Abstract:
The drying of wood is required in most forest products
manufacturing operations. Depending on the wood species,
dimensions, drying temperatures, and drying duration, the
amount of emissions and energy consumption can greatly affect
the operating cost, environment, and quality of wood dried.
As such, the forest products industry continues to explore the
use of new technologies to address these points of concern.
A study was done to evaluate the addition of a radio-frequency
(RF) heating system to a natural gas-fired
conventional veneer dryer as a means to reduce emissions,
reduce energy consumption, and improve productivity while
maintaining material quality. To establish the benefits of
RF-assisted drying, a study comparison was made for drying
wood veneer in a RF-assisted dryer and a conventional dryer.
The study was conducted at Western Veneer and Slicing in White
City, Oregon. This plant was selected because both types of
dryers, an RF-assisted dryer manufactured by Production
Machinery, Inc. and a conventional dryer manufactured by Amitec, were located at the same site and were used for drying
the same type of material.
Two comparison drying tests were conducted, one using
sliced ponderosa pine and the other using rotary peeled
Douglas-fir. The sliced veneer was selected because it was
the type of material used by the White City plant and the
rotary veneer was used because it is of the type used in the
plywood industry. The parameters measured for each drying run
were material flows, drying rates, emission rates, dryer
operating conditions, exhaust conditions, and electrical and
natural gas consumption.
It was found that although the RF-assisted dryer was able
to successfully dry the sliced veneer as it was designed to
do, it was not properly "tuned" to efficiently dry the rotary
veneer. Therefore, the results of this study should only be
made for the sliced veneer studies. The study found that the
RF-assisted dryer was able to reduce total emissions comprised
of particulate, organic, and inorganic components. The
emissions reduction was 16% based on a total throughput basis
(dry material plus redry) and 36% based on a dried production
basis. Whereas, energy use for the RF-assisted dryer in terms
of Btu/lb of water extracted was found to be approximately 15%
higher, which was due mainly to over-venting of the exhaust
system. It was recommended that the exhaust be damped to
provide comparative energy use to the conventional dryer. The
RF-assisted dryer was also found to be more productive in that
its redry rate, the amount of veneer that needed to be redried, was lower; likewise, the variance of veneer moisture
was lower. The aesthetic quality of the RF dried veneer was
described by the experienced veneer graders employed by White
City Veneer and Slicing as being better in terms of brightness
and brittleness, however we were unable to quantify this
difference.
It can be concluded that the RF-assisted system for the
study conditions appears to be an improvement over the
conventional system in terms of emissions, productivity, and
maintaining veneer quality.
