Research And Application Of SO₃Measurement In Flue Gas

The selective catalytic reduction of NOx with NH3is the most efficient and widely used technology for abataing NOx emitted from stationary power station at present. However, the wide use of catalysts, in particular sulfur trioxide produced through the oxidation of SO2, causes corrosion problems, health problem, and reduced boiler performance. However, SO3is hard to be measured accurately. This problem is so serious that the study on SO3measurement is imperative.This paper proposed controlled condensation correction method (CCCM) to measure SO3in flue gas, and the oxidation of SO2of different catalysts was studied using CCCM. The main results are shown as following:1. Test accuracy of CCCM was studied. It is found that impacts of SO2, NO, O2turn out to be small. When ammonia is absent, the correction formula, CSO3=1.538×CSO3测+0.232, is obtained at the collection condition of80℃and100L. The measurement error of CCCM is±5%. The NH3affects the accuracy of CCCM, and when ammonia slip is smaller than3ppm, the collection formula is CSO3=1.647×CSO3测+0.960.2. CCCM and other SO3measurement method-isopropanol absorption bottle method, NaOH method, spial tube method were compared. It is found that the isopropanol absorption bottle method and CCCM are more stable when there are only SO3, H2O, and N2in the fuel gas. And isopropanol absorption bottle method can absorb all the SO3in flue gas. However, SO2affectes isopropanol absorption bottle method much, and when the SO2concentration is high in flue gas, the measurement error of isopropanol absorption bottle method was up to40%. It is concluded that CCCM is better than other3methods.3. The effect of operating parameters on SO2/SO3conversion rate was studied. The SO2/SO3conversing rate decreases with increasing GHSV, lower temperature, higher SO2concentration, lower O2, and lower H2O concentration. However, SO2/SO3conversing rate is independent on NO concentration. When NH3/NO is smaller than 0.5, the SO2/SO3conversing rate decreases. But when the NH3/NO is larger than0.5, SO2/SO3conversing rate increases as the effect of increasing NH3.4. The SO2/SO3conversion rates of4catalysts were compared, It appeares that the key factor that influences the conversing process is the vanadium content, the bigger the vanadium content is, the higher the oxidation capacity is. The SO2/SO3conversing rate is suppressed by the appearance SiO2.