Page 87 - Chemical process engineering design and economics

72 Chapter 2

reys [5], the cost of a plant should include all costs required to make the plant op-
erational. Startup cost seldom exceeds 10% of the fixed capital cost. Peters and
Timmerhaus [4] recommend 8 to 10%. According to Peters and Timmerhaus, the
startup cost can be accounted for in the first year of plant operation or in the total
capital investment. We will assume that it will be accounted for in the first year of
operation.
Working capital is the money required to finance the daily operations of a
plant. As stated earlier, it consists of the money required to buy raw materials and
store products, accounts receivable, and storage of various supplies, which are
necessary to keep the plant operating. About one month's supply of raw materials
and products, and one month of accounts receivable would suffice, or 20% of the
fixed capital cost. Thus, the total capital cost,

+ 0.015 C D + f L C D + [28]
C T = C D 0.20 C F

Example 2.4 Capital-Cost Estimation of an Allyl-Choride-Svnthesis Process

Allyl alcohol and glycerin can be synthesized from allyl chloride (3-chloro-l-
propene) [19]. Gas-phase thermal chlormation of propene has been proposed as a
route to allyll alcohol. In this process, shown in Figure 2.4.1, a process furnace
heats propylene, which then mixes with chlorine in a mixer. The intersecting
streams in the eductor-mixer create turbulence and hence enhance mixing. The
chlorine reacts with propylene inside the tubes of two parallel shell-and-tube reac-
tors. Dowtherm A, a heat-transfer fluid used at high temperatures, removes the
enthalpy of reaction. A pump circulates the Dowtherm A through the shell of the
reactors and through a water cooler. The products flow through air-cooled heat
exchangers, where fans blow cool air across the tubes of the cooler to remove heat.
The cooled product stream then condenses to form a crude allyl chloride stream
containing several by-products. Finally, the crude allyl chloride flows to a separa-
tion section of the process.
The process design for the production of allyl chloride has been completed.
Table 2.4.1 lists the specifications for the major pieces-of-equipment. Estimate the
depreciable capital cost and the total capital cost as of mid-1998. The process is a
plant addition at an existing site, i.e., buildings and auxiliary facilities are avail-
able. The cost of the eductor-mixer as of mid-1998 is $ 1,000.
First, convert all equipment costs to a common basis of FOB costs as of
mid-1998. Table 2.9 contains the costs of some common equipment as of January
1990, except where indicated. Since the allyl chloride section of the process is a
small installation, use cost indexes for specific equipment rather than the plant cost
index, which is an average of all equipment. Follow the calculation procedure
outlined in Table 2.16, which uses the equations listed in Table 2.15.

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