Step 1. Calculate the gas velocity through the tower:
Step 2. Does the gas velocity meet the requirement? Yes, because the gas velocity is less than 3 ft/sec.
Step 3. Calculate the number of overall gas transfer units NOG required to meet the regulation. Recall that
Step 4. Determine the total number of transfer units provided by a tower with six spray sections.Remember that each lower spray has only 60% of the efficiency of the section above it (because of back mixing of liquids and gases from adjacent sections). Spray section NOG values are derived accordingly:
Step 5. Calculate the outlet concentration of gas.
Step 6. Does the spray tower meet the HCl regulation? Because y2 is greater than the required emission limit of 25 ppm, the spray unit is not satisfactory.