Electric Power Generation From Low-Enthalpy Heat Recovery in FPSOs Using Kalina Cycle

Abstract

The present work aims to study, by mean of the First and Second Law the Thermodynamic, the performance of a Kalina Cycle (KCS-34) using low-temperature waste heat recovery in the fourth stage of compression in the CO2 Compression Unit on a Floating Production, Storage and Offloading System (FPSO). Different parameters are evaluated associated with the evaporator to improve the heat absorption of the cycle and taking into account the area of the system too. Three different concentrations of ammonia water mixture are studied, between 65% and 85% of ammonia mass fraction, the CO2 acting as a hot fluid, entry to the evaporator of the Kalina Cycle at 135.2 °C. Some other parameters taking into account in this work are: evaporation pressure, pinch point temperature and terminal temperature differential (TTD) to reach the maximum power production and first and second law efficiency. The Aspen-Hysys software V. 8.6 is used as a tool to simulate the thermal system and Peng-Robinson Stryek-Vera (PRSV) equations of state (EoS). A power output gain in the cycle is obtained with a higher ammonia mass fraction, reaching a maximum net power output of 598 kW using 85% of ammonia mass fraction, a pinch point of 2 °C, a terminal temperature differential of 10 °C and 3500 kPa of the working pressure. Ending, a total heat exchange area calculation is determined in order to have an idea of how big the system is for the different design projects.