Study On Dry Absorption Of SO₃ In Flue Gas At The Outlet Of SCR Reactor

In order to reduce emissions of nitrogen oxides,selective catalytic reduction?SCR?is widely used.Part of the sulfur dioxide is converted to sulfur trioxide under the reaction of SCR catalyst.Sulfur trioxide not only has a corrosive effect on the follow-up device but also cause fatal influence to the environment.Therefore the focus of this study is to develop an efficient and selective dry absorbent removing flue gas SO₃ at the outlet of SCR reactor,which reduces the emission of sulfur trioxide and provides support for the improvement of SCR catalyst.In this paper,V₂O₅-WO₃/TiO₂ catalyst is placed in a fixed bed experiment system to generate SO₃.According to the conservation of sulfur before and after reaction,we can measure the generation of SO₃ through the change of SO₂.Experimental results showed that the rate of oxidation of SO₂ increased as the temperature increased in the temoerature rage of 300-500 ?,while beyong 500 ? the rate of oxidation of SO₂ decreased as the temperature increased.500 ? is optimal temperature for V₂O₅-WO₃/TiO₂.The rate of oxidation of SO₂ increased as the concentration of SO₂ decrease resulting from the same amount of the catalyst.Moreover double fixed bed experimental system is used for the experiments of sulfur oxides absorption.In order to measure the total absorption of SO₂ and SO₃,real-time measurement by FTIR is associated with the TGA analysis of samples.This paper focus on absorbents removing different concertration of sulfur oxides,including 2000 ppm SO₂?1900 ppm SO₂ and 100 ppm SO₃?1800 ppm SO₂ and 200 ppm SO₃.Experimental results showed that the order of these absorbents capacity to absorb SO₂ from strong to weak is Ca?OH?₂ > Mg?OH?₂ > CaO> MgO,which is consistent with their basicity.As the temperature is 400 ?,the conversion rate of Ca?OH?₂ ?Mg?OH?₂ ?CaO?MgO is 18%?13%?4.5%?3.5%.When the concentration of sulfur oxides is same,the overall conversion rate is Ca?OH?₂ > Mg?OH?₂ > CaO> MgO,which is consistent with the conversion rate of SO₃ or SO₂.The order of sulfur trioxide selectivity from strong to weak is MgO > CaO > Mg?OH?₂ > Ca?OH?₂,which is opposite with their basicity.For example,when these absorbents are removing 1900 ppm SO₂ and 100 ppm SO₃,the overall conversion rate is 19.05%?15.39%?5.99%?3.94%;the conversion rate of SO₂ are 16%?12.54?3.51%?1.72%;the conversion rate of SO₃ are 3.05%?2.54%?2.48%?2.22%.At last,grain model is used to simulate the law of CaO for absorbing sulfur oxides.Comparing simulation and experimental results,we can see the model is in good agreement with CaO conversion of SO₂ absorption while has some deviation with CaO conversion of SO₃ absorption.