Coal, Gas

Merchant Power On the Go

Issue 7 and Volume 104.

The numbers are astounding. The combined capacity of all the new power plants in development or under construction, both merchant and rate-based, is currently in excess of 175,000 MW, a total that has more than tripled in the last two years. According to the Electric Power Supply Association, there is also evidence that plant developers are accelerating proposed completion dates. In two of the more capacity constrained areas of the East Central and upper Midwest regions, for example, the capacity proposed for operation by 2001 has jumped to almost 17,000 MW from just 4,300 MW last September.

As every expert will tell you, not all of these plants will get built. Some will be unable to obtain financing, others will be unable to secure the necessary gas turbines, others will lack gas supply, and a number will succumb to political and public perception pressures.

Still, merchant power is no longer just an industry buzzword. Many of the plants launched under the merchant umbrella are beginning to come on-line, literally from sea to shining sea, providing a wonderful opportunity to examine how power generation will look in the 21st century. The ability to design, build, staff, operate and maintain new plants from the ground up-without the constraints imposed by existing designs, existing contractual arrangements, existing budgets-enables plant developers to demonstrate their blueprint for success in an open merchant market.

One of American National Power’s (ANP) merchant blueprints is on display 26 miles south of Dallas at the Midlothian energy facility. This facility, being built in the TXI Railport industrial park under development just outside Midlothian, Texas, features technology, staffing structures and a development plan that make it truly unique. In addition, Midlothian will be one of the largest combined-cycle gas turbine facilities in the country when the last of the six units comes on-line in December 2001.

Texas Takeoff


Demineralizer tank (left) and raw water tank (right), with plumbing for demineralizer trailers in foreground.
Click here to enlarge image

Midlothian’s history, and future, are tied to the electricity market in Texas. According to National Power, ANP’s parent, Texas is one of the best electricity markets in the U.S., with more than 50,000 MW of capacity-almost as much as the whole of Britain. Further, it is an island market, with very little interconnection to adjoining power grids, and it includes more than 25,000 MW of older gas plants that set marginal prices for a significant amount of the time.

In 1998, TXI sold 60 acres of an industrial park parcel to ANP to develop a gas-fired power plant. In 1999, ANP purchased an additional 30 acres to accommodate a two-unit expansion at Midlothian. Following the industrial park development plan, ANP will serve as the anchor tenant, attracting additional industrial tenants.

ANP received the notice to proceed at Midlothian in September 1998, began site clearance in January 1999, and will begin operation in the summer of 2000. Initially designed as an 1,100 MW power plant but recently expanded to 1,650 MW, Midlothian will provide a cost-competitive option in the deregulating Texas electricity market. Electricity from the plant will initially be sold to TXU Utilities under a two-year power purchase agreement, after which time Midlothian’s full capacity will be exposed to the merchant market. The nearby Venus substation serves as Midlothian’s entry point to the Texas grid.

Common Framework

ABB Alstom Power (now Alstom Power) is the EPC contractor at Midlothian, as well as at several other ANP merchant facilities: the 1,100 MW Hays facility under construction in San Marcos, Texas, the 570 MW Blackstone facility in Massachusetts, and the 570 MW Bellingham facility in Massachusetts. The six units at Midlothian are all based on Alstom’s GT24B reference plant outdoor design, which includes Alstom-design gas turbines, steam turbines, generators, heat recovery steam generators and assorted balance-of-plant equipment. Each turbine train at Midlothian is rated at 276 MW at ISO conditions, but will nominally provide 250 MW apiece. Units 1 and 2 will come on-line in summer 2000, Units 3 and 4 are scheduled for commercial operation by year’s end 2000, and Units 5 and 6 will go commercial by the end of 2001. The heat rate guarantee on gas is 6,866 Btu/kWh. – Air-cooled condenser with 8-blade fan.

ANP has “hung its hat on the ABB GT24B design,” but will continue to evaluate other OEM gas turbines. Although there have been some early operational problems with the GT24B, ANP is committed to making their units a long-term success.

The GT24 reference plant design features a single-shaft configuration, where gas turbine, steam turbine and generator are all on a common shaft. The single-shaft design reduces foundation and rotor costs without hampering operational flexibility. A self-synchronizing clutch between the steam turbine and the generator facilitates the different start-up characteristics of the steam and gas turbine.

The gas turbines are equipped with evaporative cooling media equipment to boost capacity during periods of hot weather. These systems, which don’t cut on until the temperature reaches 80 F, can provide up to 10 MW additional capacity. An additional 20 MW can be accomplished with steam injection for each unit.

The HRSGs selected for each turbine train feature a once-through, horizontal tube high-pressure section and a steam drum, vertical tube LP/IP (low-pressure/intermediate pressure) section. The steam cycle produces HP steam at 2,320 psi and 1,050 F, IP steam at 529 psi and 1,050 F, and LP steam at 97.2 psi and 608 F. There are no provisions for supplementary duct firing, and the units are not equipped with bypass stacks on the HRSGs. The ABB reference design does not allow for simple cycle operation.

Fuel Flexible

ANP benefits from the availability of two competing pipelines at the Midlothian site. The two 24-inch diameter pipelines, owned by Lone Star and PG&E, are capable of accommodating any future expansion plans at Midlothian. Separate compressor stations service each gas turbine. Incoming gas is normally at adequate pressure, but can be boosted to 650-750 psi in the compressors if line pressure drops below a preset value. The gas is also heated to 160 F with waste heat from the plant to optimize gas turbine efficiency. Filters remove any tramp particulate matter in the supply gas.

Despite the presence of two pipelines at Midlothian, Units 1-3 will feature dual-fuel firing capabilities. A pair of 2.2 million gallon fuel oil tanks can satisfy turbine fuel demand for 72 hours at full load, although such operation is limited to 720 hours per year.

Emissions Controls

NOx control at Midlothian is achieved using the inherently low NOx emissions from the GT24B gas turbines and a selective catalytic reduction system in the HRSGs. The aqueous ammonia SCR system, featuring a honeycomb V2O5 catalyst on a Ti/TiO2 substrate, is designed to limit NOx emissions to 5 ppm on natural gas and to 9 ppm when firing fuel oil. Ammonia slip is restricted to 10 ppm on all units. ANP anticipates a 7-8 year catalyst lifetime when operating at full load.

Water supply and water use presented particular challenges at Midlothian. Because Texas state development agencies discouraged industry from using water from lakes and groundwater sources, ANP opted for air-cooled condenser/cooling technology. The 15-cell air-cooled condensers from Balcke Durr have much lower water requirements and made permitting as a “zero discharge” facility much easier. Wet cooling technology would have increased water usage by 2,000 gpm, or 25 percent. To avoid vibration problems observed by ANP personnel with 3-blade condenser fans at other facilities, Midlothian will incorporate an 8-blade design.

The water treatment functions at Midlothian are primarily outsourced to Ecolochem. Water from the raw water storage tank is pumped though an Ecolochem demineralization trailer and then to a demineralized storage tank. The demineralization trailer contains six pressure vessels: three cation, two anion and one mixed-bed resin vessel. When the resin charge is neatly spent, Ecolochem simply brings a fresh trailer that can be plumbed to the tank farm in 10 minutes. There is space for five demineralizer trailers on site and multiple trailers will likely be in use during operation. Raw water is manifolded off the raw water tank to feed each trailer as necessary.

Staff Strength


Aerial view of Units 1-4 under construction at Midlothian.
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Midlothian’s staffing, training and personnel management approach is truly unique. All plant operators are classified as O&M specialists, creating a “flattened structure that many have attempted but few have achieved,” according to Ron Reynolds, one of the O&M specialists. ANP hired the first set of employees between January and April 1999, more than a year before commercial operations were set to begin.

Training began immediately, and the O&M specialists were immersed in a cross-functional stewardship program that covered both plant processes and plant systems. Process stewardship involved the development of manuals prior to commercial operation for a range of plant categories: administration, finance, human resources, management, technical, health and safety, lockout/tagout, emergency, chemistry, environmental and operations. System stewardship involved the design, procurement, installation, operation and maintenance of specific plant equipment or systems: gas turbine, steam turbine, HRSG, condensate/feedwater, balance of plant, air-cooled condenser, electrical systems, control system, fire systems, CMMS system and documentation.

Employees are assigned to at least one process and one system and become champions for that particular function. Demonstrating ANP’s commitment to this approach, O&M specialists were sent to Baden, Switzerland to finalize specifications and oversee design development of the GT24 turbines, and to St. Louis to evaluate and finalize specifications for the Ecolochem water treatment system. O&M specialists publicly and privately attest to the value that such responsibility has instilled in them. “We’ve truly got a servant-leader driven organization, which empowers our employees to make the plant a success,” said Mike Knisley, Midlothian plant manager.

Midlothian will employ 34 full-time personnel, with 20 on shift in five teams of four. A single centralized control room will coordinate operation of all six combined-cycle units. Midlothian is also being used to train the employees that will be bringing the Hays facility in San Marcos, Texas on-line by the summer of 2001. Because ANP uses a fairly standard plant design at its U.S. facilities, training is similar.

While only time will tell whether ANP’s merchant blueprint will stand up to the rigors of competition, the blueprint contains many of the elements business gurus have been offering as essential elements for success in the new economy: streamlined management, flattened operational structure, individual empowerment, reliance on advanced technology, outsourcing of non-critical functions, etc. The challenge now is to ensure that the commitment to these elements remains strong.