Removal of gas-phase arsenic and selenium in flue gas by a new combined spray-and-scattered-bubble technology based on ammonia desulphurization

摘要

The integrated control of multiple pollutants is a promising approach for efficient and economical pollution reduction. Inspired by the simultaneous removal of SO_2 and NO_x by the spray-and-scattered-bubble (SSB) technology, this paper further explores gas phase arsenic and selenium removal ability of this new technology. Ammonia concentration, SO_2 concentration, liquid/gas ratio and immersion depth, which are the key operating parameters of SSB technology, are evaluated to determine their effect on arsenic and selenium removal. The experimental results indicate that ammonia concentration and SO_2 will facilitate the simultaneous removal of arsenic and selenium by SSB technology. However, the excess ammonia concentration and SO_2 should avoided to prevent the decrease in removal efficiency caused by the ammonia escape, increased mass transfer resistance, and mechanical carry-over. The maximum removal efficiency for arsenic can be obtained at the liquid-gas ratio of 10 L/m~3, and for selenium, the maximum removal efficiency will be reached at 14 L/m~3. For the technology of spray-and-scattered-bubble, chemical reaction and mass transfer jointly play the role in contaminant removal. By changing the immersion depth and measuring the corresponding pressure drop, the weight assigned to the effect of chemical reaction and mass transfer effect could be ascertained to a certain degree. It is speculated that chemical reaction will play a more important role for selenium removal in the bubble zone than the mass transfer. Moreover, for arsenic, mass transfer effect will play a more important role than chemical reaction. The sensitivity analysis for simultaneous removal of arsenic and selenium by SSB technology indicating that the variation of operating conditions will lead to a greater change in arsenic removal as compared with selenium.