Unidirectional Continuous Kilns Poised for North American Breakthrough

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Scandinavia’s Valutec Group introduces continuous kiln which produces lumber quality comparable to batch kilns.


In the past unidirectional continuous kilns had a reputation for being kilns designed for sawmills looking for high capacity, rather than quality. But technical developments over the past twenty years have fundamentally improved the continuous kilns. Now, a new breed of kilns make their way into new markets every year, as they have been proven a sound investment for many types of sawmills.

The main driver of this change is quality. The continuous kilns developed today are comparable to batch kilns with regards to lumber quality.

The company behind this development is Scandinavia’s Valutec Group, a leading supplier of continuous kilns for softwood drying. With a history tracing as far back as the 1920’s, Valutec has delivered over 4,000 batch kilns and more than 2,000 continuous kilns over the years.

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During this time the company has developed more than 25 patented solutions for lumber drying and established themselves as a premium European kiln supplier. Last year, Valutec founded a North American subsidiary, Valutec Inc. with an office in Vancouver, Canada, and since then has been offering their lumber dry kilns to the North American market.

“I have spent the last year visiting a lot of sawmills and learning more about the market,” said Ingo Wallocha, managing director of Valutec Inc. “Many sawmills have shown a need for improved quality, and with our continuous kilns we offer a solution that protects the value of the lumber through the drying process and saves money for sawmills.”

Research-based Software Paved the Way

The key improvements with regards to drying quality came when Valutec started to divide its continuous kilns into separate zones. This was partly due to a mechanical development and strong housing, but it also has a lot to do with a sophisticated control system, which allows the climate to be individually controlled in each zone.

It was this control system that paved the way for the mechanics. The company took the step of improving the kilns following the development of their own adaptive control system, Valmatics, which gives the users full freedom to configure the application within their own control parameters. The intelligent control system senses and adapts the process to reality, which provides the opportunity to meet rising demands on drying economics and precise final quality.

In controlling continuous kilns, the system offers an adaptive method with automatic adjustment of temperatures and pulling interval, depending on the raw material and desired final moisture content.

An integral part of the control system is the simulator, Valusim, which has been developed in direct cooperation with research institutes and the Scandinavian lumber industry. The simulator provides optimal guidance to quickly arrive at the most time-effective drying process for every new dimension. It optimizes new drying programs considering capacity, quality and electrical energy consumption to avoid costly run-in time of new programs. In a user-friendly interface, all information is fed in regarding desired final quality together with all known basic data to simulate a process that is very close to reality.

“We have conducted a lot of live testing over the last years with sawmills, and results show that if the correct parameters are set the accuracy of the simulator is very high,” said Wallocha. “And this is really the way it should be. When we first developed the simulator, we studied over 2,000 hours of drying for different types of lumber.”

An effect is that the user doesn’t need to set probes anymore, which are inaccurate for higher moisture contents and in kilns with net lumber capacities of up to 300,000 board feet, the number of probes that need to be placed for getting a proper average reading quickly becomes unrealistically high.

For sawmills that still wish to set the end-point of the drying via online moisture monitoring all kinds of in-kiln moisture measuring devices can be connected to Valmatics and Valusim.

Continuous Kilns Reach the Alps

In Europe, there are two different types of continuous kilns. The traditional side loaded type continuous kilns (think fork lift loaded batch kilns in terms of loading direction and airflow) works best for sawmills without random length, where it’s easy to efficiently load a kiln sideways. This type is often the first choice for stud mills and for cross laminated timber (CLT) or mass timber manufacturers who usually do not work with random length boards. Typically, side loaded kilns are separated into two drying zones. In the first zone the air is quickly humidified, which reduces the surface drying and thereby the risk of dry cracks. The second zone acts as a balancing zone to reduce moisture content variation. It’s also possible to add a third reconditioning zone to satisfy even the highest quality expectations.

Valutec recently installed two side-loaded continuous kilns at one of the world’s most modern CLT manufacturing facilities – Hasslacher Norica Timber in Austria. The kilns are used to dry glue-laminated spruce lumber 44 millimeters in width to a final moisture content of 12%.

The high and consistent quality is proof that Hasslacher made the right choice in choosing continuous kilns.

“When drying large volumes with high quality requirements, and you have access to an even influx of raw material, the continuous kilns are a great advantage,” explained Bernhard Spitzer, General Manager at Hasslacher.

One benefit is the steady operation, which places an even load on the furnace. This means that the spikes in the energy consumption that can be caused by several batch kilns being simultaneously heated can be avoided. In addition, the equipment is both efficient and dependable.

“We now have drying times of just 80 to 85 hours for the large dimensions that we dry. For each package, we save up to one day on the lumber drying, compared to our traditional batch kilns,” said Bernhard Spitzer.

Flexibility and Optimized Energy Consumption

A new type of continuous kiln, the so-called TC-kiln (the TC is a Swedish abbreviation for cross-circulation) has in recent years been the most talked about kiln in Europe. The TC combines the flexibility advantages of a batch kiln with the capacity advantages of a progressive kiln. The kiln, which is equipped with doors and vents, is loaded lengthwise, like a traditional North American single or double track kiln, and is therefore a good choice for sawmills that work with random length.

In a TC the timber is dried during transport through a number of zones with separate climates. The timber is placed length-wise on trolleys and fed from a buffer track into the kiln’s input end. A fully automatic feed system transports the timber through the kiln and to the output end. Transverse axial fans in each zone blow circulation air across the longitudinal direction of the kiln, via heat coils and through the timber.

That way each and every zone can be seen as an independent little batch kiln which means that as long as one stays consistent per zone one can introduce different dimensions, different species and different moisture contents. The drying schedule follows each zone over the length of the kiln until the lumber batch has been unloaded.

“You can say that we think small batches but high capacities,” said Ingo Wallocha.

Increased Control

A major advantage with the TC-kiln is that the drying process is precise and controlled. The operator sets the final moisture content, the quality and the energy consumption of the load and thereafter the drying schedule simulator Valusim creates the optimal drying schedule.

Furthermore, since the kiln has vents which can be equipped with heat recovery units there are additional energy savings of up to 15% possible on top of the 10-15% energy savings that a continuous kiln already has compared to a batch kiln.

Forklift Traffic Minimized

Valutec’s unidirectional dry kilns have long buffer zones for loading and unloading. These zones can be equipped with shelter roofs if desired. With or without shelter roof the long zones mean that the kiln can run independently for a long time, for example over the weekend, without the need of a forklift. There is also an option to add a complete traverse system to the kiln so no forklifts are needed from after the stacker until after the planer mill.

The TC kilns are running in many mills in Europe and are gaining more and more thrust. At the SCA sawmill in Bollsta, one of Sweden’s biggest mills, Valutec has supplied a drying zone TC kiln. This kiln dries all the different side board dimensions up to one-inch pine from 120% initial moisture content down to 18% in 21 hours with a final standard deviation of only 1.5%.

“It’s the most impressive kiln I have ever worked with,” said Niclas Larsson, an experienced kiln operator at SCA Bollsta about the unit that has drawn international interest precisely because of the sought-after combination of flexibility and high capacity that so many sawmills look for when improving and investing in their production processes.

Long-term Development

Through the years, Valutec has spent at least 5% of its annual revenue on research and development. One interesting project that is currently ongoing is the installation of a scale system at one of the company’s partner mills in Sweden. Knowing the lumber moisture content before it goes into the kiln is crucial for finding the right moisture content and getting a minimal standard deviation at the end of the drying process.

The scale system is installed just before the green stacker and automatically sends the data to Valmatics. So far this has been very successful in batch kilns and the process of implementing the scale for continuous kilns is about to start. Valutec has high hopes for that.

“For us, it’s about being a trusted and highly valued long-term partner for sawmills around the world,” said Wallocha. “That is a foundation for the success of our company. And our focus on developing kiln drying to help sawmills increase their margins and to make wood more competitive wouldn’t be possible without strong research and development.

“We are about the long-term. When we arrive on a market, we stay there and work closely together with our customers to help them take the next step in their development. Our history has proven that.”