Kalina cycle based power plants are latest development in power plant technology. Owing to its unique features which try to resemble Carnot cycle, Kalina cycles work on thermal efficiency range of 40-60 %. In this video lecture you will come to know what is Kalina cycle and why it is a promising technology.
Summary of above lecture along with latest developments Kalina cycle power plants are described below.
Working fluid - Mixture of 2 fluids
What makes Kalina cycle different from conventional Rankine cycle of power production is its choice of working fluid. Kalina cycle uses mixture of 2 fluids as working fluid, most commonly used is ammonia and water mixture. To get answer why Kalina uses a mixture as its working fluid, have a look at T-s diagrams of ordinary Rankine cycle and Kalina cycle.
|Fig.1 Comparison of Rankine and Kalina cycles|
Comparison with Carnot Engine - Reason for high efficiency
In a Carnot engine heat addition and rejection happen at uniform temperature.
|Fig.2 In a Carnot engine heat addition and rejection happen at uniform temperature|
|Fig.3 Average heat addition and rejection temperatures of Kalina cycle is much wider than a Rankine cycle|
Difficulty at Condenser - Use of Separator
Kalina cycle uses high concentration ammonia mixture (around 70% ammonia) at steam turbine part, but such a mixture has got very low condensing temperature.
|Fig.4 Phase diagram of Ammonia-Water mixture|
|Fig.5 Use of recuperator in producing low concentration ammonia mixture at condenser|
Use of Recuperator
It is clear from T-s diagram of Kalina cycle that temperature at exit of steam turbine (point 4) is greater than temperature at inlet of boiler (point 2). So there exists a chance of heating up boiler liquid by virtue of this high temperature steam turbine output. This is accomplished with help of a heat exchanger called recuperator. This is shown in following figure.
|Fig.6 Increase in further thermal efficiency with help of a recuperator|
Advancements in Kalina Cycle Power Plants
Instead of ammonia-water mixture industries have started implementing organic mixture based Kalina cycles in order to harness maximum from given condition. Some examples are mixture of R22 & R114 and mixture of Hexamethyldisiloxane & Decamethyltetrasiloxane.
Thanks to its unique feature of varying thermo-physical properties by varying mixture concentration at different parts of cycle, Kalina cycle power plants are widely used in Geothermal stations and waste heat recovery units. They can easily match to any source (heat addition) and sink (heat rejection) condition by varying mixture concentration in the cycle.