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

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Petroleum residues include a wide range of heavy cuts that typically

have boiling points above 345



C(650



F). These include atmospheric

residue (AR), vacuum residue (VR), heavy gas oil (HGO) and vacuum

gas oil (VGO). Heavy oils can make up to 40% residue. These residues

usually contain high metal content (Ni, V, Fe, Cu, Na), asphaltenes and

resin. Metal deposition and coke format ion cont ribute to rapid deacti-

vation of the catalysts. Typical residue and their properties are given in

Table 13.5.

A variety of hydroprocessing schemes are being used depending on feed

properties, composition, catalyst properties and target product specifica-

tions. These can be generally classified as: fixed bed, moving bed, ebullated

bed and slurry phase processes. A comparison of the performance of these

processes is given in Figure 13.11 (Ancheyta and Speight, 2007).

13.4.2.1. Fixed Bed Process

Fixed bed processes are the most widely used in 80% of current residue

hydroconversion processes. The process details are similar to those

described for the ARDS process in Chapter 7.

13.4.2.2. Moving Bed Process

In the moving bed processes, fresh or regenerated catalyst is added to the top

of the reactor co-currently with the feed (Hycon shell process). A flow

diagram of the Hycon process is shown in Figure 13.12. More recently,

a moving bed process was developed by adding the catalyst at the top and

Table 13.5 Properties of typical residue (Morel and Peries, 2001)

Property

Type of residue

Atmospheric

Arabian

Vacuum

Kuwait

Vacuu m

Safaniya

Yield on crude

(%wt)

48 22.5 34

SG 0.988 1.031 1.035

Viscosity at

100



(mm

/s)

95 4,010 3,900

Sulphur (wt%) 3.95 5.51 5.28

Nitrogen (wt%) 0.29 0.36 0.46

Conradson

carbon (wt%)

13.8 21.8 23

asphaltene

(wt%)

5.7 9.0 11.5

Ni þ V (ppm) 104 169 203

344 Chapter 13

Reactor

Configuration

Process

Fixed bed

(trickle bed)

Moving bed

(counter current)

RCD

VRDS (Chevron)

Hyvahl (IFP)

Licensor Hycon (Shell)

Catalyst vol% 60 60

Catalyst size, mm 1.5 x 3 1.5 x 3

Particles, cm

120 120

Moving bed

(cocurrent)

OCR (Chevron)

1.5 x 3

120

Ebullated bed

(

three phase fluidizing)

H-oil (Texaco)

KLC-Fining (Amco)

0.8 x 3

250

Slurry bed

CANMET

Veba Combicracking

Aurabam (UOP)

0.002

2.4 x10

HC + H

+ Catalyst

Catalyst

HC + H

Catalyst

HC + H

+ Catalyst

Figure 13.11 Comparison of reactor technologies

Residue Upgrading 345

HDM Moving bed

reactors

HYCON fixed

Bed reactors

Distillation

Quench gas

Make up

gas

Vacuum

Residue

Catalyst

Gases

Naphtha

Kerosene

Gas oil

Figure 13.12 Hycon process flow scheme (Scheffer et al.,1997)

346 Chapter 13

the feed at the bottom (OCR Cheveron process). In both cases, the spent

catalyst is withdrawn from the bottom and regenerated outside the process.

The main advantage of the moving bed processes is that they can treat feeds

with high metal contents for a long operation.

13.4.2.3. Ebullated Bed Process

The ebullated (expanded) bed, such as H-oil is a well-established technol-

ogy. The H-oil process is based on the unique design of the reactor as

shown in Figure 13.13. This rector has several advantages over the fixed bed

reactor as follows:

Catalyst

Addition

Vapor/Liquid

Separator

Expanded

Catalyst

Level

Settled

Catalyst

Level

Recycle

Grid Plate

Gas

Liquid/Gas

Catalyst

Hydrogen and

Feed Oil

Catalyst

Withdrawal

Recycle

Oil

Vapors

Liquids

Figure 13.13 Ebullated bed reactor (Ra na et al., 2007)

Residue Upgrading 347



Due to the loose structure of flow inside the reactor, the solids do not

plug the flow.



Good mixing results in uniform temperatures.



Catalysts are added and withdrawn continuously, allowing for a long

period of operation.

Ebullated bed operability is more difficult than fixed bed because the

catalyst renewal operation is carried out at high pressure and temperatures.

A flow scheme of H-oil with two reactors is given in Figure 13.14. The

reactor operation is compared with other options in Table 13.6. A compar-

ison of the process and operating conditions is also compared with other

processes in the same table.

13.4.2.4. Slurry Bed Process

Slurry bed processes are designed to handle residue with high dirt content,

high asphalt or even high wastes. Very fine particles of catalyst in the slurry

reactor will insure low pressure drop and a high conversion of 90%. A fixed

bed reactor is used after the slurry reactor to insure refining of the produced

light fraction. Operation of a slurry reactor is difficult. The catalyst tends to

accumulate in the reactor, leading to the plugging of down-stream

equipment.

13.4.3. Aquaconversion

The main strategy in the aquaconversion process as an option for heavy,

extra-heavy crude, with properties listed in Table 13.7, is to use a conver-

sion process severity that is just sufficient to transform heavy crudes into

gasoline and diesel.

The aquaconversion process is based on the hydrogen transfer

catalyst from water to the feedstock. The typical visbreaking technology

is limited by low conversion to control the stability of the product.

The hydrogen incorporation is high enough to saturate the free radi-

cals formed in the process. Thus, a higher conversion levels can be

achieved. Typical aquaconversion reactions (Marzin et al., 1998) are

shown in Figure 13.15. The process produces high API and low viscosity

products.

Aquaconversion technology does not produce coke and requires hydro-

gen at high pressures. Aquaconversion can be carried out in the field to

reduce handling problems.

Table 13.8 shows the level of upgrading that is obtained with aquacon-

version technology. Figure 13.16 shows the scheme of the aquaconversion

process.

348 Chapter 13

Vacuum residue recycle

Fuel gas

Naphtha

Gas oil

Vacuum

Distillate

Feed

furnace

Recycle

compressor

Catalyst

withdrawal

purge

Make up

Vacuum

residue

feed

Fractionation

Figure 13.14 F1ow scheme of H-oil process with two reactors (Morel and Peries, 2001)

Residue Upgrading 349

Table 13.6 Comparison of performance of residue upgrading processes (Morel and Peries, 2001)

Fixed bed Moving bed Ebullated bed Slurry bed

Maximum (Ni þ V) content in feed

(wppm)

120–400 500–700 >700 > 700

Tolerance for impurities Low Low Average High

Maximum conversion of 550



C (wt%) 60–70 60–70 80 90

Distillate quality Good Good Good Poor

Fuel oil stability Yes Yes Borderline No

Unit operability Good Difﬁcult Difﬁcult Difﬁcult

Operating pressure, bar (psig) 140 (2100) 200 (3000) 100–200

(1500–3000)

135–205

(2000–3000)

Operating temperature,



F) 400–450

(750–800)

400–450

(750–800)

420–450

(790–800)

450–480

(840–895)

Feed characterization Low solids High metals High metals High asphaltenes

High solids

350 Chapter 13

Table 13.7 Example of heavy and extra-heavy crude (Pereira et al., 2005)

Heavy cr ude Extra-heavy crude

API gravity 22.9 8.5

Sulphur (wt%) 1.13 3.96

Nitrogen (wt%) 0.22 0.73

Asphaltene (wt%) 2.0 10.2

Conradson carbon (wt%) 4.76 15.8

Vanadium (ppm) 49 488

Nickel (ppm) 11 105

Viscosity (cSt)



C 7.4 14,257



C 5.9 5533

Pour point (



C) <51 27

TAN (mg KOH/g) 0.36 2.27

Yields (vol%)

350



Cþ 52 88

520



Cþ 21 56

R-R

Thermal Cracking

+ R

Hydrogen Transfer

O 2H + O

Hydrogen Addition

+ H

Condensation – Polymerization

Catalyst

Figure 13.15 Reactions in aquaconversion reactor

Residue Upgrading 351

Example E13.6

The following reaction occurs in the aquaconversion process:

C þ 2H

O ! 2H

þ CO

The bitumen feed (API ¼ 9) has the following elemental analysis:

84:3% C; 10:3% H and 5: 37% S

Table 13.8 Aquaconversion process performance ( Pereira et al., 2005)

Feedstock Extra-heavy crude Aquaconversion product

API gravity 8.5 14.0

Sulphur (wt%) 3.96 3.3

Nitrogen (wt%) 0.73 0.55

Asphaltene (wt%) 10.2 8.3

Conradson carbon (wt%) 15.8 13.6

Viscosity (cSt)



C 14,257 60



C 5533 –

100



C–8

Total acid number (TAN)

(mg KOH/g)

2.27 0.3

Yields (vol%)

350



Cþ 88

520



Cþ 56

Fractionation and

catalyst recovery

Units

Residue

Feed

Steam

Fresh

Catalyst

Heater

Reactor

Waste

catalyst

Recycle

catalyst

Product

(middle distillate)

Figure 13.16 Simplified process scheme for aquaconversion residue upgrading unit

352 Chapter 13

The maximum allowable density is 990 kg/m

and can be correlated with

elemental residue contents as follows:

r ¼ 1033  13:69 H wt% þ 13: 85 S wt%

How much carbon per bbl feed must react in order to meet the maximum

allowable density?

Solution:

Basis 1 bbl feed ¼ 160 kg

C ¼ 0:843ð160Þ¼134:88 kg ¼ 11 :24 kmol

Assume reaction conversion x kg C

This will produce ¼ (x/12)(2)(2) ¼ 0.33x kg hydrogen

in ¼ 0.103(160) ¼ 16.48 kg

out ¼ 16.48 þ 0.33x

wt% H

out

mass of upgraded oil

16:48 þ 0:33x

160  x  0:33x

wt% S ¼

0:0537ð160Þ

160  x  0:33x

r ¼ 990 ¼ 1033  13:68

16:48 þ 0:33x

160  x  0:33x



þ 13:85

0:0537ð160Þ

160  x  0:33x



Solving for conversion x ¼ 8.94 kg C per bbl feed

Questions and Problems

13.1. 100 kg/h residue is introduced to a deasphalting process, which

operates at 240



F. The residue has the following properties: API ¼

8, S wt% ¼ 6%. A solvent at a rate of 1200 kg/h is used. The DAO

produced has API ¼ 21. Calculate the yield of DAO and its sulphur

content.

13.2. 10,000 lb/h residue has the following properties: API ¼ 10, CCR ¼

15 wt%, S wt% ¼ 4.7 wt%, N wt% ¼ 0.7 wt%. The above feed is

introduced to a deasphalting process. Calculate the yield of DAO, its

CCR, and its sulphur and nitrogen contents.

13.3. Fuel which has the general formula C

is burned in a gasifier.

The dry basis flue gas analysis is as follows: O

0.5 vol%, SO

0.2 vol%,

CO 3 vol%, N

81.3 vol%, CO

15 vol%. Find the chemical formula

of the fuel burned.

13.4. The following reaction occurs in aquaconversion process:

C þ 2H

O ! 2H

þ CO

Residue Upgrading 353