Fired equipment safety in the oil gas industry A review of changes in practices over the last 50 years

摘要

This paper reviews how the requirements of safety, availability, energy efficiency and environmental compliance have influenced the design and operation of fired equipment over the last 50 years. It presents the various norms and standards relevant to the classes of fired equipment used in the Oil & Gas industry and highlights the differences between prescriptive norms and performance based standards. The main hazards and common causes of accidents of process heaters, petrochemical furnaces and boilers are described. Finally, this paper reviews the evolution of the risk mitigations and design best practices over the last decades. It discusses in particular the particular challenges of improving the safety performance of existing equipment.Before the first oil crisis of 1973, the price of refinery fuels was very low and it was common practice to run heaters inefficiently with high excess air (e.g. 5 to 8 % 02 in the flue gas) and high draft to reduce the probability of sub-stoichiometric combustion and positive pressure in the combustion chamber. Since the safety margin was provided by operating with high excess air and high draft, control improvements were considered unnecessary. Fired equipment safety was essentially distributed between operator response to alarms (e.g. process upset conditions), instrumented protective functions programmed in the safety instrumented system and solutions such as explosion doors and snuffing steam to mitigate the consequence of explosions.In the last 25 years, the drive for safer operation with higher energy efficiency, lower NOx emissions and fewer nuisance trips has led operating companies to adapt their approach to fired equipment safety. The modern approach to fired equipment safety is to distribute the risk across independent protection layers. These safety barriers rely on a comprehensive control system with constraints and a safety instrumented system, but also on operational excellence with well-trained operators, good operating procedures and reliability-centered maintenance and risk-based inspection. As an important benefit, constraint controls with automated fuel cutbacks have proven effective at minimizing nuisance trips by keeping the heater within operational limits.