Instrumented Protective Systems for Distillation Operations

Distillation is one of the most common unit operations in the chemical processing industry. Using relative volatility as a means of separating chemicals involves adding large amounts of energy to the system at the base of the column, typically through the use of a reboiler, and then removing that energy at the top of the column, via a condenser. Because of the high energy levels present in the column, failures within the system can result in overpressure of the column leading to a potentially catastrophic incident. The typical approach to dealing with these overpressure scenarios has been through the use of pressure relief systems. Layer of Protection Analysis (LOPA) provides a method for the evaluation of the risk presented by these overpressure scenarios. LOPA can be used to specify the required reliability of Instrumented Protective Systems (IPS) used as High Integrity Protective Systems (HIPS) which offer an alternative means of addressing some of these overpressure scenarios. This paper addresses several potential failure modes in distillation columns and then illustrates situations in which HIPS can be used to reach a safe state without reliance on the pressure relief system.