Corrosion Potential Refinery Overhead Systems
Amit Patel
Bartlesville, Oklahoma
OLI Simulation Conference
November 16-18, 2010
Whippany, NJ
Agenda
• Corrosivity – Amine Hydrochlorides
– Impact of overhead corrosion
• Overhead Corrosion
– Crude Unit Operation
– Controlling Overhead Corrosion
– Electrolyte Modeling
• Case Study - Use of OLI Stream Analyzer
– Vacuum Tower
– Coker Fractionator
• Summary
Outlet line on
crude vs. ovhd
exchanger
Note heavy build
up of salts and
corrosion products
Salts and corrosion products flowed out of exchanger where
corrosion was occurring
Corrosivity - Amine Hydrochlorides
Amine hydrochlorides are corrosive
salts formed from neutralizer
application and tramp amines
- Leaks in equipment develop leading to Health and
Safety issues
- Unscheduled shutdown of equipment results in Lost
Production
Overhead Corrosion
Salt Hydrolysis
MgCl2 + 2H2O --> Mg(OH)2 + 2HCl (g)
CaCl2 + 2H2O --> Ca(OH)2 + 2HCl (g)
NaCl + 2H2O --> NaOH + HCl (g)
Overhead corrosion control
Neutralizer
Filming
inhibitor
High
Overhead
Temperature
Salt Formation
NH3(g) + HCl(g) <=> NH4Cl(s)
R-NH2(g) + HCl(g) <=> R-NH2 HCl(s)
HCl
Organic acids
NH3, H2S
Corrosion
NH4Cl(s) <=> NH4+(aq) + Cl- (aq)
R-NH2
NH4+(aq) + Cl-(aq) <=> NH3(aq) + HCl(aq)
R-NH2 HCl(s) <=> R-NH3+(aq) + Cl- (aq)
R-NH3+(aq) + Cl-(aq) <=> R-NH2(aq) + HCl(aq)
Fe + 2HCl(aq) --> FeCl2 + H2
(Salt hydrolysis)
NH3, R-NH2
Salts (MgCl2,
CaCl2, NaCl)
Organic acids
NH3, H2S
R-NH2
R-NH2
** Similar crude
contaminants in slop oil
Water wash
Naphtha Line Corrosion – High
Corrosion Rate of in 6 O’clock position
Liquid Amine Salts Corroding the Bottom
Side of the 18-inch Carbon Steel Pipe
Leaving the Top Pump-around Draw off of
the Crude Tower
Equilibrium Salt Formation
Salt will
form
No salt
will form
Controlling Overhead Corrosion
– Reduce contaminant levels
• Improve desalting performance, desalter wash
water quality, re-route slop streams
– Increase tower overhead temperature
– Water washing overheads
– Inject neutralizer
• Change overhead chemistry
Benefits of different corrosion control options can be evaluated
using a good overhead system model
Refining Overheads – Electrolyte Modeling
Input
• Flows
Output
• Temperature
• Water dew point
• Pressure
• Salt Point (ammonia, amine)
• Water Analysis
• Properties of hydrocarbons
• Neutralizer
• Aqueous pH
• Phase behavior
OLI Equilibrium Thermodynamic Model
How can overhead modeling help ?
– Proper selection of amines for overhead system
• Different amines form salts at different temperatures
• Neutralizer amines exhibit differences in ability to control pH at
water dew point
• Model can help analyze effect of various neutralizer amines
– Troubleshoot events
• Did changes in unit operation create a corrosive environment ?
• Identify significant shifts in unit operation
– NH4Cl/Amine-HCl salt point
– Water dew point
Overhead modeling can improve overall unit performance and reliability
Case Study – Vacuum Tower
Concern: Is there ammonium chloride salt formation potential in the
main overhead line of the vacuum tower ?
Motive Steam
X-1
X-2
Vacuum Tower
X-3
Vent Gas to
Ejector/Liquid Ring Pump
Hotwell
Sour H20
Slop Oil
2/
2/
2
2/ 00
16 9
/2
2/ 009
27
/2
4/ 00
15 9
/2
4/ 009
24
/2
0
5/ 09
4/
2
5/ 00
13 9
/2
5/ 009
26
/2
0
6/ 09
5/
20
6/
15 09
/2
0
7/ 09
3/
2
7/ 00
20 9
/2
0
8/ 09
5/
2
8/ 00
18 9
/2
8/ 009
31
/2
9/ 00
17 9
/2
10 00
/2 9
/
10 200
/1
4/ 9
2
11 00
/2 9
/
11 200
/1
8/ 9
2
12 00
/9 9
12 / 20
/2 09
1/
20
1/ 09
4/
2
1/ 01
13 0
/2
1/ 010
22
/2
0
2/ 10
1/
20
10
pH
7
0.30
6
0.25
5
4
0.15
3
2
0.10
1
0.05
0
0.00
Date
pH
1/18/2010
1/20/2010
1/22/2010
1/25/2010
1/27/2010
1/29/2010
6.19
6.27
6.32
6.36
6.28
6.28
Cl
ppm
2.4
2.4
2.4
2.4
2.4
2.4
Fe
ppm
0.12
0.1
0.08
0.07
0.1
0.09
Ammonia
ppm
4
6
6
6
5
6
H2S
ppm
6
10
10
10
8
8
Iron, ppm
Lab Analysis - Condensate
0.20
Inputs
Pressure: 5 mmHg
Off-gas: 6.5 mscfh
Distillate oil: 10 gpm
Steam: 11600 lb/hr
Contaminants:
HCl 3 ppm
NH3
6 ppm
H2S 10 ppm
Salt point
Overhead Temperature, deg F
170
150
Salt Point
130
110
Fouling
Potential
90
70
Pressure ~ 5 mmHg
Fe
b10
Ja
n10
ec
-0
9
D
ov
-0
9
N
ct
-0
9
O
Se
p09
Au
g09
Ju
l-0
9
Ju
n09
09
M
ay
-
09
Ap
r-
09
M
ar
-
Fe
b09
50
Results
- calculated salt formation temperature was 129 deg F (close to the temperature where
the tower overhead operates)
Modeling shows high risk for NH4Cl salt formation
in the main overhead line
Case Study – Coker Fractionator
Concern: Increased pressure drop observed across the overhead fin fan exchanger of the
E-501
ubblecoker
Towerfractionator
Overview would lead to equipment shutdown
1.7 MMSCFD
otts Lab Data
2 DegF
26 DegF
40 TARGET
32 DegF
151 DegF
48
psig
Pressure: 50 psig
284 DegF
1
57%
3531 BPD
sid
VT 5.3 MBPD
esid 2469 BPD
71 %
0.0 MBPD
0.43psi
MBPD
MBPD
MBPD
MBPD
MBPD
0.29psi
0.02psi
796 DegF
ms Resid
BPD
45%
553 DegF
48%
39%
G-216
FIC781
23.7MBPD 606 DegF
17
19
0
Wild Na
MBPD
37%
LIC792
To Product storage
MBPD
LCGO Lab
10% 465
LCGO Predict 95% 783
95% 800
782 DegF
FBP 861
420DegF
Sour water E-209
D-207
46%
532
DegF
E-211
LIC750
E-208
G-222
213DegF
Cl-
62%
8%
1151
3 % BPD
E212
1197 lb/hr
FIC789 60%
D-208
1 ppm
H-5
0%
FIC776 HCGO Lab
10% 646
95% 979
0%
95% 1000
FBP 1158
PIC691
6100 ppm
0 BPD
HS
8800 ppm
54%
679DegF
HVGO
2
NO MBPD
DAT A
LIC755
21%
E-213A/B
G-217
0 MBPD
(Start-u
NH3
759DegF
RECYCLE RATIO:
NO DATA
3088 BPD
Contaminants:
T IC307
FIC782
LCGO
420DegF
38%
1127BPD
HC
BPD
20.5 MBPD
52%
12%
(start-up LIC to tray 20)
G-227
FIC777
What is causing the plugging across the fin fan tubes ?
71%
H-204
E-511
4.2
1802 lb/hr
FIC788 70%
29%
46%
711 DegF
79 psig
FIC794
LIC747
FIC1780
2461BPD
16
16.7
MMSCFD
8.3
71
337
psig BPD
ums
0
9
20
191 DegFCoke Drums
From
m U240
6
756DegF
62%
LIC202
G-102
FIC1780
E-214 E-207
12.3
39% MBPD
10
nced Control ON/OFF
Adv Cont.
0
O Adv Cont.
1
ot
D-206
2%
37%
63%
640DegF
sid Lab
844 DegF
CHARGE 31.4
l
7.9
l
7.8
l
7.8
l
7.8
16.3MMSCFD G501
32psig
33
9.0 MBPD
Reflux
Product: 4000 bpd
el Lab Data
Reflux: 8000 bpd
21 DegF
12 DegF Water: 6 gpm
0.00psi
13 DegF
96%
F-203
228 DegF
FIC783
5
53%
34
psig
E-206
FIC154712 mmscfd
Off-gas:
to SCT
PIC202
101 DegF
E-205A/B/C
E-205A/B/C
5.7
MBPD
Coil Charge to B-202
1448 BPD(low)
2.6 MBPD(high
Mix
FIC922
199 BPD
De
2469BPD
Very low scaling tendency for
ammonium bisulfide (NH4HS) in
the coker fractionator overhead
• NH4HS salt formation unlikely in
this temperature region
Condensing water
• water dew point 192 deg F
Performed survey
calculation (vary chloride
composition)
Salt point
NH4Cl salt can form when
HCl concentration gets
near 213 ppm in the
system
- salt formation temperature
199 deg F
Condensing water
- water dew point 192 deg F
Distillate wash caused
spike in overhead
chlorides
From
overhead
285 F
185 F
141 C
85 C
Fin Fan
100 F
To accumulator
Summary
Corrosion never takes vacation
– Health and Safety issues and LPO
Ammonia/amine salts are major contributors to refining unit overhead
corrosion
Modeling the crude unit overhead system can improve overall unit
performance and reliability
– Troubleshooting tool
– Unit monitoring
OLI Stream Analyzer has enabled us to model potential for salt
formation in refining overhead systems
Understanding when liquid amine salts form via ionic models is
important to reliable unit operation
– Need better understanding of properties that best describe formation of
amine salts
Acknowledgments
– Eric Vetters, ConocoPhillips
– Emily Amizich, ConocoPhillips
– Matt Keating, ConocoPhillips
– AJ Gerbino, OLI Systems
– Jim Berthold, OLI Systems
– Pat McKenzie, OLI Systems