In the United States, BACT comprises the equipment and methods needed to achieve the maximum degree of reduction of pollutants subject to federal regulations that are emitted from any proposed major stationary source or major modification of such a source. The pollutants subject to review under the PSD regulations, and for which a BACT analysis is required, include nitrogen oxides (NOx), carbon monoxide (CO), particulates less than or equal to 10 μm in diameter (PM10), and VOC. All PM is assumed to be PM10. The BACT review follows the “top‐down” approach recommended by the USEPA. The top‐down process calls for all available control technologies for a given pollutant to be identified and ranked in descending order of control effectiveness. The permit applicant should first examine the highest‐ranked (“top”) option. The top‐ranked options should be established as BACT unless the permit applicant demonstrates to the satisfaction of the permitting authority that technical consideration, or energy, environmental, or economic impacts justify a conclusion that the top‐ranked technology is not “achievable” in that case. If the most effective control strategy is eliminated in this fashion, then the next most effective alternative should be evaluated, and so on, until an option is selected as BACT.
The USEPA has broken down this analytical process into the following five steps:
- Step 1: Identify all available control technologies
- Step 2: Eliminate technically infeasible options
- Step 3: Rank remaining control technologies
- Step 4: Evaluate most effective controls and document results
- Step 5: Select the BACT
If there is no single BACT for any industry, it is determined on a case‐by‐case basis, taking into account cost‐effectiveness, economic, energy, environmental, and other effects of proposed solutions. Three important terms in BACT analysis are PSD, “significant emission rate” (SER), and ambient air quality analysis and national ambient air quality standards (NAAQS). The purpose of the PSD program is to implement the Federal Clean Air Act requirements for the prevention of “significant” deterioration of air quality. These insure that the permitting of proposed new industrial facilities and the associated economic growth will occur in a manner consistent with the preservation of clean air resources. The program provides for special emphasis on implementation of BACT, protecting of scenic areas such as national park, and informed public participation. SER refers to net emissions increase or the potential of a source to emit pollutants, a SER equal to or greater than the rates listed in Title 40 CFR 51. An ambient air quality analysis must be carried out for each regulated pollutant and must demonstrate that the source will not cause nor contribute to a violation of any applicable NAAQS.
As industries age and expand, they acquire new emissions units for pollutants and modify old ones. Federal law calls for a BACT analysis of each such new or altered unit of “major stationary sources.” Major stationary source, as defined in Title 40 CFR Part 51, Subpart 1, review of new sources and modification – any stationary source that (1) emits, or has the potential to emit (PTE), 250 T/Y or more of any pollutant under the CAA; or (2) emits, or has the PTE, 100 tpy or more of a regulated pollutant within one of the 28 sources categories (Title 40 CFR).
The USEPA has consistently interpreted the statutory and regulatory BACT definitions as containing two core requirements that the agency believes must be met by any BACT determination. First, the BACT analysis must consider the most stringent available technologies (i.e. those which provide the “maximum degree of emissions reduction”). Second, any decision to require a lesser degree of emissions reduction must be justified by an objective analysis of “energy, environmental, and economic impacts.”
BACT must be at least as stringent as any New Source Performance Standard (NSPS) applicable to the emissions source. With this set of data as a baseline, a BACT analysis often proceed by way of the so‐called top‐down approach recommended by the EPA. The first step is to determine for the emission unit in question the most stringent control available for a similar or identical source or source category. If it can be shown that this level of control is technically infeasible for the unit in question, the next most stringent level of control is determined and similarly evaluated. This process continues until the BACT level under consideration cannot be eliminated by any substantial or unique technical or environmental concerns. The remaining technologies are evaluated on the basis of operational and economic effectiveness (USEPA 1990).
Importance of Energy Efficiency
USEPA believes that it is important in BACT reviews for permitting authorities to consider options that improve the overall energy efficiency of the source or modification – through technologies, processes, and practices at the emitting unit. In general, a more energy efficient technology burns less fuel than a less energy efficient technology on a per unit of output basis. For example, coal‐fired boilers operating at supercritical steam conditions consume approximately 5% less fuel per megawatt hour produced than boilers operating at subcritical steam conditions (US DOE 2007). Thus, considering the most energy efficient technologies in the BACT analysis helps reduce the products of combustion, which includes not only GHGs but other regulated NSR pollutants (e.g. NOx, SO2, PM/PM10/PM2.5, CO, etc.). Thus, it is also important to emphasize that energy efficiency should be considered in BACT determinations for all regulated NSR pollutants (not just GHGs).
The emission units of a gas turbine power plant for which a BACT analysis is required include the combustion turbines, duct burners, the auxiliary boiler, and the cooling towers. Due to their status as emergency/backup units and/or very limited run time, the emergency diesel generator and the diesel fire water pump are not included in the BACT analysis. The top‐down BACT approach analysis must look not only at the most stringent emission control technology previously approved but also evaluate all demonstrated and potentially applicable technologies, including innovative controls, lower polluting processes, etc. For a gas turbine power plant, these technologies and emissions data can be identified through a review of sources made available by the EPA. Foremost among these is RBLC, an umbrella term standing for RACT/BACT/LAER clearinghouse, where RACT is reasonably available control technology and LAER is lowest achievable emission rates. Other sources are EPA’s NSR and Clean Air Technology Center websites, the EPA Technology Transfer Network, STAPPA/ALAPCO (the State and Territorial Air Pollution Program Administrators and the Association of Local Air Pollution Control Officials), and Clean Air World.
Table 6.15 presents the technologies we shall consider in the sections that follow and their approximate control efficiencies.
Leave a Reply