What Is Being Done to Abate Pollution By Plywood and Particleboard Plants?

The pollution problem in the plywood industry is similar to that in the lumber industry. Most plywood plants are able to burn wood residue with little difficulty because the average moisture content is much less than that of lumber. Sander dust is a difficult material to handle and burn without emiting a heavy load of particulate matter. One method of controlling the problem is to utilize a multiple cyclone incorporating a nest of small 9-inch diameter cyclone tubes. It is more expensive but does not absorb any more operating power and its efficiency is greater. It is possible to separate the transported material efficiently without emission from the air outlet other than a light haze. Two new bins have recently been designed. One is a circular bin with a conical bottom connected to the bin with a flexible connector. The conical bottom is agitated with a circular swirling motion, which is said to produce a vortex-type of flow in granular materials such as sander dust. It is claimed for this bin that it can produce a steady and metered flow rate. The other design is also circular, using a conical bottom; but an insert is added above the bottom cone. This insert is also more or less conical in shape, with its apex upwards. Flow therefore takes place between insert and bin sides. The particleboard industry problem is very similar to that in the plywood industry, namely, handling a finely divided material that is very difficult to separate from an airstream without discharging quite .a lot of it into the atmosphere. Practically all of the raw materials taken into the particleboard plant are used in the finished board. The effluents which cause pollution problems, therefore, arise primarily from the cyclones used to separate the material from conveying airstreams, sander dust, and the trim from the finished panels. The waste material trimmed from the boards in a particleboard plant and sometimes the sander dust as well are difficult to burn. This waste is quite heavily laden with glues and filler materials and has a relatively low calorific value, so it is not particularly attractive as a fuel. There is a certain amount of rejected board which some mills cut up and burn. Sander dust and trim material can yield more than sufficient heat to perform the initial drying operation, at a great savings in fuel costs.

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