abstract
Solar thermal power plants have attracted increasing interest in the past few years e with respect to
both the design of the various plant components, and extending the operation hours by employing
different types of storage systems. One approach to improve the overall plant efficiency is to use direct
steam generation with water/steam as both the heat transfer fluid in the solar receivers and the cycle
working fluid. This enables operating the plant with higher turbine inlet temperatures. Available literature
suggests that it is feasible to use ammonia-water mixtures at high temperatures without corroding
the equipment by using suitable additives with the mixture. The purpose of the study reported here was
to investigate if there is any benefit of using a Kalina cycle for a direct steam generation, central receiver
solar thermal power plant with high live steam temperature (450 C) and pressure (over 100 bar).
Thermodynamic performance of the Kalina cycle in terms of the plant exergy efficiency was evaluated
and compared with a simple Rankine cycle. The rates of exergy destruction for the different components
in the two cycles were also calculated and compared. The results suggest that the simple Rankine cycle
exhibits better performance than the Kalina cycle when the heat input is only from the solar receiver.
However, when using a two-tank molten-salt storage system as the primary source of heat input, the
Kalina cycle showed an advantage over the simple Rankine cycle because of about 33 % reduction in the
storage requirement. The solar receiver showed the highest rate of exergy destruction for both the cycles.
The rates of exergy destruction in other components of the cycles were found to be highly dependent on
the amount of recuperation, and the ammonia mass fraction and pressure at the turbine inlet.