QUESTIONS AND ANSWERS

A.FLUID CATALYTIC CRACKING/a.PROCESS(Contd.)

Q.4 : What reactions lead to acetone formation and how they can be mitigated in the FCC
butane/butylenes stream?

A.4 : The presence of significant acetone in the products  from an FCC GRU would be surprising given the contact with water which occurs in the front end of the plant.One potential source is an extraneous stream such as stream from a cumene unit which is fed to the back end of the GRU.

Q.5:What variables influence gasoline aromatics? In particular,please address feed prorties,catalyst,and FCC operating conditions.

A.5:The three key variables which influence gasoline aromatics are feed properties,catalyst properties,and unit operating conditions.

Lower feed hydrogen content translates to lower product hydrogen,i.e.,more aromatic products.Naphthenic feeds make more aromatic products compared to paraffinic feeds.

Catalyst properties are also important.Low hydrogen transfer(low unit cell size/low rare earth) catalyst produces a more aromatic gasoline.ZSM-5 increases aromatics by concentration effect: olefins are cracked out,leaving behind aromatics.

Operating conditions are the third major factor.Increased riser temperature increases gasoline aromatics by dealkylation of larger aromatics and cracking of paraffins,leaving aromatics behind.Cutting deeper to produce more gasoline also increases aromatics,since the aromatics tend to be concentrated in the heavier fractions.

QUESTIONS AND ANSWERS

A.FLUID CATALYTIC CRACKING/a.PROCESS(Contd.)
Q3 With the shift toward greater utilization of “opportunity crudes “ such as Canadian synthetic crudes,what shifts do you expect in FCC product yield and quality and how this will this impact the operation of the FCC unit?

A3.With the shift toward “opportunity’’crudes,FCC  feedstocks are becoming”heavier’’,which lowers API,and are increasingly derived from Canadian synthetic crudes and bitumen blends.While sweet synthetic blends make up the majority of Canadian bitumen derived crudes on the market,some sour synthetic,bitumen and condensate blends (Dilbits,SynBit,SynDilBit)are also available.Processing implications for the FCC refinery will be a function of the type of bitumen-derived crude imported and should be evaluated on a case to case basis.However general trends can be drawn based on the compositional differences between conventional refinery feeds and these “opportunity crudes’’.
    
Compared to conventional crude oil,synthetic crude oil(SCO)provides a larger volume of FCC feedstock with no residue and low total sulfur,nitrogen and metals.with a large aromatic content.On the other hand.Canadian bitumen contains a larger volume of highly aromatic 650F+material,lower API gravity,lower hydrogen content and higher levels of sulfur,nitrogen,nickel,and vanadium.The central issue is the high throughputs required to
process the additional fed that is of poorer quality.

Refiners will see a significant shift in the FCC yield pattern when processing vacuum gas oils from most bitumen -derived crudes.The aromatic nature of SCOs limits FCC bottoms
conversion with an increase in decant oil and light cycle oils yields.Other differences will be observed in the decrease of yield,especially naphtha and LPG,and quality of valuable products,with higher sulfur content in the naphtha and LCO cuts,and an increase in the levels of coke precursors and reactor coking for heavier feedstocks.Also,the LCO produced will have low cetane number due toits high aromatic content.To a certain extent yield improvements are possible with an increase in the catalyst to oil ratio,which can produce pressure balance issues,standpipe and slidevalve sizing increases,and the need to improve/debottleneck the catalyst stripper.The large percentage of VGO-range material in these unconventional crudes may result unit capacity becoming a bottleneck.A higher unit throughput can be accomplished at a high reactor severity,but this would be limited by FCC hardware constraints.All the above-the contaminant levels,composition of bitumen -derived crudes and high feed volumes-make these opoertunity crudes more challengingto upgrade into cleaner fuels and development of tailored FCC catalyst technology playing a key role in addressing these challenges

I.QUESTIONS AND ANSWERS

A.FLUID CATALYTIC CRACKING/a.PROCESS(Contd.)

Q2.For FCC units with a closed riser termination device(RTD)/cyclone systems,do you operate with the primary separator sealed or unsealed in the stripper bed? What differences in performance do you see between these modes?Which do you prefer?

The choice between sealed and unsealed operation is often dictated by the hardware design,sincesome units can only operate in one mode.For those that can operate either way,the choice is usually dictated by either dry gas make or catalyst losses.One unit starts up unsealed and switches to sealed mode when the unit operation stabilizes.

I. QUESTIONS AND ANSWERS

A. FLUID CATALYTIC CRACKING

a.PROCESS

Q1-.What  process or catalyst options are available for shifting  yield selectivity's from gasoline to distillate while minimizing the impact on light olefin yields?

How are the product properties impacted?

How does change-out rate impact the viability of the catalyst options?

A1-The suggested process options for maximizing distillate and light olefin yields are as follows:

Gasoline can be undercut,with the heavier portion dropped to distillate.Cat:oil can be reduced to reduce conversion of distillate to gasoline,which will also increase the olefinicity of the C4s.Reducing cat:oil will increase HCO relative to LCO.

The suggested catalytic options for maximising distillate and light olefin yields are as follows:

Catalytic surface area can be increased to maximize conversion to LCO while minimizing bottoms.This will reduce Gasoline yield relative to LCO while maintaining or increasing olefin yield.A bottoms cracking additive can be used as a quicker way to achieve this effect.The downside to increased matrix surface area is increased coke make.ZSM-5 can be used to increase light olefins at the expense of  gasoline.This option has the advantage of quick response but it needs to  be used in conjuction with process changes to increase  distillate yield.. Catalyst zeolite content can be decreased to minimize cracking of  ddistillate to gasoline.Zeolite rare earth can be optimised to enhance LCO  quality.Decreasing rare earth decreases hydrogen transfer from LCO to gasoline and light olefins and improves LCO product quality.Rare earth changes as well as other catalyst modifications,need catalyst testing to verify the optimum.

There is not much potential for making distillate when processing very paraffinic or heavily hydrotreated feed,since the conversion tends to be high,and gasoline and light olefins are favoured over distillates.