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From the First Continuous Kiln to Today, USNR Drying Technology Keeps Evolving

USNR has installed the largest number of continuous kilns in North America and continues to improve the design of its Counter-Flow Kiln.

By Staff
Date Posted: 7/1/2018

                USNR developed the first continuous dry kiln in 2005 and that unique drying concept has since become an industry standard. All continuous kilns are similar in design and operation, with lumber stacks running in opposite directions allowing heat coming off the dry lumber to preheat the green lumber packs, and moisture coming off the green lumber to condition the dry lumber.

                The design delivers non-stop production that increases kiln capacity by up to 55% while using an existing heating system. It also decreases standard deviation of the lumber and the number of over-dried pieces because of the gentler nature of the process. Most mills achieve noticeable grade improvements.

                Key differences can be found in the evolution of various sub-systems to deliver additional efficiency and reliability including the pushers, controls, and fuel systems.

                USNR has installed the largest number of continuous kilns in North America and continues to improve the design of its Counter-Flow Kiln as well as the design of related systems like the 8-Grate Burner. USNR’s 8-Grate Burner is the largest green fuel burner in the industry capable of producing 40 mm BTUs.

                This powerful system offers the widest variety of heat sources including steam, shavings, green fuel, and natural gas. It can also be manufactured as a hybrid burner that uses a combination of different sources in the same system. This flexibility allows mills to use the fuel that gives them the best savings.

                A new hybrid burner project in the South will have natural gas and green fuel options. The ability to switch between different heat sources gives mills more flexibility to take advantage of price fluctuations and other market conditions.

                The Counter-Flow Kiln uses a staging and loading system to keep packages moving through the kiln continuously and automatically. The pusher is the work horse of the system. It pushes the whole load and must work right every single time. Cylinder frames, carriages, lugs, and encoder wheels must be reliable in an extremely tough work environment that is hot, wet, and dirty. USNR’s pusher system is in its third-generation of advancement, and it delivers high reliability ensuring pushes are never missed or skipped. 

                Controls are also key, since the pusher speed directly effects how dry the lumber turns out. The pusher drives the load, matching residence time with the target moisture content. Accurate tracking of pusher movement is critical because this is how production is tracked. USNR uses Allen-Bradley’s industry-proven non-proprietary PLC-based controls. There is no black box and it’s not just a PC on a table.

                USNR Counter-Flow Kilns use the SmartTrac in-kiln moisture sensing system to drive the speed of the lugs through the kiln. This allows you to speed up where possible so you don’t have over dry packs, and slow down when necessary so you don’t have wet lumber.

                SmartTrac delivers accurate moisture measurements and is simple to install. The system uses a unique impedance (dielectric) technology which enables measurements accurate to within 1% of final moisture content targets. Sophisticated mathematical software analyzes the data collected in the kiln and displays it at the control center in real time.

                USNR offers a choice of materials for skinning the kiln that offer different degrees of corrosion resistance including aluminum, factory-applied epoxy coating, or stainless steel. This along with engineering advances in foundations, fan systems, and controls continue to evolve and improve the USNR Counter-Flow Kiln design. For more information visit the website at or call Alan Robbins at (904) 513-5541, or dial 800-BUY-USNR.


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