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Aalborg Solutions No. 6 · March 2004 Scaling in boiler/feedwater systems Daily maintenance of a boiler plant must address the potential of scaling, corrosion and sludge in all sections of the boiler plant and include preventative measures. This newsletter deals with scaling. Various treatment options There are considerable economic advantages to maintaining your auxiliary boiler plant well by providing good quality boiler/feedwater treatment. There are several chemical water treatment programmes available that address both physical condition of the feedwater, heating and venting of the hot well and pressurized deaeration, but also counter the harmful effects of dissolved gases, particularly oxygen. Aalborg Industries emphasizes the importance of full chemical treatment (see Aalborg Solutions No. 5) to secure a trouble-free, cost-effective operation of low-pressure boiler/feedwater systems. All sections of the system must be protected by the treatment which must be continuous. Scale can also cause accelerated cium carbonate and magnesium sulphate. If unchecked, scaling causes progressive lowering of boiler efficiency by heat retardation (it acts as an insulator). Eventually, scale build-up will cause the tubes to overheat and rupture. Main problems in boiler water The main water-related problems of a boiler/feedwater system leading to equipment failure and increased operating costs are: scaling, corrosion and sludge. Each may contribute to the severity of the others. In addition, if one or more of the problems remain unchecked in one part of the system, other parts like the host section may be adversely affected as well. corrosion. Semi-porous or discontinuous scale provides the physical environment for “crevice” or differential concentration corrosion. Water treatment goals The primary goals of a controlled water treatment programme are: to maintain clean scale-free water-side heat transfer surfaces in steam generating systems to prevent metal loss due to corrosion to ensure efficient production of steam in boiler systems without priming, foaming or carry-over contamination to prevent the formation of deposits in steam/condensate systems to minimize heat loss from the system due to excessive blow down from boilers to keep all power generating and auxiliary equipment and associated water and steam systems at their most efficient levels and thus minimize costs. Boilers scaling on boiler tubes in composite boiler Scaling in boilers Scaling is the formation of a crystalline interlocked layer of mineral substances on heat transfer surfaces. Severe scaling normally occurs only within the boiler. Its mechanism is the exceeding of solubility limits of mineral substances due to elevated temperature and solids concentration at the tube/water interfaces. Typically, in low-pressure boilers, the scale formed is mainly a carbonate/sulphate complex of calcium and magnesium embracing cal- Preventative measures