2. CNC is an ammonia plant which uses the Kellogg
Advanced Ammonia Process (KAAP), is licensed by The
Kellogg Brown & Root Company and managed and
operated by Industrial Plant Services Limited (IPSL).
Commission in June 2002 at a cost of US 300 million
dollars.
Manufactures anhydrous ammonia at a temperature of -
28ᵒF
By-product carbon dioxide from ammonia processes (0.7
million tons of CO2) is sold annually to other plants in the
Point Lisas Industrial Estate for use in methanol and urea
production.
3.
4. To evaluate the performance of the 114-C Methanator
Feed/Effluent Exchanger and determine its efficiency.
To conduct a possible redesign for the 114-C exchanger.
To estimate the capital investment required and a
payback period for the implementation of the new
exchanger.
5.
6. The 114-C exchanger is experiencing fouling in the form
crystallization and its heat transfer capacity is reduced.
Benfield solution in the CO2 Absorber column is foaming
and being carried over to the Absorber Knockout Drum.
The Knockout Drum in turn is not adequately removing
the entrained Benfield solution from the process gas,
hence Benfield is entering into the 114-C exchanger.
7.
8. Class – R – severe requirements of petroleum and related
processing applications
Type - NEN
9. Shell O.D. is 1.27 meters and made from SA 240 304
(stainless steel).
Shell outlet nozzle: 20 inch made from SA 240 304, 585
psig and 160 to 250 °F .
Shell inlet nozzle: 24 inch and also fashioned from SA
240 304, 585 psig and 590 to 795 °F.
The hot channel/tube side inlet nozzle: 20 inch and built
from SA 240 304, 585 psig and 660 to 800 °F.
The cold channel/tube side outlet nozzle: 20 inch, made
from SA 516 70 Normalized Carbon Steel, 585 psig and
428 °F.
10. Tubes: straight, 3519 tubes, made from SA 240 304,
12.192 meters long, and O.D of 12.7 mm.
Tubes are placed at flow angle of 30°, triangular pitch.
Baffles: 7 baffles, constructed from SA 240 304,
horizontal segmental type, 19% cut and placed 1.66
meters apart to decrease the pressure drop on the shell
side.
11. Baffles serve two important functions:
i. support the tubes in the proper position; prevents
flow induced vibration in the tubes which can quickly
lead to tube failure.
ii. creates turbulence; guides the shell side flow back and
forth across the tubes increasing the velocity and
therefore the heat transfer coefficient.
12. Stationary Tubesheet: 2 grooves, expand and seal
welded to the shell, heads are bolted to the tubesheet.
Expansion joint: allows thermal expansions and prevents
leakage through the exchanger.
A removable bonnet is provided to facilitate tube
cleaning.
Impingement plate: under the shell side inlet nozzle
where the shell side gas fluid enters; needed where the
shell side fluid can cause the tubes to vibrate which can
cause tube failure due to fatigue and/or wear where the
tubes strike each other or contact the baffles.
13. Mainly stainless steel is used to fabricate this exchanger
since stainless steel does not corrode easily.
Tensile strength: greater than 515 MPa
Yield strength: 205 Mpa
Modulus of elasticity: 210 Gpa
Percent Elongation: 40%
Brinell hardness: 201.
SA 240 304 contains: 0.05% carbon, 2% manganese,
0.045% phosphorous, 0.03% sulphur, 0.75% silicon, 18
to 20% chromium, 8 to 10.5% nickel and 0.1% nitrogen.
14. HYSYS was used to model the stream data which showed
that the existing 114- exchanger is performing according
to specifications, with the problem being a reduction in
heat transfer.
Rated / Design Performance Existing Overall Performance Difference
Duty / Heat exchanged
(k)W
21982.4089
Duty / Heat exchanged
(k)W
19499.9002 -2482.5087
Equivalent Overall U
(W/ m² °C)
502.5263
Equivalent Overall U
(W/ m² °C)
518.6125 +16.0862
Shell Side Pressure Drop (kPa) 27.5790 Shell Side Pressure Drop (kPa)
15.1709
(clean)
16.9914
(fouled)
-12.4081
(clean)
-10.5876
(fouled)
Tube Side Pressure Drop (kPa) 27.5790 Tube Side Pressure Drop (kPa) 19.7609 -7.8181
15. Preliminary designs for both Kern and Bell required
similar calculations as shown below.
Logarithmic Mean Temperature Difference, ∆TLM°(C) 31.9386
Heat load, Q (kW) 19499.9002
Guessed heat transfer rate, U (W/m2°C) 358.1404
Number of tubes needed, Nt 3519.0000
Bundle diameter, Db (mm) 979.7576
Shell diameter, Ds (mm) 1270.0000
Baffle spacing, lB (mm) 1523.7500
Tube pitch, pt (mm) 15.8750
16. Further calculations however, show that Bell’s design
considers leakage across the exchanger whereas
Kern does not.
KERN’S DESIGN
Tube side coefficient, hi (W/m² °C) 1808.8043
Shell side coefficient, hs (W/m² °C) 1263.0613
Overall coefficient, Uo (W/m² °C) 518.6033
Pressure drop on tube side, ∆Pt (kPa) 19.7594
Pressure drop on shell side, ∆Ps (kPa) 65.6053
BELL’S DESIGN
Ideal bank coefficient, hoc 1707.7846
Tube row correction factor, Fn 1.0500
Window correction factor, Fw 1.1300
Bypass correction, Fb 0.5931
Leakage correction, FL 0.7851
Shell side coefficient, hs (W/m2°C) 943.5578
Ideal tube bank pressure drop, ∆Pi (N/m2) 4515.4535
Pressure drop in cross flow zone, ∆Pc (N/m2) 559.1909
Pressure drop in window zone, ∆Pw (N/m2) 1389.5647
Pressure drop in end zone, ∆Pe (N/m2) 1045.9348
Number of baffles, Nb 6.9685
Clean condition pressure drop, ∆Ps (kPa) 15.1126
Fouled condition pressure drop, ∆Ps (kPa) 16.9261
17. The existing exchanger is capable of performing its rated
design duty.
Exchanger’s problem is the reduced area for heat
transfer due to the fouling aspect of the unit, and not
the unit’s actual design.
Mechanical layout and design of the exchanger including
the material of construction is suitable for preheating
the methanator feed and cooling the methanator
effluent stream.
18. Excess foaming of Hot Potassium Carbonate solution
upsets the liquid flow in the affected tower and causes
solution carryover into units downstream.
Solution loss into the process stream, if not removed by
the 102-F2 knockout drum, can result in plugging of the
114-C Methanator Feed/Effluent Exchanger and
deactivation of the Methanator (106-D) catalyst.
Clean Hot Potassium Carbonate solution does not foam.
19. Approximate composition of the feed entering the
absorber column
Hydrogen: 15,610.00 lb-mol/hr
Nitrogen: 5,737.95 lb-mol/hr
Methane: 96.01 lb-mol/hr
Argon: 69.06 lb-mol/hr
CO: 78.73 lb-mol/hr
CO2: 4,651.03 lb-mol/hr
96.01 lb-mol of methane enters the absorber every hour,
which is equivalent to 2,304.96 lb-mol per day.
20. Over time the Benfield solution accumulates inside the
exchanger, leading to heat resistance which reduces the
exchanger ability to transfer heat.
Fouling has an economic impact on overall production
rate.
HPC solvent can cause corrosion problems in carbon
steel piping and equipment and also precipitate or
crystallize in downstream equipment, notably the 114-C
heat exchanger.
21. Rich Benfield solution can crystallize at temperature as
high as 147°F while lean solution can ‘Freeze’ at 86°F.
It should be noted that the process gas stream exiting
the top of the absorber with traces of Benfield is at a
temperature of 158°F.
Benfield solution at approximately 30% potassium
bicarbonate boils between 221 to 241 °F and freezes
between -5 to 62°F.
22. Major detrimental effects: loss of heat transfer as
indicated by charge outlet temperature decrease and
pressure drop increase.
Other detrimental effects: blocked process pipes, loss of
heat transfer and subsequent decrease of charge outlet as
a result of the low thermal conductivity of the fouling
layer.
As a result of this lower thermal conductivity, the overall
thermal resistance to heat transfer is increased, and the
effectiveness and thermal efficiency of the heat exchanger
is reduced.
23. Consequent buildup of fouling layer(s) causes the cross
sectional area of the shell and tubes to be reduced.
There is also an increase in surface roughness which
increases the frictional resistance to flow.
Increased frictional resistance leads to an increase in the
pressure drop across the heat exchanger; affects the flow
rate through the exchanger.
One estimate puts the losses due to fouling of heat
exchangers in industrialized nations to be about 0.25% to
30% of their GDP.
24. When fouling occurs, the temperature of the heating fluid
must rise if the same amount of heat is to be transferred
through the tubes.
This temperature rise must be associated either with an
increase in the total energy input to the process or a
reduction in production rate, both of which represent a
cost incurred due to fouling.
Chemical cleaning is faster than mechanical cleaning, it
does not damage the surfaces, it reaches inaccessible
areas, less labor intensive and can be done on-site.
25. Operating procedures necessary to shutdown and clean
the 114-C usually takes 3 days.
1st day: depressuring and cooling
2nd day: opening and inspection
3rd day: washing and cleaning
We recommend that another 114-C exchanger be
installed in parallel to the existing exchanger.
Normally, cleaning of the exchanger is scheduled around
plant shutdown. With a parallel system, production can
remain online with no upset to the plant.
26. New exchanger can be designed exactly like the 114-C
since this exchanger is adequately designed.
Double block and bleed valving system should be installed
for the parallel system to work.
A Diaphragm Control Valve placed at the center of the
double block Gate Valves, and the bleed valve (via piping)
located between the double block and the control valve.
All valves should be constructed from their respective
materials as dictated by the piping onto which they will be
installed.
27.
28. A second Knockout Drum (102F-2B) can be used when the
initial (102-F2) Knockout Drum’s demister pad is saturated
and cannot perform according to design.
Implementation of a parallel knockout system will aid in
the removal of entrained Benfield solution in the P.G.
With a parallel system production losses/downtime due
to the 114-C exchanger fouling are minimized.
29. Again, a double block and bleed valving system should be
installed on the new and existing piping arrangement
along the two piping inlets to the exchanger and the two
piping outlets from the exchanger.
A Diaphragm Control Valve should be placed at the center
of the double block Gate Valves. Drainage piping should
be positioned between the double block and the control
valve to accommodate a bleed valve.
All valves should be constructed from SA 240 304
Stainless Steel materials and sized in accordance with the
piping onto which they will be installed.
30.
31. 114-C in 2012: Capacity = 17,581.0000 ft2 Cost = $ 10,000,000
New 114-C in 2015: Capacity = 17,581.0000 ft2 Cost = $ 1,500,000 USD
Cost of new 114-C in 2015 = Cost in 2012 𝑥
𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑖𝑛 2015
𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑖𝑛 2012
0.6
Cost of new 114-C in 2015 = $ 10,000,000 𝑥
17,581.0000 𝑓𝑡2
17,581.0000 𝑓𝑡2
0.6
Cost of new 114-C in 2015 = $ 1𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎. 𝟎𝟎
32. FIXED CAPITAL INVESTMENT FOR PROCESS PLANT
COMPONENTS COST (TTD)
Purchased equipment (delivered) $ 10,000,000.00
Purchased equipment installation 35% $ 3,500,000.00
Instrumentation (installed) 25% $ 2,500,000.00
Piping (installed) 28% $ 2,800,000.00
Electrical (installed) 9% $ 900,000.00
Buildings (including services) 10% $ 1,000,000.00
Yard improvements 6% $ 600,000.00
Service facilities (installed) 45% $ 4,500,000.00
Land 0% $ -
TOTAL DIRECT COST $ 25,800,000.00
Engineering and supervision 30% $ 3,000,000.00
Construction expenses 31% $ 3,100,000.00
TOTAL DIRECT AND INDIRECT COST $ 31,900,000.00
Contractor's fees 5% $ 1,595,000.00
Contingency 10% $ 3,190,000.00
FIXED CAPITAL INVESTMENT $ 36,685,000.00
33. Payback period for the execution of a new 114-C was not
prepared; CNC was unable to provide us with a plant
throughput when the 114-C is both on-line and off-line.
PAYMENT FOR CAPITAL INVESTMENT / LOAN
COMPONENTS COST (TTD)
Loan $ 36,868,000.00
Interest on Loan 12 %
Interest on Loan to be repaid $ 4,402,200.00
Total monies to be repaid $ 41,087,200.00
34. Every 5 to 10 years the exchangers must be changed as the asset has
failed.
By doing parallel exchangers and able to clean this will mean exchangers
can be changed out once every 30 years
This means a savings of over $10,000,000.TTD savings
With RCM maintenance strategy savings can be 4 fold and plant tonnage
will be more efficient and make 10% more over the life of the catalyst
Hence increase in profit by 4%
Repayment in less than 60 days
35. Existing 114-C exchanger is adequately designed; does not
need to be replaced.
Benfield carryover and fouling must be reduced or eliminated
to maximize the throughput of the plant.
Bell’s design proved to be more feasible in designing an
additional parallel exchanger.
Parallel systems (102-F2B & 114-CB) should be employed to
reduce Benfield carryover, and maximum heat transfer across
the exchanger and thus increase ammonia production.
Increase availability of the asset as it wont reach a functional
failure.
