Kiln Operators

Kiln Operators In The News

wood drying kiln

This invention relates to a wood drying kiln for drying timber and in particular Pinus radiata and to a method of operating a kiln. In the preparation of timber it is usual for green sawn timber to be placed into a kiln and heated. The objective is to remove moisture from the timber. If the temperature is low, the time taken to dry the timber sufficiently for commercial purposes is very high, correspondingly reducing the output of the kiln. If the dry bulk temperature is raised, say to 120° C., drying is more rapid and the output increases but problems arise in the timber. For example, there may be distortion of the timber possibly resulting from uneven drying. Cracks may appear at knots. Surface checking may occur and there may be an undesirable change in the colour of the timber.

The objective of the present invention is to provide a kiln and a method of drying timber where the kiln output is high and the known disadvantages of accelerated drying avoided at least to an acceptable level.

SUMMARY OF THE INVENTION

According to one aspect the invention provides a kiln for drying timber comprising:

an elongated housing having a base, two side walls and a top wall and two end walls defining a timber treatment zone;

a gas circulation passageway having a top passageway portion extending over said timber treatment zone, a side passageway portion extending down one side of said timber treatment zone, a treatment passageway portion extending through said timber treatment zone, and a side passageway portion extending up the other side of said timber treatment zone merging with said top passageway portion, each said side wall being sloped whereby each of said side passageway portions is broad at the top of the kiln and narrower at the bottom of the wood drying kiln thereby to provide a substantially even rate of flow of gases at various levels within said treatment zone; and

reversable gas circulation means within said top passageway for maintaining the circulation of treatment gas in said other direction through said gas passageway whereby the direction of gas flowing through said treatment zone may be reversed.

According to another aspect the invention provides a method of drying timber in a wood drying kiln of the invention. The method comprises stacking timber in spaced layers in the treatment zone, quickly bringing the kiln to its operating temperature, introducing heated treatment gas into the kiln, circulating the gas either in the first or second direction and periodically reversing the flow of the circulating gas until a desired moisture is achieved in the timber.
Accordingly, the present invention provides a kiln 8 for the drying of timber. The kiln 8 of the present invention includes an elongated housing to provide a timber treatment zone. The elongated housing is provided by a kiln base 9, a pair of kiln side walls 10, 11 and a kiln top wall 12 defining the timber treatment zone 13 therewithin as far as the lateral cross-section is concerned. A pair of kiln end walls 14, 15 complete the timber treatment zone 13.

In accordance with the invention the wood drying kiln side walls 10, 11 and kiln top wall 12 are so shaped as to provide in lateral cross-section a gas circulation passageway about said timber treatment zone. The gas circulation passageway includes a top passageway portion 16 extending over the top of the timber treatment zone, a side passageway portion 18 extending down one side of the timber treatment zone, a treatment passageway portion 19 extending through the timber treatment zone, and a side passageway portion 20 extending up the other side of the timber treatment zone to merge with the top passageway portion 16. Each of the kiln side walls 10,11 is sloped so that each of the side passageway portions is broader at the top and narrower at the bottom thereby uniformly to reduce the flow area of gases circulating within the gas circulation passageway, thus to maintain a substantially uniform velocity of gas at various levels within the timber treatment zone as will be further explained below. It will be seen then that gas within the gas circulation passageway may circulate through the top passageway portion 16 to a side passageway portion 18 through the treatment passageway portion 19 or timber treatment zone and return via the other side passageway portion 20 to the top passageway portion 16, the shape of the gas circulation passageway being such as to provide a substantially even rate of flow at various levels within the timber treatment zone.

Preferably the top passageway portion 16 merges with each of the side passageway portions 18, 20 to provide even flow, preferably by means of a rounded junction 21 between the kiln top wall 12 and each of the kiln side walls 10, 11.

The kiln structure of the present invention provides a gas circulation means preferably within the gas circulation passageway to maintain the circulation of treatment gas in the manner outlined above. Preferably, the gas circulation means is provided by one or more tube axial fans 22.

Preferably the tube axial fan 22 is reversible whereby the direction of circulation within the gas circulation passageway may be reversed.

The wood drying kiln structure of the present invention preferably includes one or more inlet ducts for hot air and other gases for timber treatment. Preferably a single longitudinal inlet duct 23 is provided substantially centrally located in the kiln 8. In one suitable form the inlet duct 23 extends longitudinally beneath the top passageway portion 16 and above the timber treatment zone so that replenishment gas may be injected to the gas circulation passageway in the vicinity of the top passageway portion 16. For the purpose one or more inlet ports 24 are provided between the inlet duct and the gas passageway. Since this top passageway portion 16 includes the circulation fan, such as the tube axial fan 22 above referred to the gas within the top passageway portion 16 will be in substantial turbulence thereby enabling early mixture of the replenishment gas and the circulation gas

About the Author

According to another aspect the invention provides a method of drying timber in a wood drying kiln of the invention. The method comprises stacking timber in spaced layers in the treatment zone, quickly bringing the kiln to its operating temperature, introducing heated treatment gas into the kiln

Questions about Kiln Operators

Kiln Operators Videos

Talking to the operator of the Bull's Trench kiln

It has never been easier to shop for Kiln Operators.

We all utilise a gallery wordpress plugin, you too?