Q & A > Question Details
Our FCC feedstock is 30% AR, 20% SR VGO, 50% CR VGO.
Our Vapor line DP increases steadily (sometimes drops) and now it became over 0.43kg/cm2.
We have some ideas about developing during TA but is there anyone who has ideas about dropping
the coke during normal operation?
We are trying
1. ROT increase
2. Feed Temp increase
3. Rx STM increase(ex. Lift STM)
4. Excluding Crude which has high asphaltene component
Is there someone who had suffered from vapor line dp and has some clue about dropping vapor line dp?
27/03/2017 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
Further to Eric Hennings' comments, a proprietary feed injector with the appropriate amount of dispersion steam can help reduce coke formation in the vapour line by delivering a well-dispersed spray of relatively small oil droplets into the circulating catalyst stream. This ensures good catalyst/oil contact, rapid vapourisation and improved yield selectivity (more catalytic cracking reactions, less thermal cracking reactions). Increasing dispersion steam flow above design (assuming slide valve dP and relief system hydraulic limits are not violated) can sometimes help reduce coke formation in the vapour line when processing very high Concarb feeds, but care is required to ensure the combined feed injector tip velocity at the increased dispersion rate does not result in increased catalyst attrition rates and decanted oil (DCO) product to go off-spec for ash content.
13/02/2017 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Coking in the Rx vapor line is likely from incomplete vaporization of feed. A proper feed injector is recommended.
On one FCC processing a "mild resid", the refiner switched from a proprietary feed injector to an alternate pipe injector. Delta P in the reactor vapor line started to increase immediately.
Asphaltenes can also cause coking in the Rx vapor line. Sometimes process changes to increase vaporization or reduce droplet size have been successful on a temporary basis. Pressure drop is irreversible until mechanical cleaning at turnaround.
12/02/2017 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
The instances of coking in plenum have been reported in NPRA proceedings. I will check the references & a try to forward.
09/02/2017 A: NS Murthy, Suez, murthy.ns.ext@suez.com
You may look into the following points.
1. Insulation check on the vapour line as any let up can lead to localized coking.
2. Even though, you may lower the asphaltenes in FCC feed, asphaltenes do get produced in FCC (from dienes) owing to some degree of thermal cracking. Hence, improving Cat Oil ratio could an option to minimize asphaltenes level (track asphaltenes content in CSO - main fractionator bottom stream).
3. Inadequate purge stream in Rx plenum chamber.