THERMAL AND OVERPRESSURE HAZARDS MODELLING AND SIMULATION: A CASE STUDY OF REFINERY FIRED HEATER
Crude oil-fired heaters are associated with considerable fire and explosion hazards. The heaters present higher risks at later operational life due to ageing, wear and obsolescence. It is therefore important to re-evaluate such heaters to determine the adequacy or otherwise of the existing safeguards. This paper presents results of studies on hazard levels in aged fired heaters through quantitative consequence modeling method. A number of credible failure scenarios were considered. In particular, characteristics of potential jet fires due to Liquefied Petroleum Gas (LPG) leaks from hole sizes: 15, 30, 50 and 100 mm were investigated. For the 100 mm hole size, it was found that thermal radiation level of up to 37.5 kW/m2 could be experienced within 25 m radius of the heater, which is enough to affect nearby operators severely and could also adversely affect critical pieces of equipment around. Fireball potential with peak thermal density of about 12.5 kW/m2 was also observed within 2 m radius. For the 100 mm hole size, lower flammability limit of the fuel could be attained within 16 m downwind which poses flash fire risks. Overpressures of 1.02, 1.14 and 1.21 bar could be experienced at 30, 6 and 4 m respectively away from the fired heater which could result in partial demolition of structures that are within the radius.Overall, the results indicate that the risk profile is very sensitive to leak sizes, operating and atmospheric conditions as well as the fuel quantity being held, among others. For the chosen case study, higher integrity protection layers, in form of safety instrumented systems, relief, blow down and alarm systems, are recommended.