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Portland General Electric is constructing what will be the most efficient natural gas-fired generator of its type in the Northwest.
By Jaisen Mody, Portland General Electric
Barring any unforeseen problems, next spring, Portland General Electric (PGE) will begin operating the United States’ first combustion turbine that uses Mitsubishi Heavy Industries’ (MHI) G1 advanced technology. Construction of PGE’s G class combined-cycle combustion turbine at the Port Westward site, adjacent to the site of its existing Beaver Plant, has surpassed the 40 percent schedule milestone. The new Port Westward Power Plant will be the most efficient natural gas-fired generator of its type in the Northwest.
PGE’s original permit application for Port Westward specified a two-turbine plant with up to 650 MW of plant capacity using F class turbine technology. However, after careful analysis of projected consumer demand, review of newly available turbine technologies, forecasts of customer elections under the state’s electricity restructuring law, the outcome of a competitive bidding process for wholesale power contracts and an analysis of the natural gas marketplace, PGE modified its original recommendations. The utility decided that, because it is more efficient than the F class turbine, the new G class unit would be a better overall long-term investment for customers.
As a result, Port Westward’s target of 650 MW from two natural gas-fired F class turbines was reduced to one unit using the more efficient G class turbine technology. Under average site ambient conditions the new plant will have an overall capacity of 407 MW, 382 MW of this being combined-cycle and the remainder duct firing.
Selection Criteria
PGE spent considerable time researching the various gas turbine technologies available for gas-fired plants. The existing F class technology was considered together with the GT-24 machines. The utility’s analysis showed that the G class option was a lower-cost option for its customers. Port Westward’s G class machine has scale advantages because it is approximately 100 MW larger than the F class option originally considered. It also has a 2 percent to 3 percent heat rate advantage over the F class alternative.
G class machines have been in commercial operation since 1997 and have logged many hours of operation. The only two G class turbine manufacturers, Mitsubishi Heavy Industries and Siemens Power Corp., were considered based on several criteria, including technology attributes, cost, number of operating plants, units deployed, units on order, reliability and technical support and service.
After completing a detailed options analysis, PGE engineers and consultants chose the Mitsubishi machine. Two main factors influenced this decision. One was the operating history of Mitsubishi’s fleet of 18 G gas turbines. This fleet of gas turbines now has more than 320,000 hours of cumulative operating history. A second was Mitsubishi’s verification approach in which new technology and design changes are first tested at the company’s verification power plant in Takasago, Japan, prior to commercial release. Port Westward’s G1 unit underwent a thorough verification and testing process, which should result in fewer problems during operation, because both the verification facility and the approach provide meaningful quantitative comparisons with design assumptions.
In addition to the two main factors, input from PGE plant operators about their experiences with Mitsubishi’s technical support and services was considered during the selection process.
Contracts
Normally, a turnkey engineering-procurement-construction (EPC) contract is negotiated with the EPC contractor who in turn procures the turbine and power island equipment. This was not an ideal approach for PGE because the utility felt it would impair its ability to have maximum interface with the original equipment manufacturer (OEM). PGE wanted close contact with the OEM to accomplish several objectives, including:
- Speedy procurement.
- Ability for hands-on discussion with the OEM.
- Ability to negotiate a long-term service agreement (LTSA) with the OEM.
Thus, PGE decided to negotiate its own turbine deal with the OEM. At the same time, however, PGE did not want to lose the benefits that come with a full-wrap turnkey EPC simply because it negotiated its own turbine/power island deal with the OEM. Therefore, PGE assigned the turbine/power island contract to the EPC, Black & Veatch Construction Inc., and now has only one entity to manage for the entire power project.
PGE also negotiated the turbine contract and the LTSA in tandem. It leveraged the turbine award to drive a hard bargain on the LTSA, assuring no major gaps between contracts.
The LTSA, which was negotiated and signed with Mitsubishi Power Systems, covers the gas turbine parts and planned maintenance inspections for 12 years. This agreement ensures ongoing reliability and OEM cost predictability for this plant. Troutman Sanders LLP assisted PGE with contract negotiations and preparation.
Gas Turbine Advances
Since the first G class turbine technology by Mitsubishi was introduced in 1997, there have been significant advances in blade cooling schemes, heat transfer, aerodynamics and sealing technologies. Mitsubishi introduced the G1 machine during its contract negotiations with PGE making Port Westward the first U.S. plant with this advanced machine. Table 1 illustrates how the G and G1 machines are the same and how they are different. The row one turbine hardware in the G1 gas turbine was improved through design technology advances. Additionally, the G1 extends steam cooling from the combustor transitions to the blade ring on the first row of the turbine (Photo 2). The upgraded hardware was installed in Mitsubishi’s verification power plant in May 2003. By April 1, 2006, the upgraded hardware accumulated more than 8,083 actual hours of operating experience and 501 start-stop cycles in daily start stop (DSS) load dispatch operation. From the time the engine began operation in 1997 until December 2005, its cumulative operating time was 22,499 hours (Figure 1).
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 Photo 1. Port Westward Plant site in late March, 2006. Photo courtesy of Black & Veatch Construction Inc. |
In addition to the gas turbine manufactured by Mitsubishi, the Port Westward Power Plant has a three-drum Deltak heat recovery steam generator, one Mitsubishi steam turbine and two Mitsubishi electric generators for the gas turbine and steam turbine. The steam turbine is a tandem-compound type-down exhaust with a crossover connection from the high pressure-intermediate pressure stage to the low pressure stage. PGE chose the down exhaust turbine on this 1x1 plant to boost efficiency. The condenser is manufactured by TEI and uses 24-gauge stainless steel tubes. Marley is building a seven cell fiberglass cooling tower that uses river water for makeup. The plant uses backup power and demineralized water from its sister plant, Beaver, one mile from the Port Westward site. Emerson is supplying the distrubted control system.
Port Westward has a static frequency converter for starting, evaporative cooling and duct firing for power boost. An auxiliary boiler will provide warm-up and startup steam required for the steam-cooled components. Steam cooling is one of the reasons Port Westward will be so efficient. Steam cooling typically includes additional equipment and protection, which exists in all Mitsubishi G class units in commercial operation.
 Photo 2. Original (L) and upgraded (R) turbine vane configuration. Photo courtesy of Mitsubishi Power Systems |
The environmental equipment includes selective catalytic reduction and a carbon monoxide catalyst that reduces nitrogen oxides to 2.5 ppm and carbon monoxide to 4.9 ppm. An ammonia injection system uses the boiler heat for vaporization. Cormetech provided the ammonia catalyst and Englehard supplied the carbon monoxide catalyst.
Port Westward includes built-in redundancy for critical equipment. Extensive reviews by PGE’s operating staff ensure adequate access and platforms will be available to assist with equipment maintenance. Black & Veatch and Deltak provided a 3-D model that was reviewed in detail by PGE’s operations staff.
Attractive Location
The site, adjacent to the Columbia River in Columbia County, Ore., takes advantage of existing electrical transmission and gas transportation infrastructure. The location west of the Cascade Mountains is attractive because the generation source will be close to PGE’s load; an eastern location could present transmission constraints. Transmission line losses will also be lower, resulting in cost savings.
Construction of a transmission line from the Port Westward site to PGE’s decommissioned Trojan Nuclear Plant site will allow power delivery directly into PGE’s grid. Transmission requirements include construction of a single circuit 230-kV transmission line from Port Westward to Bonneville Power Authority’s Allston Substation, construction of a double circuit 230-kV transmission line from Allston to Trojan, and a new line position at the Trojan Switchyard. Only one circuit is being installed at this time.
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The plant will burn natural gas received from Sumas, a hub in Washington State through which Canadian natural gas is delivered via the Williams Northwest Pipeline. The site has good access to the Kelso-Beaver (K-B) Pipeline. An 18-inch lateral pipeline coming off a 20-inch mainline will supply gas and will include a compression station.
The existing intake structure will be used for cooling water from the river. PGE holds a 99-year lease from the Port of St. Helen’s for the Port Westward site.
Stone columns
Construction started in February 2005 and is currently on schedule to meet a March 2007 commercial operation date. The plant is located on native sand and soft silt, so extensive ground reinforcement was required. Stone columns were installed in four main areas: the power block, cooling tower area, the gas compressor building and the switchyard. A total of 4,131 stone columns were installed at an average depth of 40 feet. The columns will mitigate the potential for earthquake induced liquefaction of the loose, saturated sand deposits underlying the dredged sand at the site.
Areas where piles were driven were left untreated. A total of 514 piles were driven to support the foundations for the critical equipment (Photo 3). Foundation pours started in August 2005. Crews worked for nearly 11 hours in 90 F heat in early August, pouring 840-cubic yards of concrete into rebar-reinforced forms to create a five-foot thick base pad. The operation was completed as one continuous pour, with trucks arriving every six minutes and carrying fresh batches of concrete prepared at a mixing facility a mile away.
Equipment delivery began in September 2005. Port Westward is fortunate to have road, rail and river access. Most of the heavy equipment was delivered by barge. Ships from China, Korea and Japan delivered equipment to Longview, Ore., where it was transferred to a river barge. Multiaxled, self-propelled transporters (Photo 4) moved the equipment from the barge to the laydown area. Gantry cranes assembled at the site lifted the heavy equipment. The condenser with the water boxes installed was moved as one module using a roller/rail system.
Despite some obstacles created by Mother Nature, all the equipment arrived safely during the early part of 2006 and is now being installed. The ship carrying the Mitsubishi equipment from Takasago, Japan, experienced 30-foot waves during its journey. In Oregon, excessive rains caused the Columbia River to reach flood levels, preventing the equipment from being unloaded until flooding eased.
 Photo 3. Piles being installed. Photo courtesy of Portland General Electric |
PGE is providing overall project management with a small, dedicated group of professionals, supplemented with engineers, analysts and specialists from several other PGE departments. The plant construction schedule is integrated with schedules for transmission line construction, switchyard construction and various support systems that tie into the plant. Besides scheduling and general work coordination, PGE is also managing the cost, communication and project risk.
 Photo 4. Gas turbine on transporter. Photo courtesy of Portland General Electric |
A risk matrix was developed and is constantly updated as the project goes through the various phases of construction. Management is kept abreast of the risks and their effects on plant schedule, cost and liability.
PGE will own and operate Port Westward and will hire a 17-member operations team to participate in its startup and commissioning. PGE expects the team to be on-site by July 2006.
Author
Jaisen Mody holds a master’s degree in mechanical engineering from University of Washington and has been employed by PGE since 1979. He is managing the engineering and construction of the Port Westward Project.
Reference
H. Arimura, Y. Iwasaki, Y. Fukuizumi, S. Shiozaki and V. Kallianpur, “Upgraded M501G operating experience,” Proceedings of ASME Turbo Expo, Reno, Nevada, June 6-9, 2005, paper #ASME GT2005-69135.
