Constant Venting – Koetter Dry Kiln Method to Remove Moist Air at Heart of Its Approach to Drying Lumber
Koetter Dry Kiln Inc., manufactures dry kilns.But Koetter president Michael Newton says one of the most demanding customers isKoetter’s parent company.
In addition to manufacturing kilns, Koetteralso processes more than 35 million board feet of lumber annually for its ownmillwork business.
Some two decades ago the company grewdissatisfied with drying technologies that were available and developed a newsystem for drying lumber. Koetter systems retain the best attributes ofcompetitive technologies while eliminating most of the negatives, he said. Theresult has been a lumber drying system that met Koetter’s own need for highquality lumber and also provides a solution for other lumber manufacturers.
Today, more than 20 years after Koetterdeveloped its drying technology, its method is used widely in 20 of the world’smajor lumber producing nations, and Koetter is recognized as a leader in itsfield.
Likeconventional steam kilns, which use steam to produce heat that draws moisturefrom wood, Koetter kilns also utilize boilers to heat water. Unlike steam kilns,however, Koetter kilns are then heated by the hot water itself, which runsthrough fin tubes placed strategically throughout the kiln to provide uniformheat. The technology requires a much smaller boiler system compared to steamkilns, according to Michael. In addition, the heat is applied at a temperaturethat allows the wood to dry at a natural rate.
As the moisture migrates from the wood intothe air, it must be removed from the kiln, just as in any drying system. TheKoetter technology to remove the moist air is at the heart of the company’sapproach to drying lumber.
Lumber is like human skin, explained Michael.When a person goes from warm, moist conditions to cold, dry conditions, the skinbecomes dry and cracks. When moist air is expelled from a kiln suddenly and justas suddenly is replaced with dry air, lumber may harden and split as the wateris rapidly drawn out of the wood and into the air.
Steam kilns vent the moist air sporadically;large amounts of moist air are expelled when the drying schedule calls for it,and there is a corresponding influx of dry air.
Koetter kilns overcome this problem. Moist airis constantly vented, removed slowly and steadily, and the dry air is introducedevenly. The approach avoids the rapid changes associated with steam kilntechnology and helps to prevent lumber from hardening and splitting.
In order to dry wood, moisture content nearthe surface of the wood must be lower than at the core of the wood so that waterwill travel from the core to the surface and then into the air. If the air inthe kiln is too dry or the temperature too high, water moves from the core ofthe wood to the surface too rapidly; this causes stress to the wood and resultsin cracking and checking. The lumber losses reduce a company’s profitability.
The difference between the moisture content atthe core of the wood and the surface is the gradient. As the drying processnears its end, the difference in the moisture content between the core andsurface must be equalized. Koetter dry kilns achieve a 2% moisture gradientbetween the wood surface and core, so water moves from the core and out of thewood at an even rate without undue stress.
Koetter’s technology helps prevent lumberfrom the degrading that often occurs in kilns when the interior and exteriormoisture contents are equalized. Venting stops a day or two prior to the end ofthe drying process; through a process of gradual conditioning, excess moistureleft in the core of the wood continues to move out to the surface but at alower, slower rate until the moisture content throughout the wood is equalized.
The approach is based on drying lumber at arate that does not violate wood fiber’s natural capacity to give up moisture— to remove the moisture at the same rate as it would naturally exit woodfiber when lumber is air dried. Each wood species has its own natural rate. Bystudy and experimentation, Koetter has developed a series of schedules thatallow for the most rapid drying possible for a species without degrading lumber.The result is a system that produces quality lumber efficiently at relativelylow cost and can be easily operated even by a novice.
Another advantage of the Koetter dryingconcept is that a unique correlation between controlled moisture exhaust andrestricted air intake creates lower pressure in the specially designed chamber.As a result, accelerated drying is possible without damaging high temperatures.Wood dries more evenly within time frames comparable to conventional schedules.In addition, with Koetter’s technology, kiln operating costs are lower.
Theprecision control that Koetter kilns provide is important to a company that useshardwood lumber in the manufacture of fine furniture. Gunlocke Corporation inWayland, N.Y., a subsidiary of the Hon Corporation, is a leading manufacturer oftop-of-the line office furniture. Gunlocke has been in business more than 50years and has extensive experience in lumber drying operations. The company hasbeen drying its own lumber since the mid-1950s.
Gunlocke uses lumber in a variety of speciesand thicknesses, lumber that must be dried to exact moisture requirements. Itdries over 4 million board feet of lumber annually, and its drying operationsmust accommodate a total of 56 different combinations of species, thicknesses,and moisture content, a formidable task.
Gunlocke has eight conventional steam kilns of20,000 board feet capacity and four converted predryers with 40,000 board feetof capacity. It began upgrading its drying operations a few years ago andinvested in two Koetter kilns with 3,200 board feet of capacity. The company hasbeen so pleased with their performance that it plans to add six larger Koetterkilns (6,200 board feet capacity) this year and two more of the smaller Koetterkilns in 2001.
Mike Szymanski, Gunlocke’s productionsuperintendent, is responsible for assuring a ready supply of lumber for thecompany’s furniture manufacturing operations. Gunlocke selected Koetter tosupply new kilns “because our conventional kilns were not doing thejob,” he said. “With the large number of schedules we have to run, wewere looking for a technology that would give us the ability to dry to veryprecise contents.” The company also wanted a kiln system that would givethem the ability to dry to precise moisture content with a small charge, hesaid.
Gunlocke manufactures a variety of highquality furniture, hence the need for 56 combinations of wood species,thicknesses, and moisture requirements. Because it makes a large volume ofcustom furniture, the company would inventory a large quantity of wood in allvarieties. Its operations were inefficient, and the need to floor so muchcarefully dried wood also meant degrading could occur. The solution: dryingsmall amounts of wood as it was needed.
Gunlocke got its solution from Koetter DryKiln. It can dry to very exact standards, which is particularly important formaking furniture components of bent wood; lumber for bent components must bepartially dried to 20%, then bent, then dried to its final moisture content. Thenew kilns were cost effective and produce dry lumber with fewer defects.”They’ve been everything we hoped they would be,” said Szymanski.
Onthe other side of the country, Whitethorn Construction presented Koetter DryKiln with a different kind of challenge. The company is located in Whitethorn,Calif., a remote village near the state’s northern coast. Whitethorn is basedin the region because of the market for real estate development. Over the yearsit established a small lumber yard and hardware store. Whitethorne also isinvolved in the California Hardwood Initiative, which seeks to build markets forthe unique species of hardwoods that are available in the state. Using portablemills or contracting with portable mill operators, the company saws some of thelumber offered for sale in its yard as well as specialty products for the homesit builds.
In order to market its products efficiently,Whitethorn needed the ability to produce dried lumber. Because of its remotelocation, however, it did not have access to drying technology. “If you’regoing to sell wood economically,” said millwork manager Ken Forden,”you’ve got to offer kiln dried. We decided to dry ourselves, so wepurchased a small, 600-board-foot unit from Koetter.”
The company selected Koetter to supply a kilnafter Ken attended a trade show and visited Koetter’s exhibit. “We likedthe theory and the idiot-proof nature of the process,” he said. “Koetterhas developed a kiln that is very easy to operate, and as we had littleexperience, that was important.”
Ken takes his work seriously, and he hasinvested a good deal of his own time and effort into learning how to improvelumber quality as he learned about drying technology. Of course, he went througha learning curve. The schedules Koetter had developed for precision dryinghardwoods were based on experience with species found in most areas of thecountry. However, Northern California contains abundant specialty woods, such asMadrone, Chinkapin, Tan Oak, and others. The Koetter staff worked diligently andclosely with Ken to develop drying schedules for the unusual species.”Their back-up support was just excellent,” he said.
Whitethorne is about to build on itssuccessful entry into drying by adding a second kiln. In the future it plans toadd a Koetter kiln with 6,000 board feet of capacity that will enable Whitethornto begin marketing its specialty woods outside the immediate region.
Inthe Midwest, a Koetter kiln helped Calmoutier Lumber to add value to itsproducts and take advantage of a market opportunity. The company, located inCalmoutier, Oh. about an hour’s drive from Cleveland, has a small sawmill witha 56-inch circle saw. Larry Klintworth laughingly described it as the “kindof mill you would see in an old movie where the heroine is strapped to the logand has to be saved before she is sawn in half.” Calmoutier saws about a1.5 million board feet of grade lumber per year, mostly red oak, cherry, andhard maple.
The company sold its lumber green until itrealized there was an opportunity in its own market area and decided to go intodrying. “We have a large number of furniture makers in our area,”Larry said. “Many Amish live here and create beautiful pieces of art, sothere was a tremendous demand for the top grades of lumber. We decided a kilnwould allow us to serve that local demand.”
There was a unique circumstance that had to bedealt with at Calmoutier: the need for simplicity in the drying technology.Larry’s partners in the mill are Amish, and simplicity is highly valued. Aboiler fueled by wood waste provides the heat for the kilns, and a small dieselengine that runs around the clock delivers the power.
Koetter provided service in developing asystem that relied on mechanical means of producing power and the dryingschedules needed to produce superior lumber products, according to Larry.Koetter also provided important after-the-sale support, he said. With the dryingtechnology supplied by Koetter, Calmoutier has been able to serve the Amishfurniture makers, and its lumber products now are worth as much as $400 more perthousand board feet than when they were sold green.
Koetter manufactures kilns from 650 to 140,000board feet capacity that fit small businesses as well as large lumbermanufacturing operations. In the past three months, 11 Koetter kilns rangingfrom 30,000 board feet to 60,000 board feet have come on line at installationsin Ohio, Indiana, West Virginia, Canada, Russia, and Belarus, according to ElenaIvanova, director of international marketing. Koetter’s own millworkoperations utilize 24 drying chambers that range in size from 35,000 board feetto 70,000 board feet.
A little more than two decades ago, Koetterset out to improve its own millwork operation. The result was a new kind of drykiln technology that was easy to operate and kept costs low. Of most importanceto the forest products industry, Koetter’s technology was able to reducedefects in lumber associated with other drying methods.
In developing a new drying technology that proved efficientand effective, Koetter contributed to the profitability of its customers and tothe success of the forest products industry.