Q & A > Question Details
Normally VGO feed temp. in FCC reactor is 350°C-390°C. Because of upstream side heater trip temp. goes down to 290°C.
What will be the effect on reactor regenerator operation? And using this low temp feed can I run Reactor-Regenerator for some hrs?
17/02/2011 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Fundamentally, a modern VGO FCC Unit with reserve capabilities in terms of TPH 'coke' burning capability and TPH 'catalyst circulation' capabilities [and at least recent vintage atomizing feed injector array] can operate forever at same riser ROT and 221C- volumetric conversion level with cat feed preheat temperature reduced from 350C-390C to 290C. The weight percent 'coke' make on cat feed must go up to input the differential in specific heat of the cat feed between 290C and previous cat feed preheat temperature. If the FCC regenerator is being operated cycling in a narrow temperature band [as typically optimal], this then requires the TPH catalyst circulation rate to go up.
As noted by other responders, 'problems' can ensure if the particular VGO FCC Unit is operating at or close to constraint boundaries within its unit specific multi-dimensional performance envelope, e.g. TPH 'coke' burning limit or TPH catalyst circulation limit or is still using archaic open pipe-type or NON-atomizing feed injectors.
More sophisticated RFCC Units and Heavy Distillate FCC Unit intended for high conversion at ROT = 530C-550C typically operate with "cold feed" routinely---since this is far cheaper 'heat sink' than 'cat coolers'. When cat feeds are heavier, it is no longer possible to ramp down 'coke' make to comfortable minimum for fluid catalytic cracking, i.e. minimum 'coke' = 3.8 to 4.2 wt% on cat feed. Note that 'cold feed' must be hot enough so that its kinematic viscosity does not interfere with atomization in the feed injector array and the riser reactor must have hydraulically favorable bend + lift zone + mix zone + lower riser zone.
17/02/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
If a fired heater trips, the heater can be re-started right away, I assume. That is probably faster than starting torch oil to the regenerator and adjusting its flow. If neither is started, and the regenerator continues to burn off coke, albeit at a lower temperature, the following directionally offsetting conditions will result: Cat/oil ratio increases, which is good. Carbon on regenerated catalyst increases, which is bad. Again, if the regenerator is burning, you can run that way indefinitely but not optimally. You may need to adjust the fluidization flows to maintain smooth cat circulation at the higher cat/oil ratio.
17/02/2011 A: Lefter Rinaldo, Netcodietsmann, dumitrurinaldo@yahoo.com
FCC can run with a lower feed temperature by increasing the regenerated catalyst circulation rate if DP across regenerated catalyst slide valve permits, or reducing the feed rate.