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Water treatment for cooling systems is a challenge as it must meet standards related to many inquiries from water, operation, monitoring and initial design.
- Technically, it is necessary to ensure that good controlling of deposit, scale, of corrosion and of Biofouling, microorganisms and algae.
- In terms of health, safety and environment, the harmful bacteria Legionella and other microorganisms must be good controlled (E Coli, Coliform,…).
- Meet quality and environmental standards according to LEED, Green Mark, LOTUS…
Meet Green Mark standards
- Save water consumption
- Solving the above problems will limit maintenance, replacement and system shutdown.
Limited maintenance due to costs
- Reduce costs for chemical, operation and maintenance costs, prolong equipment life, and ensure continuous production.
Reduce costs – Increase profits
- 1. Schedule a master plan of water treatment and chemical for cooling tower
- 2. Reasons to treat make up water for cooling towers
- 3. Water quality monitoring during operation
- 4. How to calculate and choose chemical yourself
1. Schedule a master plan of water treatment and chemical for cooling tower
Schedule a treatment plan is necessary to bring about a comprehensive and long-term effect.
The following factors are the most basic to note
- Assess the water source to select the optimal cycle up, along with treatment options, to ensure the quality of make up water such as reducing hardness by water softener, part of the RO water or in combination with side-filtration for cooling water. If operating with water cycle is too low, it will lost much blow down water, fail to meet the committed criteria (LEED, Green Mark…) and high cost of chemical for cooling tower. Conversely,if the high water cycle it will easily cause deposits in the system, leading to costly chemical cleaning of cooling towers, cleaning of chiller scale and heat exchangers. Understanding the water source also helps choosing the right chemical for maximum efficiency.
- System design should select a material that is compatible with the appropriate with characteristic of water source, flow velocity e.g. highly saline make up water (salt water); high cooling rate, etc. This is also an obstacle that can hardly be changed once the system has been built.
- Pre-cleaning and passivation for the new system is essential to avoid clogging and corrosion during operation. This step cannot be skipped or low quality treatment
- Choose suitable and enough quantity of chemical for cooling tower
- Good management of the quantity and quality dosing pumps system, cleaning tower, make up and blowdown water; parameters of pH, conductivity, TDS, LSI, hardness, Silica, Fe, suspended solids, microorganisms, …
- Monitor ing heat transfer efficiency with the Approach coefficient of the condenser or heat exchanger.
- Cleaning the media of tower periodically to increase the efficiency of heat exchange.
- Periodically overview quality and adjust the treatment program if necessary.
2. Reasons to treat make up water for cooling towers
2.1. Questions to make a treatment plan
For a small capacity cooling system (eg 100 m3/h), it is easy to estimate the amount of make up water, chemical quantity will be as well as whether or not to invest in an make up water treatment system because if there is a large error, its error value is small, can be easily accepted or adjusted later, but the medium to large (10,000 – 100,000 m3/h) although a small error, the result of this error is very large in terms of investment, operating costs as well as the life of the system.
Water treatment for cooling towers needs to be cost-optimized for maximum efficiency, questions such as:
- Is there any treatment for make up water, if so, to what level ?
- If investing in a make water treatment system, what will be saved, how much will the cost of chemical for cooling tower and maintenance be reduced, and how much water will be saved?
- If not any treatment, what happens and how will maintenance costs increased ?
- How to limit the frequency of cleaning work and cleaning cleaning of cooling towers and condensor, heating exchanger?
This decision cannot be feeling or copied from an existing project elsewhere but should be calculated specifically.
2.2. Set up the optimal water cycle for the cooling system
Because this content requires a lot of technical aspects, we only give a simple example. In other words, the best plan between the two is “WIN” (the maximum) this but LOST (the minimum) tother” rather than gain the max without losing anything.
For example: A system with capacity of 52,000 m3/h, after calculating the parameters and treating the feed water to avoid scale trouble such as CaCO3, MgSiO2, CaSO4…, the blowdown water was saved 117 m3/h (= 210.6 – 93.6), by increase the initial operating cycle from 5 (4-5) to 10 (9-11), and at the same time save a significant amount of chemical for cooling tower, but on the contrary, investment in a treatment system is required and itsmanagement. After considering the long-term plan, in this case, both treating the supply water and using chemicals for mtainenance is the optimal solution.
Cycle up of optimal water cycle
For each project, quality of supply water is different, so which technology should be selected for further treatment to make up to cooling system and calculating the appropriate amount of chemical to get the highest result, it’s best to discuss it early on.
3. Water quality monitoring during operation
3.1. Basic measuring equipment required and monitoring
(If need to learn more about chemical dosing and control systems, etc., please contact us as this content only focus the main points in quality monitoring).
Basic parameters such as TDS, pH, temperature, blowdown and make up water quantity can be daily measured for small systems, but larger systems should be required more parameters including chemistry, physics and microbiology, In which, online measuring device installed, transmitted to the computer screen, saved for better improvement and transferred to mobile devices for those who are authorized to monitor or control, combining periodically double check with laboratory
Illustration chart of TDS, pH, LSI of cooling water
3.2. LSI (or Ryznar Stability Index – RSI) and CaCO3 in the system
Calcium commonly is the highest percentage of ions, LSI depending on the water quality via following basic parameters:
- Total alkalinity.
- Total water soluble solids (TDS).
- The temperature promotes the generation of CaCO3 deposits or from CaCO3 deposits dissolved
LSI is a formula based on the above 4 parameters to predict whether CaCO3 deposits are creating or being dissolved. When the scale is created, it will cause scale, reduce the heat transfer coefficient, or be dissolved too much; it will cause corrosion of the pipeline.
LSI value should be from 0.0 to +2.5; if LSI < 0.0 the system will be corroded, if LSI > + 2.5 will be scaled.
In practice, it is safe to operate LSI 0.5 – 2.0.
Thus, monitoring LSI to adjust is always at a safe level from 0.5 – 2.0.
At our website https://uce.com.vn/inspection-and-estimate-for-cooling-water-treatment/ there is a spreadsheet, not only entering numbers for the results but also giving feedback when the results are out of allowable limits, such as LSI = 2.76 is unsafe, the processing program should be adjusted.
3.3. Other components causing corrosion and scale of cooling system
In addition to the CaCO3 mentioned above, other scales such as CaSO4; Mgx(SiO2)y(OH)z; Ca3(PO4)2; Fex(OH)y;… and corrosion from Chloride, low pH, suspended solid (SS), anaerobic microorganisms… so should be regularly analyzed for Ca, Mg, SO4, PO4, Fe, Cl, SS… and adjusting in safe range accordingly.
3.4. Using chemical for cooling tower for some other speical cases
In fact, there are many cases such as Silica, Calcium, Cl, SO4… which are not too high while small capacity, so it is advisable to use chemical with suitable compositions to bring the expected efficiency and cost low investment.
|Code||Funtion||Water source properties|
– Corrosion inhibitor
– Scale inhibitor
– Sludge dispersant
|Make up water with high Cl–, SO42-, TDS|
|NC-PolyA100||High LSI ( High pH, Alkalinity, Calcium )|
|NC-300Si||Best control for high Silica|
|TotalSperse-100||Apply for high TDS / Silicat, Fe|
|NonPhosAR-900||Apply in high Nutrient / BOD ( sugar, food factories )|
4. How to calculate and choose chemical yourself
UCE Co., Ltd always have tried to bring the self-control to customers to the highest level possible, from understanding water parameters to operating and maintaining instructions, calculating the amount of make up – blowdown water, including characteristics of some cooling water chemistries for individual cases.
We have made the calculation sheet at https://uce.com.vn/inspection-and-estimate-for-cooling-water-treatment/, if concern can calculate own work at any time.
However, to get the overall optimal solution with low cost and best efficiency, contact us now!