A steel pickling operation emits 300 ppm HCl (hydrochloric acid), with peak values of 500ppm, 15% of the time. The airflow is a constant 25,000 acfm at 75°F and 1 atm. Only sketchy information was submitted with the scrubber permit application for a spray tower. We are requested to determine if the spray unit is satisfactory (USEPA-84/09, p. 100).
Given
Emission limit = 25 ppm HCl
Maximum gas velocity allowed through the water = 3 ft/sec
Number of sprays = 6
Diameter of the tower = 14 ft
The plans show a countercurrent water spray tower. For a very soluble gas (Henry’s law constant approximately zero), the number of transfer units (NOG) can be determined by the following equation: