The Valley of the Sun went off the water wagon on March 4, ending a record 136 consecutive days without measurable rainfall. That first 0.05-inch sip, followed by a 0.18-inch gulp the next day, only left residents yearning for more. But Mother Nature was only teasing, because the rest of March remained dry. On March 29, Arizona’s drought threat level moved from “severe” to “extreme” due to nonexistent snow packs and one of the driest winters on record.
As the drought enters its 11th year, there are two pieces of good news. One is that the Colorado River, which supplies about one-third of Arizona’s total water supply, is at close to normal flows. The other is that local reservoirs, which hit 30-year lows early in 2005, are on the mend. But the bad news is that water supplies for power generation remain at a premium.
Demographers tell us that Arizona was the second-fastest-growing U.S. state (Nevada was No. 1) in the 1990s. Today, it has just under 6 million residents—more than twice the 2.7 million of 1980. The Arizona Department of Commerce predicts that the extraordinary growth will continue as the baby boom generation retires and that 8.5 million people will call the state home in 2030.
This rapid growth will increasingly strain Arizona’s water management and power generation infrastructures, which are already quite taxed. When all the air conditioners in Phoenix are cranked up to “max cool” on a 110-degree-plus day, the city’s residents and businesses use more electricity than Manhattan. For this reason, Arizona Public Service (APS) expects that it alone will need another 5,000 MW of generating capacity over the next decade. A reliable source of power and water capable of keeping pace with Arizona’s projected population boom is the only thing separating the state’s desert dwellers from a future of hot, thirsty summers (Figure 1).
1. Too many people. Growing baseload and peak electricity demand in the U.S. Southwest through 2008 will be met by expanding gas-fired generating capacity. Source: Salt River Project
Terrific template
Generating lots of megawatt-hours without consuming lots of water is a difficult trick to pull off, but the Redhawk Power Station (Figure 2) has done it. Owned by APS, Redhawk is located 4 miles south of the Palo Verde Nuclear Generating Station, about 60 miles west of Phoenix.
2. Desert dweller. The Redhawk Power Station is 4 miles south of the Palo Verde Nuclear Generating Station, about 60 miles west of Phoenix. Source: POWER magazine
The combined-cycle plant, which went commercial in 2002, has twin 530-MW power blocks. Each block consists of two General Electric 7FA gas turbines nominally rated at 165 MW (at 73F) and a single 200-MW steam turbine from Alstom Power. Redhawk’s two heat-recovery steam generators (HRSGs), supplied by NEM (now Louisville, Kentucky–based Vogt-NEM), are fired by duct burners so they can supply an additional 15 MW apiece when peaking power is needed during summer days. A selective catalytic reduction (SCR) system, from Hitachi Zosen Corp. with ammonia injection, keeps NOx emissions under the permitted limit of 3.0 ppm. All in all, Redhawk is a very well designed and solidly operated plant, as evidenced by its 96%+ availability factor during 2005.
Although Redhawk’s configuration is fairly standard, its water management systems—which reuse nearly 1 billion gallons of reclaimed wastewater each year—are anything but. Recycling water for all plant needs appreciably reduces the strain on already burdened local aquifers. In fact, Redhawk’s zero liquid discharge (ZLD) system all but eliminates liquid waste leaving the plant. Plant designs like Redhawk’s that generate clean, low-cost electricity within local environmental constraints set the bar high for power project developers eyeing the region.
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