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Design of binary distillation column
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COST CALCULATIONS

 

 

For preliminary design calculations the bare module cost (BMC) is calculated from the following formula

BMC = Uf (MF + MPF - 1) (BC)   (For vessel and reboiler).....eqn 2.6

BMC = UF (MPF) (BC)  (For Tray Stack and condenser)......eqn .2.7

                                           Where

UF Update Factor
MPF Materials and pressure factor
BC Base Cost
MF Module Factor

 

 

CALCULATION OF UPDATE FACTOR

 

We apply an update factor to account for inflation. The update factor is defined by:

UF = present cost index/base cost index

For cost updating we used the Chemical Engineering (CE) Plant Index reported in Chemical Engineering magazine. Representative UF for 2009 for base cost index of 1957-59 is calculated to be 6.034.

 

 

CALCULATION OF MATERIALS AND PRESSURE FACTOR

 

 

Guthrie Material and Pressure Factors for Heat Exchangers

MPF = Fm (Fp + Fd)......eqn 2.8

where, Fm, Fp and Fd are calculated from the tables given below.

TABLE 2.3 

 

 TABLE 2.4   

 

 TABLE 2.5

 

 

CALCULATION OF MATERIALS AND PRESSURE FACTOR 

 

Guthrie Material and Pressure Factors for Tray Stacks

MPF = Fm +Fs + Ft .....eqn 2.9

where, Fm, Fs and Ft are calculated from the tables given below.

 

 TABLE 2.6

 

 TABLE 2.7  

 

 TABLE 2.8  

 

 

CALCULATION OF BASE COST AND MODULE FACTOR

 

For preliminary design calculations, we note that Base costs (BC) increase nonlinearly with equipment size (S) or capacity. This behavior can often be captured with a power law expression:

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mi mathvariant=¨bold¨»BC«/mi»«mo»§nbsp;«/mo»«mo»=«/mo»«msub»«mi mathvariant=¨bold¨»C«/mi»«mn»0«/mn»«/msub»«msup»«mfenced»«mfrac»«mi mathvariant=¨bold¨»S«/mi»«msub»«mi mathvariant=¨bold¨»S«/mi»«mn»0«/mn»«/msub»«/mfrac»«/mfenced»«mi mathvariant=¨bold¨»§#945;«/mi»«/msup»«/math».................................eqn 2.10

Where the exponent is less than one, often about 0.6 to 0.7, and S0 and C0 are the base capacities and costs, respectively. For pressure vessels, for instance, the service capacity depends on volume, while the cost depends on the weight of the metal (surface area). The values of C0, S , S0, alpha, are calculated from the tables below.

 

 

TABLE 2.9 - Base Costs for Pressure Vessels
(Data from Guthrie, 1969)

 

 

TABLE 2.10 - Base Costs for Process Equipment
(Data from Guthrie, 1969)

 

 

In the above tables we give module factors for the following base costs (BC in 1968 prices)

 

 TABLE 2.11   

 

 

 

 

 

 

 

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