Discharge stack height

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 importance of the stack height (see Figure 7-73) is (a) to discharge the burning venting gases/vapors sufficiently high into the air so as to allow safe dispersion and... 

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. 

Control by dilution encompasses the subjects of both atmospheric dispersion and stack design. Stacks are expensive items of construction, and there is need for a sound basis for determining stack heights and diameters. The motion in the atmosphere primarily dictates the movement and subsequent dilution of the pollutant after discharge from a stack. The stack control system must provide ground-level concentrations that will be acceptable and not seriously affect receptors (humans, livestock, vegetation, materials of construction, etc.). 

Discharge stack number Stack diameter (m) Stack height (m)... 

Stacks shall extend to a height of at least four feet above the fan deck, not only to provide protection for operating personnel, but to properly direct the discharge air upward and away from the cooling tower. 

A coal-fired power station stack of an effective height of 20 m is discharging flue gases at a constant rate containing 1500 ppm sulfur dioxide and 8% carbon dioxide, both expressed on a volume for volume basis. 

The key factor in flare stack design is personnel escape time from the stack base at maximum discharge. Therefore, the selection of height and flare stack location should be made on the basis of safety for operating personnel as well as equipment. 

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