OCR Text |
Show kPa of flue gas pressure by an aqueous solution of alkaline NaCI02 . A greenish yellow color in the solution was always found after three minutes of operations and disappeared after 105 minutes. It is assumed that the color most likely represents CI02 or some other intermediate in the absorption of NO. The mole ratio of the total amount of NO that flowed through the reactor to NaCI02 is 0.95 at breakthrough. It should be emphasized that 80% NaCI02 was used with the rest of the starting material in solution consisting of 18% Na C03 and 2% Na2S04. Thus, the initial composition of the scru~ber liquid was qU1te alkaline. Under all conditions when NaCI02 was present, the other two reagents were also present. Low concentrations of NaOH increase the NO removal effectiveness. High concentrations of NaOH inhibited the absorption. This is most likely due to insufficient concentrations of NO or NaCI02 to neutralize the NaOH and reducethe pH into the acid range. The upper limit for NaOH concentration necessary to completely absorb NO in NacI02 aqueous solution depends on the concentration of NaCI02 . NO was absorbed quantitatively in 0.008 molar NaCI02 aqueous solution when the concentration of NaOH was equal to or lower than 0.001 molar. The upper limit of NaOH in O.OB molar NaCI02 aqueous solution is 0.1 molar. At the upper limit concentration of NaOH, absorption can not reach 100% within the first few minutes. If the NaOH concentration is a little higher than upper limit, absorption goes to zero after a few minutes of running time. NaOH in NaCI02 aqueous solution increases the effectiveness of NO to NaCI02 reactant ratio at breakthrough from 0.96 to 1.05, while 5% oxygen in the flue gas decreases it to 0.B4. Before saturation, the concentration-time curves are straight lines of different slopes. Slope of N03- is greater than that of CI-. The rate of formation of N0 3- is faster than that of CI-. The time difference between their formation is the life time of the green intermediate (presumed to be CI02). The pH value of an aqueous solution of as received sodium chlorite drops drastically from 10 to 3 within the first ten minutes of bubbling 2000 ppm NO. The as received solution consists of O.OOB molar NaCI02 , 0.0015 molar Na2co3 , and 0.00038 · molar Na 2S04 owing to the 18% (w/w) Na 2CO and 2% Na 2so 4 impurity. The pH value of this solution is 10. After three minutes of operation, the drops into the acid range. After NaCI02 in the scrubbing solution is consumed, only two products are found in the scrubbing solution. They are N0 3- and CI-. Co3- 2 is converted to H2C03 when pH falls below 3. The final pH of the scrubbing solution is 1.9. This pH, no Co3- 2 is expected to exist in solution. This is indeed verified by Ion Chromatography where no C03- 2 peak is detected. 13 |