Case Study: Collins Wood Products

Wood Fiber Separation
INDUSTRY: Pressed hardboard wood siding
APPLICATION: Scrubber process water
PARTICULATE SEPARATED: Wood fiber
PROCESS EQUIPMENT: Compound HydraKleen^® liquid-solid separator

PROBLEM:
At a major wood processing plant in southern Oregon, wood fiber, sawdust, and noxious gases are generated during the production of pressed hardboard wood siding. The plant's air treatment system utilizes water nozzles in conjunction with a multiphase biofilter/bioscrubber to separate the particulate and gases from the process air stream. The saturated particulate is then hydraulically piped to a bio-digestion tank to remove the noxious gases and thereby comply with MACT environmental air pollution regulations. It was assumed that the bacteria in the biodigestion/scrubber tank would also be able to digest the wood fibers from the production process; however, the fibers were being introduced to the tank at a faster rate than the bacteria could consume them. As a result, the tank filled with wood fiber and reduced the available water volume. This reduction in tank water volume decreased the bacteria's ability to effectively remove the noxious gases from the process air, putting the plant at risk of being non-compliant with air emission regulations.

Left: old baghouse air filter system; Right: multiphase biofilter/bioscrubber

SOLUTION:
EFS designed and constructed a HydraKleen unit to accommodate the design flow of 1,500 gpm. The client was not concerned with removal of all of the wood fiber because the bacteria can digest some fiber; however, a majority of the fiber needed to be removed. A 200µm slot size was determined through testing at EFS to be able to remove an adequate amount of fiber. The HydraKleen was designed with two screen sections facing each other sharing a solids discharge chute to accommodate the limited available footprint. Each screen section was fed by a weir to smooth the flow and provide better screen throughput. The solids chute was optimized to assist with the gravitational flow of solids to the collection tote using minimal water. The HydraKleen was able to remove 6 times the fiber as previous filter attempts and created no impeding impact on the process flow. Since the unit needed to be located at 20 feet above ground to allow it to discharge to the existing tank surface, EFS designed a custom support structure and catwalk service platform with a small footprint to maximize remaining usable floor space around the structure.