Heat recovery, adsorption thermal storage, and heat pumping to augment gas-fired tumble dryer efficiency

Thermal drying of textiles is an energy-intensive process; however, about one-third of the total input energy is rejected as waste heat. While system efficiency can be improved by optimizing system design and operational parameters, energy from the exhaust stream of the dryer can also be stored for use in future cycles. An assessment of several energy saving techniques is conducted, including exhaust gas recirculation, recuperative waste heat recovery, adsorption-based thermal energy storage, and heat pumping, to achieve reduction in energy consumption and drying time. A single-stage two-bed adsorption heat pump is also considered to investigate the potential for additional performance improvements. Based on experiments on a commercial 11.33-kg capacity gas-fired tumble dryer, it is shown that exhaust gas recirculation, recuperation, and adsorption-based thermal energy storage are able to reduce energy consumption by 9%, 15%, and 22% respectively. Combining the effects of exhaust gas recirculation with an air-to-air cross flow heat exchanger, and a 5-kg sorption bed yields a specific moisture extraction ratio of 1.174 kWh kg(w)(-1), a reduction in energy consumption by 18.2% compared to the baseline gas-fired tumble dryer, while also reducing drying time by - 355 s from the baseline 1725 s.