Recovery, Preparation, and Yield of Redwood Bark

Since redwood logs may be up to 20 percent bark, utilization must be stepped up. The essentials of initial bark removal, recovery, and processing are described. There has been an increasing trend toward bringing logs to the mill site for debarking. The principal advantage gained in hand debarking at the site of the mill stems from the opportunity to handle the logs mechanically. Removal of bark with mechanical debarkers has been limited in the redwood region. The large and often irregular shape of redwood logs and the fibrous nature of the bark have been the principal deterrents to the use of mechanical debarkers. Only one design of mechanical debarker, the hydraulic whole-log debarker, has been used on redwood logs with any degree of success. Yield of bark from a thousand board feet of logs, Humboldt Scale, has been reported to be 500 to 1000 pounds, wet basis. In a hydraulic bark-removal operation, redwood logs passing through a modified Bellingham debarker require from 30 seconds to 5 minutes to be peeled, depending on the size and shape of the log. Although approximately 400 redwood logs are processed in an 8-hour shift, this is not the capacity of the debarker. This rate may yield from 60 to 100 or more tons of bark a day on a two-shift basis and is kept down intentionally to keep in line with the sawmill’s ability to utilize the logs. With proper care, long fibers that range from 1/2 to 3 inches can be recovered from processed bark in the range of 20 to 40 percent of the total input into the processing plant. The whole lumber industry is intensely active in it efforts to get whole-log utilization; it is inevitable that bark will be subject to much additional research and development in the future.

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