The power shortage crisis in California in 2000 and 2001 was not only expensive to the state, but it also threatened a disastrous situation for residents and businesses as several brownouts occurred and a number of others were just narrowly averted. Much of the credit for preventing more serious repercussions can be credited to the rush of fast-tracked expansion projects and new installations that were put into service in a remarkably short time.

Perhaps the best examples of this rapid response were two 50-MW plants that were constructed in 2001 as part of the California Independent System Operator's (Cal ISO) Summer Reliability Program. At that time and even today, says Gregory Hughes, regional director of operations and regional plant manager for NRG Energy Inc. of Minneapolis, MN, it took 18–24 months to acquire a gas turbine that could generate 50 MW and put it into service. Yet Chowchilla II and Red Bluff, the two new plants, were designed, constructed, and brought on-line in less than seven months, thereby making a badly needed 100 MW of electricity available for capacity and energy transactions.

In large part, this remarkably short schedule was made possible by an executive order issued by Governor Gray Davis that allowed expediting of the permitting process for any new power plant with a capacity of less than 50 MW. Another major factor was the technology selected: natural-gas reciprocating engines. Not only could these engines be acquired from multiple sources in a much shorter time, but they also offered great flexibility because they could be arrayed in 3-MW increments and their record of extremely low-polluting air emissions provided a good justification for fast-tracking.

Managing the Project

The Minneapolis-based NEO Corporation, an independent power producer and subsidiary of NRG Energy Inc., decided to build the distributed-generation power plants at the northern California towns of Chowchilla and Red Bluff under the terms of a three-year contract with the state and its Summer Reliability Program. NEO then awarded two turnkey contracts, each valued at $60 million, to Stewart and Stevenson (S&S) Services Inc. of Houston, TX. S&S, founded more than a century ago, is a billion-dollar corporation that manufactures, distributes, and provides services to key industries, including the power-generation industry, worldwide. Clearly S&S had resources and experience that would be important to such a fast-track project.

In order to design and construct the two plants in just 26 weeks, S&S entered into an unusual performance agreement with NEO. S&S took responsibility for completely engineering the two plants and for procuring all of the equipment, thereby enabling itself to optimize the design, construction, and startup. S&S indeed based its design on natural-gas reciprocating engines because, according to S&S's Ruben Willmarth, "they are environmentally friendly, are more fuel efficient, are easier to dispatch, do not require water—a precious commodity in California—and are easy to permit. Moreover, at up to 50-megawatt capacity, plants based on gas reciprocating engines are quite cost competitive."

To produce this much electricity, 32 natural-gas reciprocating engines would be needed, 16 for each plant. Because it was doubtful that any supplier could supply that many engines in the short time frame available, S&S awarded two subcontracts, each for 16 engines. (This proved to be a wise move because the company even had to use a Russian Antonov cargo plane to deliver the last engine from Europe for the Chowchilla II plant.) Deutz USA provided 16 of its TBG 632 V16 engines for the Chowchilla II plant, and Wärtsilä North America provided 16 of its 18V220SG engines for the Red Bluff plant.

Each of the Deutz engines produces a gross electric output of 3,125 kW, and each of the Wärtsilä engines produces a gross electric output of approximately 2,800 kW. Therefore the Chowchilla plant is slightly larger (81,000 ft.²) and generates slightly more peak load electricity (48.1 MW of electricity to the grid with all gensets at full load). The Red Bluff plant (74,000 ft.²) supplies approximately 42.8 MW to the grid with all gensets at full load. Both facilities allow peaking power to be supplied in small increments as needed to balance demand. The outputs of Red Bluff's 16 generators are combined with those of Chowchilla II's 16 generators hundreds of miles away, thereby making nearly 100 MW of electricity (enough to meet the energy needs of 100,000 homes) available for capacity and energy transactions.

To meet the 26-week schedule, S&S assembled a multidisciplinary team, which included Material Integrity Solutions of Berkeley, CA, for mechanical and structural engineering; Encorp of Windsor, CO, for controls, power plant software, and virtual maintenance monitoring software; Sequoia Engineering of Martinez, CA, for the electrical engineering; and Miratech SCR of Tulsa, OK, for the selective catalytic system. Working extended hours, seven days a week, the team was able to design, construct, test, and bring the Chowchilla II plant into commercial operation on July 1, 2001, just five months after the program began. Then, less than two months later, they brought the Red Bluff plant on-line.

Plant Operation

Both Chowchilla II and Red Bluff are peaking power stations designed to be operated remotely and to be quickly brought on-line to meet peak-load requirements. The 81,000-ft.2 Chowchilla II plant consists of two buildings, each housing eight Deutz engine-generator sets and associated auxiliary and control equipment. The 74,000-ft.2 Red Bluff plant, conversely, consists of a single building separated into two engine rooms, each housing eight Wärtsilä engine generator sets with associated auxiliary and control equipment

Plant operation includes instantaneous, real-time generator monitoring and dispatch. Onsite operators at Chowchilla II and Red Bluff, together with trading floor managers miles away, can diagnose problems immediately with the 32 generators and remotely dispatch them when needed. Using Encorp's Virtual Maintenance Monitor and Virtual Power Plant software packages, trading floor dispatchers thousands of miles away can activate one or all 32 generators and aggregate them together to produce nearly 100 MW of electricity. Commodity brokers at NRG Energy's Minneapolis trading floor regularly sell energy from the two plants into the power grid.

Operation also includes real-time reports on metering and dispatching the 32 generators at Chowchilla II and Red Bluff to Cal ISO. This enables Cal ISO to better manage the California grid by knowing the capacity availability of the plants as power sources and the kilowatt-hour production as they come on-line.

Emissions Control

Both Chowchilla II and Red Bluff are equipped with selective catalytic reduction (SCR) equipment manufactured by HUG Engineering of Switzerland and installed by Miratech SCR. Each engine is equipped with its own SCR converter housing, catalyst, and controls to meet stack emissions requirements, and a 40% urea solution as the reductant.

According to Miratech SCR, these plants use urea as the reductant instead of the usual anhydrous or aqueous ammonia directly because the United States Occupational Safety and Health Administration (OSHA) considers anhydrous ammonia a hazardous material. Hence, its use would require additional safety equipment, training, storage requirements, and documentation. Conversely, urea reacts with water vapor in the hot exhaust stream to decompose into ammonia and carbon dioxide. The urea evaporates and decomposes in the SCR system's mixing section before droplets can touch metal surfaces and pyrolize, Miratech SCR explains.

When construction of Chowchilla II was completed in the summer of 2001, the efficiency of the plant's SCR equipment was demonstrated. Miratech SCR Technical Services, URS Corporation, and Advanced Air Testing LLC measured the permit-required emissions of carbon monoxide, volatile organic compounds (VOC), and NOx on each engine using EPA Methods 7A, 10, and 18. According to Pat Runnels at the time, the VOCs were reduced by 86%, the carbon monoxide was reduced by 92%, and the NOx was reduced by 95%. Comparable results were demonstrated at Red Bluff, Hughes adds. Not only did the plant meet all of the emissions permitting requirements, but its emissions were so low that its SCR system has met the most stringent requirements listed by the California Air Resources Board as the best available technology for reducing NOx.

Costs

NRG Energy Inc. has been operating and maintaining the two plants since they were opened in 2001, but the firm would not provide operations and maintenance (O&M) costs for use in this article. The reason, Hughes explains, is that NRG participates in the California market and actively bids competitively against other electricity suppliers, and O&M costs represent an important part of the bids. He does stress, however, that the two plants are very cost-effective. "If you compare natural-gas reciprocating engine plants with coal-fired plants or gas turbine combined cycle plants, he asserts, "the O&M costs of the natural-gas reciprocating engine plants will inherently be far less. They do not require all of the pollution control and peripheral equipment demanded of these other types of plants, not to mention all of the requirements for testing, continuous monitoring, and the like."

Although he does not divulge actual O&M costs being incurred by Chowchilla II and Red Bluff, he does say that these costs "still meet the pro-forma estimates that the plants were designed to." And at that time, an independent source estimated that the 10-year O&M costs of Chowchilla II would be $0.0017/kWh.

Current Emissions Control Results

Hughes reports that the emissions actually have been reduced from the extremely low levels determined by the 2001 tests when the plants first were opened. "The two plants are frequently retested under the stipulations of their Permits to Operate," he says. "We have to test engines for emissions once every quarter using a portable analyzer that has been certified and approved by the two air-quality districts involved in Chowchilla and Red Bluff. What's more, they select two engines at random each year for additional tests by an independent emissions-testing firm. The results of these tests consistently have shown that we still meet the original standards and that we are emitting a maximum of only 9 ppm of NOx. That's a level that meets even the BACT of the South Coast Air Quality Management District, and that's the toughest one in the state if not the whole country."

Operating Effectiveness

Overall, Hughes says, both Chowchilla II and Red Bluff are still real peaking plants. "In any given day," he says, "the plants may be fully loaded part of the day, then partially loaded during the shoulder hours, and then back to full load for the afternoon peak. The reliability and availability have been outstanding. The only changes we have had to make have been to replace some SCR and [carbon monoxide] catalysts. The plants have consistently been running well."

That's a good sign because soon the original three-year power contract with the state under the Summer Reliability Program will lapse. When that occurs, the electricity generated at Chowchilla II and Red Bluff will have to compete without this support. "We'll be completely market-driven," Hughes says, "and we'll be competing with all of the other people supplying electricity here in California. But I believe that we will be fully competitive with these other sources and that the plants will continue to be a good investment for NEO and NRG Energy Inc."

Author CHARLES D. BADER is with Dateline II Communications in Los Angeles, CA.

DE - May/June 2004