Abstract: A system and method of concentrating spent caustic at a refinery has a multi-stage flash drum for separating a spent caustic stream into an overhead output stream including vaporized water and volatile organic compounds, and a concentrated spent caustic output stream. The system also has a condenser for condensing the overhead output stream, and a separator for separating the condensed overhead output stream into a volatile organic compound stream, a liquid hydrocarbon stream and a water stream. The system further has an ejector for applying a vacuum to the flash drum to vaporize the spent caustic stream at a reduced temperature, and to the separator to remove the volatile organic compound stream. The volatile organic compounds are removed from the overhead of the separator through the ejector to a burner of a fired heater.