Analysis of an accident at a solvent recovery plant

An accident in a plant for solvent recovery from solvent-contaminated wastes was examined. An experimental investigation of the accident was carried out using calorimetric and thermogravimetric techniques. The immediate cause of the accident was an unforeseen exothermic decomposition reaction. The main underlying cause of the accident was the absence of safety culture in the plant management, that resulted in the lack of a testing procedure to evaluate the thermal stability of the process feed. A simplified screening procedure based on differential scanning calorimetry was used in order to test the thermal stability of the nonvolatile fraction of the solvent-contaminated wastes present on the plant in order to be processed. More than 75% of the samples examined showed exothermal decomposition phenomena starting at temperatures higher than 100 degrees C. These phenomena were common to solvent wastes that originated from a number of different industrial activities. Thus, the thermal instability of the process feed is one of the main problems in solvent recovery operations. Our analysis of the accident suggested that the safe operation of waste solvent recovery processes requires an accurate characterization of the thermal stability of the process feed. Process safety is also increased by an adequate emergency vent and an accurate control of operating temperature, that may be reduced operating under vacuum. Safety devices may also include a water supply for emergency quench.