Exergoeconomic performance comparison, selection and integration of industrial heat pumps for low grade waste heat recovery

Abstract

Mechanical heat pumps, absorption heat pumps, and absorption heat transformers are typical technologies for low-grade heat upgrading to save energy. However, there are few guidelines on the selection and integration of heat pumps in industrial processes, and different heat pumps need the input energy with several types or grades (i.e., mechanical work, high or medium grade heat), the coefficient of performance is not suitable to evaluate different heat upgrading technologies. In this work, an exergoeconomic criterion (i.e., exergy loss per total capital investment), measuring the exergy performance of each type of heat pumps and considers economic impact, is introduced to assist the screening of industrial heat pumps. The process models of heat pumps are developed using Aspen Plus. A systematic method for heat pump integration into an industrial process is presented, relying on Pinch Analysis of a given heat exchanger network. The impacts of different waste heat temperatures and temperature lifts on the selection of heat pumps are analyzed. A case study of a catalyst reforming unit in a petroleum refinery is used to demonstrate the applicability of the proposed method, and the energy-saving and economic performance of three types of heat pumps at different waste heat upgrading options are compared. Results show heat pump selection based on the exergoeconomic criterion can achieve better thermodynamic (exergy-based) and economic performance than that based on conventional one. The introduced guide map can simplify the heat pump integration process, and the proposed method of heat pump integration can be further extended to other industrial processes for low-grade waste heat recovery.