|Courtesy: Siemens Energy|
Set to begin commercial operation on Sept. 17, 2012, the 280-MW Lodi Energy Center is the first “fast-start” combined cycle power plant in the U.S. The advantages of the gas turbine’s shorter startup capabilities are reduced fuel costs, lower emissions, and the versatility to effectively partner with intermittent renewable energy sources. The new power plant is located next to the city of Lodi’s municipal wastewater treatment plant and uses its treated wastewater for cooling purposes.
In keeping with its reputation as an environmental trendsetter, California raised the bar for renewable energy goals in 2011 by enacting a revised renewables portfolio standard (RPS) requiring that 33% of all electricity retail sales be from renewable energy resources by 2020. The new Lodi Energy Center (LEC) was designed to incorporate fast-start technology that complements the large amount of existing and future intermittent renewable resources in the state, Michael DeBortoli, LEC project manager, told POWER in July.
With the new RPS now in effect, combined cycle plants will increasingly be called upon to serve as backup power sources. The LEC will be able to cycle up and down efficiently while staying within its emissions limits even at low-load operation, while maintaining high overall thermal efficiency.
“The new power plant is capable of producing approximately 2,400,000 MWh/year but is expected to produce 1,600,000 MWh/year as it adjusts the output to accommodate the intermittent renewable resources in California,” DeBortoli said.
The total project cost is estimated at about $375 million, or roughly $1,300 per kilowatt of new capacity, a relatively low cost for new power generation in the U.S. When the plant begins operation, it will serve the power needs of 14 different project participants. In addition to the Northern California Power Agency (NCPA, a “joint-powers agency” serving a variety of public entities), the ownership group includes Modesto Irrigation District; Power and Water Resources Pooling Authority; Port of Oakland; Plumas-Sierra Rural Electric; State of California Department of Water Resources; Bay Area Rapid Transit; and the cities of Ukiah, Lodi, Biggs, Azusa, Lompoc, Santa Clara, Healdsburg, and Gridley.
The LEC is located on a 4.4-acre site adjacent to one of NCPA’s existing combustion turbine projects (CT#2), allowing the new power plant to take advantage of existing infrastructure, easements, and corridors for gas and power lines. A new 2.7-mile gas pipeline was placed parallel to the one serving CT#2. Furthermore, the LEC will be able to tie directly into the power grid through the existing switchyard. DeBortoli said, “importantly, this means that the LEC does not need to have new transmission lines built to provide service to the project participants.”
WorleyParsons handled construction of the LEC, and ARB was the general contractor with the following major subcontractors: Cupertino Electric (all electrical work), Granite Construction (civil work), Neutron Instrumentation (instrumentation and transformer assembly), Power Industry Consultants (startup and commissioning work), and SPX (construction of the cooling tower).
Other equipment installed at the LEC included:
- Siemens gas turbine (SGT6-5000F)
- Siemens steam turbine (SST-900RH)
- Nooter/Eriksen heat recovery steam generator (HRSG)/auxiliary boiler
- Condenser (TEI)
- Control system (Siemens T3000)
- Water treatment system (IDI)
- Cooling tower (SPX)
- Gas compressors (Kobelco)
- Boiler feed pump (KSB)
- Generator step-up transformers (Alstom/AREVA)
- Auxiliary transformers (ABB)
Sustainable Water Use Practices
The LEC is located adjacent to the White Slough Water Pollution Control Facility (WPCF), which treats wastewater from the Lodi. The LEC uses WPCF’s treated wastewater in its cooling towers. This is consistent with a new trend benefiting public power—cities across the country are finding that wastewater treatment and electricity production make good neighbors (Figure 1).
|1. Partnering for efficiency. The Lodi Energy Center (LEC) is shown being constructed on a 4.4-acre site adjacent to the White Slough Water Pollution Control Facility (WPCF), which treats the wastewater from the city of Lodi. The LEC uses WPCF’s treated wastewater in its cooling towers. Courtesy: Siemens Energy|
Most new power plants being permitted in California are required to use reclaimed treated effluent with a zero liquid discharge system. DeBortoli said, “these systems have not worked very well on reclaimed water. LEC took a different approach to meeting these two requirements. We treat all of the water going into the cooling tower to allow us to increase the cycles of concentration in the cooling tower and then clean up the blowdown stream before injecting into a deep injection well.”
Integrated Fast-Start Technology
“Flex-Plant 30 technology enables a high level of operating flexibility in order to react to market opportunities,” DeBortoli said. He explained that the SCC6-5000F Flex-Plant 30 is a highly efficient combined cycle plant designed for intermediate to continuous duty that is capable of daily cycling at efficiencies of more than 57%. Using the Siemens SGT6-5000F gas turbine as the prime mover, the plant will supply high power density while requiring a relatively small plant footprint. (See “Siemens Releases ‘Shaping Power’ Option for Renewables Integration” in the December 2011 issue, available in the archives at http://www.powermag.com.)
“The Flex-Plant 30 technology allows for frequent starting or cycling of the power plant. Its startup time of 30 minutes or less can result in a CO reduction of over 200 tons per year when compared to standard F-class combined cycle plants, which will set a new standard for greenhouse gas emissions for gas-fired combined cycle power plants,” DeBortoli said.
Plant startup times are reduced by up to 50% due to integration of the following fast-start features that promote more rapid heating of the HRSG by bypassing the traditional startup hold points and allowing faster ramping of the combustion turbine: the three-pressure reheat HRSG with Benson once-through technology, the high-capacity steam attemperation, and full-capacity steam bypass systems. In addition, the innovative piping warm-up strategies, the Siemens steam turbine stress controller, the modern water treatment system, and the optimized plant standby that uses auxiliary boiler steam to maintain vacuum all help to promote faster startups. DeBortoli explained that the plant is also equipped with a small auxiliary boiler that is used to produce sparging steam and to maintain steam seals during startup and condenser vacuum during overnight shutdowns.
Dealing with Public Works Legal Obligations
DeBortoli explained that the LEC project had to be constructed in compliance with the public works legal requirements. For example, they prohibited the NCPA from committing to the project until completion and adoption of the environment assessment study.
DeBortoli said that the NPCA did as much as it could to minimize costs such as executing contracts that were contingent upon completion and adoption of the environmental studies. In addition, the contracts listed deadlines for execution and stated that if they were not executed by those specific dates, they would be canceled. However, it took longer than originally anticipated to complete the environmental studies and obtain the license. DeBortoli said that “things reached a point that the main contract with Siemens for the power island was in jeopardy of being canceled by Siemens because they had made a commitment to start this project by a certain date, anticipating approval of the license, and the contract contained a provision that had a major payment due to Siemens that the NCPA could not make.”
“Siemens had experienced a similar issue with another public entity in which the contract was eventually canceled,” DeBortoli said. “Fortunately, the NCPA was able to work with Siemens and find some creative ways to keep the contract going, and eventually the license was approved and the payment was made to Siemens.”
Environmental Compliance Issues
DeBortoli said that once the plant begins operation, its projected annual emissions will be 28 pounds of nitrogen oxides and 369 pounds of carbon monoxide (CO) for a start. He said, “the reduced amount of CO means that the annual emissions produced will be less than 100 tons, eliminating the need for a [Prevention of Significant Deterioration] permit from the U.S. Environmental Protection Agency [EPA].”
He explained that because fast-start technology is not yet proven as best available control technology, the San Joaquin Valley Air Pollution Control District’s rule requires a one-year evaluation of the fast-start capabilities. Final emissions limitations will be determined after one year of operation. The rule requires that within 15 months of the end of the commissioning period, the LEC owner/operator must submit to the district, the California Air Resources Board, and the EPA proposed new time limits for each type of startup that reflect the effect of Flex Plant 30 fast-start technology.
— Angela Neville, JD is POWER’s senior editor.