Page 172 - Low Temperature Energy Systems with Applications of Renewable Energy

162 Low-Temperature Energy Systems with Applications of Renewable Energy

Table 4.5 Sawn wood production (conifer and
non-conifer) in the top ten countries in 2017 [44].
6
Country 10 m 3 % Total
Year 2017
China 86.03 17.7
USA 80.37 16.6
Canada 49.50 10.2
Russia 40.58 8.4
Germany 23.17 4.8
Sweden 18.41 3.8
Brazil 14.60 3.0
India 6.89 1.4
Viet Nam 6.00 1.2
Indonesia 4.17 0.9
World total 485.13 100

Sawn wood is the most common form of construction lumber and is aimed at satis-
fying the needs of three categories of usage: furniture manufacture, construction, and
industry. In order to achieve high throughput and rapid return of capital, manufacturers
in the last two categories dry the raw product at high temperatures, which allows the
wood to dry in less than 2e4 days, reducing the moisture content from 100e140%
moisture to 10e20%. Rapid treatment of this type is feasible since the final quality
and appearance of the wood is not critical in construction and industry. However,
this mode of drying is unacceptable for the furniture manufacturing industry owing
to the occurrence of various types of material defects such as cracks, guttering, loss
of color, etc. Planking for this application is subjected to heat and moisture treatment
under milder temperature regimes and longer drying times to obtain high-quality ma-
terial suitable for furniture.
In dryers with traditional heat sources, increasing the drying time inevitably leads to
an increased usage of non-renewable primary fuel, and, as a consequence, to an in-
crease in the production cost. The presence of atmospheric pollutants from the com-
bustion emissions of traditional heat generators of drying plants and the concern
about the ecological aspects of vital activities of humanity, which are particularly
sharply formulated in recent times, demand that we pay attention to alternative
methods of heating for the technological processes of convective drying of wood.
Thus, energy-saving heat-pump systems were recognized and have long been applied.
Wood drying was one of the first commercial-scale applications of heat pumps for
drying purposes that require fine temperature and humidity control. The pioneer in this