Managing a cooling water treatment is quite tricky. Most often schedules of chemical addition are provided by the Chemical supplier and very often the CT owner is unaware of the chemical composition. Most often the CT maintenance team claim that there are no problems in their cooling tower. Yet there are numerous shut downs, bio fouling of condenser surfaces effecting heat transfer efficiency , frequent cleaning up of condensers , unmanageable high CFU counts , High COD of cooling tower water ( not often measured) , High AOX levels ( never measured) , unable to achieve the required Delta T – Problems that are never accepted by the maintenance team . The blow down water which is a toxic mixture of chemicals is discharged either directly without treatment or into the STP/ETP water, further increasing the cost of STP/ETP treatment. Apart from these issues scaling and corrosion are not within admissible limits
I have personally visited many cooling towers including large ones like power plants and have never seen a trouble free cooling tower. We do not expect cooling towers to be totally trouble free but there are definite ways of making the tower more efficient. “I have very good water and my tower is in excellent condition is a very common expression” Yes the tower water looks clean but on closer look lots can be done to make the tower water of better quality and make the cooling tower more efficient .
Any cooling water treatment regime strives to achieve the following
- Lower CFU counts
- Prevent bio fouling
- Try reducing organic load
- Reduce scaling & corrosion
- Increase heat transfer efficiency
- Try to reduce blow down by increasing cycles of concentration
Hidden performance parameters that are often not quantified: Other performance parameters that are mostly neglected (or taken for granted) are
- Heat transfer efficiency ( potential for high savings)
- Shut down costs of cooling tower
- ETP treatment costs
- Inventory of chemicals carrying costs
POTENTIAL OF OZONE
Large cooling towers such as power plants are water guzzlers. The operators use tonnes of toxic chemicals to keep the cooling water clean to protect the cooling towers. They discharge highly polluted blow down water that needs to be treated before discharge .There is tremendous pressure from environmentalists.
Users of Ozone Technology around the globe have always accepted the benefits of Ozonation; however the viability of using ozone in India has always been a question for lack of quantified studies and working references.
Power plants in India that have already resorted to ozonation have not found ozone very attractive. There are still frequent breakdowns, very high and monopolised maintenance costs and still addition of biocides although using ozone means Zero Biocides. Just go to the WEST and your find excellent use of ozone in Industrial cooling towers. The lack of trust in India on ozone use in cooling towers have come out of inefficient ozone systems, wrong designs, selfish motive to make one time money and run away . If ozone systems in cooling tower can work in the West, it should also work in India. Tower owner’s confidence in ozone must increase. So going to the right Technology provider is very important. Ozone has a cost but the returns can be very fast if properly implemented
The use of ozone provides the following benefits in a nutshell:
- Completely eliminates Biocides , making the discharge water cleaner
- More than reduces 90% of Sulphuric acids and de-scalents
- No hazardous chemical storage and Handling such as gas chlorine
- Enables the CT to be operated at Higher COC , reduces controlled blow down frequency
- Prevents scaling, corrosion and reduces algal growth
- Saves energy in operation of the Cooling tower
- Finally Saves water , Saves chemicals costs, allows the power plant comply with environmental needs and make them environmental friendly
In view of the restrictions for discharge of water with TDS greater than 2100, the decision to operate at a higher COC will be dependent on the quality of MUW .Using ozone; the same quality of MUW allows the cooling tower to more than double the COC of a chemically treated tower
Studies have revealed that a build-up of 0.1 inch (0.25 cm) of Calcium carbonate scale on heat exchanger surface will reduce the heat transfer by as much as 40 % .The energy savings accrue due to the fact that virtually limited scaling are noted with ozone treatment, and reduction in scale thickness improves the heat transfer efficiency of an Ozonated Cooling tower, thus saving power .Anticipated power savings can be upwards of 10 % .
Return of Investment. All of us know that calculation of return of investment means the tower operator must be transparent with his chemical and other costs. I have never come across any tower operator ( with whom I have had transactions) who can quantify entire costs (including hidden cost). Many tower operators refuse to reveal the actual chemical consumption. The Cooling tower maintenance of large industries are often out sourced and we do not get any Data here!!! I have personally taken lots of pain in gathering all cost details in one power plant supported by a progressive Chief engineer and have worked out the ROI for incorporation of ozone . The result would be astonishing – an ROI between 2-3 years .