Summary

The airless steam drying method uses superheated steam instead of air to dry moist products, the steam then generated being vented, reused or condensed. It can typically save up to 50% of the thermal energy used by conventional hot-air drying. The dryer is operated at atmospheric pressure. By dispensing with the use of air, the new method reduces fire hazard and does away with the need for a discharge clean-up system.
The new technology promises higher process rates and has already been introduced into the ceramic industry. Three Dutch companies are particularly interested in continuous airless drying on a commercial scale. The key feature of the continuous airless dryer is that it uses the density difference between ambient air and atmospheric pressure steam to create a manometric seal at both the point of entry and the point where the product leaves the dryer.
A feasibility study has shown that the following materials can be dried: wood chips (EPZ), paper rejects (Kappa Roermond) and oil-containing sludge (Van Gansewinkel). The payback period varies from 1.5 to 2 years. The researchers advise setting up a pilot plant in order to mount an extensive test programme.