corrosion potential - refinery overhead...
TRANSCRIPT
Corrosion Potential -
Refinery Overhead Systems
Amit Patel
Bartlesville, Oklahoma
OLI Simulation Conference
November 16-18, 2010
Whippany, NJ
• 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
Agenda
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
- Leaks in equipment develop leading to Health and
Safety issues
- Unscheduled shutdown of equipment results in Lost
Production
Amine hydrochlorides are corrosive
salts formed from neutralizer
application and tramp amines
NH3, R-NH2
Salts (MgCl2,
CaCl2, NaCl)
Organic acids
NH3, H2S
R-NH2
(Salt hydrolysis)
** Similar crude
contaminants in slop oil
HCl
Organic acids
NH3, H2S
R-NH2
R-NH2
Neutralizer
Filming
inhibitor Water wash
Overhead corrosion control
High
Overhead
Temperature
Salt Hydrolysis
MgCl2 + 2H2O --> Mg(OH)2 + 2HCl (g)
CaCl2 + 2H2O --> Ca(OH)2 + 2HCl (g)
NaCl + 2H2O --> NaOH + HCl (g)
Salt Formation
NH3(g) + HCl(g) <=> NH4Cl(s)
R-NH2(g) + HCl(g) <=> R-NH2 HCl(s)
Corrosion
NH4Cl(s) <=> NH4+(aq) + Cl
- (aq)
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
Overhead Corrosion
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
No salt
will form
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
• Temperature
• Pressure
• Water Analysis
• Properties of hydrocarbons
• Neutralizer
Output
• Water dew point
• Salt Point (ammonia, amine)
• Aqueous pH
• Phase behavior
OLI Equilibrium Thermodynamic Model
– 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
How can overhead modeling help ?
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 ?
X-3
Slop OilSour H20
X-1
Motive Steam
X-2
Vacuum Tower
Hotwell
Vent Gas to Ejector/Liquid Ring Pump
Lab Analysis - Condensate
0
1
2
3
4
5
6
7
2/2/
2009
2/16
/200
9
2/27
/200
9
4/15
/200
9
4/24
/200
9
5/4/
2009
5/13
/200
9
5/26
/200
9
6/5/
2009
6/15
/200
9
7/3/
2009
7/20
/200
9
8/5/
2009
8/18
/200
9
8/31
/200
9
9/17
/200
9
10/2
/200
9
10/1
4/200
9
11/2
/200
9
11/1
8/200
9
12/9
/200
9
12/2
1/200
9
1/4/
2010
1/13
/201
0
1/22
/201
0
2/1/
2010
pH
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Iro
n, p
pm
Date pH Cl Fe Ammonia H2S
ppm ppm ppm ppm
1/18/2010 6.19 2.4 0.12 4 6
1/20/2010 6.27 2.4 0.1 6 10
1/22/2010 6.32 2.4 0.08 6 10
1/25/2010 6.36 2.4 0.07 6 10
1/27/2010 6.28 2.4 0.1 5 8
1/29/2010 6.28 2.4 0.09 6 8
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
50
70
90
110
130
150
170
Feb-0
9
Mar
-09
Apr-0
9
May
-09
Jun-
09
Jul-0
9
Aug-0
9
Sep-0
9
Oct-0
9
Nov
-09
Dec
-09
Jan-
10
Feb-1
0
Ov
erh
ea
d T
em
pe
ratu
re,
de
g F
Salt Point
Fouling
Potential
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
Pressure ~ 5 mmHg
What is causing the plugging across the fin fan tubes ?
From Coke Drums
To Product storage
Sour water
E-205A/B/CE-205A/B/C
D206 Bubble Tower Overview
48
psig
284 DegF E-206
37%
62%F-203
Wild Naphtha to Light Ends4.2
MBPD
FIC794LIC202
37%
PIC202
34
psig
151 DegF 101 DegF
96%
1
5
G-102
FIC783
9.0 MBPD
63%
2%
G50116.3MMSCFD
32psig 16.7
MMSCFD
E-501
1.7 MMSCFD
E-511FIC1547
3531 BPD
53%
57%
6
9 45%
D-206
D-207
D-208
LIC747
48%
10
G-216
FIC1780
2461BPD
39%
FIC1780
12.3
MBPD39%
E-214 E-207
553 DegF
G-222
46%
8.3
MBPD
LIC792
38%
E-208
E-209
70%
1802 lb/hr
FIC788
LCGO to Production
60%
1197 lb/hr
FIC789
16
BT Diesel to SCT
LIC750
62%
46%
711 DegF
17
19
20
532
DegF679
DegF
DegF420
DegF420
FIC782
1151
BPD3 %
337
BPD
79 psig
71
psig
FIC781
23.7MBPD
29%
606 DegF
8 %
E-211
E212
G-217
G-227
54%
LIC755 21%
TIC307
0 %H-5
HCGO to tankage
3088 BPD
0 MBPD
(Start-up)
213DegF
LCGO Lab Data
95%
10%
FBP
465 DegF
783 DegF
861 DegF
95% TARGET
HCGO Lab Data
95%
10%
FBP
646 DegF
979 DegF
1158DegF
95% TARGET
BT Diesel Lab Data
95%
10%
FBP
321
612
713
DegF
DegF
DegF
Mixed Resid TK201
E-213A/B
Decant Oil
FIC777
71%
0 %
FIC776
0 BPD
2469BPD
FIC922
3 %
199 BPD
PFB from U240
VT Bottoms Resid
Coke Drums
20.5 MBPD
0 BPD
Cond. Pot
796 DegF
759DegF
1448 BPD(low)
2.6 MBPD(high)
191 DegF
U267 Resid
To U200 VT 5.3
To Tank
MBPD
0.0MBPD
10% 844 DegF
U267 Resid Lab
Mixed Resid 2469 BPD800
1000
Stab. Botts Lab Data
90%
10%
FBP
82 DegF
326 DegF
432 DegF
90% TARGET340
52%
MBPD
5.7H-204
G-218 G-213
Coil Charge to B-202
12%(start-up LIC to tray 20)
702 DegF
228 DegF
0.00psi
0.43psi
0.29psi
0.02psi756DegF
640DegF
PIC691
HCGO to U246
1127BPD
71 %
HVGO
NO DATAMBPD
57409TK201 VOL
782
LCGO Predict
DegF
COKER CHARGE
A1 Coil
A2 Coil
B1 Coil
B2 Coil
31.4 MBPD
7.9 MBPD
7.8 MBPD
7.8
7.8
MBPD
MBPD
RECYCLE RATIO:NO DATA
0 BPD
33
LCGO Adv Cont.HCGO Adv Cont.
Andvanced Control ON/OFF
01
Reflux
Contaminants:
Cl- 1 ppm
NH3 6100 ppm
H2S 8800 ppm
Pressure: 50 psig
Off-gas: 12 mmscfd
Product: 4000 bpd
Reflux: 8000 bpd
Water: 6 gpm
Case Study – Coker Fractionator Concern: Increased pressure drop observed across the overhead fin fan exchanger of the
coker fractionator would lead to equipment shutdown
Very low scaling tendency for
ammonium bisulfide (NH4HS) in
the coker fractionator overhead
• NH4HS salt formation unlikely in
this temperature region
• water dew point 192 deg F
Condensing water
Performed survey
calculation (vary chloride
composition)
NH4Cl salt can form when
HCl concentration gets
near 213 ppm in the
system
- salt formation temperature
199 deg F
- water dew point 192 deg F
Distillate wash caused
spike in overhead
chlorides
From
overhead
To accumulator 285 F
141 C
185 F
85 C
100 F
Fin Fan
Salt point
Condensing water
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