Comparing Three Methods for Design Analyses of Rankine Cycle for Waste Heat Recovery from Natural Gas Compression

Abstract

This study applies three methods for design of Rankine cycles utilizing waste heat in the oil and gas industry. The methods differ in the level of detail of heat exchanger model applied and in the flexibility with respect to heat exchanger design. All the methods involve formulating a constrained optimization problem with the objective of maximizing net power output, but vary in the constraints related to limit the size of the heat exchangers. The cycles with using two working fluids, n-butane and a n-butane/n-pentane mixture (30%/70%), are compared for each method. The methods yield different results; both the maximized net power output and the best-performing working fluid differ with respect to the method used, emphasizing the importance of method selection.