An updated acid dew point temperature estimation method for air-firing and oxy-fuel combustion processes

Abstract

The estimation of acid dew point temperature (Tadp) of flue gas, which is mainly determined by SO3 concentration and steam concentration (CH2O) in flue gas, is crucial for coal-fired boiler system design. In this work, the heterogeneous and homogeneous effects for the conversion of SO2 to SO3 in the oxy-fuel flue gas have been examined. An updated formula for Tadp estimation of flue gas was proposed, which is:Tadp=186+20lgCH2O+26lg(CSO2*(127.65CSO2*−0.585+lgAar×αflyCSO2*12×(15.191+0.071Fe+0.044Al−0.058Ca−0.117Mg)×10−2))The updated formula shows that the main effects of the Tadp were the steam concentration, initial SO2 concentration (CSO2, ppm), ash content of raw coal (Aar, %), fly ash proportion of the inherent coal ash (αfly, %), main mineral contents of coal ash (Fe, Al, Ca, Mg, g/kg). The formula was then fully validated by a large amount of data obtained from laboratory-scale experiments, pilot-scale experiments and industrial scale coal-fired power plants. The results showed that, the heterogeneous effect for the conversion of SO2 to SO3 contributed to 1.33 to 20.86% of the total SO3 formed, smaller than the homogenous effect. Furthermore, the influence of the heterogeneous effect for oxy-fuel process was 1.2–1.6 times larger than that for the conventional air-fired process. The accuracy of the updated formula was proven much higher than the conventional empirical formula for air-firing combustion. The relative deviation of the calculation for oxy-fuel combustion by the updated formula was <7.8%.