The Benefit of Chemically Treating an Open Cooling System?—?Part 4
A discussion on treating open cooling systems would not be complete without addressing total suspended solids (TSS) and the problems that can arise when they are not kept in check.
Cooling towers act as fairly efficient air scrubbers. As the draft is either forced or pulled through the cascading water, any type of solid in the air from the surrounding environment will be scrubbed out of the air and into the water. I’ve seen carbon in the basin of a tower located near a blast furnace and muck in a power plant tower that had a dirt road. I’ve also heard of a cooling tower being contaminated by the greasy air coming from a kitchen vent located directly below the tower, and concrete dust from a nearby concrete plant entering a system. You probably could cite even more examples.
These solids can wreak havoc in cooling systems. In the basin, they can harbor bacteria; in heat exchangers, they can impede heat transfer; in recirculation pumps, they can erode impellers. All of these effects should be addressed in an optimized system. Chemically treating a system is beneficial, but in tandem with good filtration, the results are even better.
I remember taking over the treatment of a cooling tower at a steel mill. The tower was right next to the 68″ hot strip mill, and the environment had a great deal of dust and particulate in the air. The engineers who designed the tower had the forethought to add filtration to the system. With the tower, they had installed twin DynaSand filters. At first, I did not think much of the filters. Later, when I was able to clearly see a dime sitting on the floor of the basin, I realized the value of the filtration. This was one of the easiest systems to treat at the facility. (The blast furnace cooling tower mentioned above was in the same facility.) The results were great, while chemical and biocide demand were reasonably low.
For any troubled system, consider the part TSS contributes to the stress and how the proper chemical treatment and filtration can make all the difference. For any new system, filtration can also help prevent future problems. Filtration comes in many technologies and sizes, and there are several excellent manufacturer resources available for finding the best filtration for a particular system. A key to finding the right filtration is knowing the environment they will be operating in.
That about wraps it up! I hope our discussion on cooling tower systems and how to handle their inherent problems has been beneficial.
Consulting scientist
7 年My 1st recommendation would be to use a mechanical valve for blow down. Not a solenoid. When high solids are in the system they block the solenoids and nobody wants to dismantle them to fix them. 2nd Make sure you can back flush the solids you want to remove. Oxidized iron is heavier (denser) than most filtration media which means it will accumulate. Iron increases the risk for amplification and virulence development of Legionella pneumophila. Iron also creates the potential for Iron Related Bacteria development within the filter which is a low flow area with a high surface area. 3rd Include your filter, if you have one, on your critical control points. When ATP coming out of the filter is higher than the one coming in and-or if free chlorine goes down more than 0.1-0.2 ppm then you need to act. In my experience, it is rare that you can control microbial amplification thru a media filter even when it is new with continuous oxidizer dosing. 4th Do your hydraulics which you need to do anyway to assess the biofilm formation tendency. If you have low flow speed pipes that are horizontal then you'll want to take that into consideration as these have a tendency to form a deposit. You may want to recommend maintaining water circulation 24/7. If the cold water basin or the internal tank is not slanted and has a tendency to accumulate debris then a basin sweeper is a good option. 5th It is always easier and lower cost to prevent suspended solids from coming in than to remove them afterward. Intake screens are cheap and will prevent bigger insects, leaves, etc from coming in. Someone needs to vacuum them obviously. 6th Evaluating filtration options, ask what proportion (%) of a certain particle size will be removed. Bag filters are thought to remove about 50% of particles of their design size in one pass. Cartridges are thought to remove about 85%. Automatic systems often quote the removal of particles of a small size without mentioning what proportion of these will be removed in one pass. A manufacturer can claim removal of small particles of a size xy. However, when you test before and after for that particle size, you see that 5% is removed. Basically, silt, pollen and similar will not be removed by a filter nor should they be. Just some thoughts.
Corporate Service & Sales Manager
7 年We use a multimedia filter plumbed into a side stream, built with a softener style column and valve head that back washes based on time or pressure differential. We have found that they preform well when sized to turn over the system volume every 12 hours.