(350c) Simulation of Work Exchange Systems for Cost-Effective Mechanical Energy Recovery Using Aspen Plus

In many process systems, the operational pressures in different process units could be very different. This renders a need to pressurize/depressurize process streams in different operational stages, where process stream compression and expansion occur. The energy consumption in those operations could be very significant. It is recognized that a great amount of mechanical energy consumed in those operations can be recovered using pressure-driven work exchangers. Note that a work exchanger operates in a hybrid mode (both batch and continuous). Thus, characterization of this type of unit is more sophisticated than that for a process unit operated in a single mode. This kind of characterization is critical to a successful use in process design and operation.

In this work, we introduce a comprehensive steady-state and dynamic simulation technique for characterizing work exchangers. These units will be discussed as a new Aspen Plus tool that can be applied in process simulation to improve the energy efficiency. The developed models are for separately describing the unit operated under isothermal, adiabatic, or polytropic conditions for the process streams in liquid-liquid, gas-gas, or liquid-gas phase. The model-based simulation can facilitate the identification of the bottleneck in mechanical energy recovery and achieve an optimal design of a work exchanger network. Case studies will demonstrate the efficacy of the simulation technique for cost-effective mechanical energy recovery.