Thermodynamic and parametric analysis of a coupled LiBr/H2O absorption chiller/Kalina cycle for cascade utilization of low-grade waste heat

Abstract

Low-grade waste heat refers to the thermal energy that is widely available in various industrial processes and different energy utilization processes. In present work, a LiBr/H2O absorption chiller and a Kalina cycle have been integrated in cascade to achieve full utilization of low-grade waste heat. A parametric analysis has been conducted to investigate the effect of key operational parameters in terms of turbine-inlet pressure, turbine-outlet pressure, ammonia concentration, segment temperature and refrigeration temperature. The coupled system is then compared with the Kalina cycle without absorption chiller, in terms of the turbine-outlet pressure and the net power output. Moreover, the comparisons between two systems are illustrated in the temperature-entropy diagram. Results show that the optimal turbine-inlet pressures in all studied cases are obtained as 3200–3300 kPa for given conditions. System net power output decreases obviously with higher turbine-outlet pressure while increases with the increasing ammonia concentration. At refrigeration temperature of 2 ℃, the coupled system produces the maximum electricity output because the system can reach to a lower turbine-outlet pressure. The optimal thermal efficiency is 0.1678. After being integrated with an absorption chiller, the net power output of the Kalina cycle is improved by nearly 45%. This paper provides a performance-enhanced power generation system for cascade utilization of low-grade waste heat.