In many industrial cleaning processes it is necessary to exhaust emissions that unavoidably result from the cleaning process. The reasons for exhaust can take on a large range –
- Remove heat that would otherwise raise the temperature in the cleaning area
- Remove humidity that would otherwise raise the humidity in the cleaning area
- Remove toxic fumes that might otherwise be dangerous to workers
- Remove mists of oil and other contaminants
- Remove dust and other particles to prevent air contamination
The process of exhausting usually starts with an exhaust fan with appropriate inlets or vents designed to capture the contaminants to be exhausted. Capturing the offending contaminants, however, is only a part of the story. Once captured, they must be collected or neutralized and disposed of appropriately.
In the case of heat and humidity, disposal is usually accomplished by venting the exhaust directly to the outside atmosphere. Many municipalities have requirements for stack height and emission limits to prevent exhaust gasses from encroaching on other nearby properties. Although in some cases, simple dilution of contaminants by the atmosphere is adequate, others require additional measures to assure capture and removal. When it comes to oil, particles and toxins the disposal issue becomes much more complex usually requiring a device called a “scrubber.”
Scrubbers come in variety of forms. For removal of oil mist, the scrubber may simply be a pipe with a number of baffles inside. The baffles are positioned in such a way that the air flowing through the scrubber reverses direction several times. As the air containing mist impinges on the baffles, the particles of oil collide with the baffles stick on them until the buildup is sufficient for the collected oil to drain by gravity to a collection point. This process may also be enhanced by the use of electrostatic devices and other more advanced technologies.
There are also wet scrubbers and dry scrubbers. In a wet scrubber, a spray head produces a mist of liquid (water or a chemical solution) through which the contaminated air stream must pass. In the process, contaminants either adhere to the liquid spray or combine with it and are neutralized. This results in a secondary contaminated liquid stream which must be disposed of, possibly after secondary treatment.
In a dry scrubber, a powder is levitated by air pressure or mechanical means. In some cases, the contaminated stream itself levitates the powder as it bubbles up through it in much the same way as a fluidized bed operates. As the contaminated air stream passes through the levitated powder, contaminants either adhere to the powder or, especially in the case of liquids, may be neutralized by it. Again, the result is usually a secondary contaminant stream although in some cases, the reaction may be of a catalyst type which is self-sustaining.
These are just a few words about how contaminants may be dealt with in industrial cleaning processes. A complete discussion of this topic (if there is such a thing as the technology is so broad) is beyond the scope of this blog. The “take away” here is that responsible handling of effluents from the cleaning process does not necessarily end with an exhaust blower and a stack.
– FJF –