For industrial companies using a cooling tower for its facility, some type of cooling tower water treatment system is usually necessary to ensure an efficient process and longer equipment service life. If cooling tower water is left untreated, organic growth, fouling, scaling, and corrosion can reduce plant productivity, cause plant downtime, and require costly equipment replacements down the road.
A cooling tower water treatment system is an arrangement of technologies that remove damaging impurities from your cooling tower feed water, circulation water, and/or blow-down. The specific configuration of your system will depend on several things, including:
•the type of cooling tower (open circulating, once-through, or closed loop)
•quality of the feed water
•manufacture-recommended quality requirements for the cooling tower and equipment
•chemistry/makeup of the circulatory water
•regulatory requirements for discharge
•whether or not blow-down will be treated for reuse in the cooling tower
•type of heat exchanger
•cycle of concentration
As mentioned above, the exact components of a cooling tower water treatment system depend on the quality of feed water and chemistry of circulatory water in relation to the quality of water needed for the specific cooling tower and related equipment (according to the manufacturer’s recommendations), but in general, a basic cooling tower water treatment system typically includes some type of:
•filtration and/or ultra-filtration
Depending on the impurities present in the water, any combination of these treatments might best suit the facility and make up the treatment system, so it’s important to consult with the water treatment specialist to ensure the right system for the specific tower is being considered. Depending on the needs of the cooling tower and process, these standard components are usually adequate. However, if the tower requires a system that provides a bit more customization, there might be some features or technologies you will need to add on.
A cooling tower water treatment system might be made up of the technologies necessary to regulate the level of:
•alkalinity: will dictate potential of calcium carbonate scale
•chlorides: can be corrosive to metals; different levels will be tolerated based on materials of cooling tower and equipment
•hardness: contributes to scale in the cooling tower and on heat exchangers
•iron: when combined with phosphate, iron can foul equipment
•organic matter: promotes microorganism growth, which can lead to fouling, corrosion, and other system issues
•silica: known for causing hard scale deposits 硬水垢
•sulfates: like chlorides, can be extremely corrosive to metals
•total dissolved solids (TDS): contribute to scaling, foaming, and/or corrosion
•totals suspended solids (TSS): un-dissolved contaminants that can cause scaling, bio-films, and/or corrosion
Specific treatment processes vary depending on the requirements of the cooling tower and quality/chemistry of the feed and circulation water, but a typical cooling tower water treatment system will usually include the following steps:
Cooling tower makeup water intake
Makeup water, or the water replacing bleed and evaporated and leaked water from the cooling tower, is first drawn from its source, which could be raw water, city water, city-treated effluent, in-plant wastewater recycle, well water, or any other surface water source.
Depending on the quality of this water, you may or may not need treatment here. If a water treatment system is needed at this part of the cooling tower water process, it is usually technology that removes hardness and silica or stabilizes and adjusts the PH.
At this point of the process, the proper treatment optimizes the tower evaporation cycles and minimizes the water bleed rate to drain beyond what might be done with chemicals alone.
Filtration and ultra-filtration
The next step is generally running the cooling tower water through some type of filtration to remove any suspended particles such as sediment, turbidity, and certain types of organic matter. It is often useful to do this early on in the process, as the removal of suspended solids upstream can help protect membranes and ion exchange resins from fouling later on in the pretreatment process. Depending on the type of filtration used, suspended particles can be removed down to under one micron.
Ion exchange/water softening
If there’s high hardness in the source/makeup water, there may be treatment for the removal of the hardness. Instead of lime, a softening resin can be used; a strong acid cation exchange process, whereby resin is charged with a sodium ion, and as the hardness comes through, it has a higher affinity for calcium, magnesium, and iron so it will grab that molecule and release the sodium molecule into the water. These contaminants, if present, will otherwise cause scale deposits and rust.
At this point in the process, there is typically the use of chemicals, such as:
•corrosion inhibitors (e.g., bicarbonates) to neutralize acidity and protect metal components
•algaecides and biocide (e.g., bromine) to reduce the growth of microbes and biofilms
•scale inhibitors (e.g., phosphoric acid) to prevent contaminants from forming scale deposits
Thorough treatment prior to this stage can help reduce the amount of chemicals needed to treat water at this point in the process, which is ideal considering many chemical treatments can be expensive.
If the cooling tower water is going to be re-circulated throughout the system, a side-stream filtration unit will be helpful in removing any problematic contaminants that have entered through drift contamination, leak, etc. A good rule of thumb is that, if the cooling tower water treatment system requires side-stream filtration, about 10% of the circulating water will filter through. It typically consists of a good quality multimedia filtration unit.
The last part of treatment required for cooling tower water is the blow-down or bleed from the tower.
Depending on how much water the cooling plant needs to circulate for proper cooling capacity, plants will choose to recycle and recover the water through some type of post treatment in the form of reverse osmosis or ion exchange, especially in places where water might be scarce. This allows liquid and solid waste to be concentrated and removed while treated water can be returned to the tower and reused.
If the water from the blow-down needs to be discharge, any discharge the system creates will need to meet all regulatory requirements. In certain areas where water is scarce, there could be large sewer connection fees, and demineralization systems can be a cost-effective solution here, as they can help minimize the cost to connect to water and sewer lines. Also, the discharge of the cooling tower bleed must meet local municipal discharge regulations if the effluent is being returned to the environment or a publicly owned treatment works.
Industrial cooling towers are large consumers of water. With water scarcity in certain parts of the world, effective water treatment that allows increased water reuse is a driving factor influencing when and where to use cooling towers. In addition, stringent federal, state and municipal water-discharge requirements will motivate more innovative methods related to cooling tower water treatment.
The closed-loop cooling systems which reduce water inflow by over 90.0% comparing with the existing cooling systems at chemical industries and thermal power plants. Thus lead to an increasing demand for closed circuit systems for cooling processes globally.
Post time: Nov-05-2020