Environmental Engineering Reference
In-Depth Information
13.4 Water Overview
When one examines power generation, there are several different aspects of water treat-
ment. Generally, they include the following:
• Cooling water
• Boiler water, ranging from low-pressure boilers to supercritical boilers
• Condensate polishing
• Water used for fuel gas desulfurization (FGD)
• Drinking water for more remotely located facilities
The above list represents an industry that requires multiple water treatment technolo-
gies, ranging from the use of specialty treatment chemicals, basic iltration, and deioniza-
tion treatments. In this section, we will briely examine the needs and concerns that drive
the power industry water treatment.
Please note that treated water is needed in thermoelectric plants, and also in those using
gas turbines. In the latter case, such facilities often also use heat recovery steam generators.
For the purposes of the remainder of this chapter section, the term “power” will refer to
both types of electrical generators.
13.4.1 Cooling Water
Power plants commonly use either cooling towers or once-through systems to cool process
liquids. For cooling towers, treatment approaches generally involve the use of specialty
chemicals to prevent and control scaling and corrosion. Biocides are used to prevent bio-
fouling and algae growth. While chlorine products have been a traditional biocide, plants
increasingly have turned to other alternatives such as chlorine dioxide. In a cooling tower,
the water is often used for several cycles before discharge.
Another approach involves once-through cooling systems that take water from the ocean
or a river and then return it. This method is common at stations bordering oceans, bays,
and rivers. For once-through cooling systems, one important concern revolves around pro-
tecting the water intake pipes against macroorganisms such as zebra mussels that can
clog the structures. It should be noted that some once-through cooling systems are being
phased out, partly because of emerging US Environmental Protection Agency (US EPA)
regulations that call for alternate approaches. Environmentalists claim warmed efluent
water from a cooling system can damage the surrounding ecology in an ocean or river,
and that water intake systems must be designed so that they protect aquatic life from
“impingement” and “entrainment” [5].
13.4.2 Boiler Water
Thermopower stations use boilers to produce steam to drive turbines to generate electric-
ity. Boilers typically have a series of tubes that are used to produce the steam. The concern
is that the tubes can fail because of corrosion, plugging, or metal weakening.
Boilers used will range from low pressure to medium pressure to high pressure. The
pressure rating determines water treatment needs. For example, subcritical to supercriti-
cal boilers typically found at large utility stations require DI, high-purity water, while
