Dry-Chemical Scrubbers Feature Reduced Maintenance

Emergency Gas Scrubbers are necessary components of wastewater treatment plants, water treatment plants, and other facilities storing large quantities of chlorine (Cl₂) or sulfur dioxide (SO₂). An accidental chemical release, even from a cylinder as small as one-ton, can result in serious environmental damage and liability. As a result, storage facilities must take precautions to protect neighboring communities.

Despite the benefits of dry-scrubbing technology, dry scrubbers have not been used as widely as wet scrubbers in emergency gas applications. However, they have begun to receive more attention domestically and internationally.

Purafil's Environmental Systems Division (ESD) offers dry chemical Emergency Gas Scrubbers (EGS) designed for emergency removal of accidentally released gas. They can remove the entire contents of a fully-loaded one-ton cylinder in a worst-case release scenario without the time and money it takes to maintain wet scrubbers.

In the event of an unintentional Cl₂ emission, dry scrubbers follow these steps to eliminate the gas from the air:

1. Released Cl₂ is drawn into the scrubber through a blower and contacts dry-scrubbing media.

2. Media react with Cl₂ and permanently convert the gas to nontoxic solids.

3. Clean air is discharged to the outdoors with a Cl₂ concentration of less than 5 parts per billion (ppb).

The systems have one moving part — a blower — and instead of using caustic, dry scrubbers neutralize Cl₂ with dry-scrubbing media. These media are highly porous, spherical pellets that permanently transform the gas into harmless solids. As long as they do not react with Cl₂, media do not need to be replaced; they only require occasional testing to determine remaining life and to project change-out dates. Non-toxic and non-hazardous, media do not require special handling and can be disposed in landfills.

Case Studies

The largest freshwater treatment plant in Michigan, Springwells Water Treatment Plant, disinfects its water with liquid chlorine, which is stored in one-ton containers. When the plant needed to purchase a new emergency gas scrubber, it chose to use dry-scrubbing technology.

A typical installation of the Purafil emergency gas scrubber system.

"With nearly a tenfold increase in storage and feed capacity, special emphasis was given to reliability and safety," said Richard Pernal, filtration supervisor. "A sister plant in our system had upgraded to a Purafil dry scrubber earlier with favorable results. With our system upgrade, the same Purafil scrubber was specified.

"The Purafil EGS has been especially trouble free. There are no corrosive liquids to handle, no valves to foul, no spills to contain. Our system looks and performs today as well as day one, with virtually no maintenance. The maintenance savings are great, and operations has a system that is not dangerous to operate," Pernal said.

Melbourne Water in Australia also installed a dry scrubber at a disinfection plant to protect human and environmental health from an accidental Cl₂ release. Its scrubber is 10 feet in diameter and 15 feet tall and holds 25,000 lbs of dry-scrubbing media.

"The Silvan Disinfection Plant is classified as a Major Hazard Facility under state government legislation," said project manager Stephen Answerth. "Under this legislation, Melbourne Water is required to reduce the risk of a chlorine release 'so far as practicable.' The dry scrubber was seen as part of this effort; [it] was selected because it is a simpler system and does not involve having liquid caustic soda on-site."