Fahim M.A., Sahhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining

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8.16.3. Petro-FCC

The Petro-FCC process is licensed by UOP. The process gives the highest

yield of propylene, lighter olefins and aromatics for petrochemical operation

from feedstocks which can include conventional FCC feeds and residual

feeds. The feed comes in contact with the blended catalyst in the riser

under sever condition. A schematic diagram of the process is shown in

Figure 8.12.

Crude

dist

BTX

HDS

CPP

Paraffinic

crude

Fuel oil

Light olefins

Diesel

Aromatics

Atmospheric residue

Vacuum gas oil

Vacuum residue

Light olefins, butadiene,

LPG

Figure 8.11 Flowchart for crude to pet rochemica l

FCC Catalyst

Section

Main Cat.

and Gas Con.

Section

Sponge Gas

Treating

LPG Treating

Aromatic

Complex

Propylene

Recovery

Splitter

Ethylene

Recovery

Benzene

p-Xylene

O + CH

Fresh Feed

Light Ends

Heavy Recycle

Raffinate

C4 to

Refinery

Figure 8.12 UOP Petro-FCC complex (PetroFCC, 2008)

Fluidised Catalytic Cracking 231

The process starts with a uniquely designed FCC unit and is capable of

producing a product of 18 LV% C

, 7 LV% C

, 10 LV% C

and 20 LV%

benzene and paraxylene. A complete comparison of conventional and

Petro-FCC yields is given in Table 8.8 (Hsu and Robinson, 2006).

Questions and Problems

8.1. Use a feed composed of AGO and VGO coming out from a distillation

unit with a conversion of 70% in a once-through operation with a

zeolite catalyst.

BPD Ton/day

Sulphur

Ton/day

Atmospheric gas oil 7451.65 1050.78 21.169

Light vacuum gas oil 4662.92 666.143 27.888

Heavy vacuum gas oil 24635.5 3674.16 169.032

Total 36750.07 5391.083 218.089

8.2. If the HCGO in the above problem is recycled to extinction, by how

much will the gasoline production be increased? How much coke will

lay down?

8.3. For the following conditions, calculate (a) the wt% hydrogen in coke,

(b) the coke yield, and (c) the catalyst-to-oil ratio.

Carbon on spent catalyst: 1.50 wt%

Table 8.8 Yield patterns of conventional FCC and Petro-FCC

units

Component

Conventio nal

FCC wt%

Petro-FCC

wt%

S, H

Ethylene 1 6

Propane 1.8 2

Propylene 4.7 22

Butane 4.5 5

Butene 6.5 14

Naphtha 53.5 28

Distillate 14 9.5

Fuel oil 7 5

Coke 5 5.5

232 Chapter 8

Carbon on regenerated catalyst: 0.80 wt%

Air from blower: 155,000 lb/h

Hydrocarbon feed to reactor: 295,000 lb/h

Flue gas analysis (Orsat) vol%: CO ¼ 12.0, CO

¼ 6.0, O

¼ 0.7,

¼ 81.3

8.4. The following operating data were obtained from an FCC unit which

is now in operation. Operating data:



Combustion air to the regenerator (dry basis: excluding water

fraction)

Flow rate: 120,000 kg/h, Temperature: 200





Composition of the regenerator flue gas (dry basis)

0.5 vol% SO

0.2 vol%

CO 3 vol% N

81.3 vol%

15 vol%



Regenerator flue gas temperature 720





Regenerator catalyst bed temperature 700





Spent catalyst temperature 550



(1) With a coke combustion balance calculation around the regener-

ator, estimate the coke yield as wt% on the basis of fresh feed oil.

(2) Estimate the flow rate of the circulating catalyst (t/min).

Note: The capacity of the FCC unit is 40,000 BPSD, and the specific

gravity of the feed oil is 0.915 (15/4



C).

8.5. 100,000 BPD crude oil, with an API of 24, is fed to a distillation

column. The crude TBP and API as a function of accumulated vol-

ume% (LV%) are as follows:

TBP



RðÞ¼ 1:5ln

100

100  LV%



2:7

þ 1

()

486

API ¼0:0004 LV%

þ 0:05 LV%

 2:4LV% þ 72

A gasoline cut is produced from the CDU unit as well as AGO and VGO

cuts which are fed to the FCC unit as shown in the flowchart. Gasoline is

also produced from the FCC as well as LCO, which is then fed to a

hydrocracking unit to produce gasoline. Calculate the total amount of

gasoline (lb/h) that is produced from all units.

CDU

100,000

BPD

FCC

72%

conversion

190-380 ⬚F

CDU-Gasoline

650-850 ⬚F

AGO

850-1050 ⬚F

VGO

Hydrocracker

3 wt%

H-severity

LCO

wt% S = 0.6%

K = 12

FCC-Gasoline

Hydrocracking-

Gasoline

Fluidised Catalytic Cracking 233

8.6. 100,000 BPD crude oil, with 3 wt% sulphur, is fed to a distillation

column. The crude TBP and API as a function of accumulated volume

% (LV%) are as follows:

TBP



RðÞ¼ 2ln

100

100  LV%



2:5

þ 1

()

490

API ¼0:0004 LV%

þ 0:05 LV%

 2:4 LV% þ 72

A gasoline cut is produced from the CDU unit as well as a VGO cut

which is fed to the coker unit as shown in the flowchart. Gasoline is also

produced from the FCC. Calculate the following:

a) CDU gasoline

b) Coker gasoline

c) Feed to FCC

d) FCC gasoline

CDU

100,000

BPD

Hydrotreating

90% severity

FCC

75%

conversion

190-380 ⬚F

CDU-Gasoline

Coker gasoline

FCC-Gasoline

Delayed Coker

VR 1050+ ⬚F

CCR = 15 wt%

850-1050 ⬚F

VGO

2 wt% S

Coker GO

API = 20

VGO

REFERENCES

Abul-Hamayel, M. (2003). Kinetic modeling of high severity fluidized catalytic cracking.

Fuel 82, 1113–1118.

Ahari, J. S., Farshi, A., and Forsat, K. (2008). A mathematical modeling of the riser reactor in

industrial FCC unit. Petroleum Coal 50(2), 15–24

Ali, H., and Corriou, P. (1997). Modeling and control of a riser type fluid catalytic cracking

(FCC) unit. Trans. Inst. Chem. Eng. 75, 401–412.

Ancheyta-Juarez, J., and Murillo-Hernandez, A. (2000). A simple method for estimating

gasoline, gas and coke yields in FCC processes. Energy Fuels 14, 373–379.

Bonifay, R., and Marcilly, C. (2001). Catalytic cracking. In ‘‘Conversion Processes,’’

Petroleum Refining (P. Leprince, Ed.), Vol. 3, Chapter 5. TECHNIP, France

Hsu, C. S., and Robinson, P. S. (2006). ‘‘Practical Advances in Petroleum Processing,’’

Vol. 1. Springer Science.

234 Chapter 8

Jia, C., Rohani, S., and Jutan, A. (2003). FCC unit modeling, identification and model

predictive control, a simulation study. Chem. Eng. Proc . 42, 311–325.

Maples, R. E. (1993). ‘‘Petroleum Refining Process Economics.’’ PennWell Publishing

Company, Oklahoma, USA.

Parkash, S. (2003). ‘‘Refining Processes Handbook.’’ Elsevier, Amsterdam.

PetroFCC

(2008). ‘‘Process for Petrochemical Feedstock Production.’’ UOP publication,

HoneyWell.

Sadeghbeigi, R. (2000). ‘‘Fluid Catalytic Cracking Handbook,’’ 2nd ed. Gulf Publishing

Company, Houston, TX.

Scherzer, J. (1990). ‘‘Octane – Enhancing Zeolite FCC Catalysts.’’ Marcel & Dekker,

Vol. 42, New York.

Tominaga, H., and Tameki, M. (1997) ‘‘Chemical Reaction and Reactor Design’’. John

Wiley & Sons, England.

UNISIM Design Suite (2007). ‘‘HoneyWell Process Solutions.’’ Calgary, Alberta, Canada.

Fluidised Catalytic Cracking 235

CHAPTER NINE

Product Blending

9.1. Introduction

Refining processes do not generally produce commercially usable

products directly, but rather semi-finished products which must be blended

in order to meet the specifications of the demanded products.

The main purpose of product blending is to find the best way of mixing

different intermediate products available from the refinery and some addi-

tives in order to adjust the product specifications. For example, gasoline is

produced by blending a number of components that include alkylate,

reformate, FCC gasoline and an oxygenated additive such as methyl tertiary

butyl ether (MTBE) to increase the octane number.

The final quality of the finished products is always checked by laboratory

tests before market distribution. Gasolines are tested for octane number,

Reid vapour pressure (RVP) and volatility. Kerosenes are tested for flash

point and volatility. Gas oils are tested for diesel index, flash point, pour

point and viscosity.

Product qualities are predicted through correlations that depend on the

quantities and the properties of the blended components. In this chapter,

various mixing rules along with correlations are used to estimate the blend

properties such as specific gravity, RVP, viscosity, flash point, pour point,

cloud point and aniline point. The octane number for gasoline is correlated

with corrections based on aromatic and olefin content.

The desired property P

Blend

of the blended product may be determined

using the following mixing blend rule:

Blend

i¼1

ð9:1Þ

where P

is the value of the property of component i and q

is the mass,

volume or molar flow rate of component i contributing to the total amount

of the finished product. For example, q

can be volume fraction x

therefore, the denominator in equation (9.1) will equal 1.

Fundamentals of Petroleum Refining

2010 Elsevier B.V.

237

The blending mixing rule expressed by equation (9.1) assumes that the

given property is additive (or linear). Additive properties include specific

gravity, boiling point and sulphur content. However, properties like vis-

cosity, flash temperature, pour point, aniline point, RVP and cloud point

are not additive. Table 9.1 lists typical properties of pure components and

petroleum cuts that can be blended for gasoline to meet market

specifications.

9.2. Reid Vapour Pressure Blending

RVP is the vapour pressure at 100



F of a product determined in a

volume of air four times the liquid volume. RVP is not an additive

property. Therefore, RVP blending indices are used. A commonly used

RVP index is based on an empirical method developed by Chevron Oil

Trading Company (1971).

RVPi

¼ RVP

1:25

ð9:2Þ

where BI

RVPi

is the RVP blending index for component i and RVP

is the

RVP of component i in psi.

Table 9.1 Typical properties for gasoline blending components (G ary and Handwerk,

2001)

Component RVP (psi) MON RON API

71.0 92.0 93.0

52.0 92.0 93.0

19.4 90.8 93.2

14.7 72.4 71.5

6.4 78.4 79.2

LSR gasoline 11.1 61.6 66.4 78.6

HSR gasoline 1.0 58.7 62.3 48.2

Light hydrocracker gasoline 12.9 82.4 82.8 79.0

Heavy hydrocracker gasoline 1.1 67.3 67.6 49.0

Coker gasoline 3.6 60.2 67.2 57.2

FCC Light gasol ine 1.4 77.1 92.1 49.5

FCC gasoline 13.9 80.9 83.2 51.5

Reformate 94 RON 2.8 84. 4 94.0 45.8

Reformate 98 RON 2.2 86. 5 98.0 43.1

Alkylate C

5.7 87.3 90.8

Alkylate C

4.6 95.9 97.3 70.3

Alkylate C

1.0 88.8 89.7

238 Chapter 9

Using the index, the RVP of a blend is estimated as

RVP;Blend

i¼1

RVPi

ð9:3Þ

where x

is the volume fraction of component i.

Example E9.1

Calculate the RVP of a blend of LSR gasoline , HSR gasoline, Reformate and

FCC gasoline. Properties and available quantities of the components are given in

Table E9.1.1.

Solution:

As illustrated in Table E9.1.2, the RVP of the blend is calculated through the

following steps:



The volume fraction of each component x

is calculated and listed in

Table E9.1.2.



The RVP index of each component is calculated. For example, the calcula-

tion of LSR gasoline gives BI

RVPi

¼ 11:1

1:25

¼ 20: 26



The volume fraction is multiplied by the index for each component

(Table E9.1.2)

From the summation, BI

RVP,Blend

¼ 14.305, then

RVP

Blend

¼ð14:305Þ

1=1:25

¼ 8:4psi

Hence, the RVP of the blended product is 8.4 psi.

Table E9.1.1 Quantities and RVP values of the blending components

Component Quantity ( BPD) RVP (psi)

LSR gasoline 5000 11.1

HSR gasoline 4000 1.0

Reformate 94 RON 6000 2.8

FCC gasoline 7000 13.9

Table E9.1.2 Summary of RVP calculations

Component Quantity (BP D) x

RV P i

BI

RV P i

LSR gasoline 5000 0.227 20.26 4.599

HSR gasoline 4000 0.182 1.0 0.182

Reformate 94 R ON 6000 0.273 3.62 0.989

FCC gasoline 7000 0.318 26.84 8.535

Sum 22,000 1.0 14.305

Product Blending 239

Additives, such as propane, i-butane and n-butane can be added to the

gasoline blend to adjust the RVP requirements. Example E9.2 illustrates

how the amount of an additive is calculated using the method of RVP index.

Example E9.2

Determine the amount of n-butane required to produce a gasoline blend with

RVP = 10 psi from the components listed in Table E9.1.1. The RVP of n-

butane is 52 psi.

Solution:

Assume V

Butane

is the volume ﬂow rate (BPD) of n-butane needed to be added

to the blend. RVP indices are calculated for all components including n-butane

and listed in Table E9.2.1.

The volume is ﬁrst multiplied by the index and then divided by the total

volume. The summation yields the RVP index for the blend.

RVP;Blend

¼ 10

1:25

314; 912 þ 139:64V

Butane

22; 000 þ V

Butane

The above equation is solved for V

Butane

to be 625.7 BPD, which is the amount

of n-butane needed to adjust the RVP of the bl end to 10 psi.

9.3. Flash Point Blending

The flash point is the lowest temperature at which vapours arises from

oil ignites. It indicates the maximum temperature at which a fuel can be

stored without serious hazard. If the flash point of a petroleum product does

not meet the required speci fications, it can be adjusted by blending this

product with other fractions. Flash point is not an additive property and

Table E9.2.1 Summary of calculations

Component QuantityV

(BPD) BI

RV P i

BI

RV P i

LSR gasoline 5000 20.26 101,300

HSR gasoline 4000 1.0 4000

Reformate 94 RON 6000 3.62 21,732

FCC gasoline 7000 26.84 187,880

n-Butane V

Butane

139.64 139.64 V

Butane

Sum 22,000 + V

Butane

314,912 +

139.64 V

Butane

240 Chapter 9

flash p oint blending indices are used, which bl end linearly on a volume

basis. The f lash poi nt of a blend is determined using the following

equation:

FP;Blend

i¼1

FPi

ð9:4Þ

where x

is the volume fraction of component i, and BI

FPi

is the flash point

index of component i that can be determined from the following correla-

tion (Riazi, 2005):

FPi

¼ FP

1=x

ð9:5Þ

is the flash point temperature of component i, in K, and the best value of

x is 0.06.

Another relation to estimate the flash point blending index is based on

the flash point experimental data reported by Gary and Handwerk (2001) .

FPi

¼ 51708  exp½ðlnðFP

Þ2:6287Þ

=ð0:91725Þ ð9:6Þ

is the flash point temperature of component i,in



F. The flash point

blending index is blended based on wt% of components.

Example E9.3

Calculate the blend ﬂash point of the components listed in Table E9.3.1. If the

resulted temperature is lower than 130



F, component D is added to the blend to

increase the ﬂash point. Knowing that the ﬂash point of D is 220



F, calculate the

amount (BPD) of component D (SG ¼0.95) to be added to adjust the ﬂash point.

Solution:

The ﬂash point indices are calculated using equation (9.6) and listed in

Table E9.3.2.

The mass ﬂow rates are calculated for each component based on the given

speciﬁc gravity and BPD.

For component A

2500

bbl

day



5:6ft

1 bbl



0:8  62:4lb



day

24 h



¼ 29; 120

lb/h

The weight fractions (x

) are then calculated and lis ted in Table E9.3.2.

Table E9.3.1 Quantities and ﬂash points of the blending components

Component BPD SG Flash point (



A 2500 0.80 120

B 3750 0.85 100

C 5000 0.90 150

Product Blending 241