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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Manufacturing sites should strive to obtain maximum benefit from water they use. Getting the most from this water usually requires a treatment system — which incurs costs and affects the facility's environmental impact.

A two-year collaboration between Ashland Hercules Water Technologies (AHWT) and BASF Nederland B.V. has shown that using a combination of ultrasonic microbiological control and corrosion inhibitors can dramatically reduce total cost of operations and enhance environmental performance.

BASF Nederland decided to assess cooling water treatment in 2007 at its resin production plant in Nijehaske. The 150-m³ half-open cooling water circuit there provides indirect cooling of chillers and direct process cooling.

The evaluation revealed the need for a new dosing and storage system for chemical treatment. Cost to fulfill all legal requirements for a new system of three 1,000-L. chemical storage containers, including frost protection and a heater as well as new dosing and measurement equipment, would have totaled around €25,000 ($33,225).

Realizing that the European Union's Integrated Pollution Prevention and Control (IPPC) directive soon would be adopted (codified January 15, 2008), the company wanted the best available technology (BAT).

Key Considerations
BASF used nine criteria to review available water-treatment programs.
  1. emission to surface water;
  2. prevention of substances' leaks from the production process;
  3. energy consumption;
  4. potential leakage of cooling water additives;
  5. storage of the additives;
  6. application of alternative (non-chemical) cooling-water treatment;
  7. selection of cooling water additives;
  8. optimization of additives' application; and
  9. reduction of water consumption
The overriding objective was to evaluate a program's environmental performance and its potential to improve the plant's environmental footprint.

BASF followed the guidelines in the IPPC document for reduction of emissions of chemical substances to water. In line with the BAT approach, the company decided to reduce emissions to the aquatic environment by:
  • replacing the present chemical storage and dosing installation;
  • upgrading the dosing and control equipment for cooling water treatment;
  • switching microbiological treatment of cooling water from bleach dosage to an ultrasonic system; and
  • changing the present corrosion inhibitor to an environmentally friendly one that doesn't need sulfuric acid for pH adjustment.

BASF, of course, also considered cost in evaluating an effective water-treatment program.




The company determined that Ashland's Sonoxide ultrasonic water-treatment system was an essential part of an optimal overall program. "We looked into the best available treatment technology for our cooling water system and the benefits of Ashland's program are clear and simple — it just works," says Eduard de Baat, senior process engineer, BASF.

Engineers from BASF and AHWT worked together to replace the dosing and storage systems for cooling water chemicals and install a Sonoxide B25 system together with an Ashland Onguard E controller in combination with a corrosion rack.

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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