A METHOD OF DRYING WITHIN A FILM ENCLOSURE

Abstract: A method of drying within a closed enclosure (5) comprises a flow (2) of a gas/vapour mixture circulated through a fan/heater aggregate (3), further to contact to a drying goods (1), from where a first part flow (21) is returned via channels (6) with negligible cooling effect to the fan/heater aggregate, while a second part flow (22) is driven to cooling contact to inside portions of the enclosure (5) and back to the fan/heater aggregate, where the part flows (21, 22) are blended.

Description: A method of drying within a film enclosure. The present invention relates to a method of drying a gas penetrable drying goods, essentially vapour tight enclosed by a load bearing platform and a thin film enclosure and compri¬ sing a flow of a gas/vapour mixture circulated in sequence through a fan/heater aggregate, to contact to said goods, to a cooling contact to inside portions of said film enclosure and back to said fan/heater aggregate. The invention relates to drying gas penetrable lots of lumber, grain material or other loosely packed or hanged material. The invention may also be used for evaporation of fluids dispersed on contact surfaces. The invention is an essential improvement on a drying technique, known from my Swedish patent 500368, where a drying goods is essentially vapour tight enclosed in a film cover.An enclosed gas/vapour mixture is circulated in contact to a heater , to the drying goods and to the inside of the cover. Vapour is con¬ densed against the cover, in its turn cooled to the outside. With the citied technique difficulties arise in order to dry efficiently energywise by lowered moisture content in the goods and the difficulties increase concurrently with a drying up of the goods. A reason for this is that the gas flow along the inside of the cover heats the film surface to temperatures exceeding the dew point in a meagre gas/vapour mixture. The purpose of the present invention is to essentially improve the drying process, especially for drying to low moisture content. This purpose is achieved by a method characterized in that it comprises a first part flow of said flow being returned after said contact to the goods directly via return channels with neglible cooling effect to said lan/heater aggregate and a second part flow driven from said contact to the goods to said cooling contact to the film enclosure and back to the fan/heater aggregate , here the two part flows are blended. The invention is described as follows in relation to the dra¬ wings, where figures 1 and 2 show plan and section of a dryer. Figure 3 shows the dryer opened for reloading of goods. SUBSTITUTE S Figure 4 shows in section exterior cooling of the dryer. Figures 5 and 6 show in plan alternate arrangements of gas circulation. By 1 is indicated a gas penetrable drying goods under drying essentially vapour tight enclosed by a load bearing platform 4 and a connected thin film enclosure 5. Inside the enclosure is enclosed a fan/heater aggregate 3 and channel forming ele¬ ments and the enclosure is filled by a gas/vapour mixture, preferably with a small overpressure in relation to the sur¬ roundings. Similar to citied drying technique a flow 2 is driven in sequence through the fan/heater aggregate, to contact to the drying goods, to cooling contact to inside portions of the film enclosure but with an essential differance in that a first part flow 21 is returned after contact to the drying goods directly via return channels 6 with neglible cooling effect to the fan/heater aggregate and in that a second part flow 22 after contact to the goods is driven to a cooling contact to the film enclosure and back to the fan/heater aggre¬ gate, where the part flows are blended. By appropriate positioned shield elements 34 the second part flow 22 is guided to skim cooling portions of the film enclo¬ sure from one end 51 to an opposite end 52, giving as long a pathway for the flow as is possible within the given enclosure. In relation to figure 4 an improved exterior cooling of the part flow 22 may be arranged by propulsion of an air flow 9 driven in counterflow fashion in a channel formed by mentioned portions of the film enclosure and an exterior confinement 92. The proportions in mass flows of the two part flows 21,22 may be regulated with regulating means 31, as illustrated by dam¬ pers positioned near suction openings 31,32 of the fan/heater aggregate. Compared to citied technique, where the total flow 2 is dri¬ ven to cooling contact to the film enclosure, the following is achieved: 1. Heat transfer to inside portions of the enclosure is accom¬ plished along an elongated pathway from one end 51 to a second °nd 52 with a sharply reduced mass flow. The tempe- SUBSTITUTE SHEET rature drop in the flow will increase sharply and so conditions for an energywise efficient dew deposition. 2. With continously lowered moisture content in the goods and a correspondingly lowered dew point in the gas/vapour mixture, the dew point is reached quicker and with less heat loss in the reduced mass flow 22. 3. Gas velocity in the flow is reduced, which will increase heat transfer resistance and temperature differance in the boarder layer gas/film surface. Surface temperature will decrease, further improving dew deposition. 4. The reduced film temperatures will reduce heat transfer to the surroundings as a token on an improved drying process . For an optimal drying process the proportions in mass flow of the two part flows 21,22 are regulated concurrently with lowered moisture content such, that the first part flow 21 is increased and the second part flow 22 is decreased and consequently will have an increased temperature drop. Various ways to orginize the flow pattern of the flows 2,21 and 22 are exemplified in relations to figures 1,2,5 and 6. Confinements with neglible cooling effect for mentioned return channels 6 and for inlet channels 7 for the flow 2 into the goods may be arranged with splitting the goods into groups of lots 11, with parts of the film enclosure inflated against exterior insulators 8 and with interior shield elements 34. In referance to figures 1 and 2 two lots 11 form an inlet channel 7 for the flow 2, while two heat insulated channels 6 on the outside will guide the first part flow 21 to the fan /heater and the second part flow to mentioned end 51 of the enclosure 5. In referance to figure 5 two lots 11 form a return channel 6 for the first part flow 21 and an outlet for the second part flow 22 towards mentioned end 51 of the enclosure 5. Heat insulated inlet channels 7 for the flow 2 are connected to inlet openings in the goods along the outside of the lots. SUBSTITUTE SHEET In referance to figure 6 four lots 11 form in intermediate spaces two inlet channels 7 for the flow 2 and one return channel 6 for the first part flow 21. Heat insulated spaces along the outsides of the outer lots serve as return channels for the first part flow 21 and as outlets towards one end 51 for the second part flow 22. In citied technique the film cover is in form of a plastic film tube knit together at the top under drying and assembled around a bottom platform under reloading the dryer. This procedure is for larger dryers, for instance for lumber lots, unpractible. Instead may be preferred in referance to figure 2, that the flexible film enclosure is hoisted to a height, that allows free handling of the lots 11. The bottom edge of the film enclosure is fixed to a frame 53, which under dry¬ ing penetrates into a waterfilled trough 41 in the platform 4, acting as a vapour lock and condensate receiver. Under reloading the frame is hoisted to a position marked 53' in referance to figure 4. o ensure a smooth folding of the film, it may slide on tube formed guides 42, anchored to the plat¬ form. For the film enclosure applies, that it should be essentially vapourtight, have a low heat resistance and have a good re¬ sistance to a drying climate, that is hot, very humid and often corrosive. As film material a thin, weldable plastic film with a high diffusion resistance to water vapour may be pre¬ ferred, such as polyetylene or ethylvinylacetate . Even if plastics deteriorate by time from heat/humidity exposure an exchange of the film enclosure may easily be made at neglible cost . An exterior shelter may shield the film enclosure 5 from ex¬ posure to wind,snow, rain and sun and also serve as framing for mentioned insulators 8 and as confinement for a mentioned cooling flow 9. This flow, absorbing the heat flux from the dryer, may be directed to heat reuse, for instance for local heating or for predrying wet drying goods. Within the scope of the invention the film enclosure may be fixed to an exterior or interior framework and be supplied with seal equipped doors for loading/unloading of the goods. SUBSTIT

Claims: CLAIMS 1. A method of drying a gas penetrable drying goods (1), essentially vapour tight enclosed by a load bearing platform (4) and a thin film enclosure (5) and comprising a flow of a gas/vapour mixture circulated in sequence through a fan/heater aggregate (3), to contact to said goods (1), to a cooling contact to inside portions of said enclosure (5) and back to said fan/heater aggregate c h a r a c t e r i z e d i n that it comprises a first part flow (21) of said flow (2) being returned after said contact to the goods (1) directly via return channels (6) with neglible cooling effect to said fan/heater aggregate (3) and a second part flow (22) of said flow (2) driven from said contact to the goods (1) to said cooling contact to the film enclosure (5) and back to the fan/heater aggregate, Where the two part flows (21,22) are blended. 2. A method according to claim 1 c h a r c t e r i z e d i n that proportions in mass flows between said part flows (21,22) may be regulated by regulating means (31). 3. A method according to claims 1 and 2 c h a r a c t e ¬ r i z e d i n that said second part flow (22) is guided by means of shield elements (34) to skim said cooling portions of the film enclosure (5) from one end (51) to an opposite end (52). 4. A method according to claims 1-3 comprising an exterior cooling flow (9) of air c h a r a c t e r i z e d i n that said air flow is driven in counterflow heat exchange to said second part flow (22) in a channel confined by said portions of the film enclosure (5) and an exterior confinement (92). 5. A method according to claims 1-4 c h a r a c t e r i¬ z e d i n that it comprises said goods (1) split into two lots (11) forming said return channel (6) and two inlet channels (7) for said flow (2) along the outside of the lots (11). 6. A method according to claims 1-4 c h a r a c t e r i¬ z e d i n that it comprises said goods (1) split into two lots (11) forming said return channel (6) and two inlet channels (7) for said flow (2) along the out- sde of the lots (11) . 7. A method according to claims 1-4 c h a r a c t e r i¬ z e d i n that it comprises said goods (1) split into four lots (11) forming with intermediate spaces two inlet channels (7) for said flow (2) and one said return channel (6) for said first part flow (21). 8. A method according to claims 1-7 c h a r a c t e r i ¬ z e d i n that it comprises said film enclosure (5) connected along its bottom edge to a frame (53), under drying penetrating into a water filled trough (41) and means to hoist said frame and enclosure to an upper position (53') under reloading the dryer. 9. A method according to claims 1-8 c h a r a c t e r i ¬ z e d i n that it comprises said film enclosure (5) under said hoisting sliding and folding around tube formed guides (42), anchored to the platform (4). 10. A method according to claims 1-9 c h a r a c t e r i ¬ z e d i n that it comprises said film enclosure (5) fixed to an exterior or interior framework and supplied with seal equipped doors. SUBSTITUTE

Inventors: ZEILON STEN OLOF, ZEILON, STEN, OLOF
Applicants: ZEILON STEN OLOF, ZEILON, STEN, OLOF
Application year: 1996
Main classification: F26B3
IPC codes: F26B9, F26B21