Companies who are involved in wood recycling, cleaning up old mill sites, wood yards or log yard debris, often encounter the problem of how to separate rock and dirt from wood products. Although numerous size trommel screens, vibratory screens or finger screens can be used for prescreening wood waste and to complete this process, the cost often begins to outweigh the benefits.
That’s where the water bath classifier or stationery trommel with water bath (float tank) comes in (see photo above).
The brand we’ve used is a Wittco stationary screening plant with a 6000 gallon water bath. As shown in the photograph, the process begins at the hopper.
A mix of wood and rock (dirty material) is loaded into the hopper. A conveyor, or feed belt then carries the product into a 28 foot long trommel screen which rotates. Different size screens can be installed into the trommel and the screens which are located at the bottom of the trommel determine the size of the product that is produced. As the wood, dirt and/or rock products pass over the screens, that which is small enough drops through, and the large pieces of wood and rock are carried through the trommel and drop into a 6000 gallon water bath (float tank).
The water bath which is attached to the trommel encompasses two conveyor belts which are partially positioned beneath the surface of the water. The wood will float, be picked up by the upper conveyor (wood belt -see photo on left), carried out of the bath and disposed of in front of the classifier. The rock and/or heavily saturated wood products will sink to the bottom of the bath and will be carried out by the lower belt (rock belt -see photo on right) and dispensed to the rear of the classifier (behind the bath).
The wood which is expelled from the bath can then be picked up with a piece of heavy equipment, taken back to the tub or horizontal grinder and be reground into wood chips. The rock can often be reused in other parts of the recycling operation, or be sold.
The classifier runs on either a diesel or electric powered engine. The controls for the trommel are located in a tower directly across the bath in line with the trommel. In the event any product gets hung up inside of the trommel, the classifier operator can stop the trommel with the flip of a switch.
The classifier can also be used for blending products such as compost and topsoil, creating a topsoil blend enriched with nutrients. It’s perfect for resizing bark products, as well.
In our wood recycling operation, learning how to separate wood from rock involved a lot of experimentation until we purchased the stationary classifier with trommel and water bath (float tank). Not only did our production increase, but we were able to reduce labor and heavy equipment costs, plus eliminated all other screening equipment.