Page 247 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

equipment, see Example 8.9.

Example 8.9

Estimate the quantities and yearly costs of the appropriate utilities for the following pieces of equipment
on the toluene hydrodealkylation PFD (Figure 1.5). It is assumed that the stream factor is 0.95 and that all
the numbers on the PFD are on a stream time basis. The duty on all of the units can be found in Table 1.7.
a. E-101, Feed Preheater
b. E-102, Reactor Effluent Cooler
c. H-101, Heater
d. C-101, Recycle Gas Compressor, assuming electric drive
e. C-101, Recycle Gas Compressor, assuming steam drive using 10 barg steam discharging to
atmospheric pressure.
f. P-101, Toluene Feed Pump

Solution

a. E-101: Duty is 15.19 GJ/h. From Table 8.3, Cost of High-Pressure Steam = $17.70/GJ

Yearly Cost = (Q)(C steam )(t) = (15.19 GJ/h)($17.70/GJ)(24)(365)(0.95) = $ 2,237,000/yr

Alternatively, Yearly Cost = (Yearly flowrate)(Cost per unit mass)

Yearly Cost = (2.48)(3600)(24)(365)(0.95)(29.97/1000) = $2,227,000/yr
(same as above within round-off error)
b. E-102: Duty is 46.66 GJ/h. From Table 8.3, Cost of Cooling Water = $0.354/GJ

Yearly Cost = (46.66 GJ/h)(24)(365)(0.95)($0.354/GJ) = $137,000/yr
c. H-101: Duty is 27 GJ/h (7510 kW). Assume that an indirect, nonreactive process heater has a

thermal efficiency (ξ ) of 90%. From Table 8.3, natural gas costs $11.10/GJ, and the heating
th
3
value is 0.0377 GJ/m .

Yearly Cost = (27)(11.10)(24)(365)(0.95)/(0.90) = $2,771,000/yr

d. C-101: Shaft power is 49.1 kW, and from Figure 8.7 the efficiency of an electric drive (ξ ) is
dr
90%.