixing chamber 27 is connected to the suction side of a fan 31 and'a further filter 32 is inserted in the connection. The fan is driven by a motor 33 the speed of rotation of which may be controlled for determining the amount of drying gas to be introduced into the tunnel. Instead or besides, adjustable dampers may be arranged for the same purpose. The outlet of the fan is connected to a pressure chamber 35 through a fire shutter 34. The pressure chamber communicates with the tunnel 12 through a lattice-work 36 having fo'rits purpose to effect an even distribution of the gas.

The plant is operated in the following way. As mentioned above, it is presupposed that the wood stacks are positioned to leave free passages for the drying gas in the longitudinal direction of the tunnel. The stacks are introduced through the right end of the tunnel (Fig. 1) and are advanced stepwise to the left, one stack length at a time, so that a new stack is introduced each time a dried stack is discharged through the left tunnel end. During the drying process the gates 15 at the discharge end must be closed so that the drying gas is forced through the wood stacks. The flow resistance in the stacks is rather great and, therefore, the fan 31 should be capable of producing a pressure which, in dependence on the length of the tunnel and the free area of flow, may amount to 50-100 mm. water column or more. At the intake end of the tunnel the gates 14 may be kept open to permit the gas to escape freely, although a separate gas outlet may be arranged. Drains may be provided in the bottom of the tunnel for removing the condense water formed in the colder tunnel zone.

A pipe socket 37 is connected to the mixing chamber 27, and two other pipe sockets 38, 39 open into the combustion chamber 24. These pipes are intended for addition of disinfecting, preserving and/or bleaching agents. The inlet 37 is preferably intended for highly volatile preparations which evaporate at a moderate temperature, while the inlet 38 is intended for less volatile preparations. The inlet 39 may for instance be used for such additions as should undergo an oxidation process.

The damper in the air intake 25 to the combustion chamber 24 is adjusted to give the gas mixture leaving the combustion chamber the desired temperature. The temperature should preferably not exceed 400 C. By adjusting the damper 30 fresh air is introduced into the mixing chamber 27 in such an amount that the drying gas leaving said chamber is given the temperature most suitable for the drying in each separate case. As mentioned, this temperature should not exceed 70 C. A heat responsive member may be inserted in the pressure chamber 35 to close the fire shutter 34 by means of a servo-mechanism, in case the temperature should rise too high.

All adjusting operations required for obtaining a desired amount of drying gas at a desired temperature,

such as controlling the fuel supply to the burner, adjusting the dampers and the number of revolutions of the fan, may be performed automatically by regulators which are actuated by indicating members mounted at suitable places. As such devices are known per se and do not constitute any part of the invention, they need not be more closely described.

In the embodiment shown in Fig. 5 the tunnel is divided into a drying zone 40, to the right, and a cooling zone 41, to the left. The two zones are separated by a mova'blescreen or curtain 42. The doors 15 at the discharge end of the tunnel are kept open to let in fresh air which passes, in counterflow, the warm wood coming from the drying zone,.whereby said wood is subjected to a secondary drying and cooling before being taken out of the tunnel. The air thus pre-heated is drawn off at the inner end of the cooling zone through a tube 43 replacing the air intake 28 to the mixing chamber 27 in Fig. 1. Otherwise, the device for producing the drying gas mixture is exactly the same as the one described above. The pressure chamber is connected to the drying zone of the tunnel immediately to the right of the screen 42. A considerable saving of heat is thus achieved by supplying pre-heated air to the mixing chamber.

Fig. 6 shows an embodiment difiering somewhat from that in Fig. 5. A fan 44 is connected to the discharge end of the tunnel 12 to force fresh air through the cooling zone. The doors 15 should be kept closed. No screen is inserted between the two sections of the tunnel, but a tube 45 connects the middle of the tunnel with a heating unit being constnlcted substantially as described above. The previous mixing chamber is here replaced by a so-called compensating chamber 46 from which control the amount of cooling air supplied.

As the flow resistance may be rather great in long tunnels, it may sometimes be suitable to mount fans at intervals within the whole tunnel. Such an arrangement is shown in Fig. 7. The fan 49 is movable into a pocket 50 at the side of the tunnel 51 so as to leave the passage free when the stacks are to be advanced. Normally the pocket is closed by a hinged shutter 52. According to another embodiment, a fan 53 is mounted stationary in a similar pocket 54, and a screen 55 is inserted in the tunnel passage opposite to this pocket to force the air through the fan. Said screen 55 may be displaced through a corresponding slot in the roof of the tunnel.

Fig. 8 shows another embodiment in which a fan 56 for supplying drying gas is connected to the end of the tunnel 12 to blow in the longitudinal direction. The tunnel has a side aperture for removing the dried wood stacks, said aperture being closed by a door 57 during the drying process. This door may be pushed aside, as indicated by dash lines, and the Wood stacks are discharged transversely by means of a wagon of some kind.

In large plants a number of separate drying tunnels may be connected to a common large aggregate producing drying gas. It is also possible to produce only hot gases in a common aggregate, in which case each tunnel has its own mixing chamber with fans for supplying drying gas having the desired temperature. Alternatively, a large tunnel may be fed with drying gas from several small aggregates. Of course, these arrangements may be varied to a great extent within the scope of the invention.

At certain occasions and weather conditions it may be advantageous to use a drying gas having a higher relative humidity than the one obtained solely by mixing with fresh air. One way of raising the humidity is to add a spray of water which evaporates in the hot gas-air-mixture. Another way is to return a portion of the moist gas mixture escaping from the tunnel or to draw 01f a certain amount of drying gas at a point along the tunnel and to return that amount to the intake end. Thereby a good heat economy is obtained and any disinfecting or preserving substances contained in the drying gas are concentrated and more fully utilized.

A plant for carrying out the modified method indicated above is shown in Fig. 9. The plant comprises three parallel tunnels 12a, 12b, 120 having a common hot-air aggregate, the fan 31 of which is connected to a drum 58 divided into three branches, one leading to each tunnel. The hot-air aggregate and the fan are enclosed in a house 59. An underground channel 60 communicating with the tunnels through apertures 61 in their floors is provided under the opposite ends of the tunnels i.e. the intake ends for the wood. One end of the channel 60 leads to a funnel 62 and its other end opens into the house 59 where an under-pressure is prevailing owing to the suction of the fan 31. Thus, moist gases are sucked through the channel 60 into the house 59 to flow into the hot-air aggregate through the various intake openings thereof. The outlet opening 63 of the channel 60 is preferably directed towards the hot-air aggregate to cause the moist gas to hit the hot surface. directly so as to prevent condensation and decrease of the relative humidity of the gases. It is suitable to provide dampers in the inlet openings 61 of the channel for controlling the amount of circulating gases.

In the plant for circulating drying gas shown in Figs. and 11 it is possible to keep different temperatures and moisture contents of the drying gases introduced into the three tunnels 64a, 64b, 640. Above each tunnel there is a channel 65 separated from the tunnel by means of a ceiling 66. Apertures 68 controlled by dampers 67 are provided in said ceiling. A house 69 is divided into three difierent chambers 70 each communicating with one of the channels 65 through openings controlled by dampers '71. Each chamber has an intake 72 for fresh air controlled by a damper. A fan 73 in each chamber 70 blows drying gases into the left end of the under-lying tunnel. A drum 74 leading from the hot-air aggregate in the house 59 has valve-controlled outlet openings 75 in the chambers 70 in front of the three channels 65.

Owing to the suction of the fans 73 under-pressure is prevailing in the channels 65. Therefore, if one of the dampers 67 is opened, drying gas from the underlying tunnel flows into the channel 65 towards its left end, where it is mixed with hot air from the drum 74. The gas mixture enters the chamber 70 connected to the channel in question and is there further mixed with air sucked from the outside. The proportions are controlled by means of the different dampers.

The humidity of the drying gas supplied by each fan 75 is controlled by means of the dampers 67. Thus, if only the damper located at the right end of the tunnel is opened, the greatest addition of moisture is obtained. On the other hand, if a damper 67 at the middle of the tunnel is opened, the moisture of the returned drying gas is lower, and at the same time a smaller amount of drying gas flows through the right section of the tunnel. In this way the drying effect may be controlled according to the requirements in each separate case.

What I claim is:

1. A method of drying wood, comprising passing the wood through a tunnel-shaped drying chamber, introducing a mixture of air, combustion gases and sulphur dioxide into the tunnel at a temperature below C., causing said gas mixture to pass in counterflow to the wood and adjusting the temperature and speed of flow of the gas mixture in response to variations of the dew point of the mixture at the tunnel end where the wood is introduced to obtain a condensation of steam on the wood last introduced into the tunnel, whereby the sulphur dioxide present will be dissolved in the condensate to form a disinfecting solution on the surface of the wood.

2. A method of drying wood, comprising passing the wood through a tunnel-shaped drying chamber, producing combustion gases containing sulphur dioxide by burning fuel oil containing sulphur and supplying air to said gases to get a gas mixture having a temperature below 70 C., introducing said gas mixture into the tunnel and causing it to pass in counterflow to the wood, the temperature and speed of flow of the gas mixture being adjusted in response to variations of the dew point of the mixture at the tunnel end where the wood is introduced to obtain a condensation of steam on the wood last introduced into the tunnel, whereby the sulphur dioxide present will be dissolved in the condensate to form a disinfecting solution on the surface of the Wood.

3. A method of drying wood, comprising passing the wood through a tunnel-shaped drying chamber, introducing into the tunnel at a point remote from its ends a mixture of air, combustion gases and sulphur dioxide having a temperature below 70 C., causing said gas mixture to pass in counterflow to the wood, introducing fresh air into the tunnel end, where the wood is discharged, and causing it to pass in counterfiow to the dried wood whereby it is preheated, withdrawing this preheated air from the tunnel and supplying it to combustion gases to obtain the gas mixture to be introduced into the tunnel, and adjusting the temperature and speed of flow of the gas mixture in the tunnel in response to variations of the dew point of the mixture at the tunnel end where the wood is introduced to obtain a condensation of steam on the wood last introduced, whereby the sulphur dioxide present will be dissolved in the condensate to form a disinfecting solution on the surface of the wood.

4. A method of drying wood, comprising passing the wood through a tunnel-shaped drying chamber, introducing into the tunnel a mixture of air, combustion gases and sulphur dioxide having a temperature below 70 C., causing said gas mixture to pass in counterflew to the wood, whereby it is preheated, withdrawing moist gases from some point along the tunnel and supplying them to the gas mixture to be introduced into the tunnel, and adjusting the temperature and speed of flow of the gas mixture in the tunnel in response to variations of the dew point of the mixture at the tunnel end where the wood is introduced, to obtain a condensation of steam on the wood last introduced, whereby the sulphur dioxide present will be dissolved in the condensate to form a disinfecting solution on the surface of the wood.

References Cited in the file of this patent UNITED STATES PATENTS Re. 8,240 Johnson May 21, 1878 105,720 Parrott July 26, 1870 170,928 Andrews Dec. 7, 1875 1,672,326 Kobiolke June 5, 1928 2,040,884 Somes May 19, 1936 2,706,344 Vaughan Apr. 19, 1955 2,707,695 Courtier May 3, 1955