# Shakshat Virtual Lab

# INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI

# 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:

.................................**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 **