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EPA's Emissions Rule: Reliability at Stake?

SIP Call in a Nutshell
Fortnightly Magazine - August 2000

year period, the maximum hourly average concentration of ozone exceeds 0.12 parts per million on an average of only one day (or less) per year. The hourly average is deemed valid if concentrations are measured for at least 75 percent of the hours from 9 a.m. to 9 p.m.

The EPA rule provides this mathematical formula to account for sampling and missing data and to calculate the number of "eceedances," as the EPA calls them: e = v + [(v/n) x 8 x (N-n-z)].

THE EIGHT-HOUR STANDARD. Satisfied if, over the most recent three-year period of consecutive and complete calendar years, the average of each year's fourth-highest maximum ozone concentration for any running eight-hour period does not exceed 0.08 parts per million.

(There are 24 different running eight-hour periods for any given day, and thus 24 different possible measured averages for any one day, or 8,760 for the year. The fourth-highest such 8-hour average for one year is added to the fourth-highest average for each of the two other years, and the sum is divided by three.)

Again, not all hours or days need be measured. A day is deemed to be measured if valid 8-hour measured averages are available for at least 75 percent of the possible hours in the day (i.e., at least 18 of the possible 24 different running 8-hour periods). A year is deemed "complete" if data is measured over that 3-year time for at least 90 percent of the days in the ozone sampling season, and no less than 75 percent of the days in the sampling season in any one calendar year.

SCR technologies achieve the greatest reductions, says Joseph S. Graves, senior vice president at PHB Hagler Bailly. But, he explains, although most other technologies can be installed within a normal planned plant outage, the installation of SCR technology can take longer than the usual four weeks allotted. The uncertain amount of time required for SCR installation can raise reliability concerns, he says.

And SCR technology can be expensive, depending on the size of the plant.

"In the case of a base-load plant, that would be a good candidate of SCR," says Jerry Eyster, vice president at PHB Hagler Bailly. "You can spread the capital over many kilowatt-hours, but you would be unlikely to put the SCR unit on the cycling unit because it would be very expensive per kilowatt-hour. There you might put [some other technology] where you have a high operating cost but lower capital. You are making decisions on technology to fit the operating characteristics of your plant."

Meanwhile, the EPA does not believe that the order is at risk of further legal challenges.

"The court denied both the petitioners' request for rehearing at the three-judge-panel level and [also rehearing by the full compliment of the court]. So we are confident that the [appeals court] has supported the NO x SIP Call, and we are going ahead," Noonan says.

Noonan adds that the EPA assumes an emission rate of 0.15 million British thermal units from utilities in those states included under the