Minimum downcomer area

ADM = Minimum downcomer area, fT ATM = Minimum column cross-sectional area, fr CAF = Vapor capacity factor CAFo = Flood capacity factor at zero liquid load CFS = Vapor rate, actual ftVsec DT = Tower diameter, ft DTA = Approximate tower diameter, ft FF == Flood factor or design percent of flood, fractional FPL = Tray flow path length, in. 

Minimum downcomer width and minimum downcomer area. As the downcomer becomes smaller, its width decreases faster than its length, turning the downcomer into a long and narrow slot. This geometry increases the resistance to liquid downflow and to upflow of disengaging vapor. Small downcomers are also extremely sensitive to foaming, fouling, construction tolerances, and introduction of debris. Smaller weirs associated with small downcomers distort the liquid flow pattern as it approaches the weir ("weir constriction effect ), which in-... 

Generally, downcomers smaller than 5 to 8 percent of the column cross-section area should therefore be avoided (1,5,10,12,30,43,50). This rule is often expressed as a minimum ratio of weir length or downcomer width to column diameter. An alternative rule for small i <10 percent of column area) downcomers (7,51) is to set the minimum downcomer area to either twice the area calculated using the normal downcomer area criteria or 10 percent of the column cross-section area (whichever is smaller). Additional discussion on small downcomers is elsewhere (1). 

AAM = Minimum active area, fF AD = Downcomer area, fP ADM = Minimum downcomer area,... 

Check the minimum downcomer area. If A m is less than 0.11 Aam then modify the minimum downcomer area to the smaller of ... 

Minimum downcomer width and minimum downcomer area. Reducing downcomer area lowers column diameter or increases tray bubbling area. This can lead to substantial cost savings when the downcomer is large. As the downcomer becomes smaller, these savings diminish and eventually approach marginal returns. When downcomer area is... 

Use one pass, tray spacing (0.6096 m), minimum downcomer area (0.10), foaming factor (1), and over design factor (1). Set the fractional approach to flooding at 0.7. Use the Fair design method for flooding.]... 

Minimum flow area at bottom (under) of downcomer per tray, ft ... 

Select a downcomer target flooding fraction, Fj). A typical design value for a new column would be 0.80 (80%). This value does not have to be the same as the jet flood design value. Determine the minimum design downcomer area ... 

For 24-inch tray spacing, a maximum downcomer loading is 175 GPM per square foot of the downcomer top area. That s for clean services. For foaming services, I use 90 GPM. It does not hurt anything to make the downcomer too big. That is, there is no minimum downcomer loading. 

My minimum downcomer clearance is 1 inch. Maybe a pressure surge will push up the downpour plate below the downcomer Maybe corrosion deposits will accumulate in this area ... 

Qpc = downcomer flow, gpm Adm - minimum downcomer flow area, fP This equation may be rewritten ... 

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