Concept of heat recovery in drying with chemical heat pump

Drying is one of the most energy intensive unit operations. It easily accounts for up to 15% of all industrial energy consumption. In the most drying processes heat is required to evaporate moisture which is later removed with a flow of air. The hot, humid air leaving the dryer is often considered as a waste stream, and a large fraction of energy is lost. The aim of the theoretical and experimental concept study presented here was to evaluate a method of reclaiming energy from low temperature waste streams and converting it to useful in industry saturated steam of temperature from 120 to 150 degrees C. Chemical heat pump concept based on the dilution and concentration of phosphoric acid was used to test the method in the laboratory. Heat of dilution and energy needed for water evaporation from the acid solution were experimentally measured. The cycle of successive processes of dilution and concentration has been experimentally confirmed. Theoretical model of the chemical heat pump was tested and coefficient of performance measured. Energy balance of the drying system and efficiency increase of the dryer supported with chemical heat pump were calculated.