Research Of SO₃ Removal From Flue-gas By Calcium-based Absorbents

During the combustion of coal, a small amount of SO2 would be further oxidated into SO3. And after the application of SCR technology, the concentration of SO3 in flue-gas is doubled. The most common problem associated with elevated concentrations of SO3 is low temperature corrosion. Moreover SO3 can pollute atmosphere and harm human health. However traditional wet desulfurization technique cannot effectively removing SO3 from flue-gas. So develop economic efficient SO3 removal technology is imperative.This paper proposed a technology of SO3 removal by calcium-based absorbent. Through fixed bed, the SO3 adsorption characteristics with different absorbents are researched. In addition, the removal SO3 experimental studies by different absorbents were finished too. Moveover, the technology of calcium-based absorbent injection into duct was optimization designed at a power plant. And the feasibility and economical efficiency of this technology is analysed at last.First, according to the literatures and experiment, several methods are compared in order to select out the best one. And then, through experiment the preparation method of SO3 is determined. Finally, this paper decided to use ozone and SO2 for prepareing SO3, use cotton plug method for getting flue-gas sample and use iodine volume method for analyzing.Secondly, using fixed bed, the SO3 adsorption characteristics was researched with Ca(OH)2,CaO and CaCO3 as absorbent at different temperature. The result show that Ca(OH)2 can absorb more SO3 than CaO and CaCOs, it's sulfurized rate can reach to 25%. This result is related with their physicochemical properties and granular surface features, the final sulphuration rate increases with temperature for range investigated for any substance above,. Moreover the SO3 adsorption rate of Ca(OH)2 is fastest among the three absorbents.In SO3 removing experiment, the removing effect is better with Ca(OH)2 than CaCO3, and can reach to 95%. For both absorbents above, the SO3 removing efficien increase with the tempreture rises, the reaction time extend and the stoichiometric ratio increase.Then, using a power plant model, the technology of calcium absorbent injection into duct was optimization designed. The nozzle position and jet angle are adjusted to get the best mixing effect of flue-gas and calcium-based absorbent. They are 35°and 45°for near wall nozzle and non-near wall nozzle. Using tooth profile anti-grinding plate can reduce the system resistance added by injection system. The result provides guidance for the application of this technology.Finally, through theoretical calculation, the feasibility of removal SO3 by calcium-based absorbent is analysed. The result shows that this technology doesn't have obvious influence on other equipments especially electrostatic precipitator. Also, the economical efficiency of this technology is analysed too. And the added cost is just 0.043 fen/kw·h. This technology has good market prospect, and is acceptable for application in China.Calcium-based absorbent injection technology can remove SO3 from flue-gas effective with little influence on other related equipment. The initial investment of this technology is and the operation cost is cheap too. This technology affords a new selection for SO3 emission and have a.good prospect.