T5-17 - Process safety at elevated temperatures and pressures: Cool flames and auto-ignition phenomena

Abstract

The chapter explains the concept of process safety at elevated temperatures and pressures. The hazards due to cool flames generation are also described. Partial oxidation processes, carried out at elevated conditions are used in the chemical industry. Detailed knowledge about relevant explosion indices is essential for a safe and economic operation in the most efficient way. Such explosion indices must be known under realistic process conditions—high temperature, high pressure, and high turbulence conditions. The cool flame phenomenon can occur in fuel (-air) -oxygen mixtures, within the flammable range and outside the flammable range, at fuel-rich composition and at temperatures below the auto-ignition temperature. It is caused by chemical reactions occurring spontaneously at relatively low temperatures and is favored by elevated pressure. The hazards of cool flames vary from spoiling a product specification through contamination and the appearance of unexpected normal (hot) flame (two-stage ignition) to explosive decomposition of condensed peroxides. Therefore, cool flame temperature and limits should be considered as a safety parameter for processes operating at elevated temperatures and pressures.