Optimization of energy-saving distillation system of absorption heat pump based on intermediate heat exchange

Deepening the energy-saving potential of the distillation process by waste heat recovery is an essential direction in the petrochemical industry. This paper proposes a distillation system of absorption heat pumps based on intermediate heat exchange through waste heat recovery and cascade energy consumption to improve energy efficiency significantly. Firstly, a mathematical model was developed using the numerical simulation software Aspen Plus for the example of a depropanizing column in a gas fractionation system with an annual capacity of 180,000 ton. Secondly, the optimization of critical parameters, including the material parameters of the intermediate-reboiler and intermediate-condenser and the operational performance of the AHP, is further investigated. The numerical simulation results show that the steam consumption can be decreased by 25% when the pressure in the distillation column is 1.3 MPa, and the heating temperature of the heat pump is 76 celcius. Finally, a complete energy-saving distillation system involving a three-column process has been designed. The effects are significant: 92,000 ton of steam can be saved annually, corresponding to a reduction of 38.8%; 33,300 ton of softened water can be saved annually, which equals to a reduction of 42.5%; an economic profit of 5,429,000 CNY can be achieved annually, and the fixed investment payback period is only 3 years.

Automated summary

This paper proposes a distillation system of absorption heat pumps based on intermediate heat exchange through waste heat recovery and cascade energy consumption to significantly improve energy efficiency. The results show that the system can reduce steam consumption, save softened water, and achieve economic benefits.