The next step in the “top‐down” process is to determine whether there are energy, environmental, or cost impacts from the use of this top technology that would render it infeasible.
Energy Impacts
Energy impacts include the energy consumed by the control technology or a reduction in energy produced, if an energy‐production process is permitted. One example of an energy impact would be the need to add heat to a low‐temperature flue gas to increase its temperature to the place where a selective catalytic reduction system that operates at a minimum temperature of about 600 °F (315 °C) could be used for NO x control. Quantitative thresholds for energy impacts have not been published, so an energy impact rejection of a top technology is discretionary. Many years ago, an analysis was done of possible technologies for reducing CO2 emissions from an electric utility power plant. At that time, the only process for reducing CO2 was a high‐pressure amine scrubber. The analysis of this alternative indicated that in order to scrub the CO2 from the power plant exhaust, more energy would be required than was produced by the power plant. Such a technology could be eliminated based on energy impacts.
Environmental Impacts
If use of a proposed control technology results in other environmental impacts, the technology may be rejected because of other environmental impacts. For example, the use of the technology might result in the production of hazardous wastes, the creation of other air pollutants than those being controlled with the technology, excess water use in an area with inadequate water supply, generation of large quantities of solid wastes or solid wastes that are difficult to dispose of, or even destruction of critical habitat if the footprint of a control technology installation extended beyond currently disturbed areas.
Cost Effectiveness
The cost effectiveness of a control technology is measured in dollars per ton of pollutant removed. It is determined by first calculating the rate of pollutant removal (tons/year). This rate is the difference between the emissions before the control is installed and the rate after control. Then the annual cost of the technology (US$/year) is determined. Cost effectiveness is the ratio of the annual cost of the technology to the rate of pollutant removal (dollars/ton). The control efficiency and rate of pollution removal are discussed in Sections 3.7.6.7 and 7.11.
Plant‐Wide Applicability Limitation
Plant‐wide applicability limitation (PAL) is a voluntary limit based on plant‐wide actual emissions, on a pollutant‐specific basis (also called an actuals PAL). A PAL is an emission limitation expressed in T/Y on a 12‐month rolling basis for a pollutant at a major stationary source. The PAL is enforceable as a practical matter and established source‐wide in accordance with 40 CFR §52.21(aa)(1) through (15) (40 CFR).
A facility that has a PAL in place is allowed to make changes to the facility or individual emission units which result in increases in the source’s or individual units’ pollutant emissions, as long as its plant‐wide actual emissions do not exceed its PAL limit. In return for this flexibility, the facility must monitor emissions from all emissions units under the PAL, and comply with record keeping, monitoring, and reporting requirements. The PAL must be included in a permit issued by the regulating state. Major NSR applicability provisions continue to apply to air pollutants which have no PAL. The PAL process has been rarely used in the United States of America.
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