9 replies to this topic

[Eric Nguyen]

Dear ALL

Sometime, our RFCC unit run at 95% even CDU capacity was at 105%. Can we inject crude oil to residue feed to RFCC for RFCC capacity compensation?.Are there any refinery used crude oil mixed RFCC feed on the world?

Hope to hear from your comment!

[PingPong]

You should ask the licensor of the RFCC whether they see a problem with your suggestion.

 

I have never heard of feeding crude to an RFCC unit, but I think it should be possible, provided that you take the crude downstream the desalter in the CDU.

 

Note however that this crude contains LPG, naphtha, kero and gasoil with are much more volatile than the atmospheric residue you presently feed to the RFCC. Feeding these lighter components to the riser will probably result in a much higher make of wet gas than present. In other words: you may not be able to feed much crude to the RFCC as the wet gas compressor may soon become a bottleneck. If the CDU has a preflash drum or a preflash column then take the bottoms liquid of those to reduce the feed of naphtha minus to the RFCC.

 

Instead of feeding crude, and assuming the present feed to the RFCC is atmospheric residue, you might consider to considerably reduce the stripping steam to the crude column bottoms. That will increase the atmospheric feed to the RFCC. But watch out for bottoms pump cavitation. And do not forget to re-open stripping steam before you run atmospheric residue to storage, or to another process unit.

You could also reduce the crude heater outlet temperature somewhat to increase the atmospheric residue feed quantity to the RFCC.

Edited by PingPong, 24 September 2014 - 05:01 AM.

[Eric Nguyen]

Dear Mr Pingpong

Crude oil downstream of the desalter in CDU is meeting RFCC feed but we are worrying about light component as you mentioned that will affect to Slurry circuit ( it may  be voporized before feeding to Riser) and also we are concerning about whatever light component affect to Slurry/HCO/LCO PA ? In my opinion we keep CDU capacity and don't want to lost Light product from CDU and 5% crude oil be injected to RFCC feed that we can increase Refinery capacity?

I heard that Reliance refinery in India used a partial crude oil as fcc/rfcc feed! But i don't know anybody here to ask about this!!

Best wish and regrards

[PingPong]

You really should ask the licensor of your RFCC unit what their advice is regarding feeding undesalted crude oil to the unit. They will want to know what crude oil it is, what its salt content is, and what catalyst you are currently using. If that catalyst is not the one supplied or recommended by the licensor they may however not be very cooperative. In that case you will need to contact your catalyst vendor for advice on coprocessing of undesalted crude oil.

 

A quote from the Fluid Catalytic Cracking Handbook:

 

Alkaline earth metals in general, and sodium in particular, are detrimental to the FCC catalyst. Sodium permanently deactivates the catalyst by neutralizing its acid sites. In the regenerator it causes the zeolite to collapse, particularly in the presence of vanadium.

 

On top of that, chlorides will form HCl which is corrosive, especially in the fractionator overhead system, and NH₄Cl which will deposit where you don't want it.

Edited by PingPong, 25 September 2014 - 04:54 PM.

[Eric Nguyen]

Dear forum

I don't worry about catalyst but could any experts in forum answer my question?   if we mix crude oil with Residue and send to Riser. Is there any cracking reaction with light component in crude oil as LPG, LGO+ HGO?

Best regards

[PingPong]

Yes, part of those components will crack to lighter ones.

[Himanshu Sharma]

Hey there !

 

Adding to what has been dicussed in the thread,

 

RFCC or FCC typically can't crack HC material lower than TBP of 320 deg C fed straight to the unit ,so that much portion of the FCC Reactor volume may remain idle.

 

In order to crack this material you have to inject special recycle injection nozzles to fit in the riser at optimum cat to oil ratio and tempeature profile.

 

Thanks and Regards

Himanshu

[Eric Nguyen]

Hey experts

I already asked licensor about my topic

1. Increase throughput from current 95% up to 100 % using Crude oil.
   1. xxx confirm that they are limited in the R2R throughput due to lack of production of enough residue from the bottom of the atmospheric tower and cannot, so far supply more than 95% of the original design.
   2. However xxx has enough crude oil to be able to supply additional crude as feed to R2R to compensate for the lack of the 5% residue lacking to feed to R2R unit up to 100%
      • If Axens well understand the questions the 5 % needed to reach the 100% throughput will be done with non-fractionated crude.
      • In this case this crude will be lighter than the feed. Therefore it should be assumed that there will be no feed injectors' problem.
      • As the total feed will be a bit lighter the yield pattern shall be quite similar with a tendency to make a bit more conversion.
      • However, more impurities will be sent to the reaction section (especially metals, S & N which normally will be dispatched in the lighter products in the Atmospheric crude unit). This may induce some loss of activities of the catalyst due to increase of pollution.
        • This could be trouble shouted by increasing the draw off (But this is already a problem in the xxx plant operation).
   3. If total S and N increase then products qualities can be affected as well as the flue gas may be releasing more Sox and NOx to the stack.
   4. However Axens think that for the time being if the total crude content in the feed is not exceeding 5% the impacts on the yield pattern, the Sox and NOx emission at the stack, and the corrosion shall not be very important and xxx might try to slowly increase its throughput up to 5% of the total feed but at each step of said 2%, stabilize the whole plant operation, take analyses and check all products qualities and emission are still within the requested one.

Any more comment for this topic. is there any guide to do this topic?

Thanks you

Edited by Hoang Tri, 02 January 2015 - 11:50 PM.

[Himanshu Sharma]

Hey There !

 

In case i assume that feed to RFCC is straight run and not Hydro treated,the amount of impurities/poisons/contaminants you are sending to RFCC with Crude Mixed will be lower than design.

 

The overall change in Unit Diet will lead to a lower CCR for which you need to carefully monitor the Heat Balance in theory and Cat to Oil Ratio in practise,in case your units has Cat-Coolers installed be cautious about cooling down catalyst too much.

 

Cracking full range Crude Oil shall require higher severity than usual Feed and i believe that Crude Mixed Feed directly injected in main Riser will not be crack to the same tune as the regular feed.Kindly refer my comment earlier in which is failed to put down this point,the comparatively smaller Molecules will need a second high severity reactor zone as compared to VGO.

 

As per my belief ,you will be effectively vaporizing crude oil fractions till gasoil range  and separate the same in Main Fractionator,only molecules above a certain TBP say above 370-380+ deg C will effectively crack. Thus change in yield will be LPG+Naphtha+Gasoil as per Crude Potential with more contribution from cracking of heavier HC.

 

This scenario to me sounds like a costly operating option as per the processing cost of RFCC units,you need to carefully assess the net GRM increase by utilizing the idle capacity  vis vis operating cost of RFCC.I normally use an LP program for this assessment.

 

Having said that,the proposed change in Unit Feed diet gradual to the tune of 1-2% leading to a max of 5% should not hurt the unit much,somehow i am not very much concerned about the downstream Gas Plant,because in case I would have designed the same (or for that matter being designed by a just Okay process engineer) it should have been built with some margin to accommodate operations flexibility and those design margins should be enough to handle such variations.

 

Hope this Helps !

 

Thanks and Regards

Himanshu

[gegio1960]

it's an interesting thread...

XX refinery would like to add 5% Crude OIl to the 95% Residue feeding its RCC to obtain the full utilization of the plant.

If the crude is not desalted, the major impacts would be on the catalyst life and on the metallurgy of the top part of the Main Fractionator.

(The refinery has already ascertained that there are no problems with "light ends", TAN, S, N content etc...).

The refinery will implement this practice if the difference between the prices of the gasoline and the crude will be enough to repay in a couple of years the expenses of a batch of catalyst and the replacement of the top part of the Main Fractionator.

The initial idea could be improved by thinking to a Fuel Oil instead of a Crude Oil.

For the long term, a careful LP analysis will indicate the best crude slate for XX refinery...