Q&A

(2011) Question 76: What can cause exothermic reactions in propylene driers and guard beds and how can these reactions be prevented?

As introduction, Propylene Recovery Units downstream of FCC units typically consist of a C3/C4 Splitter, a Deethanizer and a C3 Splitter in series.

(2011) Question 77: How prevalent is the use of low slide valve dP override control in modern FCCU DCS systems and can the over-ride be considered an "independent protection layer" (IPL) when conducting a layer of protection analysis (LOPA) to protect against a pressure reversal scenario?

The panel concluded that 100% of the FCC units in their respective companies used the low slide valve dP over-ride to protect against reversals.

(2011) Question 78: What are the locations, formation mechanisms, mitigations and removal methods for coke deposition in the riser, reactor, reactor vapor line and main column inlet nozzle?

There are two ways that coke forms in FCC reactors. These are incomplete vaporization in the feed injection zone of the riser and HC vapor condensation of high boiling point species on cooler surfaces. In both cases the hydrocarbon liquid wetted on a surface has essentially infinite residence time at elevated temperature, resulting in thermal degradation reactions that create solid coke deposits.

(2011) Question 79: What procedures do you use to overcome chloride fouling problems in FCC fractionators? What is the contribution of chloride from the catalyst?

Overcoming or preventing chloride fouling problems in FCC fractionators is a primary responsibility of the unit engineer. There are several tools that can be used to monitor an operating unit.

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Q&A

(2011) Question 76: What can cause exothermic reactions in propylene driers and guard beds and how can these reactions be prevented?

(2011) Question 77: How prevalent is the use of low slide valve dP override control in modern FCCU DCS systems and can the over-ride be considered an "independent protection layer" (IPL) when conducting a layer of protection analysis (LOPA) to protect against a pressure reversal scenario?

(2011) Question 78: What are the locations, formation mechanisms, mitigations and removal methods for coke deposition in the riser, reactor, reactor vapor line and main column inlet nozzle?

(2011) Question 79: What procedures do you use to overcome chloride fouling problems in FCC fractionators? What is the contribution of chloride from the catalyst?