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Multi-objective optimization on a heat exchanger network retrofit with a heat pump and analysis of CO2 emissions control

Kang, Lixia, Liu, Yongzhong
Applied energy 2015 v.154 pp. 696-708
carbon dioxide, energy, energy conservation, greenhouse gas emissions, heat, heat exchangers, heat pumps, models, temperature
Integrating a heat pump into a heat exchanger network (HEN) can effectively recover the low-grade heat and reduce energy consumption. In this paper, a multi-objective optimization model on a HEN retrofit with a heat pump is proposed, with the goals of minimizing the total annual cost for the retrofit and maximizing the total annual CO2 emission reduction simultaneously. The Pareto front of these two objectives is obtained by solving the proposed model. Each point on the Pareto front corresponds to the optimal configuration of the heat pump and the process heat exchangers near the pinch of the HEN. The effect of the heat pump on the economic efficiency and CO2 emission reduction of the HEN are analyzed. The results indicate that integrating the heat pump into the HEN can improve the recovery of low-grade heat and reduce energy consumption and CO2 emissions. However, the integration of the heat pump into a HEN could offset the benefits from CO2 emission reduction by energy savings, in which the CO2 emission reduction is restricted by a critical power input and a critical temperature rise. Consequently, rational installation and reasonable operation parameters of heat pump become significantly important to simultaneously ensure the reduction of CO2 emissions and energy savings in HEN retrofit.