The effect of factors on the efficiency of $SO_2$ scrubbing by use of ammonia solution was studied. The factors in this study were pH in the scrubbing solution, $SO_2$ concentration in the inlet gas, $NH_3$ concentration in the scrubbing liquor. The scrubber was 4"-OD methyl metacrylate column pacted with $\frac{1}{2}"$-plastic Raschig ring in 60 cm height. Gas flow rate was fixed to be 30 l/min, and circulating liquor rate to be 800 cc/min.
Removal efficiency increased sharply as pH increased, in the lower pH range, and became almost constant when pH was above 6. When $SO_2$ concentration in the inlet gas was 7%, removal efficiency varied from 30% to 90% with the pH range of 4.3-6.8. From these results, the optimum pH range in this study was 6.0-6.5.
$SO_2$ concentration in the inlet gas has little effect in high pH range, but as pH in the outlet liquor decreased it became important. When pH was 5.8, removal efficiency increased from 70 to 84% as $SO_2$ concentration changed from 2 to 7%.
$NH_3$ concentration in the scrubbing liquor has a little effect. Removal efficiency increased slightly with increasing the ammonia concentration in the solution, and it varied 86-90% by changing the concentration 4.5-10.2%, with pH at 6.8.
For oxidation of solution, pH was the most important factor among the three factors mentioned above. As the result, the concentration of $(NH_4)_2SO_4$ increased sharply with pH increased.
Solution analysis were performed by modified palmrose titration and ammonia-formal titration. In 5.5＜pH＜7, and 9＜pH＜11, the ratio of mole concentration of $SO_2$ to that of $NH_3$, can be expressed in the linear functions of pH.
Ammonia loss was observed by the beaker test in which air containing 5% $SO_2$ was added to the ammonia solution of 1-14% concentration. When pH of the solution is above 6.5, the rate of ammonia loss was high, while below 6.5, the pH effect was low.
