True Cost of Dry Media Replacement in Emergency Chlorine
Scrubbers

Dry emergency scrubber systems are used in municipal and industrial applications to mitigate the accidental release of heavier-than-air hazardous gases such as chlorine and sulfur dioxide. Dry scrubbers are safe, user-friendly, low-maintenance systems that consist of a fan and a vertical cylindrical FRP vessel containing a bed of chemically impregnated 1/8" diameter dry pellet media. The only moving part, the fan, produces a vacuum on the contaminated room and draws the gas-laden air from top to bottom through the media bed and out to atmosphere. The media reacts with the gas and reduces the concentration at the scrubber discharge to within the guidelines set forth by the prevailing codes. The media substrate permanently bonds the chemical impregnate and salt products from the gas reaction, allowing clean, non-toxic landfill disposal.

An alternative to dry scrubbers, wet scrubber systems are economical, simple to operate and can easily be fabricated of corrosion-resistant materials. However, the long-term investment of dry versus wet scrubbers may be surprising. To determine the true cost of dry media replacement for an emergency scrubber system, the cost of the dry media should be compared to the practical cost of the alternative wet caustic soda solution.

Caustic soda scrubbing solution used in wet scrubbers will last about five years in an installation without a leak. The reaction caused by CO² in the air - without a chlorine leak - changes the caustic soda into sodium carbonate solids that precipitate from the solution and affect the operation of the scrubber. Over 20 years of normal use, a wet emergency scrubber system will incur the costs of replacing caustic soda solution, hazardous liquid waste disposal, and labor and operator certifications for handling the spent caustic four times. In the event of an emergency, there would also be the additional costs of caustic solution replacement and disposal for each major leak.

In a particular form of dry scrubbers, dry media beads are permanently bonded with sodium thiosulfate and are landfill disposable and non-hazardous in the fresh and spent forms. Because it cannot be regenerated, the spent dry media should be discarded in a non-hazardous landfill or as required by local regulation. The solid reaction products are permanently locked in the alumina oxide substrate. When not exposed to chlorine, the dry sodium thiosulfate media has an indefinite life expectancy if not exposed to chlorine. Over 20 years, using dry media in an emergency chlorine gas scrubber, there would be no replacement cost of the dry media unless there was a major leak. Dry media replacement and disposal costs over a 20-year operational period, assuming complete media exhaustion, could be half of the cost for caustic solution.

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