以液化天然气为冷源的超临界CO2-跨临界CO2冷电联供系统
A Combined Cooling and Power System of Supercritical/Transcritical CO2 Cycle with Liquefied Natural Gas as Cool Source

为了提高超临界CO2布雷顿循环(SCO2循环)的低温余热回收效率,采用跨临界CO2循环(TCO2循环)作为底循环对再压缩式SCO2循环进行余热回收,并采用液化天然气(LNG)为冷源对工质进行冷凝,建立了以LNG为冷源的再压缩式SCO2？？TCO2冷电联供系统,以同时输出电量和制冷量。对系统进行火用分析比较,并研究了关键热力参数对系统净输出功率、制冷量、系统热效率和系统火用效率的影响。结果显示:使用LNG作为冷源,降低了TCO2循环的冷凝温度,提高了低温回收热效率,系统的热效率(动力)在给定的条件下达到54.47％;提高LNG的入口温度,可以减小系统火用损;高温回热器换热效率增加,系统热效率和火用效率均增加;SCO2透平膨胀比增加,系统热效率降低,但火用效率增加;TCO2透平进口压力升高,系统热效率和火用效率均呈现先减小再升高后减小的变化趋势;随着冷凝温度升高,系统热效率降低,但火用效率先减小后增加。
To improve the efficiency of low？？temperature waste heat recovery for the supercritical CO2 Brayton cycle(SCO2 cycle), a cooling and power system combining recompression SCO2 cycle with transcritical CO2 cycle(TCO2 cycle)and with liquefied natural gas as the heat sink was established to yield electricity and cold capacity. A TCO2 cycle was employed as a bottoming cycle to recover the waste heat in the topping recompression SCO2 cycle, and liquefied natural gas (LNG) was adopted to condense the CO2 in the TCO2 cycle to improve the heat recovery efficiency. Exergy analysis was performed and the effects of several key thermodynamic parameters on the system performance were examined according to the performance criteria, including net power output, refrigeration output, overall cycle thermal efficiency and exergy efficiency. The results show that the lower condensation temperature in the TCO2 cycle could improve the heat recovery efficiency, with the thermal efficiency of 54.47％ under given conditions when LNG was adopted as heat sink. Moreover, an increase in the LNG inlet temperature can lead to a reduction in exergy loss of the system. Furthermore, both thermal and exergy efficiency increase when the high？？temperature recuperator efficiency increases; when the SCO2 turbine expansion ratio increases, the thermal efficiency declines while exergy efficiency increases; with the increase of TCO2 turbine inlet pressure, both thermal and exergy efficiency increase first, and then declines and increases at last; as the condensation temperature increases, the thermal efficiency deceases and exergy efficiency increases firstly and then declines