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(2017) Question 26: How are developments in hydroprocessing catalyst adjusting to changes in feedstock quality? Are the new developments able to cope with and provide high activity with varying feedstock severity? 

Catalyst development has focused on this very issue in its development of several of the highest activity hydrotreating catalysts in the Unity™ hydrotreating catalyst portfolio. The catalyst support is engineered to facilitate less diffusion resistance in the same extrudate size/shape class relative to its peers, but with improved interaction between the active phase and the support, leading to greater relative effectiveness for HDN/HDS/HDA and for uptake of metals like vanadium and nickel.
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(2017) Question 27: The sulfur block is a crucial downstream component of hydroprocessing operations. What are some of your Best Practices or new developments for optimizing operations and increasing reliability?

The sulfur block is a very mature technology. There have been few new developments to optimize operations. Optimizing operations of a sulfur plant can indicate an increase of sulfur production while reducing all related sulfur emissions. Some of the new developments in a sulfur plant consist of catalyst-burner design, dip leg improvement, upgrade of ferrule types, oxygen enhancement, oxygen enrichment, TGU developments, and increase in safety stewardship.
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(2017) Question 28: Under what conditions will you strip sulfur from hydrotreating/hydrocracking catalysts?

Base-metal hydrotreating and hydrocracking catalysts are susceptible to sulfur stripping at high temperature in the presence of flowing hydrogen and in the absence of H2S. For that reason, we advise unit operators to avoid prolonged exposure of sulfided catalysts to flowing hydrogen at temperatures exceeding 500°F if the H2S content of the hydrogen is below 50 ppmv (parts per million by volume).
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(2017) Question 30: What are common mechanical defects that occur to the weld overlay material in hydroprocessing reactors? What are the most common locations for defects, and does the location play a factor in the mechanical integrity of the equipment? How do you detect and repair the defects? How often do you conduct Remaining Life Analysis (RLA) and/or Fit For Service (FFS) Assessment on critical equipment?

The common mechanical defects that occur are disbonding and cracking. Non-vanadium-modified 2¼ Cr-1 Mo material is more susceptible to disbonding than vanadium-modified 2¼ Cr-1 Mo-V material. V-modified 2¼ Cr-1 Mo has a much higher solubility of hydrogen compared to conventional 2¼ Cr -1 Mo. 
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(2017) Question 31: What are the potential impacts to hydrocracking units [i.e., deactivation rate, HPNA (heavy polynuclear aromatics) formation, etc.] as heavy coker gasoil (HCGO) rate/endpoint are increased?

Processing heavier and cracked feedstocks poses many challenges to the hydrocracking unit. Thermally-cracked feedstock such as HCGO, apart from being unsaturated, has relatively lower API, higher sulfur, and nitrogen content, higher proportion of C7 insoluble, and Conradson carbon residue (CCR). An increase in the HCGO distillation endpoint results in a significant increase in the proportion of polynuclear aromatics (PNA) and asphaltenes, both of which are coke precursors, which results in an exponential increase in catalyst deactivation rates. 
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