Improving energy efficiency of dividing-wall columns using heat pumps, Organic Rankine Cycle and Kalina Cycle

• This study investigates further energy reduction in dividing-wall columns (DWC).
• Waste heat recovery (WHR) methods: MVR, BF AHP, AHT, ORC and KC are explored.
• Techno-economic feasibility of all WHR methods for six DWC applications is studied.
• Results indicate that at least one WHR method will be favorable for a DWC application.
• Best WHR method depends on the application, steam and electricity costs.

Distillation is a widespread separation process that accounts for the largest fraction of energy consumed (∼40%) in process industries. It's very low energy efficiency has motivated many researchers to investigate energy reduction methods. Previous research mainly focussed on application of energy reduction techniques such as externally heat integrated designs, dividing-wall columns (DWCs), heat pumps, feed preheat, intermediate reboiler, intermediate condensers and electrical power generation from distillation column condenser, via Organic Rankine Cycle (ORC) and Kalina Cycle (KC). This study investigates further improvement of energy efficiency of 6 DWC applications, which are already achieving 31–44% energy savings compared to conventional 2-columns system, through WHR methods: heat pumps, ORC and KC. The technical feasibility and economic viability of each WHR configuration are evaluated. Results show that it is usually favorable to perform WHR on DWC applications, with the exception of applications involving very low Tdist (temperature of distillation overhead vapour stream) and/or very high temperature lift. Applications with Tdist > 150 °C favor ORC and KC configurations which use cooling water as the cold sink. In locations with cheap electricity, bottoms flashing or vapor recompression is profitable; in other locations with expensive electricity, absorption heat pumps and KC configurations are favored.