Investigation On The Adsorption Mechanism Of Arsenic In Flue Gas During Fuel Combustion

The emission of easily volatile trace elements such as As, Se and Hg during fuel combustion has brought serious air pollution problems. The interactions between inorganic compounds and those elements at high temperature could reduce the release of trace elements. This study focuses on the adsorption mechanism of arsenic by inorganic compound sorbents in flue gas. In order to achieve better simulation of the interactions between sorbents and arsenic, a hydride generator was used to generate stable As source in gas phase and a new fluidized bed reactor was designed to meet the requirements of adsorption experiments. Combined with the determination method of As speciation, the effects of temperature and acid gas in flue gas on As capture was illuminated. Furthermore, the methods for sorbents modification were investigated according to their adsorption characteristics in As capture. Conclusions obtained in this study could help the control of the release of As vapors in flue gas. Based on the adsorption amount and capture mode of sorbents, the proper temperature for As capture was discussed. In addition, an idea about the recycling application of fly ash contained high content of Ca was stated. The main results are as follows:CaO and active Al₂O₃ which were used as sorbents in this study were both capable to capture As from flue gas. At lower temperature?573 K?, As capture by CaO and Al₂O₃ was both through physical adsorption. Compared with CaO, Al₂O₃ which had higher surface area was more efficient for As capture. As temperature increasing to 723 K¹023 K, As capture by CaO was mainly through chemical oxidation due to the promotion of reactions by temperature. However, in this range of temperature, As capture by Al₂O₃ was still mainly through physical adsorption. As capture by CaO was significantly prevented by acid gases?such as HCl and SO₂? in flue gas while was hardly affected by Al₂O₃. At higher temperatures?1173 K¹323 K?, the adsorption performance of CaO and Al₂O₃ for As capture was both suppressed while Al₂O₃ could resist the effects of high temperature in one min's adsorption. In the investigation on sorbents modification, municipal solid waste incineration fly ash was used for CaO₂ synthesis. The purity of obtained CaO₂ was higher than 60% and the weight of fly ash was decreased by about 40%. Moreover, the capture of As in lower temperature flue gas was remarkably promoted by CaO₂. The modification of Al₂O₃ by loading compounds containing Fe to its surface helped to increase the oxidation ratio of As³⁺ in flue gas to 96%.