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Title:
DRYING CHAMBER DEHUMIDIFIED BY DIFFUSION
Document Type and Number:
WIPO Patent Application WO/2021/010876
Kind Code:
A1
Abstract:
A drying air flow circulating within a drying chamber is dehumidified via diffusion against an outdoor air flow via frames covered with multi surface cloth open to diffusion. Double frames are forming flat boxes placed in the drying air flow along a side channel and perpendicular to its back wall. The outdoor air flow is driven within the boxes concurrent with drying air flowing between the boxes. The boxes are connected via bottom channel, top channels, outdoor channel and fans to the outside via openings in the back wall

Inventors:
STEN ZEILON (SE)
Application Number:
PCT/SE2020/000019
Publication Date:
January 21, 2021
Filing Date:
July 07, 2020
Export Citation:
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Assignee:
ZEILON STEN (SE)
International Classes:
F26B21/02; F26B21/08; F26B9/06
Domestic Patent References:
WO2013158009A12013-10-24
Foreign References:
SE1700043A12018-08-29
SE1400580A12016-06-11
SE0900767A12010-09-14
SE1550341A12015-09-22
US20090158615A12009-06-25
FR2644855A11990-09-28
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Claims:
Claims

1. A drying chamber (1) comprising a fan/heater channel (12), a first side

channel (13), a drying goods (14) and a second side channel (15) where the drying chamber (1) is arranged to circulate a drying air flow (11) through the fan/heater channel (12), the first side channel (13), the drying goods (14) and the second side channel (15) and is arranged with drying air being

dehumidified against outdoor air via vapour diffusion through frames (2) covered by multi surface cloth open to diffusion, characterized in that it comprises a number in the drying air flow installed flat boxes (22) formed by doubled frames (2), whereby the boxes (22) are intended to dehumidify the drying air flow (11) via vapour diffusion to an outdoor flow (3) driven within the boxes (22),

whereby the outdoor flow (3) is by openings (8) in the drying chamber cover fan driven from the outside, driven through the boxes (22) concurrent with the drying air flow (11) driven between the boxes (22) and back to the outside, whereby the boxes (22) are preferably installed along the bottom (16) of either side channel (13, 15) and perpendicular to its back wall (17) with box bottoms being connected to a bottom channel (7) open to the outside and box tops being connected to top channels (4), openings (8), an outdoor channel (5) and one or more reversible fans (6).

2. A drying chamber (1) according to claim 1, characterized in that the boxes (22) are made with the frames (2) inclining against each other whereby is obtained varying distances (a) between the frames (2) being dimensioned in relation to chosen mass flows of the drying air (11) and the outdoor air (3), whereby cc- distances between the boxes (22) and breadths of frames (b) are being chosen so that pressure drops (p) in the drying air flow (11) and the outdoor flow (3) along either sides of the frames (2) are essentially equal.

AMENDED CLAIMS

received by the International Bureau on 28 September 2020 (28.09.20)

1. A drying chamber (1) comprising a fan/heater channel (12), a first side

channel (13), a drying goods (14) and a second side channel (15) where the drying chamber (1) is arranged to circulate a drying air flow (11) through the fan/heater channel (12), the first side channel (13), the drying goods (14) and the second side channel (15) and is arranged with drying air being

dehumidified against outdoor air via vapour diffusion through frames (2) covered by multi layer cloth open to diffusion, characterized in that it comprises a number in the drying air flow installed flat boxes (22) formed by doubled said frames (2), whereby the boxes (22) are intended to dehumidify the drying air flow (11) via vapour diffusion to an outdoor flow (3) driven within the boxes (22), whereby the outdoor flow (3) is by openings (8) in the drying chamber cover fan driven from the outside, driven through the boxes (22) concurrent with the drying air flow (11) driven between the boxes (22) and back to the outside.

2. A drying chamber (1) according to claim 1 characterized in, that the boxes (22) are installed along the bottom (16) of either side channel (13, 15) and perpendicular to its back wall (17) with box bottoms being connected to a bottom channel (7) open to the outside and box tops being connected to top channels (4), openings (8), an outdoor channel (5) and one or more reversible fans (6).

3. A drying chamber (1) according to claim 1 and 2 characterized in that the boxes (22) are made with the frames (2) inclining against each other whereby is obtained vaiying distances (a) between the frames (2) being dimensioned in relation to chosen mass flows of the (hying air (11) and the outdoor air (3), whereby cc- distances between the boxes (22) and breadths of frames (b) are being chosen so that pressure drops (p) in the drying air flow (11) and the outdoor flow (3) along either sides of the frames (2) are essentially equal.

Description:
Drying chamber dehumidified by diffusion.

The present invention relates to a drying chamber with a drying air flow circulated through a fan/heating channel, a first side channel, a drying goods and a second side channel and dehumidified by vapour diffusion to an outdoor air flow through frames covered by multi surface cloth open to diffusion.

The manner in dehumidifying drying air by diffusion through said frames to an outdoor air flow replaces conventional air exchange technique with a large saving in energy and is known from my Swedish patent SE 524 353 C2, SE 538 976 C2 and SE 540 696 C2.

With conventional technique vapour is removed from the drying air with a replacement air flow with a thermal efficiency of ca 80 % in favorable conditions to ca 40 % in unfavorable conditions in form of low moisture content and low outdoor temperatures. In the new manner vapour is removed from the drying air with a thermal efficiency well over 90 % in these conditions.

Common to above writings is a part flow drying air being deflected from the main drying air flow in order to be dehumidified in arrangement with said frames and later on being remixed into the main drying air flow.

A first purpose with the invention is to radically simplify and improve the diffusion technique by skipping said part flow and arrangements for its flow channels and heat air fans and replace it with a direct contact between the drying air and said frames in the normal flow of the drying air.

A second purpose is to achieve concurrent flow of drying air and outdoor air along either sides of said frames with a minimum of pressure differences and thus achieve a minimum of air exchange between the flows, that is harmful to diffusion efficiency.

Said purposes are achieved by a drying chamber further characterized in that it contains a number in the drying air flow installed flat boxes formed by double said frames, where the boxes are intended to dehumidify the drying air flow by vapour diffusion against an outdoor air flow driven within the boxes.

The invention is described below in reference to the figures. Figure 1 shows in section a drying chamber with a closed drying air flow circulated through a fan/heatcr channel, a side channel, a drying goods and a side channel containing boxes. Figure la shows drying chamber with reversed air flows. Figure lb shows vertical section of a timber dryer. Figures 2 and 3 show in elevation and plan box installation in a side channel. Figures 4 and 5 concern calculation of pressure drops in air flows.

In reference to figure 1 is shown a drying chamber 1 in a section, that may be either horizontal or vertical. The chamber contains a drying air flow 11 circulated in a closed loop through a fan/heater channel 12, a first side channel 13, a drying goods 14 and a second side channel 15. In the drying air flow and preferably along the bottom 16 of one of the side channels 15 and perpendicular to its back wall 17 are installed flat boxes 22 formed by double frames 2 covered with multi layer, diffusion open cloth. The cloth covers suitably also the short sides of the boxes. The boxes are on the outside swept by the drying air flow. A concurrent flow 3 of outdoor air is driven inside the boxes. Driven by a vapour pressure difference vapour will diffuse through the frames 2 from the drying air 11 to the outdoor flow 3, that is heated by vapour condensing to fog and thus heated is saturated by vapour. As a vehicle for vapour transport of vapour out from the drying chamber 1 the flow 3 thus is utterly efficient. Sensible heat leaking through the frames into the box 22 is in order of ca 4% of latent heat of the vapour flow through the frames. The outdoor flow 3 is fan driven from the outside, through the boxes 22 and back to the outside by openings 8 in the drying chamber cover . In a preferred embodiment the bottom of the boxes 22 are connected to a bottom channel 7 open to the outside and the top of the boxes are connected to the outside by top channels 4, openings 8, an outdoor channel 5 and one or more reversible fans 6. Drying goods 14 may be any moist material naturally penetrable to a flow of drying air or arranged by mechanical means to shape air contact.

Examples are for instance timber, ceramics and food products on trays, falling grain in channels, falling liquids on sloping trays etc. In figure 1 is shown an outdoor air flow 3 driven through a box 22 concurrent with drying air flow sweeping along outside of boxes. Figure la shows same dryer with the drying air 11 being reversed and driven along the outside of the boxes 22. In accordance the outdoor flow 3 is reversed. Air flows 11 and 3 are driven concurrent in order to minimize air leakage across the frames.

In order to utterly minimize harmful air leakage across the frames 2 the boxes 22 are formed with the double frames 2 inclining against each other with an against the box bottom increasing flow area, further described below in relation to a timber dryer.

In reference to figure lb showing in vertical section a drying chamber 1 for timber as an example the invention is described more in detail. The drying goods 14 is 80 cbm timber with a mass flow 11 of drying air in order 150 000 kbm/h with a dry temperature +70°C and a vapour pressure ca 250 mbar. Drying rate is ca 300 kg vapour/h removed by a mass flow of outdoor air 3 in the order of 5 000 kg/h. Per cbm the outdoor air thus absorbs 60 g vapour, wherof 17 g is vapour condensed into fog heating the saturated outdoor air for instance +5°C/+39°C. The vapour pressure in the outdoor air will thereby under passage in the boxes 22 increase from 6 mbar to 70 mbar with average 38 mbar. With a diffusion factor in the frames 2 of 0.033 kg vapour/h, sqm, mbar a frame surface of 42 sqm will be needed according to formula : 300 kg vapour = 0.033 x 42 sqm x (250-38) mbar. The latent heat of the vapour thus removed from the drying chamber is 300x 0.67 = 200 kwh. The corresponding sensible heat loss over the frame area to the outdoor flow is in order= 42 sqm x 48 degrees x 4 /1000= 8 kwh indicating a process efficiency of 96 %. Figures 2 and 3 show plan and elevation of boxes 22 mounted in a side channel 15. The figures illustrate 7 boxes 22 with 14 frames 2 with breadth = 1.0 m and height = 3.0 m and with a total frame surface =42 sqm. The frames are pairwise inclined towards each other forming 7 boxes 22 with a chosen cc distance of 0.7 m. The drying air flow is reduced in speed from 6 m/s from the fan/heater channel 12 to zero at the bottom of the side channel 15. Compressed between the boxes the mean velocity is raised to 3m/s in a position A along the upper part of the boxes and to a mean velocity 1.6 m/s in a position B along the lower part of the boxes. In reference to figures 4 and 5 below is shown that with the box section correctly dimensioned in relation to chosen mass flows essentially equal pressure drops may be obtained in the flows of drying air and outdoor air along both sides of the frames 2. Thus a minimal pressure difference and air exchange across the frames is obtained, that is essential for the efficiency of the diffusion process.

Figure 4 shows in section three boxes 22 above described. Positions A and B represent medium state for upper and lower half of the rectangular flow space of the drying air flow 11 between the boxes and positions C and D corresponding data for the rectangular flow space within the boxes for a outdoor air flow 3 in order 800 cbm/h,box. Figure 5 is a part of a known diagram showing pressure drops p mm water/m of air flow in channels according to air velocity v m/s and equal diameter d=2ab/ a+b where a and b are dimensions in meter in a rectangular channel. In the figure 5 are plotted positions A-D. Data for position A are a=0.5 m, b=1.0 m, d = 0.66 m, v = 3 m/s and p =0.013. The same p-value will be obtained at position C on the other side of the frames 2 with the following data:

a=0.15 m, b=1.0 m, d=0.26 m, air flow 800 cbm/h giving v= 1.7 m/s, p = 0.013.

Data for position B are a=0,42 m, b=1.0 m, d= 0.58 m, v=1.6 m, p=0.004. The same p-value is obtained for position D on the other side of the frames with the following data: a=0.23 m, b=1.0 m, d=0.35 m, air flow 800 cbm/h giving v=l.l m/s, p =0.004. The calculation above shows that with chosen values of mass flows of drying air 11 and outdoor air 3, chosen cc distance between boxes 22 and chosen frame width b the varied distance a between the frames is a factor that may be dimensioned so that essentially equal pressure drops p are obtained in airflow 3 inside the frames 2 and air flow 11 outside the frames.

In reference to figure lb access to timber 14 may be according to following options.

Option 1: Access via door to first channel 13. The boxes 22 are installed along a solid back wall 17 in the second channel 15. Timber packs are loaded by truck.

Option 2: Access by door to the first channel 13 and by the second channel 15. Back wall 17 is a vertically sliding door with adapted boxes 22, channels 4,5 and 7. Vertical displacement is made space for in that a cope 12 over transition between fan/heater channel 12 and channel 15 is turned upwards a quarter turn and provides a shelter for the raised boxes 22.

Rail bound transport of timber through chamber.

With the invention diffusion technique is easily installed in both existing as new drying chambers, is easily dimensioned via number and sizes on boxes 22 for different drying conditions, is easily accessible for change of used frames 2 and is improved by the frame surface being exposed to the high vapour pressure in the drying air flow 11 and by air exchange between drying air 11 and open door air 3 being minimized.




 
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