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.