By Steve Blankinship, Associate Editor
The Trimble County Station, 30 miles northeast of Louisville, is home to a highly efficient coal unit, a six-pack of combustion turbines and a wildlife refuge. Since 1990, the site has been a reliable and economical source of electric power for hundreds of thousands of customers, helped incubate a host of power industry technologies and nurtured a variety of wildlife species. And in a few years, it will become the site of one of the world’s cleanest and most advanced coal-fired generating units.
Located next to the Ohio River near Louisivlle, Ky., the Trimble County power plant is slated to see a 760 MW supercritical unit go into service in 2010. Courtesy E.ON US.
Trimble County is owned and operated by E.ON U.S. subsidiaries Kentucky Utilities and Louisville Gas & Electric. Situated on the Ohio River, the source of its process and cooling water, Trimble County was constructed in the 1980s on 2,100 acres of farmland. Total generating capacity presently consists of a single sub-critical coal unit and six combustion turbines. Within four years, a 760 MW (net) advanced supercritical coal unit will go into service.
The Trimble site was originally designed to accommodate four 500 MW coal-fired units. Unit 1 is a 514 MW sub-critical unit that went into commercial operation in 1990. TC1 is currently the lowest variable cost coal plant in the company’s fleet and is nearly always dispatched to meet the regulated, LG&E/KU native load. Primary fuel is high sulfur bituminous coal from the Illinois Basin. Coal can only be received by barge and is unloaded at an average rate of 3,000 tons an hour. No. 2 fuel oil is used to provide start-up and support. The boiler is an ABB/Combustion Engineering controlled circulation, balanced draft design using tangential firing. The turbine-generator set is a General Electric G2 tandem compound, four flow reheat unit. TC1 operates primarily as a baseload unit boasting a current capacity factor of 93 percent. Planned maintenance consists of four to five weeks of outage every two years.
In the 15 years since TC1 went into service, a half dozen gas-fired combustion turbines have been added to the site. Trimble’s six GE PG7241FA combustion turbines are all simple cycle configurations that operate primarily as peaking units. All six are similar, with a nominal rating of 153 MW for a total of 918 MW of gas-fired peaking capacity. With installed evaporative cooling, nominal unit ratings increase to 160 MW, bringing the total to 960 MW. E.ON U.S. also owns and operates a six-mile-long natural gas pipeline that feeds Trimble’s CTs. As with the coal-fired TC1, LG&E shares ownership of the combustion turbines with several other utilities.
The entire Trimble County Station is operated, maintained and managed by the same group of 83 Louisville Gas and Electric employees who support operations, maintenance and administrative functions.
In 2001, TC1 installed a Babcock Power Environmental selective catalytic reduction system and an ALSTOM low NOX concentric firing system. In 2005, the flue gas desulfurization system was upgraded to increase SO2 removal from 93 percent to 98 percent. Over the next four years, control will be migrated from the current Honeywell system to an Emerson system.
“The seemingly constant addition of new equipment and processes in the past 10 years, most of which have been achieved without increasing the number of personnel, has been a major challenge,” says John Voyles, vice president of regulated generation. “We’ll face another huge challenge in 2009 when TC1 undergoes a major outage that will include a turbine-generator overhaul, changing of the turbine-generator, boiler control system and major boiler work.”
Trimble is a zero-discharge site. Other than rainwater runoff and cooling tower blowdown (both of which have permitted discharges to the Ohio River) all process byproducts either remain on-site or are converted to a beneficially reusable product and transported off-site. Fly ash is used as concrete filler and in ceramic tile while FGD waste is oxidized to form synthetic gypsum used to make wallboard. Bottom ash is used to make blasting grit and asphalt roofing shingles. Any waste product which cannot be beneficially reused is stored in a 115-acre pond on-site.
Trimble County Unit 2, planned for commercial service in 2010, will be a 760 MW supercritical unit, which-like TC1-will be co-owned. TC2’s supercritical boiler is designed to burn a blend of eastern bituminous and western sub-bituminous Powder River Basin coals. TC2 is one of four power plants in the U.S. to receive a $125 million tax credit under the 2005 EPACT Qualifying Advanced Coal Program for high efficiency and low emission generating units. TC2 is expected to become the lowest variable cost coal plant in the fleet and will also supply the native load of the two utilities.
E.ON U.S. has provided research and development to support several technologies important to the power generation business. In the 1970s, LG&E helped set the industry standard for sulfur dioxide removal by developing and deploying scrubber technology at its coal-fired generating stations. More recently, E.ON U.S. was recognized for its use of continuous mercury monitors. EPRI presented E.ON U.S. with the 2007 Technology Transfer Award for industry leadership in testing continuous mercury monitoring technology. Due to the station’s environmental control equipment configuration, Trimble was one of two sites in the United States where testing occurred. Information gleaned from this testing will likely be instrumental in determining how more than 1,000 coal-fired generating units comply with provisions of the Clean Air Mercury Rule, which become effective in 2010.