13. vacuum distillate.pdf

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RA HCR - 00111_A_A - Rev. 2 17/01/2005

Refining-Petrochemicals-Chemicals-Engineering

PDVSA

Process Engineering Applied To Petroleum Refining

Module 8: REFINING PROCESSES (2)

VACUUM DISTILLATE HYDROCRACKING

I - PURPOSE OF HYDROCRACKING AND INTEGRATION WITH IN THEREFINING SCHEME ................................................................................................................. 1

II - PROCESS CHARACTERISTICS .............................................................................................. 8

1 - Chemical reactions.......................................................................................................................82 - Hydrorefining catalysts ...............................................................................................................103 - Hydrocracking catalysts .............................................................................................................104 - Main catalyst constraints ............................................................................................................14

III - HYDROCRACKER OPERATING CONDITIONS ................................................................... 15

1 - Feed circuit .................................................................................................................................152 - Reactor section ..........................................................................................................................153 - Refrigeration - HP and MP separators .......................................................................................154 - Distillation section.......................................................................................................................165 - Hydrocracking catalyst activation ...............................................................................................166 - Catalyst regeneration .................................................................................................................16

IV - HYDROGEN PRODUCTION................................................................................................... 18

1 - Principle of the reaction..............................................................................................................182 - Hydrogen production plant .........................................................................................................19

2005 ENSPM Formation Industrie - IFP Training


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00111_A_A 2005 ENSPM Formation Industrie - IFP Training

1

I - PURPOSE OF HYDROCRACKING AND INTEGRATION WITHIN THE REFINING SCHEME

Distillate hydrocracking is a sophisticated conversion process that simultaneously involves heat, several

types of specific catalysts and the addition of hydrogen to promote and control heavy hydrocarboncracking reactions.

It is characterized by significant upgrading of heavy feeds that are converted largely into high quality lightand intermediate products.

Unlike other conversion processes, hydrocracking has the additional advantage of offering considerableoperating flexibility which makes it possible to a certain extent to adapt unit production to marketrequirements.

A typical material balance at total conversion and main product characteristics, are shown below.

PRODUCTS YIELDS% wt of feed REMARKS

INPUT

Distillate feed 100Catalyst constraints: limited metal, nitrogen,Conradson carbon residue content

Hydrogen 3 Substantial consumption of hydrogen requiringproduction plant

TOTAL INPUT 103.0

OUTPUT

Gas (H2S, C1, C2, C3, NH3) 4.3

- sulfur plant required for H2S treatment

- process water stripping

Butane 4.6

Light gasoline 14.1 Rich in isoparaffins, high RON

Heavy gasoline 18.0 Rich in N - Excellent RON after reforming -Requires appropriate reforming capacity

Kerosene 38.0 Good cold condition characteristics - Sulfur-free

Gas oil 24.0 High cetane number - Sulfur-free

TOTAL OUTPUT 103

This example shows:

- the excellent process selectivity with respect to gasoline, kerosene and gas oil fractions- the absence of heavy products as produced by FCC- the substantial hydrogen consumption


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2

COMPARISON FCC/HYDROCRACKING

Catalytic cracking Hydrocracking

Operating conditions

H2 No Yes

Total pressure 1 bar > 100 bar

Temperature (C) 500-600 350-430

Cycle duration(between two regenerations)

A few seconds 1 to 3 years

Contact time A few seconds 1 hour

Product quality

Gasoline Relatively good Poor

Gas oil Very poor(CN 20)

Excellent(CN > 55)

Base oil Insuitable Excellent(VI > 110)

Feed processed

VR + e AR Vacuum distillate


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3

STRUCTURE OF THE PRODUCT YIELDS OBTAINEDBY THE DIFFERENT CONVERSION PROCESSES

%0

10

20

30

40

50

60

70

80

90

100

VGOfrom crudes

Vacuum residueswith low metalcontent

VGOfrom visbreaker

etc.

F. C. C.

+

GAS + LPG

Gasolines

LCO

Coke*

* self consumed

PRODUCTS

+

or

FCCFEEDS

HCO + Slurry

D

PCD

334C

Ranking ofproductquality

++ very good+ good- poor-- very poor

0

10

20

30

40

50

60

70

80

90

100

VACUUM

DISTILLATES

360 - 350C

360 -

Gasoline

Light

Heavy

Kerosene

Gas oil

102.5

++

++

+

*

* After catalytic reforming

GAS + H2S

++

HYDROCRACKING

D

PCD3

43B

PRODUCTS

FEEDSTOCKS


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4

CUT

number

ofCaverage

C32

C16

C8

C4

V

GO

Naphtha

Gas

Gas-oil

Ke

ro

Outsid

eUSA

Maxigaso

ilobjective

CRACKINGREACTIONANDHYD

ROCRACKINGCONFIGURAT

ION

SINGLESTAGE

ONCETHROUGHORRECYC

LEWITHONEORTWOREACTORS(HDT-HDC)

HYDROCRA

CKERCONFIGURATIO

N:SINGLESTAGE-T

WOSTAGE

US

A

Maxinaphth

aobjective

TWOSTAGE(NH3-H2Sremovedafterfirststage)

DPCD1173A


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5

SINGLE-STAGE

Amorphoussilica-

aluminacatalyst

Zeolitecrackingcatalyst

Single-stageoncethrough

Single-stagewithliquidrecycle

Series

flowoncethrough

Seriesflowwithliquidrecycle

DPCD2100D


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6

TYPICAL HYDROCRACKING PROCESS Flow schemes

One-stage process

D

PCD

1174A

H2 recycle

1 or 2 REACTORS

Make up H2

FRESHFEED

RESIDUE RECYCLE

SEPARATION

FRACTIONATION

FUEL OIL

MIDDLEDISTILLATES

NAPHTHA

LPG

Two-stage process

D

PCD

1174B

Make up H2 H2 recycle

1st STAGEREACTOR

2nd STAGEREACTOR

FRESHFEED

RESIDUE RECYCLE

SEPARATION

FRACTIONATION

FUEL OIL

MIDDLEDISTILLATES

NAPHTHA

LPG


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7

The incorporation of the hydrocracking process within the refining scheme requires a complex thatincludes the following units:

- a specific vacuum distillation unit allowing separation of distillate feeds that meet purityspecifications with respect to metals, Conradson carbon residue, etc.

- a hydrogen production plant using the steam reforming process which enables hydrogenproduction from light hydrocarbons (methane, fuel gas, butane, etc.)

- a hydrocracking unit, consisting of a reaction section operating at high pressure (around160 bar) and high temperature (360-400C) and a complex separation section

- a sulfur plant including facilities foramine washing of gaseous effluent for H2S recoveryand forsulfur production

- a stripper for process waterwhich contains large amounts of ammonia and H2S

A typical hydrocracker flow scheme is shown below.

HYDROCRACKING

Reaction

Separation

HYDROGEN

PRODUCTION

UNIT

(steam reforming)

VACUUM

DISTILLATION

SULFURUNIT

WATERSTRIPPER AMINE

WASHING

DISTILLATE

RECYCLE

HYDROGEN

WATER

WATER

STEAM

ATMOSPHERICRESIDUE

LIGHTHYDROCARBONS

H2S

GAS

GAS

D

PCD

1172A

FUEL GAS

SULFUR

PROPANE

BUTANE

LIGHT GASOLINE

HEAVY GASOLINETO REFORMER

KEROSENE

GAS OIL

GAS OIL

VACUUM RESIDUE


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8

The hydrocracking process does not enable separation of the distillate feed into light and intermediateproducts in one run. The conversion per run is therefore determined as the ratio of gas oil and lighterproducts (370C) obtained to the feed rate.

Conversion per run =370 product rate

feed rate x 100

and the normal value is in the range of 60 - 70%.

Consequently the fraction heavier than gas oil has to be recycled to the reaction section, whichobviously reduces the amount of fresh feed that can be run.

II - PROCESS CHARACTERISTICS

1 - CHEMICAL REACTIONSThe operating conditions used in hydrocracking processes:

- temperature of 360 - 400C- high hydrogen pressure- use of hydrorefining and hydrocracking catalysts

result in complex chemical reactions that can, for the sake of simplicity, be classified under thefollowing three headings: conventional hydrorefining reactions, hydrogenation reactions and actualhydrocracking conversion reactions.

a - Hydrorefining reactions

They are similar to the chemical conversions already encountered in conventional hydrotreating. Dueto the severity of operating conditions the reactions are virtually complete, resulting in highlypurified products. The reactions involve heavy compounds ofsulfur, nitrogen and oxygen and leadto the formation of H2S, NH3, H2O and light products.

Sulfur, nitrogen and hydrogencompounds + hydrogen

H2SNH3H2O

+ saturated, lighter hydrocarboncompounds

These reactions are exothermic and moderately hydrogen consuming. One important property is theirremoval of heavy nitrogen compounds which are poisons for acid hydrocracking catalysts.

The effectiveness of hydrorefining reactions obviously depends on the amount of sulfur and nitrogenimpurities in the distillate feedstock.


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9

b - Hydrogenation reactions

The degree of hydrogen pressure used in hydrocracking processes combined with the hydrogenatingproperties of the catalysts results in virtually complete hydrogenation of the unsaturated chemicalcompounds. This applies in particular to aromatic hydrocarbons and explains at the same time whyhydrocracked products are largely composed ofsaturated paraffinic and naphthenic hydrocarbons.

A typical chemical equation of the hydrogenation of a heavy aromatic compound is shown below.

+ hydrogen

Heavy aromatichydrocarbon

heavy naphthenichydrocarbon

It leads to the formation of naphthenic hydrocarbons.

Hydrogenation reactions are very exothermic and hydrogen consuming.

c - Hydrocracking reactions

They are an essential factor in this conversion process because they lead to the formation ofproductslighterthan those in the feed. They apply to all types of hydrocarbons.

heavy hydrocarbonsP, N or A

+ H2light

hydrocarbons

For exampleC30H62 + H2 C15H32 + C15H32

The amount ofhydrogen consumed is equivalent to the degree ofsaturation of the short molecules

cracked. At the same time these reactions are very exothermic.

It should be noted that the action of the catalyst in this process is to orient the shortest paraffinicmolecules produced toward isomerized forms. This explains the high octane number of the lightgasoline.

OVERALL it can be seen that the DIFFERENT CHEMICAL REACTIONS involved in the hydrocrackingprocess are all hydrogen consuming, which explains the high input of this component in the materialbalance of the unit. Another common factor is the exothermic nature of the reactions, which meansthat precautions have to be taken to avoid any runaway of the reaction section.


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10

2 - HYDROREFINING CATALYSTS

The first stage of the hydrocracking process is similar to conventional hydrotreating and uses

hydrorefining catalysts not very different from those used in hydrodesulfurisation of kerosene andgas oil. These catalysts are of the NiMo type and are composed of an alumina support bearing activenickel and molybdenum sulfides. They promote desulfurisation and denitrogenation, and alsohydrogenation .

They are used in the first reactor, known as the HYDROREFINING REACTOR, designed tohydropurify the feed before it undergoes the actual cracking process. Typical operating conditions forthe first reactor are as follows:

Pressure : 160 bar, chiefly due to hydrogen

Temperature : approximately 375C

Catalyst : NiMo on alumina

Exothermicity : hydrogen quench between the two beds

At the reactor outlet the reaction mixture is therefore composed of the hydropurified and partiallyhydrogenated feed, hydrogen, and H2S, NH3 and H2O formed by the chemical reactions.

3 - HYDROCRACKING CATALYSTS

Like the catalytic reforming process, hydrocracking requires dual-purpose catalysts that are used in asecond reactor called the CONVERSION REACTOR. The catalysts must simultaneously satisfy thefollowing requirements:

- they must promote cracking reactions, which calls for an acid catalyst. Synthetic silica-alumina catalysts are amorphous (non-crystalline) solids with acid properties and have beenwidely used in cracking processes.

they have currently been replaced, however, by crystalline silica-alumina systems calledZEOLITES which are significantly more acidic.

- they must possess hydrogenating properties to be able to hydrogenate the heavy hydro-

carbons in the feed and to saturate the cracked species with hydrogen. This action can beprovided by sulfide combinations of the NiMo or NiW type and in some formulations even byprecious metals such as palladium.

The fundamental property of hydrocracking catalysts probably lies in the acidity of the silica-aluminasupport. It is the acid support that is directly subject to the poisonous action of the alkaline nitrogencompounds not converted in the refining reactor, and of ammonia.


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11

The basic pattern of the silica-alumina structure is a tetrahedron. The four peaks of the tetrahedron areoccupied by oxygen atoms (valence = 2) and the centre by a silicon atom (valence = 4) or by analuminium atom (valence = 3). These two basic patterns are shown below.

Oxygen Ngative charge

Si AI

D

CH

1000C

Basic patterns of silica-alumina structures

As can be seen, due to the tri-valence of the aluminium atom, the tetrahedron in question has aresidual negative charge.

Assembly of the elementary tetrahedra is based on the valence of the oxygen atoms that remains free.The tetrahedra may be assembled by their peaks, by their surfaces or by their edges, resulting in arandom assembly in space. This leads to a structure of varying porosity, characteristic ofAMORPHOUS ornon-crystalline silica-alumina. The figure below shows a portion of such anassembly.

Na+

AlSi Al

AlAl

Al

Si

Si

SiSi

SiSi

Na+

Na+

Na+ Na+

D

CH

1000B

Positively charged sodium ions Na+ appear in the structure to compensate for the negative charges

due to the presence of aluminium atoms in the silica-alumina. Acidity is achieved by an acid treatmentthat replaces the Na+ ions by H+ ions.


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12

ZEOLITES orMOLECULAR SIEVES are silica-alumina systems that have a specific crystallinestructure. There are a great variety of them but the basic element is always the same SiO 4 or AlO4tetrahedron.

Unlike the amorphous silica-alumina systems, these elementary tetrahedra assemble exclusively bytheir peaks, which produces the basic crystalline pattern (known as sodalitic pattern) of the zeolitesused in acid catalysis.

D

CH

306A

In the figure all the oxygen, silicon and aluminium atoms are shown. To simplify the sodalitic pattern

and make it easier to see, first all the oxygen atoms not located on the edges are removed (a), andthen only the silicon and aluminium atoms are shown (b).

(a) (b)

D

CH

303A

Sodalitic pattern

The polyhedron has 6 square surfaces and 8 hexagonal surfaces. The structures are assembled eitherby the square surfaces or by the hexagonal surfaces.


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13

Assembly by the square surfaces: A SIEVE

These assembled structures are repeated in space and produce very regular, interconnected cavitieswhich give the solid a very specific crystalline structure.

Location

of "cages"Lattices assembled

by their square faces

D

CH

146B

Assembly by the square surfaces

The openings to the cavities in the A sieves vary from 3 to 5 , in size according to the nature of thepositively charged ions incorporated in their structure.

A-type sieves are used in industry for gas purification (drying) or for separating the constituents of amixture according to the size of their molecules, hence the term molecular sieves.

Assembly by the hexagonal surfaces: X or Y SIEVES (according to the proportions of silicon andaluminium)

Hexagonal face lattice assembly

D

CH14

7B

Assembly by the hexagonal surfaces


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14

Assembly by the hexagonal surfaces produces cavities of larger volume and openings exceeding 10 .

This crystalline structure of X or Y sieves is therefore more suited to the adsorption of heavy hy-drocarbon molecules which in addition can circulate within the zeolite due to the interconnectingcavities.

At the same time the ion exchange that acidifies the sieves gives them much greater acidity than theamorphous silica-alumina systems which explains why they are used for hydrocracking.

Typical conversion reactoroperating conditions are as follows:

Pressure : 160 bar approximately

Temperature : 360 - 400C

Catalyst : 3 beds of hydrocracking catalyst1 bed of hydrorefining catalyst

Exothermicity control : hydrogen quench between the secondand third bed

The use of the last hydrorefining catalyst bed is to remove the sulfur compounds that may have formeddue to the action of H2S on the intermediate products of the reaction.

4 - MAIN CATALYST CONSTRAINTS

a - Constraints connected with the feed. They concern

- nitrogen compounds and ammonia which de-activate the catalyst. This requires anincrease in the temperature or reduction of the feed rate in order to obtain the desiredconversions

- sulfur. Concentration of H2S should be within a bracket that ranges from a minimum valuenecessary to maintain the sulfur forms of the active species to a maximum value beyondwhich catalyst activity deteriorates

- metals, concentration of which is strictly limited. An initial amount is nevertheless removedby the hydrorefining catalyst

- asphaltenes and resins that may be entrained in vacuum distillation and are coke promo-ters. Conradson carbon residue is related to these compounds

b - Constraints connected with operating conditions

- moderate temperature to avoid excessive coking of the catalyst

- very high H2/HC ratio for the same reason as above

- large amount of catalyst in relation to the feed rate to ensure a sufficiently long catalyst-feedcontact time.


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III - HYDROCRACKER OPERATING CONDITIONS (Figure 1)

1 - FEED CIRCUIT

The feed circuit includes a pump capable of raising the pressure of the liquid distillate feed to a valuehigher than that of the process, and heat exchangers allowing recovery of heat from the hot effluentsfrom the reaction section.

The first reactor inlet temperature is controlled by a mixture of hydrogen-rich gas which is over 90%pure. The hydrogen alone is heated in a furnace controlled by the reactor inlet temperature. Thisavoids risks of coking. The latter is liable to occur if the feed is heated directly in the furnace.

Hydrogen pressure on the catalyst in the reactor is determined by hydrogen dilution. It is calculatedin m3 of pure hydrogen per m3 of feed. The design value is in the region of 750 - 800 m3/m3.

2 - REACTOR SECTIONThe refining reactorincludes two catalyst beds. A rise in temperature is observed in the first bed dueto the exothermic hydrorefining and hydrogenation reactions.

A hydrogen quench lowers the temperature before the feed is subjected to the second bed, bringing itmore or less to the first reactor inlet temperature. The rise in temperature in the second bed is againthe result of the exothermicity of the reactions.

At the first reactor outlet the recycle is added to the mixture. The injection of hot hydrogen regulatesconditions at the conversion reactor inlet, i.e. a slightly higher temperature than in the first reactorand greater dilution (approximately 1200 m3 H2/m3).

The exothermicity of the hydrocracking reactions results in a difference in temperature (Dt) betweenthe inlet and outlet of the 3 beds. Temperatures are controlled by two hydrogen quenches.

The reactors operate at the pressure required by the process (around 160 bar). The differences inpressure between inlet and outlet are due to pressure drops in the mixture as it moves through thereactor. Pressure drops increase with catalyst coking, fouling and plugging.

3 - REFRIGERATION - HP AND MP SEPARATORS

At the second reactor outlet the mixture of hydrogen and cracked products is cooled by heat exchangewith the feed, the hydrogen and the liquid effluent of the MP separator. Condensation is completed byair coolers upstream of the HP separator. It should be noted that injection of process water before theair coolers can prevent condensation to solid state of salts such as ammonium sulfide formed by theaction of H2S or NH3. Figure 2 indicates the conditions for formation of solid ammonium sulfide. Theseparator is maintained at 160 bar and separates:

- a gas phase rich in hydrogen to which is added make-up hydrogen from the hydrogenplant via the make-up compressors. The resulting mixture is compressed by the recyclecompressors and routed to the reaction section

- a liquid phase including the products of the process water reaction. The process water isseparated and treated

The resulting liquid is expanded before being routed to the MP separator. The gas phase in theseparator contains H2, H2S and light hydrocarbons and is routed to the HP amine washing installation.

The liquid phase is reheated to the required temperature and fed to the fractionation section.


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4 - DISTILLATION SECTION

The section includes:

- a debutaniserthat separates C4 gases from gasoline and heavier fractions

- a depropaniserthat produces a C1 - C2 - C3 - H2S - NH3 gas fraction for amine washing,and a butane fraction

- an atmospheric distillation column that separates light gasoline, heavy gasoline and ke-rosene fractions

- a vacuum distillation column that separates the gas oil fraction from the recycle

5 - HYDROCRACKING CATALYST ACTIVATION

Hydrocracking catalysts are manufactured as oxides (usually by metals salts impregnation on asupport, followed by calcination) and need to be sulfided before use.

Sulfidation:

- MoO3 + 2 H2S + H2 MoS2 + 3 H2O- 3 NiO + 2 H2S + H2 Ni3S2 + 3 H2O

Sulfiding methods

Under H2 pressure, with a sulfiding agent added in gas phase, or more frequently in the liquid, whichdecomposes into H2S and hydrocarbons.

Dimethyl disulfide DMDS

CH3 S S CH3 + 3 H2200C

2 H2S + 2 CH4

Passivation

The cracking function of the zeolite is very active and has to be passivated to avoid early coking of thecatalyst, this is done by an injection of aniline. The aniline breaks in NH3 which temporarily neutralizesthe active sites of the catalyst. The catalyst activity is then restored by a temperature increase whichdesorbs NH3.

6 - CATALYST REGENERATION

The deactivation is the result of coke deposition. The activity is recovered by burning the coke. It isdone either in-situ or ex-situ after catalyst unloading under inert atmosphere.

However metals contamination is irreversible.

Regeneration consists in a controlled coke burn off. Sulfides are also converted back to oxides.


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Reactions

Mo S2 +72 O2 Mo O3 + 2 SO2

Ni3 S2 +72 O2 3 Ni O + 2 SO2

C + O2 CO2

H2 +12 O2 H2O

In-situ method

- shutdown unit- nitrogen purge- combustion of coke- presulfiding

Ex-situ method

The used catalyst is pyrophoric and the contact with air should be avoided. The catalyst should beunloaded under nitrogen in drums and sent to an outside company for regeneration.


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IV - HYDROGEN PRODUCTION

1 - PRINCIPLE OF THE REACTION

The hydrogen required by a hydrocracking unit comes chiefly from the hydrogen atoms linked to thecarbon atoms in the light hydrocarbon molecules constituting the feed of a hydrogen production plant.The thermal breakdown of hydrocarbons produces hydrogen gas. Thus methane, for example, givesthe following result:

CH4 Csolid + 2 H2thermal

breakdown

Hydrogen production is automatically accompanied by solid carbon deposition which makes theprocess unusable.

The carbon deposit can be eliminated by operating in the presence ofsteam. At high temperature thewater reacts chemically on the solid carbon and forms two gaseous products, carbon monoxide andhydrogen.

Csolid + H2O CO + 3H2

The breakdown of methane in the presence of steam leads to the following reaction:

CH4 + H2O CO + 3H2

The hydrogen so formed comes partly from the methane and partly from the water which is

chemically broken down by the reaction.

The process based on this principle is called STEAM REFORMING.

The reaction involved in reforming is extremely endothermic (60 kcal consumed per mole of methaneconverted). It is promoted by high temperatures and the operating temperature is generally around800C. It also requires moderate pressure of around 20 bar, a substantial amount ofexcess steam(about 3 tons of steam per ton of hydrocarbon feed) and a specificcatalyst (Nickel on Alumina) todirect the conversion process toward maximum hydrogen production and to limit carbon deposition.

In addition to the steam reforming reaction, the carbon monoxide formed may react on the excesssteam, producing supplementary hydrogen gas:

CO + H2O CO2 + H2

This conversion is called the CO CONVERSION reaction or SHIFT reaction.

Unlike the reforming reaction, CO conversion is exothermic (10 kcal per mole of CO converted). Hightemperatures have a negative effect on the reaction and a high rate of conversion is obtained onlywith a moderate temperature. The reaction also requires a specific catalyst (Iron or Chromium).

As can be seen, hydrogen production consequently has to be divided into two successivechemicalstages:

- first, the steam reforming reaction that takes place at high temperature

- second, supplementary hydrogen production by CO conversion, carried out at lowtemperature after cooling the reformer effluent.


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2 - HYDROGEN PRODUCTION PLANT

The principle of the hydrogen production plant is shown in Figure 3 and the plant in Figure 4. A number

of important operations are involved.a - Preparation of the feed

The catalysts used in the hydrogen plant are very sensitive to some POISONS, mainly SULFUR andCHLORINE.

The light hydrocarbons used as feed for the unit:

- CATALYTIC REFORMING PURGE gas- HP and LP FUEL GAS after AMINE WASHING- commercial BUTANE

must therefore be carefully purified.

The purge gas from the catalytic reformer contains traces of hydrochloric gas (HCl) and isdechlorinated on beds of specific ADSORBENT (caustic soda). After compression and reheating tothe required temperature, intensive desulfurisation of the feed is performed by conventionalCATALYTIC HYDROTREATMENT in a reactor containing a catalyst consisting of cobalt molybdenumon an alumina support. The H2S generated by the desulfurization reactions is chemically trapped bythe ZINC oxide contact mass.

b - Steam reformer furnace

The purified feed, combined with the superheated MP steam (approximately 3 tons of steam per ton offeed) is routed to the reformer furnace. The reforming reaction requires substantial addition of veryhigh temperature heat, which calls for original technology. The feed mixture is distributed evenly in alarge number of tubes 10 m long and placed vertically in the radiation chamber of the reformer furnace.The feed circulates from top to bottom of the tubes heated by the radiation of the burner flames and onits way it contacts the catalyst which is present inside the tubes in the form of small rings about 1 cm insize. NICKEL, on an inert alumina support, is the active substance of the catalyst. It also containsPOTASSIUM which activates breakdown of the water and thereby limits carbon deposition.

Operating pressure is in the region of 20 bar and temperature is around 800C.

A significant amount of heat is recovered from the very hot flue gases leaving the radiation zone ofthe furnace. It is used to generate HP and MP steam, to preheat the feed and the furnace combustionair.

c - CO conversion

The effluent leaving the furnace contains a large amount of hydrogen (70 - 80% volume excludingsteam), a small amount of carbon dioxide and non-converted methane, and a non-negligibleamountof carbon monoxide (generally over 10% volume). After cooling to around 350C by heat exchange ina steam generator, the CO conversion reaction takes place. The converter reactor contains a fixedbed ofiron and chromium based catalyst. The carbon monoxide is partially converted by the steaminto hydrogen. The reaction is exothermic and the temperature rises as the effluent passes throughthe catalyst bed. At the converter outlet the gaseous effluent is hydrogen enriched and its carbonmonoxide content has been drastically reduced (to about 1% volume on dry gas).


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d - Hydrogen purification

The converter effluent is cooled and the dilution water is condensed. The final hydrogen purification isperformed by adsorption. The hydrogen passes through a fixed adsorbent bed and the impurities arefixed on the adsorbent. Once it is saturated the adsorbent has to be regenerated. The normalregeneration method is to raise the temperature of the bed by circulating a hot gas through it whichdesorbs the impurities. The bed then has to be recooled before it can be used again for adsorption.Although this method of desorption by temperature variation, known as thermal swing adsorption(TSA) is very effective, it nevertheless has a disadvantage. The heating and cooling phases are timeconsuming and consequently it cannot be applied to frequent cycle operation.

It also possible to regenerate adsorbent beds at ambient temperature by reducing the operatingpressure. This method is known as pressure swing adsorption (PSA). Its advantage is that it is veryfast and therefore lends itself to operation by cycles in close succession, thus making it possible toprocess large quantities of gas effluent with a high impurity content.


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360

185

Vacuumdistillate

125

M

GAS

SEPARATION

170

20

380

420

420

quench

HP

SEPARATOR L

P

SEPARATOR

VACUUM

COLUMN

Recycle

DEBUTANIZER

AUXILIARY

COMPRESSOR

Pro

cess

water

RECYCLE

CO

MPRESSOR

FRESH

HYDROGEN 3

.5

60

CONVERSION

REACTOR

quench

C4-

C5

+

ATMOSPHERIC

COLUMN

GASOILK

EROSENE

HEAVY

GASOLINE

LIGHT

GASOLINE

BUTANE

PROPANE

GAS

+NH3

+H2S

FURNACE

FURNACE

HYDROTREATMENT

REACTOR

vacuum

FEED

VACUUM

DISTILLATE

DPCD315B

Figure1

2003ENS

PMFormationIndustrie

"SERIESFLOW"

HYDROCRACKER

Simplifiedflowscheme


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2003 ENSPM Formation Industrie

Possible formation

of solide NH4 HS

For any temperature t

NH3 (g) + H2S (g) NH4HS (s)

No solid

NH4 HS

PartialpressureH2S

0.1 0.2 0.40.3 0.60.5 0.7 0.80.9 1 2 3 4 5 6 7 8 9 10

Temperature45C40

C35

C30C

25C

20C

15C

10C

Partial pressure NH3

Partial pressure H2S (bar)

Partial pressure NH3(bar)

0.10.1 0.1

0.2

0.3

0.4

0.5

0.6

0.70.80.91

2

3

4

5

6

78910

0.2 0.40.3 0.60.5 0.7 0.80.9 1 2 3 4 5 6 7 8 9 10

0.2

0.3

0.4

0.5

0.6

0.70.80.91

2

3

4

5

6

78910

From H2S and NH3 gas as a function of temperature

H2S and NH3 partial pressures of the gas

DP

CD9

08B

Figure 2

POSSIBILITIES OF SOLID NH4HS FORMATION


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HYDROGEN FROMCATALYTIC

REFORMER

MP AND FUEL GAS

FROM AMINE WASHBUTANE

HCIREMOVAL

VAPORISATION

HYDRO-DESULFURATION

H2SREMOVAL

STEAM

REFORMING

CO

CONVERSION

CONDENSATERECOVERY

PSA

PURIFICATIONCONDENSED WATER

Hydrogen from PSA

PURGE GASTO FUEL

% Vol.78.9

5.2

14.5

1.4

H2

CH4

CO2

CO

100.0

% Vol.73.3

6.0

9.7

11.0

H2

CH4

CO2

CO

100.0

% Vol.

99.99

traces

H2

CH4CO2

CO

100.0

% Vol.

29.0

17.5

46.0

7.5

H2

CH4

CO2

CO

100.0

TO HYDROCRACKER

+ traces H20

+ H20

MP STEAM

22

340

t C

P bar

PRINCIPE OF HYDROGEN PRODUCTION PROCESS Figure 3

23

800

24

340

DP

CD2

002B 20ppm

2003 ENSPM Formation Industrie


25/27

REFORMERFURNACE

MPGENERATOR

REACTOR

Hydro

desulfurisation

HCI

ABSORBERS

CO

CONVERTE

R

Condensates

EA02

E04

F01

Gas

from

PSA

R04

B04

B05

R03B

R01B

R02

E03

E02

K01

M

B01

ToPSA

ToPSA

R0

1A

EA01

E

01

A-B-C

FG

FG

MP

steam

Vaporiser

R03A

Temperatures(c)

Pressures(bar)

Flowrate(t/h)

Waterandsteam

E05

08

H2S

ABSORBE

RS

H2

fromPSA

H2

fromCATALYTIC

REFORMER

HPFG

HPFG

LIQUID

BUTANE

RAW

H2toPSA

FG

44tube

sperrow

11burnersperrow

Steam

Steam

water

Preheater

water

DPCD1175A

HYDROGENUNIT

F

igure4

2003ENS



26/27

2003ENS


Stack

gases

STEAMREFORMING

FURNACE

C

atalyst

tubes

800C

25

bar

HYDROGEN

99.9

%

COconversionreaction

CO

+H2O

CO2+H2

CH4

6

H2

73

CO2

10

CO

11

100

%

CH4

6

H2

79

CO2

14

CO

1100

%

COconversionreaction

CO+H2O

CO2+H2

Steamreformingreaction

CH4+H2O

CO+3H2

CATALY

TIC

CONVER

SION

OFRESIDUAL

CO340C

20ba

r

HYDROGEN

PURIFICATION

(PSA)

FEED

SULFUR-FREE

LIGHT

HYDROCARB

ONS

HYDROGENPRODUC

TIONUNIT-STEAMREFO

RMING

F

lowscheme

Figure5

STEAM

(3t/t)

CH4

100%

Fuel

CO

CO2

CH4

DPCD316B


27/27

2003ENS


EDS

sbroken

vacuum

esidueb

itumen

sp.gr.15=1.169

6%wtsulfur

V=800

ppmweight

YGEN

1300

1450

Feed+

Carbon

32.5

BURNERS

(X2)

70

PS

A

68

HYDROGEN

99.5%

CO2

H

S

toCLAUSunit

E

LIMINATION

H2SandCO2

Purge

tofuel

gas

Figure6

H

Pregulatingsteam

28.6

40

SteamHP

i.e.60,000Nm3/h

66

WATER

WASHING

OFGASES

CONVERSION

OF

CO

CO

+H2O

CO2+H2

HYDROGENPRODUCTIONUNIT-

PARTIALOXIDATIO

N(POX)

P

roce

ssflowscheme

Separation

carbon-ash

2

From

"Petro

lesetTechniques"-Sept.-Oct.1994(TexacoProcess)

Tow

aste

watertreatment

Water

Water

Water

DPCD317B

Ash

+

m

etals

5.7

13.1

4

13. vacuum distillate.pdf

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