This paper chronicles a control system retrofit for a 38,000 horsepower refrigeration compressor drive at Novacor’s Ethylene #1 Plant, Red Deer, Alberta, Canada (Fig. 1). The changes were designed to meet a 3-year continuous operation requirement. When the plant was constructed in the late 1970’s, annual turnarounds were considered normal operating procedure.
The project replaced original electronic controls on a 23,500 horsepower G. E. Frame 5, Model R gas turbine and a 18,300 horsepower Elliott 2 NV starter/helper steam turbine. Both turbines are connected at opposite ends of a single compressor drive shaft (Fig. 2). Because of the cost associated with any control system malfunction, a programmable triple modular redundant controller was selected as the replacement.
Among the modifications performed to enhance system reliability were wiring dual exhaust thermocouples directly into the system and triplicating critical field devices. Another important aspect of this upgrade was replacing deteriorating underground field instrumentation wiring with cabling in overhead cable trays. The original wiring was over stressed by “frost heaving,” causing several unplanned shutdowns. In April of 1991, the project team initiated a schedule to meet an early August delivery. System specification, checkout, and start-up, as well as its first year of performance are discussed.