NOVA Chemicals, headquartered in Sarnia, Ontario, produces plastics and chemicals essential for everyday life. The company supplies materials to customers worldwide who produce consumer, industrial and packaging products. Nova Chemicals manufactures high-density polyethylene (HDPE) and low-density polyethylene (LDPE) from ethylene, in an exothermic reaction. It is extremely important that excess heat generation is controlled to a predetermined operating temperature during this process to prevent product instability that can lead to lost revenues. Therefore, Nova Chemicals uses a jacketed reaction vessel with a circulating liquid coolant to facilitate temperature control. They have also installed chillers on the closed cooling loop to remove heat from the cooling liquid and thus maintain desired reactor temperatures. Chillers are crucial equipment in any chemical manufacturing facility, and proper procedures must be taken to protect the chillers against critical failure. One method of protection is the use of a safety relief valve (SRV), as shown in Figure 1.
Maninder Bhamra, a University of Waterloo co-op student who worked as a Process Safety Valve Analyst at Nova Chemicals, was asked to perform preliminary sizing of safety relief valves intended to provide overpressure protection for the chiller’s evaporator unit.
The teaching objective of this case is to illustrate topics in critical thinking, process safety, and valve sizing. The case could be used as a conceptual design case for CHE 100 (Chemical Engineering Concepts). It could be used to complement lecture material, specifically in CHE 480 (Process Analysis and Design), and CHE 482 (Chemical Engineering Design Workshop).