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ABSTRACT Electric utility and cogeneration (Cogen) plants offer numerous possibilities for the reuse of water in both boiler and cooling systems. However, these plants have specific water quality requirements. Careful evaluation of potential sources of reuse water is needed and water treatment processes must be tailored to the site specific needs of a particular plant, These needs vary based on the design of the plant and often on the geographic location. This paper describes the water quality needs in electric utility and cogeneration facilities and the opportunities for reuse waters to fulfill these needs INTRODUCTION In many parts of the world water is a scarce resource. In some areas water availability is the major issue and in other areas, water quality is the major issue. Some locations face issues of both quality and quantity. In response to these growing problems, industry has been challenged to find ways to utilize poorer quality water while reducing the quantity of water used. In some parts of the United States, treated sewage is being offered to industrial customers at prices that are deeply discounted when compared to the primary the water supply. In other cases, industry is encouraged to look inward and find ways to reduce water use or to forge partnerships with neighbors to utilize their wastewater. Steam/electric plants are large consumers of water, therefore, they are in the forefront of efforts to conserve water and utilize lower quality water. These challenges are compounded by the fact that they must be accomplished in an environment that is increasingly emphasizing plant reliability and cost containment. One of the key elements in the quest to minimize water use is the recycling of water from one use to another, Recycle can be on a macro scale such as the reusing of the effluent from a municipal sewage plant or it can be on a micro scale such as the reuse of boiler blowdown in a cooling tower. Each situation is unique and poses special problems that must be solved for the application to be successful. For steam/electrical power generators, the challenges are both old and new. The boiler-water quality guidelines that have served the industry well for many years are still good guidelines and should be continued. However, older concepts of what water could or could not be processed and used as either boiler feedwater or cooling tower water must be rethought. WATER QUALITY NEEDS OF ELECTRIC UTILITY AND COGENERATION PLANTS Cogeneration (Boiler Needs) The typical power cycle for a cogeneration plant consists of a gas turbine, a heat recovery steam generator, (HRSG, waste heat recovery boiler), a steam turbine, and an electrical power generator, Figure 1 illustrates a cycle that generates steam at two pressure levels, However, it is common to find HRSG?s that produce steam at three pressure levels, Intermediate pressure steam generation is frequently used to improve the cycle efficiency by producing steam at an advantageous pressure for the steam users, In most cases, high pressure steam is generated at pressures ranging from 600 to 1,800 psig and generally at 30 psig in the low-pressure section. The make-up quality needs are determined by: o Highest pressure that steam is generated o Design of the heat recovery steam generator (waste heat boiler) o Steam purity requirements of the steam turbine o Steam purity requirements of the steam users The make-up water quality requirements can be divided into inorgan
- Water & Waste Management > Water Management > Water Supplies & Services (1.00)
- Energy > Power Industry (1.00)
- Water & Waste Management > Water Management > Lifecycle > Treatment (0.52)
- (2 more...)
ABSTRACT INTRODUCTION Reuse water can be defined as used water that can be recycled for cooling, boiler or process applications. It may be treated to remove contaminants that will cause problems in that application. This treatment may be simple or very extensive. Certainly, water short areas (or plants) may have a higher priority than cost to make water available for plant applications. Each facility must determine its own priorities for water reuse. Thus, water reuse is site specific. To successfully reuse any used waters, it is necessary to first establish the requirements (or purity) of the water needed for that specific application. If the used water constitutes a small percentage of all waters to be used, the combined water quality must be considered. Matching water quality with water-using equipment requirements is the key to successful reuse.. Using a used water without proper pretreatment will almost always result in unsatisfactory results. This lack of success often results in excess or premature damage to the water-using equipment and excessive treatment costs. Economics often will dictate how much treatment should be performed of a specific used water. Thus, knowing your equipment requirements is extremely important in successfully reusing used waters. Treated municipal waste water, most often defined as reclaimed water, has seen substantial reuse during the past IO+ years to replace fresh waters. Reclaimed water use has expanded to many plants - specifically utility, power, petroleum refinery, petro-chemical, chemical, cogen, automotive, electronics, and even commercial and institutional facilities. RECLAIMED WATER QUALITY Reclaimed water can be characterized as to quality, though variations can be considerable. This depends upon the water quality of the surrounding area in addition to the municipal waste water treatment. Typical water quality often is: Specific water characteristics common to reclaimed waters are the phosphate, ammonia and organic contents (total COD, BOD and TOC). These parameters can be beneficial (phosphate, nitrate) or detrimental (ammonia, silica, total dissolved solids) depending upon the water systems utilizing this reclaimed water. Further treatment (such as softening, clarification, nitrification, etc.) can produce a water of very good quality. When high total dissolved solids are present horn chlorides, sulfates, fluorides, nitrates, etc., treatment by reverse osmosis may be required for some users who need lower dissolved solids.