Study Of NO_X Absorption In Ammonia-based Wet Flue Gas Desulfurization And Denitrification Process

The combustion of coal lends to the emission of pollutions, because SO2 and NOx have serious effects on human health and the ecosystems, their emission have been the major environmental concern. Although the removal of NOx and SO2 in flue gas is usually achieved by means of dry as well as wet techniques, the economical removal of NOx and SO2 still represents one of the greatest challenges in environmental protection. Recently, considering the capital investment, operation cost and space for equipment, attempts have been made to find an effective method to remove SO2 and NOx simultaneously in the same temperature rang and in a single reactor. As the ammonia-based wet process can remove SO2 and NOx simultaneously and has the ability to generate ammonium fertilizer, thus ammonia-based desulfurization and denitrification technology has drawn an increasing attention in China. The main objective of the paper is to study the absorption of NOx in ammonia-based wet flue gas desulfurization and denitrification process, and to study the absorption mechanism of NOx into absorption solution, meanwhile, to investigate the influence factor of NOx absorption.The gas-liquid phase compositions on NOx absorption in ammonia-based wet flue gas desulfurization and denitrification process is investigated in the double stirred tank reactor. The absorption rate of NO2 and NO in (NH4)2SO3 is higher than them in NH4HSO3 solution, and the effect of molar ratio for HSO3- to the total salt concentration on the NO2 absorption rate is larger than that for NO. Then, as the (NH4)2SO3 (or NH4HSO3) concentration is constant, the NO absorption rate increases with the increase of NO2 inlet concentration, and when the concentration of NO2 is large enough the NO absorption rate reduces with the increase of NO2 concentration, and that the presence of NO in the gas phase is favorable to the absorption rate of NO2. Meanwhile, the presence of SO2 in the gas phase is also favorable to the absorption rate of NOx, that because of NO generated by the reaction between NO2 and SO2. However, the presence of O2 in the gas phase is also favorable to NO absorption, but it is unfavorable to NO2 absorption, that because of the oxidation of NO and SO32- by O2. The total results suggest that the coexistence of NO and NO2 (or SO2 and NOx) in the flue gas could enhance the absorption of each other to some extent.The absorption of NOx into ammonia-based wet flue gas desulfurization and denitrification absorption solution have been investigated in the double stirred tank reactor, and determine the experimental conditions by optimizing the process conditions. The experimental results demonstrate that NOX absorption reaction is controlled concurrently by gas-and liquid-film, and the reaction may be mainly influenced by gas-film when the (NH4)2SO3 concentration is above some critical value. Meanwhile, a simplified mathematical calculated model is applied to simulate the total absorption process. Using the experimental data the relationship between reaction orders (or reaction rate constants) and the ratio of NO2/NOx also can be achieved, Then through the experiment the property parameters can be determined and a kinetic equation for total NOx absorption can be obtained. The comparison between calculated values (calculated by the kinetic equation) and experimental values of the NOx absorption rate, and it can be seen that the calculated values fit the experimental data well. So it is feasible definitely to simulate NOx absorption using the simplified mathematical calculated model.