Cooling Water Treatment Provides Sound Results

Teaming ultrasonics with corrosion inhibitors offers environmental and economic benefits.

By Olaf Pohlmann, Ashland Hercules Water Technologies

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Ultimately, BASF opted to replace its complete cooling-water program, which was a conjugated phosphate treatment requiring pH adjustment through sulfuric acid dosing, with Ashland's Enviroplus scale and corrosion inhibitor. The new program is non-toxic and minimizes environmental impact by making use of natural, biodegradable and renewable ingredients (biodegradable "BCA" polymers and low phosphorous PSA phosphonate). This eliminated the need for bleach and sulfuric acid.

Implementation
Engineering and design work for the installation began immediately after BASF accepted the AHWT proposal. BASF completed the stainless steel pipe work for the Sonoxide ultrasonic treatment unit within a few days. Ashland engineers installed and connected the B25 Sonoxide unit in a day. Because chemical changes now only would be necessary two times per year, dosing and monitoring systems could fit into the existing production building, obviating a new outside dosage building and providing initial money savings.

The cooling water now runs four cycles of concentration instead of the previous three cycles. The additional cycle cuts overall water consumption and reduces blowdown by 30%. A controller regulates conductivity and pH, while coupons measure corrosion rate.

The patented Sonoxide water-treatment technology works by passing water through an ultrasonic chamber where bacterial cells are exposed to a combination of low-power high-frequency ultrasound and micro-bubble aeration (Figure 1). This kills some bacteria cells and impairs others, reducing overall bacteria levels and eliminating biofilm from the entire cooling-water system.

The biofilm removal actually caused total plate counts in the system to increase a few days after startup of the Sonoxide treatment. This prompted immediate dosing of the system with the former bleach treatment on a shock basis; such extra treatment only was required three times during the first two months. (BASF removed the former dosing equipment and chemicals from site after the first year of successful treatment.)

The cooling water system now has been running for two years under this program. Ashland regularly monitors microbiological control; results consistently show water quality levels well within acceptable technical guidelines. Samples tested for Legionella also confirm that control is being maintained.

In addition, the new regime has lowered general corrosion rates to 0.23 mpy from 0.3–0.4 mpy, as measured by steel corrosion coupons.

BASF engineers found that the Sonoxide system has reduced operating expenses by 80% and chemical use by 90% and provided feed water savings of 20% compared to the previous water-treatment approach. Results show a preliminary annual savings of €20,000 ($26,580) from feed-water and chemical-use reductions.

Initial installation costs for the system depend upon a number of variables that include size and service requirements. The Sonoxide system is part of the complete water-treatment program and is invoiced on a monthly base as a service fee, which is in the same range as that for advanced microbiological control programs.

Besides savings and performance improvements, BASF reduced its overall environmental concerns. "We've eliminated the need for our utility operator to handle concentrated acid and chlorine containers. This means that he can now focus on more meaningful parts of his job, which can lead to new improvements in other areas of system performance," notes de Baat.

BASF applied for the Responsible Care award of the VNCI (the chemical industry trade association in the Netherlands) in 2009 and received an honorable mention for its efforts in improving its environmental profile by using Ashland's Sonoxide ultrasonic water-treatment system.

Olaf Pohlmann is Sonoxide commercial lead EMEA for Ashland Hercules Water Technologies, a commercial unit of Ashland Inc., Barendrecht, the Netherlands. E-mail him at opohlmann@ashland.com.

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