Optimization of Tehrmodynamic Cycles

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The present study is to find out the optimum condition of various thermodynamic power cycles. The cycles we examined are the combined cycle which uses Kalina cycle as a bottoming cycle, HAT cycle and a composite power cycle to recover cold energy of liquefied natural gas (LNG). We obtained an optimum operating condition for each cycle and compared their performance with those of conventional combined cycle by gas turbine and Rankine cycle.Pure methane (CH4) was the fuel in all calculations covered and we assumed that the exit temperature of combustion chamber in open Brayton cycle ranges from 800 to 1400ﾟC.Other parameters for Kalina cycle are the ratio of flow rate of exhaust gas in topping cycle to that of working fluid in bottoming cycle, the pressure and concentration of ammonia at the inlet of turbine in bottoming cycle. On the other hand, for HAT cycle, the parameters are the air ratio in combustion chamber, the exit temperature of humidifier and the flow rate of cooling air in g … More as turbine. The amount of NO_x in each condition was obtained.The combined cycle by Kalina cycle as the bottoming brings higher performance when the temperature of heat source is relatively low, while its performance decreases when the temperature of heat source is higher. The HAT cycle enhances efficiency with less NO_x emission compared with the conventional gas turbine cycle.Finally, we examined a composite power cycle by R-13 and natural gas to recover cold energy of LNG.The R-13 cycle uses seawater as the hot heat source and LNG as the cold source. The LNG passing through R-13 cycle is heated by seawater and expands in two natural gas turbines. The parameters are the system pressure and the ratio of flow rate of R-13 to LNG.The result shows that the work produced by R-13 cycle is a half of the natural gas cycle, the increase in work by R-13 cycle will bring higher total efficiency of the combined cycle and the cycle effectiveness can be raised by decreasing the temperature difference between R-13 and natural gas in the high pressure condenser. Less