Chemical Engineering Chapter 8 The simple answer is that the cooling water

Chapter 8

8.1 The term 0.18FCI has nothing to do with the interest on capital investment. From Table

8.2 we see that the following costs are based on the FCI:

Maintenance and repairs

8.2 The number of operators per shift is multiplied by approximately 4.5 to get the total

number of operators required by the plant because it is assumed that a single operator

works 5 shifts a week and 49 weeks per year.

8.3 Stream Factor (SF) = # Days plant operated per yea

r

365 (Equation 8.5)

8.5 The simple answer is that the cooling water cost does not vary very much with return

temperature because the main costs are associated with pumping (electricity), fans (power),

cost of water make up and chemical addition.

8-2

8.6 No  this is not the reason for the factor of 1.23 multiplying CRM. The reason is that in the

derivation of Equation (8.2) from the data in Table 8.2 some of the costs are based on the

COMD. Thus when all terms are added, the factor multiplying COMD is 0.19COMD.

8.7 Yes, the 2.73 multiplier does include costs for supervisory and clerical labor but also

includes:

8.8 From Table 8.1 we have

Direct Costs Costs that vary with the rate of production

e.g. raw materials, utility costs.

8-3

8.9

(a) Options (i) and (ii) are not reliable, and option (iii) is the best. If you do not have

time to dig up information on the new plant then (i) is probably better than (ii) unless

8.10 (a) 10,000 kg/h, 58.6 barg  SH = 165 C

(i) Discharge P = 4 Hg absolute

(ii) Discharge P = 4.82 barg

From Table 8.5, theoretical steam rate = 6.45 kg steam/kWh

(c) a-(i) Turbine #1 in Figure 8.6 (HP surface condenser)

a-(ii) Turbine #2 (HP LP)

b Turbine #4 (MP LP)

8-4

8.11 Costs for cooling water are:

Pumping costs (electric)

(b) Power Cost (%) = 0.06 2.36 1.61

0.354 100 67.3%

8.12 (a) Using Chemcad and SRK package for k-values and enthalpy calculations, the

following data are found: at 45 C vapor pressure of propane = 1556 kPa

(b) At -50 C vapor pressure of propane = 69.47 kPa

(e) Using 5 kPa P in exchangers and a 75% compressor efficiency we get:

For Qevap = 1 GJ/h

8-5

8.13 (a) Repeat problem 8.12 using propylene as refrigerant

Vapor pressure (45 C) = 1,876 kPa

(b) Repeat problem 8.12 using ethane as refrigerant

Vapor pressure (45 C) = No result Tcritical 32 C

(c) Repeat problem 8.12 using ammonia as refrigerant

Vapor pressure (45 C) = 1,797 kPa

Note: For problems 12 and 13 only single stage compressors have been used.

Because the pressure ratios are all much greater than the recommended maximum of

Cost 232.6 kW 0.06 1.837 GJ/h 0.354 $14.61GJ

For the solutions to Problems (8.14-8.19), fixed capital investment figures (FCI) were

taken from the results of Problems (7.22-7.27), using the CAPCOST program. The

utility costs (CUT) were also estimated using the results of CAPCOST and the utility

costs given in Table 8.3. Raw material costs (CRM) were taken from the stream tables

Factors/assumptions in analysis that may require modification:

Raw material costs given in Table 8.4 are a single snapshot of prices at a

given point in time – historical trends of product and raw material prices are

8-7

8.14 Operating Costs for the Ethyl Benzene  Project B.2

Note that full credit is given for the steam generated in E-301  304 (In CAPCOST, this credit is

activated by using a negative duty for the exchanger)

FCI (from Problem 7.21 CAPCOST Output for CTM) = $12,455,000

CUT = $390,000/yr

COMd =0.180FCI + 2.73COL + 1.23(CUT + CWT + CRM) = 0.180(12.46) + 2.73(0.894) +

1.23(0.390 + 0 + 59.82+35.18) = $122,013,000/yr

CUT

8-8

8.15 Operating Costs for the Styrene Process  Project B.3

Note that full credit for the HPS and LPS in Exchangers E-403 and E-404 has been taken and that credit

for the high temperature steam from E-402 has been taken as LPS (which is low).

COMd =0.180FCI + 2.73COL + 1.23(CUT + CWT + CRM) = 0.180(131.28) + 2.73(0.953) + 1.23(64.7 + 0 +

136.54) = $273,757,000/yr

COMd = $298,300,000/yr

8-9

8.16 Operating Costs for the Drying Oil Process  Project B.4

Note that the utility cost for the Dowtherm exchanger (E-402) is accounted for in the natural gas

for the fired heater and lps credit is given for E-501 and E-506.

COMd =0.180FCI + 2.73COL + 1.23(CUT + CWT + CRM) = 0.180(6.01) + 2.73(0.834) + 1.23(.085

+ 0 +23.56) = $32,442,000/yr

COMd = $32,442,000/yr

CUT

8-10

8.17 Operating Costs for the Maleic Anhydride Process  Project B.5

Note that credit is taken for hps in E-602 and E-603

0.5 0.5

2operators

6.29 31.7 0.23 6.29 0.23(13) 3.05 shift

OL np

N P N

COMd =0.180FCI + 2.73COL + 1.23(CUT + CWT + CRM) = 0.180(17.46) + 2.73(0.834) +

1.23(0.61 + 0 + 24.90) = $36,797,000/y

C

UT

8-11

8.18 Operating Costs for the Ethylene Oxide Process  Project B.6

Note that credit is taken for hps in R-701 and R-702 that correspond to E-710 and E711. This process

looses enormous amounts of useful energy in E-704 and E-706. Heat integration can significantly reduce

the utility burden. A turbine in Stream 29 could also reduce the electrical utilities. See note at bottom

CUT

8.19 Operating Costs for the Formalin Process  Project B.7

Note that credit for the mps generated in the reactor is taken account of in E-807, which

represents the reactor exchanger.

COMd =0.180FCI + 2.73COL + 1.23(CUT + CWT + CRM) = 0.180(4.23) + 2.73(0.834) + 1.23(4.15

+ 0 + 13.58) = $24,846,000/y