The invention relates generally to the art of conditioning peeler logs for the plywood industry and more particularly to a closed water and steam conditioning system.
As those skilled in the art are aware, the plywood industry found early in its inception that the handling of large peeler blocks or logs could most easily be accomplished by flotation in log ponds. While in the ponds, the wood remained wet and resulted in satisfactory peeling of the logs into veneer. In order to thaw frozen logs some large vats were heated with steam. Even in warmer weather heating the vats, and hence the peeler blocks, was found to further improve the peeling operation.
As large diameter peeler logs became scarce, the industry turned to the smaller logs. A different handling problem was presented and thus forklifts and log handling machines replaced ponds and vats as new small log veneer plants were built. In order to thaw frozen logs and obtain high quality veneer, mill operators began building conditioning tunnels. Heat was introduced into the tunnels by adding a low quality steam direct from the boiler or it may have been added in the form of hot water. The steam condensate or water was permitted to drain from the conditioning tunnel into nearby waterways such as rivers, streams, ponds or lakes. The dirty water condensate is usually of low pH (acidic) due to the leeching of wood acid from the logs. Also the water contained floating debris such as bark, wood splinters and the like.
Increased awareness of environmental problems, followed by regulations governing discharges into waterways, has made it necessary to change the practice of adding steam and/or hot water to conditioning tunnels without recovery or treatment of the waste water or effluent, commonly referred to as dirty condensate in the industry. The problem has been further magnified by the increasing costs of generating steam without the return of pure steam condensate to the boiler.
Under the old system, the logs were removed from the pond or a field where they were stacked and first debarked. Subsequent to debarking, the peeler logs are cut into two lengths suitable for the lathes in the mill. Generally, logs from a pond or from a dry stack, if peeled without being conditioned result in erratic and low quality peels. The veneer will curl and tear and will develop ragged edges on the sheets. As the industry turned to conditioning tunnels, it was found that conditioned logs resulted in much smoother peeling with fewer tears thus resulting in higher productivity and better quality veneer. The advantages of conditioned logs together with the regulations imposed by local, state and federal government brought about the need for a system which not only conditions but which at the same time does not violate environmental rules, regulations and statutes.
The plywood industry has used various methods for peeler block conditioning, including hot water tubs for soaking, hot water showers, steaming and a combination of steaming with showers. However, none of the prior art conditioning systems has employed a closed system for the conditioning fluids.