Dry Emergency Scrubber Proves Cost-effective Solution
in Stockton, California

Since its construction in 1977, the Stockton East Water District's Dr. Joe Waidhofer Water Treatment Plant in Stockton, California, has utilized two Fischer & Porter model 70C4500 series gas chlorinators with 71P1100A pressure reducing valves for water disinfection. For more than 29 years, the equipment provided reliable and efficient disinfection for the 290,000 plus residents of the Stockton area, located 80 miles due east of San Francisco.

In 1997, the district began investigating the replacement of its system with new, state-of-the-art gas chlorination equipment. However, budget constraints prevented the district from purchasing new equipment until 2005. At that time, Richard Bermudez, operations supervisor, worked with Ward Technical Products, Inc. to investigate ways of meeting the Uniform Fire Code (UFC) while maintaining gas chlorination equipment as their primary disinfection treatment. The UFC requires that a self-contained scrubbing system be available for emergency use when using gas chlorination.

The most common scrubber systems used by municipalities are wet scrubbers. Such systems are economical, simple to operate and can easily be fabricated of corrosion-resistant materials. However, dry scrubbers are increasingly being placed in municipal water systems across the country. While these systems are typically more expensive than wet systems, the full long-term investment of dry versus wet scrubbers is not well understood.

Ward Technical Products recommended the EST™ Dry Emergency Scrubber, Type DES, from Severn Trent Services. The system was engineered and tested for use in municipal and industrial applications where the potential exists for 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 as 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. In addition, dry scrubbers do not require liquid chemical leak containment or double wall vessel construction and operate at sub-zero temperatures without the use of heaters.

The EST Type DES is designed to neutralize a leak from an overfilled one-ton portable tank in accordance with the UFC worst-case release of hazardous gas through a fusible plug. For one-ton applications, three model sizes are offered corresponding with the required room exhaust rate and type of dry media utilized. The EST Type DES 3000 has a room exhaust rate of 3000 cubic feet per minute. Higher exhaust rates such as 5000 or 7000 cubic feet per minute are normally considered when the gas capacity needs to be split between two or more rooms or when a single room volume exceeds 50,000 cubic feet. When sulfur dioxide is present and needs to be scrubbed either alone or in conjunction with chlorine, the model suffix will be "PHD" indicating the kind of chemical media to be used. The "STS" media is considered when chlorine is the lone containment gas present.

In December 2005, the district issued an award to Ward Technical Products for the EST Type DES and also issued an award to Telstar Instruments for the installation of the scrubber and for new chlorination equipment, the Capital Controls® Advance gas feeder series WX4144 from Severn Trent Services.

The equipment was installed and started up by June 2006. Award, submittal, supply, installation and startup were completed in six months.

"Believe me, there was little enthusiasm for listening to another presentation on chlorine containment," said Bermudez. "We were prepared to go with a chlorine cylinder containment system, even though its protection was limited to cylinder leaks. But after hearing about the EST Type DES, there was an immediate 180-degree turn. The dry scrubber had it all - total chlorine leak protection, easy maintenance and no hazardous chemicals."

According to Chuck Ward, president of Ward Technical Products, "Dry scrubbers' lower operational and maintenance costs and their ease of use make them an excellent alternative to traditional wet scrubbers."