Membrane Gas Separation

Dew Point (°F, 1 atm)
Dry Gas Recovery
Figure 16.10 Effect of sweep and fi bre inner diameter variation on dry gas recovery as a 
function of dew point: solid – no variation, short dash – sweep variation = 0.2, long dash 
 – inner diameter variation = 0.2
Shell
Internal
Offset
Lumen
Shell
Figure 16.11 Three different sweep confi gurations used in explicit sweep distribution 
calculations to determine module performance. The arrows indicate the macroscopic fl ow 
direction. The thick solid lines indicate the location of the inlet and outlet

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The Effect of Sweep Uniformity on Gas Dehydration Module Performance
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Dew Point (°F, 1 atm)
Dry Gas Flow (SCFM)
Figure 16.12 Effect of sweep confi guration on dry gas fl ow rate as a function of dew 
point: diamond – internal, circle – shell, triangle – offset. The solid line corresponds to 
uniform sweep distribution. Note the diamond and circle symbols overlap
Figures 16.12 and 16.13 illustrate the performance predictions for the different confi gu-
rations. The locations of the inlet and outlet regions for the sweep have little effect on 
performance. Dry gas fl ow rate and recovery decrease by less than 5% over the dew point 
range considered. The change in performance increases as dew point increases. Such 
results are consistent with the results obtained assuming a Gaussian distribution of the 
sweep around each fi bre – variations in sweep fl ow rate do not signifi cantly affect module 
performance.
The simulation results provide detailed concentration profi les within the module. Figure 
16.14 illustrates a typical radial concentration profi le for a module cross - section along 
the tube sheet at the retentate outlet (i.e. the dry gas product end). Clearly radial variations 
in concentration exist. The shell concentration increases by 600% from the periphery of 
the fi bre bundle to the centreline while the lumen concentration increases by 60%. The 
difference in lumen and shell concentrations decreases by 400%.
Surprisingly, the large variations in concentration that exist do not impact overall 
module performance. The mixing cup average concentrations calculated from the con-
centration and velocity fi elds are nearly identical to the concentrations calculated assum-
ing uniform sweep distribution and no radial variation in the concentration or velocity 
fi elds. This fortuitous result implies the inlet and outlet locations for the sweep are not a 
critical design variable.