Thermodynamic Optimization of Organic Rankine Cycles at Several Condensing Temperatures: Case Study of Waste Heat Recovery in a Natural Gas Compressor Station

Abstract

In this article, the authors performed the thermodynamic optimization of organic Rankine cycles (ORCs) using several working fluids and considered the effect of three heat rejection media in the condenser: cooling water, ambient air, and hot water at high temperature for co- or trigeneration applications. The ORC system was modelled and optimized using the Aspen Hysys process simulator. The objective function is the maximization of turbine power output. Most natural gas compression stations use no heat recovery system. In this study, they applied the optimization procedure to the recovery of waste heat from gas turbines used to drive natural gas compressors in natural gas pumping stations. They used operational data from an existing pumping station to illustrate the potential benefits of ORC systems for this application, taking into account also non-thermodynamic aspects such as toxicity, flammability, and investment cost return. The highest ORC turbine output powers were obtained with aromatic hydrocarbons, then with aromatic fluorocarbons, n-hydrocarbons, and siloxanes (in that order). For the case studied here — a gas turbine of 2.6 MW of mechanical power— the proposed ORC can produce around 1 MWe, with a thermal efficiency of up to 24 per cent depending on the working fluid and condensing temperature.