The Monticello Steam Electric Station (Figure 1), comprising three supercritical units collectively rated at 1,880 MW (net), is located in northeast Texas, just southwest of the city of Mount Pleasant and about 120 miles east of Dallas. Monticello Units 1 and 2 are each rated at 565 MW and are powered by a Combustion Engineering boiler and a Westinghouse turbine-generator. They came on-line in 1974 and 1976, respectively. Steam conditions are 3,500 psi and 1,005F. Unit 3, rated at 750 MW, is powered by a Babcock & Wilcox boiler and a turbine-generator from General Electric. Unit 3, with identical steam conditions, went into service in 1978.
1. Ten-year test bed. Monticello Steam Electric Station has been blending PRB coal with Texas lignite since 1995. Courtesy: TXU Power
At the Monticello plant, electrostatic precipitators and baghouses remove particulate matter while a scrubber removes sulfur dioxide and low-NOx burners limit the formation of nitrogen oxides. Monticello recycles and reuses process water, so it has no need to discharge it. Some of the ash by-products of burning lignite and PRB coal are recycled into products such as concrete, ready-mix cement, road de-icing material, and clay and concrete blocks. The Monticello plant is cooled by 2,000-acre Lake Monticello, a popular fishing and recreation site.
Monticello operates in baseload mode throughout much of the year. The units do some load following—for frequency control—during the spring and fall, when few natural gas–fired units are dispatched to the Electric Reliability Council of Texas (ERCOT) grid. As Table 1 shows, Monticello's equivalent availability and capacity factors are now approaching 90%. Over the past five years, the plant's equivalent forced outage rate has fallen to below 6%, from a peak in the mid-twenties a few years prior.
Table 1. Monticello's recent performance stats. Source: TXU Power
During its first two decades of operation, Monticello exclusively burned local lignite, its design fuel. In 1995, management began blending PRB coal with the lignite to improve overall fuel quality. Over time, the share of PRB was increased slowly; today, it accounts for 50% of Monticello's total fuel tonnage. Last year, Monticello burned nearly 6 million tons of it. Table 2, which compares four key characteristics of the lignite and PRB coal burned at Monticello, makes clear that the blending indeed represented a fuel upgrade.
Table 2. Lignite vs. PRB (as received). Source: TXU Power
Significantly, the increasing share of PRB coal in the fuel mix slowly but surely reduced Monticello's emissions of pollutants, including mercury (Table 3). The positive, downward trends were a key reason that TXU Power's parent, Dallas-based TXU Corp., recently proposed building 11 new coal- or lignite-fired units in Texas (including Monticello Unit 4) with a total capacity of 9,079 MW by 2010—as well as another 5,000 to 8,000 MW of coal-fired capacity in the Pennsylvania-New Jersey-Maryland region (see box).
Table 3. Monticello's production and environmental performance over the past seven years. Source: TXU Power
Much of the credit for the success of the blending program in recent years must go to Barry Boswell, director of generation at Monticello for almost five years prior to November 2005, when he left to become director of TXU Power's Martin Lake plant. Boswell provided the leadership needed to bring about the changes that ultimately led to Monticello's being named the PRB Coal Users' Group Plant of the Year for 2006.
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