AT-19-C049 -- A Liquid-Desiccant-Based Heat Recovery System for Gas-Fired Boilers in District Heating Networks ✓ Most Recent

In district heating networks, natural gas fired boilers or turbines are more and more widely used in replace of coal fired boilers for the sake ofenvironmental protection. The flue gas of natural gas boilers contains a lot of vapor carrying considerable latent heat. However, the conventionalcondensing boiler can hardly recover the latent heat as the dew point of the flue gas is only marginally higher than the temperature of the return water fromheating networks. Therefore, a liquid-desiccant-based total heat recovery system combined with direct contact condenser is introduced in this paper toincrease the dew point by humidifying the oxidizing air. The system mainly consists of three packed tower, where the flue gas or air contacts directly withthe liquid desiccant or the cooling water. The liquid desiccant in the system serves as a medium to transfer water vapor from the flue gas to the oxidizingair. The cooling water sprayed into the condenser, on the other hand, recovers sensible heat and latent heat from the flue gas and then transfers it to thereturn water. A mathematical model for the system is established and a simulation is conducted. The simulation results show that the thermal efficiency ofthe novel system is 101.4%, compared with an efficiency of 97.5% of the condensing boiler. Besides, the flue gas is discharged to the atmosphere with arelative humidity of 56% rather than 100%. Moreover, the cooling water mixed with alkali liquor can dilute the condensate and absorb NOx, whichcontributes to the reduction of water and air pollution. The novel heat recovery system is promising in practical application since it is energy-efficient, costeffectiveand environmentally friendly. See more