June 2, 2017 at 11:58 am #25608
In our FCCU we have a turbo expansion in the flue gas. The FCCU turnaround typical period is 5 years, but the turbo expansion do not support this period between turnaround. The catalysts deposit inside the turbo-expansion. What is it the typical turnaround for turbo-expansion ? We have a third cyclone stages in the FCCU. Any suggestion how to increase the turbo-expansion turnaround ?
June 2, 2017 at 12:36 pm #25609
Alan R. EnglishModerator
It is very difficult to predict the reasonable period between turnarounds for an expander because experience has varied greatly across the industry. Some practitioners can successfully make a 5 year turnaround while many struggle to keep the expander online for more than a year. Usually, the culprit causing is deposition of catalyst fines on the expander blades which in turn causes vibration. In the past decade much improvment in blade coatings and machine design have been achieved. Your expander manufacturer can likely discuss these options with you. From a process perspective, the key to achieving long run lengths is to always operate the expander at its design point. This is because a properly designed expander will experience uniform flow throughout the flow path which will help prevent deposits. Operating above or below the design point may allow eddy currents and dead spaces to develop which will foster blade erosion or allow deposits to form. This means that the unit should be designed such that some flow to the bypass is required even when the unit is at design feed rate so that control of the flow through the expander can be maintained.
Routine cleaning of the expander (with rice, walnut shells, etc) is also important. Don’t wait for deposits to become a problem because these can also affect the flow pattern and prevent the cleaning agent from getting where it is needed. Many practitioners clean on a weekly basis.
June 2, 2017 at 1:34 pm #25613
I completely agree with Al’s comments. Rice and walnut shells have worked successfully.
June 13, 2017 at 12:30 pm #25794
Paul R OrlowskiKeymaster
Great points Alan, we walnut shell nightly now and vary the size of this medium. We also complete an expander spall usually every 6 to 8 months.
Douglas Stieb, PMP
I’ve seen walnut shelling as often as every shift. Might also consider the activities involved to bypass the expander during an FCC run. If you envision bypassing fairly often, to service the expander, could install additional equipment to isolate and blank more efficiently – and safer to personnel installing the blanks.
As per my little experience with turbo expander , TSS efficiency in view of fines to be taken care, try to operate expander on a constant load and periodic thermal cycling also helps
Makes sense Douglas Stieb, PMP to install additional isolation valves if expander is frequently bypassed for service.
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Are you using walnut shell injection? Do you monitor efficiency drop? Do you take frequent photos from the port to see how deposits looks like? Any use of SOx abatement additives?
Review the internal flow path by doing CFD. Also you need to know if deposition is on blade or on shroud for proper root cause analysis.
December 10, 2017 at 2:57 pm #27731
Good discussion. How Can I predict when I need to stop the FCCU turbo expander related with catalyst loss from regenerator ? During the FCCU regular campaign there is a loss catalyst from the regenerator to turbo expander and it increase. What do I need to measure in order to shutdown the turbo expander if the loss catalyst reach a determined point ? We need to know this point to protect the turbo expander from FCCU loss catalist.
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