# Energy Analysis of Kalina and Kalina Flash Cycles Driven by Renewable Energy
## 3 Results and Discussion
### Performance of Kalina Cycle (KC) and KFC with Optimal Flash Pressures  
In this section, the exergetical performance of KC and KFC are comparatively investigated, in which the pressure of the flash vessel installed only in KFC is assumed to be a pressure yielding the  
Figure 4: Dependence of (**a**) separate and (**b**) cumulative ratios of exergy consumption on the flash pressure for \(x_{b}=40\%\). Figure 5: Dependence of (**a**) separate and (**b**) cumulative ratios of exergy consumption on the flash pressure for \(x_{b}=60\%\). maximum exergy efficiency for a specified set of other parameter values. Figure 6 is the characteristic diagram of net power vs. exergy efficiency illustrating the system performance of KC and KFC for the ammonia fraction, \(x_{b}\), from 40% to 80% and separator pressure, \(P_{H}\), from 16 bar to 48 bar. In both systems, net power has a local maximum when the separator pressure is low (16, 24 bar); while it monotonically increases with the ammonia fraction, i.e., to the right, at higher separator pressures (32, 40, 48 bar). By contrast, exergy efficiency has a local maximum when the separator pressure is high (24, 32, 40, 48 bar) and monotonically decreases with ammonia fraction, i.e., downward, at the lowest pressure of 16 bar. For each separator pressure the ammonia fraction producing maximum net power is higher than that yielding maximum exergy efficiency. With respect to separator pressure, maximum net power production shows an increasing-decreasing pattern, while exergy efficiency shows a decreasing-increasing pattern in the considered parameter range. The diagram clearly shows that the KFC gives higher optimal values of net power as well as exergy efficiency than KC for all separator pressures. In fact each point in the diagram representing a set of values of \(P_{H}\) and \(x_{b}\) of the KFC locates at the right and upper position of the corresponding point of the KC; implying better performances of the KFC. Figures 7-9 are comparative illustrations of exergetical performance of the KC and KFC. Figure 7 depicts the dependence the exergy efficiency (\(\eta_{ex}\)) and exergy destruction ratios of condenser (\(Dc\)) and regenerator (\(Dr\)) on the ammonia fraction (\(x_{b}\)) for separator pressure of 24 and 36 bar. Both cycles show peak points on the exergy efficiency curves, which move to the right and downward with the rise of separator pressure. Although the gap shrinks rapidly with increasing ammonia fraction, KFC gives higher exergy efficiency than KC. Condenser heat transfer increases when the mixture becomes richer in ammonia or separator pressure is lowered. The contrary is true of the regenerator. Therefore, the ratio of exergy destruction of condenser and regenerator are monotonically increasing and decreasing function of ammonia fraction, respectively. In addition exergy is destroyed more in the condenser and less in the regenerator for lower separator pressure, respectively. The effect of flashing is also opposite in the condenser and regenerator: the exergy destruction in the condenser is larger in KFC than KC, and vice versa for the regenerator. Similar to the exergy efficiency, the gaps between the KFC and KC rapidly shrink at higher ammonia fractions. This implies that the flashing effect is more influential for ammonia-poor basic solutions. Figure 6: Diagram of net power production vs. exergy efficiency of Kalina cycle (KC) and KFC. Figure 8 depicts the dependence of the exergy destruction ratios of HRVG (\(D\)s), power components (\(D\)w), and throttle valve (\(D\)v) on ammonia fraction for P\({}_{\rm H}\) = 24, 36 bar in KC and KFC. In both systems, exergy destruction at the HRVG increases with the increase of the ammonia fraction or decrease of the separator pressure, mainly because these factors enhance the heat transfer at the HRVG. By contrast, exergy destructions occurring at power components and throttle valve decrease with the increase of ammonia fraction or decrease of separator pressure.