Page 59 - Chemical process engineering design and economics

Production and Capital Cost Estimation 45

Operating Labor

To determine the operating labor calculate L, the number of hours to produce a
kilogram of product, from Equation 2.1. First, determine the number of process
units, N, using the guide lines discussed previously. To determine N examine the
flow diagram for the process shown in Figure 2.1.1.
MEA, hydrogen, ammonia, and recyled gases mix before flowing into the
packed-bed catalytic reactor, shown in Figure 2.1.1. After reaction the gas stream
cools, condensing the condensable components. The gas-liquid stream leaving the
condenser separates in a phase separator into a gas stream, consisting mainly of
unreacted ammonia and hydrogen, and a liquid stream. The compressor then com-
presses the gases and recyles them back into the inlet of the reactor. Next, a series
of distillation columns separates the liquid product stream. The distillation
columns remove the more volatile components first. The first column removes
ammonia, the second column water, and the third column separates EDA and PIP
from HEP, AEP, BETA, and MEA. The MEA recycles backed to the reactor inlet.
Because the process is proprietary, Figure 2.1.1 does not show the purification and
the polyamine separation sections in any detail. To obtain an approximate labor
cost, we will assume that one column in the Purifcation Section separates the EDA
and PEP and two columns in the Polyamine Separation Section separates the more
complex solution. According to the guidelines for determining N, the heat ex-
changers, compressors, and phase separators are not process units. Thus, there are
six columns and one reactor for a total of seven process units.
Assuming that the process is highly automated, we find from Table 4 that b
= 0.76 and that the process productivity, K = 0.174. Assume that p, the labor pro-
ductivity increases at an annual rate of 2% since 1952. Twenty-six years have
elapsed since 1952, therefore n = 26. Substituting into Equation 2.1, the number of
hours of operating labor for a kilogram of the total product,

0.174 7
3
3
L= —————— ————— =3.224xlO" h/kg(1.46xlO~ h/lb)
0 76
(1+0.02) 26 (1250) '
Fixed Capital Cost
A typical plant life is ten years. Thus, the fixed capital cost, C F, in dollars per kilo-
gram of total product is,

y
10.3xl0 6 $ 1 r It
= —————— ————— ————— = 0.103$/kg (0.0467 $/lb)
C F
10 yr IxlO 4 t IxlO 3 kg

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