Applications of Aqueous Process Modeling to Petroleum Refinery Corrosion Control

Transcription

1 Applications of Aqueous Process Modeling to Petroleum Refinery Corrosion Control Jim Feather ExxonMobil Research & Engineering OLI 23 rd User Conference October 5-6, 2005

2 Presentation Outline Challenges with corrosion prediction Application Overview Example Applications Looking Ahead 2

3 Refinery Corrosion Analysis Corrosion control applications often focus on a particular section of a process unit Complex modeling tools aren t easily applied to routine operating envelope management Chemistry of corrosion environment remains complex Corrosion rates at complex conditions or across a process may not be easily predictable 3

4 Analyzers Bring Modeling Tools to the Corrosion Engineer OLI Analyzers are facilitating evaluations of conditions important to aqueous corrosion Aqueous phase dew point Aqueous phase condensation profile Application of corrosion control methods Changes in operating conditions readily evaluated for their impact on chemistry Effectiveness of corrosion control measures more readily evaluated 4

5 General Application of Analyzers to Corrosion Prediction Tools used in several ways to improve corrosion predictions Model chemistry and use other tools for corrosion rate predictions Model chemistry and compare with operating envelope constraints Direct estimation of corrosion rate with Corrosion Analyzer Assess the impact of changes or mitigation measures in the process on corrosion Water wash & chemical treatment programs Validation of 3 rd party corrosion inhibitor programs 5

6 Example Refinery Applications Common applications of interest Crude distillation unit overhead Acid condensate corrosion, water wash application FCCU overhead systems Sour water corrosion, Carbonate stress corrosion cracking, water wash application Coker overhead systems Sour water corrosion Hydrotreater reactor effluent systems Sour water corrosion, water wash application Estimation of corrosivity of environments without readily available corrosion data 6

7 Application to Crude Distillation Unit Overhead DESALTER NEUTRALIZER INHIBITOR CRUDE FEED Acidic Water Condensate Naphtha Acidic Water Condensate Kerosene Light Gas Oil Heavy Gas Oil Steam Reduced Crude 7

8 Conditions of Untreated Overhead 8

9 More Corrosive Conditions at Dewpoint 9

10 Est. Corrosion through Condensation Range 10

11 Impact of Neutralizer Addition in CDU Overhead 11

12 Effect of Neutralizer During Condensation 12

13 Controlling Corrosion in FCCU Overheads Carbonate stress corrosion cracking in non-stress relieved carbon steel piping is a growing problem May be associated with operations which increase NH 3 & CO 2 in overhead water while unit feed sulfur is being reduced by hydroprocessing Greatest likelihood of cracking occurs: ph < 9.0 and CO 3 > 100 ppm -2 ph between 8.0 and 9.0 and CO 3 > 400 ppm Direct measurement of carbonate is not straightforward General corrosion control also an important issue, often managed by water wash 13-2

14 Carbonate SCC 14

15 Conditions promoting SCC in FCCU s SCC Likely SCC Possible ph SCC Not Likely Log CO 3, ppm 15 From NACE C/90 Paper 206, Kemetz & Truax

16 Analyzer Used to Evaluate FCCU OH Analyzer used to model changes in operations with other model as input Outputs ph & carbonate ion concentration to support cracking likelihood assessment Benefit of corrosion & cracking control mitigation measures evaluated General corrosion balance corrosion vs operational issues with excess water Model impact of measures taken to reduce tendency for cracking Dilution ph adjustment 16

17 Looking Ahead Prediction of salt deposition a needed capability Corrosive NH 4 Cl salt forms in refinery processes Crude distillation Hydroprocessing FCCU s & Cokers Amine chloride salt important in neutralizer applications Corrosion predictions nice to have but modeling of deposition more important 17