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Industry News


Non-Conventional Scale Fighting in Cooling Towers
By Yitzkhak Rosner, ScaleTech Ltd.
Mar 9, 2004
  E-mail article
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Beer Sheva, Israel -- The conventional methods of fighting scaling in cooling tower water are addition of chemicals and/or softening of the make-up water. These methods are expensive, they consume big quantities of water and request a huge amount of maintenance work . The chemicals and resins used are disposed off to the sewage and create an irreversible process of contamination in deep water reservoirs.

In the last decade, some water treatment companies tried to find methods of cooling tower water treatment, to overcome the disadvantages of the conventional methods. The main efforts were made in the direction of devices based on electrolysis, due to the fact that this obviously is the best solution for the separation of mineral salts that create scaling and fouling of cooling towers.

The main problem of the existing electrolysis scale remover devices is how to discharge the collected scale. Some of the devices invert the current polarity in order to discharge the scale plated on the cathode, which is made of carbon steel. Changing the polarity of the electrical current turns the cathode into anode and thus iron ions are liberated into the cooling water and inevitably produce corrosion. Some manufacturers recommend periodic manual removal of the scale from the cathode. This situation explains the limited use of electrolytic devices in cooling tower water treatment.

ScaleTech has developed a completely new technology that overcomes the weaknesses of the existing electrolysis devices. The ST-ASR scale remover, is indeed based on electrolysis of the cooling water, but the removal of the scale particles from the cathode is made fully automatic by hydro-mechanic power and not by reversing the polarity of the DC current. Therefor the ScaleTech ST-ASR scale remover is the only electrochemical scale remover which prevents scaling without producing corrosion. The ScaleTech method is patent protected.

How scale remover operates

The ST-ASR device is installed in parallel with the cooling tower. Its build-in pump circulates all the cooling water through the electrolytic chamber. The electrical current between the cathode (negative electrode) and the anode (positive electrode made of spacial coated titanium) performs the scale removing process. Both cathode and anode are circular and concentric. Due to the wide active area, the electrolysis process is highly effective although we use low values of current.

The scaling constituents of the water (calcium, magnesium, silica etc.) are deposited on the cathode surface. Due to the evolved hydrogen gas, this deposit is spongy. It is removed automatically from the cathode, by a system of rotating activated by the PLC. On the positive electrode, oxygen and carbon dioxide gas evolve. The oxygen and controlled hypochloride bleach are dissolved in the water and produce disinfecting conditions against microorganisms growth. Chlorine, ozone gases and hydrogen peroxide are not produced under the operating conditions of the ST-ASR.

The electrochemical process in ScaleTech ST-ASR scale remover counteracts the cooling tower water concentration, which is due to water evaporation and to the intake of dust particles, oxygen, sulfur and carbon containing gases from the surrounding air. The ScaleTech ST-ASR scale remover is supplied as a complete system and is skid mounted. It is an environmentally friendly apparatus and is operating in big air condition systems of molls, office buildings, hospitals etc.

The main advantages of the ScaleTech ST-ASR scale remover are:
- Elimination of all chemical additives, including all the logistics (purchase, handling and storage).
- Reduced blow-down 30% less make-up water.
- The device is ecologically safe and environmentally friendly.
- Water drained by the ScaleTech ST-ASR scale remover may be used for irrigation.
- Almost no maintenance costs

All ScaleTech ST-ASR scale remover models are equipped with a stabilized electronic power supply and a sophisticated, PLC based control panel, with LCD display and industrial keyboard, which performs the whole operation full automatic, collects process data and has the ability to transmit them to any Central Data Acquisition System.

All the parts of the ScaleTech ST-ASR scale remover are made of high quality material. The main parts of the device electronic power supply, electrodes, and control panel are guaranteed for three years.

Efficiency

A good test case that presents ScaleTech ST-ASRs efficiency is the case of Margalit moll in Hod Hasharon, Israel. The moll has a central air condition system with a capacity of 500 TR. The system includes two cooling towers of 250 TR each. Until 2001 the cooling tower water was treated by chemical additives In the spring of 2001 a ScaleTech ST-ASR scale remover was installed and all other water treatment was stopped.

After every year of operation the cooling towers were opened and checked for scaling. No blocked nozzles and no scale deposit whatsoever were found. Water consumption went down by 32%. No maintenance work was necessary. The cooling towers continued to operate at their optimum operation level - ΔT = 4.5 ˚C.

The system operates at an average water conductivity of 2,650 S whereas the average conductivity of the make-up municipal water is 970 S which is a ratio of 2.75. The LSI (Langellier Saturation Index) during all this period was negative (- 0.121 average), which indicates that no potential scale deposition occurs. All water analyses indicated zero for iron in the cooling water.

For more information contact:
ScaleTech Ltd. Water Technologies
Ophir Industrial Park, POB 17346
Beer Sheva 84840, ISRAEL
Telephone: 972 8665 1008
Fax: 972 8665 1371
Email: info@scale-tech.com
Web site: http://www.scale-tech.com/

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