Stacks effective height

Effective Stack Height Plume Rise, US EPA Air Pollution Training Institute Pub. SP.406, with Chapts. D, E, and G by G. A. Briggs and Chapt. H by D. 

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. 

Under stable conditions, the lowest value of Eq. (20- 6a) or (20-7) is usually taken as the effective stack height. 

H = effective stack height Oy = diffusion coefficient in the y-direction, m = diffusion coefficient in the z-direction, m... 

The importance of plume rise is that it determines the effective stack height, or the height at which most calculation procedures assume dispersion to initiate. The plume rise added to the actual height of the stack is known as the effective stack height, described by the following expression ... 

At the effective stack height, the dispersion of the pollutants are assumed to spread out as a Gaussian distribution. The basic dispersion equation considers... 

Emissions of gases or particles less than 20 microns (larger particles settle more quickly due to gravitational effects) disperse with an origin and plume centerline at the effective stack height. Pollutant concentrations are greatest within one standard deviation of the plume centerline. Thus, the determination of the value of these standard deviations is an important factor in calculating ambient concentrations. 

Because of extreme venting conditions assumed, effective stack heights and resultant plumes from both 3- and 5-minute discharge conditions attain heights beyond the micro-meteorological conditions assumed in accepted computation models. It is therefore highly probable there will be considerably further atmospheric dispersion and diffusion of the VCM than predicted in the results shown. That is, the ground level concentration can be expected to be considerably lower than the values shown in Table 6. 

The maximum ground concentration of stack gases subjected to atmospheric diffusion occurs about 5-10 effective stack heights dow tiw ind from the point of emission. 

Ground concentrations can be reduced by the use of higher stacks. The gromid concenuntion varies inversely as tlie square of the effective stack height. 

The effective stack heights for various wind speeds and stabilities arc summarized in Table 12.10.1. 

An inventory of SO2 emissions has been conducted in an urban area by square areas, 5000 feet (1524 meters) on a side. The emissions from one such area are estimated to be 6 g/s for lire entire area. This square is composed of residences and a few small commercial establislunents. What is lire concentration resulting from tliis area at tlie center of tlie adjacent square to tire nortlt when tlie wind at 2.5 m/s The average effective stack height of tliese sources is assumed to be 20 meters. 

The problem for the designer is to determine the appropriate stack height. This is illustrated in Figure 25.34. This shows that the effective stack height is a combination of the actual stack height and the plume rise. The plume rise is a function of discharge velocity, temperature of emission and atmospheric stability3. 

A trash incinerator has an effective stack height of 100 m. On a sunny day with a 2 m/s wind the concentration of sulfur dioxide 200 m directly downwind is measured at 5.0 X 10-5 g/m3. Estimate the mass release rate (in g/s) of sulfur dioxide from this stack. Also estimate the maximum sulfur dioxide concentration expected on the ground and its location downwind from the stack. 

Vertical dispersion cannot be described in such simple terms (Kaimal et al., 1976). First, varies throughout the planetary boundary layer. In the region, L < z < O.lzi, o- , z, and a- scales with w, only above O.lzi. For Zi = 1500 m and an effective stack height of 400 m, the dispersing plume is controlled by an inhomogeneous region that is almost half the effective stack height. 

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