Corrosion and Scale in a Cooling Loop

Company: Denka Advantech, Singapore
Denka Advantech had a problem with water quality in their new cooling tower system for several months. Their rust in the cooling tower water became very pronounced. They tried flushing out the rust into the drain and adding clean makeup water into the cooling tower system. They were unable to dose excessive chemicals into the system due to the nature of the piping system. The plant has copper, mild carbon steel and stainless steel piping in the same cooling loop. Excessive dosage of any one sort of water treatment chemicals will corrode one or the other of the piping material. Initially, they tried to use magnets to solve the problem but this produced no difference in water quality.
Regular sampling of the cooling water was done. The samples were taken at the return line to the cooling loop, just before entering into the sump. As can be seen, the sample at the left was totally rusty with brown water. A 10" Pursanova TM Bio Disk was installed at the return line of the cooling loop just before entering the cooling tower. Within only one week there was a clear difference in the water quality in the cooling tower sump. The water became clearer and there was very little rust in the water. Samples were collected in clear plastic bottles and the difference was more pronounced. The practice of taking samples in water bottles is a very easy way to compare visually the color and the turbidity of the water. This method is often used by Pursanova TM in order to save the cost of the laboratory.
Another cooling loop system, consisting of a cooling tower which was used to cool several furnaces for making silica powder, was found to have bad scaling, rust and bio-fouling problems. Even though there was a chemical water treatment program using rust & scale inhibitors and biocides, the fouling problem still persisted. Even magnets were installed at the water supply pipe hoping it could solve the scaling problems. The furnace is cooled by a water film that falls along the side walls of the furnace. Due to the calcium carbonate deposits and rust along the walls of the furnace – maintenance became a constant headache for the plant operators.

Constant checks were done on the furnace external walls and over several weeks – chunks of calcium carbonate begins to fall off without any human intervention, as can be seen in the photo below. Algae & biofilm in the flow sight glass begins to die. Furthermore, the customer will check the bacteria in the cooling towers. This is part of the HSE, because certain bacteria in the cooling tower vapor might cause serious health problems to people. When checked, the bacteria with the standard plate count (bacteria count) had fallen drastically. From in the top 9,400 CFU/mL to less than 100 CFU/ml. This 100 CFU/mL is in line with the requirements of the authorities.