Abstract
The Kalina cycle (KC) has been recognized as one of the most efficient conversion systems of low-grade heat sources. The Kalina flash cycle (KFC) is a recently proposed novel cycle which is equipped with an additional flash process to the KC. In this study, the exergy performance of KC and KFC driven by a low-grade heat source are investigated comparatively. The dependence of the exergy destruction at each component as well as the system’s exergy efficiency on ammonia concentration, separator pressure and, additionally, flash pressure for KFC, are systematically investigated. Results showed that KFC can be optimized with respect to flash pressure on the base of exergy efficiency, and the component where largest exergy destruction occurs varies for different separator pressure and ammonia fraction in both systems. It is also shown that the maxima of net power production and exergy efficiency in KFC with optimal flash pressure are superior to those in KC.
Highlights
Due to the limited fossil fuel resources and environmental problems, the efficient conversion and storage of renewable energy has been increasingly important [1]
An earlier theoretical study by El-Sayed and Tribus [4] showed a potential of Kalina cycle (KC) for a 10%–20% enhanced thermal efficiency than RC
As these two systems are the same except for the added components of the flash vessel and turbine 2, the same location numbers in KC are allotted to the corresponding locations in the Kalina flash cycle (KFC)
Summary
Due to the limited fossil fuel resources and environmental problems, the efficient conversion and storage of renewable energy has been increasingly important [1]. The organic Rankine cycle (ORC) and the Kalina cycle (KC) have been recognized as the feasible and efficient ways of generating power by exploiting a low-grade heat source. KC uses a solution of ammonia in water for working fluid, whose boiling points differ. It usually operates as an absorption cycle with varying concentration during the cycle. An improved efficiency is expected owing to the reduced thermal mismatch between the source and mixture during the heat acceptance process [2,3]. The early KC proposed by Kalina and Leibowitz [5] was shown to produce a higher power output than ORC for a specific geothermal application
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