Q&A

(2013) Question 44: What are refiner’s practices or procedures to remove catalyst from a reactor when the catalyst will not free flow dump? What is the industry's experience with hydro drilling for removal of non-free-flow catalyst from fixed-bed units?

We typically vacuum out catalyst in an inert atmosphere if the reactors do not free-flow dump. We also wet dump some of our reactors, which involves vacuuming out the catalyst after removing the water. For people who are involved in turnaround planning, unloading rates for free-flowing catalyst are approximately 200 cubic feet of catalyst per hour.

(2013) Question 45: What are the procedures/rules governing the transportation and disposal of catalyst contaminated with arsenic, mercury, barium, or other heavy metals? Are there maximum limits for any of these?

The spent catalyst needs to be shipped offsite and sent for metals reclamation or disposal. If it is going for disposal, it will have to be characterized to determine if 1) it is a hazardous waste, which it is most of the time, and 2) it meets the applicable Land Disposal Restrictions (LDRs). It would have to be treated, as part of disposal, to meet the LDRs.

(2013) Question 46: What are the main considerations in converting a fuel hydrocracker into lubes services in terms of equipment modifications and catalyst selection?

The conversion of a fuel hydrocracker to a lube hydrocracker mainly depends upon the product quality requirements and unit constraints. If you are producing lube-based stock as your main product, then the operating parameter needs to be examined in detail.

(2013) Question 47: What evaluations are required for hydrocracking units to increase conversion due to processing heavier feedstocks?

Pilot plant studies should be done to evaluate catalyst performance with new proposed feeds. If you are planning to make revisions to your unit, you certainly want to consider catalytic changes, perhaps more selective to diesel or gasoline. Your operating cycle could possibly decrease or increase with conversion, depending on which way you are tending to go.

(2013) Question 48: What are the typical guidelines for reactor loading if the decision is to not fully load with catalyst? Is it acceptable to short load a reactor, and what are the recommended minimum and maximum distances below the inlet distributor?

First of all, it is a bit unclear why one would want to short-load the reactors. Can it be done? Yes, especially if it is a gas-phased operation. If it is a mixed-phase operation, then it probably could become an issue.

(2013) Question 49: What are the criteria for levelness during dense loading of a catalyst bed? What are the preferred monitoring techniques, and what is the best approached to correct an uneven bed profile if it is detected?

Really, it is not so much that you want to maintain a definite level bed, but what comes with that is making sure you are truly loading your reactor correctly and that you have an even distribution of densities through your entire bed. We also recommend that you check loading densities at some prearranged interval. Initially, it may be 10 or 15% of the start-of-run and then every 25% throughout the load until you are finished.

(2013) Question 50: What are the technology evaluations and engineering studies required for revamping a diesel hydrotreating unit to substantially increase throughput?

In any major revamp of throughput for a DHT (distillate hydrotreater), establishing a realistic design basis and engineering certainly never really exists. The idea is to look not just to the point but at deviations and feedstock properties, expected changes in compositions, and past history of contaminants.

(2013) Question 51: For hydroprocessing reactor modifications that involve the addition or removal of distribution trays and flexible thermocouples, what is your Best Practice for welding support rings or support lugs on a reactor wall? What is your Best Practice for removal of these items when they are no longer required?

When you are trying to remove the attachments from the reactor, do not touch them unless it interferes with your process flow, catalyst loading, or internal installation or access. When the rings are welded to the support rigs, remove the rings and leave the lugs in its place.

(2013) Question 52: What is the configuration of thermocouples that can be used to effectively monitor radial temperature differences, and what is the acceptable radial temperature spread in hydrotreaters/hydrocrackers?

The UOP bed thermometry consists of a stab-in type of assembly with three thermocouples on top of the bed. Typically, a multipoint thermometer is provided in the case of the first bed of a hydrotreating unit and if the bed length is more than 11 feet for a hydrocracking bed. At the bottom of the catalyst bed, industry-standard flexible-type multipoint thermocouples are specified.

(2013) Question 53: With respect to hydrotreating, what is the typical (CO + CO2) impurity in hydrogen produced from pressure swing adsorption (PSA): 10 ppm or 50 ppm? What problems can be expected if the (CO + CO2) exceed this value? If the hydrotreaters can handle higher than (CO + CO2), is it possible to run the PSAs harder and produce more hydrogen?

UOP has designed around 1000 PSA units. For most of the refinery applications, the impurity limit has been set to less than 10 ppm. The table shows a comparison between specs when relaxed from 10 to 100 ppm. H2 recovery was also checked when specs were tightened from 10 ppm to 1 ppm.

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