Anti-Biofouling Ozone System for Cooling Water Circuits. II – An Application To Seawater

A new anti-biofouling ozone system which intermittently supplies high-concentration ozone was demonstrated to be effective for preventing marine biofouling in test cooling tubes (titanium, aluminum brass and epoxy-coated PVC) simulating condenser and intake conduit systems of power plants. Injection of ozone of about 5 mg/L for five minutes once each day was enough to keep them clean. Corrosion of titanium and aluminum brass tubes after the three-month test was found tobe negligible.     

Ozone Treatment in Cooling Water Systems

Ozone treatment for preventing the biofouling in cooling water systems is investigated.

In the fresh water system, the separating effect of the ozonated water on the microorganisms such as the sphaerotilus and the zoogloea which adhere to the piping and form the slime is recognized. When the ozonated water is supplied intermittently to the piping without stopping the flow of the cooling water, a constant volume of cooling water can be maintained. At the velocity of 1 m/sec, the amount of metal corrosion produced by the ozonated water is reduced on the mild steel, increased on the copper and does not change on the cast iron, when compared with that produced by the water containing no ozone.

In the seawater system, since many substances are oxidized by the ozone, the same treatment as that in the fresh water system cannot be applied. However, if the seawater in the cooling system can be replaced with ozone-containing air intermittently once a week, the adhesion of organisms such as barnacles and mussels to the piping can be prevented without having a bad influence on the other living oceanic organisms.     

An Antibiofouling Ozone System for Cooling Water Circuits. I - Application to Fresh Water Circuits -

A new antibiofouling ozone system with an intermittent injection of high-concentration ozone has been developed. The system was demonstrated to be effective for preventing biofouling on surfaces in fresh water stream. The application of the system reduces remarkably both the capital and the running costs compared to adopting conventional ozonation method.     

One Year Full-Scale Study Of Ozone Cooling Water Treatment At A German Electric Power Station

This paper presents operating results of ozone treatment of the water in a cooling system with open loop recycling containing the following elements:

- Main cooling water pumps

- Cooling water storage tanks

- Distribution manifold to cooling water users

- Cooling water collecting basins

- Cooling water recycling pumps

- Cooling tower.     

Ozone Treatment of Cooling Water: Results of a Full-Scale Performance Evaluation

This paper is the first technical status report of a continuing evaluation of ozone treatment for cooling tower water. Data will be presented that illustrate the results of ozone treatment in a 3,400-ton air-conditioning cooling system at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, which is operated by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy. Heat transfer data and equipment inspections confirm that a threshold surface temperature exists, below which heat exchange surfaces remain free of mineral scale. Heat exchange surfaces that exceed the temperature threshold experience calcium carbonate scaling. The temperature threshold effect may explain why ozone treatment has been reported as a successful treatment for air conditioning cooling towers, but has not been successful in higher temperature process cooling systems. Plans for future ozone investigations will be discussed.     

Ozone Cooling Tower Treatment With and Without Mineral Removal

This paper builds on a prior paper by this author, McGrane (1991). In that paper, ozone is used as the sole means of cooling tower water treatment. The paper discusses water conservation by increased cycles of concentration, greatly increased efficiency through extremely low biological populations, and corrosion data which is compared to ozonated and chemically treated towers.

New in this paper are the results from the combination of a low pressure reverse osmosis system with ozone treatment for cooling tower water. Scale formation has continued to plague cooling towers with high concentrations of calcium in the make-up water. The use of a mineral removal system in cases of extremely hard water has made ozone an attractive alternative to traditional chemicals in many areas.     

Optimization Of Ozone Plants For Water Works In Switzerland

The disadvantage that chlorine as processing agent in the treatment of surface waters can lead to undesirable production of chlorinated hydrocarbon products, provided the impulse to involvement in alternate means of oxidation. This inevitably led the way to the means of oxidation used the most intensively in water treatment - ozone.

Extensive development work has been performed to optimize the dosage of ozone for water treatment. Potential users are kept informed on this technology through published data. Theory, however, is only one side of the problem, practical application quite another. Here technicians and engineers have been required to integrate oxidation and disinfection with ozone, into the technology for water treatment and to make this economic.

In Switzerland since the 1950s, more than 40 waterworks have been converted to ozone. The development and the experience that has been collected since the introduction of this technique is the subject of this paper, primarily in regard to cost development and cost economy through innovative engineering services for development, engineering and project execution.     

Cooling Water Treatment with Ozone

Small scale tests oruan open recirculating cooling system with a cooling water flow of 10 m³/h conducted for a period of two years have shown that ozone could be a viable alternative to chlorine and other commonly used biocides. An average ozone dosage of 0.05 mg/L was applied continuously to the cooling water. Corrosion rates of copper alloy samples immersed in ozonized water were lower than the rates of samples in non-ozonized water. No corrosion was detected for the Cr-Ni steel alloys DIN 1.4306 and DIN 1.4404 as well as for titanium either in the presence or absence of ozone in water. This is ascribed to the formation of a thin protective layer in both cases.

A pilot plant has been set up at the EVS Heilbronn coal-fired power station in West Germany in order to confirm the results obtained on small scale. The open recirculating cooling system has a cooling water flow of 1,000 m³/h and is fed by conditioned Neckar river water. An air-fed ozone generator is used to ozonize a 10% side stream of the cooling water. A bubble diffuser contactor is used to introduce ozone into the water and an air heater is operated to decompose excess ozone leaving the contactor. The plant can be run to yield either a constant ozone residual concentration in the water or a constant ozone dosage to the water leaving the contactor. All relevant data are registered continuously and the plant presently is operated automatically with a constant ozone dosage in the side stream. Corrosion experiments are performed using laboratory heat exchangers, and all physical, chemical, and microbiological data of the cooling water are acquired. The operation started February 1, 1989 and is scheduled to be terminated by the end of 1990.     

A Comprehensive Investigation On The Application Of Ozone In Cooling Water Systems –– Correlation of Bench–Top,Pilot Scale and Field Application Data

The first comprehensive study – bench–top laboratory investigations, pilot scale testing, and critical monitoring and evaluation of field applications – addressing the effects of ozone as a stand–alone cooling water treatment program is presented. The study also represents the first critical comparison of ozone–treated systems with non–treated systems. Excellent corrosion control can be attained in ozone–treated cooling water systems. However, the corrosion rates are completely dominated by the water chemistry of the system and have no dependence on the presence of ozone at typical use levels. Good control of fouling can also be attained. However, as was the case with corrosion control, deposition on the heatexchange surfaces is not determined by the presence of ozone, but by several factors that traditionally influence fouling in a system. The strong biocidal properties of ozone resulted in excellent microbiological control in all Pilot Cooling Tower (PCT) investigations and in both case studies. Excellent agreement was observed among all stages of testing.     

Application Of A Single-Bubble Model In Estimation Of Ozone Transfer Efficiency In Water

A single-bubble model of mass transfer in gas-liquid systems enables the estimation of transfer efficiencies under different process conditions. In particular, it can be applied to simulate the effects of bubble size, value of the mass transfer coefficient, kinetics of reactions taking place in water and depth of the contact chamber. The results of such modelling in terms of transfer efficiency are presented for physical and chemical absorption of ozone in water at different hydrodynamic conditions (bubble size, water temperature, water depth in the contact chamber, and initial ozone concentration in the bubbles). The results of computations are compared with some reference data on ozone absorption in water in industrial-scale contact chambers.     

A New Practical Index For Predicting Safe Maximum Operating Cycles Of Concentration In Ozonated Cooling Towers

A new useful index for predicting the maximum safe operating cycles of concentration in ozonated cooling systems is reported. This index utilizes simple, easily obtainable makeup water quality parameters including conductivity, alkalinity, calcium and magnesium hardness, chloride, and sodium and is easily calculated. The index provides greatly improved correlation with real-world-derived scaling tendencies in ozonated cooling systems compared to conventional scaling indices such as the Langelier Saturation Index (LSI), the Ryznar Stability Index (RSI), and the Puckorius Stability Index (PSI). A simplified version of the index utilizing only total hardness also can be used to establish quickly maximum operating cycles of concentration in well characterized, but very rapidly changing water supplies.     

An On-Site Cooling Tower Treated by Stand-Alone Low-Concentration Dissolved Ozone

We report on an on-site 500 RT cooling tower ozone treatment process, in which chemicals other than ozone itself were completely eliminated. Ozone in an amount leading to less than 0.1 ppm of dissolved ozone was continuously introduced via side-stream injection into the circulating water returning from the chiller. The ozonated water was initially made to flow from the distributor to the filler in order to eliminate the growth of algae, and then to the chiller to reduce the corrosion and the fouling in the water. Positive ions such as Ca⁺² and Mg⁺² in the circulating water were precipitated by chelating them with carboxylic acids formed by the oxidation of organic compounds. We observed that using an ozone dosage of 0.1 ppm resulted in a colony-forming unit (CFU) less than 2 × 10³ /mL. With that well-controlled CFU, corrosion controlling and scale reducing were achieved as well.     

Theoretical Analysis Of Ozone Disinfection Performance In A Bubble Column

Modelling the efficiency of ozone disinfection in a bubble column was completed using two kinetic approaches: an axial dispersion model (ADM) and a back-flow cell model (BFCM). Using these models, the effects of flow directions and mixing on disinfection performance were examined. Both models predicted the concentration profiles of dissolved ozone in water equally well. However, the BFCM could be solved much more easily than the ADM with regard to the degree of inactivation without the solution being plagued by divergence.     

The Installation of GAC and Ozone Surface Water Treatment Plants In Anglian Water,UK

The surface water treatment plants in Anglian Water are being upgraded in order to more reliably meet the requirements of the EEC Drinking Water Directive. Ozone and additional GAC filtration capacity are being installed at 11 waterworks treating river and reservoir water, with capacities ranging from 11 to 360 ML/d. The installations and reasons for the plant designs are discussed.     

Practical Guidelines For Safe Operation Of Cooling Tower Water Ozonation Systems

Guidelines for the successful use of ozone as a stand-alone cooling tower water treatment method are discussed. Included are recommendations for system sizing, proper ozone residuals, mixing and distribution of the ozonated water, and potential problems and solutions. These include excessive or insufficient cycles of concentration, chemical contamination, low flow rates, high heat exchanger temperatures, and extended system turnover times. Also discussed are recommended maximum system downtimes, preferred types of towers and heat exchangers to treat with ozone, use of filtration systems, and elastomer compatibility with ozone. System monitoring and maintenance procedures are discussed along with ozonation safety considerations. With this information, two recently reported ozonation system failures are analyzed and the causes of failure are discussed.     

Effects Of Ozone On Biodegradable Dissolved Organic Carbon And Heterotrophic Plate Counts In The Distribution System

The impacts of ozone dose in the formation of biodegradable dissolved organic carbon (BDOC) were studied at the North Bay Regional Water Treatment Plant (NBR). Increasing the ozone to total organic carbon ratio to 0.45 (mg/mg) resulted in the formation of BDOC. Sedimentation and filtration/adsorption were effective in removing BDOC to non-measurable levels prior to the water entering the distribution system. Data from an on-going distribution system monitoring program indicate no discernible adverse impacts on microbiological parameters from using ozone during water treatment. Heterotrophic plate count (HPC) levels were similar before and after the use of ozone. Maintaining chlorine residual levels above 0.3 mg/L appears to be important for controlling HPC levels.     

Development Of An Ozone Disinfection Contactor Using A Physical Scale Model

This paper presents the design of a 1/5 scale model study of a five-stage counter-current ozone disinfection contactor. The selection of appropriate scaling laws is discussed and model test runs are presented and compared with the preliminary rule-of-thumb design. Simple modifications to the internal baffle design were tested leading to improved residence time characteristics.     

冷却水处理技术分析

对国内通常的冷却水处理方法做了简单介绍和对比。化学水处理法操作简单,综合效果好,在经济上比较合理,并具有广泛的发展前景。物理水处理法其处理效果总体看不如化学水处理法,其理论研究和应用技术的开发值得专业人员不断探索。     

Ozone Use In Cooling Tower Systems – Current Guidelines – Where It Works

This paper was prepared to provide guidelines for effective ozone use in cooling tower systems based on known scientific actions of ozone and practical cooling system operation. It does not attempt to explain the unknown or unpredictable actions attributed to ozone. Guidelines for ozone use in cooling tower systems usually can be predictable, depending upon the specific industry or site conditions found. Ozone is not a panacea as a stand–alone treatment in most cases, but can be under the right conditions. Applicability of ozone depends upon specific criteria that must be evaluated prior to its consideration or use. If ozone is to be tested, then it is critical to have adequate monitoring tools in place to evaluate its performance, rapidly, before system damage may occur. Ozone has a place today in cooling tower system protection, and likely a greater consideration and use when a better understanding of its mechanisms of action is developed.     

The Development Of An Ozone Contact Tank Simulation Model

Anglian Water (AW) operates ozone facilities as a treatment stage at all its surface water sources. The main ozone treatment stage takes place after filtration in multi-compartment concrete ozone contactors. These have two stages of ozone gas injection via ceramic bubble diffusers and two decay stages.

To enable AW to gain a better understanding of the contact tank performance, a computer simulation model incorporating Computational Fluid Dynamics and ozone process modeling was developed in conjunction with AEA Harwell. The model was calibrated using site data from Alton WTW. The results were used to improve the tank design and to optimize the ozone dose; this resulted in improved performance and a significant reduction in ozone dose.