SPRAY BOOTH AIR VELOCITY AND CAPTURE EFFICIENCY
Q: A company that I work with uses electrostatic bells and is permitted by OSHA to reduce the air velocity through its spraybooths to 60 fpm. Also, the company is required by the state air quality agency to capture at least 90% of the VOCs emitted from the painting operations and abate them in a carbon adsorber. How does the reduced air velocity affect the capture efficiency of the spraybooth?
A: The answer really depends on the spraybooth design rather than on the velocity. If the booth is properly designed and maintained air turbulence will be minimal and all or most of the air entering the booth will move to the filters from where the solvent-laden air can be directed to the abatement device.
If the booth is poorly designed or poorly maintained airflow through the booth will be turbulent regardless of the air velocity. In this case, the solvent-laden air will be able to escape from the booth through conveyor openings, and even from the back of the booth where access doors might be located. Therefore, the key to having a high capture efficiency is to insure that the booth is designed so that one can always keep the airflow in balance. I have written several columns in recent years on this topic and encourage you to read about the many parameters that affect this property.