3 replies to this topic

[amtchd]

For last couple of months, we've experienced hard catalyst deposits on FCC flue gas slide valves which prevents the valve from opening fully during shutdowns. This one a UOP designed FCC with guide type slide valves which control the Dp between reactor & regen. This is cold wall type design, which has got both thermal & erosion refractory inside the valve with no insulation outside. The purge air for stuffing box is utility air which is not exactly dry. We've tried to establish root cause of the deposit formation, but coudn't pin point the cause. Surely there are catalyst carry over, but our concern is why they're forming deposits only in the slide valve guides where temp is 700'C. We didn't observe substantial deposits elsewhere. Can anyone with FCC operation or maintenance suggests any solution or modifications which wither can eliminate the deposits or make the valves operable-?

[Profe]

Hi Amtchd.

About your concerns:

 

When catalyst fines reach low speed zones, these lose its fluidization and settle. If found moisture gets worse because the catalyst is very hygroscopic and forms hard solids aggregates that clog the small space between the guides and the disc of the flue gases slide valve (FGSV).

 

If I remember correctly, the Purge Air to the regenerator should be dry. The service air contains much moisture that interacts with catalyst fines (best to use instrument air because is dry). To remove moisture, you must install a small moisture separator in the air main header for Regenerator DA points. Specially for the guides of FGSV. The separator must have a level sight glass to check the water content and by a valve to evacuate the separated water.

 

In addition you should check that the DA points are operational, ie with no obstructions to the entrance of air. Also the restriction orifices of air are placed, and that the air pressure is equal to that specified.

 

I think that will be useful.

Good luck

Fausto

Edited by Profe, 25 February 2014 - 03:22 PM.

[sfoskett]

Deposits of this type are usually related to contaminant Fe&Ca, forming low melting eutectics with Na and SiO2 (from deactivated zeolite typically). Such deposits may be found in these places - orifice chamber, FG slide valve, secondary cyclone diplegs. The deposits will have a layered appearance of red layers (high Fe/Ca) and white (catalyst fines). The red layers are the "glue".

 

Apart from controlling metals levels on Ecat, perhaps with flushing catalyst, I don't have a good solution to this one.

[Eric Nguyen]

We had the same problem which you mentioned. You should check and keep a Delta pressure about 0.4 kg/cm2 between purging air and flue gas  pressure. It is very important .

Rgs