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Our FCCU (Stone & Webster) shows high BS&W in CLO stream, even though charge rate is low at around 150 tonns/hr. Design capacity is 215 tonnes/hr without any bottom (CLO) recycle to the feed. Now lab result of BS&W shows in the range 0.4 to 0.7 . Our intension is it keep it always below 0.4 . What are the remedies to tackle this problem without shutdown?
 
Answers
30/03/2015 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
We recommend sampling of solids in the CLO to determine if it is catalyst or coke. AA-method is preferred. Generally, solids are catalyst. A particle size distribution can confirm if the material is from attrition (very small PSD) or cyclone efficiency (full-sized particles).
Coking in one Rx cyclone can decrease efficiency. Coking can occur when processing highly asphaltenic feeds, particularly at low temperature (in Rx or mix-zone). Usually, increased fouling in the CLO circulation is seen at the same time.
If the cause is attrition, on-line remediation consists of a thorough survey of riser-Rx and elimination of high velocity gas injection. If the issue is a partially plugged dipleg, it must be fixed at turnaround.
Note that there are settling aid chemicals which can help remove solids in tankage.