The Texas Commission on Environmental Quality on Feb. 24 put out draft approvals of Prevention of Significant Deterioration air permits for an expansion, by Exelon‘s (NYSE: EXC) Colorado Bend II Power LLC, of the existing Colorado Bend gas-fired plant.
The draft PSD approvals cover both greenhouse gas and non-greenhouse gas emissions from the project. The permits would authorize construction of additional electric generating units at the Colorado Bend Energy Center located at 3863 South State Highway 60, near Wharton in Wharton County. The permit applications were filed in April 2014 and November 2014. The GHG application from November came after the U.S. Environmental Protection Agency turned over GHG permitting in the state to the TCEQ’s newly formulated permit program, and is being handled on an expedited basis.
This permits authorize two natural gas-fired combustion turbines (CTs) to operate in combined cycle with heat recovery steam generators (HRSGs) and a steam turbine. Each CT shaft will drive an electric generator and each HRSG supplies steam to a single steam turbine which drives a third electric generator. The CTs may employ evaporative cooling for power enhancement.
Each HRSG is to be equipped with natural gas-fired duct burners. The duct burners in each HRSG are limited to a maximum heat input of 770 million British thermal units (Btu) per hour (MMBtu/hr), based on the high heating value (HHV) of the fuel. Exhaust emissions are controlled using selective catalytic reduction (SCR) and oxidation catalysts located in the HRSGs.
The permiting authorizes construction and operation of two General Electric model 7HA.02 CTs. The CTs are authorized to operate in normal operation, defined as operation anywhere between and including 45% and 100% of full load and the SCR has been placed into operation. The CTs are authorized to operate at reduced load, defined as operation below 45% of full load that is not MSS operation.
Each CTG is site-rated at 328 MW gross electric output at 70°F ambient temperature. At this condition, two HRSGs with duct burner firing produce enough steam to generate an additional 501 MW, for a total of 1,157 MW gross, or with about 5% losses, about 1,100 MW net output.
“The proposed GE F7 HA.02 CT is a new model, advertised as the ‘world’s largest, most efficient gas turbine in its class’ by GE,” said the TCEQ. “The proposed CBII CTs would be serial numbers 1 and 2 of this 60 Hz version; GE’s press release on the proposed CBII project says the CTs are expected to be shipped in 2016. Although a new CT model, the emission-generating combustors will be the existing DLN 2.6+ design. A review of the CCGT ratings in Gas Turbine World (GTW), ‘2014 Performance Specs’ confirms that the GE F7 HA.02 is the largest CT in the 60 Hz market, although Siemens (S) SCC5-8000H in the 50 Hz market is larger at 400 MW.”
Black & Veatch announced on Feb. 19 that it had been selected as owner’s engineer by the Exelon Generation unit of Exelon for the installation of two 1,000-MW combined cycle natural gas units in Texas. The units will meet growing electricity demand in Texas while reducing the amount of water used to produce power in the drought-prone state. They are being built at Exelon’s gas-fired stations in Colorado Bend, southwest of Houston, and Wolf Hollow, west of Dallas. General Electric gas turbine technology (7HA.02 model) will make the units among the cleanest and most efficient in the U.S. The units will use dry cooling instead of the traditional wet cooling towers to minimize overall water usage. They are designed for rapid start-up and turndown efficiency to address varying power demands. B&V said construction on both plans began in January.