Novel flue gas waste heat recovery system equipped with enthalpy wheel

Waste heat recovery from flue gas is an efficient way to increase the thermal efficiency of a gas-fired boiler. This paper proposes a novel flue gas waste heat recovery system, which comprises a condensing heat exchanger and an enthalpy wheel. The flue gas firstly flows through the condensing heat exchanger for heating boiler water, and then flows through the enthalpy wheel. The wheel, covered with desiccant material, acts as a medium for further heat and moisture transfer from the flue gas to the oxidizing air, resulting in an increase in the dew point temperature of the flue gas. Experimental results show that the average boiler efficiency reaches 106% and the average total recovery efficiency reaches 88%. The dew point temperature of the flue gas discharged from the boiler increases to around 60 degrees C, higher than that of conventional flue gas (around 55 degrees C). Consequently, more latent heat is recovered in the condensing heat exchanger by virtue of the proposed system. A mathematical model is established for further analysis based on the experimental results. The rotation speed of the enthalpy wheel and backwater temperature are key factors influencing the system performance.