understanding o&g-mdso 801 (2nd vol)

8/13/2019 Understanding O&G-MDSO 801 (2nd Vol)

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uf o n

~; k ; k k f D r o

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U N I V E R

S I T Y

O F P E

T R O LEUM & E N E R

G Y

S T

U D I E S

MDSO - 801 (Vol. 2)

UNDERSTUNDERSTUNDERSTUNDERSTUNDERSTANDINGANDINGANDINGANDINGANDING

OIL & GAS BUSINOIL & GAS BUSINOIL & GAS BUSINOIL & GAS BUSINOIL & GAS BUSIN

COLLEGE OF MANAGEMENT AND ECONOMIC STUDIES (CMES)

EMBA - Oil & Gas Management


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Course Code: MDSO - 801 (Vol. 2)

Course Name: Understanding Oil & Gas Business

UNIVERSITY OF PETROLEUM & ENERGY STUDIES


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Unit 5 G a s P rocessin g ..................................................................................................... 1

Unit 6 P et roleum Refin ing ............................................................................................ 34

Unit 7 P et rochem ica l In du st ry ................................................................................... 101

A n n e x u r e t o Vo l u m e-2 .......................................................................................................... 140


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Unit 5 1Notes

Objectives After reading this unit, you will be able to:

Understand properties and the characteristics ofnatural gas.Understand the objectives for processing the gas andconfiguration of a gas processing complex.Get familiar with processing schemes for various gasprocessing units.Understand the technical aspects of LNG business

Characteristics of Natural Gas

Physical Properties

0Natural gas is gaseous at any temperature over -161 C0(258 F). Since that is a very cold temperature, we normally

consider natural gas as a gas. Natural gas boils at0atmospheric pressure and a temperature of -161 C,0exactly like water turns into a vapor (steam) at +100 C.

Natural gas is handled in a wide range of operating0conditions - as a liquid below -161 C (LNG) and also ascompressed gas at 200 Bar (3,000 psi) for automobile(CNG).

In its pure state, natural gas is odorless, colorless, andtasteless. For safety reasons, however, an odorant calledMercaptan is added, so that any leak can be easilydetected because of the typical smell.

Concept of Volume and Weight

The volume of natural gas is measured in cubic meters3(M ) or cubic feet (cu.ft. or cft)

3Its flow in M /hr or cu.ft./hr or cfh at operating condition.

The production figures are normally given in StandardCubic Meters per Day (SCMD) or Standard Cubic Feetper Day (SCFD).

Gas Processing


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NotesSince the quantity of gas per unit volume is highlysensitive to pressure and temperature of the gas, thevolumetric capacity is always referred to a standardreference temperature and pressure . In metric unit. 1SCMD means 1 cubic meter of gas at a standard

0condition of 0 C and 1 atmosphere pressure. Similarly 10SCFD means I cubic foot of gas at 60 F and 1 atmosphere

pressure.

One SCMD equals 37.8 SCFD.

3One cubic meter (SM ) of natural gas weighs roughly 0.83Kg. Comparatively one M of oil weighs about 800 Kg.

Because of large volume the gas occupies, itstransportation is more expensive than oil for equivalentweight.

For transportation across the seas, Natural gas iscondensed to LNG and put into marine tankers. Thisreduces the volume more than 600 times.

3That means 600 cubic meters (M ) of gas (which is

roughly 480 Kg) is made into 1 cubic meter of LNG.

The Composition of Natural Gas:

The composition of natural gas varies widely from onefield to the other. The main constituents of natural gas arethe lightest hydrocarbons i.e. Methane, ethane, propane,butane, and traces of heavier components like pentane.However, methane is generally the largest component.Methane is normally between 85% to 95% of the totalvolume. Other components like nitrogen, carbon dioxide,oxygen, hydrogen sulfide and traces of other gases can bepresent.

Hydrogen sulfide (H S) and carbon dioxide (CO ) are often2 2present in the gas. CO is corrosive to the pipeline and2equipment in presence of water. H S is both corrosive and2very toxic (hazardous to health). The range of compositionof natural gas has been presented in Unit 1 .

Understanding Oil & Gas Business


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3

Activity 5a

UNIT 5 Gas Processing

Important Physical Properties of Natural Gas

Calorific value of a hydrocarbon is measure of heatreleased by burning unit volume or weight of thehydrocarbon. Heavier the gas, lower is the calorificvalue per unit weight of the gas and higher the calorificvalue per unit volume of the gas.

Specific gravity of a gas is defined as the weight of agiven volume of the gas compared to the weight of thesame amount of air at the same temperature and pressure,where air weight is taken as reference (= 1).

Specific gravity of air = 1.00

Specific gravity of methane = 0.55

Specific gravity of natural gas = typically 0.60

Specific gravity of propane = 1.56

Specific gravity of butane = 2.00

This means that natural gas being lighter than air will rise if

escaping, thus dissipating from the site of a leak. Thisimportant characteristic makes natural gas safer than mostfuels.

Natural gas does not contain any toxic component;therefore there is no health hazard in handling of the fuel.Heavy concentrations, however, can cause drowsinessand eventual suffocation.

Chemical Properties

The air-to-fuel ratio (AFR) indicates the amount of airrelative to the amount of fuel used in combustion. Theminimum amount of air relative to fuel for completecombustion is called the stoichiometric ratio. Thestoichiometric ratio for natural gas (and most gaseousfuels) is normally indicated by volume. The air to naturalgas (stoichiometric) ratio by volume for completecombustion is 9.5:1 to 10:1 . This ratio is approximate onlybecause of the variations in fuel composition.

Estimate the specificgravity of methane andbutane.


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4

NotesThe Lower Explosive Limit (LEL) and the UpperExplosive Limit (UEL) determine the range offlammability. For natural gas, the LEL is 4%, while theUEL is 14%. It means that a natural gas mixture igniteswithin a range of 25:1 to 7:1 air-to-fuel ratio by volume. Bycomparison, a propane mixture ignites within a range 2%LEL to 10% UEL. It means a gas leaner or richer outsidethe explosive limits is not explosive.

Natural gas has a very high octane number ,approximately 130. By comparison, propane isapproximately 105, and gasoline 92 to 94 at best. Thismeans that a higher compression ratio engine can be used

with natural gas than gasoline. Indeed, many racing carsuse the high octane rating of natural gas to give them morepower.

Processing and Utilization

At the oil/gas fields, a number of processing steps are put inplace before the gas is sent to the consumer. Theseinclude:

separation to remove liquids (oil or condensate), andwater.

dehydration to minimize moisture,

compression to meet destination pressure and

if necessary Sweetening to remove Hydrogen sulfideand Carbon dioxide

The processing of gas needed in the oilfield has beendiscussed in Unit 4 .

The transportation of natural gas is normally done by longdistance cross-country pipeline ( Unit-8 ). When the cost oflaying a pipeline is prohibitive or it is not practicable due totechnical, socio-political or any other reason, gas isliquefied as LNG and transported over the high seas byLNG tankers.

The further processing of gas for its utilization andvalorization is described in this section.



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5

Activity 1aOverview of Gas Processing

Why Gas Processing

The purpose pf gas processing operation is three fold:

Removal of impurities like moisture, hydrogen sulfide,carbon dioxide etc. to make it suitable for transportationand consumer acceptability.

Liquefaction and recovery of hydrocarboncomponents like ethane, propane, LPG, generally bylow temperature refrigeration or cryogenic processes.These go as feedstock for petrochemical manufacture.

Liquefaction of the entire gas to LNG under0cryogenic temperatures (-160 C) for transportation

purposes.

A gas processing plant may be built to meet one or more ofthe above objectives. Now let us get an overview of the gasprocessing facilities in terms of block diagrams.

Removal of Impurities

The main impurities present in the gas are moisture,carbon dioxide, hydrogen sulfide, nitrogen, mercury.

Some of these need to be removed totally (to a few ppmlevel), while some need to be brought down inconcentration.

Gas Dehydration : The gas need to be dehydratedbecause -

Moisture causes corrosion in the pipeline particularlywhen carbon dioxide or hydrogen sulfide are present.

Also any condensation reduces pipeline efficiency.

Natural gas forms hydrates during low temperaturegas processing operations. As explained earlier,hydrates tend to choke or block the equipment.



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NotesGas Sweetening: Removal of carbon dioxide andhydrogen sulfide from gas is called gas sweetening. Gasbearing hydrogen sulfide is called acid gas.

Why carbon dioxide need to be removed:

Carbon dioxide corrodes pipeline and equipment

It forms ice during cryogenic processing

Why hydrogen sulfide need to be removed:

It is very toxic

It is highly corrosive

Mercury removal: In some of the gas fields, the gasescarry mercury. Removal of mercury is necessary as itdamages the steel equipment in gas processing.

Recovery of Hydrocarbons

The objective is to recover hydrocarbons like ethane,propane, butane by condensing them at very low

temperatures and then purifying by fractionation. The word'cryogenic' is used for low temperature processing.

The operating condition for recovery of the hydrocarbons ingas are:

0Recovery of NGL : +5 to 10 C at high pressure0 2Recovery of LPG : -35 to -45 C at 12 Kg/cm

0Recovery of Ethane : -65 to -75 C at 30 to 402

Kg/cm .Liquefaction of Gas

For liquefaction of gas for transportation purpose (LNG),0temperature below -160 C is required at atmospheric

pressure. During liquefaction normally LPG and ethane arerecovered when temperature levels mentioned above arereached. The remaining bulk of the gas, mainly methane, istransported as LNG. As mentioned later, LNG by itself is alarge and complex industry.



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7

Activity 1b

There could be processing at lower temperatures forhelium recovery or nitrogen rejection for gases containinghigh amount of nitrogen.

Essentially to recover any component, the gas need to bechilled to a temperature at which the component willcondense.

The flow diagram and brief description of the processes aregiven later.

An overall block diagram of the processing steps in a gasprocessing plant is given in Fig. 5.1.

Gas received from pipeline often comes along with 'slugs'of liquid (NGL). This is trapped in ' Slug catcher '. Theliquids are separated in the slug catcher. The gas is firstsweetened to remove H S (if it is a sour gas). Some amount2of carbon dioxide also gets removed along with H S. 2Normally H S is not allowed to be discharged into the2atmosphere. It is converted to sulfur in a sulfur recoveryplant. Sulfur comes out as a byproduct.

Gas is then compressed to the desired pressure anddehydrated to bone dry (below 1 ppm water) state forcryogenic processing. Presence of moisture in the gas cancreate hydrate formation. If cryogenic processing is notdone, dehydration requirement is still there, but lesssevere.

Cryogenic processing of the gas is then carried out forseparation of the hydrocarbons into

LPG for use as domestic fuel

NGL for sale to refinery or petrochemical plant

Ethane/propane mix as feedstock for petrochemicalplant

Methane is used to generate power or make fertilizersand other chemicals.


Search and describeONGCs gas processingfacility at Hazira andUran.


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8

Notes


F i g

. 5 . 1

G a s

P r o c e s s

i n g G

a s

S w e e

t e n i n g

G a s

C o m p r e s s

i o n

G a s

D e h y d r a

t i o n

S l u g

C

a t c h e r

F e e

d G a s

C o n

d e n s a

t e P r o

d u c t

D e w

P o i n t

C o n

t r o l

G a s

t o P i p e

l i n e

L o w

T e m p .

P r o c e s s i n g

S u l

f u r

P l a n t

S u

l f u r

P r o

d u c t

H 2 S , C

O 2

C o n d e n s a

t e

S t a b i l i z a t

i o n

C 5 +

C 5 +

L P G

C 2

L N G


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9

Notes


There are two possible ways the methane rich gas afterrecovery of heavy hydrocarbons is transported to the user:

Through pipeline

Converting the gas to LNG and exporting by marinetankers

If LNG is to be made, a deeper cryogenic process will be0needed to bring the temperature of the gas to -160 C. LNG

is normally exported after recovering the LPG out of thegas.

Part or whole of the gas can be sent by pipeline to theconsumers if transportation by pipeline is feasible. Beforesending to the pipeline, the gas is chilled to the lowesttemperature it will face in its route to the destination. Thishelps to drop out and separate the NGL or condensatewhich would otherwise drop off in the pipeline as liquids,reducing pipeline efficiency and capacity to transport thegas.

This process of chilling the gas to moderately lowtemperatures to prevent further condensation in thepipeline is called Dew Point Depression or Dew PointControl . Literally, it means processing to prevent formationof hydrocarbon dews in the pipeline due to cooling.

Condensates from various units of gas processing plant(C5+ components) are passed through separators to dropthe pressure and stabilize it. Condensate is sold to arefinery or a petrochemical feedstock. The refineries distillit as blending stock for gasoline and kerosene.

Condensate could be a good feedstock for thepetrochemical plant also for

cracking to olefins and

polymerization of the olefins to plastics.

Thus gas processing plant essentially prepares thefeedstock for further processing at refinery andpetrochemical plants.


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10

Activity 1 b


Process DescriptionGas Dehydration

There are two types of gas dehydration processes:

Adsorption Processes: These are solid bed processesusing reagents like Molecular Sieve or Alumina asadsorbents.

Absorption Processes: These use liquid absorbentswhich absorb the moisture from the gas.

Normally Absorption Process using liquid absorbents are

used in the oilfield dehydration of natural gas. In the oil/gasfield gas is saturated with water vapor. To prevent corrosionin the pipeline caused by moisture in presence of othercontaminants like carbon dioxide, the gas need to be driedto a level of moisture content of 7 lbs/Million StandardCubic Feet (about 120 ppm) . This is suitably achieved by

Absorption Process using Glycols as the reagent forabsorbing moisture from gas. Normally Tri-EthyleneGlycol (TEG) is used as the reagent. A flow diagram of theprocess is given in Fig. 5.2 .

Wet natural gas is introduced in the A bsorber (also calledContactor ) at the bottom and goes up through contactorplates in the column. It contacts lean glycol solution fed atthe top of the column and traveling down the column. Themoisture from the gas is absorbed by the glycol and the drygas leaves the absorber for further processing. The richglycol (glycol with absorbed water) is drawn from thebottom.

The rich glycol (glycol plus water) is then regenerated in a

stripping column at near atmospheric pressure using0heat to boil off the moisture at around 200 C.

The absorption column operates at high pressure (atpressure of the gas) in the range of 30 ata to 70 ata whilethe stripper is operated at near about atmosphericpressure. There is a heat exchange between rich glycoland hot regenerated lean glycol which reduces the energyrequirement in the stripper and cools the lean glycol beforeit is re-circulated to the absorber.


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Notes


F i g

. 5 . 2

G a s

D e h y d r a

t i o n

U s i n g

T E G ( G l y c o

l D e h y d r a t i o n

)

M o i s t

N a t u r a l

G a s H

y d r o c a r b o n

I n l e t

S e p a r a t o r

L i q u

i d s

t o T a n k

R i c h

G l y c o

l

A b s o r b e r

G a s

/ G l y c o

l

H e a

t

E x c

h a n g e r

D r y

N a t u r a l

G a s F

l a s h

G a s

t o

V e n

t , F u e

l , o r

S t r i p p i n g

G a s

L e a n

G l y c o l

P h a s e

S e p a r a t o r R

i c h G l y c o

l

S u r g e

T a n

k

R e

b o

i l e r

N a t u r a l

G a s

B u r n e r

E x h a u s t

F i l t e r

S t i l l

S t r i p p i n g

G a s

V e n t o f

f - G a s

G l y c o

l

C i r c u

l a t i o n

P u m p


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Notes


F i g

. 5 . 3

D r y

B e d

g a s

D e h y d r a

t i o n

W e

F e e d

G a s

F e e

d G a s

S e p a r a t o r

M o l e c u l a r

S i e v e

D r y e r s

M o l e c u l a r

S i e v e

B e d s

S p e n

t R e g e n e r a t

i o n

G a s

R e g e n e r a t

i o n

G a s P

r o d u c

t

O u

t l e t G a s

F i l t e r

C o n

d e n s e

d

L i q u

i d


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Activity 1d Gas Sweetening

Hydrogen sulfide, carbon dioxide and mercaptans can beremoved from natural gas by several processes. Thevarious processes for sweetening used are:

Amine as absorbents (shown here) utilizing monoethanolamine (MEA), di-ethanolamine (DEA), DGA.

MDEA (methyl di-ethanolamine) and MDEA basedproprietary amines (for all three - effectiveness varies forMercaptans) as absorbents.

Molecular Sieves (removes H S and mercaptans only)2

Batch processes such as Iron Sponge, Sulfa Check andChem Sweet (for H S removal)2

Physical solvents such as Sulfinol and Ifpexol

Membrane process to remove H S 2

The choice of sweetening process depends a number of

factors such as:

Hydrogen sulfide and carbon dioxide content

Specification of treated gas

Temperature and pressure of gas

Volume of gas

Requirement of converting the hydrogen sulfide to sulfur Gas sweetening using an amine solution is among the mostwidely used method. Fig. 5.4 represents a simple aminetreating facility. Sour gas is introduced in the absorber atthe bottom and goes up through contactor plates in thecolumn. It contacts lean amine solution (amine solution ofhigh concentration, free of H S and CO ) fed at the top of2 2the column and traveling down the column.



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NotesThe acid gas components, H S and CO , are absorbed by2 2the amine solution and the sweet gas leaves the absorberfor further processing. The rich amine (amine withdissolved hydrogen sulfide and carbon dioxide) is drawnfrom the bottom.

The absorption column operates at high pressure (atpressure of the gas) in the range of 30 ata to 70 ata whilethe stripper is operated at closer to atmospheric pressure.The temperature at the absorption column is close to the

0ambient temperature (30-40 C).

The rich amine is sent to a flash tank to drop the pressureand absorbed hydrocarbons exit as the flash-tank vapor.The rich amine flows through the lean/rich amine heat

0exchanger increasing the temperature to above 100 C.

Fine particles, resulting from wear and tear of the pipingand other equipment, collect in the amine solution, whichultimately lead to blocking and foam generation in thecolumn. So there is a amine filtration step before theregeneration in the stripping column.

The rich amine (amine with dissolved hydrogen sulfideand carbon dioxide) is separated (regenerated) in a laterstep using steam in the stripping column. From the top ofthe regeneration column mainly hydrogen sulfide andcarbon dioxide mixture with a little quantity of hydrocarbonsabsorbed by the amine come out.

The hot rich amine is stripped at low pressure removing theabsorbed acid gases, dissolved hydrocarbons, and somewater. Considerable amount of energy is required to stripthe amine. Heat is supplied by a firetube type reboiler. Thetemperature at the bottom of the stripping column can be

0over 200 C.

The stripped or lean amine is sent back through thelean/rich exchanger decreasing its temperature. A pumpboosts the pressure such that it is greater than the absorbercolumn. Finally, a heat exchanger cools the lean solutionbefore entering the absorber. The lean amine entering the

0absorber is usually 40 to 45 C.



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Notes


F i g

. 5 . 4

A m

i n e S w e e

t e n

i n g

P r o c e s s

S w e e

t G a s

A m

i n e

C o n

t a c t o r

A m

i n e

B o o s

t e r

P u m p

C h a r c o a

l

F i l t e r

A m

i n e

C o o

l e r

&

R e

f l u x

C o n

d e n s e r

A m

i n e

S t r i p p

i n g

S t i l l

A c

i d G a s

R e

f l u x

A c c u m u

l a t o r

R e

f l u x

P u m p

A m

i n e

R e

b o

i l e r

A m

i n e

F i l t e r

A m

i n e

F l a s h T a n

k

L . C .

R i c h / L e a n

H e a

t E x c

h a n g e r

S o u r c e : w w w . n

a t c o g r o u p . c

o m

A m

i n e

P u m p

S o u r

G a s


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Activity 1cLiquefaction and Recovery of Hydrocarbon

The objective is to recover hydrocarbons like ethane,propane, butane by condensing them at very lowtemperatures and then separating by fractionation . Asindicated earlier, the temperature to which gas need to bechilled depends on what we are trying to recover. LPG can

0be recovered by chilling to -15 to -35 C. To make the gas to0LNG, chilling is required belo -160 C. Condensation of part

of the gases takes place at these temperatures.Fractionation of the condensed liquid is carried out toseparate the components.

To chill the gas, refrigeration is required. There are threetypes of processes:

(i) Processes using refrigeration supplied by externalrefrigeration systems to chill the gas. Normallysome component of natural gas itself like ethaneor propane is used as refrigerant using conventionalcompression refrigeration equipment.

(ii) Processes using expansion of the gas itself to

attain cooling . Gas chills when its pressure isdropped just as it gets heated when it iscompressed. Turbo-expander process is used toexpand the gas while doing the work of driving aturbine like equipment called turbo-expander. Thusit attains cooling by losing its internal energy byexpansion as well by driving the turbo-expander machine.

(iii) Processes using a combination of external andinternal refrigeration.

A simple conceptual diagram of an external refrigerationprocess for LPG Recovery is depicted in Fig.5.5. Theimportant steps in the process are :

Natural gas coming from the source at high pressure isfirst dried in molecular sieve dryers.

It is then chilled by exchanging heat with the chilled gas


List down all gas LPGRecovery plants in Indiawith their location, owner and capacity.


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Notes


F i g

. 5 . 5

E x t e r n a l

R e f r i g e r a

t i o n

P r o c e s s

f o r

L P G R e c o v e r y

D R Y I N G

S Y S T E M

( M o l

S i e v e

)

H X R

C h i l l e r

F e e d

G a s

3 5 0 C

, 5 0 B a r

S a l e s

G a s

2 0 0 C

, 4 8 B a r s

P r o p a n e

R e f r i g .

S e p a r a t o r -

1

L i q u

i d s

f o r

f r a c

t i o n a

t i o n

- 3 5 0 C - 3

5 0 C S

e p a r a t o r -

2

- 1 5 0 C

2 0 0 C

L i g

h t

E n d s

L P G

N G L

F r a c

t i o n a

t o r


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Notes coming out after LPG Recovery.

0The gas is further chilled to around -35 C using externalpropane refrigeration package.

At each of the two stages of chilling there are separators0to collect the condensed liquids from the gas. At -35 C,

almost all C4 andC5+, most of C3 and some amount ofC2 and C1 components condense.

This liquid need to be fractionated to take the light ends(C1 and C2) out to meet the LPG specifications. LPG andC5s (NGL) are also separated by the fractionationsystem. Generally this is done in a series of twofractionating columns.

When C2 also need to be condensed and separated, lower0temperatures (-50 to -60 C)are needed and more than two

fractionation steps may become necessary. The lowertemperatures are obtained by expanding the gas to lowerpressures and by using external ethylene as refrigerant.

Lower temperatures can be achieved by using external

ethylene refrigeration cycle or by Turbo-expanderprocess shown in Fig.5.6 . The diagram actually shows acombination of external refrigeration and turbo-expander.The energy given to the turbo-expander is used to re-compress the outgoing gas. But due to the efficiency factorof turbo-expander process, it can be recompressed to apressure much lower than its original pressure.

By an appropriate combination of external refrigeration andturbo-expander process, very low temperatures can beobtained. The choice of the process depends on variousfactors like:

Pressure of the gas

Temperature to which the gas need to be chilled andcomponents to be recovered

Pressure requirement of the outgoing gas by thecustomer.



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Activity 1dThe LNG Cycle

Natural Gas is a highly desirable energy source: it burnscleanly, with little pollution, it is often inexpensive toproduce and can be transported easily through pipelinelike any other petroleum product. The demand for naturalgas is growing at a fast pace as a source of energy andpetrochemicals.

At present, however, the technology does not exist to buildlong distance pipelines through the depths of the ocean.So moving natural gas between continents requires analternative approach.

Conversion of natural gas to Liquefied Natural Gas (LNG) is a proven commercial technology for transportinglarge volumes of natural gas across oceans by marinetankers. The utility of liquefying Natural Gas is thesubstantial volume reduction gained by liquefaction(1:620 ). This volume reduction makes the transportationand storage of the gas much more convenient.

Typical composition and characteristics of LNG is

presented in Table- 5.1


Table 5.1LNG Characteristics

LNG Composition (Typical Mol %)

N 01.0 %2Methane 85.1 96.7 % (Lean)Ethane 1.9 8.6 % (Rich)Propane 0.68 4.1 %i- Butane, nButane TracesMol. Wt. 16.8 19.3 (Rich)

3

Gross Heating Value 10.450 Kcal/NMS. G. 0.455

Methane in Natural Gas does not liquefy under pressure. To makeLNG Natural Gas must be liquefied through refrigeration.

Becomes liquid at -160 deg C at atmospheric pressure.

Volume reduces by 620 times when liquefied.

Spilled LNG will crack a steel plate like boiling water hitting frozenglass.

Identify the major producers of LNGin the world and themajor importers.


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Notes


The LNG industry is economic when liquefaction and thetransportation of LNG is done in very large volumes (sayabove 5 Million SCMD and above). This involves a numberof major investment and contractual activities including

Liquefaction by the producer of the gas

Storage facilities at producer end

Loading in tankers and Transportation

Receiving/unloading terminal and storage at buyersend

Re-vaporization of LNG to gas, and

Distribution to the consumers with a cross countrypipeline network.

This is depicted in Fig. 5.7 and is known in the industry asThe LNG Cycle . This was developed for conceptualizingone of the LNG projects planned with the LNG Receivingterminal planned in the eastern coast of India. This would

involve buying of LNG from one of the South East Asiancountries or Australia Fertilizer plant and power plant,which are large consumers of gas was proposed to beinstalled near the receiving terminal. The balance gas wasproposed to be transported by pipeline with a northern gridof pipeline and a southern grid to various parts of India.Themagnitude of investment in such a project is very large .

The facilities at the producer end of the cycle is called LNGupstream and the buyer end is called LNG downstream .

LNG upstream comprises of gas treatment andliquefaction steps as explained earlier in this section alongwith LNG loading facility for loading in marine tankers. Thisis shown schematically in Fig. 5.8.

The down stream section comprises of unloading fromtankers, storage, pumping, re-vaporization, andtransportation by pipeline. This is shown schematically inFig. 5.9.


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Notes


F i g

. 5 . 7

T h e

L N G C y c

l e

L N G

S O U R C E

T A N K E R S

P O R T

T E R M I N A L

S t o r a g e /

V a p o r i z a

t i o n

F e r t

i l i z e r

P l a n

t

P o w e r

P l a n

t

C r o s s

C o u n

t r y

P i p e l

i n e

( T o

N o r t

h )

C r o s s

C o u n

t r y

P i p e l

i n e

( T o

S o u

t h )

P h a s e

-

I

P h a s e

-

I I

P

e t r o c h e m

i c a l

P l a n

t

F e r

t i l i z e r

P l a n

t

P o w e r

P l a n

t


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24

Notes


F i g

. 5 . 8

L N G U p s t r e a m

F e e d

G a s

f r o m

O f f s h o r e

C O

2 + H

2 S

L N G

S t o r a g e

L o a d

i n g

L i q u i d s

L N G

S u

l f u r

T r a i n 2

T r a i n 3

T r a i n 1

R e c e i v i n g

S t a t i o n

A c i

d G a s

R e m o v a

l

D e h y d r a t

i o n

M e r c u r y

R e m o v a l

C h i l l i n g

a n d

L i q u e

f a c t

i o n

S u

l f u r

S t o r a g e

L o a d

i n g

L P G

C o n d e n s a

t e

F r a c t

i o n a

t i o n

S u l

f u r

R e c o v e r y


29/156

25

Notes


L N G T a n

k

L N G T a n

k

H P P U M P

V a p o r i z e r

B O G

C o m p r e s s o r s

R e t u r n

G a s

B l o w e r s

F l a r e

/ V e n

t

R e c o n d e n s e r

V a p o r

R e t u r n

A r m J

E T T Y

V a p o r

R e t u r n

A r m J

E T T Y

F i g

. 5 . 9

L N

G D o w n s t r e a m


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26

Notes

Storage of Liquefied Gases

Storage and handling of gases is dealt with in latersections. But it is important to know at this stage that thereare two ways liquefied gases are stored;

Pressurized storage where gas is in liquid phase underpressure at ambient temperatures.

Cryogenic or low temperature storage (generally atatmospheric pressure)

LPG is often stored in pressurized containers although it isalso stored under cryogenic conditions. Fig. 5.10 showstwo types of pressurized LPG storages - sphere and bullet.

LNG is always stored under cryogenic conditions (below0-160 C) at atmospheric pressures. At such temperatures,

steel becomes brittle like glass. The storages are made ofspecial nickel steel as normal steel becomes brittle at thatlow temperature.

They are heavily insulated to minimize heat leakage from

the atmosphere into the tank. They are often double walledwith concrete outer shells utilized as additional resistanceto tank damage and as containment in the unlikely event oftank leakage. This type of tank with containment of leakageis the most costly, and has most often been used for thestorage of LNG.

Some leakage of heat do take place from the surroundingatmosphere into the storage tanks. There is some amountof liquid vaporization and boil-off. The vapors are

compressed, condensed by refrigeration and put back intothe tank.

The tankers carrying LNG also have spherical domedstorage tanks along with refrigeration system for boil-offvapors.

LNG tanks could be on ground or mounded under earth.Fig. 5.11 depicts an LNG receiving terminal with an LNGtanker, jetty and LNG storage facility.


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27

Notes

Fig. 5.10LPG Storage

Fig. 5.11LNG Receiving Terminal

The LNG tankers can have a carrying capacity from 20,000cubic meter to 135,000 cubic meter. A large LNG storagetank can be holding around 100,000 cubic meters of LNG.For this capacity, the tank would be about 70 meters indiameter. Japan is the world's largest importer of LNG andimports 94% of its gas as LNG.


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28

Notes

LNG Project Economics

Basic gas price at source for LNG facilities are relativelycheap varying around US$ 3 per Million BTU of energyequivalent, based on large and easily produced reserves.Processing (Liquefaction) and transportation equipment iscapital intensive and highly specialized, requiring largeinvestment for each new facility. For each million cubic feetof gas delivered to end use, less than 30 percent of the costis associated with the raw material price (gas price atsource). The balance is the cost associated withprocessing and transportation.

The investment cost of a LNG chain (production,shipping, re-vaporization) for 10 Million SCMD of naturalgas per year would be approximately 3 billion US Dollars.

Re-vaporization plant costs are considerably lower thanliquefaction plant costs. Approximate breakdown of thecost would be:

Liquefaction US Dollars 1.5 BillionShipping US Dollars 0.8 Billion Re-vaporization US Dollars 0.7 Billion.

Liquefaction is a very energy-intensive process. Typically,about 8 to 9 percent of the natural gas delivered as rawmaterial at an LNG plant, is used as plant fuel forliquefaction . The number of tankers required is a functionof the distance between the export terminal and the importterminal and the number of days it takes to move betweenthe source of gas and destination. The unit cost of marinetransport is primarily a function of the capital cost of thetanker, distance, the financing terms and acceptable rate ofreturn for the tanker owners.

Complexity of an LNG Project

The complexity of a LNG project (ref: Fig.5.7, LNG Cycle )is due to:

Sheer size of the project. Liquefaction, transportationand re-vaporization of LNG can be economic at a verylarge capacity, at least 5 to 10 Million SCMD. Thisrequires investment on billions of Dollars.


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29

NotesLarge number of 'operations blocks' or projects ofdiverse technologies need to be developedsimultaneously, integrated and planned together. Forexample Liquefaction plant, Loading facilities,Unloading facilities and re-vaporization facility alongwith large consumers have to come up simultaneously.

Numerous locations covering countries and states.

Numerous agencies, consumers involved.

Market Development for the LNG by the buyer.

Strong technology base and support required.

Numerous contract negotiations.

Long Term Contract between LNG supplier andbuyer.

Long Term Contract between LNG buyer andtransporter.

Long Term Contracts between LNG buyer and LNGusers like Power Plant, Fertilizer Plant etc.

Because of enormous effort required on planning anddevelopment of the project and numerous contractinginvolved, the gestation period of an LNG based grass-rootsproject is normally quite long (4 to 6 years).

Due to the immense costs of each link in an LNG cycle,such projects can be undertaken only by largeorganizations with great financial capacity and projectmanagement skills. A successful project requires

cooperation and selling of the idea to:The government of the country having gas source

The company that owns the natural gas

The government in the consuming country

Consuming organizations

Financiers


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30

NotesThe Indian Scenario

Recovery of LPG and Petrochemical Feedstock

Gas processing facilities in India started with thecommissioning of ONGC s Uran gas processing facilitieswith capacity of processing 4 MMSCMD of gas to producearound 200,000 tons per year of LPG . This was based ongas from Mumbai High as feedstock, Uran at Mahrashtrabeing the first onshore terminal. Later Uran was expandedto more than double the capacity and ethane along withpropane was recovered from the gas to provide feedstockfor a petrochemical complex (Mahrashtra Gas Cracker

Complex at Nagothane). Later with a bigger gasprocessing terminal at Hazira, ONGC became a majorproducer of LPG. Currently ONGC is producing over 1.2Million Tons per year of LPG.ONGC produces close to 1million tonnes of LPG at its Uran and Hazira terminals.

Another 175,000 tons are produced at Ankleshwar andaround 60,000 tons are produced at Gandhar.

Another major player emerged once Gas Authority of IndiaLtd (GAIL) was formed to transport and distribute the gas.

A number of LPG plants were built along HBJ Pipeline.Currently GAIL has extensive network of gas pipelingasprocessing complexes to produce LPG, and one toproduce propane as feedstock for a petrochemicalcomplex. It also own a petrochemical complex based onfeedstock it generates from its own gas.

The facilities of GAIL is presented in Table - 5.2.Table - 5.2

Pipeline and Gas Processing Facilities of GAILGas Pipelines 4700kms

(100 MMSCMD Capacity)

LPG Pipeline 1265 Kms(2.5 MMTPA Capacity)

Gas Processing Plants 737 MMSCMD1 MMT / Annum LPG

Petrochemical Complex 3,00,000 TPA Ethylene1,00,000 HDPE1,60,000 LLDPE / HDPE


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31

NotesLNG Facility

As indicated in Unit-2 , there is a large gap betweendemand and supply of gas in India. In the ninetiesambitious plans were drawn out by the government as wellas private sector Indian and Multinational companies toimport LNG and build LNG terminals in India. Thegovernment facilitated formation of Petronet LNG Ltd. inthe public sector to lead the drive to import LNG and boostgas supply in the country. Most of the plans have notmaterialized.

As stated earlier, the success of LNG projects depends ona number factors: reliable and continuous supply of LNG inlarge volumes, constant technological support, reliablelong-term market demand and ability to finance. Many ofthe companies who intended to enter into the LNGbusiness, has got into such detailed planning. As a result,most of the LNG projects planned have failed to take off.

The first LNG terminal in India was built by Enron for itsDhabol power plant .

The next LNG projects that are likely to see the light of theday are the projects of Petronet LNG and Shell . PetronetLNG project at Dahej is ahead of another LNG project beingimplemented by Shell at Hazira.

With the Dahej LNG import terminal nearing completionand expected to be commissioned by December 2003.Five million tonne gas (20 million metric standard cubicmetres) will be supplied to users along HBJ Pipeline.

Shell LNG project , which will be completed by December2004 will improve the prospect of significant augmentationof gas supply in the country.

The large discovery of gas in 2002 off Andhra Coast byReliance and ONGC`s discovery at Vasai and near Suratare expected to give further boost to the gas supply and gasprocessing industry.

It should be noted that India being LNG importing country,the LNG facilities planned fall under the category of LNGupstream. For the import of LNG, the long term tie-ups arewith producers in the Middle East.


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NotesSummary

Basic properties and characteristics of natural gas wasdescribed in the beginning.

This was followed by highlighting the need or objectives ofprocessing natural gas - namely - removal of impurities andseparation of the components of gas.

Various processes used in gas purification was decsribedwith simple flow diagram. The importance of gasdehydration and gas sweetening was highlighted.

Liquefaction of the gas to LNG and separation of variouscomponents of gas were described with simple flowdiagrams. Various methods of getting low temperatures forcondensation of gas was described.

The LNG cycle was defined. The costs involved in an LNGproject and the complexity of such a project washighlighted.

A brief description of gas processing industry in India was

given at the end.

Review Questions

(1) What are the objectives of gas processing? Name thevarious gas treatment or purification processes.

(2) Write down a brief description of gas dehydrationprocess with simple flow diagram.

(3) Write down the approximate levels of temperaturerequired to recover ethane, LPG from natural gas. Howthese temperatures are obtained. Describe a lowtemperature LPG Recovery process with flow diagram.

(4) What do you understand by an LNG Cycle. Describewith a schematic diagram.

(5) Describe upstream and downstream of LNG facility.


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33

Notes

Category Question Answer

Tr ue or False Natural Gas is a major ingredient inplastics.

Short Answer What are the 2 most abundantelements in natural gas ?

True or False The dominant component in naturalgas is Ethane

Short Answer Name four major hydrocarboncomponents in natural gas.

True or False Gas containing Nitrogen is called Short Answer Gas containing Hydrogen Sulfide is

calledShort Answer What is associated gas?

Short Answer Name 3 ways that gas istransported

Short Answer What is C3H8

Short Answer What is LEL

Short Answer What is the property of CNG orgasoline thatIndicates its performance asautomobile fuel?

True or False NGL contains mainly methane

True or False Natural Gas is highly toxic

Short Answer List four uses of natural gas

True or False Sweet gas contains high levels ofsulfur.

True or False Methane is heavier than air

True or False Natural gas has strong smell

True or false CNG is used as feedstock forpetrochemicals

Objective Type Questions


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Unit 6 34Notes

Objectives After reading this unit, you will be able to:

Understand the important specifications of petroleumproducts and their significance.Get familiar with the refinery process configurationsused to meet the specifications and market demand.Understand the basic process schematics of importantprocesses used in a refinery.Understand the infrastructure requirement and broadeconomics of refinery operation

Why Refining

What does a petroleum refinery do? Why do we needrefining? In a nutshell the main functions of a refinery are:

Primary Separation: Crude oil is a mixture of around 500components. They need to be separated into usefulproducts. The separation is not done to recover individual

components but as products which are mixtures of suitableboiling ranges. This is done by distillation, where variouscuts or fractions are taken out as gasoline, kerosene,diesel etc. which are essentially raw material orintermediate products.

Processing to Meet Quality Specifications: Typicalexample of this type of processes are those used forimprovement of octane number to meet gasolinespecification. Raw gasoline cut or naphtha as it comes outof distillation has low octane number (may be around 40 to60 ON). But for the market we need octane numbers of 87and above. Processes are used to improve the octanenumber by converting the low octane components ofgasoline to high octane components. For exampleCatalytic Reforming process convert straight chain paraffinin the raw gasoline to aromatics which have high octanenumber. Similarly isomerization process converts normalparaffin components of naphtha to iso-paraffins whichhave higher octane number.

Petroleum Refining


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35

Notes


F i g .

6 . 1

R e f

i n e r y

U n d e r

C o n s t r u c t

i o n


40/156

F i g .

6 . 2

R e f

i n e r y

C o m p

l e x

f r o m

D i f f e r e n

t A n g

l e s

36

Notes

UNIT 6 Petroleum Refining


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37

NotesProcess ing to Mee t Env i ronmen t Re la t edSpecifications: The most common processes of this typerevolve around removal of sulfur. Typical process units areHydro-desulfurization of kerosene and diesel oil to meetthe sulfur related specifications in the product.

Conversion of Residual Products: The residues orheavy cuts from the distillation or other process units of arefinery can not be used as value added product likegasoline or diesel. Molecules of such stocks are broken intolighter molecules to get products like diesel or gasoline byconversion processes called cracking .

Finishing and Blending Operations: This step involvesgetting the product in finished form by treatment to get goodmarketable color, blending with intermediate products fromthe refinery, putting additive to enhance certain properties.

Product Specifications

Quality Related Specifications

Since most of the operations in the refinery are to meetcertain specification of products, it is necessary to know ofcertain important specifications and their significance.Normally each country has its own institutions to define thestandards and specifications. There are several items ofspecifications for each product. The more important headsare stated below. The detailed specification of some of theproducts as per Indian Standards Institution (ISI) are givenin the Annexure. There are standard laboratory proceduresand methods under controlled conditions to measure thesespecifications for a product.


Table 6.1Important Specifications for Main Refinery Products

No. Refinery Product Specification1 LPG Vapor Pressure at 65

o C, Propane content

2 Gasoline Octane No., Boiling Range, Sulfur, Aromatics3 Naphtha Boiling Range4 Kerosine Smoke Point, Flash Point, Sulfur 5 Jet Fuel Freezing Point, Flash Point, Boiling Range6 Diesel Oil Cetane No., Carbon Residue, Pour Point, Flash Pt7 Lubricating Oil Viscosity, Viscosity Index, Carbon Residue


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38

Notes


Vapor Pressure: It is a very important property of LPG forsafety and handling, particularly as it is handled at home ascooking gas. It restricts maximum pressure a cylinder candevelop and helps to set the design pressure for thecylinder. Propane being more volatile of the otherconstituent (butane) of LPG, it can develop more pressureand hence its content in LPG is limited by specification.

Flash Point: It is the minimum temperature at which theproduct generates enough vapor to form an explosivemixture with air.

Flash point is significant to the safety during storage. During

storage it can form explosive mixture in the empty part ofthe tank above the liquid surface. It is preferable to store aproduct below its flash point. Each country has its ownspecification of flash point depending upon the climaticconditions of the country.

Octane Number (ON or O.N.): This signifies ignitionquality of the gasoline in automobile engines. The enginehas cylinders with pistons where the fuel (gasoline) and airmixture is injected. The cylinders of an automobile pass

through a cycle of expansion, compression and ignition formovement of the pistons, which drive the wheels through acrankshaft. For optimum delivery of power to the engine,the fuel air mixture injected to the engine should ignite at theright timing. Due to heat of compression, the temperature inthe cylinder goes high and there could be mistimed ignitionof the fuel due to the heat generated by compression. Ahigh octane gasoline, is better for ignition. A mistimedignition creates knocking in the engine and this results inloss of power.

The different hydrocarbon content in gasoline (like in crudeoil) are straight chain paraffin, iso-paraffins, naphthenesand aromatics. Normally for the same carbon number andsize of the molecule straight chain paraffins have the lowestoctane number . Branched chain paraffins (isomers),naphthenes have the higher octane number . Olefins also have high octane number but they are undesirable ingasoline because they tend to polymerize to form resins orgum in the tank.


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39

Activity 6aTypical octane number of various constituents are given inthe table below.

Octane Number (ON) is defined as the percent volume ofiso-octane in a mixture of iso-octane and normal heptanethat gives the same knocking as that of the fuel whentested under defined conditions.

Iso-octane is assigned a value of 100 and normal heptaneis given the value of zero. Other octane numbers emergeas relative ignition quality or anti-knock quality of thecomponent.

Aromatics : Although it has high ON, its content in gasolineis being limited by specification due to its carcinogenicnature.

Pour Point: When heavy petroleum products like fuel oil ordiesel containing wax are cooled to certain temperatures,the wax separates out from them making the oil immobile. Itbecomes difficult to move or pump the oil. The temperatureat which the oil becomes immobile is termed as pour point.It happens because separated wax forms honeycomb likestructures.

High wax crude oils like Mumbai High have high pour pointO(30 to 35 C). Many of the South East Asian crude oils have

high pour point.


Table- 6.2Octane Number of Some Hydrocarbons

Carbon Number

Hydrocarbon

Octane No.

C6 Straight Chain n-Hexane 24.8C6 Isomer Methyl Pentane 73.4C6 Isomer Dimethy l Butane 91.8C6 Naphthene Cyclohexane 83C6 Aromatic Benzene 98C7 Paraffin n-Heptane 0C7 Isomer Dimethyl Pentane 88C8 Isomer Iso-Octane 100

C7 Aromatic Toluene 107

Search and list downcurrent Indian specifica-tions on sulfur contentof diesel oil.-


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40

NotesBoiling Range: The volatility of oil is indicated by its boilingrange and distillation characteristics. The oil should havesuitable boiling range (volatility) so that it can be used in aparticular application. For example, Motor Gasoline hascertain boiling range specifications.

In case of naphtha, a specific boiling range is chosen foruse as feedstock for petrochemical plant. For examplearomatics like Benzene, Toluene and Xylene are goodfeedstock for petrochemical manufacture. A boiling rangeof naphtha is chosen where concentration of thesecomponents will be high.

Smoke Point : It is the length of flame in a standardlaboratory test, which produces smoke. It is an importantproperty of kerosene. Smoke point depends on the type ofhydrocarbon constituents of the fuel. Paraffins have highsmoke points followed by naphthenes and then byaromatics. Higher smoke point means less smoky.

Cetane Number: While the octane number indicatesignition quality of engines using spark ignition (gasolinefuelled cars), this test is applicable to diesel fuels which use

ignition by compression.

Cetane number is defined as the percent by volume ofn-cetane in a mixture of n-cetane and alpha methylnaphthalene that would give the same ignition quality andengine performance as that of the fuel under test.

This test has reverse characteristics of octane number ,which gives low value to fuels which self ignite easily.Unlike octane number, normal paraffins have higher

cetane number followed by naphthenes, iso-paraffins,olefins and aromatics .

Sulphur: Sulphur is corrosive to the fuel systems and alsois a pollutant to the environment. The specifications onsulfur content in petroleum products are becoming moreand more stringent world wide. Sulphur specification isapplicable to all products. Considerable investments aretaking place every year in the refineries to improve sulfurrelated specifications..



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41

Notes Viscosity: Viscosity is the resistance to flow. It indicatespumpability of the product. Viscosity is an importantproperty for lube oils because higher viscosity is required toprevent wear and tear in the moving parts of a machine. Forfuel oils, it gives flow properties which are needed for pumpselection for transporting.

Viscosity is measured in several ways. The most commonunits are centi-stokes (cst), centi-poise (cp) and SSU(Saybolt Seconds Unit).

Viscosity Index: This specification signifies change ofviscosity with temperature. This is an important

specification for Lubricating oils. In the machinery, frictiongenerates heat. For any petroleum product, viscosity islower as the temperature increases. The lube oil viscosityshould not go down too much with heating as it will lose itslubricating property. Higher the Viscosity Index less is theeffect of temperature on viscosity.

Carbon Residue: Fuel as it burns, forms a carbon deposit.This carbon deposits on burner tips or cylinders reducesefficiency. Carbon residue test gives an indication of the

amount of carbon that would form when the oil is crackedand burned.

There are several other specifications like color, coppercorrosion test, bromine number etc. all of which have somesignificance on the quality of the products.

More details about the specifications are given in theannexure at the end of this volume.



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42

NotesRefinery Processes Overview and History

Types of Processes

Refining comprises of four types of processes:

Primary Separation: The first step in refinery isatmospheric and vacuum distillation of crude oil. Variousproduct cuts or fractions like LPG and gasoline come outof the top of distillation column. The medium heavyliquids like kerosene, ATF and diesel come out next inthe lower part of the column. The residue left is vacuumdistilled to separate heavier liquids, called gas oils .These products do not meet the specifications. To meetthe specifications they require further processing. Forexample some of the gas oil from vacuum distillation formbase stock to make lubricating oil for further processing.Other products are also treated to meet certainspecifications. For acceptance as high-value products,such as gasoline, much more additional processing isrequired as given below.

Conversion Processes: Conversion processes are

essentially breaking and rearranging of the molecules ofthe intermediate products to convert them to high valueproducts meeting specification. We can put suchprocesses in two sub-groups:

(a) Product up-gradation: Certain productslike gasoline are processed to meet octanenumber or other specifications. Example ofsuch processes are ca ta ly tic re forming,isomerization etc. These processes areessentially restructuring of molecules to

improve the specifications.

(b) Conversion of heavy residues to lightproducts: This is done by cracking of thelarge heavy molecules into smaller andlighter molecules under high temperature,and pressure with or without a catalyst. Thecracking processes covert residues andheavy gas oils to light products like gasoline,kerosene and diesel resulting in value addition.



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43

Activity 6 bTreatment Processes: To meet environment relatedspecifications and for giving finish to the products furthertreatments are required. This is the final step before theproducts are tested to meet quality and dispatched bytanker or pipeline to the market. Example of suchprocesses are Hydro-desulfurization of distillationproducts to remove sulfur , Sweetening of gasoline toremove traces of sulfides, Hydro-finishing of lube oil togive right color with mild hydrogenation.

Processing for Lube Oils: Processes to remove wax,asphalt etc. from the lube oil base stocks to meet thequality requirement of lubricants.

Processes for making lube oil is made into a distinctcategory because lubricating oils can not be produced fromall types of crude oils. When a crude oil is suitable forproducing lubricating oil, specific cuts called lube oil basestocks are distilled during primary separation step andpasses through a series of processes to make lube oil.

A common terminology used for a refinery, which does notproduce lube oils, is Fuels Refinery . One which produceslube oil is called Lube Refinery .

History

Let us trace the history of development of the variousprocesses in the refining industry ( Table 6.3 ).

It can be seen from the table that at first only separationprocesses were used. Then came gasoline upgradationprocesses to meet motor gasoline specification andconversion of heavies to lighter products like gasoline to

meet the increased demand of light products. Finally thedrive was environment related specifications - processesto meet strict specification on sulfur, and otherspecifications like aromatic content and lead removal etc.

As we can see from Table 6.3 , almost all the currentprocessing in the refineries came into existence by thefifties. Later the changes and innovations were relatedmainly to minimizing residues in the refinery and to meetsulfur and other environment related specifications.


Search and list downall the process units in Reliance Refineryat Jamnagar


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44

Notes


T a b l e

6 . 3

H i s t o r y o f

R e f

i n i n g

I n i t i a l l y

d e v e

l o p e

d t o c r a c

k h e a v y r e s i

d u

a l f u e

l t o

r e d u c e

i t s v

i s c o s

i t y .

L a

t e r

f u r t

h e r

d e v e

l o p e

d

t o

i n c r e a s e

g a s o

l i n e

p r o

d u c t

i o n

w i t h

e x p a n s

i o n

o f

A u

t o m o

b i l e i n d u s

t r y .

D e v e l o p m e n

t i n t h i s p e r i o

d w a s m o s

t l y a u

t o m o

b i l e

i n d u s t r y

d r i v e n . T

h e

b o o m

i n a u

t o m o

b i l e i n d u s

t r y a n

d

i m p r o v e

d ,

m o r e

p o w e r f u

l e n g

i n e s r e s u

l t e

d

i n

i n c r e a s e

d d e m a n

d o

f g a s o

l i n e a n

d h i g h e r o c

t a n e

n u m

b e r r e q u

i r e m e n

t . D e m a n

d f o r a v

i a t i o n g a s o

l i n e

w i t h v e r y

h i g h o c

t a n e n u m

b e r

( o v e r

1 0 0 O

. N . )

a n

d n e e

d f o r

b e

t t e r q u a

l i t y o

f l u b r i c a

t i n g o

i l s f o r

t h e

e n g

i n e s a

l s o c r e a

t e d d r i v e

f o r n e w p r o c e s s e s .

H i g h e r

O . N .

g a s o

l i n e ,

a v

i a t i o n g a s o

l i n e ,

k e r o s e n e ,

d i e s e

l ,

l u b r i c a

t i n g o

i l s , b

i t u m e n .

N a p

h t h a ,

t a r ,

f u e

l o i l ,

l u b r i c a

t i n g o

i l ,

f e e

d s

t o c

k f o r c r a c

k i n g

I n c r e a s e

d p r o

d u c

t i o n

o f

g a s o

l i n e .

N a p

h t h a ,

t a r ,

f u e

l o i l

Y e a r s

P r o c e s s

D r i v i n g F o r c e s

P r o d u

c t s

1 8 6 0

1 8 7 0

1 9 0 0

1 9 3 0 t o 1 9 4 0

A t m o s p

h e r i c

D i s t i l l a t i o n

V a c u u m


T h e r m a

l C r a c

k i n g

S u

l f u r r e m o v a

l p r o c e s s e s ,

p r o c e s s e s

f o r

i m p r o v e

d q u a

l i t y

o f l u b e o

i l ( D e w a x i n g ,

S o

l v e n

t

E x

t r a c t i o n

) , G a s o

l i n e q u a

l i t y a n

d

d e m a n d

d r i v e n

p r o c e s s e s

( C a

t a l y t i c

C r a c

k i n g ,

A l k y

l a t i o n ,

P o

l y m e r

i z a

t i o n

)

D i s t i l l a t i o n w a s u s e

d t o s e p a r a

t e f u e

l , l i g h t o i l s a n

d t a r .

N o

f u r t h e r p r o c e s s

i n g w a s r e q u

i r e

d .

L u

b r i c a n

t s w e r e

d i s t i l l e d o u

t u n

d e r v a c u u m

t o m e e

t

t h e

l u b r i c a

t i n g o

i l r e q u

i r e m e n

t s f o r

t h e m a

c h i n e r i e s .

L a

t e r i t w a s

d e v e

l o p e

d t o g e

t f e e

d s

t o c

k f o r

t h e r m a

l

c r a c

k i n g

( C o

k i n g

) .


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T a b l e

6 . 3 ( C o n

t d . . )

H i s t o r y o f

R e f

i n i n g

S t r i c t e r s p e c

i f i c a

t i o n s

o n

s u l f u r c o n t e n

t f o r a

l l

p r o

d u c

t s ,

c o n c e r n

f o r e n v

i r o n m e n

t a n

d

r e g u

l a t i o n s

o n e n v

i r o n m e n

t r e s u

l t e

d i n a

l o t o f i n v e s t m e n

t o n s u c

h

p r o c e s s e s .

T h i s

m a

d e

r e f i n e r y

o p e r a

t i o n s

n o n -

p r o

f i t a b l e

. R e s

t r i c t i o n o

f a r o m a

t i c s

i n g a s o

l i n e

l e a

d t o

g r e a

t e r u s e o

f o t h e r o c t a n e

b o o s

t i n g p r o c e s s e s .

T h e

i n v e s

t m e n

t s t o m e e

t q u a

l i t y a n

d e n v

i r o n m e n

t

s p e c i f i c a

t i o n s m a

d e

t h e o p e r a

t i o n o

f a s

t a n

d - a

l o n e

r e f i n e r y u n e c o n o m

i c .

I n c r e a s e

d a m o u n

t o f

l i g h t

p r o

d u c

t s

H i g h e r

q u a

l i t y

a n

d

e n v

i r o n m e n

t f r i e n

d l y f u e

l s

f o r a u

t o m o

b i l e

. I n c r e a s e

d

s u

l f u r p r o

d u c

t i o n

a n

d

h y

d r o g e n

d e m a n

d

i n

a

r e f i n e r y .

I n c r e a s e

d

p r o

d u c t

i o n

o n

p e

t r o c

h e m

i c a

l f e e d s

t o c

k

a n

d

i n t e g r a

t i o n

w i t h

p e

t r o c h e m

i c a

l u n

i t s .

L e s s o

f f u e

l o

i l , m o r e o

f

w h i t e P r o

d u c t s ,

p e

t r o c

h e m

i c a

l f e e

d s t o

c k

.

Y e a r s

P r o c e s s

D r i v i n g

F o r c e s

P r o d u

c t s

1 9 4 0 t o 1 9 6 0

1 9 7 0 o n w a r d s

1 9 6 0 t o 1 9 7 0

1 9 9 0 o n w a r d s

D e e p e

r

s u

l f u r

r e m o v a

l

i n t e g r a

t i o n

o f r e

f i n e r y

w i t h

p e

t r o c

h e m

i c a

l a n

d

o t h e r

i n d u s t r i e

s .

G r o w t h

a n

d

i n v e s t m e n

t s

t i l l a u

t o m o b i

l e

i n d u s

t r y

d r i v e n .

F u r t

h e r

d e v e

l o p m e n

t o

f s u

l f u r r e m o v a

l

p r o c e s s e s .

P e

t r o c h e m

i c a

l f e e

d s t o c k g e n e r a

t i o n .

B e

t t e r q u a

l i t y s p e c

i f i c a

t i o n s

f o r w

h i t e p r o

d u c

t s w

i t h

w i d e r r a n g e o

f f e e

d s

t o c

k .

H y d r o - d e s u

l f u r i z a

t i o n , i

m p r o v e

d

c r a c

k i n g

p r o c e s s e s ,

g r o w

t h o

f

P e

t r o c h e

m i c a

l I n d u s

t r y

D e e p

H y d r o - d e s u

l f u r i z a

t i o n , o

t h e r

s u

l f u r

r e m o v a

l p r o c e s s e s ,

r e p

l a c e m

e n

t o

f T E L b y

M T B E a s

o c

t a n e b

o o s

t e r , u s e o

f a

l k y

l a t i o n

a n

d

i s o m e r i z a

t i o n

t o

g e

t h i g h

o c

t a n e g a s o

l i n e .

H y d r o c r a c

k i n g

45

Notes



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46

Activity 6c


F i g .

6 . 3


C o l u m n s

i n a

R e f

i n e r y

Identify the equipmentin the pictures on thispage.


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47

NotesPrimary Separation

Let us discuss Primary Separation in greater detail. It isdone by Atmospheric Distillation and Vacuum Distillation.This is diagrammatically represented in Fig. 6.4

Atmospheric Distillation

Atmospheric Distillation is the first step in the refineryprocessing to separate out the raw products (cuts) bydistillation under pressures above atmospheric pressures(Atmospheric Distillation).

Atmospheric Distillation is done to separate the light cuts by0heating the crude oil to 350-370 C at pressures close to

atmospheric pressures.

At these temperatures light and white products like motorgasoline, kerosene, Aviation Turbine Fuel (ATF), diesel etcare distilled out as raw products for further processing.Residue which is left behind at the bottom of the distillationcolumn after atmospheric distillation is called longresidue . The next step in distillation is Vacuum

Distillation of the long residue.

Vacuum Distillation

The limitation of distilling at higher temperatures is becausedeterioration of crude oil starts at temperatures above 350-

0370 C. Crude oil starts 'cracking' at high temperatures i.e.the heavier molecules start breaking into smallermolecules. Uncontrolled cracking process results in cokeformation and production of unstable olefinic (doublebonded) hydrocarbon products.

Vacuum distillation unit yields vacuum gas oil as distillatewhich are used as feedstock for cracking to lighterproducts. Vacuum gas oil also can form the base oil forprocessing into lubricating oils.

In vacuum distillation, the residue from atmospheric0distillation is heated to around 350-370 C and distilled

under vacuum conditions.



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49

Activity 6dGasoline Up-gradation

Gasoline up-gradation is a typical example of conversionprocess to meet specification of the product. OctaneNumber of gasoline cut from distillation is low. Octanelevels need to be raised to the desired specification forengine performance requirements.

In the sixties and seventies, Catalytic Reforming was themost prevalent process to increase Octane Number. Theprocess essentially converted paraffin in the gasoline cutinto aromatics, which have high ON. For further boostingthe octane number, small dosage of Tetra Ethyl Lead (TEL -

Octane Booster) was added.

Aromatics generated by Reforming process was found tobe carcinogenic and Lead was found to be health hazard .

With lead addition eliminated, new octane boosters (etherslike MTBE or other oxygenated compounds) weredeveloped.

With stricter aromatics specification in gasoline, use ofreformate gasoline (product from catalytic reforming) as

gasoline blending stock was reduced. New processes weredeveloped for converting naphtha to high-octane gasoline.Some such processes are -

Isomerization to convert straight chain paraffins tobranched chain isomers

Alkylation to combine paraffin components with butane toform isomers.

Polymerization to transform some lighter hydrocarbonsinto high octane gasoline.

Fluid Catalytic Cracking (FCC) units also became one ofthe main sources of high-octane gasoline.

Conversion of 'Heavies' to 'Light Oils'

Conversion of heavy cuts (e.g. gas oil from vacuumdistillation) and residues which are dark colored, low valueproducts to light and valuable products are important forrefinery economics. This is done by Cracking Processes .


State why then refineryindustry is calledautomobile industrydriven.


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50

NotesCracking essentially breaks the large heavy molecules intoa number of smaller lighter molecules. The processgenerates gases and white products by cracking the heavyvacuum distillates and residues.

A typical reaction in cracking process:

oCatalyst and heat (450-500 C)

C H C H + C H16 34 8 18 8 16

There are several components of the heavy oilsundergoing such reactions generating light products aswell as gases .

The cracking processes more common are thermalcracking, fluid catalytic cracking and hydrocracking .

Thermal Cracking is done with heat alone at hightemperatures. Depending upon severity of reactionconditions and nature of feedstock, the thermal crackingprocesses are named as

Visbreaking Coking etc.

Fluid Catalytic Cracking (FCC) is carried out with afluidized bed of catalyst. FCC yields gasoline of higheroctane number along with gases, kerosine and dieselfractions. Some heavy oil is also produced from FCC calledcycle oil .

Hydrocracking is cracking under heat, pressure andpresence of hydrogen. It takes wider variety of feedstockand gives stable, good quality product.

Treatment Processes

Sulfur Removal

Hydro-desulfurization is one of the processes to removesulfur by reaction of hydrogen with sulfur bearingcomponents of oil. This produces hydrogen sulfide, whichis also toxic. Hydrogen sulfide is converted to sulfur in therefinery by a process known as Claus Process .



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51

NotesWith stringent specifications for sulfur in production,deeper and deeper Hydro-desulfurization is coming intoapplication.

Finishing of Products

The final polishing of products is done to remove traces ofcontaminants, to have the right color of products andstability by treating with hydrogen or other reagents.Examples of such processes are Hydrotreating,Hydrofinishing, and Merox Sweetening of LPG andgasoline.

It is important to note that hydrogen finds extensiveuse in a modern refinery.

In addition to the basic processes mentioned above,there are a few other important operations in therefinery of today -

Petrochemical Feedstock Generation

Propylene, naphtha and aromatics are separated or

extracted out of the refinery products as feedstock forproduction of petrochemicals.

Formulating and Blending

Formulating and blending is the process of

Mixing and combining the various cuts or fractions fromdistillation, cracking and other process units. Themultiplicity of processing units in a refinery creates anumber of intermediate products of the same boilingrange which are finally blended to get the right amount ofproduct of right quality.

Dozing of the products with additives (chemicals to givestability, storage life, performance etc.) .

Formulating and blending gives the final finished products,which are tested and marketed.



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Activity 6eLube Oil Manufacture

Lubricating oils need to be viscous, have stability during theheat generated by friction of the machine, and the viscosityshould not fall sharply with the rise in temperature due tofriction. These qualities are met by vacuum gas oils i.e. highboiling cuts distilled by vacuum distillation of crude oil.These gas oil cuts are called lubricating oil base stocks .

All crude oils do not give good lube base stock . Forexample waxy crude oils like Mumbai High or some SouthEast Asian crude oils are not good for lube oil manufacture.Yield of suitable lube base stocks are lower in these cases(as the oil is light) and wax creates a lot of operationalproblems during lube extraction process. Some of themedium heavy Middle East Crude oils give good qualitylube base stocks.

A schematic diagram of modern lube oil complex is given in Fig.6.5. The various processing steps are:

De-asphalting Unit: Here asphalt from the lube base stockis removed by solvent extraction process because asphalt

is not good to meet lube oil specifications.

Aromatics Extraction: Aromatic hydrocarbons areremoved by solvent extraction process to improveviscosity.

De-waxing: This is another solvent extraction processwhich removes wax from the lube base stock. This is alsosolvent extraction process.

Hydro-finishing : After these series of extractionprocesses, the lube oil base stock is treated with hydrogen(hydro-finishing process) to improve color and givestability.

Finally additive chemicals in small dozes are added toboost certain properties.


Identify the refineriesin India which producelubricating oils.


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54

NotesRefinery Configurations

The previous section gave an overview of various types ofprocesses used in the refinery. The process units in therefinery and their capacities are determined by:

Product DemandProduct PricesProduct SpecificationsCrude Oil Characteristics

The investor arrives at optimum selection of process unitsand their capacities by economic optimization techniques.The techniques as described later, are based oninvestment and operating costs of various units and yieldand quality of products from them. The combination of theprocess units is called refinery configuration .

Configuration of the Sixties

Out of the parameters mentioned above, the productspecifications have started changing the refineryconfiguration a lot since the 1960s.

Let us first have a look at how the refinery configurationlooked in the sixties . Fig. 6.7 depicts a typicalconfiguration of a refinery in the sixties.

The crude oil was first distilled at pressures close toatmosphere (Atmospheric Distillation) to separate out rawcuts of naphtha, gasoline, kerosene and diesel oil. Theresidue left was being used as a component of fuel oil.

Gasoline was processed in Catalytic Reforming Unit toboost its Octane Number. Finally Tetra-ethyl Lead wasadded to the gasoline in small doses as Octane Enhancer.

Sulfur specifications were not very stringent those days.Wherever the sulfur content exceeded the specification(diesel in the flow diagram

understanding o&g-mdso 801 (2nd vol)

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