BPG Polysulphide Use

CONFIDENTIAL Best Practice Guide Polysulphide Use BPG MAT-06-I Revision 0 September 2005 Document Revision Log Number Rev 0 Issue Date: September 2005 Comments / Changes International Version of BPG MAT-06 This report has been classified as Confidential and is subject to US Export Control regulations and has been classified as ECCN EAR 99. This document is for use by the operating units constituting Shell Global Solutions and the companies with which they have a licence or a service agreement
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    CONFIDENTIAL   1 Best Practice GuidePolysulphide Use BPG MAT-06-IRevision 0September 2005Document Revision Log NumberIssueDate:Comments / Changes Rev 0September2005International Version of BPG MAT-06 This report has been classified as Confidential and is subject to US Export Control regulations and has beenclassified as ECCN EAR 99.This document is for use by the operating units constituting Shell Global Solutions and the companies withwhich they have a licence or a service agreement only, and is provided subject to the terms of the relevant licence or service agreements. It should not be applied in any specific situation without having obtained further clarification and advice from Shell Global Solutions. No member of the Royal Dutch/Shell Group of companies accepts any liability for the application of this document by anyone.Copyright of this document and the accompanying documentation is vested in one or more companies of theRoyal Dutch/Shell Group of companies. All rights reserved.© 2005 Shell Global Solutions International B.V. and Shell Oil Company.  CONFIDENTIAL2 Table of contents PAGE  SCOPE-------------------------------------------------------------------------------------41.0 POLYSULPHIDE DESCRIPTION, SAFETY AND HANDLING CONSIDERATIONS-----41.1 POLYSULPHIDE DESCRIPTION AND STABILITY--------------------------------41.2 SAFETY CONSIDERATIONS-----------------------------------------------------51.3 HANDLING CONSIDERATIONS--------------------------------------------------52.0 POLYSULPHIDE PROTECTION MECHANISM-----------------------------------------62.1 WET HYDROGEN SULPHIDE CRACKING----------------------------------------72.2 NH4HS CORROSION AND THE ROLE OF CYANIDES---------------------------82.3 EFFECT OF POLYSULPHIDE ON STABILITY OF FeS FILM----------------------92.4 EFFECT OF POLYSULPHIDE IN REMOVING HCN--------------------------------103.0 GUIDELINES FOR POLYSULPHIDE USE----------------------------------------------113.1 TEMPERATURE GUIDELINES----------------------------------------------------123.2 pH GUIDELINES-----------------------------------------------------------------123.3 DOSAGE RATE-------------------------------------------------------------------133.4 WETTING OF STEEL SURFACES-------------------------------------------------143.5 INJECTION METHOD-------------------------------------------------------------143.6 INJECTION POINT METALLURGY------------------------------------------------143.7 CHOICE OF INHIBITOR CATION------------------------------------------------153.8 CO-INJECTED WATER QUALITY-------------------------------------------------153.9 INJECTION SYSTEM CONFIGURATION-----------------------------------------163.10 LIMITS ON THIOCYANATE CONCENTRATION --------------------------------164.0 POLYSULPHIDE USE IN CATALYTIC CRACKING UNITS-----------------------------164.1 MAIN FRACTIONATOR OVERHEAD----------------------------------------------174.2 INTERSTAGE OF THE WGC------------------------------------------------------184.3 AFTERSTAGE OF THE WGC------------------------------------------------------194.4 RECTIFIED ABSORBER (RA) COLUMN------------------------------------------205.0 POLYSULPHIDE USE IN COKING----------------------------------------------------216.0 POLYSULPHIDE USE IN SOUR WATER STRIPPERS---------------------------------226.1 INTRODUCTION-----------------------------------------------------------------22  CONFIDENTIAL3 Table of contents (cont’d) PAGE  6.2 GUIDELINES FOR POLYSULPHIDE ADDITION TO SOUR WATERSTRIPPERS-----------------------------------------------------------------------236.3 SPECIAL CONSIDERATIONS ON MONITORING IN SOUR WATERSTRIPPER SYSTEMS-------------------------------------------------------------247.0 MONITORING POLYSULPHIDE EFFECTIVENESS------------------------------------247.1 SOUR WATER ANALYSES--------------------------------------------------------257.1.1 BASE-SOLUBLE IRON----------------------------------------------------257.1.2 COLOUR TEST FOR RESIDUAL POLYSULPHIDE-------------------------267.1.3 IRON CYANIDE “SPOT TEST”--------------------------------------------267.1.4 TOTAL SOLUBLE IRON (UNFILTERED)----------------------------------267.1.5 pH------------------------------------------------------------------------277.1.6 CHLORIDE, AMMONIA, SULPHUR---------------------------------------277.1.7 NON-ROUTINE CYANIDE ANALYSES------------------------------------277.2 DIRECT MONITORING OF HYDROGEN ACTIVITY-------------------------------277.2.1 INSERTION PROBES----------------------------------------------------- SHELL PROBE--------------------------------------------------- OTHER INSERTION PROBES-----------------------------------287.2.2 PATCH PROBES---------------------------------------------------------- ELECTROCHEMICAL-------------------------------------------- PRESSURE------------------------------------------------------ VACUUM--------------------------------------------------------297.2.3 PLACEMENT OF PROBES-------------------------------------------------297.2.4 READING OF PROBES---------------------------------------------------30References ---------------------------------------------------------------------------31APPENDIX A ANALYTICAL PROCEDURE----------------------------------------------41APPENDIX B IN-SITU GENERATION OF POLYSULPHIDE-----------------------------42APPENDIX C POLYSULPHIDE USE AT DPR CAT CRACKING UNIT-------------------44APPENDIX D POLYSULPHIDE USE AT MARTINEZ REFINERY CCU-------------------48APPENDIX E POLYSULPHIDE USE AT MARTINEZ REFINERY FLEXICOKER----------50APPENDIX F CORROSION OF AIR COOLERS AND POLYSULPHIDE USE ATMARTINEZ REFINERY SWS--------------------------------------------52  CONFIDENTIAL4 SCOPE This Best Practice Guide (BPG) covers various aspects of polysulphide technologyapplied to refinery sour water systems. Covered are properties of polysulphideimportant for its intended use, its activity as a film-forming inhibitor against carbonsteel corrosion, and its reactivity with cyanides. Also discussed are techniques to beconsidered in the practice of injection of polysulphide into vapour and water streams,and analytical methods for detecting whether polysulphide activity is adequate. Thisdocument compliments the Best Practice Guide MAT-13-I, Guideline to AmmoniumHydrosulphide Corrosion Control , to be issued. 1.0 POLYSULPHIDE DESCRIPTION, SAFETY AND HANDLINGCONSIDERATIONS1.1 POLYSULPHIDE DESCRIPTION AND STABILITY Polysulphides are metastable compounds of sulphur and ammonium or sodiumsulphide. The chemical formula is (NH 4 ) 2 S x or Na 2 S x , where S x represents a sulphurchain, with x ranging from 2-5. Activity increases with increasing sulphur in themolecule. Due to this activity, the polysulphide sulphur is able to act as a sulphidingagent in stabilization and enhancement of surface films, or to react with cyanide ion toform thiocyanate.The “active” sulphur atoms are those most likely to break off the sulphur chain of thepolysulphide molecule.For example, when the S5 ammonium polysulphide molecule decomposes, thefollowing occurs:(NH 4+ ) 2   ⋅ [S ⋅ S ⋅ S ⋅ S ⋅ S] -2   → (NH 4+ ) 2   ⋅ [S ⋅ S ⋅ S ⋅ S] -2 + S 0  Reactivity decreases significantly with decreasing sulphur on the molecule; S 5 and S 4  are most likely to break off the chain and are the most reactive, S 3 and S 2 react onlyslowly, and the sulphide sulphur [(NH 4+ ) 2 S -2 ] is not reactive at all. In the presentcontext “active” is considered the same as “reactive”; one standard test forpolysulphide “activity” of a sour water sample is to measure the conversion of a knownamount of cyanide added to the sample.Commercial ammonium polysulphide typically contains 40-50% (NH 4 ) 2 S x , 25%-35%ammonium hydroxide, NH 4 OH, and balance water. The ammonium hydroxide is usedto keep a high pH (pH ca. 11), necessary to prevent the (NH 4 ) 2 S 5 from breaking downinto lower sulphur species, (NH 4 ) 2 S 4 and (NH 4 ) 2 S 3 . NH 4 OH is preferred to other bases,so as not to introduce another cation (e.g., Na, K, etc.). ∗   ∗   An example of a commercial ammonium polysulfide formulation is 49%w(NH 4 ) 2 S x , 33%w NH 4 OH, and balance (18%w) water, according to theMaterials Safety Data Sheet (MSDS) from one manufacturer (HicksonKerley). S x is almost all S 5 , which has been verified by tests. Thus the totalsulfur in this formulation is [5 * MW S / MW (NH 4 ) 2 S 5 ] * 49% = (160/196)* 49% = 40%w. Since all sulfur in commercial polysulfide is S 5 andconsidered active, the active sulfur in this formulation is (128/196) * 49%w= 32%w (all sulfur but the sulfide sulfur), leaving the inactive sulfide sulfur(S -2 ) as 8%w.

Sindromul Laron

Jan 19, 2018
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