Optimization of Tehrmodynamic Cycles

本研究旨在找出各种热力动力循环的最佳条件。我们研究的循环是采用卡利纳循环作为底部循环的联合循环、HAT循环和用于回收液化天然气(LNG)冷能的复合动力循环。得到了各循环的最佳运行条件，并与常规燃气轮机联合循环和朗肯循环的性能进行了比较。所有计算均以纯甲烷为燃料，并假定开式布雷顿循环燃烧室出口温度范围为800~1400ﾟC。另一方面，对于HAT循环，参数为燃烧室空气比、加湿器出口温度和冷却空气在…中的流量。更像是涡轮机。结果表明，当热源温度较低时，以卡利纳循环为底循环的联合循环性能较好，而当热源温度较高时，性能较差。与常规燃气轮机循环相比，HAT循环在提高效率的同时减少了NOx的排放。最后，本文研究了以海水为热源、LNG为冷源的R-13与天然气复合动力循环回收LNG冷能的方案。经过R-13循环的液化天然气由海水加热，在两个天然气透平中膨胀。结果表明，R-13循环产生的功是天然气循环的一半，增加R-13循环的功会带来更高的联合循环总效率，降低R-13与天然气在高压冷凝器中的温差可以提高循环效率。较少

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