(69c) Electrified Separation: Advancing Heat Pump and Vapor Recompression Technologies in Process Industries

Downstream processes are primary contributors to energy consumption in process industry. Smart and efficient electrification is a crucial component in advancing towards a CO₂-neutral process industry. Vapor recompression presents an obvious method for recycling waste heat. However, its practical application in distillation is generally restricted to the separation of close-boiling systems with high pressure and feed rate. Through practical examples, we will demonstrate how these limitations can be addressed and how mechanically assisted heat recovery systems can expand into new applications in the process industries with significant economic potential.

We will begin by examining single columns. By exploring the full permissible pressure range, it may become feasible to utilize vapor recompression and heat pumps in vacuum systems. For wide-boiling systems, feed preheaters, side-reboilers and/or side-condensers can be used to provide a substantial fraction of the total required energy at a lower temperature lift using multistage compressors. Even in small-scale applications, economically viable designs are possible using off-the-shelf heat pump technologies that are rapidly being developed by suppliers.

In extractive distillation, the absorbed component is typically stripped from the rich entrainer at elevated temperature using (high-pressure) steam as heating medium. It is industrial practice to re-use a large fraction of the enthalpy in the hot lean solvent stream for preheating of the feed to the desorption column. Nevertheless, substantial cooling duties need to be applied to cool the entrainer temperature to the specified value. Using an extractive distillation system, we show how the established heat-integration network can be modified to integrate a heat pump substituting steam and removing the need for entrainer cooling almost entirely. This approach is directly applicable to most absorption / desorption systems.

To reach the ambitious goal of CO₂-neutral process plants, optimizing single unit operations is not sufficient. We propose an integrated approach to harvest waste heat from various sources and upgrade it through a heat-pump system. This system delivers heat to lower-temperature heat sinks and produces low-pressure steam, which can be compressed to the necessary pressure levels. Consequently, a "total heat-integration network" can be established, tailored to the specific needs of individual plants or even interconnected with other plants or sites. This holistic strategy not only enhances energy efficiency but also significantly contributes to reducing the carbon footprint across the industry.