Thermodynamic analysis and optimization of a hybrid cascade supercritical carbon dioxide cycle for waste heat recovery

A hybrid cascade carbon dioxide cycle (HCCC) is proposed to recover the waste heat in this paper. In the HCCC, the top cycle uses the energy of the high-temperature flue gas and part of the low-temperature flue gas, and the bottom cycle utilizes the energy of middle-temperature flue gas and the other part of low-temperature flue gas. Compared with the traditional series cascade carbon dioxide cycle (SCCC), the HCCC can achieve lower flue gas outlet temperature, lower exergy destruction of heat regeneration process, higher bottom cycle output power and higher system output power. Under the design condition, the output power of the HCCC is 17.02% higher than the SCCC. The heat transfer performances of the recuperators are analyzed in detail to clarify the superiority of the proposed HCCC. The results of parametric analysis show the optimal split parameters exist to achieve best system performance. The pinch point temperature differences have great impacts on the thermal performance and system compactness. The multi-objective optimization is performed and the information of some important points are given. The specific heat conductance of HCCC is 7%similar to 11% lower than the SCCC for the same power output. Therefore, the thermal performance and system compactness of the proposed HCCC are better than the SCCC. The system performance under different waste heat sources is also discussed from the perspective of engineering application.

Automated summary

A hybrid cascade carbon dioxide cycle (HCCC) is proposed to recover waste heat. Compared with the traditional series cascade carbon dioxide cycle (SCCC), the HCCC shows higher system performance and better thermal performance.