Hope all of you are doing well. Today's topic is focusing on the general practice sometimes followed in industry related to the set point of Pressure Relief Devices of process equipment. Many times during PHA, I have come across a general philosophy of keeping the set point of the reactor's pressure relieving devices equivalent to its design pressure. This might be adequate for a non-reactive system. But the question is, is it adequate for a reactive system?
Here, the reactive system is one where there are hazards due to a chemical reaction, including the possibility of decomposition or polymerization or some side reaction, etc. We know based on normal kinetics that the rate of reaction is directly proportional to the temperature which in turn is proportional to pressure. In simple terms, it is said that the rate of a chemical reaction doubles with every 10 deg C rise in the reaction temperature. Hence it can be said that:
Higher set pressure leads to a correspondingly higher "set" temperature (i.e. the relieving temperature). This, in turn, leads to a higher rate of reaction which results in higher self-heating or higher temperature rise rate (dT/dt i.e. deg C/min) and a higher pressure generation rate (dP/dt i.e. bar/min). This is very important because for a chemically reactive system the required pressure relief area depends directly on the self-heating and pressure rise rates at the relief conditions.
