Paper No 354 – Thermally driven industrial ionic liquid absorption heat pump dryer – 14th IEA Heat Pump Conference, Chicago, USA
Drying, an energy-intensive process that is indispensable to many industries, accounts for 10–20% of the total industrial energy use in most developed countries. Thus, there are great incentives to reduce energy use in drying to lower its carbon footprint and improve process economics. However, challenging thermodynamic barriers have limited the opportunities to reduce energy consumption in the drying industry. The vapor compression system heat pump (VCSHP) has been established as a promising technology to improve the drying process efficiency. Fuel-flexible heat pump systems (operated by waste heat, solar-thermal, biomass, and green hydrogen) provide an off-grid alternative to VCSHP with attractive efficiency and economics. Here, two configurations of a thermally-driven ionic liquid semi-open absorption heat pump drying system are studied. Both systems utilize an adiabatic absorber to remove latent heat (moisture) from the process air and return its latent energy content as sensible heat to the process air (i.e., latent to sensible energy exchange takes place in the absorber). The systems’ condenser heat is then recovered to further increase the process air temperature prior to its entry into the drying kiln. Test results show that our semi-open ionic liquid absorption heat pump approaches a moisture removal efficiency (MRE) of ~1.2 kg H2O/kWhprimary comparable with the VCSHP drying systems (available products have an average MRE 1.4 kg H2O/kWhprimary). This level of performance, coupled with its fuel-flexibility, demonstrates the viability of the ionic liquid absorption heat pump technology in industrial drying.