Preliminary Design Considerations

DESIGN OF COMPLEX COLUMNS USING COLUMN PRORLE MAPS 

FIGURE 623 For a= [6,1,3] and Xoi = 0.95 (a) The effect of distillate product purity on the best potential sidestream composition and (b) the maximum purity of in die sidestream from a set distillate at different X2 impurities in the distillate. 

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Myers, D.P. Hieftje, G.M. Preliminary Design Considerations and Characteristics of an Inductively Coupled Plasma-Time-of-Flight Mass Spectrometer. Mi-crochem. Joum. 1993,48, 259-277. 

Myers, D. P. and Hieftje, G. M. (1993) Preliminary design considerations and characteristics of an indnctively coupled plasma time-of-flight mass spectrometer. Microchetn. J., 48,259. 

Both the reboiling and condensing processes normally take place over a range of temperature. Practical considerations, however, usually dictate that the heat to the reboiler must be supplied at a temperature above the dew point of the vapor leaving the reboiler and that the heat removed in the condenser must be removed at a temperature lower than the bubble point of the liquid. Hence, in preliminary design at least, both reboiling and condensing can be assumed to take place at constant temperatures. ... 

Commercial computer computation services are being set up to provide shortcut calculation options. These provide considerable savings for preliminary design studies. 

In preliminary design, the heat duty and furnace efficiency are the prime considerations. However, if the tube area needs to be specified, a preliminary estimate can be obtained from an assumed flux. In the radiant section, this usually lies in the range of 45,000 W m-2 to 65,000 W m 2 of tube surface, with a value of around 55,000 W m 2 most often used. The heat flux is particularly important if a reaction is being carried out in the furnace tubes. Overall heat transfer coefficients in the convection section are in the range 20 to 50 W m-2 K-1. 

This chapter has mainly been based on textbooks generally used in undergraduate courses on mass transfer and separation processes.1 6 Most of these textbooks contain sections on both basic calculations as well as some design considerations. Coulson et al is devoted entirely to design. Perry,7 in addition to basic theory, also includes thermodynamic data for many common mixtures which may be used for preliminary... 

Evaluation of the alternate design. The alternate design is attractive and can save considerable capital compared to the preliminary design, but the user must be convinced that it will work before proceeding with it. 

If sufficient information is available, a preliminary design may be developed in conjunction with the preliminary feasibility survey. In developing the preliminary design the chemical engineer must first establish a workable manufacturing process for producing the desired product. Quite often a number of alternative processes or methods may be available to manufacture the same product. Except for those processes obviously undesirable, each method should be given consideration. 

There is considerable uncertainty in the contact conductance data reported in the literature, and care should be exercised when using them. In Table 3-2 some experimental results are given for the contact conductance between similar and dissimilar metal surfaces for use in preliminary design calculations. Note that the thermal contact conductance is highest (and thu.s the contact resistance is lowest) for soft metals with smooth surfaces at high pressure. 

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