Page 211 - Plant design and economics for chemical engineers

COST ESTIMATION 185

where the three installation-cost factors are, in turn, defined by the following
three equations:
logf, = 0.635 - 0.154logO.OOlE - 0.992; + 0.506;

log fp = -0.266 - 0.0141ogO.OOlE - 0.156; + 0.556; (6)

log f, = 0.344 + 0.033 logO. E + 1.194; (7)
i
and the various parameters are defined accordingly:
E = purchased-equipment on an f.o.b. basis
f, = indirect cost factor always greater than 1 (normally taken as 1.4)
fF = cost factor for field labor
fp = cost factor for piping materials
f, = cost factor for miscellaneous items, including the materials cost for insula-
tion, instruments, foundations, structural steel, building, wiring, painting,
and the cost of freight and field supervision
Ei = cost of equipment already installed at site
A = incremental cost of corrosion-resistant alloy materials
e = total heat exchanger cost (less incremental cost of alloy)
f, = total cost of field-fabricated vessels (less incremental cost of alloy)
p = total pump plus driver cost (less incremental cost of alloy)
t = total cost of tower shells (less incremental cost of alloy)

Note that Eq. (4) is designed to handle both purchased equipment on an f.o.b.
basis and completely installed equipment.

METHOD E POWER FACTOR APPLIED TO PLANT-CAPACITY RATIO. This
method for study or order-of-magnitude estimates relates the fixed-capital
investment of a new process plant to the fixed-capital investment of similar
previously constructed plants by an exponential power ratio. That is, for certain
similar process plant configurations, the fixed-capital investment of the new
facility is equal to the fixed-capital investment of the constructed facility C
multiplied by the ratio R, defined as the capacity of the new facility divided by
the capacity of the old, raised to a power X. This power has been found to
average between 0.6 and 0.7 for many process facilities. Table 19 gives the
capacity power factor (x) for various kinds of processing plants.
C,, = C(R)" (8)

A closer approximation for this relationship which involves the direct and
indirect plant costs has been proposed as
C,, =f[D(R)X+I] (9)