Severe fines deposition in FCC unit 1

[rumirav]

In one of our FCC units (Kellog Orthoflow model), we are suffering severe problems of fouling (fines deposition) in the turboexpander. The scheme of the flue gas circuit is: two stage cyclones in the regenerator + Shell Third Stage Separator before turboexpander + 4th Stage Separator (cyclon) to recover flue gas from fines coming from TSS.
We have also observed high level of moisture in the fines from 4th Stage Separator (10-15%wt). So we suspect that the fouling of the expander is due a cold point in the flue gas circuit (where flue gas humidity is condensed) or an uncontrolled inlet of water / steam.

Has anyone experienced this kind of problems in an FCCU? What could be the potential causes of the severe fouling of the expander?

 

[SeanB]

What is your current feed rate vs the original design of the unit?

 

[rumirav]

Our current feed rate is around 60% vs the original design of the unit. However, we have experienced the same problem both at current feed rate (low feed rate, close to minimum technically possible) and at maximum capaciy

Best regards

 

[0707]

You should check your third stage separator cyclones. Have you the possibility to take samples on the bottom of the TSS to analyse the catalyst fines?
Overall efficiency of the separator depends on the efficiency of regenerator cyclones; the separator should remove 70-90% of the particles for high and low regenerator cyclone efficiency, respectively. Most of the fines which pass through the separator are smaller than ten 10 microns. These small particles are the least damaging to the expander blades.

You said you also observed high level of moisture in the fines from 4th Stage Separator (10-15%wt). Do you have a continuous water injection on bottom of regenerator? Do you make thermal Shocks at turbo expander?

LM

 

[rumirav]

Dear 0707,

Thank you very much for your reply. We have checked TSS and it seems to be working properly. The aprticle size distribution at the bottom is OK.

We do not have a continuous water injection on bottom of the regenerator. However, I do not discard another uncontrolled water entry in the regenerator
We use thermal shocks to remove the blades deposits. We have also tried wallnut cleaning, but it was not succesfull

 

[0707]

You said you use thermal shocks to remove expander blade deposits.

Downstream the point where you inject the thrermal shock steam have you experienced any kind of cracking in the flue gas like?

thank you

LM

 

[rumirav]

We have not experienced any kind of thermal cracking in the flue gas line, downstream the point where we inject the thermal shock steam.

We also inject 1 t/h of cooling steam just in the inlet point of the expander, as reccommended by the licensor of the turbine. It seems to be a huge ammount of steam, but we have insisted to the licensor on the neccesity of this steam, and he respondes that it is neccessary to protect the machine (??)