The U.S. Environmental Protection Agency’s Region 6 office is taking comment until Nov. 28 on a draft air permit for a gas-fired project in Texas of Tenaska Brownsville Partners LLC.
In February 2013, Tenaska Brownsville Partners submitted to EPA Region 6 a Prevention of Significant Deterioration (PSD) permit application for Greenhouse Gas (GHG) emissions for this project. In connection with the same project, Tenaska applied for a PSD permit for non-GHG pollutants to the Texas Commission on Environmental Quality (TCEQ) in February 2013, which was subsequently issued by TCEQ on April 29, 2014.
Tenaska proposes to construct a natural gas-fired combined-cycle gas turbine (CCGT) plant, known as the Tenaska Brownsville Generating Station (TBGS), to be located in Brownsville, Cameron County, Texas. The TBGS will consist of one or two combustion turbines (CTs), each shaft-connected to electric generators (CTGs) and exhaust-ducted to supplemental-fired heat recovery steam generator(s) (HRSGs), which will provide steam to power a single steam turbine generator (STG). Each HRSG will use duct burners for supplemental firing to boost the CT exhaust energy when needed for additional steam electric generation.
The TBGS will generate either 400 MW or 800 MW of net electrical power, depending on whether one or two combustion turbines are constructed. The TBGS will consist of the following sources of GHG emissions:
- One or two natural gas-fired combustion turbines;
- One or two natural gas-fired duct burner systems;
- Natural gas piping and metering;
- One diesel fuel-fired emergency electrical generator engine;
- One diesel fuel-fired fire water pump engine;
- One natural gas-fired auxiliary boiler; and
- Electrical equipment insulated with sulfur hexafluoride (SF6).
Although the proposed permit authorizes two CTGs (2×1 CCGT), the final design selected by Tenaska may consist of only one CT (1×1 CCGT). The 1×1 configuration gross electrical power output is based on one combustion turbine producing a nominal 274 MW at 62°F ambient temperature and one steam turbine to produce an additional nominal 159 MW, or 433 MW total plant gross electric output. In this smaller configuration, the net summertime electric output is about 400 MW. The draft permit provides for deleting one CT if the single CT configuration is selected.
The proposed plant includes up to two Mitsubishi 501GAC natural gas-fired CTGs and two HRSGs. The CTGs burn pipeline quality natural gas to rotate an electrical generator to generate electricity. The main components of a CTG consist of a compressor, combustor, turbine, and generator. The compressor pressurizes combustion air to the combustor where the fuel is mixed with the combustion air and burned. These hot exhaust gases then enter the turbine where the gases expand across the turbine blades, driving a shaft to power an electric generator. The exhaust gases then exit the CTG and are ducted to the heat recovery steam generator (HRSG) for steam production. The steam produced by the two HRSGs is routed to a single steam turbine. The high pressure steam is expanded across the steam turbine blades, driving a shaft to power the steam turbine generator (STG) to generate electricity.
The HRSGs are to be equipped with duct burners (DBs) for boosting steam production. Like the CTGs, the DBs are fired with pipeline quality natural gas. Each DB has a maximum heat input capacity of 250 million British thermal units per hour (MMBtu/hr). The DBs are located in the HRSGs upstream of the selective catalytic reduction (SCR) system and oxidation catalyst (OC) used for NOx, CO, and VOC emission control. Each CTG/HRSG has an exhaust stack through which the unit’s exhaust gases are emitted to the atmosphere.
The normal DB operation will vary from 0% to 100% of the maximum capacity, depending on electricity demand. The CTGs and STG may operate at reduced load to respond to changes in system power requirements and/or stability.
A project contact is: Larry Carlson, Vice President, Environmental Affairs, Tenaska Inc., (402) 938-1661.