12. VACUUM RESIDUE.pdf

RA DAS - 00029_A_A - Rev. 0 17/01/2005

Refining-Petrochemicals-Chemicals-Engineering

PDVSA

Process Engineering Applied To Petroleum Refining

Module 8: REFINING PROCESSES (2)

VACUUM RESIDUE DEASPHALTING

I - OBJECTIVE .............................................................................................................................. 1

II - PROCESS ................................................................................................................................. 1

III - EFFECTS OF DEASPHALTING ON THE PHYSICO-CHEMICAL CHARACTERISTICSOF THE DEASPHALTED OIL ................................................................................................... 1

IV - PROCESS FLOW...................................................................................................................... 5

V - PROPANE DEASPHALTING UNIT - SINGLE EFFECT EVAPORATION................................. 7

1 - Deasphalting circuit ...................................................................................................................... 72 - Solvent recovery from the asphaltic phase .................................................................................. 83 - Solvent recovery from the oil phase ............................................................................................. 8

VI - IMPROVEMENTS TO THE PROCESS..................................................................................... 8

VII - INFLUENCE OF THE OPERATING CONDITIONS ................................................................ 10

1 - Proportion of propane versus vacuum residue (dilution) ............................................................ 102 - Extraction temperature ............................................................................................................... 103 - Influence of the temperature gradient ........................................................................................ 13

VIII - SUPERCRITICAL SOLVENT RECOVERY ............................................................................. 15

2005 ENSPM Formation Industrie - IFP Training

00029_A_A 2005 ENSPM Formation Industrie - IFP Training

1

I - OBJECTIVE

The process is used for manufacturing bright stock for lube oil refining, for preparing lube hydrocracker feed,fuels hydrocracker feed and catalytic cracker feed. The process produces also asphalt which may be used asa blending component of bitumen, as a fuel oil blending component, as a feedstock to a heavy oil conversionunit such as a coker or a gasification by partial oxidation. The process may be used to upgrade heavy crudeoil.

II - PROCESS

The vacuum residue has the form of a colloidal solution composed of a continuous oily medium containingmicellae or aggregates of juxtaposed heavy molecules called asphaltenes. They contain carbon and hydrogenand many hetero-atoms such as sulfur, nitrogen and metals. The addition of light liquid paraffins to thissolution greatly modifies the characteristics of the oily medium, causing precipitation of the asphaltenes andsometimes even of the resins.

The deasphalting uses light paraffins as an antisolvent for asphaltenes. It is a liquid-liquid separationoperation that extracts the last of the easily convertible hydrocarbons from the vacuum residue. Solventsemployed are light paraffins: propane, butane and pentane. The lower molecular weight hydrocarbons havethe lower solvent power and will precipitate more asphalt. The yield in deasphalted oil increases with themolecular weight of the solvent, but its quality decreases.

Although the process is primarily used to remove asphatic materials from the feedstock, it also removes otherundesirable materials such as sulfur, nitrogen, aromatics and metals. The wax content of the deasphalted oilincreases.

Propane is more suited for the manufacture of lube feedstocks because greater quantities of the asphaltenesand resins must be removed to produce a quality base oil as compared to preparation of cracking feedstocks.Butanes and pentanes are generally used to prepare FCC and hydrocracker feedstocks because they providea higher yield of deasphalted oil, and precipitate less of the asphalt than does propane. The use of heavysolvent results in rock asphalt being produced.

III - EFFECTS OF DEASPHALTING ON THE PHYSICO-CHEMICAL CHARACTERISTICS OFTHE DEASPHALTED OIL

The purpose of deasphalting is to remove the heaviest and most aromatic molecules. Consequently, theeffects on the deasphalted oil in relation to the vacuum residue are as follows:

- density decreases- viscosity decreases significantly- viscosity index tends to increase- carbon residue decreases- the color is improved- sulfur content decreases- metal content decreases


2

CH

iC10

iC15

iC15

C

CC

C CC

CC C

Ni

V

S

N H

C 10

C 10

C 12

C 10

C

iC10

CH3

C

C 10 iC

10

C 10

CC

CC 1

2C 1

2

iC5

C 5

CHCH

3CH

CH3

CH3

CH3

(CH2) n

CHCH

3(CH

2) nC 5

CH3

C

LUBO

IL BA

SES

LUBOIL BASES

WAXE

S

WAXES

RESI

NS**

RESINS

ASPH

ALTE

NES*

ASPHALTENES

Arom

atics

and

heter

ocyc

licco

mpo

und

Cond

ense

d poly

arom

atics

Metal

comp

ound

s

High

ly bra

nche

d-cha

inna

phthe

nes a

nd pr

arffin

sNo

rmal

paraf

fins

n =

50 to

100

* in

collo

idal s

tate

** in

solut

ion

High

ly bra

nche

d-cha

inar

omati

cs

D PPC 1003 A


3

DEASPHALTING OF ARABIAN LIGHT VACUUM RESIDUE Influence of the solvent

SOLVENTS C3 C4 C5

FEED RAFFINATE RAFFINATE RAFFINATE

Yields % weight 100 45.15 70.10 85.50

Specific gravity

Viscosity at 100 cSt

Conradson carbon % wt

Asphaltenes (insoluble C7) % wt

Nickel ppm

Vanadium ppm

Sulphur % wt

Nitrogen % wt

1.003

345

16.4

4.2

19

61

4.05

0.29

0.939

35

1.65

< 0.05

1

1.4

2.55

0.12

0.959

63

5.3

< 0.05

2

2.6

3.3

0.19

0.974

105

7.9

< 0.05

7

15.5

3.65

0.22

ASPHALTENICCOMPOUNDS



Specific gravity

Penetration at 25C

Softening points C

Sulphur %

1.063

11

59

5.3

1.102

0

110

5.8

1.140

0

155

6.4


4

DEASPHALTING PROCESS VARIABLES: influence of the solvent

Deasphalting conditions C3 C4 C5

Solvent dosage vol. % 500-1000 400-700 300-500

Temperature C 45-90 80-130 140-210

Pressure bars 30-45 30-40 20-40

Yields (% wt) Examples 40 70 85

The temperature and dosage are the process conditions which are varied with feedstock quality anddeasphalted oil quality requirements.

DEASPHALTING PROCESS VARIABLES: effect of solvent to feed ratio and temperature

At content temperature, increasing solvent to feed ratio:

- increases:

DAO yield DAO SG DAO viscosity DAO carbon residue DAO metals, sulfur and nitrogen

- decreases: viscosity index

At constant solvent to feed ratio, increasing temperature:

- decreases:

DAO yield DAO SG DAO viscosity DAO carbon Conradson DAO metals, sulfur and nitrogen

- increases: viscosity index


5

IV - PROCESS FLOW

Feed and light paraffinic solvent are mixed then charged to an extractor. The extractor is a vertical towercontaining baffles or a rotating disc contactor RDC. The feed enters at the middle of the extractor and thesolvent near the bottom.

The solvent riche phase (extract) consisting of deasphalted oil and solvent leaves the top of the treating tower.The solvent lean phase (raffinate) consisting of asphalt and solvent leaves from the bottom of the treatingpower.

Different types of solvent recovery are used:

- conventional: single or multiple effect evaporation

- supercritical:

ROSETM (Residuum Oil Supercritical Extraction) process licensed by Kellogg Brown& Root, Inc.

DEMEX UOP

A description of a deasphalting unit with single effect evaporation is given in paragraph V and withsupercritical solvent recovery in paragraph VIII.


6

Deas

phalt

ed oi

l /Pr

opan

e sep

aratio

n

Asph

alt 70

%Pr

opan

e 30%

40 to

50C

Dilut

ion ra

te 5

to 12

/1Pr

opan

ePr

opan

e

Prop

ane

Stea

m

Deas

phalt

ed oi

l + pr

opan

e

Heati

ng ar

eaby

ste

am co

ils

Asph

alt / P

ropan

ese

parat

ion

55 to

70C

EXTR

ACTIO

NCO

LUMN

D PCD 076 B

30

bar

FEED

STOC

KVA

CUUM

RESID

UE

DEAS

PHAL

TED

OIL

D.A.

O.

ASPH

ALT


7

V - PROPANE DEASPHALTING UNIT - SINGLE EFFECT EVAPORATION

1 - DEASPHALTING CIRCUIT (see figure on page 9)

The feed arrives from the refinery storage tanks at the pump intake at a temperature of 120C. Thepump then discharges it through a flow controller into a shell and tubes cooler in which the temperatureis lowered to 71C, then through the shell of a second air cooler in which the temperature is furtherlowered to 53C.

Between the outlet of the first cooler and the inlet of the second one it is possible to inject liquidpropane at 50C into the product to adjust its viscosity before it enters the second cooler. The productthen enters the extraction column at a temperature of 53C at one of the two inlets. The lower inlet islocated about halfway up the column, and the upper one about two thirds of the way up. Theasphaltenic content of the raw material generally governs the inlet used. If the asphaltenic content ishigh and requires a longer contact time, the upper inlet is used. On the contrary, if asphalteniccompounds are entrained in the column overhead then the lower inlet should be used.

On entering the column the feed is dispersed by the distribution rack to ensure an even distributionthroughout the column which is equipped with trays that promote good countercurrent contact betweenthe oil and the ascending propane.

The oil containing the asphaltenic compounds, resins and other undesirable substances flows downthe column and contacts the ascending liquid propane which enters the bottom of the column belowthe lowest plate. When the cold propane encounters the oil circulating in the column, more and more ofthe undesirable components are dissolved in the ascending current of propane. It is only in the lowerpart of the column that the asphaltenic compounds contained in the oil are not dissolved in thepropane.

The asphaltenic compounds continue to descend to the bottom of the column where they are drawnoff, via a flow controller and a level controller, and sent to solvent recovery and separation of theasphaltic phase.

The propane solution continues towards the top of the column where it is reheated by the steamcirculating in a system of four coils installed inside the column.

Since the propane solution is reheated, the relatively insoluble products are removed from the solution.These products form a secondary phase containing the resins which have properties intermediatebetween those of the asphaltenic compounds and those of the oil. The resins flow downwards andencounter the ascending current of propane containing the dissolved oil. The resins are graduallydissolved in the propane solution. This repeated action of dissolving and precipitating generates thereflux in this part of the column.

At the point where the feed enters the column the resins which have not already been dissolved areentrained by the descending current of asphaltenic compounds and are gradually washed as theasphaltic phase descends to the bottom of the column.

The asphalt-free oil continues to the top of the column where it is drawn off via a pressure controllerand sent to solvent recovery and separation of the oil phase.

The previously mentioned steam coils are designed to maintain a temperature gradient between thefeed inlet and the top of the column.


8

2 - SOLVENT RECOVERY FROM THE ASPHALTIC PHASE

The bottom product from the extraction column is composed of approximately 70% asphalteniccompounds and 30% propane. The product leaves the bottom of the extraction column under level andflow control at a temperature of 45C and enters a furnace which heats the mixture to a temperature ofaround 260C. The asphalt mixture is then sent to the evaporator, which operates at a pressure of 19bar gauge. All the propane, except for a very small amount (about 2%), that was previously dissolvedin the asphaltic phase, is removed in the form of gas at 260C. It leaves the evaporator via the gasline, through the cooler to return in liquid form to the propane accumulator FA-1. The pressure in theaccumulator is 18 bar gauge and the temperature is 50C.

The asphaltenic compounds are liquid at 260C and still contain a very small amount of propane. Thephase enters the stripper, which operates more or less at atmospheric pressure, at the level of the toptray.

The steam and gaseous propane from the stripper are routed to the condenser. Before entering thecondenser, the gases are mixed with the steam and propane from the deasphalted oil stripper. Themixture enters the condenser at a temperature of 200C.

The steam free gaseous propane leaves the top of the condenser to the compressor inlet. The propaneis compressed to the same pressure as that of the accumulator, after which the gas is condensed andcooled from 82C to 50C so that it can return to the accumulator. The propane is ready to enter theextraction column again and the cycle is complete.

3 - SOLVENT RECOVERY FROM THE OIL PHASE

The deasphalted oil and propane solution, commonly known as the deasphalted oil mixture, leaves thetop of the column at around 65C and the pressure controller reduces the pressure from 30 to around20 bar gauge. After this reduction in pressure the deasphalted oil mixture enters the evaporators.

The propane gas goes to the propane condenser where it is condensed, and then returns to theaccumulator at a temperature of 50C.

The deasphalted oil stripper is designed to remove the propane from the oil by steam injection. Thepropane-free deasphalted oil leaves the bottom of the stripper and is sent to the intermediate productstorage tanks.

The propane and steam mixture leaves the top of the stripper and is sent to the condenser, asmentioned above. Before entering the condenser it is joined by an identical product from the asphaltstripper.

VI - IMPROVEMENTS TO THE PROCESS

The most significant progress has been made in energy consumption in particular, with marked reductions(about 50% of a single flash vaporization) through propane recovery via flashes at 2 pressure levels.

Processes known as supercritical processes exist. They separate liquid propane by settling and require verylittle heat.


9

30

200.0

7

18

108

0.6

150

200

0.02 1

5

16

1.2

0.07

16 0.8

0.4

24

250 16

0

19

1119

260

120

45

4550

24

53 12040

65

PR

OPAN

EDE

ASPH

ALTIN

GUN

IT

30 %

Deas

phalt

ed oi

l + C

3

Stea

m reh

eatin

g coil

s

Stea

m

EXTR

ACTIO

NCO

LUMN

As

phalt

+

C 3

Feed

PROP

ANE

ACCU

MULA

TOR

To B.

D

70%

30%

EVAP

ORAT

OR

COMP

RESS

OR

MP S

team

ASPH

ALT

STRI

PPER

Pres

sure

Tem

perat

ure (

C)Flo

w ra

te (t/h

)DE

ASPH

ALTE

D

STRI

PPER

MP S

team

COND

ENSO

R

Fluxin

g gas

oil

DEAS

PHAL

TED

OI

L

ASPH

ALT

orBI

TUME

N

VACU

UMRE

SIDU

EFE

ED

Wate

r

C 3

OIL

D PCD 1181 A


10

VII - INFLUENCE OF THE OPERATING CONDITIONS

Pressure does not affect product quality provided that it is high enough to maintain the propane in liquid state.

1 - PROPORTION OF PROPANE VERSUS VACUUM RESIDUE (dilution)

Increasing the proportion of propane in relation to the residue increases the yield of deasphalted oil.Parallel to this increase in the proportion of propane, and consequently in the yield, the molecularweight, the specific gravity, the viscosity and the Conradson carbon content of the oil also increase.

At the same time the softening point of the precipitated asphalt increases with the proportion ofpropane to residue.

The following graphs show the propane-residue ratio on the abscissa and the oil yield and theprecipitated asphalt melting point on the ordinate.

It can be seen that at a given operating temperature the oil yield effectively increases with dilution, asdoes the asphalt softening point.

2 - EXTRACTION TEMPERATURE

Propane behaviour above 40C is the opposite of that of usual solvents such as furfurol, NMP, etc.which have a capacity to dissolve oils that increases with the operating temperature.

Above 40C the capacity of propane to dissolve oils decreases as the temperature rises. This isbecause as propane nears its critical temperature of 97C it gradually regains its gas properties. Itssurface tension and its solvent capacity decrease.

It can thus be seen that as the temperature rises the proportion of asphalt at the bottom of the columnincreases whereas that of deasphalted oil decreases. The asphalt is softer and softer since it isincreasingly diluted by the oil fractions that are insoluble in the propane at the operating temperature.

These results are shown on the graphs. It can be seen that the percentage of deasphalted oil obtainedis proportionately smaller when the temperature of the mixture is higher, and that the ring and ballsoftening point of the precipitated asphalt is proportionately lower when the temperature is higher.

Consequently, to obtain the highest possible yield of deasphalted oil a large proportion of propane hasto be used in relation to the raw material and the operating temperature should be moderate.


11

OIL YIELD AS A FUNCTIONOF THE PROPANE/RESIDUE RATIO

Deas

phalt

ed oi

l, weig

ht %

70

60

50

40

30

20

10

0 4 62 8 10 12 14 16 18 20

80 C

65 C

52 C

PropaneResidue

ratio

D AN

A 01

3 C


12

ASPHALT MELTING POINT AS A FUNCTIONOF THE PROPANE/RESIDUE RATIO

8 2

7 7

7 1

6 5

6 0

5 5

4 9

0 42 8 106 1 2 1 4 1 6 1 8 2 0

PropaneResidue

ratio

52 C

65 C

80 C

R an

d B so

ftenin

g poin

t of a

spha

lt

4 3 D ANA

1000

A


13

The table below gives the main characteristics of the vacuum residue of a Near East crude oil and ofthe two products resulting from the propane deasphalting operation.

RESIDUE DEASPHALTEDOILASPHALTENICCOMPOUNDS

% of feed

Density at 15C

Flash point

Engler viscosity at 100C

Viscosity index after dewaxing at -12C

Freezing point

Total sulphur content

Penetration at 25C

R & B softening point

100

1020

290

155

5

250 to 300

37

29.80

930

279

4.75

78

+ 51

2.90

70.20

5.78

14

61

3 - INFLUENCE OF THE TEMPERATURE GRADIENT

Establishing a temperature gradient in the column creates a reflux of the heavy fractions of thedeasphalted oil and improves separation as shown in the diagram below.

WAXE

S

LUBO

ILBA

SES

T < ToT = To

T > To

RESIN

S

ASPH

ALTE

NES

Column bottomTop of column

Operation without temperature gradiant

With temperature gradiant

D PC

D 11

82 A

The temperature at the bottom of the column is low in order to ensure good solvent capacity forparaffinic components, and the temperature at the top is higher to improve selectivity for separating thearomatic components.

The temperature gradient may be modulated, as illustrated by the two cases shown in the followingfigure in which the results are slightly different. Case 1 will have a slightly lower yield and a darker

colour than case 2 .


14

PROPANE DEASPHALTING COLUMN

TRAYS T = 65

Case 2 Case 1

5 06 0

Asphalt settling

Resin recycleand washing

Settling

Feed

Temperature (C)

4 5

Asphaltand

propanephase)

Feedflow rate

Propane(light phase)

Resin removal

Deasphalted oil + majority of

propane (light phase)

Steamreheating

coils

D PC

D 08

0 AVacuumresidue

(heavy

Steam

Predilution


15

VIII - SUPERCRITICAL SOLVENT RECOVERY

The process flow of the supercritical solvent recovery processes ROSETM and DEMEX are very similar. TheDAO and solvent are separated under supercritical conditions. As the temperature increases above the criticalpoint, the density of the solvent significantly decreases to values approaching that of dense gases.

The oil is virtually insoluble in the solvent as a supercritical fluid and a phase separation occurs. The DA oil-solvent passes into a settler for separation of the DA oil and solvent as separate liquid. The energyrequirement is significantly reduced compared to the flash vaporization method.

The solvent from the asphalt rich phase is recovered in the usual manner. The supercritical solvent recoveryhas a greater energy saving as the molecular weight of the solvent increases. This is the reason why propanedeasphalting generally uses the conventional flash vaporization with double or triple effect evaporation.

Supercritical DAO flow diagram - UOP DEMEX

VACUUMRESIDUECHARGE

D PC

D 11

83 A

DAO SEPARATOR

DAO STRIPPER

DAOPITCH

PITCHSTRIPPER

EXTRACTOR


16

IX - DAO AS A FCC FEEDSTOCK COMPONENT

To be a suitable FCC feedstock, the DAO must meet the following specs:

- nitrogen < 2000 ppm- carbon Conradson < 2% for a conventional FCC- carbon Conradson < 7% FCC for an heavy feed FCC (with dispersion steam, catalyst cooler)- metals < 25 ppm

Taking into example the Arab Light DAO characteristics given in page 4:

- a VGO-C3 DAO blend can be processed on a conventional FCC- a VGO-C4 DAO blend can be processed on a FCC able to handle heavy feed- a VGO-C5 DAO cannot be processed on a conventional FCC an is at the upper limit of a FCC with

cat cooler

However, the compliance with an overall gasoline limit of 50 ppm (or less) will require to reduce the sulfurlevel of FCC gasoline. The FCC-feed pretreating is a possible route to lower gasoline sulfur with theadvantages of increasing the FCC gasoline yields (hydrogenation of aromatics to paraffins) and reducing thesulfur content of the LCO.

VGO

VACU

UMDI

STILL

ATIO

N

DAO

DAOVacuum residue

DEASPHALTING

ATM.RESID

FCCHDT

HDT

DAO

C3 Asphalt

C3

NaphthaDiesel

C4 Asphalt

C4

C5 Asphalt

C5 D

PCD

1184

A

FCC feed preheating

It is also possible, as described in the chapter on hydrocracking technologies to achieve some conversion inthe FCC pretreater (MHDC) to produce a good quality Diesel.

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12. VACUUM RESIDUE.pdf