Modeling of a Combined Kalina and Organic Rankine Cycle System for Waste Heat Recovery from Biogas Engine

Abstract

Converting waste heat into electricity has captured the interest of scientists for years because of its enormous potential to improve energy efficiency and to lessen environmental impacts. While there are numerous applications to recover lost energy, they are often not efficient or cheap enough to make a real-world impact. The aim of this study is to develop a heat recovery system for the waste recycling factory operating in Hatay, Turkey. We combined the Kalina Cycle (KC) with the Organic Rankine Cycle (ORC) to extract exhaust gas and jacket water waste heat from a combined heat and power engine. An ammonia–water mixture was selected as the working fluid in KC, while R123, R236ea and R124 were chosen and tested for the ORC. The selection of working fluids was made based on certain environmental impacts such as global warming or ozone depletion potential, without further exploring other working fluid options, which could be considered a limitation of this study. The optimal values of KC parameters, including mass fraction, turbine inlet pressure and inlet temperature, were found to be 90%, 430 °C and 90 bar, respectively. The KC was then combined with the ORC using three different working fluids, among which R123 yielded the best results. The net power, exergy and thermal efficiency of the combined cycle were calculated as 211.03 kW, 52.83% and 26.50%, respectively, while the payback period was estimated to be 4.2 years. It should be noted that the applicability domain of the obtained results is limited to the climate conditions studied here. We concluded that the combination of the KC and ORC can be efficiently used for the recovery of waste heat energy.