6 replies to this topic

[Ronak12]

Hello everyone.

Greetings.

 

For a past few years I am observing frequent fouling in FCC Bottom slurry exchangers. within Every 5-6 months a lot of coke deposition occurs in tube side of exchanger and it needs to be cleaned. Tube side of exchanger has slurry service while shell side has VGO. There are two exchangers in configuration with both the sides in series.

 

Some additional information are below mentioned.

• It is a hard coke with no catalyst deposition .
• Slurry temperature is below 360 C as per UOP guidelines.
• We are maintaining velocities above 1.4 m/s [ typically 1.8 m/s most time].
• There is no mixing of VGO with Slurry.

 

I have gone through some literature and checked all the possibility of fouling in a exchanger but unable to find major reason for this.

 

Kindly discuss this issue with probable causes/solution.

[manojkaila]

Dear Ronak12

 

1 If you have bypass of the feed exchanger on slurry side you can open it & reduce the head load because some sudden temp change will create the coke formation. ( Your steam generation will increase)

2 Some time coke formation depends on the type of crude . Check for type of crude & fouling any correlation.

3 If problem is very severe you can drop some HCO in bottom & can make slurry more light.

4 Are you using hot feed or cold feed. Is it happening during mainly cold feed % are higher?

 

I hope this few tips will helpful.

 

Regards, 

[Ronak12]

Hi ManojKaila

 

I have some counterpoints/confusion regarding the suggestion you gave.

 

1. If I open the slurry bypass, it will reduce the velocity through exchanger and it will result in more fouling.
2. If type of crude can be a reason, then resid FCC should also face frequent fouling. But it does not. Although I will check this thing also.
3. We are already droping some LCO in MCB in order to maintain Viscosity and density. We dont draw HCO as product.
4. We are processing mainly hot feed. Pure cold feed was never processed.

 

Please provide comments over this.

 

Regards,

[breizh]

Hi ,

I was wondering if technology like Turbotal can reduce  the deposit in your HX .

 

Hope this helps

 

Breizh

Edited by breizh, 24 November 2015 - 10:44 PM.

[manojkaila]

Hello everyone.

Greetings.

 

For a past few years I am observing frequent fouling in FCC Bottom slurry exchangers. within Every 5-6 months a lot of coke deposition occurs in tube side of exchanger and it needs to be cleaned. Tube side of exchanger has slurry service while shell side has VGO. There are two exchangers in configuration with both the sides in series.

 

Some additional information are below mentioned.

• It is a hard coke with no catalyst deposition .
• Slurry temperature is below 360 C as per UOP guidelines.
• We are maintaining velocities above 1.4 m/s [ typically 1.8 m/s most time].
• There is no mixing of VGO with Slurry.

 

I have gone through some literature and checked all the possibility of fouling in a exchanger but unable to find major reason for this.

 

Kindly discuss this issue with probable causes/solution.

There are two exchangers in configuration with both the sides in series.

 

Dear,

 

Do you have any specific ( Like more deposition ) in only first or second exchanger. What about the pre heat temp. Did this phenomena increase after some pre heat temp increase because we are always trying to get more pre heat feed temp for more conversion. 

 

Different type of crude has different type of coke formation tendency. So have a look for that also. Same time is there any change in recycle properties like slop or other stream like Naphtha ?

 

Regards,

[Ronak12]

 

Hello everyone.

Greetings.

 

For a past few years I am observing frequent fouling in FCC Bottom slurry exchangers. within Every 5-6 months a lot of coke deposition occurs in tube side of exchanger and it needs to be cleaned. Tube side of exchanger has slurry service while shell side has VGO. There are two exchangers in configuration with both the sides in series.

 

Some additional information are below mentioned.

• It is a hard coke with no catalyst deposition .
• Slurry temperature is below 360 C as per UOP guidelines.
• We are maintaining velocities above 1.4 m/s [ typically 1.8 m/s most time].
• There is no mixing of VGO with Slurry.

 

I have gone through some literature and checked all the possibility of fouling in a exchanger but unable to find major reason for this.

 

Kindly discuss this issue with probable causes/solution.

There are two exchangers in configuration with both the sides in series.

 

Dear,

 

Do you have any specific ( Like more deposition ) in only first or second exchanger. What about the pre heat temp. Did this phenomena increase after some pre heat temp increase because we are always trying to get more pre heat feed temp for more conversion. 

 

Different type of crude has different type of coke formation tendency. So have a look for that also. Same time is there any change in recycle properties like slop or other stream like Naphtha ?

 

Regards,

 

Dear,

• Relatively more fouling is there in first exchanger [slurry side].
• When exchanger is cleaned and taken in line, it gives more preheat and then slowly it decreases. We try to keep a fix flow through exchanger irrespective of preheat. In general we don't change flow to  increase preheat, so whatever preheat comes we operate it.
• There is no recycle at all.
• I also have doubts on type of crude. Do you know any qualitative/quantitative parameter which can be monitored for fouling? more clear picture will be reflected if this parameter is for Slurry.

 

Thanks

[manojkaila]

Dear,

 

Small good article I found on net.

 

May be helpful.

 

Regards,

 

Manoj

 

 

Attached Files

•  Slurry exchanger fouling.pdf   694.17KB   41 downloads