It is well known that heat pumps reduce primary energy consumption by efficiently utilizing waste heat [1]. Despite their effectiveness in reducing energy demand, the application of heat pumps in the industry is limited, owing to high capital costs, primarily attributed to the expense of compressors. Additionally, conventional methods of pumping heat in scenarios with significantly larger temperature lifts (≥ 80°C) due to greater temperature differences between the heat sink and the heat source, require multiple compressors due to the use of multiple external cascade systems [2, 3]. In this talk, we propose a novel
mixed component internal cascade heat pump that is adept at transferring heat over significantly larger temperature lifts without the need for multiple compressors. The proposed
internal cascade uses a mixture of light and heavy components as its working fluid. It leverages the properties of lighter components to achieve lower temperatures at near-ambient pressure and heavier components to reach higher temperatures at relatively lower pressures [4]. This system effectively functions as an external cascade heat pump loop but without the need for multiple compressors.
We demonstrate the application and benefits of the proposed internal cascade heat pump system in terms of compressor power, volumetric flow rate, pressure ratio, and cost in the context of distillation through multiple case studies involving:
- Pumping heat over a large temperature range in double-effect distillation (from the condenser of the low-pressure column to the reboiler of the high-pressure column).
- Pumping heat from the condenser to the reboiler in a binary distillation case study from literature, involving hexane/hexadecane separation [5].
The proposed technology can potentially be applied in a plethora of industrial processes (including but not limited to distillation) involving the pumping of heat from a source to a sink with a large temperature difference between the two, thereby aiding in decarbonization efforts.
References:
- Null, H. R. (1976). Heat pumps in distillation. Chem. Eng. Prog.; (United States), 72:7. https://www.osti.gov/biblio/7239419
- Bamigbetan, O., Eikevik, T. M., Nekså, P., & Bantle, M. (n.d.). Extending Hydrocarbon Heat Pumps to Higher Temperatures: Predictions from Simulations.
- Arpagaus, C., Bless, F., Uhlmann, M., Schiffmann, J., & Bertsch, S. S. (2018). High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials. Energy, 152, 985–1010. https://doi.org/10.1016/j.energy.2018.03.166
- Zhao, L., Zheng, N., & Deng, S. (2014). A thermodynamic analysis of an auto-cascade heat pump cycle for heating application in cold regions. Energy and Buildings, 82, 621–631. https://doi.org/10.1016/j.enbuild.2014.07.083
- Chavez Velasco, J. A., Tawarmalani, M., & Agrawal, R. (2022). Which separation scenarios are advantageous for membranes or distillations? AIChE Journal, 68(11), e17839. https://doi.org/10.1002/aic.17839
