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There is little published information on estimating HETP for third-generation packings in this service. The only published relevant method is that by Strigle (15) for the stripping of light hydrocarbons from heavier ones using IMTPĀ® [Eq. (9.37) in Table 9.3]. The column simulation gives a typical bottom section molecular weight of 58 in the depropanizer. For #50 IMTP*, Eq. (9.37) in Table 9.3 gives

HETP = 4.5 - 0.6 In 58 + 0.53 = 2.6 ft For argument sake, it will be assumed that this equation applies for the rectifying section as well. With an average molecular weight of 40 in that section, and assuming #40 IMTPĀ®, Eq. (9.37) from Table 9.3 gives

Assuming these HETPs apply to the current example, the heights are

Top section

Bottom section

2.6 ft x 11 stages = 28.6 ft (say 30 ft) Alternate design. Comparison to the preliminary design follows:

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