Invenergy Nelson Expansion LLC has applied to the Illinois Environmental Protection Agency’s Bureau of Air for a construction permit primarily for two new gas-fired peaker units at an existing power plant located at 1311 Nelson Road in Rock Falls, Illinois.
The Illinois EPA said Aug. 1 that it is accepting comments prior to making a final decision on this application until Aug. 27.
Invenergy Nelson Expansion has requested a construction permit for two new peaking units. Natural gas will be the principal fuel for the new units. Ultra-low sulfur diesel (ULSD) will be used during periods when natural gas is in short supply, such as during the winter months, and for periodic operational testing to confirm the ability to burn ULSD.
The Illinois EPA has reviewed the construction permit application for the proposed project and made a preliminary determination that it meets applicable air pollution control requirements. The Illinois EPA has prepared a draft of the construction permit that it would propose to issue for the proposed project.
The existing Nelson Energy Center has two combined cycle combustion turbine generating units that were developed to serve as intermediate load units rather than peakers. The proposed project involves the construction of two simple-cycle combustion turbine generators. The nominal summer-time rated electrical output of each turbine would be 150 MWe (combined output of 300 MWe). The turbines would be equipped with evaporative cooling systems for the inlet air to enhance output during hot summer weather.
The Invenergy LLC website shows the existing plant as a 584-MW facility that went into commercial operation in 2015.
Emissions from the new combustion turbines would be controlled or minimized by using good combustion practices, low-NOx combustors and, for ULSD, water injection. The proposed project would also include construction of a small natural gas-fired fuel heater. This unit will heat the natural gas burned in the new turbines to prevent condensation in the fuel piping due to the cooling that occurs when the pressure of the gas is reduced to the operating pressure of the burners in the turbines. The proposed project would also include construction of a storage tank for ULSD.
In its application, Invenergy Nelson Expansion requested that each turbine be permitted to operate for 2,400 hours annually. This would accommodate operation in a year in which there was a high call for peaking electricity from the proposed units. The application also indicated that it would be more typical that each turbine would operate for no more than 1,275 hours annually.
Larger ‘frame’ turbines picked over aero-derivative turbines
For the proposed project, Invenergy Nelson Expansion has selected so-called “frame turbines.” Frame turbines are designed for land-based use. They are heavier than “aero-derivative turbines,” which are adapted from designs of turbines that are used in jet airplanes. As such, frame turbines can be larger and have generating capacities that are much greater than available with aeroderivative turbines. Invenergy Nelson Expansion has selected two frame turbines for this project because it would meet the objectives for this project.
This plant was originally developed for four frame turbines, all as combined cycle turbines. Only construction of the two existing turbines at the plant was completed. However, much of the infrastructure for the two other turbines was completed, including foundations and electrical switch gear. As such, additional frame turbines of the same model as originally planned for the plant will be able to be readily worked into the existing operation of the plant. The new turbines will share spare parts with the existing frame turbines at the plant. The operational control for the existing turbines will also be expanded to address the new turbines.
Invenergy Nelson Expansion conducted a cost evaluation for use of aero-derivative turbines for this project. This evaluation shows that the cost of requiring use of aero-derivative turbines for this project would be excessive. The capital cost of four General Electric Model LMS100 aero-derivative turbines is estimated to be more than $180 million greater than the cost for two GE Model 7FA.03 frame turbines.
Aero-derivative turbines would not make use of existing infrastructure at the site, requiring significant construction of additional foundations and major retrofit to the switchyard to accommodate more than two units. Also, aero-derivative turbines are more expensive to maintain.
Invenergy Nelson Expansion also conducted an evaluation for the cost of using newer GE Model 7FA.04 or 7FA.05 frame turbines for this project. The GE Model 7FA.04 would provide a nominal 2.5% improvement in thermal efficiency and the same NOx emission rates in ppm. The increase in capital cost would be $10 million per unit. The calculated cost-effectiveness for NOx would be $134,242 per ton of NOx reduced (maximum annual operation) or $520,629 per ton of NOx reduced (expected annual operation). The GE Model 7FA.05 turbines would provide a nominal 6.5% improvement in thermal efficiency for natural gas. They would also have a lower NOx emission rate, 5 ppm, than the GE Model 7FA.03 turbines, 9 ppm. (For ULSD, the emission rate would be the same, 42 ppm.) There would be an increase in direct capital cost of over $74.8 million. The calculated cost-effectiveness for NOx would be $90,199 per ton of NOx reduced (maximum annual operation) or $255,231 per ton of NOx reduced (expected annual operation). These cost impacts for both GE Model 7FA.04 or 7FA.05 turbines are clearly excessive, the agency noted.