4 The record articles

Combined Cycle Gas Turbines: Part of a Balanced BACT Analysis?

Posted: March 29th, 2012

Author: All4 Staff 

What ingredients make for a healthy Best Available Control Technology (BACT) analysis when you’re looking at greenhouse gas (GHG) emissions? As Prevention of Significant Deterioration (PSD) activities for GHGs build momentum, we’re getting a picture of what new and modified GHG emitters must consider in order to pass muster. Add-on controls for GHG emissions are not nearly as mature as analogous controls for criteria pollutants like NOx and SO2. Thus, EPA guidance emphasizes considering inherently lower-emitting processes when planning a GHG emitting project. The tricky aspect of GHGs is that considering lower-emitting processes may require “fundamentally redefining the source,” which regulatory agencies cannot require, per the Clean Air Act (CAA). For example, if you would like to build a new coal fired power plant, the agency (allegedly) couldn’t require that you include an evaluation of a natural gas-fired plant instead in your BACT analysis – that would fundamentally redefine the nature of your project.

So where is the line between a similar but lower-emitting project and a completely redefined project? The line got a little murkier last week, when EPA’s Region V weighed in on a draft permit for a proposed power plant located at a wastewater treatment plant in Wisconsin. The facility proposed to replace existing natural gas-fired turbines with single-cycle landfill gas-fired turbines. In its response, U.S. EPA asked the facility to “revise the BACT analysis to consider both combined-cycle turbines and CHP [combined heat and power] systems, along with simple-cycle turbines, or provide an explanation in the record as to why these were not considered available control options for this particular source.” Natural gas combined cycle (NGCC) turbines are more energy efficient but much more expensive than the proposed single-cycle turbines, and some industry sources maintain that it would constitute a source redefinition and/or make the project economically unviable. U.S. EPA and environmental groups, however, were quick to point out that including NGCC in the early stages of BACT analysis does not necessarily mean that using NGCC will be required, especially if it can be proven financially infeasible.

It’s also important to note that no BACT analysis result can be less stringent than the corresponding Standards of Performance for New Stationary Sources (NSPS). With impeccable timing as usual, on March 27, 2012, U.S. EPA proposed the nation’s first CO2 NSPS, regulating power plants. The proposed standard is 1,000 pounds of CO2 per megawatt-hour (MWh). EPA stated in guidance that this is easily attainable for uncontrolled NGCC plants, but others may need to consider control options such as sequestration. Stay tuned to the ALL4 Blog for more coverage of the new power plant carbon pollution standard.


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