Study On The Preparation Of Porous Calcium Based Absorbents And The SO₃ Control Of Flue Gas In Power Plants

Coal combustion will produce a lot of pollutants such as SO₂ and NO_X.In view of these pollutants,coal-fired power plants have applied the technology of desulfurization,denitrification and dust removal technology to control the pollutant emissions in a large scale at present.However,a small amount of SO₂ in the pollutants is further oxidized to SO₃.After the widespread application of SCR denitration technology,the concentration of SO₃ in flue-gas almost doubled.The presence of SO₃ in the flue gas not only corrodes the flue pipe,threatens the operation of the power plant,but also causes pollution to the atmosphere and endangers human health.The feasibility of preparing SO₃ by thermal decomposition was studied in this paper.Four substances,NaHSO₄,KHSO₄,Na₂S₂O₈ and K₂S₂O₈,were investigated respectively on the thermal decomposition experiment.Moreover,the influences of reaction temperature,time and gas humidity on the thermal decomposition were discussed.Through the experiments,we determined the SO₃ production by pyrolysis method using K₂S₂O₈ as the decomposition material.It was confirmed that SO₃ can be generated stably when the heating temperature is 400?,the heating time is 20min,the amount of reactant substance is 0.1mol and the flue gas flow rate is 5L/min.Aiming at the difficulty in measuring SO₃ concentration in flue gas,two commonly used SO₃ concentration measurement methods were studied and compared.It is determined that the method of controlled condensation for flue gas SO₃ collection and the analytical method of chemical titration for SO₃ concentration test have higher accuracy and stability.In this paper,the SO₃ removal test in flue gas was carried out by using different calcium-based absorbents aiming at the technology of spraying calcium in flue gas.Ca?OH?₂,CaCO₃ and a kind of porous CaCO₃ prepared in laboratory were selected as adsorbents to remove SO₃.The effects of different adsorbents,temperature and calcium/sulfur ratio on SO₃ adsorption efficiency were investigated.The results show that the removal efficiency the three sorbents tested to SO₃ are from high to low as follows:porous CaCO₃>Ca?OH?₂>CaCO_3,the increase of temperature is beneficial to the improvement of SO₃ removal efficiency.In addition,each substance could achieve the ideal SO₃ removal efficiency when the calcium/sulfur ratio of Ca?OH?₂,CaCO₃ and porous CaCO₃ were 15,15 and 10 respectively.