Research on heat and mass transfer characteristics of direct contact heat pump for recovering waste heat from coal-fired boiler flue gas

LIU Zengbin

doi:10.3969/j.issn.1007-7677.2025.02.004

Abstract：Due to the large moisture content in the flue gas of coal-fired industrial boilers after wet desulfurization,there is a waste of residual energy.The direct-contact heat pump can condense the water vapor in the flue gas by di-rectly contacting the heat-absorbing working fluid with the flue gas.This significantly improves the heat transfer per-formance of waste heat recovery and effectively reduces the emission concentrations of SO2 and NOx in the exhaust gas,achieving a dual effect of energy conservation and emission reduction.This experiment focuses on studying the ability of a direct-contact heat pump for a 14 MW coal-fired boiler to recover the waste heat of flue gas and its emission re-duction effect.Specifically,the influence on the heat transfer performance is explored from three aspects:the spray flow rate and the liquid-gas ratio,the temperature difference between the spray water and the flue gas,and the spray height.The corresponding pollution emission reduction effects are also analyzed.Orthogonal analysis method and sen-sitivity analysis are employed to discuss the influencing factors of the heat exchange for the recovery of condensing waste heat from flue gas,and the variation laws of the heat transfer performance with various factors are obtained.The experimental results show that as the liquid-gas ratio increases,the heat transfer performance of the condensing waste heat recovery from the flue gas improves.With the rise of the spray water temperature,the ability to recover the condensing waste heat from the flue gas decreases significantly.Increasing the spray height can effectively enhance the heat transfer performance of the condensing waste heat recovery from the flue gas and the level of pollutant emission reduction.