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Hydroprocessing Units
November 2004
Pedro da Silva
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Why Hydroprocessing?
CO, NOx, HC,
Particulates
BEFORE
NOW
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Why Hydroprocessing?
Desulphurisation units become more and more
important in refineries
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Market of solid catalysts in refining, (IFP data,1994)
tons /yearCatalytic cracking 440 000
Hydroprocessing 80 000
Claus 20 000
Hydrocracking 8 000
Reforming 5 000
isomerization 1 000
other 12 000
TOTAL 566 000
More than 80% of refined molecules see at least
one catalyst in their liver !
Why Hydroprocessing?
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Hydroprocessing Units Layout
in a Refinery Scheme
A t m o s p h e r
i c D i s t i l l a t i o n
Heavy fuel
Crude
V
a c u u m D
i s t i l l a t i o n
CatalyticCracker
FCC
Visbreaking
Reforming
propanebutane
gasoline
naphtha
Hydrodesulphurisation
kerosene
diesel
H2
Amine wash
HDT
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Hydroprocessing Units Layout
in a Refinery Scheme
A t m o s p h e r
i c D i s t i l l a t i o n
Heavy fuel
Crude
V
a c u u m D
i s t i l l a t i o n
CatalyticCracker
FCC
Visbreaking
Reforming
propanebutane
gasoline
naphtha
Hydrodesulphurisation
kerosene
diesel
H2
Amine wash
HDT
HDS
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Hydroprocessing Units Layout
in a Refinery Scheme
A t m o s p h e r
i c D i s t i l l a t i o n
Heavy fuel
Crude
V
a c u u m D
i s t i l l a t i o n
CatalyticCracker
FCC
Visbreaking
Reforming
propanebutane
gasoline
naphtha
Hydrodesulphurisation
kerosene
diesel
H2
Amine wash
HDT
HDS
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Typical operating conditions of
Hydrodesulphurisation Units
PROCESS Pressure
(bar)
Temperature
(°C)
Flowrate/
catalyst volume
(h-1) Naptha 7-30 280-320 3-10
Kerosene 15-50 300-330 2-6
Diesel oil 15-90 320-390 1-4
VGO 30-100 340-410 1-2
ARDS 80-200 370-410 0.2-0.5VGO, residue
hydrocracker100-200 370-410 0.5-1.5
- The most important parameters followed in these units (apart from productqualities!) are the temperature and unit pressure drop
- The difference on activity and stability of different catalysts is measured by °C
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Chemical Reactions in
Hydroprocessing
Not limited by thermodynamics
Refractory compoundS
Hydrogen consumption
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Chemical Reactions in
Hydroprocessing
222120191817161514131211109876543210
48 000
46 000
44 000
42 000
40 000
38 00036 000
34 000
32 000
30 000
28 000
26 000
24 000
22 000
20 000
18 000
16 000
14 000
12 000
10 000
8 0006 000
4 000
2 000
0
-2 000
-4 000
-6 000
S P W 0 . 2
0
.
RT [min]
µV A21 41838-01_1.DATA
S
C1
S
C2
S
C4
S
C3
S
S
C1
S
C2
S
C3
S
C4+
S
C5
Soufre peu réfractaire Soufre très réfractaire
Soufreréfractaire
S
S
BT:Benzothiophène
DBT:Dibenzothiophène
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Soufre total=6 ppmS
S
S
S
S
S
S
4,6-EtMeDBT
1,4,6-TriMeDBT
2,4,6-TriMeDBT
4,6-DiMeDBT
4,6-DiEtDBT
3,4,6-TriMeDBT
4,6-PrMeDBT
Chemical Reactions in
Hydroprocessing
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Chemical Reactions in
Hydroprocessing
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Chemical Reactions in
Hydroprocessing
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Température (°C)
% H
D A
S o u f r e e f f l u e n t ( p p m )
T1 T2
HDS
Régime thermodynamique
(HDA)
Régime cinétique
(HDA)
Equilibre thermodynamiqueHDA
Chemical Reactions in
Hydroprocessing
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Chemical Reactions in
Hydroprocessing- Hydroprocessing reactions are exothermic- Temperature and pressure are needed for hydroprocessing reactions- Reactor delta temperature:
8-9°C rise per 1 wt% sulphur removal1-2°C rise per 1vol% of polyaromatics removal1°C rise per bromine number removal
quench
f o u r lit 1
lit 2
0
R1
Opération normale
R1
température
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Simplified Scheme of an
Hydrodesulphurisation Unit
2
Partial by-pass
Recycle
compressor
Raw feed
Make-up
compressor
Make-up
hydrogento fuel
gas
H.P.
Flash drumFurnace Reactor
Air
coolers
Heat
Exchangers
Stripper
Quench
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Hydroprocessing reactor andinternals
Vapor/liquid
distribution tray
Catalyst bed
Varies between 3 to 15 m
Catalyst supportgrid
Quenchdistributor
Mixing chamber
Outlet collector
Inlet diffuser
Unloading nozzle
Reactor diameter variesbetween 1,5 to 4,5 m
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Hydroprocessing Reactor andInternals
Catalyst bed
reactor outlet
collector
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Hydroprocessing Reactor andInternals
Additional
gasketing
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Hydroprocessing Reactor andInternals
What techniques can be used to check the gas-liquid distribution inside thereactor?
0
5
10
15
20
0 100 200 300 400 500 600
Days on stream
R a d i a l T d i s p e r s i o n ( ° C )
R1 B2 outlet
R2 B1 outlet
R2 B2 outlet
Radial temperature dispersionRadioactive tracers
Unit start-upUnit response to flow variations
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Hydroprocessing Catalysts
- Generally HDS catalysts are constituted by metal oxides from columnsVIA (Mo,W) and VIIIA ((Co),Ni) periodic table
- The active phase of HDS catalysts consists in the sulphided form of theseoxides – MoS2 slabs
Al2O3γ
Mo
Mo
S6Å
30Å
..
...
.
. .. . .
- Co or Ni are activity promoters and ‘decorate’ the edge of MoS2 slabs- CoMo catalysts are generally used for low pressure units and were the mainobjective are HDS reactions
- NiMo catalysts are generally used for higher pressure units and were the
main objective is density and cetane gain (hydrogenation reactions)
Co
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Hydroprocessing Catalysts
Used catalyst
Sulphide + coke
Regeneration of used catalyst is possible by carefully burning sulphur and
coke. The resulting catalyst will in its oxide form.
Fresh CoMo cataltyst 1.2-2.5 mm
Oxide state
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Hydroprocessing Catalyst’s Life
Were should I go on holidays?Why not a reactor of a
diesel hydrotreater?
Unloading under inert
atmosphere as I’mquite keen to react
with air
RotaryRotary KilnKiln
OvenOven
Spent CatalystSpent Catalyst
Hot Air Hot Air
Let’s do it again
Nice staying here, it’s always hot!
however, it’s also always raining
and it smells !!
catalyst
loading
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Catalyst Loading
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Catalyst loading
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Catalyst loading
L o c a l p o r o s i t y , ε
Catalyst bed grading must be adapted in order
to avoid pressure drop build-up
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Catalyst loading
Different particles are available to be loaded above the
main catalyst and minimize pressure drop build-up
good ‘hold’ inert balls or…
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Catalyst Activation
Oxide catalystMoO3
reactor
Reductionto MoO2
Unactive phase
Under H2T > 230-250°C
Oxide catalystMoO3
ex situ
‘preSulphided’
MoOxSy
ex situ
Active catalyst
MoS2
reactor
in situSulphidation
‘preSulphiding’Sulficat, Acticat,
EasyActive
H 2 Activation
Active catalyst
MoS2
ex situ
ex situ sulphiding Totsucat, XpresS
H2S
DMDS
Final step
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Catalyst Activation
R e a c
t o r i n l e t t e m p e r a t u r e ( ° C )
350
300
250
200
150
100
50
00 2 4 6 8 10 12 14 16 18 20
Time (hours)
Drying(120-150
°C)
Pre sulphiding step(reactor T < 15°C)
Catalyst sulphiding(320-350°C)
Catalyst wetting(liquid flow)
1.Catalyst wetting at lower temperature allows better gas-liquid distribution2.The drying step should always be below 150°C to avoid molybdenum oxide reduction
3.DMDS injection 1 hour before reaching presulphiding step
4.Maximum reactor exotherm should be below 15°C to avoid high catalyst temperaturesin without H
2
S
5.Catalyst sulphiding step temperature depends on catalyst type and unit operation
DMDS injection
Unit under pressure
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Kinetic Models
Feed + H2
Desulphurized product+ H2 + H2
[ ][ ]S k
dt
S d ×−=
LHSV
ek tck
Sout
Sin T R
Eact
×−
×=×=
0ln
××−=
0
)/ln(ln
k
LHSV Sout Sin R
E T
act
[ ][ ] [ ][ ] ∫∫∫∫ =⇔−= tcSin
Sout
tcSout
Sindt k
S
S d dt k
S
S d
00
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Kinetic Models
Typically, for HDS reactions on diesel and VGOEact = 25000 - 29000 cal/moleExample - Catalyst volume = 200 m3
Catalyst AFlowrate = 300 m3 /h
Bed 1 Tin = 345°C, Tout = 365°C, Bed 2 Tin = 360°C, T = 370°CWABT = 362,5°CSin = 7000 wtppmSout = 40 wtppmk0 = 1,5E10 h-1
Catalyst BFlowrate = 280 m3 /hBed 1 Tin = 342°C, Tout = 362°C, Bed 2 Tin = 352°C, T = 362°CSin = 7000 wtppmSout = 33 wtppm
WABT = 359,9°Ck0 = 1,4E10 h-1
Catalyst A is 2°C more active than catalyst B
(this value is higher with more precise models!)
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Kinetic Models - Cycle Length
Other parameters that must be taken into account in the kinetic models are:- hydrogen partial pressure
- feed severity (nitrogen, density, aromatics, T95, other)
- hydrogen/oil ratio, hydrogen sulphide and ammoniac partial pressure
Time
SOR EOR
Feed rate
Max temp
Cycle length
R e g en er a t i on or c a t al y s t c h a
n g e o u t
Temperature
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Kinetic Models - Cycle Length
Time
Feed rate
Max temp
C cle len th
Temperature
Time
Feed rate
Max temp
C cle len th
Poor catalyst performance High pressure drop
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Kinetic Models - Cycle Length
- Average Reactor Temperature = 1/3 inlet T + 2/3 outlet T- Temperature increase with time due to coke formation and poisons adsorption
- 3,5°C/month deactivation
320
330
340
350
360
370
380
390
400
0 40 80 120 160 200 240 280 320 360Days on stream
R e a c t o r A
v e r a g e T e m p e
r a t u r e ( ° C )
10°C difference
Catalyst B
Catalyst A
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Kinetic Models - Cycle Length
320
330
340
350
360
370
380
390
400
0 40 80 120 160 200 240 280 320 360Days on stream
R e a c t o r A
v e r a g e T e m p e r a t u r e ( ° C )
Normalized temperature
1,5°C/monthActual temperature
3,5°C/month
- Normalized temperature allows to correct for unit conditions and feedvariations
- Assessment of the real performances of the unit and the catalyst are muchmore precise
H d i U i
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Hydroprocessing UnitCold Scheme
Advantages: higher H2% in recycle gas, simpler, light feeds can be processed
Disadvantages: lower energy efficiency, larger high pressure separator
H d i U it
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Hydroprocessing UnitHot Scheme
Advantages: better energy efficiency, no need for stripper feed heating (most cases)
Disadvantages: need for recycle gas amine wash, loss of hydrogen
H d i U it
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Hydroprocessing UnitStripping section
The objective of the stripping section is to removed light ends from the diesel (H2S, CH’s)and/or to remove products lighter than the unit main product
H d i U it
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Gasoline hydrotreaters
In general, the objective of the gasoline hydrotreaters is to remove sulphur and nitrogenfrom reformer or isomerization feeds.Indeed, sulphur and nitrogen will poison anddegrade the performances of reforming and of isomerization catalysts
Gasoline hydrotreaters operate on 100% gaz phase, there is no need for distribution trays
Kerosene and Diesel hydrotreaters
The objective of the diesel hydrotreaters is to remove sulphur, reduce density and improve
cetane index. In the case of kerosene hydrotreaters, the objective is also to respectaromatics specification (naphthalenes and smoke point)
Diesel hydrotreaters operate in gas/liquid phase – reactor needs good distribution trays
Vacuum Gasoil hydrotreatersThe objective of the VGO hydrotreaters is to remove sulphur and nitrogen to prepare the
FCC feed. The objective is to be abble to produce 10 wtppm S gasoline and to improveFCC yields
VGO hydrotreaters operate in gas/liquid phase – reactor needs good distribution trays
Hydroprocessing Units
Hydroprocessing Units
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Hydroprocessing Units
Kinetic Models
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Kinetic Models
Feed + H2
Desulphurized product+ H2 + H2
[ ] [ ] 1, >×−= nS k dt
S d n
LHSV
ek tck
S S n
T R
Eact
n
in
n
out
×−
−−
×
=×=
−×−0
11
11
1
1
×
−×
−×
−=
−− 011/11
1
1ln k LHSV S S n
R
E T
n
in
n
out
act
[ ]
[ ]
[ ]
[ ] ∫∫∫∫ =⇔−=
tcSin
Sout n
tcSout
Sin n
dt k
S
S d dt k
S
S d
00