Q&A

(2014) 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.

(2014) 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.

(2014) 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.

(2014) 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?

(2014) 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.

(2014) 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.

(2014) 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.

(2014) Question 38: What design modifications, such as pre-reforming and ATR (Autothermal Reforming), do you considered for greater feedstock flexibility, higher efficiency and capacity debottlenecking?

We have used pre-reforming to provide feed flexibility especially for feed stocks that are liquid such as naphtha and when co-processed or as an alternate to feeds such as natural gas/ LPG. Pre-reformers can provide for higher efficiencies depending on the relative value of fuel and steam.

(2014) Question 39: How can we improve temperature control in steam methane reformer tubes? What monitoring practices do you recommend to avoid overheating the furnace tubes?

Regular visual inspection of the reformer tubes is still an important practical way of monitoring the condition of the steam methane reformer especially during transients when online analytical, or instrumentation may be out of calibration or range for the conditions being seen. Historically, the most severe tube failures in SMR’s have occurred during transients, in particular start-ups.

(2014) Question 40: What are your best practices when crimping pigtails on a hydrogen plant? Are there any metallurgical limitations?

Most owners take the unit down and pinch off the top and the bottom pigtail with a double crimping device and physically separate the pigtail from the cat tube. Itis recommended that the cat tube also be removed. This prevents a damaged or unused tube from distorting and affecting adjacent tubes or perhaps even falling in the firebox causing other damage.

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