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I am in charge of DHDT (produce 10ppm ULSD) catalyst performance monitoring, recently WABT was increased fast out of my expectation, meanwhile ULSD color was getting worse (DHDT has decolor reactor), observed cut point (T95) of feedstock SRLGO had a fluctuation in last few weeks, what is the possible cause of this abnormal WABT jump?
 
Answers
15/05/2017 A: Sarathsatyakalyan Konda, Engineer, sharathsatya@gmail.com
Increase in boiling point will bring higher S and N including difficult species of S & N, Both requires require higher temperature for conversion. Depending upon the species, sometimes nitrogen compounds remain in the product resulting is greenish yellow colour of SR LGO
22/03/2017 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
When the feed gets heavier, the difficult sulfur & nitrogen in feed increases requiring higher reactor temp.With high temp side reactions of cat. deactivation increase. It is a vicious cycle. Check for RG flow issues, make up gas flow & purity, poisons in feed.
21/03/2017 A: NS Murthy, GE, murthy.ns@ge.com
Couple of points which you may like to look into: -
1. Check the rise in DHDT has any correlation with slop processing in Crude unit. As your unit feedstock is reported to be SR LGO any ingress of olefins could be thru slop processing in Crude unit.
2. Check the routing of Hy. diesel from vac tower top side draw. It is likely that this could bring in heavier material and push T95% in case this stream too processed in this unit.
3. Most colour is due to nitrogenous compounds in diesel fraction. drop in colour can be due to drop in H2 to Oil ratio and or H2 PP at reactor exit. also, check for any crude mix change.
4. Last but not the least, check that there is no leak in Feed vs Reactor Effluent Exchanger which also can increase the T95% of diesel product along with colour deterioration and sulphur pick up which will make operator to raise the Rx temp (in turn WABT) to compensate final sulphur level in diesel.
21/03/2017 A: Ganesh Maturu, Reliance Industries Limitied, maturu.ganesh@gmail.com
Since you mentioned both color and deactivation issues, it could be one reason that you are processing more cracked feed than desired. Increasing T95 increases deactivation but increasing T95 of cracked feed significantly increase deactivation and color problems. Check your feed blend.
Also for aDHT units after 375-380 deg c, deactivation increases significantly near EOR. I suggest stopping cracked feed during aEOR to increase cycle length for few months.
20/03/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
A sudden change in WABT is almost always due to a change in the feedstock quality. In your case, you mention a change in the T95, so I assume that the T95 increased. Increasing T95 increases both the total amount of S to be removed, but more importantly also increases the amount of difficult to treat sulfur compounds such as benzothiophenes and dibenzothiophenes. Sometimes a relatively small increase in T96 can cause a dramatic shift in where these difficult to treat compounds go. If they shift to the DHDT feed, then a significant increase in WABT may be needed to stay below product S limits.