Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Patent
1998-05-21
1999-08-24
Bennett, Henry
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
34493, 34497, F26B 700
Patent
active
059409843
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of drying wood in accordance with the preamble of claim 1.
Wood is dried industrially in so-called chamber dryers, by circulating air of given temperature and humidity around cross-laid layers of wood through openings defined between mutually superposed wood packs. The circulation air functions as a heat transferring and moisture transporting medium, wherein the heat required to dry the wood is supplied to the air through the medium of heating batteries, while the air is dehumidified by ventilation, for instance by diluting with cold, dry outdoor air.
Chamber-drying processes are at present controlled in many different ways. The principle on which drying climates are controlled is normally based on an established control schedule which allows air temperature and air humidity to vary in a predetermined manner throughout the whole of the drying process. It is known from experience, for instance, that the rate at which wood is dried must be constrained during the first stage of the drying process, otherwise the wood will split. Similarly, the chamber temperature is often increased during the latter part of the drying process, in order to maintain the slow migration of moisture in the wood when the water is in a bound state.
There are at present many different types of drying schedules, which are either proposed by the supplier of the wood dryer or which have been tested locally in individual sawmills and wood yards. However, controlling of the drying process has a serious principle deficiency, since the state of the circulation air is not controlled in a feedback manner, i.e. the process control does not take into account the prevailing moisture-emitting properties and the initial moisture quotient of the wood. This can result in serious errors of judgement on the part of the operator responsible for the drying operation with regard to choice of drying schedule, with subsequent damage to the wood or time losses as a direct result. Judgement errors will also result in energy losses, of course. Excessive drying of the wood will also result in splitting and excessive shrinkage of the wood.
The object of the present invention is to provide a highly attractive and advantageous method of drying wood. This object is achieved with a wood drying method that has the characteristic features set forth in the following claims.
The following advantages are among the many advantages that are afforded by the invention: Because the drying process is controlled as a feedback system, the drying process can be adapted very effectively to the true drying requirements of the batch of wood concerned, therewith resulting in optimal drying of the wood. The invention also enables the establishment of a reliable time-point at which a desired final moisture quotient (average moisture quotient) is achieved, therewith enabling the drying process to be automatically interrupted and switched to an optional conditioning phase. This will avoid, for instance, excessive drying of the wood with subsequent splitting and excessive shrinkage of the wood. The inventive drying method is also highly energy-saving. The invention thus affords both technical and economical advantages.
The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which FIG. 1 is a vertical sectional view of a drying chamber; FIG. 2 is a horizontal sectional view of the drying chamber shown in FIG. 1; and FIG. 3 is a time-temperature diagram illustrating the inventive wood-drying method.
FIGS. 1 and 2 illustrate an example of a wood-dryer 1 with which the inventive method can be applied. The illustrated drying chamber 1 has a construction typical in the field and includes fans 2 and heating batteries 3. In addition, the chamber naturally also includes a floor, walls, ceiling and baffles for guiding circulating drying air through a batch of wood 10 to be dried in a desired manner. The batch of wood 10 will normally comprise a plurality o
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Bennett Henry
Gravini Steve
Utec Sm AB
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