EVIDENCE OF THE OXIDATION OF DEPOSITS IN HEATED BITUMEN STORAGE TANKS

Thermal analytical techniques have been used to examine the exothermic nature of the deposits found in heated bitumen storage tanks and to determine if they could act as an ignition source to flammable vapours. The deposits were found to undergo an oxidation/smouldering reaction at temperatures found on the underside of the roof of the tanks. Onset temperatures for exothermic behaviour ranged from 337 to 406 K. Deposits taken from refinery tanks were found to have an activation energy in the range of 80-90 kJ mol-1. The self-heating found in deposits constitutes a smouldering reaction which could deplete the oxygen concentration and so contribute to the conditions suitable for the formation of pyrophoric material. In a situation where cross-ventilation can occur and air is allowed to pass over the surface of the deposits, the rate of reaction would increase leading to higher temperatures and increasing the risk of fire.