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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsOil Refinery Co...Oil Refinery Co...Spent/Fresh Caustic - RefinerySpent/Fresh Caustic - Refinery
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11/21/2007 9:00 AM
 
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I'd like help on the following issue. We are about to install a new spent + fresh caustic drum in the refinery. The caustic will be added to crude. The spent caustic originates from LPG washing (Reformer) and is expected to contain sulfides. The fresh caustic is 15Be (10-11%wt). Water will be added to dillute the sollution up to 3-4Be. I would like to know whether I can use Fresh Water for dillution or I have to use DemiWater (that is what we already do)? Is there any problem with salts contained in Fresh Water in caustic environment? Furthermore is there any restriction to the amount of spent caustic that I can add to fresh caustic? Drum and pipping is CS. Pipping is steam traced and insulated. The positive displacement pump adding caustic to crude has internals of 316SS and PTFE diafragm. The drum, pipping and pump will operate at near ambient temperatures. Drum and pipping prior pump will operate at <1barg while the pump will discharge at about 44barg. We intent to PWHT all lines and drum. Thanks in advance
 
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11/21/2007 9:00 AM
 
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For diluting causting it is preferable to add DM water.Since the potable water will have lot of salts and other impurities it will contaminate the caustic strength/quality.Further chlorides in the water will aggrevate further corrosion in the CS piping while reacts with caustic. Regarding steam tracing if the line operates at ambient temperature there is no need of tracing.As you aware if the caustic temperature is above ambient, the corrosion rate in CS will be 3 fold.Hence, it is advisable not to put steam tracing in service. As per recent practice PWHT is advisable for all CS welds.For ambient temperature the impeller material is O.K.If you are planning to increase the temperature then you have to select higher grade like Monel-400 etc. Hope the above clarification will clear your doubts.If you have any further clarification,please feel free to contact. sriramchandra@rediffmail.com regards,
 
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11/22/2007 9:00 AM
 
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with compliments to Krish, PWHT is an essential requirement for Caustic Service to mitigate Caustic SCC. You can refer to caustic soda Service graph at http://hghouston.com/naoh_gph.html to have an insight about requirement of PWHT vs. caustic temp. regards
 
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