Hydroprocessing Units

November 2004

Pedro da Silva

Why Hydroprocessing?

CO, NOx, HC, Particulates

BEFORE

NOW

Why Hydroprocessing?

Desulphurisation units become more and more important in refineries

Market of solid catalysts in refining, (IFP data,1994)

tons /year Catalytic 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 leastone catalyst in their liver !

Why Hydroprocessing?

Hydroprocessing Units Layoutin a Refinery Scheme

Atm

osph

eric

Dis

tilla

tion

Heavy fuel

Crude

Vacu

um D

istil

latio

n

CatalyticCracker

FCC

Visbreaking

Reforming

propanebutane

gasoline

naphtha

Hydrodesulphurisationkerosene

diesel

H2

Amine wash

HDT

Hydroprocessing Units Layoutin a Refinery Scheme

Atm

osph

eric

Dis

tilla

tion

Heavy fuel

Crude

Vacu

um D

istil

latio

n

CatalyticCracker

FCC

Visbreaking

Reforming

propanebutane

gasoline

naphtha

Hydrodesulphurisationkerosene

diesel

H2

Amine wash

HDT

HDS

Hydroprocessing Units Layoutin a Refinery Scheme

Atm

osph

eric

Dis

tilla

tion

Heavy fuel

Crude

Vacu

um D

istil

latio

n

CatalyticCracker

FCC

Visbreaking

Reforming

propanebutane

gasoline

naphtha

Hydrodesulphurisationkerosene

diesel

H2

Amine wash

HDT

HDS

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 0.2-0.5 VGO, residue hydrocracker 100-200 370-410 0.5-1.5

- The most important parameters followed in these units (apart from product qualities!) are the temperature and unit pressure drop

- The difference on activity and stability of different catalysts is measured by °C

Chemical Reactions in Hydroprocessing

Not limited by thermodynamics

Refractory compoundS

Hydrogen consumption

Chemical Reactions in Hydroprocessing

222120191817161514131211109876543210

48 00046 00044 00042 00040 00038 00036 00034 00032 00030 00028 00026 00024 00022 00020 00018 00016 00014 00012 00010 0008 0006 0004 0002 000

0-2 000-4 000-6 000

SP

W 0

.20

ST

H 1

0.00

TI

OF

F

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

Soufre réfractaire

S

S

BT:Benzothiophène

DBT:Dibenzothiophène

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

Chemical Reactions in Hydroprocessing

Chemical Reactions in Hydroprocessing

Température (°C)

% H

DA

Souf

re e

fflue

nt (p

pm)

T1 T2

HDS

Régime thermodynamique(HDA)

Régime cinétique(HDA)

Equilibre thermodynamiqueHDA

Chemical Reactions in Hydroprocessing

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

four lit 1

lit 2

0

R1

Opération normale

R1

température

Simplified Scheme of an Hydrodesulphurisation Unit

2

Partial by-passRecycle

compressor

Raw feed

Make-up compressor

Make-up hydrogen

to fuel gas

H.P.Flash drum

Furnace Reactor

Air coolers

Heat Exchangers

Stripper

Quench

Hydroprocessing reactor and internals

Vapor/liquid distribution tray

Catalyst bed

Varies between 3 to 15 m

Catalyst support grid

Quench distributor

Mixing chamber

Outlet collector

Inlet diffuser

Unloading nozzle

Reactor diameter varies between 1,5 to 4,5 m

Hydroprocessing Reactor and Internals

Catalyst bed

reactor outlet collector

Hydroprocessing Reactor and Internals

Additional gasketing

Hydroprocessing Reactor and Internals

What techniques can be used to check the gas-liquid distribution inside the reactor?

0

5

10

15

20

0 100 200 300 400 500 600

Days on stream

Rad

ial T

dis

pers

ion

(°C

)

R1 B2 outlet

R2 B1 outlet

R2 B2 outlet

Radial temperature dispersionRadioactive tracers

Unit start-upUnit response to flow variations

Hydroprocessing Catalysts

- Generally HDS catalysts are constituted by metal oxides from columns VIA (Mo,W) and VIIIA ((Co),Ni) periodic table

- The active phase of HDS catalysts consists in the sulphided form of these oxides – MoS2 slabs

Al2O3γ

Mo

MoS6Å

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 main objective 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

Hydroprocessing Catalysts

Used catalystSulphide + 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 mmOxide state

Hydroprocessing Catalyst’s Life

Were should I go on holidays?Why not a reactor of a

diesel hydrotreater?

Unloading under inertatmosphere as I’mquite keen to react

with air

RotaryRotary Kiln Kiln OvenOven

Spent CatalystSpent CatalystHot AirHot Air

Let’s do it again

Nice staying here, it’s always hot!however, it’s also always raining

and it smells !!

catalystloading

Catalyst Loading

Catalyst loading

Catalyst loading

Loca

l por

osity

, ε

Catalyst bed grading must be adapted in orderto avoid pressure drop build-up

Catalyst loading

Different particles are available to be loaded above themain catalyst and minimize pressure drop build-up

good ‘hold’ inert balls or…

Catalyst Activation

Oxide catalystMoO3

reactor

Reductionto MoO2

Unactive phase

Under H2T > 230-250°C

Oxide catalystMoO3

ex situ

‘preSulphided’MoOxSyex situ

Active catalystMoS2

reactor

in situSulphidation

‘preSulphiding’Sulficat, Acticat,

EasyActive

H2 Activation

Active catalystMoS2

ex situ

ex situ sulphidingTotsucat, XpresS

H2S

DMDS

Final step

Catalyst Activation

Rea

ctor

inle

t tem

pera

ture

(°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 reduction3.DMDS injection 1 hour before reaching presulphiding step4.Maximum reactor exotherm should be below 15°C to avoid high catalyst temperatures

in without H2S5.Catalyst sulphiding step temperature depends on catalyst type and unit operation

DMDS injection

Unit under pressure

Kinetic Models

Feed + H2

Desulphurized product+ H2 + H2

[ ] [ ]SkdtSd

×−=

LHSVektck

SoutSin TR

Eact×

−×

=×=

0ln

××

−=

0

)/ln(lnk

LHSVSoutSinR

ET act

[ ][ ]

[ ][ ] ∫∫∫∫ =⇔−=

tcSin

Sout

tcSout

Sindtk

SSddtk

SSd

00

Kinetic ModelsTypically, for HDS reactions on diesel and VGO Eact = 25000 - 29000 cal/moleExample - Catalyst volume = 200 m3

Catalyst AFlowrate = 300 m3/hBed 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 wtppmWABT = 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!)

Kinetic Models - Cycle LengthOther 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

Regeneration or catalyst changeout

Temperature

Kinetic Models - Cycle Length

Time

Feed rate

Max temp

Cycle length

Temperature

Time

Feed rate

Max temp

Cycle length

Poor catalyst performance High pressure drop

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

Rea

ctor

Ave

rage

Tem

pera

ture

(°C

)

10°C differenceCatalyst B

Catalyst A

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

Rea

ctor

Ave

rage

Tem

pera

ture

(°C

)

Normalized temperature1,5°C/monthActual temperature3,5°C/month

- Normalized temperature allows to correct for unit conditions and feed variations- Assessment of the real performances of the unit and the catalyst are much more precise

Hydroprocessing UnitCold Scheme

Advantages: higher H2% in recycle gas, simpler, light feeds can be processed

Disadvantages: lower energy efficiency, larger high pressure separator

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

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

Gasoline hydrotreaters

In general, the objective of the gasoline hydrotreaters is to remove sulphur and nitrogen from reformer or isomerization feeds.Indeed, sulphur and nitrogen will poison and degrade 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 respect aromatics specification (naphthalenes and smoke point)

Diesel hydrotreaters operate in gas/liquid phase – reactor needs good distribution trays

Vacuum Gasoil hydrotreaters

The 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 improve FCC yields

VGO hydrotreaters operate in gas/liquid phase – reactor needs good distribution trays

Hydroprocessing Units

Hydroprocessing Units

Kinetic Models

Feed + H2

Desulphurized product+ H2 + H2

[ ] [ ] 1, >×−= nSkdtSd n

LHSVektck

SSn

TREact

nin

nout

×−

−−

×=×=

−×

−0

11

111

1

×

−×

−×

−=

−− 011 /111

1ln kLHSVSSn

R

ET

nin

nout

act

[ ][ ]

[ ][ ] ∫∫∫∫ =⇔−=

tcSin

Sout n

tcSout

Sin n dtkSSddtk

SSd

00