Corrosion Potential - Refinery Overhead Systems

Transcription

1 Corrosion Potential - Refinery Overhead Systems Amit Patel Bartlesville, Oklahoma OLI Simulation Conference November 16-18, 2010 Whippany, NJ

2 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

3 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

4 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

5 Salt Hydrolysis MgCl 2 + 2H 2 O --> Mg(OH) 2 + 2HCl (g) CaCl 2 + 2H 2 O --> Ca(OH) 2 + 2HCl (g) NaCl + 2H 2 O --> NaOH + HCl (g) Salt Formation NH 3 (g) + HCl(g) <=> NH 4 Cl(s) R-NH 2 (g) + HCl(g) <=> R-NH 2 HCl(s) Corrosion NH 4 Cl(s) <=> NH 4 + (aq) + Cl - (aq) NH 4 + (aq) + Cl - (aq) <=> NH 3 (aq) + HCl(aq) Overhead Corrosion Overhead corrosion control Neutralizer Filming High inhibitor Water wash Overhead Temperature HCl Organic acids NH 3, H 2 S R-NH 2 R-NH 2 HCl(s) <=> R-NH 3 + (aq) + Cl - (aq) R-NH 3 + (aq) + Cl - (aq) <=> R-NH 2 (aq) + HCl(aq) Fe + 2HCl(aq) --> FeCl 2 + H 2 (Salt hydrolysis) NH 3, R-NH 2 Salts (MgCl 2, CaCl 2, NaCl) Organic acids NH 3, H 2 S R-NH 2 ** Similar crude contaminants in slop oil R-NH 2

6 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 Naphtha Line Corrosion High Corrosion Rate of in 6 O clock position

7 Equilibrium Salt Formation Salt will form No salt will form

8 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

9 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

10 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 NH 4 Cl/Amine-HCl salt point Water dew point Overhead modeling can improve overall unit performance and reliability

11 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 Vacuum Tower X-2 X-3 Vent Gas to Ejector/Liquid Ring Pump Hotwell Sour H20 Slop Oil

12 ph Iron, ppm Lab Analysis - Condensate /2/2009 2/16/2009 2/27/2009 4/15/2009 4/24/2009 5/4/2009 5/13/2009 5/26/2009 6/5/2009 6/15/2009 7/3/2009 7/20/2009 8/5/2009 8/18/2009 8/31/2009 9/17/ /2/ /14/ /2/ /18/ /9/ /21/2009 1/4/2010 Date ph Cl Fe Ammonia H2S ppm ppm ppm ppm 1/18/ /20/ /22/ /25/ /27/ /29/ /13/2010 1/22/2010 2/1/

13 Inputs Pressure: 5 mmhg Off-gas: 6.5 mscfh Distillate oil: 10 gpm Steam: lb/hr Contaminants: HCl 3 ppm NH 3 6 ppm H 2 S 10 ppm Salt point

14 Overhead Temperature, deg F Salt Point Fouling Potential 70 Pressure ~ 5 mmhg 50 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Results - calculated salt formation temperature was 129 deg F (close to the temperature where the tower overhead operates) Modeling shows high risk for NH 4 Cl salt formation in the main overhead line

15 bble coker Tower fractionator Overview would lead to equipment shutdown tts Lab Data DegF 6 DegF 0 TARGET 2 DegF to SCT l Lab Data 1 DegF 2 DegF 3 DegF id VT 5.3 MBPD sid 2469 BPD 0.0 MBPD id Lab 844 DegF t ms U240 Off-gas: FIC mmscfd 3531 BPD 57% 53% From 191 DegFCoke Drums s Resid Pressure: 50 psig Product: 4000 bpd Reflux: 8000 bpd Water: 6 gpm 20.5 MBPD H % HARGE 31.4 MBPD 7.9 MBPD 7.8 MBPD 7.8 MBPD 7.8 MBPD ced Control ON/OFF Adv Cont. 0 Adv Cont. 1 0 BPD 796 DegF 0 BPD 5.7 MBPD 0.00psi 0.43psi 0.29psi 0.02psi Case Study Coker Fractionator Concern: Increased pressure drop observed across the overhead fin fan exchanger of the 48 psig 1 5 D DegF E-205A/B/C E-205A/B/C FIC783 63% 9.0 MBPD 151 DegF 101 DegF What is causing the plugging across the fin fan tubes? E-206 FIC1780 E-214 E % MBPD 9 45% 553 DegF 640DegF FIC BPD 39% 16 G DegF 759DegF 46% 29% 711 DegF 79 psig 71 psig RECYCLE RATIO: NO DATA FIC MBPD FIC BPD 3 % 337 BPD 52% Reflux 228 DegF 606 DegF 8 % G-217 E212 37% LIC747 48% 1802 lb/hr FIC788 70% E % (start-up LIC to tray 20) 1197 lb/hr FIC789 60% 34 psig F-203 LIC750 62% G-102 D-207 D-208 PIC202 96% 2% 33 46% % LIC202 DegF G % 679DegF G MBPD TIC307 Coil Charge to B MMSCFD 32psig FIC794 37% To Product storage Sour water E-208 H-5 0 % HVGO NO MBPD DATA E MBPD Contaminants: Cl- NH 3 H 2 S LIC755 21% E-213A/B G DegF E-511 LIC792 38% 1.7 MMSCFD 16.7 MMSCFD Wild Na LCGO 420DegF LCGO Lab E % 465 LCGO Predict 95% DegF 95% 800 FBP DegF 1 ppm 6100 ppm 8800 ppm 3088 BPD 0 MBPD (Start-u 0 FIC776 HCGO Lab BPD 10% % % 95% 1000 PIC691 FBP BPD HC FIC BPD(low) 2469BPD 2.6 MBPD(high 71% FIC922 Mix 199 BPD De

16 Very low scaling tendency for ammonium bisulfide (NH 4 HS) in the coker fractionator overhead NH 4 HS salt formation unlikely in this temperature region Condensing water water dew point 192 deg F

17 Salt point Performed survey calculation (vary chloride composition) Condensing water NH 4 Cl 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 285 F 141 C 185 F 85 C 100 F To accumulator Fin Fan

18 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

19 Acknowledgments Eric Vetters, ConocoPhillips Emily Amizich, ConocoPhillips Matt Keating, ConocoPhillips AJ Gerbino, OLI Systems Jim Berthold, OLI Systems Pat McKenzie, OLI Systems