Analysis of explosion accidents with heat recirculation dryers and their inherent safety improvement

The explosion accidents occurred at the drying workshops in China were found mostly to be caused by explosive gas mixtures formed in drying chambers. During the heat recirculation drying of surface coatings, solvent vapors are released forming explosive mixtures when the lower explosion limit of their concentration in air is reached. The analysis of exploded dryers and the numerical modeling served their inherent safety improvement ideas presented in this research. The improvement in heat recirculation drying safety was achieved with evacuation and oxygen concentration control Using nitrogen. The drying gas double circuits at inlet and outlet of the drying chamber were installed to maintain an inert gas minor excess pressure (<= 0.1 MPa) in the drying chamber. Oxygen concentration thus did not exceed 7.0 vol %. The drying time was substantially shortened, and the energy consumption was thus reduced for 67%. The present study provides an explosion prevention strategy with regard to inherent safety of heat recirculation dryers in design and operation. (C) 2016 Elsevier Ltd. All rights reserved.