Page 186 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

where A= Equipment cost attribute

C = Purchased cost

n = Cost exponent

Subscripts: a refers to equipment with the required attribute

b refers to equipment with the base attribute

The equipment cost attribute is the equipment parameter that is used to correlate capital costs. The
equipment cost attribute is most often related to the unit capacity, and the term capacity is commonly used
to describe and identify this attribute. Some typical values of cost exponents and unit capacities are given
in Table 7.3. From Table 7.3, it can be seen that the following information is given:

Table 7.3 Typical Values of Cost Exponents for a Selection of Process Equipment

1. A description of the type of equipment used
2. The units in which the capacity is measured
3. The range of capacity over which the correlation is valid
4. The cost exponent (values shown for n vary between 0.30 and 0.84)

Equation 7.1 can be rearranged to give

(7.2)

where

Equation 7.2 is a straight line with a slope of n when the log of C is plotted versus the log of A . To
a
a
illustrate this relationship, the typical cost of a single-stage blower versus the capacity of the blower,