Development of a low-temperature heat engine using rapid thermal swing adsorption of CO2 onto activated carbon

This study presents a lab-scale, low temperature difference heat engine based on rapid thermal swing adsorption. The engine’s four step cycle consists of isochoric heating/desorption, isothermal expansion/desorption, isochoric cooling/adsorption, and isothermal compression/adsorption. Rapid temperature changes in the sorption bed are enabled by a loose packing of activated carbon into a heat exchanger. Four system configurations are tested, comparing pelleted vs. powdered activated carbon, and shell-and-tube vs. plate-and-frame heat exchangers. Each configuration is tested with a hot side temperature of 72 °C, cold side temperature of 13 °C and starting pressure of 3 bar, and is assessed based on cycle duration, work, power, and thermal efficiency. The ideal thermal efficiency under the operating conditions is 6.9 %. In practice, the device generates 215 J of work per cycle with a cycle time as low as 40 s; however, the thermal efficiency is low at an estimated 0.07 %. This highlights the impact of parasitic heat loss in indirect heating designs.