KILNS
Solarkilns continues innovation – Mega kilns
I
F NECESSITY is the mother of invention then ingenuity must surely be the father ... an old adage that rings true, especially for Victorian-based Solarkilns. They wanted a solar kiln control concept that absorbed and used available solar heat during the day (when it is abundant) and ideally stored it at night. Many kilns run venting at night and consume auxiliary heating to keep the kiln at set points while sucking in cold ambient air. A solar kiln is ideally not set up that way, instead close all venting at night and letting the humidity rise in the kiln. “This allows the drying to slow, preserving the free energy gathered ready for the next day’s top-up solar contribution and accelerated drying,” said Solarkilns General Manager Kevin Long. “This has been the catalyst and basis for our unique Advanced Cyclic drying practises using a high humidity treatment each night that applies higher daytime temperatures and faster drying during the day and reconditioning for the timber every night,” he said. Now, after 16 years and $3.2m of its own research and development one of the keys to Solarkilns’ energy efficient operation is an innovative (and patented) highly developed control system that is programmed to work with the cycles of day and night. “The controls take advantage of daylight hours and the superior capture of sunlight by increasing daytime drying capacity and then conserving and better managing thermal energy at night,” Kevin explained. “This ‘cyclic’ control method produces less waste and degradation in almost all of the large number of species dried by Solarkilns in past years and that’s without compromise to process times.” Kevin says this claim is backed by results from Sydney University research conducted in collaboration with Solarkilns with assistance from a prestigious Australian Research Council grant. The Solarkilns integrated system is exceptionally carbon and greenhouse friendly. The kiln controls are programmed to primarily operate using solar contribution prior to any auxiliary heating, turning the timber drying schedules into an almost thermalenergy free process. “This is in stark contrast to a conventional timber drying kiln process that typically consumes 60% of the considerable amount of energy required to convert a tree into a piece of dry timber,” says Kevin. Solarkilns has just released
22
its latest Mega kiln range, with capacities ranging from 75m3 to 300m3 in a single charge. These units are capable of ultra-low cost timber pre-drying and/or final drying because the primary heating source is the sun. “Additionally, the expensive and sophisticated electronics package is amortised against a larger load capacity. This superior technology costs a fraction of that of a conventional pre-dryer and its associated boiler and fuel feed systems,” he says. The first of Solarkilns’ Mega units have been installed in NSW, with 2 x 150m3 units currently drying high quality north coast hardwood flooring and decking. These units are being used to dry from green off the saw as well as final drying with exceptional results from all batches dried. “Over the summer period no auxiliary heating has been required to final dry these hardwoods to 1012% moisture in as good a time as any traditional kiln. These kilns are now charged with green sawn loads which during the cooler months have not required auxiliary heating in the initial ‘pre-dry’ stages of drying from green to fibre saturation point. “For continued guaranteed productivity during winter these Solarkilns may optionally use minimal supplementary heating during the final stages of drying, always maximising solar contribution in the first case,” Kevin says. Notable points regarding the innovation and two blocks of patents that protect this all-Australian invention: • The technology well exceeds
the performance of earlier flat collector systems due to an array of unique, smarter-drying features. • The kilns are installed in a north/ south orientation so that the sun hits the dome shape of kilns at an optimal angle from sun up till sun down -- maximising solar collection. • Whenever the sun is shining on the kiln free energy is being absorbed directly into the kiln without the costs, losses and energy inputs associated with heat exchangers. • The triple skin design with black inner layer transfers heat immediately to the kilns recirculation air flow. And at night the triple skin provides twin double-glazed insulation barriers to conserve energy. • A huge area -- the large surface of the kiln that is always facing the sun -- is absorbing energy from sun up to sun down. • The control system has been specifically designed to maximise thermal energy conservation within the kilns. The ‘cyclic’ schedules likewise run in collaboration with the day night cycles always maximising solar contribution and conservation in the first case. “Not only does the controller work with the daily energy cycle, it works with the climate cycles, constantly making calculations about the comparative state of
Australian Forests & Timber News
June 2016
the kiln set points and outside absolute humidity and temperature conditions. “It then makes intuitive controller decisions that avoid energy wastage that no other known technology is capable of avoiding,” Kevin says.
Recent achievementssmarter drying: a. Solarkilns have dried a range of species including collapsing eucalypts faster, at lower cost, with less environmental carbon impacts and in the same or lesser process time, to higher standards than ever before. Some examples are: b. P re-dried Mountain Ash (E.Regnans) regrowth 27mm boards to 25% ready for final drying in 14 days with minimal collapse. c. Pre -dried & final-dried (greenfully dry) silvertop (E.Sieberi) 40mm boards to 12% in 52 days with minimal collapse or drying degrade without steam reconditioning. d. S pecies of plantation timber that are currently impossible to dry to economical standards may now be utilised due to smarter drying.
Knowledge breakthroughsa. T he underlying cause of collapse and checking in many hardwoods is linked to critical moisture differential. That is stress caused when one part of a board falls below fibre www.timberbiz.com.au