complete disregard to the alternate use of more technically feasible and cost-effective chemical-based treatment options. The end result are planı designs unable or barely capable to meet the performance specifications of critical equipment such as steam and gas turbines even during the start-up phase, leading to start-up delays and legal disputes, and later translating into high water treatment operating costs, planı downtime and potential expensive planı modifications. This paper will discuss water treatment technologies such as membrane separation (e.g. reverse osmosis), electrodialysis and electrodionisation (EDI), and the fading yet unique role that ion exchange can play. it will also address the critical role that well qualified chemical water treatment companies can play in avoiding costly mistakes during Power plant design, how to best fit chemical treatment options, and what can go severely wrong when the raw water to the plant is not critically evaluated. INTRODUCTION "Long before ground was broken tor the new Power plant, all aspects of water treatment were carefully considered and evaluated by a team of dedicated experts. At start-up, the selected unit operations functioned in unison, delivering per design flow rates without significant water chemistry upsets". The norm in ali projects, wouldn't you say? Not quite. My own experience has consistently shown that water treatment is a common contributor to delayed start-ups, subsequent poor planı heat rates, and a cause of unscheduled downtime. 1 also believe that water treatment is the orphan of plant designers, seen as .the necessary evil on the overall project's flow schematic, and as such it often does not receive the attention it deserves. Engineering, Procurement and Construction firms (so-called EPCs) used to employ in-house water treatment specialists that were knowledgeable in the selection of equipment. Ditto for many planı owners and end-users' engineering departments who contributed valuable input to planı designers during the conceptual design phase. Following years of manpower rationalization, many of these resources are no longer available. Furthermore, very competitive bidding processes during the detailed engine ering phase exert added pressure on capital equipment selection, often resulting in very unsound, albeit least expensive, choices being made. The "cheapest bid is the best bid" brigade is alive and well. Once the operating phase begins, responsibility tor all water treatment related matters generally falls upon the selected chemical water treatment company. However, the latter is often not consulted until the commissioning or operations stages, when it is too late to undo critical errors made in the design phase. it often takes costly retrofits and many hours of lost production to rectify mistakes and return the plant to "normal", optimized performance. Successful water treatment in any plant hinges upon the proper integration of the right water chemistries with the correct choice of equipment at every applicable unit operation. it starts, as straightforward as it may sound, with a thorough evaluation of the water sources that are to feed the Power planı. This, 1 believe, is one of the most neglected steps in the overall process. in the following pages, 1 hope to share with you some of the common mistakes made, discuss the besi use of new and old technologies, and offer general good advice that can save you money and avoid some of the "water treatment disasters" 1 have been unfortunate to witness. 1 . Asset Protection in today's combined cycle plant, the most important assets to protect are the combustion and steam turbine units. Although water reaches many parts of the plant, the above-mentioned are undoubtedly key items, both in terms of capital cost and plant operability impact. The following is a list of the main applications of water and steam in a typical Power plant: t Feedwater for steam generation t Low, medium and high-pressure steam generation t Cooling of high-temperature combustion turbine (steam) t NOx control and/or power augmentation (water/steam) t Combustion turbine air inlet cooiing (water) t Cooling water for steam turbine condenser t Combustion turbine open/closed cooling (e.g. lube oil) t Combustion turbine compressor washing (water) .... - ı t � lıa.lll Figııre 1. Water Treaııneııı lıııeracıioıı in a Modern Combiııed, Cyc/e P/cı111. Steam turbine manufacturers impose strict limits on steam purity tor their machinery (see Table 1). These limits essentially set the water quality criteria tor the boilers (or heat-recovery steam generators), which in turn define a minimum level of purification technology tor the water treatment plant. Naturally, the extent of pre-treatment to this very planı is strong influenced by raw water quality. Fig. 1 above helps visualise this. Another critical component in the Power plant is the steam condenser and associated cooling system. ENERJi DÜNYASI EYLÜL 2006 77
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