Tall stacks

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

Personnel are protected in working with tritium primarily by containment of all active material. Containment devices such as process lines and storage media are normally placed in well-ventilated secondary enclosures (hoods or process rooms). The ventilating air is monitored and released through tall stacks environmental tritium is limited to safe levels by atmospheric dilution of the stack effluent. Tritium can be efficiently removed from air streams by catalytic oxidation followed by water adsorption on a microporous soHd absorbent (80) (see Absorption). 

Stone and Clarke, Briti-s/j Experience with Tall Stacks for Air Pollution Control on Large Fossil-Fueled Power Plants, American Power Conference, Chicago, 1967. 

Cramer, H. E., Improved techniques for modeling the dispersion of tall stack plumes. "Proceedings of the Seventh International Technical Meeting on Air Pollution Modeling and Its Application." North Atlantic Treaty Organization Committee on Challenges of Modern Society. Pub. No. 51. Brussels, 1976. (National Technical Information Service PB-270 799.)... 

Tall Stacks and Inteimittent and Supplementary Control Systems... 

V. TALL STACKS AND INTERMITTENT AND SUPPLEMENTARY CONTROL SYSTEMS... 

Tall stacks are no longer considered to be an acceptable alternative for controlling emissions from electric power generating plants. (See further discussion in Chapter 26, Section V.)... 

Tall stacks for SO2 dispersion have been used in the past but are no longer acceptable as the sole means of SO2 control. Acid plants have been installed at many smelters to convert the SO2 to sulfuric acid, even though it may not be desirable from an economic standpoint. 

Venkatram, A. (1980). The relationship between the convective boundary layer and dispersion from tall stacks. Atmos. Environ. 14, 763-767. 

JACADS has one large process building where munitions are disassembled and their various components processed and incinerated in three combustion units. There are also a tall stack, auxiliary process off-gas trains, building HVAC eqnipment, and several auxiliary buildings. 

The wind trajectory method Is a supplement to other methods, not a replacement, as It has some weaknesses. Although we are already certain of being able to pick up emissions from Cu and Zn smelters, a pigment plant and steel plants, the method may not work on sources that have no dominant element. It may not work on widely distributed, ubiquitous sources such as gravel quarries, or on sources with very tall stacks. Despite these limitations, the method will be a useful supplement to the others and It should be fully exploited. 

The emphasis in the present work is on leachates derived from fly ash disposal, but it must not be forgotten that fine ash particles may escape from power plants. The transport and dispersion of particulate emissions from tall stacks has been actively researched over the last 20-30 years. A review by Carras (1995) records that plumes have been observed to remain as coherent units up to distances of at least 1800 km and thus deposit pollution far from source. However, maximum particulate surface loadings are likely to be found adjacent to old power plants with limited fine-particle fly ash entrapment. Evans et al. (1980) estimated that in a period of 23 years the cumulative stack ash load at a distance of 1.7 km from an 83 MW... 

Carras, J. N. 1995. The transport and dispersion of plumes from tall stacks. In Swaine, D. J. Goodarzi, F. (eds) Environmental Aspects of Trace Elements in Coal. Kluwer Academic Publishers, Dordrecht, 146-177. 

Figure 107. Concentration of Settled Smoke Issuing from a Tall Stack. Note Position of Maximum Concentration Downwind. Data from Bosanquet and Pearson (1936).

The main U. S. response was restrictions on the use of high sulfur fuels within metropolitan areas, which had the effect of forcing in-town sources to switch to low sulfur oil and gas and for new plants to have tall stacks and be built outside of cities. As documented by Altshuller (1), these measures reduced urban levels of S02 to nearly rural levels. 

Tuncel et al. tabulated S/Se ratios for particles from many locations (4). The ratio is about 3000 at rural sites downwind, but outside of coal-burning areas. In the midst of the ORV, it is depressed to about 1700, in agreement with the model. In the midst of cities in which substantial coal is burned, the ratio is depressed to 1000 or less. Except for a few samples at Allegheny Mt. collected downwind from three power plants, Tuncel et al. did not see sudden drops in the S/Se ratio that one would expect to see occasionally in fresh plumes from coal-fired plants. A major flaw in the Gor-don/Olmez model is the assumption of uniform vertical concentration profiles, which is surely a poor assumption just beyond a source. Most power plants have tall stacks, whereas, measurements are at ground level. The S/Se ratio will surely be depressed near the plume centerline, but the effect will usually be washed out before the plume hits ground level. However, around cities, there are probably some ground level sources. 

---