A semiconductor plant faced biofilm and scale in cooling towers and chiller tubes. They came to Chemtex to reverse these problems and increase heat transfer efficiency and simultaneously reduce copper corrosion. Chemtex crafted a custom solution to control scale and biofilm formation.
Chemtex partnered with the semiconductor manufacturer to prevent biofilm and scale in cooling towers and chiller tubes. Our cooling tower cleaning ultimately restored efficiency in the cooling towers and decreased operation costs.
The System: A 15,000 gallon, four-tower system and approximately 2,000 tons across four chillers that runs 24 hours/day year round.
This plant experienced high process load in the summer months at peak production.
Three Silver Bullet non-chemical devices had been installed 18 months previously and were still online.
The Problem: During the time that the Silver Bullet units were online, biofilm and scale formed in all four cooling towers and chiller tubes.
The following issues were reported:
- The decreased heat transfer efficiency due to these conditions reduced the temperature differential across the cooling towers to 1.5 degrees F.
- Chiller approach temperatures increased significantly from 1.5 – 2 degrees to 5 degrees which nearly caused the facility to shut down.
- Corrosion coupons were analyzed at 120 days: The copper corrosion result was considered poor at 0.67 mpy.
Based on the facility’s operation costs, a 10% decrease in cooling efficiency due to scale and biofilm would increase monthly operational costs by $7,500. The facility was also prepared to create a once through cooling system using city water if necessary; the estimated cost of water to run at one cycle was $24,600 per week.
The Solution: The plant clearly needed an experienced water treatment company.
Chemtex proposed a chemical water treatment program, since the Silver Bullet was clearly not able to control scale or biofilm formation. To improve the condition of the cooling tower system, a scale dispersant was applied followed by acid cleaning of the chillers and cooling towers. Costly applications of biocide and an organic dispersant were necessary to remove the biofilm in the system.
Cooling tower maintenance strategies included putting a conventional scale and corrosion inhibitor online 9 months into the trial period and reinstating a cooling tower biocide program when the Silver Bullet units were removed after 18 months online.
The Results: Once the system was cleaned and the chemical water treatment program was reinstated, the system has been performing as designed.
Here’s how the improved water cooling towers perform:
- Approach temperatures are acceptable at 2 degrees.
- Airflow measurements across the cooling tower were taken when the system was most fouled and again following a 60 day online cleaning with dispersant; a 57% improvement in airflow was recorded.
- Weekly microbiological testing shows that the biocide program is successful at maintaining a low ATP level (Fig 1).
- With adequate corrosion protection, corrosion rates for copper and mild steel improved significantly (Fig 2).