Experimental investigation of a liquid desiccant cooling system driven by flue gas waste heat of a biomass boiler

This paper presents the preliminary experimental results of a liquid desiccant cooling system driven by the flue gas waste heat of a biomass boiler. The desiccant cooling system is mainly composed of a regenerator, a dehumidifier and an evaporative cooler. The flue gas waste heat is applied to the regenerator to regenerate the desiccant solution. The environmentally friendly liquid desiccant potassium formate (HCOOK) solution is used in the dehumidifier for air dehumidification due to its less corrosion, lower cost, lower density and lower viscosity. A cross-flow heat and mass exchanger for indirect evaporative cooling is adopted in the evaporative cooler to ensure that product air meets the indoor air quality and thermal comfort standard. The desiccant cooling system operated in Autumn days in Nottingham was found to be able to decrease the air temperature by 4 degrees C and reach a cooling capacity of up to 2381 W. Moreover, the dehumidifier is able to reduce the relative humidity of the humid air by 13%. The biomass boiler's flue gas waste heat extracted and supplied to the regenerator was found to be 554 W, which is insufficient to regenerate the dilute liquid desiccant solution under current experimental conditions. To obtain sufficient heat to regenerate the liquid desiccant, the existing first-of-its-kind concentric helical coil heat exchanger extracting the waste heat of the boiler needs to be redesigned, and, in particular, the concentric helical coils of the heat exchanger need to be placed inside the chimney to enhance the waste heat extraction.