LETTERS Power plants Dear Sir: I was pleased to read the story on the Southwestern power plants (€S&T, June 1976, p 532), especially since San Onofre 2 and 3, Palo Verde 1-3, Cholla 1-4, Mohave 1 & 2, and Navajo 1-3 are all C-E fossil or nuclear-fueled units. One minor error appeared, however. On the top of page 537 you refer to the (now cancelled) Kalparowits plant as being the largest coal-fired plant in the world, at 4 X 750 = 3000 MW. There is a larger station currently operating with C-E units and two more planned with C E units. They are: (1) Plant Bowen, Units 1-4 Georgia Power Co. (operating) 2 X 750 and 2 X 880 = 3260 MW (2) Plant Scherer, Units 1-4 Georgia Power Co. (planned) 4 X 810 = 3240 MW (3) White Bluffs, Units 1-4, Arkansas Power & Light Co. (planned) 4 X 850 = 3400 MW S. D. Barreit
Combustion Engineering, Inc. Windsor, Conn. 06095 Southwest power plants Dear Sir: We refer to the informative special report “A Southwest Power Plant Saga” (€S&T, June 1976, p 532). We believe that the final program report on the Navajo Generating Station SO;!Field Monitoring Program will lead to the answer to your concluding question as to the requirement for western utilities to scrub (Rockwell International, Meteorology Research, Inc., and Systems Applications, Inc., “Navajo Generating Station SO2 Field Monitoring Program” v. 1. Final Program Report. Salt River Project, Phoenix, Ariz., September 1975). The answer to this question is approached by addressing an earlier query. You state, . . one might still ask what the emissions will be.” The report addresses this important matter. After lengthy analyses of the Black Mesa mine core-sample data and the mining and coal handling procedures, it was established that the highest 3-h SOz emissions will occur during the 1982-85 period. On the average, Navajo’s emission rate will be 1004 g/s per unit during full-load operations, which is equivalent to 1.1 1 lbs/106 Btu compared to the national new source performance standard of 1.2 lbs/106 Btu. This rate is based on the characteristics of the 1982-85 coal as burned: average sulfur content 0.675 % , standard deviation 0.083 YO,and heat content 12 204 Btu per pound. (It is noted that the plant at times operates in, excess of rated capacity and, since the study was completed, is reI‘.
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ported to have used other than Black Mesa coal.) Based on the air-quality data collected, analyses of the dispersion potential of the Lake Powell area and the expected future emission rate at full-load operations, it was concluded that highest SO2 concentrations occur about 15 miles from the plant and the expected frequency of exceeding a 3-h average of 1300 ~ g / m 3is less than twice per year. Wor‘sbcase analysis, assuming that only Black Mesa coal is burned, indicated the second highest concentration at 1285 pg/m3; best estimates were in the 1000-1150 pg/m3 range. Based on these analyses, national ambient air quality standards for SO2 are unlikely to be violated. This conclusion may or may not apply to other facilities of western utilities. Navajo is isolated. It uses some of the best quality coal available in the entire nation. Certainly, if a facility is larger than Navajo, if its coal has a higher sulfur content or a lower heat content, or if it is less favorably located than Navajo, measured to reduce the emissions by coal or flue gas treatment are likely to be in order. H. H. Slater, W. P. Freas, 111, T. C. Curran EPA
Research Triangle Park, N.C. 277 11 .I. Van der Hoven Air Resources Lab. NOAA Silver Spring, Md. 20910
Opacity Dear Sir: The authors are pleased that Wolbach and Key of the Source Evaluation Section of the Texas Air Control Board feel that, “no responsible control agency, especially the Texas Air Control Board, would attempt to enforce a mass emission regulation” by means of opacity measurements (Letter, €S& T, September 1976, p 847) and that, we are “laying to rest a technique which should not be considered as a serious option.” Unfortunately, not all regulatory agencies share this view. For example, the response of the EPA to public comments on “Opacity Provisions under Standards of Performance for New Stationary Sources of Air Pollution” states, ”EPA believes that the use of opacity standards to control emissions is within the intent of the Act and that the standards are subject to an accurate, reproducible and objective test procedure.” (Ref. 1) The EPA also stated, “any source which is meeting the applicable concentration or mass standards will also be meeting the applicable opacity standard. If the source is exceeding the opacity standard, it is due to failure of that source to properly maintain its air pollution control equipment, and if tested, the source
would have emissions in excess of the applicable concentration or mass standard.” (Ref. 2) Thus the EPA position is that opacity can be used to enforce mass emission regulations. This is also the case with several other regulatory agencies. It appears that Wolbach and Key assume that transmissometer measurements are synonymous with opacity measurements. The EPA position is, “Method 9 is being retained as the primary and accepted means for determining compliance in order to have a consistent regulatory enforcement approach for all stationary sources. Data from in-stack transmissometers are not accepted as a means for demonstrating compliance with opacity standards . . . . However, in-stack transmissometer data may be submitted as probative, (but not conclusive) evidence of the actual opacity of emissions.” (Ref. 2) The requirement for visual observation to determine opacity is also stated in a number of local regulations. There was no extrapolation from “EPA work with transmissometers on opacity/ mass correlations for an asphalt concrete plant” as Wolbach and Key stated. The EPA based the “Functional Opacity-Mass Relationship for an Asphalt-Concrete Plant,” on visual opacity measurements, not transmissometer data. The Public Comment Summary confirms this. “The opacity standard for asphalt concrete plants is based on observations at three well-controlled asphalt-concrete plants.” (Ref. 4) “The opacity observations of emissions were taken according to practices taught at EPA smoke schools and Method 9 as it was then written . . . . Specifically, the observers read the emission points from a position with the sun located in the quadrant to their back.” (Ref. 5 ) Secondly, our paper was based on experimental data, including plume opacity observations by trained smoke observers, which correlated well with light scatting theory. Our only “extrapolation” was to use U S . Navy publications to calculate the sun’s altitude as a function of time and date in Florida, Washington, Alaska, and Hawaii. We did not make visual observations in those states, but used the correlation between opacity and sun altitude obtained in Nevada (and confirmed experimentally again in California), to predict the opacity that would occur if the same power plant were located in different parts of the U S . We are concerned with Wolbach and Key’s statement, ”A control agency concerned with the appearance and visibility of a plume will choose to regulate the worst case without regard for time of day, season or geographic location, providing that the proper observation conditions are met.” Our data have established
