Page 252 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

give another reason for using the factor of 1.23.

In Equation (8.2), the cost of operating labor, C , is multiplied by a factor of 2.73. One reason for
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7. this is that the value of C includes only plant operators and not supervisory and clerical labor costs.
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Is this statement true or false? What other factors (if any) account for the multiplication factor of 2.73?

Explain the difference between direct costs, fixed costs, and general expenses. Give two examples of
8.
each.

Problems

You are employed at a chemical company and have recently been transferred from a plant that
manufactures synthetic dyes to a new facility that makes specialty additives for the polymer resin
industry.

a. You have been asked to estimate the cost of manufacturing at this new facility. Would you
9. i. Use Equation (8.2) to estimate COM ?
d
ii. Use data from the old plant where you worked, because you are very familiar with all the
aspects of manufacturing for that process?
iii. Dig up information on the new process and use these figures?

b. When would you use a relationship such as Equation (8.2)?

When a chemical plant needs steam at multiple pressure levels, it is often economical to generate all
the steam at a high pressure and then to let the steam down through pressure-reducing turbines to the
desired pressure. This principle is illustrated in Figure 8.6. The downside of this approach is that as

the exhaust pressure of the turbine increases, the theoretical (and actual) steam requirements increase,
meaning that less energy is extracted. To illustrate this point, do the following.

a. Estimate the amount of energy extracted from 10,000 kg/h of 58.6 barg steam superheated by

10. 165°C when connected to the following turbines (each 80% efficient).
i. Exhaust pressure is 4” Hg absolute.
ii. Exhaust pressure is 4.82 barg.

b. Estimate the amount of energy extracted from 10,000 kg/h of saturated, 10.0 barg steam when
connected to a turbine (80% efficient) exhausting at 4.82 barg.

c. Identify the locations of each of the three turbines described above on Figure 8.6.

What are the operating costs associated with a typical cooling water system? Based on the example
given in this chapter, answer the following.

a. What percentage of the operating costs is the makeup water?

11. b. By how much would the cost of cooling water increase if the cost of power (electricity) were to

double?