Effective stack

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... 

These effective stack parameters are somewhat arbitrary, but the resulting buoyancy flux estimate is expected to give reasonable final plume rise estimates for flares. However, since building downwash estimates depend on transitional momentum plume rise and transitional buoyant plume rise calculations, the selection of effective stack parameters could influence the estimates. Therefore, building downwash estimates should be used with extra caution for flare releases. 

This chapter explores the design of stacks from the point of view of the downwind observer whose task is to determine the connection between stack design, process emissions, meteorology, and, most important, environmental effects. Stacks must be designed to specifications based on meteorological conditions and environmental air quality standards, which may be quite umelated to process requirements... 

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. 

All of these point defects are intrinsic to the heterogeneous solid, and cirise due to the presence of both cation and anion sub-lattices. The factors responsible for their formation are entropy effects (stacking faults) and impurity effects. At the present time, the highest-purity materials available stiU contain about 0.1 part per billion of various impurities, yet are 99.9999999 % pure. Such a solid will still contain about IQi impurity atoms per mole. So it is safe to say that all solids contain impurity atoms, and that it is unlikely that we shall ever be able to obtain a solid which is completdy pure and does not contain defects. 

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. 

When the plates are placed in the incubator, temperature and evaporation gradients start to form inside the plates which result in positional biases (edge effects) that introduce noise in the final data. The most affected samples are the ones in the periphery of the plate. Filling the spaces between the wells with PBS reduces the edge effect. Stacking the plates inside the incubator will also influence the evaporation gradient inside the plate, especially when the top plate of a stack is compared to the bottom plate of a stack. If the plates must be stacked then the plates that are to be compared direcdy should be in the same position on different stacks. 

For yet larger injections, other, more specialized techniques such as pH mediated stacking [47] (for zwitterions) or transient isotachophoresis (difficult to implement) can be considered [44], Neutral molecules can also be effectively stacked using charged surfactants or CDs [48,49],... 

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