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Controlling Scale Deposition

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Controlling Scale Deposition EDITOR’S EMPHASIS By Jan de Baat Doelman, Scalewatcher North America, Inc. C&I A commercial & industrial article Industrial Fouling Controlling Scale Deposition ook at the heating element of a overheating and cooling tower plates washing machine or dishwasher can collapse due to the weight of scale L in a hard water area and you deposits. Erosion damage can occur as will see a white encrustation containing a result of scale particles breaking loose hardness salts. This commonly is referred and then subsequently impinging upon to as limescale and is an example of other surfaces. domestic fouling. The limescale (calcium carbonate) that deposits on the heating Pipework scale reduces the available cross- element will, if untreated, reduce the section area, and fluids are affected by efficiency of the machine, induce increased pipewall friction. A larger, more corrosion of the element and ultimately power-consuming pump will be required lead to appliance failure. to maintain throughput volumes but this may allow only a temporary solution to Industrial fouling poses a far greater the problem. Plants that need to be shut problem than anything in the domestic down for cleaning cost money. sector. Huge volumes of fouled fluids are handled, and the systems that The formation of a thin uniform layer contain the fluids can become fouled as of scale or wax temporarily can reduce well. The quality of water streams used steel corrosivity, but eventually stagnant by industry varies widely and gives rise conditions develop under the deposit to numerous fouling problems. and electrochemical reactions will algae and bacteria (biofouling) and the layer on heat transfer surfaces. This corrode the steel surfaces. The result Type of Fouling consolidation of loose particles (e.g., leads to more power being consumed can be fluid leaks and equipment Mineral scale deposition occurs as particulate fouling— corrosion or to the installation of heavier duty, failure, which is potentially very a result of heat transfer or pressure byproducts and the accumulation more expensive heat exchangers to dangerous. In the food industry, the changes. Calcium carbonate scaling of “coke-like” deposits). compensate. It is estimated that 40 incorporation of even undesirable trace from hard water, and calcium percent more energy is needed to heat particulates can lead to off-flavors or 1 phosphate and oxalate formation in What Can Go Wrong? water in a system fouled with ⁄4 inch of off-colors, reduced shelf-life or even sugar refineries are examples. Other Process managers should be concerned calcium carbonate scale. Scaled boiler making the product not fit for selling. types of fouling include the growth of about fouling. Deposits are an insulating tubes mechanically fail as a result of Not only is plant and product integrity at risk but personnel health and safety may be compromised. Safety valves or emergency process sensors that are fouled may not operate in an emergency. Overheated boilers have been known to explode. Failure to control bacterial growth in cooling water can create conditions hazardous to health (e.g., production of Legionella pneumophila) or, in anaerobic conditions, may allow the production of toxic hydrogen sulphide from sulphate-reducing bacteria. Recognizing Fouling As scales and other deposits generally form inside closed systems, it is not always evident that deposition is occurring. There are some clues that can provide the evidence that is necessary. It is useful to try to answer the following questions. • Do energy/heating bills reduce immediately after cleaning the plant? • Is it necessary to arrange significant planned and/or unplanned downtime? • Are heat exchangers performing below design? continued on page 30 28 Water Quality Products www.waterinfocenter.com November 2002 LearnMore! For more information related to this article, go to www.waterinfocenter.com/lm.cfm/wq110202 A successful treatment strategy continued from page 28 treatment strategy will maintain fluid will maintain fluid flow, flow, reduce corrosion effects and • Is corrosion a problem in the plant? provide a safer environment. In reduce corrosion effects , save money • Are there signs of unexpected deposit addition, it will save money. formation within the system? and provide a safer environment. Solving the Problem The more times that the answer is “yes,” A process audit would identify the need for expensive external control can affect descaling downstream of the the more likely it is that there is fouling. extent of the current problem, the point measures. Minor changes in the process point of installation. A softening and If fouling can be controlled, there is a in the system corresponding to initial temperature, pressure, pH or fluids loosening of existing scale several weeks potential to save energy, prevent equip- fouling and, of most use, why there is a composition significantly could reduce after installation commonly is reported. ment failure and reduce maintenance problem. From the evidence, it may be the fouling potential for little to no cost. time and costs. Furthermore, a successful possible to suggest a solution without the To understand the mechanism, some Treatment options include inhibitor knowledge of mineral scale precipitation chemicals, descalers, ion exchange and is necessary. We know that in order to physical cleaning such as pipeline form a scale deposit three conditions pigging or the installation of permanent must be met. magnets or electronic devices. • The solution must be supersaturated. Although it usually is possible to find a • Nucleation sites must be available chemical solution to a fouling problem, at the pipe surface. environmental and safety pressures • Contact/residence time must demand that chemical consumption is be adequate. reduced wherever possible. Increasingly, restrictions are being To prevent scale it is necessary to applied regarding the use of chemicals remove at least one of these preconditions. due to their environmental impact. Clearly contact time is not an alterable factor. To be effective, any device must Physical Methods affect either the supersaturation value A range of physical methods can be or the nucleation process. used to remove fouling deposits. Water jetting, sand or plastic-bead blasting The direct effect on electronic devices can be used in accessible locations. For is on the nucleation process and, in other applications, such methods may particular, to enhance initial nucleation be expensive and possibly can cause the through the creation of new nucleation abrasion of surfaces. sites within the bulk fluid flow. Crystal growth then occurs at these points of Magnetic, Electronic Descaling nucleation and not at the pipewall. Unlike other preventative techniques, Suspended solids increase with a corre- these devices do not stop precipitation sponding drop in the level of super- but rather alter the shape of the crystals saturation, and these effects have been to reduce the adherence and build-up of observed in the field. The localized pH deposits on the pipewall. Perhaps the most increase near the pipewall caused by remarkable observation is that devices hydroxyl radicals formed by electromechanical interactions is one mechanism that drives the changed Ozotech,Ozotech, Inc. Inc. nucleation characteristics. 2401 Oberlin Road 2401 Oberlin Road Electronic devices are not flow-rate Yreka, Ca 96097 Yreka, Ca 96097 dependent and can be built to fit pipe PH 530 842-4189 FX 530 842-5319 PH 530 842-4189 FX 530 842-5319 diameter up to 60 inches. The units are e-mail [email protected] e-mail [email protected] lightweight, easy to install, can be retrofitted and produce no significant Did you know that a .1 to .4 ppm residual of magnetic field. They usually are ozone at your filler means that you are compliant effective on calcium carbonate claimed with the IBWA specification for disinfection? to reduce iron fouling and appear to prevent fouling by various WEWE DODO other substances. WQP Ozotech’sWE turn-key DO systems are About the Author Jan de Baat Doelman is president of designed to help you meet that specification Scalewatcher North America, Inc. Scalewatcher North America, Inc.’s You have questions? We have answers ! research of electronic systems in the United States, Europe and Asia has led to Ozone Destructs the implementation of an effective scale See all of our products!! deposit-control strategy. The patented Visit our web site Scalewatcher Electronic Scale Control http://www.ozotech.com System, originally launched in 1989, pro- vides a nonintrusive, chemical mainte- Terminator 250 nance-free method of removing Download limescale from pipes and equipment. ourTerminator product catalog120 Terminator 25 30 Water Quality Products www.waterinfocenter.com November 2002.
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