Energy and exergy recovery from exhaust hot water using organic Rankine cycle and a retrofitted configuration
Exhaust hot water (EHW) is widely used for various industrial processes. However, the excess heat carried by EHW is typically ignored and discharged into the environment, resulting in heat loss and heat pollution. An organic Rankine cycle (ORC) is an attractive technology to recycle heat from low-temperature energy carriers. Herein, ORC was used to recycle the heat carried by EHW. To investigate the energy and exergy recovery effects of EHW, a mathematical model was developed and a parametric study was conducted. The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa, R113 and R123 as the working fluids. The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system. Under given EHW conditions, an optimum evaporation temperature exists corresponding to the highest exergy efficiency. To further use the low-temperature EHW, a configuration retrofitted to the ORC by combining with flash evaporation (FE) was conducted. For an EHW at 120 °C and 0.2 MPa, the maximum exergy efficiency of the FE-ORC system is 45.91% at a flash pressure of 0.088 MPa. The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.
Key wordsexhaust hot water (EHW) organic Rankine cycle (ORC) energy efficiency exergy efficiency flash evaporation (FE)
Unable to display preview. Download preview PDF.
- ROGERS J E. Energy efficiency: The fifth fuel [J]. Electric Perspectives, 2007, 32(2): 88. [2018–02–24]. http://connection.ebscohost.com/c/speeches/25528984/energy-efficiency-fifth-fuel.Google Scholar
- KARELLAS S, SCHUSTER A. Supercritical fluid parameters in organic Rankine cycle applications [J]. International Journal of Thermodynamics, 2008, 11(3): 101–108. DOI: 10.5541/ijot.217.Google Scholar
- WANG Zhi, ZHOU Nai, LUO Liang, ZHANG Jia, TONG Dao. Comparison of thermodynamic performance for waste heat power generation system with different low temperature working fluids [J]. Journal of Central South University: Science and Technology, 2010, 41(6): 2424–2429.(in Chinese)Google Scholar
- WEI L, ZHANG Y, MU Y, YANG X, CHEN X. Efficiency improving strategies of low-temperature heat conversion systems using organic Rankine cycles: An overview [J]. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2011, 33(9): 869–878. DOI: 10.1080/15567036.2010.531514.CrossRefGoogle Scholar
- WU S Y, ZHOU S M, XIAO L. The determination and matching analysis of pinch point temperature difference in evaporator and condenser of organic Rankine cycle for mixed working fluid [J]. International Journal of Green Energy, 2016, 13(5): 470–480. DOI: 10.1080/15435075.2014. 966371.CrossRefGoogle Scholar