Abstract
Based on the characteristics of temperature evolution during steam energy release, the idea of energy sectionalized conversion is proposed, and a dual-stage organic Rankine cycle (DORC) that can be respectively matched with varying temperature process and constant temperature process of the steam is constructed to enhance effective energy input from the energy input end. Besides, an absorption heat pump (AHP) is considered as the bottom cycle to recycle all exhaust vapor waste heat of DORC to achieve closed utilization of heat energy. The coupling of DORC and AHP to form a DORC-AHP cogeneration system can simultaneously improve the energy conversion efficiency of medium–low temperature steam from both the energy quality and quantity perspectives. Energy, exergy and economic assessments are carried out to disclose the superiority of the new energy utilization method. Compared with the singular-stage organic Rankine cycle (SORC) and DORC, the thermal efficiency of DORC-AHP is enhanced by 84.74% and 84.15%, the exergy efficiency is enhanced by 10.48% and 8.36%, and the exergy loss is decreased by 912.15 kW and 687.25 kW as the saturation temperature of the steam, superheat degree and mass fraction of R600 are 132℃, 40℃ and 0.10. Furthermore, there is an optimal saturation temperature and superheat degree of the steam to make the exergy efficiency of new cogeneration system the highest. Meanwhile, there is an optimal steam saturation temperature that enables AHP to assimilate all the exhaust vapor waste heat of DORC with the lowest driving heat source flow rate ratio between AHP and DORC. In addition, compared with the SORC and DORC, the exergy cost of new cogeneration system is decreased by 0.0007 $/kWh and 0.0006 $/kWh, multiple of investment cost (MOIC) is increased by 5.02 and 5.35, and dynamic payback period (DPP) is shortened by 2.46 years and 3.00 years. The DPP and MOIC of DORC-AHP system are both gradually close to those of SORC and DORC with the rise of electricity price. The results indicate that the new energy sectionalized closed conversion pattern demonstrates distinct superiority in the thermal and economic performance. The study achievement can lay a theoretical foundation for improving medium–low temperature steam energy utilization degree.
Published Version
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