number 106 fall 2009 - grace.com ·...

NUMBER 106 Fa l l 2009

FIFTIETHANNIVERSARY

ISSUE

A message from the editor...

Dear Refiners:

“We need to communicate more often and to communicate more information…Our small

publication…will have material about what Davison is doing. But we hope to incorporate other

values…a forum for discussion of matters of mutual interest to refiners and chemical suppliers.”

So said Grace Davison Vice President Robert Goodall in the editorial of the first issue of the Catalagram® in 1959.

In the half-century since then, we’ve worked diligently to meet these goals through this publication.

Reviewing all the back issues, it’s interesting to note some major trends in FCC history:

• When the first Catalagram® was issued, it featured equilibrium catalyst analysis results. In 1959, our Ecat

Testing Program was already over 10 years old (introduced in 1947). See page 30 for an update on

how we keep this industry-standard testing program current for today’s refiner.

• The Catalagram’s® first guest editor was our Director of Research, Dr. Frank Ciapetta, in Issue #6, 1960. Dr.

Ciapetta was only the first to highlight the commitment we have to design and commercialization of

state-of-the-art FCC catalysts.

• In Issue #13, we introduced our first Glass Model Cat Cracker. The current iteration of this working model was

just demonstrated at a Family Day at a major U.S. refiner and continues to educate everyone from young

children to new FCC process engineers.

• Jim Blazek’s seminal article “Catalytic Cracking-Part One, History and Fundamentals” debuted in Issue #36,

1971. This and the two following parts, became the foundation of our famous “Silver Bullet” in the 1970’s and

later, the “Grace Davison Guide to Fluid Catalytic Cracking, Parts I, II, and III,” which has become an industry-

recognized training guide for FCC engineers in its ten-year history

To celebrate the 50th Anniversary Issue, we have pulled together several classic articles from past Catalagrams®

that have stood the test of time. The introduction to each article highlights why that particular subject has remained

relevant through the years.

Finally, our deepest thanks to you, our readers, for continuing to read, comment, and contribute to the

Catalagram®. With your help, it will continue to be a valuable resource for another fifty years.

Joanne DeadyVice President, Global Marketing

Grace Davison Refining Technologies

IN THIS ISSUE

Coke Selectivity FundamentalsBy Charles C. WearThe 1980's saw the advent of more coke selective zeolites for increasedresid processing and octane.Reprinted from Catalagram #75, 1987

Trouble-Shooting FCC Standpipe Flow Problemsby Raymond W. MottA timeless classic on a critical FCC hardware issue from the early 90's.Reprinted from Catalagram #83, 1992

IMPACT®: A Breakthrough Technology for Resid Processingby Scott K. Purnell, Ph.D.Coke selectivity is the hallmark of all Grace Davison FCC catalysts.Six years later and going strong, Impact is still the catalyst to beatfor coke selectivity.Reprinted from Catalagram #93, 2003

Use Hydrogen in Coke Number to Determine Coke Make Accuracyby David HuntWe saw a return to tech service/troubleshooting articles in the 2000's.This article also complements the coke selectivity article.Reprinted from Catalagram #100, 2006

Clean Fuels: An Opportunity for Profitability Using Gasoline SulfurReduction Technologyby Lauren Blanchard, Craig Borchert (Valero Energy) and Min Pu (ValeroEnergy)A commercial example of the use of Grace Davison Clean FuelsTechnologies to deal with hydrotreater outages.Reprinted from Catalagram #101, 2007

CATALAGRAM 106Fall 2009

Managing Editor:Joanne Deady

Technical Editor:Rosann Schiller

Contributors:Raymond W. MottCharles C. WearScott K. PurnellDavid Hunt

Lauren BlanchardKristen WagnerCraig Borchert

Min Pu

Please addressyour comments to

[email protected]

©2009W. R. Grace & Co.-Conn.

NUMBER 106 Fa l l 2009

FIFTIETHANNIVERSARY

ISSUE

The information presented herein is derived from our testing and experience. It is offered, free of charge, for your consid-eration, investigation and verification. Since operating conditions vary significantly, and since they are not under our con-trol, we disclaim any and all warranties on the results which might be obtained from the use of our products. You shouldmake no assumption that all safety or environmental protection measures are indicated or that other measures may not berequired.

Grace Davison Refining Technologies7500 Grace Drive • Columbia, MD 21044 • 410.531.4000

www.e-catalysts.com

11/09

FIFTIETHANNIVERSARY

ISSUE

Catalagram 106 Fall 2009 1

3

11

23

33

37

Editor’s Note:

The FCC cracking reaction is endother-mic by nature. It is the unique trait ofthe FCC unit that the heat required forcracking is supplied primarily by thecombustion of one of its products, coke.The challenge for catalyst suppliers is toprovide FCC catalysts that will managethe delicate balance between heatrequired and heat supplied. Central forunderstanding the unit heat balance is aconcept termed “delta coke”.

In this article, we discuss the relevanceof coke selectivity and “delta coke” tooverall unit performance and the eventu-al product slate. The article highlightsthe impact of FCC catalyst selection, feed quality, and operating conditionson delta coke and the overall coke selectivity.

Over the years Davison R&D has made significant improvements in catalytictechnology to optimize coke selectivity. Coke selectivity is the most importantconsideration during the development of new FCC catalysts. Later in thisissue, we will discuss the success of IMPACT® catalyst, which remains abreakthrough technology; delivering superior coke selectivity in many FCC’sworldwide.

Charles Wear, principle author of this article, is currently working in ourhydroprocessing joint venture, Advanced Refining Technologies. This articlefirst appeared in Issue #75, 1985

www.e-catalysts.com2

ANNIVERSARY ISSUE

oke selectivity is a term thatoften means different thingsto different people. So to lead

off our discussion, let’s focus on adefinition: Coke selectivity is the rela-tive coke-making tendency of anygiven cracking catalyst. In the vernac-ular, a catalyst that has “good cokeselectivity” means it produces lowercoke compared to some referencecatalyst. This is usually considered afavorable characteristic, since liquidyields are preferred.

That seems fairly straightforward, butthe often misunderstood part is justwhat the phrase “coke-making ten-dency” really means. Many times it isconfused with coke yield asexpressed in say, weight percent offresh feed. However, the coking ten-dency of a catalyst in the context of“coke selectivity” is actually its ten-dency to produce delta coke.

The Concept of Delta Coke

The concept of delta coke is neithernovel nor complicated. It is simplythe difference between coke onspent catalyst (at stripper outlet)and coke on regenerated catalyst,expressed as a weight percent ofcatalyst.

More correctly, delta coke can bethought of as the amount of cokeformed on the catalyst for a singlepass of the catalyst through thereactor which, in the continuoussteady-state operation of a com-mercial FCCU, is also equal to theamount of coke burned off the cat-alyst in the regenerator.

Delta coke also has kinetic signifi-cance, especially on the reactor-side of the process where it formed.The coke on catalyst per pass is a

Charles C. Wear


CokeSelectivity

Fundamentals

C

Losses

StrippingStream

Recycle

Fresh Feed

Reactor Vapors

Flue Gas

Air

Heat ofReaction

Heat ofCombustion

ENERGY INFresh FeedRecycleAirStripping Stream

ENERGY OUTReactor VaporsFlue GasMisc. Losses

=

energy to heat the fresh feed, recyclefeed and stripping steam to reactoroutlet temperature, to heat the air toflue gas temperature, to supply theendothermic heat of reaction and anylosses to the atmosphere--all of thismust come from the coke’s heat ofcombustion. A portion of the feed-stock is therefore “consumed” to sup-ply the energy requirements of theprocess.

One consequence is that the cokeyield as weight percent feed is deter-mined by the sum of these energyrequirements, not by the catalyst cokeselectivity (or feed coking tendencyfor that matter). This is the key conceptthat distinguishes delta coke, which iscatalyst and feed related, to cokeyield, which is not. We will return tothis concept in a moment.

The principle of energy balanceholds for the individual reactor andregenerator as well as the overallprocess, as shown in Figure 2.Table I lists the simplified compo-nents to balance each vessel. Byequating the regenerator heat pro-duction to the heat transferred bycatalyst, a useful relationship canbe derived:

Noting that the catalyst heatcapacity (CpCat) is constant forany particular case, along with thecoke’s specific heat of combus-

function of many variables, includ-ing but not limited to: feed qualityand dispersion at the nozzle, reac-tor temperature and pressure, cata-lyst activity and contact time, andlast but not least, catalyst cokeselectivity.

Therefore, when all other variablesaffecting delta coke are more orless constant, a catalyst that pos-sesses “coke selectivity” will exhibitlower delta coke at any given activi-ty.

A “coke balance” around the regen-erator results in a useful expressionfor delta coke. The coke yield mustequal the difference in coke enter-ing and leaving the regenerator.Therefore,

Note that coke yield and cat/oil mustbe expressed on the same feedbasis, fresh or fresh plus recycle, toyield a meaningful number.

Since coke yield and cat/oil arerelated to delta coke in the above-mentioned manner, it follows that acoke “selective” catalyst candecrease coke “yield”, but not nec-essarily. For instance, in manycases, coke selective catalysts willoperate with higher cat/oil ratioswith little or no change in coke yield.An understanding of this requiresexamination of the FCCU heat bal-ance and the interaction of processoperating variables.

Heat Balance Effects

A commercial unit, like all steady-state processes, must be in energybalance. This means that the totalenergy coming into the processmust equal the energy leaving theprocess, as shown in Figure 1. The

Coke Yield = C/O (CSC-CRC)orCSC-CRC = Coke Yield = Delta Coke

C/O

where:Coke Yield is wt.% FeedC/O is Cat Circulation,lb. Cat/lb. Feed

CRC is Coke on Spent Catalyst,wt.% Catalyst

CRC is Coke on Regenerated Catalyst,wt.% Catalyst


Figure 1Simplified Overall Energy Balance

Heat of Coke Combustion + Other Terms= Heat Transferred by Catalyst

C/O

Coke Yield (ΔHc)~= C/O CpCat (TRegen - TRx)

Delta Coke =~= CpCat

ΔHc(TRegen - TRx)Coke Yield

Losses

StrippingStream

Recycle

Fresh Feed

Reactor Vapors

Flue Gas

Air

Heat ofReaction

Heat ofCombustion

REACTORHEAT BALANCE

REGENERATORHEAT BALANCE

Spent Cat

Regen Cat

Losses

tion (Hc) when hydrogen in cokeand degree of CO combustion areconstant, the following proportional-ity holds:

This implies that a coke selectivecatalyst will, for a constant reactortemperature, reduce regeneratortemperature. This is exactly what isobserved commercially. Considerthe unit in full combustion that haschanged to a catalyst with differentcoke selectivity. Depending on theshift in delta coke, the changesshown in Figure 3 occur.

Of course, unit response to cokeselective catalysts is not limited toregenerator temperature reduc-tions. Consider the unit in partial COcombustion, where a drop in regen-erator temperature could possiblyresult in a undesirable increase inregenerated catalyst carbon level.For this case, it would be wise forthe operator to intervene--viaincreased promoter additionsand/or air rate-to burn more CO to

Delta Coke, wt.%

Sample A

Routine Feed

Sample B

Sample C

Reactor Temperature 980˚FFeed Temperature 450˚FNo RecycleFull Combustion2 mol.% O2 in Flue Gas

1340

1320

1300

1280

1260

9.0

8.0

7.0

6.0

1360

1380

1400

5.0

0.70 0.80 0.90 1.000.60

Deg

rees

˚FW

t.%C

oke

Yie

ldo

rC

/O

Example:

C/O

Coke Yield, wt.%

Regen Temp, ˚F

Delta Coke (TRegen - TRx)

Figure 3Typical Effect of Delta Coke on FCC Operation


Figure 2Energy Balance of Reactor and Regenerator Involves Catalyst Circulation Rate

CO2 and thus return the dense bedto original temperature.

In this example, these “externalstimuli” from the operator directlyaffect the overall heat balance byincreasing the heat release perpound of coke burned (higherCO2/CO). It therefore takes the com-bustion of less coke to satisfy theenergy demand of the process. So,for this partial combustion case,coke yield will drop at the same ornearly the same reactor/regeneratortemperatures (and therefore cat/oil).It has to, because the catalystcaused a reduction in the deltacoke, and by definition coke yieldmust be lower if delta coke drops atconstant cat/oil!

Remember earlier in this discussionit was stated that catalyst (and feedquality) have a direct effect on deltacoke, but that the unit heat balancedetermines coke yield. As the pre-ceding example showed, some-times it’s difficult to separate whatchanges were caused directly bycatalyst (or feed) as opposed toheat balance changes made by theoperator.

In reality, the difference is not veryimportant in many cases. Theimportant point is that coke selec-tive catalysts will, in more casesthan not, allow an operator to havemore flexibility in running his plant.Below are some of the ways we

have seen operators use Davisoncoke selective catalysts to their fullestextent, and thus alleviate operatingconstraints and improve refinery prof-itability:

• Increase reactor temperature toproduce maximum gasolineoctane.

• Increase cat circulation forincreased conversion.

• Increase resid content for addi-tional bottoms destruction.

• Increase feed rate to satisfyincreased product demand.

• Increase CO2/CO for lower

coke yield.

As with many things in life, “more” cat-alyst coke selectivity in all cases doesnot necessarily mean “better”. A thor-ough review of the base operation,including goals and constraints,should be performed before any cata-lyst change is considered. For exam-ple, some operations are precludedfrom the use of incremental catalystcoke selectivity. Consider the unit infull combustion, at maximum catalystcirculation and feed temperature, thatcannot “heavy-up” the feed noraccept a lower reactor temperature.This obviously is not a unit that wouldprofit from catalyst coke selectivity. it isa unit, however, which could greatlybenefit by removing these limitations,and many have done exactly that viarevamps.

Heat Transferrredby Catalyst

Reactor HeatRequirements

Regen HeatProduction

+ Heat of Reaction

+ Heat Up Feed+ Heat Up Recycle+ Heat Up Strip Stream

+ Account for Losses

- Heat from RegenEntrainments

+ Heat of CokeCombustion

- Heat Up Air- Heat Up Coke- Heat Up RxEntrainments

- Account forLosses

(C/O) Cpcat (TRegen-TRX)

A Check on Data Consistency

The fact that delta coke can bemeasured directly by comparingthe difference in coke levelsbetween spent and regeneratedcatalyst samples was discussedearlier. Delta coke determined inthis manner, versus the calculationsof delta coke from the unit heat bal-ance, can be a useful tool to checkdata consistency.

Most process engineers will calcu-late coke yield using air rate andflue gas composition, and then cal-culate catalyst circulation rate byheat balance. These coke yield andcat/oil results can then be used tocalculate a delta coke. If this “heatbalance method” to obtain deltacoke differs substantially from thedirect sampling method, it couldmean one or more of the following:

• Incorrect flue gas analysis orair rate (the most commonproblem).

• Nonrepresentative catalystsamples (also a commonproblem).

• Error in heat balancemethod, data or assump-tions.

• Excessive entrainment ofinterstitial hydrocarbonsthrough the stripper.

Types of Delta Coke

It is convenient to define compo-nents of delta coke as to source,and several proposed breakdownshave been published. A sampling islisted in Table II. The three compo-nents of delta coke defined belowcan be influenced by proper cata-lyst design:

1.Catalytic-the coke depositformed when hydrocarbon iscracked via acid site cataly-sis.

2.Cat/Oil-adsorbed/unstrippedhydrocarbons entrained bycatalyst flowing through thestripper.

Table IEnergy Balance Relationship


Relative Zeolite/Matrix Activity Ratio

Pilot Plant Data930˚F Reactor Temperature75 Sec. Contact Time1.1

1.0

0.9

0.8

0.7

1.2

1.3

1.4

0.0 1.0 2.0

Rel

ativ

eD

elta

Co

ke

0.6

0.5

0.4

3.0 4.0 5.0

Aromatic Feed @60 LV%

Conversion

Paraffinic Feed @75 LV%

Conversion

3.Contaminant-coke produced asbyproduct of contaminantmetal (V, Ni, Cu, Fe) dehydro-genation activity.

Catalytic Delta Coke

Most cracking catalysts have twosources of acid sites, and thereforetwo types of activity-zeolite andmatrix. Zeolite is crystallinesilica/alumina with a specific struc-ture. In the usual case it is wheremost of the overall catalyst activityresides.

The balance of the catalyst particleis defined as the matrix. it may besimilar to the zeolite in composition(silica/alumina), but does not havethe particular crystalline structureunique to zeolites. Many of today’smatrices resemble the amorphouscatalysts of the 1950’s and 60’s.†

The activity associated with the zeo-lite and the matrix have very differ-ent selectivity patterns, especially inregard to coke. This is illustrated inFigure 4. As matrix activity relativeto zeolite is minimized, delta coke atconstant activity decreases--thecatalyst becomes more “cokeselective”.

Differences in zeolite type also affectcoke selectivity. The key issue is thechemical composition (Si/Al ratio) ofthe equilibrated zeolite, which ismeasured by X-ray as the unit cellsize. Zeolites that equilibrate with highSi/Al ratios (low cell sizes) exhibitretarded hydrogen transfer rateswhich, among other things (such asincreasing gasoline octane), reducecatalytic coke make. Davison’s experi-ence with these zeolites, genericallyreferred to as “ultrastable” or USYtypes, is unmatched in the industry.The premium form of USY, patentedby Davison as “Z-14US”, is the core

technology behind Davison’s cur-rent octane catalyst product line.The coke selective properties ofthese octane catalysts have beenthoroughly treated in earlierCatalagrams (Numbers 73 and 74).

Cat/Oil Coke

Cat/oil coke is perhaps the mostinsidious component of delta cokebecause1 it is totally independent ofany beneficial chemical reactiontaking place, such as making gaso-line, and2 it has the highest heat ofcombustion (highest hydrogen con-tent) which leads to high intraparti-cle temperatures during regenera-tion.

A properly designed and operatedcatalyst stripper will minimize theamount of hydrocarbons that flowinto the regenerator along with thecirculating spent catalyst. Strippingsteam rates of at least two lb. per1000 lb. of catalyst circulated aretypically recommended. Increasingcatalyst level (residence time) in thestripper can also be effective in min-imizing carry-over. The commoncommercial practice is to increasesteam rate and/or stripper level untilno further reduction in regeneratortemperature is observed, providing,of course, reactor-side catalystlosses do not increase.

UNIT

CATALYST

FEED TYPE

DELTA COKE TYPES

Catalytic

Cat/Oil

Contaminant

Feed/Nondistillable

TOTAL

Wt.% Cat

0.52

0.12

0.12

0.04

0.80

% Total

65

15

5

15

100

Wt.% Cat

0.40

0.10

0.40

0.50

1.40

% Total

29

14

29

28

100

Gas Oil Resid

Zeolite-Low Metals Zeolite-High Metals

A B

Table IITypical Delta Coke Breakdowns (1, 2)


Figure 4Effect of Zeolite/Matrix Activity on Catalyst Coke Selectivity

†In the 1980's most high matrix catalysts were neither selective nor metals tolerant. Today's high MSA MIDAS® catalysts have been shown to improve coke selectivity

by eliminating and cracking coke precursors.

CATALYST Fresh

68.50.212.6

70.00.424.15

79.00.454.0

1Deactivation Conditions: 1350˚F, 100% Steam, 15 psig, 8 Hrs.2Aged 13 Cycles in Cyclic Fixed-Fluid Bed Pilot Units; 40 WHSV, 3 c/o, 1000˚FReaction/1100˚F Regeneration

3Typical Matrix Surface Area

Super-D (50 m2/gm)3

MA, V%H2, Wt.%Coke, Wt.%

Competitor B (115 m2/gm)3


Competitor A (220 m2/gm)3


Aged2

69.50.082.5

68.00.384.2

78.00.353.9

Aged2

69.00.0752.45

69.50.145

2.8

77.00.143.8

500 ppm Ni (Impregnated AfterSteam Deactivation1) 500 ppm Ni + Sb

Steam injection displaces hydrocar-bon vapor between catalyst parti-cles-it is not very effective in revers-ing surface adsorption or pore con-densation. In some cases, higherreactor (stripper) temperatures havebeen found to reduce cat/oil coke.The mechanism may involve volatiz-ing and/or further cracking of des-orbed material.3

Cat/oil coke is also influenced bycatalyst matrix pore size and sur-face area. Catalyst “strippability”can be measured in the lab by sub-jecting an inert porous material toheavy oil, followed by nitrogen strip-ping at typical reactor operatingconditions. The results is shown inTable III as a function of strippingtime and temperature.

High intraparticle temperaturesassociated with adsorbed hydrocar-bon have been the subject of sever-al studies,4,5 which showed thathigh surface area (hence, moreadsorptive) catalyst particles areprone to deactivate rapidly whenregenerated. Particle temperaturesseveral hundred degrees higherthan average regenerator bed tem-peratures were calculated.

To summarize, catalysts designed tominimize the cat/oil component of deltacoke should have low surface area,large average pore diameter matricesto discourage hydrocarbon adsorptionand enhance “strippability”.

Contaminant Delta Coke

The hydrogen-producing effect offeed metals-particularly that of nick-el, copper, and vanadium-deposit-ed on the cracking catalyst is wellknown. Coke is a companion prod-uct of dehydrogenation, and fromTable II it is clear that contaminantcoke can be a substantial percent-age of the overall delta coke formetals-laden catalysts.

The passivation of nickel by antimo-ny (licensed by Phillips PetroleumCo.) and of vanadium by tin addi-tives is being practiced commer-cially.ƒ Claims of a 50% reduction inhydrogen and coke produced bycontaminant metals have been pub-lished.6,7,8,9

We have found that the level ofhydrogen and coke production dueto contaminant metals is also afunction of catalyst matrix composi-tion. Matrices with low alumina con-tent and low surface areas are moreeffective in minimizing contaminantmetal dispersion and dehydrogena-tion activity√ (Table IV).

Surface Area, M2/g

Pore Volume, cc/g

Volume Avg. Pore Diameter, A

439

0.89

72

Stripping Temperature

900˚F

990˚F

900˚F

990˚F

389

1.8

184

105

1.14

436

Unstripped Coke (Wt.% FF) After 1 Minute

17.3

2.0

17.7

1.7

6.4

1.3

1.5

1.7

Unstripped Coke (Wt.% FF) After 15 Minutes

1.3

0.9

1.1

0.8

Conditions: MAT REACTOR: 5 gm. Charge, 16 WHSV, 3 C/O,WEST COAST FEED, N2 STRIPPING AT 30 SCCM,

Volume Avg. Pore Diameter: 40,000 (pore Volume)

Surface Area

Table IIIEffect of Surface Area on Hydrocarbon Stripping

Table IVMetal Aging Study Results(10)


ƒTin passivation is no longer practiced in the industry. Integral vanadium traps, such as those in IMPACT, are much more effective for selectivity preservation in highmetals operations.√See note on page 7.

Coke Selective CatalystProperties

As can be seen from the precedingdiscussion, catalyst design has adirect bearing on the formation ofvarious components of the overall“delta coke”. Certain catalyst prop-erties, associated with the true“coke selective” catalyst system, actto minimize delta coke for any givenactivity level. The essential ingredi-ents are1 a zeolite that will equili-brate at low unit cell size, whileretaining the appropriate activitylevel to dominate that of the matrixand2 a matrix of controlled surfacearea with large pores to maximizestrippability and control dispersionand dehydrogenation activity ofcontaminant metals.


Davison has used these principles foryears to design a wide range of cata-lysts. Current examples are membersof the Octacat, GXO, and Nova fami-lies that have led the industry in cokeselectivity, as well as octane enhance-ment. Davison R&D is focused on acontinuous program of improvingthese products, as well as on thedesign of new coke selective gradessuch as the DXB family.

References

1. Cimbalo, R.N., Foster, R.L., and Wachtel,S.J.; O&GJ; May 15, 1972; p. 112.

2. Mauleon, J.L., and Courcelle, J.C.; O&CJ;October 21, 1985; p. 64.

3. Schuurmans, H.A.J.; Ind. Eng. Chem.Process Des. Dev.; 19(2); 1980; p. 267.

4. Bondi, A., Miller, R.S., and Schlaffer, W.G.;Ind. Eng. Chem. Process Des. Dev. 1(3); 962;p. 196.

5. Wilson, W.B., Good, G.M., Deahl, T.J.,Brewer, C.P., and Appleby, W.G.; Ind. Eng.Chem.; 48(11), November 1956; p. 1982.

6. Johnson, M.M. and Tabler, D.C.; US No.3,711,422.

7. Dale, G.H. and McKay, D.L.; HydrocarbonProcessing; September 1977; p. 97.

8. English, A.R. and Kowalczyk, D.C.;O&CJ, July 16, 1984; p. 127.

9. Barlow, R.C.: “Commercial Application ofVanadium Passivation Technology”, NPRASpring Meeting, 1986.

10. Ritter, R.E.; Catalagram No. 73; 1985; p.14.

Gatte Named North American General ManagerBob Gatte has been appointed General Manager - North America, RefiningTechnologies. In his new role, Bob will have overall responsibility for theNorth American business activities in support of the global RefiningTechnologies strategy. Bob will also be a member of the RefiningTechnologies global management team.

Bob has worked in key roles at Grace for the last 21 years. He has previous-ly held positions as the Vice President Sustainability and New Ventures; VicePresident and General Manager of the Discovery Sciences business,

General Manager Grace Catalyst AB in Stenungsund, Sweden, and Vice President and COOof e-Catalysts, Inc. In the earlier part of his career, Bob held positions as Technical SalesManager for FCC, and a Manager of Business Development for Davison Catalysts.

Bob has a PH.D in Chemical Engineering from the Pennsylvania State University and aBachelor of Science in Chemical Engineering from Rensselaer Polytechnic Institute.

Editor’s Note:

The most profitable operation of anFCCU requires the integration of a supe-rior FCC catalyst as well as optimizedoperating conditions for a given feedstream. However, the physical charac-teristics of the unit also play an impor-tant role in achieving optimal unit prod-uct yields and profitability.

It is necessary to operate the FCCU atsteady conditions to ensure the heat bal-ance required to achieve these goals.This means that, along with other operat-ing parameters, steady catalyst circula-tion is necessary to guarantee a smoothoperation that will produce a productslate of maximum earnings for the refiner.

Occasionally, problems with catalyst flow in the standpipes can hinder contin-uous catalyst circulation from the regenerator to the riser, causing major prob-lems in the unit and in extreme cases, a unit shutdown.

In this article we discuss how to diagnose and solve flow problems in theFCC standpipes. We will look at the importance of pressure profiles in thestandpipes, catalyst compression mechanisms, and show an example of thecalculation of standpipe tap aeration requirements.

This article, originally published over 15 years ago is still a trusted referencefor the industry when evaluating and solving catalyst fluidization problems inthe FCCU.

Principal author Ray Mott is a recognized FCC expert who consults for GraceDavison. This article was first published in 1992, issue #83.


ANNIVERSARY ISSUE

Introduction

roubleshooting the perform-ance of an ill-behaved FCCstandpipe can present one

of the most difficult challenges thatthe FCC process engineer faces. Notonly is the nature of the catalyst circu-lation problem very nebulous, but theexistence of a catalyst circulationproblem places a great deal of techni-cal and economic pressure on theprocess engineer’s shoulders.

This paper will discuss how to system-atically diagnose the operation of anFCC standpipe with chronic problems.In the process, some of the causes forthe behaviors observed in standpipeoperation will be investigated, andsome engineering bench marksagainst which the operation of theFCC standpipe can be compared willbe presented.

Symptoms of Standpipe FlowProblems

There are a whole range of catalystcirculation symptoms that show up inFCC standpipes. Many of these symp-toms are interrelated, and there are

several distinctly different problemsthat exhibit the same symptoms. Allof this makes troubleshootingstandpipe flow problems extremelychallenging.

Some of the symptoms of catalystcirculation problems that commonlyoccur in standpipes include:• Low slide valve (or plugvalve) differential pressure.• An inability to circulate addi-tional catalyst despitechanges in slide valve posi-tion. Often this is accompa-nied by an inability to controlreactor temperature.• Erratic slide valve differentialpressure that threatens theloss of catalyst circulation.• Physical bouncing or hop -ping of catalyst standpipes.

Any of these symptoms can makesmooth FCC operations impossible.However, before we dive into troubleshooting, it is worth looking into thedetailed mechanics of catalyst flowin standpipes to establish a frame-work for investigation.

Raymond W. Mott


Troubleshooting FCCStandpipe Flow

Problems

T

Pressure Profiles in the FCCStandpipe

One way to glimpse into the work-ings of the FCC standpipe is to con-duct a pressure survey along itslength. Usually, the most readilyavailable way to do this is to con-duct a single gauge survey. In thistype of survey, a single calibratedpressure gauge is carried up anddown the FCC structure to measurethe pressure at various locationsalong the length of the vessels andstandpipes. This helps reduce theerrors that reading many separategauges would introduce.

In principle, the FCC standpipe isexpected to behave analogously toa pipe full of water. The pressuremeasured at any depth in the stand-pipe should be roughly proportionalto the density of the fluidized cata-lyst and the height of the catalystabove the point where the pressureis being measured. Figure 1 showsthe “idealized” pressure profile thatwould be observed in a perfectlybehaved FCC standpipe. The pres-sure is linearly increasing withrespect to depth in the standpipe.

In practice, when a standpipe is expe-riencing operating difficulty, the pres-sures observed at any point along thelength of the standpipe may be goingthrough wild gyrations. So, taking ameaningful single gauge pressuresurvey will require patience.

Obviously, FCC catalyst differs fromwater in the important sense that it isactually a fluidized solid. Less obviousis the fact that non-fluidized powderscan support their own weight againstthe walls of their container. For exam-ple, as an empty storage silo is filledwith corn or wheat, the pressure onthe floor of the silo initially increasesas the height of grain in the siloincreases. However, when the grainreaches a depth of approximatelythree times the diameter of the silo,the pressure on the floor of the silostops increasing. The grain in theupper levels of the silo supports mostof its own weight against the silo wallsinstead of the floor!

The implications for FCC catalyst flowin a standpipe are dramatic. If the cat-alyst loses its fluidization, it, too canstart supporting a portion of its weightagainst the standpipe walls, and theslide valve at the bottom of the stand-pipe will see a reduced pressure

Standpipe Inlet Standpipe Inlet

Normal PressureIncrease

Standpipe withCirculation Problems

Incr

easi

ngD

epth

Incr

easi

ngD

epth

Increasing Pressure Increasing Pressure

Bed “Level” Bed “Level”

Slide ValveSlide Valve

buildup. A pressure survey will pro-vide a better idea of what is goingon inside the standpipe, and mayhelp isolate where such local prob-lems as defluidization are occur-ring.

Figure 2 shows the pressure profilefor a standpipe that is experiencingmoderate circulation difficulties. Atfirst, the pressure is increasing nor-mally as you descend the stand-pipe; however, this standpipe hastrouble building additional pressurebelow the second aeration tap(counting from the top down).

A more extreme problem is shownin Figure 3. In this standpipe, thepressure profile actually shows aloss of pressure below the secondaeration tap, and an inability to buildup much pressure below this point.

The single gauge pressure surveysshown in Figures 2 and 3 suggestthat the catalyst flow may beobstructed by a foreign object or bybubbles. Another possibility is thatthe catalyst may be losing its flu-idization in some sections of thestandpipe so that a portion of thecatalyst weight is supported againstthe walls.

Figure 1Idealized Pressure Profile in a Standpipe



The Narrow Operating Window ofthe FCC Catalyst

FCC catalyst only has a narrowrange of conditions under which itwill flow well in standpipes. At oneend of this operating range, the cat-alyst is at the point of incipient bub-bling. If any more gas were presentin the fluidized catalyst emulsion,then there would be a tendency forthe system to generate bubbles. Instandpipes, bubble formation tendsto impede catalyst flow because thebubbles act as obstacles that thecatalyst must flow around.

Incipient fluidization represents theother end of the well-behaved oper-ating spectrum. If there were anyless gas present in the catalystemulsion at this point, the fluidizedcatalyst would then revert back to apacked bed.

These two extremes of fluidizationare often measured in terms ofvelocity, and many articles havebeen written on measuring thesuperficial gas velocity at incipientbubbling (Uib) and the superficial

Standpipe Inlet

Incr

easi

ngD

epth

Increasing Pressure

Bed “Level”

Slide Valve

Standpipe with SevereCirculation Problems

Loss ofStandpipe Pressure

gas velocity at incipient fluidization(Uif) in beds of FCC catalyst. In anoperating FCC standpipe, however,gas velocity has only a very nebulousmeaning because it is difficult todetermine what the relevant gasvelocity is.

Fortunately, the well-behaved operat-ing range can also be defined in termsof the density of the fluidized emul-sion. Thus, the range of densitiesbetween the density of the emulsion atits point of incipient fluidization (ρ if),and its point of incipient bubbling(ρ ib) can be considered the range ofdensities over which a fluidized FCCcatalyst will be well-behaved in astandpipe.

The catalyst beds encountered incommercial FCC units do not general-ly operate as quiescent fluidized bedsthat are confined to operate within therange of densities mentioned above.The typical catalyst bed found in theaverage FCC regenerator, for exam-ple, is usually operating as a veryactive bubbling bed. In open fluidizedbeds, bubbles do not present a flu-

idization problem. However, in astandpipe, bubbles need to beavoided. Thus, as the bubbling bedof catalyst begins to enter an FCCstandpipe, it needs to shed itself ofthe excess gas bubbles to avoiddragging them down into the stand-pipe. The standpipe inlet geometryand location of the standpipe inletsshould be carefully designed toallow this initial shedding of excessgas to take place in an orderly fash-ion.

It is beyond the scope of this paperto go into how the specific inletgeometry should be arranged; how-ever, from the troubleshooting pointof view, the process engineer needsto be aware that this process ofshedding excess gas is takingplace at the inlet to the standpipe.Thus, introducing aeration right atthe standpipe inlet often causesmore problems than it solves.

The Compression of Catalyst in aStandpipe

After the fluidized FCC catalystemulsion enters the top of thestandpipe and begins its descent, itstarts to undergo a form of com-pression. As the catalyst descendsthe standpipe, the pressure headthat is seen at any given depth inthe standpipe increases. Thisincreasing pressure compressesthe interstitial gas that is surround-ing the catalyst particles, as well asthe gas that is in the pores of thecatalyst particles. The net result ofall this gas compression, is that thevolume of the fluidizing gas sur-rounding the catalyst particles isreduced. So the catalyst particlesmove closer together, and the densi-ty of the emulsion increases.

If the standpipe is long enough,and if no aeration is introducedalong the length of the standpipe,then this process of compressionwill continue as the catalyst travelsdeeper and deeper into the stand-pipe. This will cause the density ofthe catalyst emulsion to continue toincrease until the catalyst emulsionreaches its incipient fluidization



Standpipe Inlet

Bed “Level”

Slide Valve

Aeration Counteracts theCompression of the CatalystEmulsion in the Standpipe

density. If the catalyst emulsion iscompressed past this point, theemulsion will change phase from afluidized bed to a packed bed, andthe catalyst will have trouble circu-lating.

On FCC units that use standpipeaeration, the purpose of the stand-pipe aeration is to supply justenough additional gas to the cata-lyst as it passes each aeration tap torestore the catalyst emulsion to itsoriginal volume, as in Figure 4.

The ration of ρ if/ρ ib is known as the“Stable Expansion Ratio” for a flu-idized catalyst. The higher this ratio,the more forgiving the fluidized cat-alyst is to changes in density, andthe more easily it will tend to circu-late in an FCC unit.

Another way of interpreting this ratiois to realize that it represents themaximum compression factor thatthe catalyst emulsion can beexpected to tolerate as it descendsthe standpipe before losing its flu-idization.

Abrahamsen and Geldart1 haveshown that the ratio of the superfi-cial gas velocity at incipient bub-bling to the superficial gas velocityat incipient fluidization is a functionof the physical properties of thecatalyst as shown below.

Where:

Uif =Superficial Gas Velocity atIncipient Fluidization, m/sec.

Uib =Superficial Gas Velocity atIncipient Bubbling, m/sec.

ρg =Gas Density, kg/m3.

ρp =Particle Density, kg/m3.

µ =Gas Viscosity, kg/m sec.F =0-45 micron Fines Fraction in

Catalyst.

dp =Mean Particle Diameter, meters.

g =Gravitational Constant,

9.81m/sec2.

They also show that the MaximumStable Expansion Ratio (MSER) canbe estimated from the equation below:

Inspection of Equations 1 and 2shows the following:• Very low fines content in theequilibrium catalyst greatlyreduces the maximum stableexpansion ratio. Thus, stand-pipes that normally operatewell will often fail when thecyclone performance deterio-rates and the 0-40 micronfines content of the equilibri-um catalyst falls.• Catalyst with a very highequilibrium apparent bulkdensity (ABD) also can

aggravate standpipe circula-tion problems because themaximum stable expansionratio decreases with increas-ing catalyst particle density1.

Both of these effects are clearly illus-trated in Figure 5 which is taken fromwork published by Magnussun2.Figure 5 shows the measuredMaximum Stable Expansion Ratiosfor a series of equilibrium FCC cata-lysts at room temperature and pres-sure. The sensitivity of the measuredMSER in Figure 5 to changes in ABDand the 0-40 micron fines fractionappears to be significantly greaterthan what Equation 2 would predict.This lack of precise agreement iscommon in the field of fluidization. Itis mentioned here to illustrate thatpublished correlations and measure-ments need to be applied cautiously.

Equation 2 and Figure 5 both pro-vide estimates of the MSER for FCCcatalyst under “ideal” conditions. Inactual practice, the effective MSER

UibUif

=2300ρg0.126 μ0.523 e (0.716˚F)

dp 0.8 g 0.934 (ρp-ρg) 0.934(1)

MSER = ρifρib = Uif

Uib( ( (2)

Figure 4Compression of Catalyst in a Standpipe


1High apparent bulk density (ABD), typically correlates with high particle density in equilibrium FCC catalyst.

0-40 Micron Fines Content of Catalyst, wt.%

0.83 ABD

Max

imu

mS

tab

leE

xpan

sio

nR

atio

0 5 10 15 20 25

1.25

1.2

1.15

1.1

1.05

1

0.92 ABD

0.87 ABD

0.85 ABD

0.81 ABD

Measured at Room Temperature and Pressure

of the catalyst in the FCC standpipeappears to be only a fraction of thisestimated number, so the MSERshould not be taken at full facevalue when looking at standpipecompression. However, the relativechanges predicted in MSER byEquation 2 and Figure 5 due to par-ticle size, ABD, viscosity, and gasdensity are very real effects. it isthese relative movements in MSERthat are very useful for troubleshoot-ing.

In an operating FCC unit, one of theramifications of Equations 2 andFigure 5 is that the ability of theequilibrium catalyst to tolerate com-pression can change dramaticallydue to subtle effects like a loss offines, or an increase in ABD thatmight accompany a catalystchange out.

The limited ability of equilibriumFCC catalyst to tolerate compres-sion places a great deal of impor-tance on proper standpipe designand aeration practices.

With these ideas in mind, let’s moveon to troubleshooting standpipe cir-culation problems.

Assess the Situation; GatherFacts and Figures

When troubleshooting, a good wayto get started is to gather somefacts about the status of the stand-pipe’s operation for comparisonagainst useful bench marks. In theprocess, ask as many questions aspossible about the history, andrecent operation of the troubledstandpipe. Some of the typicalavenues of investigation are out-lined below.

Catalyst Flux

A quick calculation of the catalystflux passing through the standpipewill help indicate how high the dutyof the standpipe is. Calculate thecatalyst flux rate (kg/m2 second) atwhich the standpipe is operating.

How does this compare with pastoperating experience for the unit inquestion? Many FCC standpipes willoperate with a flux as high as 980-1220 kg/m2 second (200-250 lbs/ft2

sec). Some standpipes have beenobserved operating as high as 1465kg/m2 second (300 lbs/ft2 sec). If yourcatalyst flux is up at these levels youmay be operating near the practicalcapacity of your FCC standpipe. If, onthe other hand, the catalyst flux is sig-nificantly lower than this, then it is like-ly that something other than a sheercapacity limitation is causing the cata-lyst circulation problem.

Look at the Standpipe PressureProfile

Conduct a single gauge pressure sur-vey along the length of the standpipeand the vessel from which it is coming.What type of pressure profile is thestandpipe generating? How does thiscompare with the idealized profilesdiscussed earlier? Usually, you arelooking for a section of standpipe thatis not generating the expected pres-sure head as a clue to where the prob-lem is located.

Sometimes it is difficult to visualizewhat is going on inside those sectionsof the standpipe that are not buildingpressure. There are really several dif-

ferent phenomena that can createthis type of pressure profile.• The catalyst might be deflu-idized so that it is supportingits weight against the walls.• There may be stationary bub-bles2 in the standpipe thatare acting as obstructions.• There may be a real obstruc-tion like a piece of droppedrefractory or a workman’sshovel.

In any case, the section of thestandpipe immediately below anobstruction will have a tendency tooperate with a dilute rain of catalystfalling through an essentially emptystandpipe. This type of flow doesnot generate the pressure buildupthat the standpipe needs to pro-duce.

Check the Standpipe AerationPractices

The aeration rates being used onthe standpipes should be checkedagainst the theoretical aerationrates calculated in the next section.Defluidization of the catalyst fromunder-aeration, or obstructions inthe form of bubbles from over-aera-tion, can both be caused by errorsin the standpipe aeration.Unfortunately the symptoms for

Figure 5Maximum Stable Expansion Ratio

Versus Fines Content of Equilibrium Catalyst


2Unlike the gas contained in the continuous emulsion phase, bubbles can arise at velocities that are competitive with the velocity of the descending catalyst emulsionin the standpipe. Thus, if bubbles form in the FCC standpipe, they can rise against the flowing catalyst, be pulled down by the flowing catalyst, or remain stationary inthe standpipe, depending on the relative bubble and catalyst emulsion velocities involved.

Standpipe Inlet

Distance from Top of Bedto Inlet is 1.83 m

Operating Conditions of Regenerator:

Catalyst Circulation, Metric Tons/Min. 12.0Regenerator Pressure, kPa gauge 87.2Regenerated Catalyst Temperature, ˚C 682Molecular Wt. of Aeration Medium 18.0 (Steam)

Bed “Level”

Distance from Inlet toFirst Aeration Tap is 2.85 m

Assume that the Standpipe Density will be 560.65 kg/m3

You need to know the skeletal density of the catalyst.This can either be measured or estimated from composition.For this example use 2549.9 kg/m3

560.7kg/m3

both these problems are very simi-lar, so it is necessary to use a theo-retical aeration rate as a point of ref-erence.

It is very important to calculate theaeration required by each individualaeration tap location along thelength of the standpipe. This infor-mation provides a great deal ofinsight into how the standpipewants to operate, and provides abasis for comparing the actual aer-ation rates. Not calculating the indi-vidual aeration tap requirements isa serious mistake because theopportunity to look at the operatingrequirements for each section of thestandpipe may be missed.

Also, ask as many questions as pos-sible about the standpipe aeration.Some questions that come to mindare:• How much aeration is beingused in the standpipe?• Is steam, air, or some othergas being used for aeration?Why is this particular mediabeing used?• If the standpipe is beingaerated with steam, is itabsolutely dry steam, orcould there be condensateslugging into the standpipe?• How much aeration is beingsupplied to each individualtap?• How does the aeration ratecompare with the theoreticalaeration rate calculated foreach individual tap?• Could some of the aerationtaps be plugged?• How is the aeration beingdistributed to the taps?• Does the aeration systemuse rotometers for each tap,or are orifices being used toobtain distribution?• How confident are you thatthe aeration is going whereyou think it is going?

• How does the aeration ratecompare with theoretical andhistorical bench marks?(More on these later.)• Are the aeration tap locationscorrect? Don’t automaticallyassume that they are.(More on this later also.)

If the standpipe does not have aera-tion, read on, since this is where theplot thickens.

Calculation of Standpipe AerationRequirements

The calculation of the aeration, need-ed at any one of the pressure taps, isrelatively straightforward. The stepsrequired are outlined below, followedby a worked example.

1) Calculate the volume of cata-lyst that is descending thestandpipe.

2) Calculate the volume of voids

that are circulated with the cat-alyst3.

3) Calculate the absolute press-ure that should be observed atthe stand-pipe inlet and at thevarious aeration taps along thestandpipe length using anassumed emulsion density.

4) Calculate the change in gasvolume due to the pressureincrease between adjacent aer-ation taps.

This is the theoretical volume of gasthat should be introduced into the tapunder investigation. However, in prac-tice only about 60-70% of this quan-tity of aeration is usually needed.

The example discussed below isillustrated in Figure 6.

Example 1

Calculate the steam required to aer-ate the first aeration tap in a regen-

Figure 6Calculation of Aeration Requirements


3The circulation of the catalyst in the standpipe actually pumps the gas that occupies the spaces between (and inside) the particles down the standpipe with the cat-alyst.The minimum fluidization velocity of FCC catalyst is on the order of 0.003m/second, while the velocity of the catalyst descending the standpipe is several orders of

magnitude higher than this. So the gas that is in the continuous emulsion phase between and inside the catalyst particles is, in effect, dragged down the standpipewith the catalyst.

erator standpipe that is operating atthe following conditions:

Catalyst circulation:12 metric tons per minute

Regenerator Temperature:682˚C (1260˚F)

Regenerator Dilute Pressure:82.7 kPa gauge (12 Psig)

Molecular Weight of Aeration Gas:18.0 (Steam)

The distance from the surface of thecatalyst bed in the regenerator ves-sel to the inlet of the standpipe is1.83 meters (6 feet).

The distance from the inlet of thestandpipe to the first aeration tapbelow the inlet is 2.85meters (9.35 Ft).

You will need to assume a densityfor the fluidized catalyst inside thestandpipe. for the sake of these cal-culations, it is customary to assumea density of 560.65 kg/m3 (35lbs/ft3).

You will also need to know the skele-tal density of the equilibrium (notfresh) FCC catalyst being used.This can either be measured usinghelium pycnometry, or the skeletaldensity can be approximated fromthe calculation below:

Where:

ρskeletal = Skeletal density ofcatalyst, kg/m3.

Al2O3 = Weight fractionAlumina in catalyst.

SiO2 = Weight fraction silicain catalyst.

For this example, a skeletal densityof 2549.9 kg/m3 was measuredusing the equilibrium catalyst.

1) Calculate the volume of the cata-lyst emulsion that is traveling downthe standpipe per minute:


ρskeletal (3)Al2O31000

= SiO23.4 2.1

+

Where:

QCatalyst = Catalyst circulation,metric tons per minute.

Vemulsion = Volume of fluidized cat-alyst emulsion m3/min.

ρemulsion = The assumed standpipe fluidized density of560.65 kg/m3.

2) Calculate the total volume of inter-stitial and intraparticle gas that is cir-culated with the catalyst:

1000 Qcatalystρemulsion =Vemulsion (4)

OrVEmulsion= 1000

(12.0)= 21.40 m3/min

560.65

Where:

VGas = Volume of gas circulat-ed down the standpipe with the cata-lyst, m3/min.

3) Calculate the absolute pressure atthe standpipe inlet, and the first aera-tion tap:

Where:

PInlet = Pressure at thestandpipeinlet, kPa absolute.

PTap 1 = Pressure in thestandpipe at thelocation of the firstaeration tap downfrom the stand-pipe inlet, kPaabsolute.

ρemulsion (5)

Or

=

Vgas Vemulsion= ( (1-( ρskeletal (Vgas 21.40( (1-( (560.65

2549.9

PDilute = Pressure in thedilute phase ofthe vessel, abovethe catalyst bed,kPa absolute.

ΔHInlet Surface = Height of the cata-lyst bed above theinlet to the stand-pipe, meters.

ΔHTap 1-Inlet = Difference in depthbetween the loca-tion of the stand-pipe inlet and thefirst aeration tap,meters.

ρEmulsion = Assumed densityof the fluidizedemulsion(560.65 kg/m3).

g = GravitationalConstant,9.81m/sec2.

4) The change in gas volume duethe pressure increase can then becalculated:

PInlet(ρemulsion)

=

(ΔH(Inlet -Surface))

(6)Or= 1000

(82.74 + 101.32) +

194.12 kPa Absolute1000

PDilute+(g)

PInlet =

(560.65)(9.81)(1.83)

The Pressure At The Inlet Is:

209.80 kPa

PTap 1(ρemulsion)

=

(ΔH(Tap-1 Inlet))

(7)Or= 1000

194.12 1000

PInlet +(g)

PTap 1= (560.65)(9.81)(2.85)

The Pressure At Tap 1 Is:

+

Where:

ΔVGas = The change in gas volumeat the temperature andpressure of the standpipedue to compression.

In order to counteract the compres-sion effect and restore the neededvolume to the catalyst emulsion, anincremental 1.25m3 of gas perminute (at 682.2˚C., 209.80 kPaabsolute) must be injected into thestandpipe at Tap 1. Using a molec-ular weight of 18.0 and PV=nRT thisworks out to 0.59 kg/min of steam atthis tap location.

The theoretical aeration requirementserves as a useful bench mark tojudge aeration rates when firstexamining the operation of thestandpipe. However, few FCC unitsactually operate with exactly this

PTap 1ΔVgas (8)PInlet= Vgas

Vgas

OrΔVgas = 16.70

(16.70)(194.12)

= 1.25 m3/min209.80

quantity of aeration. In the realworld, the actual aeration rateshould initially be set to approxi-mately 60-70% of this theoreticalaeration requirement. Subsequentadjustment of the aeration ratesfrom this initial point can then beused to seek out additional improve-ments. Some FCC units will end upoperating somewhat above the the-oretical aeration requirement, whileothers will operate below this theo-retical aeration rate. In any case thebest place to start is with an aera-tion rate that is 60-70% of theoreti-cal.

Figure 7 which is taken from a paperby R.E. Wrench, J.W. Wilson, and G.Guglietta3 shows how the pressuregenerated in a standpipe respondsto variations in aeration rates. Notethat over-aeration produces a dra-matic loss of standpipe pressure.This behavior provides anothergood reason to use less than the fulltheoretical aeration rate when firstsetting up standpipe aeration.

It should be expected that as thephysical properties of the equilibri-um catalyst change, the shape ofthe aeration response curve shownin Figure 7 will also change. As theMSER of the equilibrium catalystincreases, the more tolerant itbecomes to improper aeration.

Note that the aeration requirementsof a standpipe is dependent on thecatalyst circulation rate. So it is con-


venient to calculate the aerationrequirement in terms of kg aerationper metric ton of catalyst circulated. Inthis example, the theoretical aerationat the first tap is 0.049 kg steam/met-ric ton of catalyst circulation.

The aeration calculation should berepeated incrementally from tap to tapdown the length of the entire FCCstandpipe. All of the actual aerationrates can then be compared to thetheoretical bench marks provided bythe calculation. Often this exercise willreveal that some portion of the stand-pipe is being improperly aerated.

When doing these aeration calcula-tions along the length of the stand-pipe, it is handy to know that if the dis-tances between the taps are equal,then the theoretical aeration required

by the equally spaced taps will allbe the same. Table I illustrates thisfor the regenerator used in theexample above. Aeration taps 2through 10 are all equally spaced ata distance of 3.5 meters from eachother.

Standpipe CompressionRequirements

Calculating the change in catalystemulsion density that is taking placein the standpipe from tap to tap isalso very revealing. As was men-tioned earlier, there is only a verylimited range of densities overwhich FCC catalyst will remain fluid.If the increase in pressure from tapto tap is too large, the catalyst willbe compressed past its point ofincipient fluidization.

Using data from the previous exam-ple, the percent change in catalystdensity required from tap to tap canbe calculated from:

Where:

ΔρEmulsion = The percent changein emulsion densitythat is taking placefrom tap to tap.Percent Theoretical Aeration

Sta

nd

pip

eD

elta

P,k

Pa

0 50 100 150 200

60

50

40

30

20

10

Figure 7Standpipe Delta P

Tap #

Inlet12345678910

Tap Location,Meters BelowBed Surface

1.834.688.1811.6815.1818.6822.1825.6829.1832.6836.18

∆H,Meters

1.832.853.503.503.503.503.503.503.503.503.50

AerationRequired,

kg/min of Steam

None0.590.730.730.730.730.730.730.730.730.73

Table I

VEmulsion

21.401.25

=100

Or using the numbers from Example 1:

ΔρEmulsion% ΔVGas

ΔρEmulsion = 5.84%

=100

Tap #

Inlet12345678910

Tap Location,Meters BelowBed Surface

1.834.688.1811.6815.1818.6822.1825.6829.1832.6836.18

∆H,Meters

1.832.853.503.503.503.503.503.503.503.503.50

DilutePressure82.7 kPaGauge

5.846.566.055.615.244.914.624.364.133.92

DilutePressure206.0 kPa

Gauge

3.674.264.043.843.663.503.353.213.082.97

Percent CompressionRequired in Standpipe

Table II


What we are really doing here is cal-culating the amount of compressionthat the standpipe is requiring thecatalyst to undergo. The greater therequired percentage increase indensity from tap to tap, the moreprone the standpipe is to circulationdifficulties. Calculating the percent-age compression from tap to tap,often pinpoints where the FCCstandpipe will be most likely toexperience compression problems.FCC units that are suffering fromcatalyst over-compression, and thesubsequent loss of fluidization thatit brings on, will often find that theseproblems are occurring in the upperhalf of the standpipe because thisis where the greatest amount ofcompression per meter of descenttakes place in the standpipe.

This standpipe compressionrequirement is a function of the FCCdesign pressure, and the spacingbetween the taps on the FCC stand-pipes. For example, it is commonlyobserved that lower pressure FCCunits, where the regenerator may bedesigned to operate at 82 kPagauge (12 psig), generally havemuch more difficulty circulating cat-alyst in standpipes than do higherpressure designs where the regen-erator may be operating at 207 kPa

gauge (30 psig). A quick calculationof standpipe compression require-ments reveals that the low pressuredesigns inherently have much higherstandpipe compression requirement,per meter of standpipe descent, thando the higher pressure designs.

Table II shows how the compressionrequirements for a standpipe changedramatically with respect to the dilutephase pressure of the vessel fromwhich they are drawing catalyst.

The standpipe that is operating at thelower design pressure requires thecatalyst to undergo significantly morecompression between the aerationtaps. In fact, at the top of the stand-pipe where the compression require-ments are greatest, the low pressuredesign shown here requires 58%more catalyst compression per meterof standpipe descent.

One way to mitigate this compressionrequirement when the unit is designedfor lower pressure, is to place the aer-ation taps closer together along thelength of the standpipe.

As a rule, the aeration taps for lowpressure standpipes should normallybe spaced so that less than 4.5-5.0percent compression is required

between the taps. By keeping thecompression requirement low, thestandpipe circulation will be moretolerant of the changes in catalystparticle size distribution thataccompany cyclone deterioration atthe end of a run.

In terms of absolute numbers, 4.5or 5.0 percent compression doesnot seem very high. However, if theunit is circulating a catalyst with alow stable expansion ratio (Low 0-40 fines content and high ABD),then a 5.0 percent compressionrequirement in the standpipe cancreate catalyst circulation problemsvery quickly.

Choice of Aeration Media

Inspection of Equations 1 and 2suggests that if the aeration mediahas a higher density and a higherviscosity, then the MSER for the sys-tem will be higher. Air is significant-ly higher than steam in both viscos-ity and density.

Thus, changing the aeration mediafrom steam to air in regeneratorstandpipes that are suffering fromcompression problems has some-times produced a dramatic improve-ment in catalyst circulation. If, due topoor cyclone performance, the par-ticle size distribution and density ofthe catalyst have moved into aregion where the catalyst has trou-ble circulating in a standpipe with a5.0 percent compression require-ment, then changing the aerationmedia from steam to air canincrease the compression tolerance(Effective MSER) to almost 1.08.This type of change in compressiontolerance from 1.05 to 1.08 repre-sents almost 60 percent improve-ment.

The possibility of condensate slug-ging into the standpipe is alsogreatly reduced by using air insteadof steam.

The refiner should be aware thatthere are occasional gasoline gumor stability problems that can arisefrom the additional oxygen that is


carried into the reactor by air in theregenerator standpipe. But theseproblems are relatively infrequent,and if they do occur, then the stand-pipe can be switched back tosteam.

Note that this change in aerationmedium is only appropriate in unitsthat are operating with completecombustion in the regenerator.

Catalyst Design

In order to help mitigate a refiners’catalyst circulation problems, thereare a number of things that the cat-alyst manufacturer can do to thecatalyst.

First of all, if the FCC unit is limitedin the amount of catalyst that it cancirculate, then an increase in equi-librium catalyst activity should beconsidered. This will allow the refin-er to achieve his best possible con-version with the limited catalyst cir-culation that is available. Increasingthe activity of the equilibrium cata-lyst will also raise the regeneratortemperature, which in turn willreduce the amount of catalyst thatmust be circulated at a given set ofoperating conditions. These twoeffects complement each othernicely.

Equations 1 and 2 along with Figure5 clearly show that the MaximumStable Expansion Ratio of the equi-librium FCC catalyst is a function ofcatalyst ABD and the 0-40 micronfines content of the inventory.Manufacturers of FCC catalyst havea great deal of flexibility in theirmanufacturing process whichallows them to modify the ABD ofthe equilibrium catalyst withoutchanging the chemical composi-tion, or the catalytic selectivity pat-terns of the catalyst. Thus, a reduc-tion of the equilibrium ABD can bedesigned into the fresh catalyst sothat the MSER of the equilibriumcatalyst can be enhanced.

In addition, the particle size distri-bution of the fresh catalyst can bemodified in favor of a smaller aver-

age particle size with a higher 0-40micron fines content which also tendsto aid circulation.

Attrition resistance of the catalyst isanother feature that can be modifiedso that the tendency to generate 0-40micron fines can be enhanced. This issometimes helpful when the cycloneshave deteriorated and the ability of theFCC unit to hold the necessary 0-40micron fines in its inventory is dimin-ished.

By judicious application of these prin-ciples, the catalyst manufacturer canprovide the refiner with a great deal ofrelief from standpipe circulation prob-lems.

Pulling it All Together

From the foregoing discussion itshould be clear that there are reallyfour disciplines that need to be exam-ined when trouble-shooting catalystcirculation problems in standpipes:

1. The Design of the FCC UnitItself.

2. The FCC Unit Operations.3. The Fluidization properties ofthe Equilibrium FCC Catalyst.

4. The Design of the FreshCatalyst.

The FCC standpipe design needs tobe looked at to confirm that its com-pression requirements are reason-able, to determine where the stand-pipe is making the most demands onthe circulating catalyst, and to deter-mine what the theoretical aerationbench marks are.

FCC operations need to be looked atto insure that the standpipe is beingoperated properly, and to insure thatthe rest of the FCC hardware is reallydoing what it is suppose to be doing.For example, a false level reading cantrigger circulation difficulty by upset-ting the bed levels which may uncoverthe cyclone diplegs, etc. One thingleads to another, and soon the fineshave been lost from the inventory, andthe standpipe circulation is in jeop-ardy.

Since the cyclone operation deter-mines the particle size distributionof the equilibrium catalyst, anexamination of cyclone perform-ance should be considered an inte-gral part of trouble-shooting stand-pipe circulation problems.

As shown above, the equilibriumcatalyst properties provide muchindirect information about how com-pression tolerant the catalyst will bein the standpipe. Thus, the equilibri-um catalyst properties should beclosely scrutinized for any subtlechanges that may have triggeredthe standpipe upset.

Since a great deal of relief canoften be obtained by modifying thefresh catalyst design, the catalystmanufacturer should be consultedto determine how much latitude isavailable for changing physicalproperties or activity. Modification ofthe fresh catalyst design to mitigatecirculation difficulties is just anotherexample of the benefits that accruefrom close cooperation between therefiner and the FCC catalyst manu-facturer.

References

1. Abrahamsen, A.R., and Geldart, D.,Powder Technology, Vol 26, 1980, pp35-55.

2. Magnussun, J.E.: “Fluidization Propertiesof Equilibrium FCC Catalyst”, Paper presentedat the 1985 Katalistiks Seminar.

3. Wrench, R.E., Wilson, J.W., Guglietta, G.:“Design Features for Improved Cat CrackerOperations”, Paper presented at “The FirstSouth American Ketjen Catalyst Seminar, Riode Janeiro, Brazil, September 1985.


Have you ever wished it werethis easy to remove sulfur?

With the products and expertise available through GraceDavison and Advanced Refining Technologies, our teamnow offers a one-stop shop for clean fuels solutions.

Grace Davison GSR® technologies continue to provide30%-45% gasoline sulfur reduction in the FCC. This suc-cess has been proven in over 85 commercial units world-wide and is the result of over 15 years of continuous R&Deffor ts. Our clean fuels product portfolio currentlyincludes D-PriSM® and GSR-5 additives, as well asSuRCA® and NeptuneTM catalysts.

Our GSR technologies are used around the world in avariety of FCC operations, with and without hydrotreatinghardware, to provide feedstock flexibility, operating flexi-bility during hydrotreater outages, gasoline stream blend-ing options, and gasoline octane preservation. In-unitreduction of FCC gasoline sulfur continues to create avariety of opportunities and options for refiners to driveprofitability.

For refiners with FCC pretreaters, the ApARTTM CatalystSystem utilizing combinations of AT575, AT775 and AT792offers the opportunity to significantly increase sulfurremoval in the hydrotreater while at the same time maxi-mizing FCC feed quality. The improved performance ofthe pretreater results in higher gasoline potential in addi-tion to decreasing FCC gasoline sulfur.

For ULSD processing, the SmART Catalyst System® uti-lizes state-of-the-art catalyst technology which is stagedin the proper proportions to provide the best perform-ance, while at the same time meeting individual refinerrequirements. The catalyst staging is designed to selec-tively take advantage of the different reaction mecha-nisms for sulfur removal with efficient hydrogen usage.CDXi and 420DX, our newest generation of high activityCoMo catalysts, efficiently removes the unhindered, easysulfur via the direct abstraction route, while NDXi, our highactivity NiMo catalyst, then attacks the remaining sterical-ly hindered, hard sulfur. The SmART system provideshigher activity than either the traditional CoMo or NiMocatalyst alone while effectively helping the refiner managehydrogen utilization.

w e b www.e-catalysts.come m a i l [email protected]@

information

Editor’s Note:

FCC catalyst optimization has taken dif-ferent directions over the years but arecurring goal has been improving cokeselectivity. Ultimately, this would allowthe refiner to process heavier feed-stocks, increase unit throughput, andoperate within hardware limitations exac-erbated by the deleterious effects ofcontaminants such as nickel and vanadi-um. Over half of refiners blend someresid into their feed.

Intense R&D efforts have resulted inmultiple generations of successful cata-lyst families with improved coke selectiv-ity. One such success story is theIMPACT® series of catalysts. In this arti-cle, we discuss the application of IMPACT catalyst in its early phase of com-mercialization. It is clear that expectations of enhanced coke-to-bottomsbased on pilot plant studies were exceeded in the first commercial applica-tion some six years ago. IMPACT contains the only integral vanadium trap inthe industry. In the years since, IMPACT has delivered enhanced coke andgas selectivity in a broad range of applications, from severely hydrotreatedgasoils to heavy resid feeds.

Since its initial commercial launch, we have sold over 200,000 tons ofIMPACT catalyst and have employed the technology successfully in over 70units worldwide.

Scott Purnell, principal author, serves as General Manager and ManagingDirector of Advanced Refining Technologies. This article first appeared inIssue #93, 2003.


ANNIVERSARY ISSUE

s the availability of light,sweet crudes has declinedand prices have increased,

refiners have reconfigured their oper-ations in order to be able to upgradeheavier, less desirable feedstocks intolighter, more valuable products.Declining fuel oil demand has onlyadded to the urgency for effectiveupgrading of heavy resid. Fluid cat-alytic cracking is one of the most effi-cient and economic ways of achiev-ing this upgrading, and it is estimatedthat about half of the refiners blendsome amount of resid into their FCCfeeds.

For resid operations, optimal design ofthe FCC catalyst is critical. Obviously,minimizing diffusional limitations forthe large molecules found in vacuumresidue is an important considerationin the design of resid catalysts, but

coke selectivity remains para-mount. These units processingresid are impacted by high levelsof contaminant metals andConradson carbon, and are oftenlimited by air blower capacityand/or regenerator temperatures,making coke selectivity the mostimportant catalyst performancecharacteristic. Coke selectivitydetermines the FCC unit conver-sion level at a given set of condi-tions, and improvements in cokeselectivity have the greatest valueto the refiner. Improvements incoke selectivity can allow the refin-er to increase feed rate, increaseconversion, or process heavier,less expensive feedstocks, all ofwhich lead to increased profit mar-gins.

IMPACT®: A BreakthroughTechnology for Resid Processing

Commercialization Update


Scott K. Purnell, Ph.D. A

In this article we will describe abreakthrough new resid catalysttechnology with unsurpassed cokeselectivity, known as IMPACT®, andshare data from the first commer-cial applications of this promisingnew technology.

Breakthrough New ResidCatalyst: IMPACT

Technology Description

Grace Davison is highly committedto its FCC catalyst business andhas an active R&D program todevelop and commercialize higherperforming products. Through ourstage-gate new product develop-ment process, we have successful-ly commercialized the AURORA,ATLAS, AdVANTA, and VANGUARDcatalyst families within the last twoto three years. Recent efforts havefocused on further raising the per-formance bar for resid catalysts.Our scientists have strived to com-bine all the important catalyst func-tionalities for resid cracking intoone superior catalyst. The goal wasto invent a catalyst with step-outimprovements in coke selectivityand stability over current industrybenchmarks, VANGUARD andAURORA-LC, while optimizing the

matrix design for additional bottomscracking. Industry leading unit reten-tion characteristics and resistance toiron poisoning were also desired.

These efforts have led to the develop-ment of a breakthrough new residcatalyst family, known as IMPACT.IMPACT combines next-generationintegral vanadium trapping,advanced zeolite stabilization, andsuperior matrix metals passivation toachieve the ultimate in coke selectivi-ty, and has demonstrated trulyremarkable performance in laboratorytesting. Figure 1 illustrates one com-

Conversion, wt%

Co

ke,w

t.%

8

7.5

7

6.5

6

5.5

5

4.555 60 65 7570

DCR Testing on Resid FeedstockCPS Deactivation at 1450˚F:

2500 ppm Ni, 5000 ppm V

Coke SelectiveResid Catalyst Benchmark

Figure 1IMPACT Delivers 30% Better Coke Selectivity

Figure 2Stability of IMPACT

Total Metals (Ni+V) (ppm)

MAT

Act

ivity

80

75

70

65

60

55

50

45

0 1000 2000 4000300040

5000 6000 7000 90008000 10000

CPS Deactivation at 1450˚F: Ni/V=0.5

Resid CatalystBenchmark

ConventionalCatalyst

parison between state-of-the-arttechnology and IMPACT. Thesedata were generated in the DavisonCirculating Riser (DCR) pilot plantwith a heavy resid feedstock. Thecatalysts were deactivated with2,500 ppm nickel and 5,000 ppmvanadium using our CPS cyclicdeactivation protocol. This figureindicates that the IMPACT technolo-gy offers nearly 30% improvementin coke selectivity. Improvements ofthis magnitude over industry-lead-ing technology are extraordinary.

In addition to coke selectivity, wehave also compared the stability ofIMPACT to industry benchmarks.Figure 2 summarizes a metalsdeactivation study that comparesIMPACT to a state-of-the-art cokeselective resid catalyst and a con-ventional FCC catalyst at increasinglevels of vanadium. This figureshows that both the resid bench-mark and IMPACT technologiesoffer a much higher tolerance tovanadium than conventional cata-lysts (the curves are much flatter).Note however, that the activity curveof IMPACT is slightly flatter than theindustry standard, and the baseactivity achieved at 9,000 ppm totalmetals (Ni + V) is also higher.Comparing the zero metals case to9,000 ppm total metals, themicroactivity of IMPACT declinedonly about 2 numbers, while a


decline of 25-30 numbers wasobserved for the conventional cata-lyst. This phenomenal stability willgive IMPACT even better commer-cial coke selectivity as it resists thezeolite deactivation and metals poi-soning found in resid operations.

Furthermore, IMPACT is based onthe Grace Davison proprietary alu-mina sol catalyst platform. Thus, inaddition to the truly step-out cokeselectivity and stability perform-ance, users of IMPACT will enjoythe additional benefits characteris-tic of Davison alumina sol catalysts,namely industry-leading unit reten-tion, maximum resistance to ironpoisoning, and enhanced bottomscracking.

In fact, IMPACT further distinguish-es its performance through step-out improvements in coke-to-bot-toms selectivity. When formulatingresid catalysts, coke-to-bottomsperformance often tends to fall on asingle line with some catalystsdemonstrating outstanding cokeselectivity, but with poor bottomscracking, and yet other catalystsshowing excellent bottoms upgrad-ing, but with high coke yields. Thisphenomenon is illustrated in Figure3 where the coke-to-bottoms per-formance of IMPACT is gaugedagainst other industry benchmarks.

Figure 3Step-out Coke-to-Bottoms Selectivity of IMPACT

Coke, wt%

Botto

ms,

wt%

8.0

7.5

7.0

6.5

6.0

8.5

5.5

5.0

9.0

2 76543 8

DCR Testingon Resid Feedstock

CPS Deactivation at 1450˚F:4000 ppm Ni, 4000 ppm V

Max CokeSelectivityBenchmark

Max BottomsCrackingBenchmark


This chart shows the bottoms yieldsmeasured vs. coke in a riser pilotplant study where the catalysts weredeactivated via cyclic propylenesteaming (CPS) at 1450°F with 4,000ppm vanadium and 4,000 ppm nickeland run with a resid feedstock. In thisstudy, the two industry benchmarkcatalysts can be seen to fall on essen-tially the same line, one with bettercoke selectivity and the other withbetter bottoms cracking. However,IMPACT showed a dramatic improve-

ment over these technologies,demonstrating a step-change inboth bottoms cracking and cokeselectivity. At a constant coke yieldof 4 wt.%, IMPACT showed a 2.0wt.% reduction in bottoms (25% rel-ative) over the coke selective residcatalyst benchmark, while at a con-stant bottoms yield of 6 wt.%,IMPACT showed a 2.3 wt.% reduc-tion in coke (37% relative) over thebottoms cracking resid catalystbenchmark. When this bottomscracking capability is combinedwith its phenomenal coke selectivi-ty, the coke-to-bottoms perform-ance of IMPACT is nothing short ofextraordinary.

The superior performance charac-teristics of IMPACT, as describedabove, will lead to enhanced oper-ating flexibility and increased prof-itability for the refiner. The cokeselectivity improvement alonewould allow many refiners toincrease throughput, increase con-version, or process heavier, lessexpensive feedstocks. Table Ishows the estimated yield shifts fora refiner contemplating a switchfrom a very successful operationwith an industry-leading resid cata-lyst technology to IMPACT. In this

Table IEstimated Economic Benefit from IMPACT

(based on a 50,000 bpd RFCCU)

Base CaseBase Case

Yields

Total C2-, wt.%Total C3’s, wt.%Total C4’s, wt.%C5+ Gasoline, wt.%LCO, wt.%Bottoms, wt.%Coke, wt.%

$/BBL$/Day$/Year

3.87.5

10.741.619.811.74.8

---

0.21.21.61.5-1.7-2.30.0

$0.45$22,500> $8MM

IMPACTChange fromBase Case

Table IIRefiner A: Change in Operation with 30% Turnover to IMPACT®

Table IIIRefiner A: Commercial Yield Shifts with 30% Turnover to IMPACT

Table IVRefiner B: Yield Shifts Observed inEquilibrium Catalyst ACE Evaluation


particular case, the premium cokeselectivity of IMPACT is projectedto give an astonishing conversionincrease of 4.0 wt.%. Using typicalproduct values, this conversionincrease would translate into a$0.45/bbl advantage for IMPACT, or$22,500/day (greater than $8 mil-lion annually) for a 50,000 bpd residFCCU.

Commercial Experience

IMPACT is in the "CommercialTesting" stage of our new productdevelopment process and is cur-rently being evaluated in four com-mercial FCCU’s. Data are still pre-liminary, but initial results are verypromising, meeting our high expec-tations for this exciting new technol-ogy. We will share some of thehighlights here.

In the first application, IMPACT wasadded to a UOP High Efficiencyunit in the US Gulf Coast. The unitruns more than 60,000 bpd of feedand operates in full combustion. Atonly 30% turnover to IMPACT, areduction in regenerator tempera-ture and an increase in catalyst cir-culation rate were observed (TableII). These observations are clearlyconsistent with the superior cokeselectivity of IMPACT.

The reduction in fresh catalyst addi-tions combined with increased con-taminants in the feed led to anincrease in equilibrium catalyst Ni +V levels of 30%. However, at only30% turnover and at the higher met-als level, IMPACT maintained ecatmicroactivity and increased conver-sion by 1.3 vol.% while reducingdry gas. IMPACT also dramaticallyreduced slurry. Yield shifts aresummarized in Table III.

In a second application in the USGulf Coast, IMPACT was added tothe inventory of another UOP HighEfficiency unit, operating in fullcombustion and charging morethan 50,000 bpd of feed. An ACEpilot plant study was conducted tocompare the performance of twoequilibrium catalysts taken from theunit – one from prior to IMPACT

IMPACT @ 20% Turnover(Change from Base Case)

Coke, wt.%Delta, wt.%Conversion, wt.%Hydrogen, wt.%Dry Gas, wt.%LCO, wt.%Bottoms, wt.%

Base-0.05+2.0-0.06-0.2-0.4-1.6

Change from Base Case

Regenerator TemperatureCatalyst CirculationCat-to-Oil RatioFresh Catalyst Additions

-12˚F+4.8 tons per min

+0.5-15%

Change from Base Case

ConversionDry GasGasolineSlurry

+1.3% vol.%-12 scf per bbl feed

+1.1 vol.%-2.3 vol.%


additions and the other at 20%turnover to IMPACT. The yield shiftsobserved in this study are summa-rized in Table IV. In this ACE study,the IMPACT-containing equilibriumcatalyst showed a 2.0 wt.%increase in conversion at constantcoke. Again, the conversionincrease came mainly throughupgrading of slurry, while hydrogenand dry gas were also reduced.

It may seem remarkable that theselarge yield shifts were observed atrelatively low levels of IMPACT in cir-culating inventory. However, theperformance benefits of IMPACThave been shown to track turnoverand are apparent almost from thefirst additions. Figures 4-6 showimprovements in equilibrium cata-lyst performance observed forEcats taken from a third IMPACTapplication and tested in GraceDavison’s standard equilibrium cat-alyst monitoring program. This thirdIMPACT application is in yet anotherUOP High Efficiency FCCU operat-ing at a rate of more than 70,000bpd.

Status

Although early in the commercial-ization process, IMPACT is nowreadily available in commercialquantities. The completion of amulti-million dollar expansion to thefluid cracking catalyst (FCC) facilityat the flagship Lake Charles,Louisiana manufacturing complexwill allow Davison to meet anticipat-ed future demand for IMPACT. Theexpanded facility (Figure 7), whichwent on-stream in May, 2003, willalso allow Davison to produce otherpremium cracking catalysts charac-terized by superior coke selectivity,including AURORA™-XLC, a furtherenhancement of the very success-ful AURORA catalyst family.

Summary

In the optimal design of resid crack-ing catalysts, coke selectivityremains paramount. Recent R&Defforts focusing on coke selectivityin resid applications have led to thedevelopment of a truly break-

Figure 4Refiner C: Equilibrium Catalyst Gas FactorDecreases with Turnover to IMPACT®

Gas

Fact

or

8.0

7.0

6.0

5.0

05Nov'01DateDate

Base turnover to

13Feb'02 24May'02 01Sep'02 10Dec'02 20Mar'03 28Jun'03 06Oct'03

4.0

2.0

3.0

1.0

0.0

Start of Additions

Gas Factordecreaseswithincreasingturnover

Figure 5Refiner C: Equilibrium Catalyst HydrogenDecreases with Turnover to IMPACT

Yiel

d,SC

FB

230

210190170

05Nov'01DateDate

Base turnover to

13Feb'02 24May'02 01Sep'02 10Dec'02 20Mar'03 28Jun'03 06Oct'03

150

110130

90

705030

Start of Additions

H2 yielddecreaseswithincreasingturnover

Figure 6Refiner C: Equilibrium Catalyst Coke Factor

Decreases with Turnover to IMPACT

05Nov'01 13Feb'02 24May'02 01Sep'02 10Dec'02 20Mar'03 28Jun'03 06Oct'03

Coke

Fact

or

2.0

1.9

1.7

1.5

DateDate

Base turnover to

1.3

0.9

1.1

0.7

0.5

Start of Additions

Coke Factordecreaseswithincreasingturnover

Figure 7Expansion at Davison’s Lake Charles Plant to Produce IMPACT


through new resid catalyst knownas IMPACT. IMPACT has shownextraordinary enhancements in bothcoke selectivity and stability overcurrent industry benchmarks in pilotplant testing, while also providingstep-out improvements in coke-to-bottoms selectivity. Since IMPACT isbased on Davison’s proprietary alu-

mina sol technology, industry-leadingunit retention and resistance to ironpoisoning are additional benefits.

IMPACT is now available in commer-cial quantities and is currently beingevaluated in four FCCU’s. Data arestill preliminary, but initial results arevery promising. Dramatic improve-

ments in coke and gas selectivitieshave been observed in the Ecatdata from the start of IMPACT addi-tions and track with turnover. In twoof the applications, increases inconversion of 1-2 vol.% (mainlygasoline at the expense of slurry)have been observed with only 20-30% IMPACT in inventory.

The GENESISTM Catalyst System

www.grace.com 7500 Grace Drive • Columbia, MD 21044 USA

Most refiners need flexible catalyst systems that allow them to

take advantage of changing economic scenarios. Grace Davison

delivers this flexibility with the GENESISTM catalyst system. GENESISTM

catalysts provide a means to maximize yield potential through optimization of

discrete cracking catalyst functionality. GENESISTM catalysts are a blend of

two catalyst types. The key component is MIDAS®, which maximizes conver-

sion of bottoms and improves coke selectivity by eliminating coke precursors.

The other GENESISTM component is most often an IMPACT® catalyst. The

inclusion of IMPACT® provides critical zeolite surface area and activity as well

as superior coke and gas selectivity in a broad range of applications, from

severely hydrotreated gasoils to heavy resid feeds.

GENESISTM catalysts demonstrate a true yield synergy with a superior

coke to bottoms relationship than either component alone. The synergy

exists because each component cracks specific feed species.

Maximize yield withGrace Davison’s

GENESISTM FCC catalyst.

GENESISTM catalyst providesthe ultimate in formulation

and FCC operational flexibility.

For more information, contact your Grace Davison Technical Sales Manager

Grace Davison’s Equilibrium CatalystAnalysis ProgramGrace Davison recognized the importance of equilibrium catalysts analyses early in the history

of cat cracking. That’s why we instituted the industry’s first Equilibrium Catalyst Analysis (Ecat)

program in 1947, only five years after the startup of the first FCCU.

As analytical technology has advanced, we’ve installed sophisticated equipment and included

many more critical tests for the program. Through the years, we developed and reported many

analysis of Ecat chemical and physical properties that have helped FCC operators understand

their circulating catalyst health and use this information to optimize their operations.


Your link to real-time Ecat analyses

Continuous improvements to our system have evolved into recent developments including

online access to immediate test results through www.e-Catalysts.com. Currently, we analyze

for the following properties:

• Microactivity

• Surface Area

• Elemental Analysis

• Pore Volume

• Carbon

• Apparent Bulk Density

• Particle Size Distribution

• Unit Cell Size

sm

For more information on Grace Davison’s

industry-leading Equilibrium Catalyst Analysis

program, contact your technical sales rep or

log on to www.e-Catalysts.com.

©2009 W. R. Grace & Co.-Conn. All rights reserved.


Editor’s Note:

Over the years we have focused on therefiners’ needs to optimize FCC per-formance as it impacts product slateand product quality. We have alsosupplied valuable information on theinteraction of unit operating parame-ters and catalyst technology.

The basic concept of fluid catalyticcracking is the cracking of hydrocar-bon molecules, followed by the eventu-al transfer of hydrogen to produceproducts that are lighter and morevaluable than the feed. Simultaneously,heavier products, such as coke, aregenerated.

Hydrogen in coke is a necessary parameter for the calculations of the unitcoke yield. It can also be an indicator of inefficient stripping that cancause fluctuations in regenerator temperature. Accurate flue gas analysis isalso important for many emissions regulations, such as MACT II, which arebased on coke yield.

In this article, we discuss that hydrogen in coke is more than a measure ofstripper efficiency; it is a reflection of other key unit operating parametersand controls.

Our Technical Service Manager, David Hunt, is the principal author of thisarticle, which originally appeared in issue #100, 2006.


ANNIVERSARY ISSUE

N U M B E R 1 0 0 Fa l l 2 0 0 6

efiners often use hydrogen incoke as a parameter to judgethe performance of their FCC

catalyst stripper. However, the use ofthis parameter for process monitoringis often the subject of significantdebate. The main questions are whathydrogen in coke number truly indi-cates good catalyst stripping and howvalid is the number itself.

I propose refiners use the hydrogen incoke number to help confirm theaccuracy of their coke make, otherheat balance parameters and flue gasanalysis. Any hydrogen in coke valueless than 5 wt.% or greater than 9wt.% is likely due to poor flue gasanalysis.

Since the flue gas analysis is the basisfor the heat balance calculations, itinfluences many of the calculatedoperating parameters such as the unitcoke production, heat of reaction, cat-alyst circulation rate, and most dra-matically, the hydrogen in coke. Anartificially low hydrogen in coke num-ber resulting from an incorrect flue

Use the Hydrogen in CokeNumber to Determine CokeMake Accuracy

David Huntgas analysis will result in a calculat-ed coke production from the unitthat is higher than actual.

An accurate flue gas analysis andhydrogen in coke number is espe-cially important when you considerthat many throughput limitations areset by emission regulations basedon coke production. When consid-ering this, the use of the hydrogenin coke number to judge strippingefficiency should be a secondaryconcern.

Calculating Hydrogen in CokePractical Limits

If your heat balance calculationsyield a hydrogen in coke result of 4wt.% does this mean you have aworld-class stripper? Or if yourhydrogen in coke is 12 wt.% shouldyou plan on a stripper revamp dur-ing the next turnaround? Theanswer to both questions is likely“no”.

R


Generally the industry accepts 5 to6 wt.% hydrogen in coke as the low-est attainable from ideal stripping2.This is based on the assumptionthat if the FCC stripper performedperfectly it would only allow cokeconsisting of highly unsaturatedhydrocarbons to pass through to theregenerator.

In order to define the upper reason-able limit for hydrogen in coke, youmight consider a case where a sub-stantial amount of product isburned in the regenerator. Burningthe equivalent of slurry oil (mainfractionator bottoms) in the regener-ator as coke could be consideredan extreme case. In this circum-stance, the hydrogen in coke wouldbe ~ 9.0 wt.%, which is the nominalhydrogen content of a slurry oil withan API of ~ 01.

So, at best you may argue that thestripper produces coke with ahydrogen content of 5 wt.% and atan extreme case it might produceup to 9 wt.%. Data outside thisrange is likely explained by bad fluegas data. An inaccurate value ofCO2 is often the culprit; however,poor O2 results will cause errors inthe calculations as well.

Co

keY

ield,w

t.%F

reshF

eed

Rate, bpdAir, mscfmCO, ppmO2, vol.%

50,0001151002.0

Hyd

rog

enin

Co

ke,w

t.%

151413121110

987654321

13.0 13.5 14.0 14.5 15.0 16.015.5 16.5 17.0 17.5 18.0

CO2, vol.%

Hydrogen in Coke, wt.% Calculated Coke, wt.% Feed

6.5

6

5.5

5

4.5

4

-20.9579.05 (100-CO2-CO-O2) (O2+CO2+ CO)1

2A=

and regenerator �ue gas CO2, CO and O2 units are mole % on a dry basis.1

Note that this equation is not accurate for units using supplemental oxygen.

Hydrogen inCoke, wt.%

= 100*AA+2.979*(CO2+CO)

where A is

Hydrogen in Coke can be calculated by the equation:

The Influence of CO2 on Hydrogenin Coke

Figure 10 shows the calculated hydro-gen in coke and coke yield as a func-tion of the measured flue gas CO2content for a FCC operating in fullcombustion with constant excess O2.Questionable data is indicated by thedashed lines for hydrogen in cokedata outside of the 5 to 9 wt.% range.

The impact of CO2 is significant andcan affect not only the hydrogen incoke value but perhaps more impor-tantly the calculated coke yield. Figure10 suggests that coke yield could beoff more than 10% due to bad flue gas

data. Many FCC emission regula-tions, like MACT II, are based oncoke production so accurate cokemeasurement is critical3.

The coke yield was calculated usingthe method described in the GraceDavison Guide to Fluid CatalyticCracking, Part One4.

Next time you see a high or lowhydrogen in coke number in youroperating data, instead of immedi-ately thinking about your stripperperformance, you may want tocheck the validity of your flue gasanalyses and realize that the report-ed coke yield (as well as other heatbalance parameters) may be inerror.

References

1. J. Deady, Interpreting Yield Estimates,Catalagram No. 82, 1991.

2. R. Sadeghbeigi, Fluid Catalytic CrackingHandbook 2nd Edition, Gulf Publishing,Houston, TX 2000, pg. 166.

3. National Emission Standards forHazardous Air Pollutants (NESHAP),40CFR63 Subpart UUU.

4. Grace Davison Guide to Fluid CatalyticCracking Part One,1993 pg.84-85.

Figure 10Influence of Flue Gas CO2 Value on Hydrogen in Coke and Coke Yield



The Grace Davison Guide To Fluid Catalytic CrackingParts I, II, and III

The recognized industry source for fundamental FCCprocess, hardware and catalyst knowledge.

Grace Davison’s commitment to the refining industry extends beyond that of a traditional catalystsupplier. It has always been our philosophy to complement the use of our premium, value-addedFCC catalysts with the industry’s finest technical support.

The Guide features the following articles:

Part One1. History of Cracking2. Cracking Reaction Mechanism3. The Fluid Catalytic Cracking Process4. Vessel and Mechanical Equipment5. Feedstock6. FCC Operation

Part Two7. Fluid Cracking Catalysts8. Equilibrium Catalyst Analysis9. Fluid Cracking Catalyst Additives10. Reformulated Gasoline and the FCC Unit

Part Three11. Laboratory Evaluations of Fluid Catalytic Cracking12. Yield Estimates13. Cat Cracker Problems and Solutions

All three parts of the Guide are now available on CDas searchable PDF documents. To order a copy of theGuide on CD, contact your Grace Davison salesrepresentative or [email protected].

Editor’s Note:

The use of Grace Davison FCC catalystsand additives has provided improvedoperating flexibility to refiners for decades.Fluctuating product values, some season-al, others triggered by evolving economicparameters, have created a dynamic mar-ket for products that can address shortterm and long term operating objectives.With the application of new strict environ-mental regulations on a global level, andthe ever changing feed slate, the refinermust adapt quickly in order to maintain aprofitable and acceptable operation.

One such challenge is meeting regulationswith respect to sulfur levels in products likegasoline and cycle oils. There are obvioushardware options such as hydrotreatingand hydroprocessing units but there are also catalytic options that a refiner canimplement to complement the refinery configurations. Grace Davison innovationresulted in our patented gasoline sulfur reduction or GSR® family of productsdesigned specifically to achieve compliance with new fuels regulations.

In this article we will discuss a scenario where a FCC feed hydrotreater plannedshutdown caused a burden on the refiner to meet gasoline sulfur specificationsduring the unit outage. We will present the step-by-step approach that was imple-mented by Grace Davison and the refiner in providing the refiner an action planincluding the use of GSR to allow them to continue meeting the product sulfurspecification while processing a poorer quality feed during the outage.

The short-term application was such a success that the refiner decided to contin-ue GSR usage even after starting up the FCC feed hydrotreater.

Principal author Lauren Blanchard is currently Strategic Global MarketingManager for Advanced Refining Technologies. This article first appeared in Issue#101, 2007.


ANNIVERSARY ISSUE

Introduction

n most refineries, FCC gasoline isone of the largest, if not the largestcontributor of sulfur to the overall

gasoline pool. Regulations limiting theamount of sulfur in gasoline have high-lighted the importance of reducing sul-fur in the FCC gasoline stream. GraceDavison has been providing catalystsand additives to the industry that reduceFCC gasoline sulfur by 35% or more forover ten years. These technologies havebeen proven in 80 units worldwide.Another popular alternative to reducegasoline sulfur is the installation of hard-ware. Increasingly stringent regulationshave forced refiners to install FCC feedhydrotreaters and gasoline post-treatersto meet ultra-low sulfur gasoline regula-tions. Interestingly, the phase-in of hard-ware has not eliminated the benefit ofsulfur reducing catalysts and additives.Grace Davison's gasoline sulfur reduc-tion technologies are complementary to

hardware solutions. They are beingused at numerous refineries aroundthe world in conjunction with hard-ware to drive refinery profitability byproviding feedstock flexibility, mini-mizing octane loss and providingoperational flexibility during hydro-treater outages.

Proper management of FCC feedhydrotreater outages is becomingincreasingly important as more andmore refiners rely on hydrotreatingto meet their per-gallon gasolinesulfur limits. About half of all FCCunits now have feed hydrotreaters.Some are run at higher severity thanin the past to achieve these newultra-low gasoline sulfur targets.Running at higher severity increasesthe frequency of turnarounds.Conventional methods of ensuringthat the gasoline pool stays belowthe sulfur limit during the

Clean Fuels:An Opportunity for Profitability UsingGasoline Sulfur Reduction Technology

Lauren BlanchardAdvanced RefiningTechnologies,Columbia, MD

Craig BorchertValero Energy,Wilmington, CA

Min PuValero Energy,Wilmington, CA


I

hydrotreater turnaround are pur-chasing low sulfur feed or reducingFCC throughput. Either approachcan significantly reduce refineryprofitability. Another option is to useone of Grace Davison's sulfurreducing technologies during theoutage to provide feedstock flexibil-ity while maintaining sulfur compli-ance.

This paper presents a case study inwhich Grace Davison and ValeroEnergy’s, Wilmington, California, USArefinery worked closely together tominimize the impact of a FCC feedhydrotreater outage. Significant plan-ning and preparation took place,including selecting the best pur-chased feeds to run during the out-age as well as the best sulfur reduc-tion technology to use to meet theirobjectives given the sulfur species inthe FCC gasoline. The use of GraceDavison's GSR®-5 sulfur reductionadditive allowed Valero to processfeed that was higher in sulfur thantheir routine feed yet remain in gaso-line pool sulfur compliance. Valeroestimates that the use of GSR-5 addi-tive saved them $1.7 million duringthe hydrotreater outage. The resultswere so encouraging that Valero haselected to use GSR-5 additive on anon-going basis and estimatesincreased profits of over $8 millionannually.

Evolution of Sulfur ReductionTechnologies

In 1992, well before the industry real-ized the need to reduce FCC gasolinesulfur, Grace Davison anticipated thisrequirement and began a researchand development effort for catalyticreduction of FCC gasoline sulfur. Theobjective was to develop a family ofFCC catalysts and additives to helprefiners meet clean fuels specifica-tions. Established technologies thatevolved from over 14 years of continu-ous R&D include D-PriSM additive,SuRCA catalyst, GSR-5 additive, andNeptunecatalyst.

A road map for product selection isshown in Figure 1. When formulat-ing a solution for a customer, GraceDavison experts consider the FCCgasoline stream targeted for sulfurreduction, the desired level of gaso-line sulfur reduction, and whether acatalyst or an additive is preferred.Careful selection of the appropri-ately engineered solution for eachapplication has resulted in consis-tent product performance andmeeting or exceeding customerexpectations. Twenty-three refinersare currently using Grace Davisongasoline sulfur reduction productsworldwide, making Grace Davisonthe leading supplier of gasoline sul-fur reduction catalysts and addi-tives. Many of these refiners havebeen using these products on acontinuous basis as part of theiroverall sulfur reduction strategy.(Figure 2).

For refiners who desire FCC addi-tives for maximum operating flexibil-ity, Grace Davison's D-PriSM addi-tive is effective at reducing sulfurspecies in light and intermediateFCC gasoline. It has been used inmore than 25 refineries worldwide.D-PriSM additive has provided up to35% sulfur reduction on light FCCgasoline with no FCC yield deterio-ration.

Figure 1Grace Davison's Portfolio of Gasoline Sulfur Reduction Products

PreferredTechnology

CATALYST

ADDITIVELight or Intermediate

Gasoline

Full RangeGasoline

Light & Intermediate

Solution

D-PriSM 10-35%reduction

35%reductionor more

20-35%reduction

Light, Intermediate and Full range gasoline

Neptune

GSR -5SuRCA

gasoline

®

®

TM

®

Figure 2Grace Davison Experience in Sulfur Reduction Applications

51>100 days

>365days

# of Applications

Length ofApplications

27

10 20 30 40 500 60

TIME

388Days

5.9Years

Longest Application

(ongoing)

Average Length forall 85 Sulfur ReductionApplications Worldwide

85 Total Applications WW to Date => 25 Current Users


Grace Davison's SuRCA catalystfamily is designed to completelyreplace the conventional FCC cata-lyst in the circulating inventory. Thisproduct provides gasoline sulfurreduction of up to 35% on full rangegasoline while maintaining or evenenhancing existing yields andselectivities. Additionally, reductionsof 10-15% in LCO sulfur have beenobserved in some applications.Over 45 SuRCA catalyst applica-tions have occurred worldwide, with10 current users having employedthe technology for an average ofmore than three years. These refin-ers have incorporated SuRCA cata-lyst into their operating strategies forlong-term profitability and operatingflexibility.

Appreciating refiners’ desire for aproduct that provides the perform-ance of SuRCA catalyst but can beused as an additive for maximumoperating flexibility, Grace Davisoncommercialized the GSR-5 additivein 2004. It is based on the SuRCAcatalyst chemistry and providessimilar gasoline sulfur reductionwith base cracking catalyst func-tionality. There are currently fiverefiners benefiting from the use ofGSR-5 additive.

To further expand the sulfur reduc-tion portfolio for continuousimprovements in both performanceand cost effectiveness, GraceDavison has recently commercial-ized a new gasoline sulfur reductioncatalyst family. This next generation

technology, Neptune, is a step outimprovement, providing 35-50% fullrange gasoline sulfur reduction com-mercially with full catalyst formulationflexibility.

Pre Turnaround Preparation

The Valero, Wilmington refineryapproached Grace Davison fourmonths prior to their scheduled FCCfeed hydrotreater shutdown to helpthem get a better understanding oftheir options during the outage. Valeroand Grace Davison worked togetherto determine if the use of a gasolinesulfur reducing technology wouldenable Valero to improve their eco-nomics and remain within their FCCgasoline sulfur limit during the shut-down.

During the outage, the refineryplanned to purchase severalhydrotreated feeds. These wouldbe different than the pretreated feednormally charged to the FCC unit.The refinery planned to blend pur-chased feeds with their routinefeed. The candidate feeds weresent to Grace Davison for testing tocompare the potential effects of thefeeds on the refinery's FCC yieldsand gasoline sulfur.

Analysis of the candidate feeds andValero, Wilmington's pretreatedRoutine Feed is shown in Figures 3-5. Candidate feeds (Samples A, B,and C) were heavier and more aro-matic than the Valero, WilmingtonRoutine Feed (Figure 4) makingthem more difficult to crack (Figure3). Additionally, the three samplefeeds contained significantly moresulfur and nitrogen species, whileconcarbon levels were similar to theRoutine Feed (Figure 5).

The four feeds were tested using arepresentative Valero, Wilmingtonequilibrium catalyst (Ecat) sample inthe pilot plant. The results suggest-ed that all of the candidate feedswould suppress conversion by atleast 4 wt.% (Figure 6). Yields inter-polated at constant coke are shownin Table I. All feeds showed thepotential for increased LCO andbottoms. These feeds also yieldedsignificantly less gasoline withslightly lower octane.

Figure 3Feed Distillation Profile

300

400

500

600

700

800

900

1000

1100

1200

0 10 20 30 40 50 60 70 80 90 100

Percentage

Bo

ilin

gP

t(°

F)

Sample A

Routine Feed

Sample B

Sample C

300

400

500

600

700

800

900

1000

1100

1200

0 10 20 30 40 50 60 70 80 90 100

Percentage

Bo

ilin

gP

t(°

F)

Sample A

Routine Feed

Sample B

Sample C

Figure 4Feed Properties

10

15

20

25

30

35

40

45

50

55

60

°API Aromatic Carbons, Ca (wt.%)

Napthenic Paraffinic Carbons,

Routine Feed

Sample A

Sample B

Sample C

Carbons, Cn (wt.%) Cp (wt.%)


In addition to shifting yields towardless favorable products, the feedsalso increased gasoline sulfur.Samples B and C increased sulfurby 200%, while Sample A more thantripled FCC gasoline sulfur relativeto the Routine Feed (Figure 7).

The gasoline sulfur concentrationfor the Routine Feed produced inthe pilot plant is significantly lowerthan what is sent to blending fromthe Wilmington FCC unit. A numberof “tramp” gasoline streams gener-ated at other process units are cur-rently processed in the FCC gasplant. These streams elevate theapparent “FCC gasoline sulfur” as itis received in blending.

To help align the estimated FCCgasoline sulfur that would resultfrom processing the candidatefeeds with predicted commercialperformance, the gasoline sulfurspecies produced in the pilot plantusing the Routine Feed were com-pared to the commercially pro-duced gasoline samples. The com-mercial gasoline samples were pro-duced in the Valero, WilmingtonFCC unit while processing two dif-ferent feeds (Figure 8). There isgood agreement for both individualsulfur species, and the relativeamount of each species presentwhen comparing the two sets ofsamples. Therefore, we can reason-ably replicate the sulfur distributionof the commercially producedgasolines in the pilot plant. Cutgasoline sulfur is the sum of thespecies (mercaptans through C4thiophenes) and is higher for thecommercially produced gasoline,suggesting the presence of addi-tional sulfur from the “tramp”streams.

Another potential reason for differ-ences between the pilot plant gen-erated gasoline sulfur and that pro-duced commercially is the methodused to measure the sulfur concen-tration. Refiners typically measuregasoline sulfur by the bulk x-raygasoline sulfur method. The meas-urement of gasoline sulfur pro-

Figure 5Feed Properties

Figure 6Feed Study Conversion vs. Coke

0.00

0.05

0.10

0.15

0.20

0.25

Sulfur (wt.%) Basic Nitrogen(wt.%)

Total Nitrogen ConradsonCarbon (wt.%)(wt.%)

Sample A

Routine Feed

Sample B

Sample C

Sample A

Routine Feed

Sample B

Sample C

64

66

68

70

72

74

76

78

80

82

84

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Coke (wt.% Feed)

Co

nve

rsio

n(w

t.%

)

Sample A

Routine Feed

Sample B

Sample C

Sample A

Routine Feed

Sample B

Sample C

Table IInterpolation at Constant Coke (3 wt.%)

78.97.00.041.65.11.50.775.313.30.4021.554.417.43.791.381.8

71.76.30.041.64.51.20.795.011.20.4518.550.321.36.990.580.7

74.46.40.041.54.61.30.784.911.70.4219.152.320.35.290.881.2

74.26.20.051.64.81.20.795.311.80.4519.451.820.25.690.981.0


duced in the pilot plant utilizes agas chromatograph to identify theindividual sulfur species and totalsulfur concentration.

Sulfur species in the gasolines pro-duced by the candidate feeds werecompared to species present ingasoline generated by the RoutineFeed. The candidate feeds all pro-duced the same gasoline speciesas the gasoline generated from theRoutine Feed except in higher con-centrations (Figure 9).

Gasoline samples for each candi-date feed in Figure 9 were normal-ized to account for the deltabetween FCC-produced and pilotplant-produced methods (fromFigure 8). Additionally, data wasnormalized to an x-ray basis toreflect the levels of sulfur that wouldbe observed on the FCC unit.Finally, gasoline sulfur for each can-didate feed was adjusted to main-tain the same gasoline sulfur to feedsulfur ratio observed on theWilmington FCC unit resulting in thedata in Figure 10.

The results from the pilot plantstudy, along with information on theValero, Wilmington FCC unit opera-tion (both routine and during a pre-vious pretreater outage) were thenused by Grace Davison to evaluatethe performance of various gasolinesulfur reduction technology options.The GSR-5 additive, which containsbase cracking functionality, wasdetermined to be the best solution.Based on the normalized species inthe gasoline produced by SamplesA through C, Grace Davison esti-mated that the GSR-5 additivewould reduce gasoline sulfur by 19-23%. This narrow range reflectsextensive understanding of the cus-tomer's operation and the up-frontpilot plant work.

The Valero, Wilmington refinery poolgasoline sulfur limit is 30 ppm. Therefinery also must produce gasolinebelow California NOx emissions lim-its, which are influenced heavily bythe sulfur and olefins content of the

Figure 7Total Gasoline Sulfur vs. Coke

Figure 8Comparison of Commercially Produced and Pilot Plant Gasolines

0

4

8

12

16

Mer

capta

ns

Thiophen

e

Met

hylThio

phenes

Tetra

hydro

Thiophen

e

C2-Thio

phenes

Thiophen

ol

C3-Thio

phenes

Met

hylThio

phenol

C4-Thio

phenes

Cut Gasolin

eSulfu

r

Su

lfu

r(p

pm

)

1 - FCC Commercial Sample2 - FCC Commercial Sample1 - Pilot Plant2 - Pilot Plant

Includes Tramp Streams

Figure 9Pilot Plant Produced Gasolines

0

5

10

15

20

25

30

35

40

Mer

capta

ns

Thiophen

e

Met

hylThio

phenes

Tetra

hydro

Thiophen

e

C2-Thio

phenes

Thiophen

ol

C3-Thio

phenes

Met

hylThio

phenol

C4-Thio

phenes

Cut Gasolin

eSulfu

r

Su

lfu

r(p

pm

)

Routine Feed

Sample A

Sample B

Sample C

0

10

20

30

40

50

60

70

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Coke (wt.% Feed)T

ota

lG

aso

line

Su

lfu

r(p

pm

)

Sample A

Routine Feed

Sample B

Sample C

Sample A

Routine Feed

Sample B

Sample C



gasoline streams blended into thepool. The results of the pilot planttesting confirmed that the refinerywould need to store Routine Feed toblend with candidate feeds duringthe pretreater outage to keep FCCfeed sulfur levels low enough toremain below their limits. Based onthe pilot plant results, Valero con-cluded that Feed A was too risky inboth gasoline sulfur and FCCyields/selectivities. The decisionwas made to purchase the otherfeeds and blend them at variousratios with available Routine Feedduring the outage.

GSR-5 Additive Application

As is common in many refineries,the FCC gas plant at Valero'sWilmington facility processesstreams from outside the FCC unit.These streams contain sulfur that isnot affected by the GSR-5 additivesince the additive works by partici-pating in the cracking reactions thattake place in the FCC unit.Unfortunately, the Wilmington refin-ery sampling configuration does notallow for direct sampling of the FCCgasoline prior to the inclusion of the“tramp” streams. The presence ofthese streams in the gasoline sam-ples used to evaluate GSR-5 addi-tive performance reduces theapparent performance by reducingthe calculated percentage sulfurreduction.

Valero began use of GSR-5 additivetwo months prior to the 45-day feedhydrotreater outage. Coordinatedefforts with Grace Davison allowedValero to receive material and base-load their inventory in 14 days. Ablend of the candidate feeds alongwith the Routine Feed was fed to theFCC prior to the outage, whichincreased feed sulfur by 20-35%.Additive additions proceeded smooth-ly and the projected performance wasexceeded in less than 30 days withgasoline sulfur reduction of 20-25%.Figure 11 depicts a year's worth ofnormalized gasoline data vs endpoint.The three periods represented aretypical operation (Base Period), GSR-5 additive before and during the out-age, and finally GSR-5 additive follow-ing the outage. Throughout the out-

age, Valero remained within theirFCC gasoline sulfur limits while pro-cessing all candidate feeds. Afterthe outage, continued addition ofGSR-5 additive allowed them to run10-15% higher feed sulfur.

Economics

The candidate feeds also increasedthe FCC gasoline olefins content,which combined with the increasein the projected gasoline sulfurwould have forced Valero tohydrotreat approximately five MBPDof FCC gasoline to comply withCalifornia NOx emission specifica-tions. The loss of octane fromhydrotreating the FCC gasolinewould have reduced the amount oflow octane streams, such as LightStraight Run (LSR) and Heavy CatNaphtha (HCN), that could beblended into the pool. The sulfurreduction provided by the GSR-5additive allowed Valero to avoidhydrotreating the five MBPD FCCgasoline stream, the value of whichwas calculated to be $0.25/BBL or$1.7 million over the three monthperiod surrounding the outage.

After the pretreater was back on-line, Valero evaluated the econom-ics of continued GSR-5 additiveusage. They determined that bycontinuing to use it, they could con-sistently feed high sulfur VGO totheir FCC feed hydrotreater insteadof medium sulfur VGO and remain

Figure 11Normalized FCC Gasoline Sulfur vs. T95

GSR-5 provides 20-25% reduction

200

250

300

350

400

450

500

550

310 315 320 325 330 335

D86 T95 (°F)

Gas

olin

eS

ulf

ur

/F

eed

Su

lfu

r(p

pm

/wt%

)

Base Period (Days 1-71)

GSR-5 & Outage (Days 90-115)

GSR-5 After Outage (Days 116-375)

Figure 10Normalized Pilot Plant Produced Gasolines

0

10

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30

40

50

60

70

Mer

capta

ns

Thiophen

e

Met

hylThio

phenes

Tetra

hydro

Thiophen

e

C2-Thio

phenes

Thiophen

ol

C3-Thio

phenes

Met

hylThio

phenol

C4-Thio

phenes

Cut Gasolin

eSulfu

r

Su

lfu

r(p

pm

)

Routine Feed

Sample A

Sample B

Sample C


under the refinery pool gasoline sul-fur limit of 30 ppm. Valero esti-mates the incremental profit for pro-cessing high sulfur VGO is $4.4 mil-lion per year (using a conservative 3cents per gallon differentialbetween high and medium sulfurVGO). Accounting for the cost ofthe GSR-5 additive and incrementalSOx additive required to remain inSOx emission compliance (higherFCC feed sulfur yields higher SOxemissions) the net profit is $3.8 mil-lion.

The Wilmington refinery targets atwo-year cycle on the FCC feedhydrotreater. The cycle length isdetermined by the catalyst activity,which is influenced by operatingseverity and throughput. Valerodetermined that by using the GSR-5additive to control FCC gasoline sul-fur, they could reduce hydrotreaterseverity (even with higher sulfurVGO feed to the hydrotreater),which allowed them to processmore VGO through the unit. Valerowas able to increase hydrotreaterthroughput by 4%. The excesshydrotreated FCC feed is periodi-cally sold at a premium over regulargasoil (using a seven cents per gal-lon differential between hydrotreat-ed and regular gasoil) for an esti-mated annual profit of $4.5 million.

The total benefit from the GSR-5additive for the Wilmington refineryis calculated to be $8.3 million peryear - a return of over 18 times theincremental cost of the GSR addi-tive technology.

The refinery has also determinedthat managing the tramp gasolinestreams using a different process,rather than processing them in theFCC gas plant, will allow them toachieve significant flexibility in theirgasoline pool blending operation.They plan to revamp an existingtower into an LSR splitter, which willremove C3's and C4's before send-ing gasoline material directly toblending. The operation of the FCCunit is expected to shift in favor ofmore light olefins with the new

equipment in service. The impact ofthe change in FCC operation on FCCgasoline sulfur and olefins will be eval-uated to determine if GSR-5 econom-ics remain favorable with the newprocess configuration.

Conclusion

Proper management of hydrotreateroutages is becoming increasinglyimportant as more and more refinersrely on hydrotreating to meet gasolinesulfur limits. Outages of either FCCfeed hydrotreaters or gasoline post-hydrotreaters create opportunities forrefiners to incorporate GraceDavison's sulfur reduction catalystsand additives into their planning. Thiswould allow for significant savings inpurchased feeds or mitigation of thecost of constraints caused by non-routine operation leading up to andduring the outage. With hydrotreatingequipment in service, these technolo-gies can generate significant revenuefor refiners who want to optimize oper-ations to drive profitability. Reductionof FCC gasoline sulfur allows for high-er feed sulfur to the FCC unit or to anupstream FCC feed hydrotreating unitwithout risking gasoline sulfur non-compliance. Lower FCC gasoline sul-fur can also allow for reduced severityoperation on either the FCC feedhydrotreater or the gasoline treatingunits, creating revenue in the form ofoctane recovery, higher throughput, orextended cycle life.

The Valero, Wilmington case studypresented here was made possible byincorporating discussions betweenValero and Grace Davison into theplanning stages of the FCC feedhydrotreater outage. Based on thosediscussions, pilot plant testing wascompleted which assisted Valero inselecting the purchased feeds theywould run during the outage.Estimates provided by Grace Davisonshowed that the GSR-5 additive wouldallow Valero to achieve their shutdownobjective of keeping their gasolinesulfur in compliance while running thehigher sulfur purchased feeds. Theuse of GSR-5 additive during the out-age resulted in $1.7 million in savings.

With the proven product perform-ance of the GSR-5 additive, Valerowas then able to optimize their oper-ation once the FCC feedhydrotreater was put back in serv-ice. The FCC feed hydrotreater unitseverity was reduced, allowing forhigher throughput, and the incre-mental hydrotreated gasoil was soldat a premium over regular gasoil.Additionally, Valero was also able tofeed high sulfur VGO in place ofmedium sulfur VGO to the FCC feedhydrotreater without exceeding theFCC gasoline sulfur limits. Bothoperating changes resulted in acombined profit of over $8 millionper year for the refinery.

While each refinery configuration isunique, and the economics present-ed here are specific to the ValeroWilmington refinery, this exampledemonstrates that Grace Davison'sgasoline sulfur reduction productscan provide enhanced operatingflexibility in any operation and signif-icantly improve refinery profitability.

Acknowledgements: The authors wish tothank Valero Energy and Grace Davison forpermission to release this information.Natalie Petti (consultant), is gratefullyacknowledged for her contribution of dataevaluation and critique.

Break the Bottom of Your Barrelwith Grace Davison’s MIDAS® FCC Catalyst

Grace Davison’s revolutionary MIDAS®-300 catalyst is commercially proven to upgrade

the bottom of your FCC barrel. Designed by Grace Davison specifically for max bottoms

destruction, MIDAS®-300 catalyst offers high activity matrix surface area, balanced with

an optimized zeolite level.

MIDAS®-300 FCC catalyst is just the latest result of our 60+ year commitment to

understanding bottoms cracking mechanisms and catalysts. Contact us for information

on how Grace Davison can provide catalytic solutions to your bottoms cracking needs.

Grace Davison Refining Technologies7500 Grace DriveColumbia, Maryland 21044 USA+1.410.531.4000 • +1.410.531.8245 (fax)www.e-catalysts.com

[email protected] [email protected]

Catalagram®, Grace®, Grace Davison®, MIDAS®, IMPACT®, GSR®, AURORA®, ADVANTA®, Super DESOX®, D-PriSM®, SuRCA®,GSR®-5 and SmART Catalyst System® are registered trademarks in the United States and/or other countries,of W. R. Grace & Co.-Conn.

NEPTUNETM and GENESISTM are trademarks of W. R. Grace & Co.-Conn.

This trademark list has been compiled using available published information as of the publication date of this brochure and may notaccurately reflect current trademark ownership.

© 2009 W. R. Grace & Co.-Conn.

© 2009 W. R. Grace & Co.-Conn.

Grace Davison Refining TechnologiesAdvanced Refining TechnologiesW.R. Grace & Co.-Conn.7500 Grace DriveColumbia, MD 21044410.531.4000

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