Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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ECONOMICS 765
Table 17.1.7. Scheme 1. Addition of thermal cracker
simple economic analysis
Item $ mm
Capital cost of plant 125.490
Associated costs 18.823
Total investment 144.313 mm $/year
Gross income 77.709
Less
Operating cost 10.331
Depreciation 8.030
Net income before Tax 59.348
Tax @ 42.5 % 25.223
Net income after Tax 34.125
Pay-out time 3.4 years
Return on investment 23.7%
Depreciation
In the economic analysis of the various processes the depreciation of the plant value
must be taken into account. Details of depreciation will be described and discussed
later in this chapter. For the purpose of the screening study the following depreciation
factors may be used:
Crude distillation units 6.6% of capital cost per year
Cracking units 6.6% of capital cost per year
Light end units & gas plants 5.0% of capital cost per year
Hydrotreaters 6.0% of capital cost per year
The screening analysis based on a pay-out time and a Return on Investment (ROI) is
given in the following table (Table 17.1.7). Note the ROI is given by
Net Income After Taxes
Net investment cost
× 100 = %ROI
and Pay-out time is given by
Net investment cost
Net income after taxes +depreciation
= Years.
Details of the other schemes
Scheme 2. This calls for the vacuum distillation of the atmospheric residue to produce
a waxy distillate and a heavy vacuum residue. The waxy distillate is cracked in a
FCCU (Fluid Catalytic Cracker) to give gas, LPG, naphtha for gasoline, gas oil for
766 CHAPTER 17
diesel. The heavy vacuum residue is also cracked in a thermal cracker to give gas,
LPG, naphtha feed to the cat reformer, gas oil for diesel.
The total capital cost for these additional facilities = 218.580 mm $.
Total additional product income = 108.202 mm $/year and
Total operating cost is an additional 13.856 mm $/year.
Scheme 3. This is the same as scheme 2 except the vacuum residue is not cracked.
Details of this scheme are:
Total capital costs for additional facilities = 194.780 mm $.
Total additional product income = 96.509 mm $/year.
Total operating cost is an additional 8.122 mm $/year.
Scheme 4. This also includes the vacuum distillation of the atmospheric residue as in
schemes 2 and 3.The wax distillate in this case however is routed to a hydrocracker
where LPG, naphtha for reforming to gasoline, and diesel is produced. An additional
hydrogen plant is required for this scheme. Details of the scheme are summarized
below:
Total capital cost for additional facilities = 306.012 mm $
Total additional income 119.502 mm $/year
Total operating cost is an additional 12.6 mm $/year.
Table 17.1.8. Comparison of the economic analysis of the schemes studied
Scheme 1234
mm $
Capital cost 125.490 218.580 194.780 306.012
Associated costs 18.823 32.828 29.217 46.080
Total investment 144.313 251.408 223.997 352.092
mm $/year
Gross income 77.709 108.202 96.509 119.502
Less
Operating cost 10.331 13.856 8.121 12.600
Depreciation 8.030 15.007 13.237 18.361
Net income before tax 59.348 79.339 75.150 88.541
Tax @ 42.5% 25.223 33.719 31.939 37.630
Net income after tax 34.125 45.620 43.211 50.911
Payout time years 3.4 4.15 3.97 5.1
Return on investment% 23.7 18.1 19.2 14.4
ECONOMICS 767
The obvious selection in this case is scheme 1 with the lowest pay-out time and the
highest ROI.
Preparing more accurate cost data
Once a selected configuration or study case or cases have been selected from the
screening study it is now necessary to firm up as much as possible the cost data used
in those studies. Three items of data fall into this category. These are:
r
The capital cost estimate
r
The associated costs
r
The operating cost
Development engineers supply the basic data from which an update can be arrived
at. This level of data is arrived at from a process design of the facilities making
up the case studies. The process design will include a material balance and a firm
process flow sheet. Sufficient data will be generated for all equipment to allow man-
ufacturers to give a good and realistic equipment budget cost. Where applicable too
the manufacturers will be requested to provide equipment efficiencies from which
utility usage for the various items can be calculated. Where options exist within
the process design itself these will be optimized for equipment sizing and layout.
An example of such an optimization is the case of the process heat exchange sys-
tem. Full and complete equipment data sheets need not necessarily be developed for
this part of the study. Usually manufacturers are able to provide good budget costs
from equipment summary sheets similar to those given in the Example Calculation
below.
Where licensed processes are included in the case study the Development Engineer
will need to develop a specification to a suitable licensor soliciting:
r
A budget estimate for the plant (installed)
r
The utility requirements and the operating cost
(Note: In the case of a catalytic process part of the operating cost will be the catalyst
usage or loss in operation.)
r
First inventory of catalyst or chemicals where applicable
r
The licensing fee
The specification must include the capacity of the plant and the required product
quality. It must also of course give the licensor(s) details of the feedstock, utilities
conditions, and in most cases local climatic conditions. The additional information
concerning feed and product pricing together with utilities costs will enable the li-
censor to respond with a firmer and optimized cost data.
768 CHAPTER 17
Figure 17.1.6. The process flow sheet for a thermal cracker.
ECONOMICS 769
Figure 17.1.6. (Cont.)
770 CHAPTER 17
The following example follows the study screening given in Item 2.0 above.
Example calculation
From the screening study the new plants included in the selected case (which was
case 1) were as follows:
r
Naphtha hydrotreater (13,500 BPSD) licensed
r
Naphtha splitter (13,500 BPSD)
r
Catalytic reformer (9,000 BPSD) licensed
r
De-propaniser (3,830 BPSD) and de-ethanizer (2,176 BPSD)
r
Diesel hydrotreater (9,000 BPSD) licensed
r
Thermal cracker (34,320 BPSD)
The existing debutanizer is to be revamped and a new sized equipment list will be
prepared for this unit.
The units of normally licensed processes are indicated as such in the above list.
The thermal cracker may be licensed or can be designed by some major engineering
companies as a nonproprietary process. It is a major item of cost and for this example
the degree of process engineering required at this stage of the study is demonstrated
for this unit.
The process design of the thermal cracker
The process flow sheet for this unit is given in Figure 17.1.6. This process flow sheet
contains the overall material balance for the unit together with the calculated reflux and
quench flows. Major process stream routes are shown with stream temperatures where
appropriate. The material balance table also gives the flow conditions (temperature
and pressure) for those major streams. The pump capacities are shown on the flow
sheet next to the respective pump. These quantities are flows in gallon per minute at
the pump temperature.
The major item in a thermal cracker is the furnace or heater. This has two duties,
the first being to heat the feed to its reaction temperature and the second to maintain
the feed at its reaction temperature for the prescribed period of time. Note therefore
that the duty of this heater is shown on the flow sheet as the duty to heating the
oil (which also includes the steam in this case) and the duty to supply the heat of
reaction.
Data for the remainder of the equipment are given in Tables 17.1.9, 17.1.10, and
17.1.11. Sufficient data for obtaining a cost and efficiency for the heater is provided
ina“Process Specification”shown in Table 17.1.12. A special specification sheet
ECONOMICS 771
Summary data sheets
Table 17.1.9. Centrifugal pumps
Item No P106 A&B P301 A&B P302 A&B P303 A&B P304 A&B
Service Feed S water REF +PR PA/PROD Bot Prod
No of units 1 + 1 spare 1 + 1 spare 1 + 1 Spare 1 + 1 spare 1
Fluid Resid Water Naphtha Gas oil Cr res
lbs/hr 479,879 58,200 421,953 207,093 374,488
Pump temp
◦
F 620 90 90 415 600
Sg @ PT 0.758 0.995 0.592 0.692 0.732
Visc @ PT Cs 1.8 0.76 0.33 0.25 1.2
Rate (norm) @ PT GPM 1,281 117 1,420 599 1,024
Rate (Max) @ PT GPM 1,470 130 1,700 690 1,178
Norm suct press PSIG 39 63 63 75 72
Max suct press PSIG 89 132 132 135 122
Discharge press PSIG 475 152 85 135 480
Diff press PSI 436 89 22 60 408
Diff head Ft 1,332 207 86 200 1,290
NPSH avail Ft >15Ft >15Ft >15Ft >15Ft >15Ft
Hyd horse power 323 6.1 18.3 20.9 244
Corr/erros Sulph H2S H2S Sulph Sulph
Driver R (Note 2) S Motor Motor Motor Motor Turb
Turb Motor Turb Motor Note 1
Notes: 1.0. May be common spared with P106 A&B. 2.0. Driver R =Normally running, S =Normally
spare.
Table 17.1.10. Vessels
Item No T 301 D301
Service Syn Tower Ref drum
Type Vert Horiz
Dimensions: Feet Feet Feet Feet
Top Sect I/D
Top Sect T-T 13.5 6.5
Bot Sect I/D 74.0 20.0
Bot Sect T- 7.5 4.0
Overall T-T 31.0 6.0
Skirt 108.0(1) 20.0
15.0 In Struc
Internals:
Trays Top Sect
30 sieve None
Bot Sect
4Disc Don
Operating conditions:
Press PSIG
Temp
◦
F 55/67 50
230/650 90
(Cont.)
772 CHAPTER 17
Table 17.1.10. (Cont.)
Design conditions:
Press PSIG
Temp
◦
F 125 125
Vacuum PSIA 920 810
Min Temp
◦
F 7.0 7.0
Max Liquid Level Ft 90 90
8.0 N/A
Materials:
Shell C.S (2) C.S
(Corr allow) 0.125
0.125
Internals 11/13 Cr
(Corr Allow) 0.125
Trays Monel/Cr None
(Corr Allow) 0.125
Packing. N/A
Insulation:
Yes/No YES No
Stress relieved:
Yes/No No Yes
Notes: 1. Swage Sect 3.0 ft 2. Clad with 11/13 Cr.
Table 17.1.11. Air condensers/coolers
Item No E 301 E302
Service O/Head cond Gas oil Cooler
Type Forced Forced
Duty mmBtu/hr 157.373 9.941
Fluid Nap + H
2
O Gas oil
Temp
◦
F In Out In out
230 90 415 210
Liquid
M lbs/hr HC 422 88.8 88.8
H
2
O 58.2 nil nil
Sg@60
◦
F HC .607 .828
Visc @ 60 Cs HC .12 .52
Therm cond HC .07 .06
Specific Heat .73 .80
Btu/lb
◦
FHC
Vapour
M lbs/hr HC 422
H
2
O 58.2
Mol wt HC 96
Therm Cond .009
Specific Heat .41
Btu/lb
◦
F
Fouling HC factor —
Ambient Air Temp
◦
F60
Allowable psi 5.0 10.0
ECONOMICS 773
Table 17.1.12. Process specification for a thermal cracking heater/reactor
Item number: H 301 Thermal cracker heater
Overall heat duty: 370.895 mmBtu/hr.
Feedrate lbs/hr: 479,879 lbs/hr.
Temperature of feed in: 620
◦
F temperature of effluent: 920
◦
F.
Specific gravity of feed @ 60
◦
F: 0.960 (+650
◦
F TBP Kuwait Residue).
Effluent TBP and EFV curves are attached Figure 1.
Effluent Sg curves versus mid Bpt curve is attached Figure 2.
Feed conversion to gasoline of 390
◦
F cut point = 30 vol%.
Coil temperature profile (oil + steam) versus coil volume given as Figure 3 attached.
Steam (600 psig) injected at coil volume of 50 cuft and 150 cuft, respectively. Total steam to be injected
is 74,000 lbs/hr.
Outlet pressure of effluent to be 250 psig. This pressure to be maintained by downstream pressure control
valve (supplied by others).
Coil pressure drop to be 225 psi max.
is required for this item because besides being an oil heater it is also a cracking reactor.
In this function the design of the unit must be such as to allow the oil to be retained
for a specific period of time at the reaction temperature.
Coil tubes should be standard 4
11/13 Cr with wide radius bends. The firebox should
be constructed to heat the incoming feed to a temperature of about 870
◦
Finthe
first 150 cuft of coil. This should constitute the HEATER SECTION. The SOAKER
SECTION and crossover should be designed to heat the oil to 920
◦
F and retain
it at this temperature. The sections should be divided by a firebrick wall so that
temperatures on both sides of the wall can be controlled independently by burner
adjustments.
Table 17.1.13. Summary of accepted prices
Price $/unit
Pumps HHP BHP Pump Motor Turbine
P 106 A 323 430 606,826 489,082 –
106 B 606,826 – 503,903
P 301 A 6.1 10.1 14,253 19,563 –
301 B 14,253 19,563 –
P 302 A 18.3 28.1 39,655 39,126 –
302 B 39,655 – 40,312
P 303 A 20.9 32.2 45,441 48,908 –
303 B 45,441 48,908 –
P 304 A 244 325 458,648 – 453,513
Total 1,870,998 665,150 997,728
The above are accepted vendor prices for equipment delivered to
site, subject to updates
Total pumps and drivers = 3,533,884 $.
774 CHAPTER 17
Vendor may recommend that the convection side of the heater be used for additional
heater capacity or for steam generation or to remain unused if better temperature
control may result.
Vessels
r
T 301 syn tower
Shell and heads 1,766,810 $
Trays 1,590,129 $
Internals 176,681 $
Total 3,533,620 $
r
D 301 Reflux drum
Shell and heads 561,222 $
Lining 37,415 $
Internals 24,943 $
Total 623,580 $
Total vessel account = 4,157,200 $
Coolers and condensers
r
E 301 Overhead condenser
Unit including fans & structure = 1,627,540 $.
r
E 302 Gas oil cooler
Unit including fans = 243,196 $ (unit located in pipeway, no stand alone struc-
ture).
Total cooler & condenser account = 1,870,740 $
Heater/reactor
r
H 301 Thermal cracker heater
This unit will be field erected. Included in this account is the cost of fabricated material
delivered to site.