Experimental and simulation study on heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas heat recovery

Abstract

Direct-contact total heat exchange with liquid desiccant produces enormous gains in both sensible and latent heat recovery of low-grade flue gas. Previous studies related to that has tended to focus on the system performance rather than the heat and mass transfer characteristics, which is equally essential to their design, simulation and operation. This paper establishes an experimental system to investigate the heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas total heat recovery. Ceramic structured packing is adopted considering its corrosion and high-temperature resistances; calcium chloride aqueous solution is employed as the coolant and absorbent for its low cost and high latent heat recovery capability. Based on those, the effects of flue gas and solution inlet parameters on the performance indices, including sensible and latent heat recovery capacities, latent heat rate and total heat recovery rate, are tested and analyzed. Coupled heat and mass transfer models between flue gas and solution in this process are developed, which feature the enthalpy of dilution. By combining the models and experimental data, heat and mass transfer coefficients are calculated and fitted. In addition, the effect of packing height on total heat recovery capacity and ratio is investigated through simulations. The results show that the total heat recovery rate of 74.7% can be achieved at packing height to 1.5 m when liquid–gas ratio is 5.172.