Fig. 4, X-axis represents the generation count in the evolution process,
while Y-axis represents the best fitness of each generation. It is
demonstrated that the optimization is rapidly convergent after a
certain number of iterations. Tables 5 and 6 list the property data at
each state point of the optimum operating conditions in detail based
on maximum first law efficiency and second law efficiency respectively.
Table 7 gives the results of energy analysis for the proposed
combined power cycle to compare the performances under three
different conditions. The optimized values are marked in italics in
Table 7. It can be observed that the optimization of the operating
parameters is of great significance to improve the performance of
the combined power cycle. Compared to the typical operating
conditions, the optimized first law efficiency is increased by 6.31%.
The corresponding net power output is increased to 8.77 MW and
the temperature of hot water leaving the system drops to 35.7 C.
Meanwhile, 68.2 t/h LNG can be gasified. Similarly, the optimized
second law efficiency is increased by 7.15%. There is an obvious
reduction in the total exergy loss. But the corresponding net power
output and first lawefficiency are both lower than those under other
two conditions. This is mainly because the LNG turbinework output
is decreased due to the increased LNG turbine outlet pressure, and
the lowered ammonia mass fraction results in a lower ammonia
turbine work output. Besides, the optimization results show that
some independent variables converge to their upper or lower
bounds, which agree well with the expected results in parametric
analysis. Also the best value of other independent variables can be
found exactly. It should be noted that some combinations of the
variables, even though corresponding to greater fitness values, are
eliminated because of the departure of given constraints.