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Hardwood lumber kiln drying schedules typically keep the dry bulb temperature below 80 °C (176 °F). Difficult-to-dry species might not exceed 60 °C (140 °F). Dehumidification kilns are very similar to conventional kilns in basic construction.
Modern high-temperature, high-air-velocity conventional kilns can typically dry 25-millimetre-thick (1 in) green wood in 10 hours down to a moisture content of 18%. However, 25-mm-thick green red oak requires about 28 days to dry down to a moisture content of 8%.
Wood in this process must have a moisture content at 12% or lower which can be attained through simple drying processes. The wood is then placed in a high nitrogen atmosphere with no more than 2% oxygen content. [8] The Perdure Process is relatively similar to retification but holds the wood at a lower temperature. [9]
These processes autoclave the treated wood, subjecting it to pressure and heat, along with nitrogen or water vapour to control drying in a staged treatment process ranging from 24 to 48 hours at temperatures of 180 °C to 230 °C depending on timber species. These processes increase the durability, dimensional stability and hardness of the ...
Torrefaction is a thermochemical treatment of biomass at 200 to 320 °C (392 to 608 °F). It is carried out under atmospheric pressure and in the absence of oxygen.During the torrefaction process, the water contained in the biomass as well as superfluous volatiles are released, and the biopolymers (cellulose, hemicellulose and lignin) partly decompose, giving off various types of volatiles. [4]
A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Various industries and trades use kilns to harden objects made from clay into pottery , bricks etc. [ 3 ] Various industries use rotary kilns for pyroprocessing —to calcinate ...
For instance in wood (timber) drying, air is heated (which speeds up drying) though some steam is also added to it (which hinders drying rate to a certain extent) in order to avoid excessive surface dehydration and product deformation owing to high moisture gradients across timber thickness. Spray drying belongs in this category.
The use of wood as a fuel source for heating is much older than civilization and is assumed to have been used by Neanderthals. Today, burning of wood is the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating, and occasionally for fueling steam engines and steam turbines that generate electricity.