I.FLUID CATALYTIC CRACKING/A.PROCESS(Contd.)
Q-22:
Some refiners have installed gas injection in FCC secondary cyclone diplegs to increase capacity and avoid defluidization problems.Please describe your experience operating with gas addition in the diplegs and any maintenance issues.What advice would you give to others considering this installation?
A-22:
Cyclone dipleg aeration is a technique used to improve cyclone dipleg fluidization.It involves adding a stream of purge gas,usually air or steam,to a location near the bottom of the cyclone dipleg ahead of the trickle valve.It assures that the cyclone dipleg does not defluidize and plug,This can be a problem for secondary cyclone diplegs that are lightly loaded.
The purge flows aee small and regulated via restriction orifice as per normal instrument purges.Purge piping for the coldwall Regenerators enters the top of the vessel and is routed along the diplegs.Purge piping for the hotwall Reactors enters the vessel near the bottom.The purges need to be commissioned before catalyst loading to avoid plugging the aeration point.Erosion at the injection points has not been an issue.The routing of the purge piping needs to consider thermal expansion as well as impingement.Failure of the internal piping is a concern.
Q-23:
Several refiners are considering continuous operation of the combustion air heater to maintain minimum regenerated temperature when processing light feed stocks.What control systems and general precautions should be considered?
A-23:
The combustion air heaters are not always models of reliability,either during ,or perhaps because of their infrequent use.Reliability issues and safety shutdown system design would be required before cinsidering use of these air heaters.
Q-22:
Some refiners have installed gas injection in FCC secondary cyclone diplegs to increase capacity and avoid defluidization problems.Please describe your experience operating with gas addition in the diplegs and any maintenance issues.What advice would you give to others considering this installation?
A-22:
Cyclone dipleg aeration is a technique used to improve cyclone dipleg fluidization.It involves adding a stream of purge gas,usually air or steam,to a location near the bottom of the cyclone dipleg ahead of the trickle valve.It assures that the cyclone dipleg does not defluidize and plug,This can be a problem for secondary cyclone diplegs that are lightly loaded.
The purge flows aee small and regulated via restriction orifice as per normal instrument purges.Purge piping for the coldwall Regenerators enters the top of the vessel and is routed along the diplegs.Purge piping for the hotwall Reactors enters the vessel near the bottom.The purges need to be commissioned before catalyst loading to avoid plugging the aeration point.Erosion at the injection points has not been an issue.The routing of the purge piping needs to consider thermal expansion as well as impingement.Failure of the internal piping is a concern.
Q-23:
Several refiners are considering continuous operation of the combustion air heater to maintain minimum regenerated temperature when processing light feed stocks.What control systems and general precautions should be considered?
A-23:
The combustion air heaters are not always models of reliability,either during ,or perhaps because of their infrequent use.Reliability issues and safety shutdown system design would be required before cinsidering use of these air heaters.
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