Aqua Save – Advanced Technology For Cooling Tower Blowdown Reduction
Background
Drought conditions and increased water demand have combined to decrease the availability and increase the cost of good quality, low hardness and dissolved solids, water desired for use as cooling tower makeup. At the same time, stricter environmental restrictions on effluent discharge have resulted in increased fees for disposal of cooling tower blowdown. Given these trends, there is a growing need to increase the cycles of concentration (COC) obtained in cooling tower operation so that makeup and blowdown can be reduced, giving the lowest water usage and total cost for system operation. At the same time, control of scale, corrosion, deposition, and biological growth in the cooling water system must be maintained by the water management program to prevent capital equipment damage, excess energy usage, and extra maintenance costs.
Standard cooling water treatment chemistry uses phosphonate and organic polymer to safely increase COC to 2 over that achievable without any chemical treatment. Use of acid for pH adjustment can increase COC by two, or more, over that obtained by standard treatment chemistry. Acid, however, is a safety hazard for operating personnel, is difficult to control, is not environmentally responsible, is costly, and will cause severe equipment damage if control is lost.
Aqua Save Technology
Utilizing expertise in organic polymer and crystal chemistry, we invented advanced acid free products, which can often double the COC obtained using standard cooling water chemistry or eliminate the use of acid pH adjustment for scale control. The basic technology for obtaining higher cycle operation is use of carboxylated phosphonate formulated at a specific ratio to multiple organic polymers. Operating COC is calculated using the equation:
COC = 2+ √110,000/ (CaH x TA)
This discovery is the basis of unique, patented* Aqua Save water management technology. In an Aqua Save program, the blowdown conductivity set point (based on calculated COC) is adjusted to obtain minimum blowdown each time a makeup water sample is analyzed. As makeup water quality often varies substantially with time, routine testing and adjusting cycles based on test results is required to minimize water use. Phoenix, Arizona, which has variable hard, high alkalinity makeup waters, was selected for introduction of Aqua Save technology in 2010. It has proven to be a great success and is currently utilized in many of our Phoenix accounts.
Close control of inhibitor concentration in the cooling water is a key to obtaining minimal blowdown without problems due to scale formation. To obtain close control, an accurate control test is needed. We invented the patented* BlueTrace photometric tracer to provide an accurate, low cost, easy to use control test. This technology provides the means to obtain the desired close control of inhibitor. Aqua Save products utilize BlueTrace or low level molybdate for control of inhibitor feed.
BlueTrak is our completely automatic on line unit for control of inhibitor level in treated cooling water. It utilizes a flow through photometer to determine the level of BlueTrace in the cooling water and adds product as needed to maintain set control levels. When teamed with a MegaTron controller, BlueTrak provides complete real time monitoring and tracking via the internet as well as remote cellular alarm capability for loss of control events.
Water Use Reduction
The following table shows blowdown amounts from an annual ,000 ton thermal load cooling tower at various COC and the water savings obtained by increasing COC from a baseline of 2.
| COC | Blowdown – gal/yr | Water Savings – gal/yr |
| 2.5 | 6,460,500 | 3,230,250 |
| 3.0 | 4,845,375 | 4,845,375 |
| 3.5 | 3,876,300 | 5,814,450 |
| 4.0 | 3,230,250 | 6,460,500 |
| 4.5 | 2,768,786 | 6,921,964 |
| 5.0 | 2,422,688 | 7,268,063 |
| 6.0 | 1,938,150 | 7,752,600 |
Economics
Standard Phosphonate-Polymer Program
The operating cost for an Aqua Save water treatment program will typically be 25 to 35% less than standard phosphonate-polymer water treatment programs. In general, existing feed and control equipment can be used; any upgrades needed are easily covered by the reduction in water and sewerage bills.
To demonstrate the economics of Aqua Save as compared to standard programs, we have undertaken the following cost analysis on an annual 1,000 ton thermal load cooling tower system.
The following data was used for this analysis:
| System evaporation | 9,690,750 gpy | City water cost | $5.17/1,000 gal |
| Sewerage cost | $3.71/1,000 gal | Makeup conductivity | 1020 mmhos |
| Makeup total alkalinity | 120 mg/l | Makeup calcium hardness | 160 mg/l |
A typical phosphonate polymer product, PCT 6215 M, at 100 mg/l, with a target COC of 2.5 is compared to an Aqua Save program based on Aqua Save 6218 M at 300 mg/l with a target COC of 5.0 and no acid feed.
Using product prices of $3.70/lb and $3.35/lb for PCT 6215 M and Aqua Save 6218 M respectively, the following table was calculated.
Standard Phosphonate-Polymer Aqua Save Program
| Calculated values | COC = 2.5 | $/yr | COC = 5.0 | $/yr |
| Blowdown, gpy | 6,460,500 | 2,422,688 | ||
| Makeup, gpy | 16,151,250 | 12,113,438 | ||
| Blowdown cost | $23,968 | $8,988 | ||
| Makeup cost | $83,502 | $62,626 | ||
| 6215 M use/cost | 5,776 lb | $21,371 | ||
| 6218 M use/cost | 6,065 lb | $20,318 | ||
| Total Program Cost | $128,841 | $91,932 |
Water Savings = 4,037,812 gallons per year
Cost Reduction = $36,909 per year
Acid pH Adjust for Scale Control Program
While not commonly used due to environmental, health, and safety considerations; acid pH adjust for scale control is another means to increase COC. Aqua Save technology can often be utilized to replace acid pH adjustment with a net decrease in operating cost while maintaining the desired high COC. In general, existing feed and control equipment can be used; any upgrades needed can be paid for by elimination of acid costs.
To demonstrate the economics of Aqua Save in comparison to acid pH adjustment programs, we have undertaken the following cost analysis on a 1,000 ton daily annual load cooling tower system. The following data was used for this analysis:
| System evaporation | 9,690,750 gpy | City water cost | $5.17/1,000 gal |
| Sewerage cost | $3.71/1,000 gal | Makeup conductivity | 1020 mmhos |
| Makeup total alkalinity | 120 mg/l | Makeup calcium hardness | 160 mg/l |
| Target pH | 7.5 |
The acid program will use a phosphonate polymer product, PCT 6215 M, at 100 mg/l, with a target COC of 5.0 and cycled pH of 7.5 compared to an Aqua Save program based on Aqua Save 6218 M, at 300 mg/l, with a target COC of 5.0 and no acid feed.
Using product prices of $3.70/lb and $3.35/lb for 6215 M and 6218 M respectively, and $0.50/lb for 50% sulfuric acid, the following table was calculated.
Standard Phosphonate + Acid Aqua Save Program
| Calculated values | COC = 5.0 | $/yr | COC = 5.0 | $/yr |
| Blowdown, gpy | 2,422,688 | 2,422,688 | ||
| Makeup, gpy | 12,113,438 | 12,113,438 | ||
| Blowdown cost | $8,988 | $8,988 | ||
| Makeup cost | $62,626 | $62,626 | ||
| 6215 M use/cost | 2,022 lb | $7,481 | ||
| 6218 M use/cost | 6,065 lb | $20,318 | ||
| Acid use/cost | 47,351 lb | $23,676 | ||
| Total Program Cost | $102,771 | $91,932 |
Water Savings = none
Cost Reduction = $10,839 per year
Benefits
Using an annual 1,000 ton thermal load cooling tower for demonstration purposes, conversion of a standard phosphonate-polymer program to an Aqua Save program reduces water used for blowdown by over 4 million gallons per year. This is significant considering that the average household uses about 90,000 gallons per year. The water use reduction obtained by a simple conversion to an Aqua Save product would thus supply fresh water to 44 households for a year.
An overall significant cost reduction of $36,909 per year is obtained. Proportional water savings and cost reduction can be obtained on any cooling tower by replacing standard water treatment programs with Aqua Save technology.
As noted, most conversions from standard water treatment programs to Aqua Save technology have no capital cost as existing control and feed equipment can be utilized.
The major benefit from converting an acid pH adjustment program to an Aqua Save program is the elimination of dangerous to handle and use acid while keeping a high COC. In our 1,000 ton example, the amount of acid required to maintain the desired pH was quite substantial at 47,351 lb/yr with the result that conversion to Aqua Save technology resulted in an overall cost reduction of $10,839 per year.
Performance
We analyzed the performance of an Aqua Save program at the City of Phoenix Sky Harbor Airport against the previous phosphonate-polymer program. In 2013, cooling tower water use was reduced by about 4,000,000 gallons during the high demand months of June, July, and August. Corrosion rates were excellent, steel averaging 0.49 mils/yr and copper averaging 0.03 mils/yr. Chiller approach temperatures remained constant during operation in the 1 to 3 degree F range and the annual condenser inspection showed the chiller condensers to be scale free with no corrosion.
Environmental, Health & Safety
All Aqua Save products are biodegradable at use concentrations and have been approved for discharge to the sanitary sewer. Some products have also been approved for direct stream discharge by various state regulatory agencies. Aqua Save products do not contain any phosphate, zinc, or chromium.
Aqua Save products are non-toxic based on oral LD 50 values for product at normal use levels ranging from a low of 1,504 g/kg to a high of 4,444 g/kg, differences based upon corrosion control chemistry of the product.
Sole Source
Due to patents on Aqua Save technology, ProChemTech and its associated firms are the only suppliers of this unique, water saving technology. Please contact us to discuss how we can reduce your water use and costs for water and sewerage.
ProChemTech International, Inc.
Innovation in Water Management
Apache Junction, AZ and Brockway, PA 15824
480-983-5385 www.prochemtech.com 814-265-0959
*Aqua Save US# 8,496,847 and 9,227,864
* BlueTrace US# 7,932,091