Abstract:
HAZOP, a qualitative risk assessment tool, has been widely used. Frequency and the worst credit consequence for each hazardous scenario are evaluated. The consequences of hazardous scenarios are normally decided by brainstorming and human experiences. Proper consequence assessment is crucial for risk level determination. Aspen steady model for a heavy aromatics rectification column in the heavy aromatic rectification process of aromatics combined unit has been established and then converted to dynamic model. Process data is used to correct and verify the model results. The simulation results agreed with actual operation situation of the device very well. The method combining dynamic simulation with the traditional HAZOP is applied for quantitative consequence determination and risk assessment. Two failure scenarios of full opening of steam valves in tower bottom reboiler steam valve and cooling of tower top condenser in a heavy aromatics rectification column are chosen. Deviations are simulated by Aspen dynamic model. Temperature and pressure at rectification column top and bottom are tracked as two important parameters. Aspen dynamic model can predicate the worst consequence for each scenario. A comparison is made between traditional HAZOP and new HAZOP based on the dynamic model. It is shown that the new HAZOP process is more efficient and that the consequence of deviation is clearly defined. Also, the result of the dynamic modeling can be used to define alarm/interlock set points.