This article is the third on CCR Naphtha Reforming and moves forward from CCR Rx Turnaround I and Turnarounds II covering the inspection of catalyst collectors, both internal and external. The article will discuss how to avoid catalyst flow obstructions and important considerations on lift line evaluation and change out. We’ll share frequently overlooked differences in Dur-O-LokTM fittings and how to avoid making mistakes that are not easily undone, and their consequences. We will review the two most commonly used catalyst lift line assemblies (lift engagers and “L” valve assemblies). Note: Some newer unit designs will have intra-reactor lifts for multiple stacks and lifts, but for this article we’ll assume there is only one Rx stack with one lift to the regenerator and one back to the Rx’s.
Dur O Lok Fittings:
These fittings have been used to create a seamless connection for catalyst transfer pipes for decades. Now owned by Bete Fog Nozzle these Dur O LokÒ fittings play an important role in minimizing catalyst attrition (catalyst fines make) in catalyst lift lines for CCR units worldwide.
Here are some recommendations (consistent with those from Bete) that may save users grief with leaks and potential safety concerns. Dur O Lok fittings are made for both high temperature (> 450 F / 232 C) and reduced temperatures not to exceed 450 F (232 C). This lower temperature style coupling has an elastomeric “O” ring as opposed to the high temperature variety that has a flat graphite gasket; thus, they have visibly different seating surfaces. During a new unit startup – before the coupling hubs are welded in place – be careful not to mix the parts of these two different couplings. Best practice is to keep them assembled or reassemble them loosely (by hand) and keep the two different styles completely separated. These fitting are supposed to be steel-stamped with designations OR76 or GRF100. A statement from the manufacturer website: “Warning: Low temperature (OR76) and high temperature (GRF100) design DUR O LOK couplings and their gaskets are NOT interchangeable.” The lower temperature “O” rings are used in catalyst transfer piping (CTP) outside of the Rx’s and the higher rated graphite gaskets can be used to couple CTPs inside the Rx’s.
The GRF100 coupling and gasket would be nice to use both inside and outside of the Rx’s, but the graphite gasket has not proven reliable against leakage. GRF100 coupling and gasket can be used inside the Rx’s, as if there is a small leak, it would be internal and not a safety concern, as opposed to an external leak on the regenerated catalyst lift line with H2 as the lift gas.
If you have any questions on why this is so important, please submit them through this post. Also, please visit the Bete website on Dur O Lok fittings to review their very important Dur O Lok Installation Instructions.
Catalyst collector designs are either “internal or integral” or “external”. Both serve the same purpose of stripping residual hydrocarbons from the catalyst as it cools prior to transfer to the regenerator side. Both designs will have a clean “dry gas” purge that is temperature controlled but can have a few different physical and control layouts. Bottom line, they need to work correctly or will present significant operational problems as follows:
- Catalyst that contains residual hydrocarbons may result in catalyst flow problems, and this is generally picked up by an increase in lift line dP that is also erratic.
- Possible hydrocarbon (HCBN) carryover to the regenerator.
- If the catalyst from the catalyst collector is not stripped of residual hydrocarbons, there is an inline H2/Hydrocarbon analyzer in the circulating gas stream of the DH. If detected, an alarm will sound alerting operations to the condition. Important Note: Some designs have a single analyzer that must be switched between process streams. The default position for this inline analyzer should always be the dedicated N2 header that supplies nitrogen to the regenerator. As needed or outlined in your GOM, this analyzer can be re-positioned to look at the circulating gas stream in the DH. This is how one can confirm the presence of HCBN’s and operational problems with the catalyst collector. Safety: Always remember to place the analyzer back in position to look at the dedicated N2
External v Internal: An external catalyst collector has insulated catalyst transfer pipes (CTP’s) extending from the last Rx that connects to the catalyst collector, whereas the internal design is integral to the Rx stack.
External Catalyst Collector: The external cat collector should be inspected to ensure each CTP is free of obstruction, and visually inspected for any physical damage. It’s not unusual to observe dented and/or flattening of these CTP’s. This occurs when one or more of the CTP’s is not flowing during operation and a steel hammer, or other object, is used to strike the CTPs to try and jar the obstruction loose. This type of response to a plugged CTP can severely damage, flatten or even crack the CTP’s while in service. Moreover, while trying the hammering method, the insulation is removed and frequently not replaced.
Licensors will have procedures in their General Operating Manuals (GOM’s) on how to safely backflow gas through these lines to unplug them. Reach out to your licensor for direction on how to use this procedure if needed.
Lastly, make sure the purge gas and vent piping are free of debris, and all restriction orifices that control the purge gas flow rates are not obstructed and are sized correctly. Note: At times these restriction orifices (RO’s) are located within a pipe union and not obvious unless you know to look there.
Integral Catalyst Collector: The integral cat collector is equipped with a baffle and temperature-controlled purge gas flow. To complete an inspection of this design there is likely a body flange near the bottom that must be removed before cleaning and inspection. With the bottom head off, check the annular gap around the circumference of the baffle, it should be uniform +/- 2 ~ 3 mm’s.
Some designs may have an inline filter on the purge gas outlet line. This filter should be removed, cleaned, and replaced. Note: The filter insert may be directional, so be sure to reinstall it in the correct orientation. Also, make sure to blow out any debris in the line upstream the filter, prior to re-installation of the clean filter. DO NOT blow out the downstream side of this filter into the next piece of equipment without understanding where it will end up. Check with your supervisor as you may be simply moving a problem to a downstream piece of equipment.
Lock Hopper (LH) #1 is unique to older CCR designs (UOP Atmospheric CCR Platforming TM), but there are over 100 still in service worldwide, so certainly worth covering. LH #1 is beneath the catalyst collector as shown in the image (above center). This piece of equipment is where the atmosphere of the gas and catalyst is changed over from H2/Hydrocarbon to nitrogen, prior to its transfer to the DH on regenerator side.
This LH is accessible for cleaning, inspection and a LH load size calibration. The LH load size calibration procedure is in your GOM) or a separate document that your licensor can provide. If a LH load size calibration is desired, the nuclear source strength and/or position may need to be adjusted to get the correct load size. If you need support with this calibration, your licensor or qualified instrument specialist can typically support this request. These specialists may also provide input on the detector performance which can also decay with time. Lastly, don’t hesitate to contact the vendor if you have any questions or concerns. Safety: Always lock the shutter closed on all nuclear sources before opening any vessel for inspection, work, or cleaning.
Note: The are different valves and valve types that support the correct operation of the LH. Leaking valves are a frequent cause for problems with LH sequencing and TA is the best time to carry out leak testing. Some of these valves are intended to be gas tight, while others are designed to close on catalyst and have an acceptable leak rate. This information can be found in your process engineering and design manuals, along with diagrams and explanations of how to use the testing apparatus.
Catalyst Transfer: There are two different types of catalyst lift designs in CCR Reforming. The first is the Lift Engager (LE) and the other is the “L” valve assembly that is used exclusively with UOP CCR Platforming TM units. The older lift engagers are still in use on many CCR Reforming units. The LE on the Rx side is beneath the LH and receives catalyst in batch modes, each load is delivered slowly over the course of ~ 20 minutes. The LE’s purpose is to transfer catalyst using N2 as the lift gas to the Disengaging Hopper (DH) above the regenerator while minimizing any damage to the catalyst, i.e. catalyst fines generation.
In the older LE design the lift gas comes down the outer of two concentric pipes and forces catalyst up the inner pipe. For TA, any rough or sharp edges must be eliminated as catalyst is now moving at a much higher velocity during the lift. Where the two concentric pipes terminate, the edges on both the inner and outer pipes should be smooth. Note: Generally, a machinist will bevel these edges or smooth them with a fine emery paper to meet smoothness requirements. Moreover, these two pipes must be concentric. There are 3 adjustment screws on the outer pipe to help center the inner pipe.
Lastly, it is common practice for customers to check the wall thickness of the catalyst lift line, with special attention to long radius 90’s or elbows. This is a location where flowing catalyst is making contact on the lift pipe as it makes it’s turn leaving the lift engagers and when it turns toward the Rx. These points often thin with time, and most customers will use UTM to check wall thickness or replace these sections on a scheduled basis.
Setting the correct catalyst transfer rate is largely determined by the lift gap between the outer and inner pipe. Setting this “lift gap” is a trial-and-error effort. Generally, an 8 ~ 10 mm gap is a good starting point.
Note: Please read all notes on every drawing, as these notes are frequently overlooked but contain valuable information.
The UOP “L” Valve TM assembly and lift line with their Impactless Elbow TM” are a much better solution to transporting catalyst from grade to the top of the Rx and regenerator. This design is largely employed on most UOP CycleMax TM, because it minimizes catalyst attrition significantly and is a much more elegant solution to catalyst transfer by comparison to older lift engagers and lift pipe layouts. Regarding TA, pay careful attention to all notes associated with the correct construction of the “L” valve assembly, i.e. elevation, length of line, slope, etc. These are critical to this design working correctly.
Disengaging Hopper (DH):
As with most refinery equipment, the name of the vessel is consistent with its purpose. This vessel receives spent catalyst from the Rx side that has been cooled and now in a N2 environment. The goal is to disengage the catalyst fines from whole catalyst pills, and to prevent the smaller chips and fines from entering the regenerator and plugging the inner screen. These catalyst chips and fines are removed and diverted to a dust collection or fines removal system. (Fines removal systems will be a topic for another article). For TA on the DH, there is likely a screen in lower part of the vessel to catch larger objects that may have gotten into the lift system and may cause problems if they get past the DH and into the regenerator. It is important to clean this screen and make any needed repairs.
There is likely a nuclear level detection system on this vessel and can be calibrated if needed. Safety: Always close the shutter on the nuclear source and lock it closed before entry.
Note: There are CCR designs that use H2 instead of N2, but this design is less common. If yours is one of those, Becht can help you as well.
Lastly, if you are a licensee of a CCR Naphtha reforming technology and are not getting all of the information that you need, then please reach out to Becht. We can provide it.