In FCC we are having start up steam/lift steam at riser bottom & atomizing at u/s of feed nozzles.
If I need to increase the partial pressure of hydrocarbon, which one is effective?
Answers
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13/10/2013
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
I am 100% in agreement with Ralph Ragsdale regarding steam rate to the atomizing feed injectors in the feed injector array. This should always be kept at the kg/hr rate used for injector design. As side note, injector steam should be superheated and medium-pressure.
Minimum lift steam to the base of the riser is determined by the technology supplier's recommended density and velocity of the fluid solids entering the mix zone [swage segment where atomizing feed injectors are located]. There are important operational factors underlying density and velocity entering the mix zone.
Lift steam can be increased above the minimum lift steam to DECREASE hydrocarbon partial pressure at the mix zone outlet.
Question must be asked why there is interest in either lowering or increasing hydrocarbon partial pressure at outlet of the mix zone.
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07/10/2013
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
In most feed nozzle designs, the steam flow for atomization of the hydrocarbon is set by the fixed orifices. Unless you are throttling the steam supply, the steam flow rate is not adjustable without modifying the nozzle internals. As you know, these nozzle designs and their operation are crucial to achieving the intended product distribution and should not be adjusted for other reasons.
Other steam entry points are for fluidization or stripping H.C. from spent catalyst. Fluidization steam flow should be adjusted only to achieve smooth cat circulation. Riser bottom lift steam is part of that system. Stripping steam flow should be optimized to limit H.C. carry to the regenerator.
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