| American Fuel & Petrochemical Manufacturers

Question 37: What are your typical design criteria for injection quills (i.e. slotted vs. nozzle, direction, spray pattern, filter mesh, metallurgy, etc.)?

NACE has a Technical Committee Report 24215 that addresses Refinery Injection and Process Mix Points that is a good reference for this discussion. The answer is complicated due to potential quill uses, such as for wash water, corrosion inhibitors, antifoulants, or other additive applications.

Question 36: Can you provide insight to best practices for prevention and repair as it relates to chloride stress cracking and polythionic acid stress cracking of stainless steel equipment in hydroprocessing units?

Specific to hydroprocessing units, chloride stress corrosion cracking (Cl SCC) is really only an issue on the outside of piping and equipment. During normal operation the process side of units that have austenitic stainless steel operate too hot for liquid water to be present; a requirement for Cl SCC to occur.

Question 35: What is your criteria for retiring a hydroprocessing reactor? What kind of failures have you seen? What are the inspection techniques you use and your frequency of inspection?

As far as Inspection techniques and methods, the following should be employed. Application of these would be based on customer’s inspection plan and/or Risk Based Inspection (RBI). Other things that would trigger examination would be thermal excursions or checking for in service cracking after 15 years.

Question 34: What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

Question 33: What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

Color chemistry is very complex and strongly influenced by the feed molecules and the unit operating conditions. Dehydrogenation of saturated aromatics (condensation) and/or insufficient removal of nitrogen containing molecules can both result in off spec product color issues. Dehydrogenation or condensation reactions are favored by low H2pp and high temperatures.

Question 32: How does catalyst activity, run length, H2 uptake, volume swell, reactor temperatures, price of the catalyst and product quality impact optimizing the business case for a catalyst selection? Compare a regen catalyst, moderate activity and next generation catalysts in a cheap H2 available market.

Refinery Process Engineers are often confronted with a complex and time-consuming process when it comes to choosing a catalyst for their hydrotreating units.

Question 31: As more and more refiners consider installing zeolite catalyst in their hydrotreating units, what are your recommendations for a depressuring system?

Though many hydrotreating units operate at lower pressures than most hydrocracking units, loading zeolite catalysts poses a risk of temperature excursion which should be mitigated. Reactor thermometry, depressuring system capacity, and automating depressuring based on indication of excursion must be evaluated when cracking catalyst is loaded in a hydrotreating unit.

Question 30: What is your minimum charge heater firing limit, especially when highly heat integrated or when processing cracked stocks? Do you have any hydroprocessing units run without firing the charge heater?

The low firing limit is caused by burner instability. Heaters can be turned down by completely shutting off some burners; but there is also a firebox temperature component. Burner instability would be noticed visually – examples being flickering, irregular flame pattern plus increased CO emission.

Question 29: What are your current best practices for protecting the charge heater from backflow?

Our design practice for a gas only heater uses a check valve at the outlet of the heater mainly to cut down on the chance of liquid flowing back into the heater during a compressor trip.

Question 28: What is your best practice for determining the maximum allowable temperature rise in hydrotreating beds? What solutions do you have for managing temperature rise?

Operating philosophy regarding the maximum allowable temperature rise in hydrotreating beds from a design perspective is determined by several factors.