Thermodynamic performance of Kalina cycle system 11 (KCS11): feasibility of using alternative zeotropic mixtures

With the ever increasing demand for energy, exploiting low-temperature heat sources has seen significant interest recently. The conventional organic Rankine cycle (ORC) is a typical approach used to exploit low-temperature heat sources but suffers from low efficiency. The Kalina cycle is a reversed absorption cooling system that normally utilizes an ammonia–water binary mixture as the working fluid. This paper investigates, using thermodynamic modelling, the performance of Kalina cycle system 11 (KCS11) used for low-temperature heat sources below 200°C compared with the ORC based on pure ammonia and R134a. The cycle performance was investigated at various operating conditions including the evaporator pressure of 10–50 bars, heat source temperature of 333–473 K, heat sink temperature of 283 K and in the case of KCS11 various ammonia mass fractions at the evaporator outlet. Results show that the KCS11 can produce up to 40% increase in the efficiency compared with the ORC when using ammonia and up to 20% increase when using R134a. Although the ammonia–water working pair has zero ozone depletion potential (ODP) and very low global warming potential (GWP), it is toxic and needs special safety procedures against leak as ammonia is part of this binary mixture. Therefore, further investigation was carried out to explore the feasibility of using alternative working pairs that are non-toxic and outperform the ammonia–water pair for the Kalina cycle. Nineteen working pairs were investigated and results showed that propane and propylene-based mixtures have the potential to replace the ammonia–water pair in the KCS11.