Page 231 - Plant design and economics for chemical engineers

202 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

rule of thumb,? the labor requirements for a fluids-processing plant, such as an
ethylene oxide plant or others as shown in Table 22, would be in the low range
of 5 to 2 employee-hours per ton of product; for a solid-fluids plant, such as a
polyethylene plant, the labor requirement would be in the intermediate range of
2 to 4 employee-hours per ton of product; for plants primarily engaged in solids
processing such as a coal briquetting plant, the large amount of materials
handling would make the labor requirements considerabIy higher than for other
types of plants with a range of 4 to 8 employee-hours per ton of product being
reasonable. The data shown in Fig. 6-8 and Table 22, where plant capacity and
specific type of process are taken into account, are much more accurate than
the preceding rule of thumb if the added necessary information is available.
In determining costs for labor, account must be taken of the type of
worker required, the geographical location of the plant, the prevailing wage
rates, and worker productivity. Table 20 presents data that can be used as a
guide for relative median labor rates and productivity factors for workers in
various geographical areas of the United States. Tables 23 and 24 provide data
on labor rates in dollars per hour for the U.S. Gulf Coast region and average
labor indexes to permit estimation of prevailing wage rates.

Direct Supervisory and Clerical Labor
A certain amount of direct supervisory and clerical labor is always required for
a manufacturing operation. The necessary amount of this type of labor is closely
related to the total amount of operating labor, complexity of the operation, and
product quality standards. The cost for direct supervisory and clerical labor
averages about 15 percent of the cost for operating labor. For reduced capaci-
ties, supervision usually remains fixed at the MO-percent-capacity rate.

Utilities
The cost for utilities, such as steam, electricity, process and cooling water,
compressed air, natural gas, and fuel oil, varies widely depending on the amount
of consumption, plant location, and source. For example, costs for a few :
selected utilities in the U.S. Gulf Coast region are given in Table 23. A more
detailed list of average rates for various utilities is presented in Appendix B.
The required utilities can sometimes be estimated in preliminary cost analyses i
from available information about similar operations as shown in Table 22. If
such information is unavailable, the utilities must be estimated from a prelimi-
nary design. The utility may be purchased at predetermined rates from an
outside source, or the service may be available from within the company. If the
company supplied its own service and this is utilized for just one process, the
entire cost of the service installation is usually charged to the manufacturing
process. If the service is utilized for the production of several different products,

tJ. E. Haselbarth, Updated Investment Costs for 60 Chemical Plants, Chem. Eng., 7425x214 (Dec.
4, 1967).