(209e) Experience Using Inexpensive Water Overflow Experiment to Demonstrate SIS Concepts

Richmond, P. C., Lamar University
Benson, T. J., Lamar University
Rasel, M. A. K., Lamar University

This paper describes our experience using an inexpensive hands-on water overflow experiment to improve undergraduate chemical engineering students’ understanding of Safety Instrumented Systems (SIS). The experiment was designed to demonstrate how adding a SIS improves the probability of failure on demand for the process activity of filling a tank, a very serious issue for tank farms used to store petroleum products. This lab experience was coupled with classroom instruction on how SISs are used to protect chemical process operating personnel and equipment.

Two Arduino microcontroller boards and a pair of relays were used to create the control systems and pressure sensors were used to measure the level. A submersible pump and acrylic tank were used to represent the process. One microcontroller was used as the basic control system (BCS) and it was programmed to fill and then empty a water tank with a predetermined failure probability of overfilling the tank. The SIS device was created using the other Arduino board and a different tank level instrument separate from the basic control system. The SIS device was programmed with a second independent failure probability. The failure probabilities were implemented in the Arduino codes with pseudo random numbers.

The students used a Layer of Protection Analysis (LOPA) to calculate the SIS probability of failure required for a given BCS failure probability and a desired mitigated failure rate. The experiment was then used to physically demonstrate how the SIS reduced the probability that the water filling operation would result in water overflowing from the tank. We tested their understanding before and after they used the experiment to see if it improved their understanding of SISs.