Investigation On Simultaneous Desulfurization And Denitrification By Ammonia Absorption

Ammonia absorption method for simultaneous desulfurization and denitrification is a technology which combine ammonia desulfurization with selective catalytic oxidation(SCO). In order to achieve the purpose of simultaneous desulfurization and denitrification, NO was partly oxidized to NO2 using the method of catalytic oxidation, then SO2 and NOx was removed by absorption using ammonia solution. Ammonium sulfate and ammonium nitrate can be obtained by oxidation and crystalline. The absortion of SO2 and NOx, oxidation of (NH4)2SO3 and crystallization of NH4NO3 and (NH4)2SO4 was investigated in this article.Firstly, the investigation on simultaneous desulfurization and denitrification was carried out in a self-designed reactor using ammonia as the absorbent. The effect of pH value, liquid-gas ratio(L/G), temperature of absorption solution, SO2 concentration, NOx concentration, NO2 and NO concentration ratio and the SO32- concentration of absorption solution on the removal efficiency was investigated. The results show that when the air flow is 100L·h-1, NOx concentration is 400×10-6, SO2 concentration is 2000×10-6, pH value is 5, NO2 and NO concentration ratio is 1, the temperature is 50℃, NOx removal efficiency is 72%. SO2 removal efficiency is 99%. NO2 plays an important role in promoting the absorption of SO2. The removal efficiency of SO2 and NOx is decreased with temperature increasing. SO32-which has a strong reduction, can promote the absorption of NO2 and inhibit the removal of NO.Secondly, the influence of pH value, temperature, forced-oxidation air capacity, concentration of (NH4)2SO3 and (NH4)2SO4 on the oxidation velocity of (NH4)2SO3 was investigated. The results show that oxidation rate of (NH4)2SO3 increases as the temperature increases and as the forced oxidation increases. The oxidation rate of (NH4)2SO3 decreases as the pH value increases. The addition of NOx is beneficial for (NH4)2SO3 oxidation. NOx plays an important role in promoting (NH4)2SO3 oxidation when the (NH4)2SO3 concentration is low. But NOx has no significant effect of (NH4)2SO3 oxidation when the initial (NH4)2SO3 concentration is 1mol·L-1.Finally, the crystallization of NH4NO3 and (NH4)2SO4 mixed solution has been investigated. The effect of pH value, stirring speed, temperature, and fly ash content on crystallization product was investigated. Then the product size distribution and crystalline appearance were analyzed. The analysis reveal that the ammonium sulfate crystals at single crystallization is irregular polygons and it is chunky. Mixed crystals is cubic. It is regular rectangular and thin crystals. Temperature and pH has a greater impact on mixed crystals. The most homogeneous crystal distribution is obtained when the evaporation temperature is 60℃pH value is 5, stirring speed is 200r-min-1. The addition of ammonium nitrate is beneficial for crystal growth. The particle size of ammonium sulfate crystals at single crystallization was less than that of mixed crystals in the absence of fly ash.