Thermal analysis of absorption heat pump implementation in an industrial dryer

Abstract

Industrial dryers are very energy-intensive, contributing to a large share of the thermal energy demand in industry. Most of this energy is discharged as moist air to the environment. The calorific content of the exhaust air is high due to the large amount of water vapour in this waste stream. Heat pump systems can be used to recover heat from the exhaust air, hereby raising the energy efficiency of the dryer. Simulations have been performed using data from an existing drying installation with conventional heating. The increase in energy efficiency is analyzed for the implementation of several types of absorption heat pumps in the drying cycles. The simulation results show the influence of different working fluid pairs and different configurations: type I, type II and double lift cycle. The highest amount of energy savings is achieved with type I absorption heat pumps using water–lithium bromide as the working fluid pair. With optimized temperature levels in the different components, the thermal energy use of the complete dryer can be reduced with 20%. The performance of absorption heat pumps in drying systems is however still bounded by the temperature limit of the waterlithium bromide working fluid pair. Searching for alternative working fluid pairs for higher temperature applications is therefore still essential and can increase energy savings even more.