Drying and gas or vapor contact with solids – Apparatus – Houses – kilns – and containers
Patent
1994-05-27
1996-05-07
Gromada, Denise L.
Drying and gas or vapor contact with solids
Apparatus
Houses, kilns, and containers
34217, F26B 1900
Patent
active
055134440
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention is related to a method and a device for drying timber, elongated wood pieces, such as boards or planks, being treated with dry warm air during storage in a drying room.
1. Prior Art
In conventional drying of timber, the boards or planks obtained in the saw mill in question are placed on stickers while forming stacks, which are introduced into voluminous drying rooms, in which the stacks are subjected to treatment with dry warm air during a comparatively long time. More specifically, such board stacks are formed by a plurality of horizontally lying layers of boards, said layers being separated from each other by means of so called stickers in the form of long, narrow and non-expensive wood battens, which are orientated substantially perpendicularly to the boards. In each of the various board layers, the boards are placed at a certain distance to each other, so that the individual boards may be surrounded by the dry treatment air not only via the horizontal air gaps formed by the stickers but also via the spaces between adjacent boards in each layer. When the individual board stack has been located in the drying room sufficiently long to reduce the moisture content to a desired level, the stack is removed and transferred to a packaging station, where the stack is taken apart and the boards are arranged in layers immediately adjacent each other in packages surrounded by bands and often protected by plastic wrappings, whereas the stickers, to the extent that the same still are intact and useful, are transferred back to the sawmill for repeated sticking.
2. Disadvantages Associated to the Prior Art
One of several serious disadvantages in connection with the drying technique reflected hereinabove is that the boards in the uppermost layers of the stacks often is deformed during the drying process in view of the natural inherent tendency of the sawn-out wood piece to adopt, on heat treatment, the shape of growth of the tree, from which the board has been recovered. The boards in the uppermost layers of the stack are not influenced by the weight of any above-lying boards but may move more or less freely. This means that deformation during heat treatment may occur unrestrictedly in these board layers. The boards which are deformed in this way and which either has to be discarded or classified into a more non-expensive price class may form 2-10% of the entire contents of boards in the stack; this represents considerable economical losses.
Another disadvantage with the known drying technique is the need for providing stickers in the board stacks. Even if the formation of the stack before drying as well as the disintegration thereof after drying nowadays often is mechanised, both of these work operations are time and cost consuming. A considerable cost occurs in this connection due to the fact that the weak stickers easily break during the handling and must be replaced with new ones. The fact that the stickers are weak causes, for the rest, also that the air gaps between board layers in the stack become relatively narrow. This involves the consequence that drying air only with difficulty may flow through the stack. In other words rapid circulation of air through the stack is hampered.
A further disadvantage with the prior art is the bad usage of the heat energy required for carrying out drying. Although present modern drying devices are provided with heat exchangers of various natures for recovering heat energy from the moist exhaust air evacuated from the drying room, the drying devices consume, all the same, considerable amounts of energy, not only as a consequence of the peer circulation of air through the board stacks but also as a consequence of a lot of energy being wasted in the voluminous spaces occurring between the stacks subjected to drying. As a further example on the waste of energy which occurs it can be mentioned that the board stack when completely dried is taken out of the device immediately after completion of the drying and is placed outdoors to cool p
REFERENCES:
patent: 4261110 (1981-04-01), Northway et al.
patent: 4299036 (1981-11-01), Schregenberger
patent: 4663860 (1987-05-01), Beall
Gromada Denise L.
Tinker Susanne C.
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