PLENUM DESIGN

Erosion in the nozzle or orifices is often associated with weepage of solids. This can be avoided by carefully designing a grid with the proper pressure drop criteria as presented in Sec. 3.2. Poorly designed bubble caps tend to have erosion problems due to the secondary circulation of solids. Therefore, bubble caps should be designed to minimize secondary circulation of solids. 

System temperature and pressure affect the momentum of grid jets via the gas density (see Ch. 2). The momentum of the gas jets is p AC/A. When the temperature is increased, the gas density decreases. For the same gas jet velocity this decreases the momentum of the jets and, therefore, decreases the jet penetration and the attrition at the grid. Similarly, when system pressure is increased, gas density increases, gas jet momentum increases and, therefore, the jet penetration and the attrition at the grid are increased. 

The plenum, or windbox, is the chamber immediately below the grid. If the bed-pressure-drop-to-grid-pressure-drop ratio is high enough, the plenum design will probably not be that important. However, for the case where this ratio is marginal, the plenum design may determine whether the bed will operate satisfactorily. 

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When sizing return air ducts, keep in mind that calculated room leakage rates are empirical and will vary depending on construction tolerances the acutal return air (R.A.) quantities may vary from theoretical design. Return ducts should be sized to handle at least 25% more than design airflow. Return air plenum designs should be avoided unless there is no potential for contamination problems. 

Karri, S.B.R. Werther, J. Gas distributor and plenum design in fluidized beds. In Handbook of Fluidization and Fluid-Particle Systems Yang, W.C., Ed. Marcel Dekker New York, 2003 155-170. 

Are exhaust inlets, ducts, and plenums designed, constructed, and supported to prevent collapse or... 

Locating air coolers too close together or improper plenum design can cause the air discharging from one fan to be pulled into the fan of another condenser. This recirculation can be verified by comparing the average air inlet temperature to the ambient temperature. 

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