Economic Operation of continuous flow dryers - Ingo Edler

Rising energy costs are forcing operators to optimize all industrial processes which rely on high power consumption. One such application is the continuous flow dryer or drying oven, which is used in lacquering, coating and finishing processes to dry freshly coated surfaces quickly and reliably. This desire to reduce energy costs, however, must not conflict with the need for operational safety.

Explosion Hazards in Continuous Dryers

Inside a continuous flow dryer the solvent which is essential for the coating process is removed from the coating material (paint, adhesive etc.). These solvents, which tend to be combustible, vaporize and are removed by a continuous flow of air. The amount of solvent depends primarily on the process used, and is also affected by the proportion of solvent in the coating material, the applied coating thickness and the speed of the conveyer belt or feed rate of the foil to be coated. If too much solvent is placed in the oven or the air flow is insufficient, concentrations of solvent vapour can build up inside the continuous flow dryer which exceed the LEL (lower explosive limit) applicable to the solvent in question. Such hazardous situations arise as a result of incorrect operation or process errors. Studies have shown that increase rates of 10% LEL per second can be reached if, for example, material starts piling up on the conveyer belt or the ventilation system fails. This extremely quick change from safe to unsafe operation was the reason for standards to be drawn up which have to be complied with when planning and constructing continuous flow dryers.