15 May 2023

Presentation 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.