Effective Height of Emission

For an emission heiglit, die calculational sequence begins by estimating die effective heiglit of the emission, employing an applicable plume rise equation. Tlie nia. inimn GLC may dien be delennmed using an appropriate auiiospheric difflision equation (considered in die next Section). 

Tlie effective heiglit of an emission rarely corresponds to die physical height of die source or the stack. If die plume is cauglit in die turbulent wake of die stack or of buildings in die vicinity of die source or stack, die effluent will be mixed rapidly downward toward the ground. If die plume is emitted free of these turbulent zones, a number of emission factors and meteorological factors influence die rise of the plmne. 

The Davidson-Bryant mcdiod is empirical because it is based on Bryant s wind tumicl experiments It is restricted to gases below I25°F and to stacks of moderate lieight and larger. It docs not give maximum plume rise because it is a function of momentum only, not buoyancy. Although its values 

The Holland equation is valid for effluent gases hotter than 125°F and for neutral 8 

R = universalgas constant (1833.35dyiie-ni/K-gmol) MW = molecular weight of theclTluciii (g/ginol) 

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A truck carr) ing two tanks containing a very unstable and hazardous gas is involved in an accident that results in tlie consecutive explosion of the tanks -one innncdiately, the second approximately a minute later. The total mass of tlie emission resulting from the explosion of each tank is 30,000 g. The wind velocity is 1 m/s from the north, and tlie effective height of emission is 30 meters at the time of tlie accident. Calculate the concentration of tliis gas at 500 meters south but 100 meters east from the site 10 minutes after tlie explosion of tlie first tank. Assume tliat stability category D applies. 

A power plant burns 10 kg h of coal containing 2.5% sulfur. The effluent is released from a single stack of height 70 m. The plume rise is normally about 30 m, so that the effective height of emission is 100 m. The wind on the day of interest, which is a sunny summer day, is blowing at 4 m s . There is no inversion layer. Use the Pasquill-Gifford dispersion parameters from Table 18.2. 

Ejfective Height of an Emission The effective height of an emission rarely corresponds to the physical height of the stack. If the plume is caught in the turbulent wake of the stack or of buildings in... 

The effective stack height (equivalent to the effective height of the emission) is the sum of the actual stack height, the plume rise due to the exhaust velocity (momentum) of the issuing gases, and the buoyancy rise, which is a function of the temperature of the gases being emitted and the atmospheric conditions. 

Maximum Ground-Level Concentrations The effective height of an emission having been determined, the next step is to study its path downward by using the appropriate atmospheric-dispersion formula. Some of the more popular atmospheric-dispersion calculational procedures have been summarized by Buonicore and Theodore (op. cit.) and include ... 

Building Downwash A review must be conducted for each stack to determine if building downwash effec ts need to be considered. Atmospheric flow is disrupted by aerodynamic forces in the immediate vicinity of structures or terrain obstacles. The disrupted flow near either building structures or terrain obstacles can both enhance the vertical dispersion of emissions from the source and reduce the effective height of the emissions from the source, resulting in an increase in the maximum GLC. 

The stack of a smelter in a rural area emits very fine particles containing metals such as nickel, copper, and lead. Wind speed is 5.5 m/sec, and insolation is slight. The emission rate of nickel is approximately 0.1 g/sec at an effective height of 120 m. Analysis of the data from a vertically oriented wind speed instrument, which produces data corresponding to the plot of w versus time in Fig. 4-26, indicates that the standard deviation of vertical air velocity is 0.15 m/sec. The corresponding standard deviation of v (perpendicular to the wind) is 0.25 m/sec. What is the nickel concentration at ground level directly downwind, 8 km from the stack ... 

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