抽汽-乏汽联合回热对低温蒸汽ORC系统热力性能影响

Study of the Influence of the Extraction SteamExhaust Steam Combined Recuperation on the Thermal Performance of a Low Temperature Steam ORC System

为充分回收矿藏热采过程中尾端的低温蒸汽余热,根据热力学第一、第二定律,在单独抽汽回热、单独乏汽回热系统的基础上,提出一种新型抽汽-乏汽联合回热系统,并建立以低温蒸汽为热源的抽汽-乏汽联合回热理论模型。通过编制计算程序分别对带抽汽回热的ORC循环、乏汽回热ORC循环以及联合回热ORC循环的热力学性能进行了分析,并与无回热ORC循环的性能进行了比较。结果表明:3种回热循环的热效率、净输出功以及火用效率均随蒸发压力升高而升高,其中联合回热循环的热力性能最高,分别能达到11.37%、7 593 kW及51.9%,比相同工况下的无回热ORC循环分别增高百分比为19.6%、12.5%及15.1%;对于单位功耗火用损,各循环则表现为随蒸发压力的升高而逐渐递减,且有联合回热循环的单位功耗火用损<抽汽回热<乏汽回热<无回热ORC循环,在蒸发温度为105℃时,对应单位功耗火用损分别为0.91、0.95、1.06及1.22;同时,在相同抽汽压力下,联合回热循环的抽气系数α小于单独抽汽回热循环,工质质量流量基本相同,联合回热循环具有更好的热力性能。

To fully recover the steam produced from low temperature waste heat during the hot exploitation of mineral resources in the tail portion,in line with the first and second law of thermodynamics and on the basis of an independent extraction steam recuperation and independent exhaust steam recuperation system,proposed was a new type extraction steam-exhaust steam combined recuperation system and established was an extraction steam-exhaust steam combined recuperation theoretical model with the low temperature steam serving as the heat source. By preparing a calculation program,the authors analyzed respectively the thermodynamic performance of an ORC cycle with steam extracted, exhaust steam recuperation ORC cycle and combined recuperation ORC cycle and compared with that of an ORC cycle with no steam extracted. The research results show that all the thermal efficiency,net output power and exergy efficiency of the three recuperation cycles will increase with an increase of the evaporation pressure,among them, the combined recuperation cycle has the best thermal performance,the thermal efficiency,net output power and exergy efficiency hitting 11. 37%,7 593 kW and 51. 9% respectively and 19. 6%,12. 5% and 15. 1% respectively higher than those of the ORC cycle with no steam extracted under the same operating conditions. For the exergy loss by unit power consumption,various cycles will exhibit a gradual descending tendency with an increase of the evaporation pressure and the ranking of the exergy loss for unit power consumption can be listed as follows: combined recuperation cycle < extraction steam cycle < ORC cycle with no steam extracted. When the evaporation temperature is 105 ℃,the corresponding exergy losses for unit power consumption are 0. 91,0. 95,1. 06 and 1. 22 respectively. In the meantime,at the same extraction steam pressure,the extraction steam coefficient of the combined recuperation cycle α will be lower than that of the independent extraction steam recuperation cycle. Under the condition that the mass flow rate of the working medium is basically the same,the combined recuperation cycle will result in better thermal performance.