Moisture content in wood chips used for energy can significantly influence system performance. Consequently, equipment and methods used to dry wood chip fuel are constantly evolving, as companies strive to perfect their respective processes, meet the needs of system operators and maximize plant efficiency. Drying methods today include simple, passive drying techniques to the advanced and energy-intensive methods.
Adam Sherman, executive director of the Vermont-based Biomass Energy Resource Center, says that moisture content in wood fuels is a universal problem, and over the past couple of years, the trend has been importing European boilers to help with the job. “In order to meet the efficiency and emissions standards that get more stringent each year, fuel quality becomes more important, and moisture content is really a big deal for efficiency because of latent heat loss, and also because the moisture vapor is often times a carrier for ultrafine particulates from an emissions standpoint,” he says. “We’re seeing some producers of wood chips realize there is an emerging market where a drier chip is desired and has value.”
Sophia Ren, a wood pellet plant consultant for Azeus Pellet Mill, manufacturer of pellet machines for biomass, says drying methods can run the gamut from using forced ambient air and residual heat from electricity generation to using larger-scale dryers. “Drying is done through various methods, including passive evaporation from airflow and from active heating,” she says. “Air drying will occur if the ambient air passing through has a lower relative humidity than the wood chips. Evaporation of water can also be achieved through heating, generally with forced hot air. Wood chip piles can also self-dry, where compacted piles reach temperatures above 40 degrees Celsius (104 degrees Fahrenheit) through microbial action.”