Energy & Fuels, Vol.34, No.2, 2055-2063, 2020
A Prospective Method for Absorbing NO2 by the Addition of NaHSO3 to Na2SO3-Based Absorbents for Ship NOx Wet Absorption
A high nitrate concentration in scrubber water is a major factor that restricts ship applications of NOx wet absorption technology. In this paper, an absorption system (Na2SO3/NaHSO3) that can effectively improve NO2 absorption and reduce the concentrations of nitrate and nitrite was studied. Several factors that affect the NO, absorption efficiency and the concentrations of nitrate and nitrite were investigated in a bubble reactor by using Na2SO3 and Na2SO3/NaHSO3. In addition, the reaction mechanism for the process of NO2 absorption was deduced. The results illustrate that increases in S(IV) concentration and initial NO2 concentration could enhance the NOx absorption efficiency while increases in the NO/NO2 ratio and SO2 concentration decreased the NOx absorption efficiency. Moreover, the maximum NOx absorption efficiency was 97.8% at 0.15 mol/L S(IV) and 1400 ppm of NO2 when using the Na2SO3/NaHSO3 absorption system. The S(IV) concentration was the main factor affecting the NQ absorption efficiency and the concentrations of nitrate and nitrite. Increasing the SO2 concentration slightly affected the NOx absorption efficiency but was beneficial for decreasing the concentrations of nitrate and nitrite. The performance of the Na2SO3/ NaHSO3 absorption system was better than that of Na2SO3 in the presence of oxygen. Furthermore, the minimum concentrations of nitrate and nitrite were 13.5 and 0 mg/L, respectively, in the Na2SO3/NaHSO3 absorption system for 1100 ppm of NO2 and 0.3 mol/L S(IV) and were much lower than current regulations for scrubber water. Finally, compared with other experimental results, the Na2SO3/NaHSO3 absorption system exhibits great potential for ship NO, wet absorption, and the addition of NaHSO3 plays a key role in decreasing the concentrations of nitrate and nitrite.