chapter 9 gasoil conversion - أ.د. طارق البحري - conversion.pdf649 675 734 6–(-14) -...

Petroleum Refining – Chapter 9: Conversion

9-1

Chapter 9 GASOIL CONVERSION

Introduction

• Processes that convert gasoil to lighter products are

1. Hydrocracker

2. FCC

• Significant change in the IBP and FBP

1. The Fluid Catalytic Cracking (FCC)

Introduction

• Location → Only in MAA.

• Designer → UOP.

• Capacity → 40,000 BPSD.

• Objective → To convert gas oil to lighter and more valuable products like; LPG,

gasoline, distillate, and cycle-oil.

• FCC is a high temperature low pressure catalytic unit in which heavy hydrocarbons

are cracked into lighter molecules.

• Originally cracking was accomplished thermally.

• The catalytic cracking of gasoil has replaced thermal cracking because (through

catalyst design) it gives

- Better yields.

- Better selectivity

• Catalytic Cracking processes

1. Thermafor Catalytic Cracker (TCC)

– Moving bed reactor.

– Not very common

2. Fluid Catalytic Cracker (FCC)

– Fluidized bed reactor.

– More common.

• The basic operation of the two is similar.

Feeds and Products

• FCC Feed is a mix of the following refinery streams:

1. VGO from MAA.

2. VGO from MAB.

3. CGO from MAB.

4. Hydrocracker fractionator bottoms.

Table 9-1. Hydrocracker feedstock properties.

API, gravity

S, wt%

N, ppm wt

Ni, ppm wt

Va, ppm wt

ASTM distillation, ºF, IBP

50%

FBP

24.5

0.6

1000

< 0.1

< 1

550

830

1050

Prof. Tareq A. Albahri 2018 Kuwait University Chemical Engineering

9-2

• FCC Product yields depend on mode of operation: (There are two modes)

1. Gasoline mode.

2. Distillate mode.

• Distillates are usually blended into diesel, jet fuel, and furnace/heating oil.

Table 9-2: FCC unit products, weight %.

Product Gasoline mode Distillate mode

Off gas (C3-)

LPG vapor

Light gasoline

Heavy gasoline

Distillate

Light cycle oil

Heavy cycle oil

Coke

4.29

17.88

35.54

14.76

13.05

0.83

7.32

4.8

Table 9-3: FEED 40,000BPD (VGO 75v%, CGO 26v%) FCC products yields

Product wt%

Off Gas 4.35

LPG 20.40

Light Gasoline 32.98

Heavy Gasoline 13.37

Distillate 15.94

LCO 0.64

HCO 7.70

Coke 4.62

TOTAL 100.0

Table 9-4: Typical product properties.

Treated light

gasoline

Treated heavy

gasoline

Distillate

Light

cycle oil

Heavy

cycle oil

API

Distillation, º F

IBP

50%

90%

FBP

70.6

95

158

248

302

33–43

280

340

387

410

16–26

399

500

662

734

10–13

621

649

675

734

6–(-14)

-

815

930

-

Process description (MAA refinery)

• The FCC unit consists of four main sections (Figure 9-8Figure 9-1):

1. Reactor/regenerator section.

2. Fractionator section

3. Gas concentration and recovery section.

4. Flue gas power recovery section.

1. Reactor/regenerator section

• The reactor in MAA FCC is an all-riser cracking reactor. Other designs have separate

reactor/riser sections.


9-3

• The feed is preheated by a series of heat exchangers (recovering heat from within the

unit).

• It is then mixed with hot regenerated catalyst at the base of the riser.

• Heat from the catalyst further heats up and vaporizes the gasoil.

• The gasoil and catalyst travel up the riser (this is where the main cracking reactions

occur) into a region of low pressure.

• The cracked hydrocarbons are separated from the catalyst (by a two-stage cyclone

system) and exit the reactor/riser top.

• The separated catalyst travel down the reactor riser into the reactor stripper section.

• In the reactor stripper section, stripping steam is used to separate the spent catalyst from

the hydrocarbon vapors.

• The spent catalyst travels down through a standpipe to the lower part of the regenerator

(combustor).

• In the regenerator, air is used to burn off the coke deposited on the catalyst particles.

• The regenerated catalyst and the flue gases travel up to the upper section of the

regenerator where they are separated by a two-stage cyclone system.

• The hot regenerated catalyst is mixed again with the feed at the bottom of the reactor.

• The flue gases are sent to the power recovery section where they are used to generate

steam or run a turbine.

2. Fractionator section

• The feed to the main fractionator is superheated vapors (this makes the heat removal a

major operation).

• Large quantities of light gases pass overhead with light gasoline. This is sent to the gas

concentration section.

• Heavy gasoline is withdrawn as a side cut.

• Heavy cycle oil is removed from the bottom of the column.

3. Gas concentration and recovery section.

• The feed to this section is the fractionator overhead product.

• This is separated using a stabilizer column to produce:

- Non-condensable gases (C1-C4).

- LPG (C3/C4).

- Stabilized light gasoline.

• The non-condensable gas is separated into two streams;

- Ethane and lighter (C2–).

- Propane and heavier (C3+).

• Two Merox units are provided to remove mercaptans1 from the following final products;

1. Light gasoline (from the stabilizer).

2. Heavy gasoline cut (from the main fractionator).

1 (Mercaptans are undesirable due to their acidity and offensive odor)


9-4

Figure 9-1. FCC process description.


9-5

Figure 9-2: FCC Cyclone separator


9-6

Figure 9-3. FCC Reactor new installation

Figure 9-4. FCC reactor head internals


9-7

Figure 9-5. Installation of a new FCC reactor head internals

Figure 9-6. FCC process unit


9-8

Table 9.3: FCC major operating conditions (gasoil feed).

Gasoline mode Distillate mode

Reactor temperature (ºF).

Reactor pressure (psig).

Regenerator O/H temperature.

Regenerator pressure (psig).

Air to regenerator (MMSCFD).

Circulated catalyst:

Regenerated catalyst (lb/hr).

(lb/sec).

(lb/hr) per BPSD of feed.

Spent catalyst (lb/hr).

(lb/sec).

(lb/hr) per BPSD of feed.

Main fractionator:

Overhead temperature (ºF).

Overhead pressure (psig).

Bottom temperature (ºF).

970

25

1330

28

98.47

2,669,100

741

67

2,688,510

747

67

209

19

690

915

25

1310

28

98.15

2,413,960

671

60

2,433,140

676

61

213

19

690

Catalytic Cracking Reactions

Figure 9.2: A simplified catalytic cracking Reaction

Table 9-5: Elementary steps in the catalytic cracking of HC on dual function catalysts.

Feed Lewis Sites Bronsted Sites Lewis & Bronsted Sites

Paraffins 1. Hydride

Abstraction

2. Hydride

Donation

3. Protolytic Scission

4. Deprotonation

5. Hydride Transfer

6. -Scission (cracking)

7. PCP-Branching

8. PCB-Branching

9. Methyl Shift (isomerization)

10. Ethyl Shift (isomerization)

11. Hydride Shift (isomerization)

Olefins 12. Protonation

13. Cyclization

Naphthenes 14. Intra Ring Alkyl Shift

15. Ring Contraction

16. Ring Expansion (PCP-

Branching)

17. Exocyclic -Scission

18. Endocyclic -Scission

(Decyclization)

Aromatics 19. Alkylation

20. Dealkylation

21. Disproportionation

22. Condensation

+


9-9

FCC Catalysts

• FCC Catalyst are very fine (powder like) particles

• Diameter = 70 microns (0.07 mm).

• It behaves as fluid when aerated with a vapor.

• Commercial Catalysts available are:

1. Acid treated natural aluminosilicates or clay (old).

2. Amorphous synthetic silica-alumina combinations

(Si/Al ratios 20, 40, 70, etc.)

3. Crystalline synthetic Si/Al combinations (New).

(Also called zeolites or molecular sieves).

4. Mixture of 2 and 3.

• Zeolites are the most comment because

1. Higher activity

- Ability to achieve higher conversion without over-cracking.

- Permit short residence (reaction) time (good for riser reaction operations).

2. Higher selectivity

- Produce higher gasoline yield for a given conversion.

- Produce gasoline containing more paraffins and aromatics.

- Produce more isobutene (higher ON).

- Lower coke yield (less catalyst fouling/deactivation) which means higher

throughput at a given conversion.

Additional advantages of the new FCC commercial catalysts

1. Give higher gasoline octane number (0.5–1.5 RON improvement).

2. Resist deactivation due to sulfur or metals in the feed.

3. Transfer sulfur from the regenerator to the reactor (to reduce SOx in the regenerator

flue gas).

• Only 10 – 40% of the total catalyst is zeolite (15% is very common). The remainder is

amorphous Silica Alumina.

1. Cheaper (Lower cost & make-up rates of amorphous catalyst).

2. Higher abrasion resistance (lower attrition rate) greatly improves particulate

emission rates.

3. Higher activity and gasoline selectivity of Zeolites.

• Catalyst use is affected by;

1. Feed type.

2. Mode of operation.

3. Environmental considerations.

4. Economic Considerations.

Pore Size Distribution of Catalyst

• Catalyst for FCC units have to be designed with a range of pore size distribution to handle

feed processing.

• For the processing of heavy residue, catalysts are designed with large pores to handle the

large molecules (>30 Å) and also smaller pores to give higher activities.

Table 9-6: Pores Size Distribution (RFCC feeds). Pore size distribution Feedstocks Activity Purpose

Large pores (>100Å) Liquid catching pores Lower activity Control coke and gas make

Mesopores (20-100Å) aromatic and naphthenic Higher activity

Small pores (<20 Å) paraffinic V. high activity

Amorphous

Zeolite


9-10

Figure 9-7:FCC catalyst pore structure

Catalyst Poisons

• Oil constituents which act as catalyst poisons.

1. Basic Nitrogen Compounds

- Nitrogen reacts with the acid centers on the catalyst and lowers the catalyst

activity (by lowering the number of the active cites available for reaction).

2. Metals (Iron, Nickel, Vanadium, Copper)

- Metals deposit and accumulate on the catalyst and cause a reduction in

throughput by

a. Reducing catalyst activity by occupying active catalytic sites (resulting in

lower conversions).

b. Reducing catalyst selectivity by promoting the formation of gas and coke

and reducing the gasoline yield at a given conversion.

c. Decreasing the amount of coke burn-off per unit of air (by catalyzing coke

combustion to CO2 rather than CO, which requires more air).

• Ni has about 4 times more effect on catalyst activity and selectivity than vanadium.

- A factor is used to correlate the effect of metals loading,

F1 = 4Ni + V

F2 = Ni + V/4

F3 = Ni + V/5

Combating Catalyst Poisoning

1. The effect of Ni is partially offset by the addition of passivators2 to the feed.

2. Metal traps3 are used to trap vanadium (V) in a guard bed.

3. Reactivating the catalyst by cycling a slip stream through a metal removal system

(Demet). To control metal concentration at the level at which the desired activity and

selectivity of the catalyst are maintained.

HW: FCC Material Balance

2 (antimony & barium compounds) 3 (metal traps are catalysts containing Tin, Barium Titanate, Strontium Titanate, or

Magnesium Oxide).


9-11

Simplified FCC process


9-12

Figure 9-8: FCC unit in MAA refinery


9-13

2. The Hydrocracker Unit (HCR)

INTRODUCTION

Licensors

• Chevron √ → introduced the first modern hydrocracking process in 1959.

• IFP.

• Shell.

• Unocal and UOP.

Objective

The objective of the HCR unit is to upgrade gasoil product from various refinery units

to lighter more valuable distillate products.

Hydrocracking of atmospheric & vacuum residue include the H-Oil and Isomax, respectively.

Capacity

Table 9-7: Hydrocracking capacity in Kuwait.

Refinery Number Throughput

(BPSD)

Feed

ZOR

MAB

MAA

Unit 84

Unit 14

Unit 84

38,000

40,000

Vacuum unit, light VGO

Vacuum unit, VGO

Vacuum unit, VGO & Eocene waxy distillate VGO.

Total 78,000

Feed

Hydrocracker feed can be introduced from several sources including both straight run and

cracked stocks,

1- VGO form vacuum unit

2- EOCENE waxy distillate VGO.

3- Coker gas oil.

4- Diesel HTU bottoms. (Heavier than diesel)

5- FCC cycle oils. (Heavier than diesel)

Products

Table 9-8: Hydrocracker Distillate Products.

MAA MAB ZOR

Gas

LPG

Naphtha

Light ATK

Heavy ATK

Diesel

Gas

LPG

Light Naphtha

Heavy Naphtha

ATK or IK

LP Diesel

In the gasoil range


9-14

Table 9-9: A list of Chevron’s commercial Hydrocracker installations.

No Company Location Product Start-up Capacity

(BPSD)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

IS

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

Sohio

Chevron

Shell Canada

Toaco

Caltex

Golden Eagle

Chevron

Chevron

Chevron

Sohio

Nippon Mining

Gult

Gult

Mobil

NIOC

Tenneco

KNPC

Mobil

EMP

Chevron

Idemitsu

Sohio

Chevron

Sun

Pennzoll

BP Oil

Irving Oil

KNPC

Petro-Canada

Ssangyong

Hawaiian Independent

NIOC

NIOC

Petro-Canada

Pennzoll

Chevron

Chevron

KNPC

NPRC Muroran

KNPC

Slnopec

Indian Oil

Ohio

Mississippi

Ontario

California

Germany

California

Port Arthur

California

California

Ohio

Japan

Louisiana

Louisiana

California

Iran

Louisiana

Shuaiba, Kuwait

Texas

Spain

California

Japan

Ohio

Mississippi

Puerto Rico

Pennsylvania

Pennsylvania

Canada

Shuaiba, Kuwait

Ontario

South Korea

Hawaii

Iran

Iran

Alberta

Louisiana

California

California

Mina Al-Ahmadi, Kuwait

Japan

Mina Abdullah, Kuwait

Qi-Lu PRC

Gujarat

N

N

N/S/D

N

N/K/D

N

N

N/K/F

N/K

N/F

G

N/K/D

N

N

K/D

N

K/D

N

G

N/K

L

N/L

N/K

L

L

N

N/D

K/D

L

L

K

K/D

K/D

N/K/D

L

L

L

K/D

K/D

K/D

N/K/F

K/D

1962

1963

1963

1963

1964

1964

1965

1966

1966

1966

1966

1966

1966

1967

1968

1968

1969

1969

1969

1969

1969

1970

1971

1972

1972

1975

1977

1978

1978

1980

1981

1981

1981

1983

1983

1984

1984

1986

1987

1988

1990

1992

12,000

28,000

4,000

22,000

8,500

11,000

15,000

30,000

50,000

25,000

3,000

3,200

7,300

16,000

14,000

16,000

18,000

29,000

20,000

50,000

13,000

20,000

32,000

12,200

2,700

20,000

31,000

44,000

10,000

6,000

12,000

15,000

15,000

15,000

5,000

18,500

12,000

38,000

13,000

38,000

11,500

25,000

G = LPG, N = Naphtha, S = Solvents, S = kerosene jet, D = Diesel, L = Lubes, F = FCC Feed

Modernization


9-15

Table 9-10: The product pattern of MAB Hydrocracker unit.

Product

Yield V% on Feed

Destination BP range (ºF) ATK mode BP range (ºF) Diesel mode

Gas

Lt naphtha

Hvy Naphtha

ATK or IK

Diesel

C4 –

C5 – 180

160 – 260

260 – 550

-

17.2

16.7

74.7

0

C4 –

C5 – 180

160 – 330

-

330 – 700

12

24.3

0

70.9

Gas treating

Storage/MAA

Storage/MAA

Storage

Storage

Total 108.6 107.2

PRPCESS DESCRIPTION (Figure 9-11)

• The Hydrocracker consists of two reaction stages each with its own feed effluent heat

exchange, feed heaters, product separators and gas recycle system.

– The two stages normally operate in series

– They can also operate in parallel to increase throughput (at lower conversion).

– One stage operation is also possible (also at lower conversion) during shutdown of the

other stage.

• Both of these stages are served by a common fractionation system to separate the

products.

• The hydrogen consumption for Hydrocracker varies between 1,100 and 1,380 scf/bbl of

feed depending upon

– The mode of operation

– Age of catalyst.

• The Hydrocracker is a high-pressure unit;

– First stage separator pressure: 2,200 psig SOR and 2,210 psig EOR.

– Second stage separator pressure: 2,295 psig SOR and 2,245 psig EOR.

• Hydrocracking unit consists of four major sections:

1. Make-up Hydrogen Compression Section.

3. First stage reactor section.

4. Second Stage reactor section.

5. Distillation section.

1. Make-up Hydrogen Compression Section

Three parallel-stage compressor trains supply the reactor (at 2500 psig) with make-up

hydrogen necessary for the hydrocracking reactions.

2. First Stage Reactor Section

• The feed is first filtered from suspended solids then introduced to a surge drum to avoid

any fluctuations due to upstream vacuum unit upsets or emergencies. Usually these feed

surge drums provide for about 20 minutes of normal operation.

• The feed is then pumped to the reactor pressure by high pressure feed pump and is mixed

with recycle gas (mainly H2).

• The mixture then enters the top of the reactor after being preheated through Feed/Reactor

effluent exchanger (for heat recovery) and the reactor feed Heater.

• Makeup Hydrogen, pre-heated using the reactor effluent, enters the annulus from the

bottom of the reactor (to cool the reactor shell) and combines with the feed at top of the

reactor.

• The reactor has four beds of catalyst with inter-bed quenches to control their temperatures.


9-16

• The reactor effluent is cooled by series of heat exchangers (heating other streams in the

unit for heat recovery) and coolers then enters a High Pressure Cold Separator (HPCS),

where water, gases and liquid hydrocarbons are separated.

• The gas stream from HPCS (mainly H2) is compressed by a recycle gas compressor and

recycled to the reactor feed and a portion is used for inter bed quenching.

• Being at high pressure, the hydrocarbon liquid stream from the HPCS is drawn on a level

control and drives a power recovery turbine (to provide power for the first stage feed

pump) before flowing to the Low Pressure Cold Separator (LPCS).

• LPCS gas is sent to Hydrogen Recovery (HR) unit through a K.O. drum while the liquid

stream enters the H2S stripper after heating with the reactor effluent.

• Superheated steam is introduced at the bottom of the stripper to remove H2S. The sour gas

from the stripper goes to the Amine treating unit (for further H2S concentration).

• The bottom stream from H2S stripper is heated through a series of heat exchangers and

fractionator feed heater before entering the Fractionator.

3. Second stage reactor section

• The second stage reactor section is similar to the first stage except for the following;

– The feed to second stage is the fractionator bottom.

– The reactor effluent undergoes both a hot and cold high-pressure separation.

• The reactor effluent is flashed in a high pressure hot separator (HPHS) before final

cooling.

• This cooled effluent is then separated into H2-rich recycle gas and oil in the high pressure

cold separator (HPCS).

• The gas is compressed and recycled to the second stage reactor as quench and recycle.

• Oil is drawn on level control and mixes with the oil products from the first stage and

feeds the low pressure cold separator (LPCS).

• The vapor from the HPHS is cooled by heating the recycle gas and then further cooled in

air coolers.

• The liquid from the HPHS drives the power recovery turbine to provide power for the

second stage feed pump and is then flashed again in the Low Pressure Hot Separator

(LPHS).

• Vapor from the LPHS is mixed with first stage liquid products and cold liquid products

from the HPCS. The combined stream is sent to the LPCS.

• Liquid from LPHS is sent as hot feed to the H2S stripper.

4. Distillation Section

4.1 Product Fractionation

• The fractionator operates like the crude unit fractionator to separate the converted

products from unconverted feed;

Overhead → naphtha.

Side-cut → light ATK, heavy ATK and gas oil.

Bottoms → unconverted feed.

• The fractionator bottoms (unconverted oil) is recycled to the second stage reactor section

for extinction.

• The fractionator has two pumparound circuits to improve/control column

fractionation/traffic and provide heat for reboilers and feed preheat.

• The fractionator overhead is totally condensed (using fin-fan coolers) so that no gas is

produced.


9-17

• The condensed hydrocarbon (naphtha) and water (from steam) are separated in the reflux

drum.

- The water is sent to sour water unit (SWT) for treatment.

- The hydrocarbon liquid is split into two streams:

1. Overhead reflux which is returned to the column (Tray 50) to control

fractionator overhead temperature.

2. The naphtha product stream to the naphtha stabilizer then splitter.

• Light ATK is drawn from Tray 38 and is reboiled in the light ATK stripper to remove the

light ends and maintain the desired flash point and IBP.

• Heavy ATK is drawn along with the top pumparound at Tray 27 and is reboiled in the

heavy ATK side stripper using fractionator bottoms.

• All products are pumped to storage after cooling in a process, water, or fin-fan coolers.

4.2 Naphtha Stabilizer & Splitter

• The stabilizer removes butane and lighter material from the product naphtha to control

RVP and flash point.

• The stabilized naphtha (the stabilizer bottom) can then be

1. Sent directly to tankage as product (bypassing the splitter), or

2. Fed to the naphtha splitter and split into a light naphtha product (overhead)

and a heavy naphtha product (bottom).

• The products at the stabilizer overhead reflux drum are;

1. Gases: sent to the fuel gas system.

2. LPG: portion is used as reflux and the rest is sent to the hydrogen sulfide

recovery (HSR) unit.

• De-superheated steam reboils the splitter to hold a constant temperature on Tray 2 of the

column.

• Overhead, light naphtha is cooled (condensed) on temperature control then partially

refluxed back to the column to maintain the required ASTM gap specification between

light and heavy naphtha, and the rest is cooled then sent to storage.

• Heavy naphtha from the splitter bottoms is cooled then sent to storage.

FEATURES & APPLICATIONS

1. HCR Modes of operation

• The Hydrocracker has two modes of operation for which a particular liquid product yield

is maximized.

MAA Hydrocracker

1. ATK mode: where Aviation Turbine Kerosene yield is maximized. (This is the

primary mode of operation)

2. Mid-distillate mode: where ATK & diesel yield are maximized.

MAB Hydrocracker

1. ATK mode: maximum naphtha plus jet fuel (ATK) yield.

2. Diesel mode: maximum diesel yield.

2. The Complete conversion mode of operation

• The majority of the commercial hydrocrackers operate in a severe extinction recycle

mode to convert 100% of the feed to light products.


9-18

• Chevron hydrocracking technology has been applied commercially in the full range of

process flow schemes

– Single-stage, once-through liquid.

– Single-stage, partial recycle of heavy oil

– Single-stage, extinction recycle of oil (100% conversion)

– Two-stage, once-through liquid.

– Two-stage, partial recycle of heavy oil

– Two-stage, extinction recycle of oil (100% conversion) ← more common

• During extinction scheme some fractionator bottom bleeding is done periodically to

prevent accumulation of non-converting high MW materials in the system.

• The preferred flow scheme depends on the feed properties, the processing objectives, and,

to some extent, the specified feed rate.

3. Reactor

• Chevron’s gasoil hydrocracking technology uses multi-bed reactors.

• In most applications, a number of catalysts (usually four beds) are used in a reactor.

• The catalysts are used in a layered system to optimize the processing of the oil

(intermediate H2-quenching) as its properties change along the reaction pathway.

• Process conditions in the reactor are general to give an 18- to 24-month operating cycle

before catalyst regeneration is needed.

• The HCR provides superior product quality such as high smoke point kerosene and high

cetane diesel fuel.

4. Catalyst

• Chevron develops and manufactures its own catalysts offering a complete family ranging

from;

1. Amorphous catalysts for high yields of heavy products (lubes, middle distillates, etc.)

2. Zeolite catalysts for the most cost-effective production of light products (naphtha, jet

fuel, etc.).

3. Hybrid amorphous/zeolite catalysts to provide a lower cost option for heavy product

production with only a small sacrifice in yields.

5. Reactions

• Unlike the catalytic cracking reactions that are characterized by high volume of olefin

production, the catalyst used in hydrocracking reactions saturates the molecules with

hydrogen feed after cracking.

• Average reaction temperatures range between 550 and 750 ºF. Reaction pressure is about

2300 psi.

• Hydrocracking reactions are very complicated, but for simplicity the following reaction is

presented.


9-19

Steps:

1. Cracking

2. Isomerization (rearrangement)

3. Saturation

Figure 9-9: A Simplified Hydrocracking reaction

HW

Hydrocracker material balance

+ +

Feed (Low API & small volume)

Products (High API & large volume)


9-20

Figure 9-10: Simplified schematic Representation of the hydrocracking process


9-21

Figure 9-11: Detailed schematic Representation of MAB refinery hydrocracking process

chapter 9 gasoil conversion - أ.د. طارق البحري - conversion.pdf649 675 734 6–(-14) -...

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