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Sixteen sulphur dioxide recorders have been sited around a modern 1,000 MW power station situated in a rural area. The recorder layout was in the form of a ring, the radius of which was the distance of calculated maximum ground-level pollution. The results from their operation during the period October, 1963, to September, 1964, are reported. On a long-term basis the overall average effect of the power station on the concentration of sulphur dioxide as measured at these sites was small (0.1 to 0.2 p.p.h.m.) compared with that already to be found in the area (3 to 5 p.p.h.m.). Most of the pollution appeared to come from distant cities and industrial areas. The most persistent effect from the power station, amounting on average to only 0.6 p.p.h.m., was to the north-east of the station and is thought to be due to the combined effects of wind frequency and strength in that direction. Short-term (3 min) power station contributions were often detectable, but under the dispersing effect of the wind, were not usually persistent at any one site. There was no significant pollution from the power station in stable atmospheric conditions, with or without fogs,

This is an example of the careful work that should be done with increasing frequency when new plants are planned and put into service. Again I would point to the record that there was no significant pollution from the plant during stable (i.e. inversion) atmospheric conditions, conditions which would however, create a great deal of difficulty for low-level emissions.

High stacks are an excellent tool when they can be designed into the plant, or even if a substantial fraction of the life of an existing plant is still ahead of it. But what can be done for plants fast approaching the end of their useful lives? Here research is badly needed and some at least is underway. This has taken the form of investigating limestone or other alkaline additives to react with the SO, and S03 present in the stack. The following groups have been active:

(a) Paper study of reactive rate of limestone and sulfur dioxide being done at Battelle for U.S. Public Health Service.

(6) Study of limestone characteristics by Bituminous Coal Research.

(c) In American Electric Power Service Corp., a modest research program jointly with Arthur D. Little, Inc., has just been initiated. This will cover a small section of the problem that ap

pears particularly susceptible to direct attack at this time. It is not expected that additives would be used full time, but as a means of operating through adverse meteorological conditions.

Possibly the most significant research program of all, since it seeks to correct our basic ignorance on the long-term, low-level effects of SO2, is that announced since January 1966 by the Electric Research Council. In this work to be done by the Hazleton Laboratories, Inc., under contract with the council, 18-month exposures of guinea pigs and primates to SO, levels comparable to those found in cities and industrial areas will be conducted. Heretofore, most experimentation has been at concentrations seldom, if ever, reached even in acute air pollution disasters such as London in 1952. In order to explore the possible synergistic effects of fly ash and So, mist, a number of parallel exposures will be made using these materials in conjunction with SO.

This statement has been somewhat longer than I first contemplated. However, the subject is one of critical importance to the power industry and is indeed an area in which it is altogether too easy to lose sight of the industry's long history of constructive activity to abate air pollution. For example, the reduction in plant heat rate from an average 22,600 British thermal units per net kilowatt-hour in 1927 to 10,493 in 1962 represents a major reduction in the potential air pollution from this source, since only 46 percent as much fuel is being used per unit of output as was the case 35 years earlier. Further, electrostatic precipitators were commonly employed to clean flue gases in the power industry a generation before the passage of the Clear Air Act of 1963.

PIONEERING EXPERIENCE WITH High STACKS ON TIE OVEC AND AMERICAN

ELECTRIC POWER SYSTEMS

(By Philip Sporn' and T. T. Frankenberg ?)

1. INTRODUCTION

In October 1952, the Ohio Valley Electric Corporation (OVEC) undertook the building of two very large plants to serve a new gaseous diffusion plant of the United States Atomic Energy Commission. These plants would be located on the Ohio River, one in southeastern Ohio and the other near Madison, Indiana (1%). The net capacities were originally estimated to be 1,000,000 kw for the Ohio location and 1,200,000 kw at the Indiana site. At that time the ten largest thermal-electric plants in the United States had an average size of less than 600 mw. Both new plants represented difficult assignments from the standpoint of controlling air pollution. Due to the economic availability of coal of rather low quality the plants might burn fuel containing as much as 4 percent sulfur, and would discharge at least twice the amount of sulfur dioxide as any previous plant. Further, their locations in predominantly rural areas insured that any inadequacies in the disposal of the flue gases would be glaringly apparent. Therefore every effort was made to design the plants so that they would have a negligible effect on the ground level concentration of sulfur dioxide after reaching full load operation.

2. PLANNING

Arrangements were made to conduct wind tunnel studies of the site at Madison, Indiana, subsequently named Clifty Creek, since preliminary evaluation of this location indicated that from the aerodynamic standpoint it would present unusual difficulties. In the prevailing downwind direction from the plant, the flood plain is very short followed by an abrupt escarpment-like rise of the terrain to a plateau approximately 350 feet above the plant grade. Situated on this high plateau, at its closest approach to the plant, there is a very popular state park with an inn directly overlooking the plant site. On the same plateau, slightly further removed from the site, there is the Southeastern Indiana State Hospital for mental patients. It was deemed absolutely imperative that the highly concentrated stack plume should not descend on either of these very sensitive areas of habitation under any foreseeable circumstances. The wind tunnel work included the terrain shown in areas A and B of Figure 1, which lay in the most critical direction of the plant.

It was found that if the stack plume intersected the turbulent flow along the sharp rise to the plateau, it would immediately be brought to the ground around the inn. If the stack height was chosen so that the plume could be kept above this boundary layer, then a definite lift of the plume occurred, as shown in Figure 2. This lift varied between 50 and 150 feet and was so obvious in the wind tunnel that an allowance of 50 feet was made for the "ski jump" effect when selecting the stack heights.

3. THEORETICAL DIFFUSION CALCULATIONS Gas diffusion calculations were carried out to determine the ground level concentrations of So, at distances well beyond those that could be modeled in the wind tunnel. The Bosanquet, Carey and Halton equation (2) was used to calculate a stack gas rise and thus determine the effective stack height. With this calculated, the Sutton equation (3) was used to determine ground level concentration but with somewhat less conservative parameters (4).

1 President, Ohio Valley Electric Corporation.
2 Consulting Mechanical Engineer, American Electric Power Service Corporation.
3 Numbers in parenthesis refer to references at the end of paper.

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Irving A. Singer and Maynard E. Smith, Air Pollution and Meteorological Consultants, made almost all of the diffusion calculations for the stacks. These calculations were made using an exit gas velocity of 120 feet per second based on the wind tunnel results.

It was necessary to make some choice of the limiting value of So, that would be acceptable at ground level. A value of 0.5 parts per million for a one hour period was chosen as being one fourth of the odor threshold, and low enough to keep instantaneous peak below 2–3 ppm. Only strong wind conditions would produce values in excess of 0.5 ppm SO2 and such winds occur during a very small percentage of the total hours in the year. Thus, it can be seen that with regard to an entire year and to the whole terrain around the plant, the actual long-term factor of safety was very much greater than four.

After careful consideration of all the data and with considerable concern for possible adverse conditions during the breakup of the nocturnal inversion, a stack height of 683 feet was chosen.

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Having determined the stack heights for Clifty Creek on the basis of all the factors considered previously, it became an easier matter to select a proper height for those at the smaller Kyger Creek Plant. No aerodynamic considerations were present and since diffusion studies indicated that a height of 535 feet would provide acceptable conditions both in the valley and on the hills, this was the height chosen.

5. VERIFICATION OF CHOICE Basic to the pioneering work on these two large plants was the decision to make the necessary effort to verify the design by testing for both SO, and dustfall prior to operation and for a substantial period after commissioning. Dustfall studies were discontinued three years after full load was reached when it became abundantly clear that the plants had had no significant effect on this variable.

Three Thomas Autometers were installed near each plant to obtain a continuous record of sulfur dioxide at or close to ground level. One was located in the valley, Station A, while Stations B and C were on the plateau. A careful review of the sulfur dioxide records made late in 1959, after approximately four years of operation of both OVEC plants, showed no hourly mean concentrations above 1 ppm of sulfur dioxide for either plant. It was agreed that concentrations slightly above that level may occur infrequently on the plateau north of Clifty Creek Plant, with an occasional peak value just reaching the odor threshold. In general it was found that the original calculation of concentrations at both plants had given somewhat higher values than were actually experienced.

The most gratifying finding was that the meteorological condition which was expected to give rise to a severe problem, namely the breakup of nighttime inversions, with calculated concentrations of 5 to 10 ppm, failed completely to follow the mathematical model. This model, which did not involve the Sutton equation, was based on the idea that the gas would all be confined to a narrow wedge of quite limited height below the inversion. Although there was a tendency for the recorded ground level concentrations of sulfur dioxide to occur during the mid-morning hours, there was not a single case of the very high concentrations typical of fumigations. The results seem to indicate that the more restrictive ideas concerning the maximum size of thermal plants based on purely theoretical fumigation calculations (5) should be reviewed and considerably modified toward permitting larger aggregation of power generation equipment at a given site.

It was found that recording of any sulfur dioxide was an unusual event, averaging only 1.8% of the daylight hours, with a maximum at the valley station of 3.0%. Night hours showed So, present only an average of 0.3% of the time. When sulfur dioxide was present it averaged only 0.10 ppm with short-term peaks at some stations reaching 0.40 ppm. The records clearly establish the fact that these tall stacks eliminate ground level concentrations during inversions. Only a small proportion of the observed concentrations occurred at night when the inversions were normally present. When concentrations did occur at night, it was generally apparent from the winds, temperatures, or observations by the plant personnel that no inversion was present. Thus, the inversion which is so often described as a “lid” holding down noxious gases, actually becomes a shield preventing the return of stack gases if they are first emitted at a height, velocity and a temperature which are reasonable and appropriate.

6. CARDINAL STACKS

The design of the stacks for Cardinal Plant which will have a total generation on one site of approximately 2100-2300 mw represents, in many ways, the culmination of all of the information, design and operating experience obtained since the building of Clifty and Kyger Plants. The similarity of this terrain to that at Clifty is shown on Figure 3. Here again, the plant is upwind of a substantial plateau but this plateau is broken by major and minor streams in a highly irregular fashion.

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COMPARISON OF CRITICAL DIRECTION AT CLIFTY CACIK VITII 2 DIACCTIONS AT CARDINAL,

FIGURE 3

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