Naphtha Cracker Plant Report

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A
Project Report
On
Naphtha Cracker Plant
Submitted in partial fulfillment towards the bachelor’s
degree in the field of Chemical Engineering
Prepared By
Shreenath M. Modi
Ch- 22 (I.D.No. 104024)
Under the Guidance of
Dr. Vimal Gandhi
Department of Chemical Engineering
Faculty of Technology, Dharmsinh Desai University
College road, Nadiad – 387 001
April -2014

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CERTIFICATE
This is to certify that Mr. Shreenath M. Modi durably submitted his
Training report on Naphtha Cracker Plant as partial fulfilment of his
graduation in department of Chemical Engineering in D.D.U.
(Dharmsinh Desai University), Nadiad.
Dr. Vimal Gandhi Dr. PREMAL SHUKLA
Associate Professor (GUIDE) Professor& HOD,
Chemical Engineering Department, Chemical Engineering Departement,
DDU, Nadiad. DDU, Nadiad.
Date: Date:

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PREFACE
Theory of any subject is important but without its practical knowledge it becomes
useless particularly for the technical students. A technical student can’t become perfect in his
field without practical understanding of the branch.
Visual observation of actual chemical plant operations is one of the best ways of
learning what goes on in a typical chemical industry. It is essential that chemical engineering
student should have a comprehensive picture of the chemical industries.
For this reason, the industrial training is necessary addition to reading assignments and
classroom discussions.
The principle objectives of the plant training is to get details about the operations,
which are carried out in the industry and more about the working and details of equipment
used in the chemical industries. Another attractive feature is to learn industrial management
discipline as well as safety aspects which is equally important in life.
Hence this training provides golden opportunity for all teaching students.
Shreenath Modi
Sem – 8
Chemical Engg. Dept.
DDU, Nadiad.

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ACKNOWLEDGEMENT
Any accomplishment requires the effort of many people. I
thank my professors & especially my guide Dr. Vimal Gandhi,
whose guidance & support was instrumental in accomplishing this
task. I thank my all colleague whose diligent efforts also made this
training successively progressive.
Many fundamental aspects, flow sheets, equipment details
& process fundamental are cleared during this training period. For this
much effective efforts, I am really very thankful to all industrial
persons who have given me the great experienced knowledge &
guidance to me for better understanding & to complete my training
with higher achievement.
Shreenath M. Modi
B.tech. Sem – VII
DDU.

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INDEX
1. Introduction to ETHYLENE
1.1 Ethylene overview
1.2 Physical and chemical properties of ethylene
1.3 Ethylene products uses
1.4 Ethylene manufacturers
2. Selection of Process
2.1 Process
2.2 Types of cracking method
2.3 Principle of Steam Cracking
2.4 Mechanism of cracking
2.5 The principle and governing variables of cracking operation
3. Characteristics of Naphtha
3.1 Physical and Chemical properties of Naphtha
3.2 Handling and storage of Naphtha
3.3 Hazards identification of Naphtha
4. Process Description
4.1 Numbering of Equipment
4.2 General information about cracking operating parameter
4.3 NCP flow diagram
4.3.1 Process description of AB -zone
4.3.2 Decoking
4.3.3 Process description of C-zone

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4.3.4 Wash oil
4.3.5 Process description of D-zone
4.4 Dryer Regeneration
4.5.1 Green Oil absorber
4.5.2 Mechanism of Catalyst hydrogenation reaction (in MAPD)
4.6 Equipment Description
5. Utilities
5.1 Process water
5.2 Cooling tower
5.3 D.M.Plant
5.4 Steam
6. Process description of ETP plant
7. General safety
8. Plant location

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1. INTRODUCTION OF ETHYLENE:-
1.1 ETHYLENE OVERVIEW:-
• Ethylene is a basic building block for the chemical industry, and it is one of the
largest volume organic chemicals produced globally. It is the simplest of the family of
hydrocarbons called olefins, which are characterized by a carbon-carbon double bond.
Ethylene is produced commercially from petroleum and natural gas feedstocks.
Ethylene is primarily used as a reactive monomer to make polyethylene. It is also
used as an intermediate in the production of compounds, such as ethylene dichloride,
ethylene oxide, ethyl benzene, and other organic chemicals.
1.2 PHYSICAL AND CHEMICAL PROPERTIES OF ETHYLENE:-
Appearance Colourless
Odour Odourless
Flammability of the product Flammable
Auto-ignition temperature 490°C (914°F)
Flash point Closed cup: -135.85°C (-212.5°F)
Flammable limits Lower: 2.7%, Upper: 36%
Molecular weight 28.06 g/mole
Molecular formula C2=H4
Boiling/condensation point -104°C (-155.2°F)
Melting/freezing point -169.2°C (-272.6°F)
Critical temperature 10°C (50°F)
Vapor density 1 (Air = 1), Liquid Density @ BP: 35.3 lb/ft3
(566kg/m3
)
Specific Volume (ft3
/lb) 13.8007
Gas Density (lb/ft3
) 0.07246
HAZARDS IDENTIFICATION:-

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Health Hazards: High gas concentrations will displace available oxygen from the
air; unconsciousness and death may occur suddenly from lack of oxygen.
Vapours may cause drowsiness and dizziness. Exposure to rapidly
expanding gases may cause frost burns to eyes and/or skin.
Signs and Symptoms: Central nervous system (CNS): may cause tremors and
convulsions. Other signs and symptoms of central nervous system (CNS)
depression may include headache, nausea, and lack of coordination.
Safety Hazard: Electrostatic charges may be generated during pumping. Electrostatic
discharge may cause fire. This material is shipped under pressure.
Flammable gas. May form flammable/explosive vapour-air mixture.
Environmental Hazards: Harmful to aquatic organisms. May cause long-term
adverse effects in the aquatic environment.
Additional Information: Not classified as dangerous under EC criteria.
1.3 ETHYLENE PRODUCT USES :-
 Ethylene is primarily used as a reactive monomer (chemical building block) to make
polyethylene, and as an intermediate in the production of other organic compounds, such
as ethylene dichloride and ethylene oxide. Products produced from ethylene are used to
make chemicals and plastics used in other industrial processes and in consumer products
such as detergents, automotive antifreeze, and plastic articles of many types. A minor
commercial use for ethylene is as a ripening agent for fruits and vegetables.
 High-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-
density polyethylene (LLDPE) – used to make bins, pails, crates, bottles, piping, food
packaging films, caps, trash liners, sacks, bags, wire and cable sheathing, insulation, and
surface coatings for paper and cardboard.

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 Ethylene dichloride (EDC), vinyl chloride (VC) and polyvinyl chloride (PVC) – used to
produce packaging films and bottles; and pipe, tile and flooring for building and
construction.
 Ethylene oxide – used as a chemical intermediate to produce: ethylene glycol, which is
used to make automobile antifreeze and polyethylene terephthalate polyester (PET) for
fibers, films and bottles; glycol ethers for solvents; surfactants and detergents;
polyglycols; and ethanolamines.
 Ethylbenzene and styrene – used to make plastic products used in toys, construction pipe,
foam, boats, latex paints, tires, luggage, food-grade film, insulation and furniture.
FIG-1.1.
1.4 ETHYLENE MANUFACTURERS:-
RELIANCE INDUSTRIES LTD – 1.VADODARA-naphtha cracker
2. DAHEJ – natural gas cracker
3. NAGOTHANE – natural gas cracker
4. HAZIRA – naphtha cracker
5. JAMNAGAR – gas cracker

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IOCL – VADODARA
OPaL – DAHEJ – gas cracker

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2. SELECTION OF PROCESS:-
2.1 PROCESS –Ethylene is produced commercially from petroleum and natural gas
feedstocks. Ethylene is produced by gas-phase steam/thermal cracking of light
hydrocarbon feedstocks at 800–870° C in a tubular reactor, followed by a series of
purification steps to separate heavy and light components for recycle or for use as
other products. A simplified process flow diagram is shown below.
FIG – 2.1
2.2 TYPES OF CRAKING METHOD
There are three method for cracking naphtha.
1. Catalytic cracking
2. Hydro cracking
3. Steam cracking
Catalytic cracking

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o Fluid catalytic cracking is a commonly used process, and a modern oil refinery
will typically include a cat cracker due to the high demand for gasoline
o Initial process implementations were based on low activity alumina catalyst and
a reactor where the catalyst particles were suspended in a rising flow of feed
hydrocarbons in a fluidized bed.
o In newer designs, cracking takes place using a very active zeolite-based catalyst
Hydro cracking
o In 1920, a plant for the commercial hydrogenation of brown coal was
commissioned at Leuna in Germany.
o Hydrocracking is a catalytic cracking process assisted by the presence of an
elevated partial pressure of hydrogen gas. Similar to the hydrotreater, the
function of hydrogen is the purification of the hydrocarbon stream from sulfur
and nitrogen hetero-atoms.
o The products of this process are saturated hydrocarbons; depending on the
reaction conditions (temperature, pressure, catalyst activity) these products range
from ethane, LPG to heavier hydrocarbons consisting mostly of isoparaffins.
Hydrocracking is normally facilitated by a bifunctional catalyst that is capable of
rearranging and breaking hydrocarbon chains as well as adding hydrogen to
aromatics and olefins to produce naphthenes and alkanes.
o Major products from hydrocracking are jet fuel and diesel, while also high
octane rating gasoline fractions and LPG are produced. All these products have a
very low content of sulfur and other contaminants.
o It is very common in Europe and Asia because those regions have high demand
for diesel and kerosene. In the US, Fluid Catalytic Cracking is more common
because the demand for gasoline is higher.
Steam cracking:-
o Steam cracking is a petrochemical process in which saturated hydrocarbons are
broken down into smaller, often unsaturated, hydrocarbons. It is the principal
industrial method for producing the lighter alkenes (or commonly olefins),
including ethene (or ethylene) and propene (or propylene).

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o In steam cracking, a gaseous or liquid hydrocarbon feed like naphtha, LPG or
ethane is diluted with steam and briefly heated in a furnace without the presence
of oxygen. Typically, the reaction temperature is very high, at around 850°C, but
the reaction is only allowed to take place very briefly. In modern cracking
furnaces, the residence time is reduced to milliseconds to improve yield,
resulting in gas velocities faster than the speed of sound.
2.3 PRINCIPLE OF STEAM CRACKING
 Cracking is the process where heavy hydrocarbons are broken down into simpler
hydrocarbons, thermally or by using catalysts.
 Naphtha is cracked thermally by using the process of steam cracking.
 Naphtha contains a large number of hydrocarbons and during steam cracking a large
number of chemical reactions takes place, most of them based on free radicals. Thus
the actual reactions that take place are complex and difficult to model.
 However, pyrolysis of ethane provides a simple illustration to understand the
phenomenon of free radical mechanism.
1. Initiation: Ethane molecule splits homolytically into two methyl radicals.
CH3CH3 2 CH3*
2. Hydrogen Abstraction: Methyl radical removes hydrogen radical from another
ethane molecule to give an ethyl radical.
CH3* +CH3CH3 CH4+ CH3CH2*
3. Radical Decomposition: Ethyl radical decomposes to give ethylene molecule
and hydrogen radical.
CH3 CH2* CH2-CH2+H*
4. Hydrogenation: The hydrogen radical attacks ethane molecule to give a hydrogen
molecule and a new ethyl radical.
H*+CH3 CH3 CH3CH2*+H2
Reaction (4) is followed by reaction (3) and thus, they constitute a chain mechanism.
The net effect can be represented by the equation

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CH3CH3 CH2-CH2+H2
Reactions (2) and (3) are called transition reactions.
5. Termination: The chain cycle will terminate when two free radicals react with
each other to produce products that are not free radicals. This happens in any of the
following ways:
H* + CH3* CH4
H* + CH3CH2* CH3CH3
CH3CH2* + CH3* CH3CH2CH3
CH3CH2* + CH3 CH2* CH3CH2CH2 CH3
When the chain is interrupted, it becomes necessary to generate new radicals via
reactions (1), (2) and (3) to start a new chain.
Apart from the primary reactions discussed above, secondary reactions occur too that
will be described in the next section.
2.4 MECHANISM OF CRACKING :-
The reactions taking place can be broadly classified into two categories:
1. Primary Reaction: When naphtha along with the steam is heated to such a
temperature that the heavier naphtha molecules break down into smaller molecules, these
are known as primary reactions.
2. Secondary Reaction: The cracking operation comprises of reactions other than the
primary reactions, these are called primary reactions.
They are as follows:
a) Dehydrogenation gives olefins.
b) Dehydrocyclizaton gives aromatics.
c) Condensation Two or more, smaller fragments combine to form large stable
structures. It gives gas oil, fuel oil & tars.
d) Hydrogenation gives paraffin, diolefins and acetylene are obtained from olefins.

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e) Reactions involving further pyrolysis of olefins. It results into formation of olefins,
diolefins and acetylene.
2.5 THE PRINCIPLE AND GOVERNING VARIABLES OF CRACKING
OPERATIONS:-
The overall cracking reactions are endothermic. High temperature and low partial pressure
of the hydrocarbons favour the reactions.
1. Residence Time: It is defined as the length of time for which the naphtha feed is in the
cracking furnace at or above its cracking temperature. This variable is the prime factor in
deciding the yield pattern of the cracking furnace. Other things being equal, a short residence
time gives a higher yield of ethylene due to the suppression of secondary reactions.
The residence time is usually kept as 0.5 second.
2. Severity: The severity of the operation is dependent on the following:
a) Coil Outlet Temperature (COT): Higher the COT, more severe is the cracking.
b) Residence Time of naphtha cracking: With feed rate and steam rate, the residence
time also gets fixed.
c) Pressure in the cracking coils: Lower the pressure, higher the severity of cracking
for a furnace of definite design and dimension. The minimum pressure available at the
charge gas of the first stage suction drum governs the coil pressure.
Thus, the only process variable which controls the severity of cracking is the COT.
3. Selectivity: Hydrocarbon undergoing pyrolysis is the most complex, mixture of molecules
and free radicals, which reacts with one another in multiple ways simultaneously.
Based on established theories and supported experimental data, the production of
olefins and diolefins has been found to be favoured by two ways:
a) Short Residence Time
b) Lower Hydrocarbon Partial Pressure
4. For liquid feedstock, the methane to ethylene ratio found in the heater effluent was used
as a good overall indicator of pyrolysis heater selectivity.
Low Methane to Ethylene Ratio corresponds to a high total yield of ethylene,
butadiene and butylenes.

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5. Steam Cracking is done as it has the advantage of lowering the partial pressure of the
hydrocarbons in the feed and reducing the deposit of coke.
The following reaction variables have been suggested as the optimum conditions for
naphtha cracking
Temp = 760º C to 860º C
Total Pressure = 1 atm
Hydrocarbon/Dilution Steam = 2:1 to 1:1
Residence Time = 0.5 s
DMDS: For Naphtha = 100 ppm
For Ethane = 150 ppm
GUJARAT OLEFINS PLANT
GOP is the mother plant of RIL, VMD. Here, naphtha is cracked to produce feed stock for
other plants at RIL.
The main products of GOP are ethylene, propylene, gasoline and C4 raffinate.
 Ethylene is supplied to LDPE and EG plants.
 Propylene formed has two grades, based on the level of purity.
o Polymer Grade (PG), 99% pure, supplied to PP4.
o Chemical Grade (CG), 95% pure, treated for the removal of impurities.
 Mixed C4 products are used in the formation of rubber at PBR-I, II plants.

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The GOP consists of the following units:
 Naphtha cracker plant (NCP)
 Benzene butadiene hydrogenation (BBH)
 Pyrolysis gasoline hydrogenation (PGH)
 Benzene extraction
 Butadiene extraction
 Feed purification unit
 Off sites
NAPHTHA CRACKER PLANT
The Naphtha Cracker Plant RIL-VMD, designated as Unit-21 of Gujarat Olefins Plant is
designed by Mis ABB Lummus Global and its detailed engineering is done by Mis ElL. It
was commissioned in March 1978. It was designed at for nameplate capacity of 130 KTA.
Product:
 Ethylene
By-products:
 Propylene ( PG, CG)
 Mix C4
 Pryolysis gasoline
 CBFS
 Fuel gas (HP, MP, LP methane)
 Hydrogen
Here the naphtha is cracked continuously, so it’s continuous process plant .
NAPHTHA is use as raw material.
3. CHARACTERISTICS OF NAPHTHA

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Naphtha is the raw material for NCP. Naphtha is a colourless, volatile and
flammable liquid mixture of hydrocarbons, having specific gravity of 0.69. Based on
the boiling points, naphtha is of two types- light and heavy. Light naphtha (boiling
range -35º C to 135º C) is thermally cracked to obtain olefins.
3.1 PHYSICAL AND CHEMICAL PROPERTIES OF NAPHTHA
Physical state and appearance Liquid.
Odour Petroleum odour (Slight.)
Molecular Weight Not available.
Colour Clear Colourless.
pH(1% soln/water) Not applicable.
Boiling Point 86°C (186.8°F)
Melting Point -73°C (-99.4°F)
Critical Temperature Not available.
Specific Gravity 0.69 (Water = 1)
Vapor Pressure 1.4 kPa (@ 20°C)
Vapor Density 3.8 (Air = 1)
Dispersion Properties See solubility in water, methanol, diethyl
Ether, n-octanol, acetone.
Solubility Easily soluble in methanol, diethyl ether,
Acetone. Soluble in n-octanol. Very
slightly soluble in hot water. Insoluble in
cold water.
Flammability of the Product Flammable.
Auto-Ignition Temperature 232°C (449.6°F)
Flash Points CLOSED CUP: 10°C (50°F).
Flammable Limits LOWER: 1.4% UPPER: 12.6%.
Fire Hazards in Presence of Various Substances: Highly flammable in presence of
open flames and sparks. Flammable in presence of heat, of oxidizing
materials.

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Explosion Hazards in Presence of Various Substances: Risks of explosion of the
product in presence of mechanical impact. Risk of explosion of the product
in presence of static discharge.
Fire Fighting Media and Instructions: Flammable liquid, insoluble in water. SMALL
FIRE: Use DRY chemical powder. LARGE FIRE: Use water spray or fog.
Special Remarks on Fire Hazards: Vapour may travel considerable distance to source
of ignition and flash back.
3.2 HANDLING AND STORAGE OF NAPHTHA
Precautions:
Keep locked up. Keep away from heat. Keep away from sources of ignition. Ground all
equipment containing material. Do not ingest. Do not breathe gas/fumes/vapour/spray.
Wear suitable protective clothing. In case of insufficient ventilation, wear suitable
respiratory equipment. If ingested, seek medical advice immediately and show the
container or the label. Avoid contact with skin and eyes. Keep away from
incompatibles such as oxidizing agents.
Storage:
Store in a segregated and approved area. Keep container in a cool, well-ventilated area.
Keep container tightly closed and sealed until ready for use. Avoid all possible sources
of ignition (spark or flame).

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3.3 HAZARDS IDENTIFICATION OF NAPHTHA
Potential Acute Health Effects:
Hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of
inhalation. Slightly hazardous in case of skin contact (permeator). Severe over-
exposure can result in death.
Potential Chronic Health Effects:
Hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of
inhalation. Slightly hazardous in case of skin contact (permeator). The substance is
toxic to skin, eyes, central nervous system (CNS). The substance may be toxic to blood,
kidneys, lungs, the nervous system, mucous membranes, peripheral nervous system,
gastrointestinal tract, upper respiratory tract, ears.
TABLE-3.1, According to PIONA analysis, the average composition of naphtha is as
follows:
Component Specification
(Wt %)
Maximum
(Wt %)
Minimum
(Wt %)
Paraffin's 75 74.26 79.99
Naphthenes 18 14.13 19.08
Aromatics 6.5 5.28 7.23
Olefins 0.5 0.18 0.61
Sulphur (ppm) 170 105 308
Specific Gravity 0.6824 0.678 0.692
VENDOR - Naphtha is obtained from crude oil refining done in RIL, Jamnagar Plant. It is
transported to Dahej via shipping and then from here to the storage tanks in
Vadodara Plant via pipelines.
Provisions have also been made to import naphtha from Kandla and Dahej.

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4. PROCESS DESCRIPTION
4.1Numbering of Equipments
At RIL NCP PLANT,there is a numbering system that assigns a number each to equipments
of the plant. For e.g., 21-11-333.
It is as follows:
 NCP unit code: 21
TABLE – 4.1
Equipment No. Section
100-199 Cracking
200-299 Heat Fractionation and compression
300-399 Chilling
400-499 Propylene Refrigeration
500-599 Ethylene Refrigeration
TABLE – 4.1
Code Equipment
11 Heat Exchanger
12 Vessel
13 Column
14 Reactor
15 Pumps
16 Furnace / Heaters
17 Blower / compressor
18
Filter/Desuperheaters/Miscellaneous
Equipments

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PROCESS BLOCK DIAGRAM –
FIG – 4.1
NAPHTHA
HEATERS
ETHANE
HEATER
GASOLINE
FRACTIONATOR
QUENCH
TOWER
CHARGE GAS
COMPRESSOR
DRYER
CHILLING
SECTION AND
DEMETHANISER
METHANATOR
ACETYLENE
CONVERTER
ETHYLENE
FRACTIONATOR
DE-
PROPANISER
DE-
ETHANISER
MAPD
CONVERTER
PROPYLENE
FRACTIONATOR
DE-
BUTANISER
C2 / C3 REFIREGERATION
UNIT

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4.2 GENERAL INFORMATION ABOUT OPERATING PARAMETER:-
4.2.1 Factors Affecting Heater Operation
1. Feed Rate: Increasing the feed rate will decrease the residence time. However, it will
require greater high heat duty.
2. Dilution Steam Rate: Increasing dilution steam rate will decrease the residence time
and decrease the hydrocarbon partial pressure also resulting in better selectivity and more
valuable products. But, more dilution steam will increase operation cost.
3. Coil Outlet Temperature: High temperature gives higher conversion and higher yield
of ethylene. However too high temperature may give too high fouling rate and can also
decrease the yield of propylene and butadiene. Varying the outlet temperature can vary
the ratio of ethylene to propylene, thus will be varied according to the market demand at a
particular time.
4.2.2 Factors For Coil Design
1. Heat Flux: This is a measurement of heat that is transferred through a unit surface area
of the radiant tubes per unit time. A high heat flux is necessary in cracking heater coils to
get feedstock heated to the cracking reaction temperature within fraction of second.
2. Mass Velocity: The mass velocity of the gases going through the radiant tubes is very
high to achieve the short residence time condition. It also helps in increasing the flux in
the coils. This is dependent on the coil tube diameter.
3. Cross Over Temperature: It is the temperature at which the gases crossover from the
convection zone of the furnace to the radiation zone of the furnace.

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For maximum efficiency of cracking, this temperature should be as near as the possible to
the cracking reaction temperature, so that the cracking doesn’t happen in the convection
zone but starts in the radiation zone.
4.2.3 Function of Dilution Steam in Cracking:
1. It reduces the hydrocarbon partial pressure and thereby encourages higher selectivity
of the desired olefin products.
2. It reduces the partial pressure of the high boiling aromatic hydrocarbons in the zone of
high conversions, lessening the tendency to form coke within the cracking coils &
deposit on the walls of the TLE (Transfer Line Exchangers).
3. It has a sufficient adding effect on the tube metal to significantly diminish the catalytic
effect of iron and nickel which otherwise would promote the carbon forming reaction.
4.2.4 Effects Of Partial Pressure During Cracking:
1. The partial pressure of the hydrocarbon affects the chemical equilibrium arid the
reaction rates and thus influences the product distribution.
2. Optimum partial pressure is P = 0.5-10.6 kg/cm2
g.
3. Optimum total pressure is P = l atm.
4.2.5 Functions of DMDS In A Feed Stock:
1. Coke formation in the pyrolysis furnace and TLE presents serious operating problems.

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2. When unsaturated hydrocarbons diffuse through the gas film boundary layer to the high
temperature tube well, they undergo dehydrogenation reactions leading ultimately to
coke formation.
3. The sulphur on the feed stock or the decomposed DMDS (which is injected along with
the feedstock) forms a sulphide film in the active tube metal, temporarily poisoning the
catalytic effect of Nickel and Iron and thus reduces coke formation.
4.2.6 Factors on which yield depends:
1. On stream hour
2. Coil Outlet Temperature (COT)
3. Residence time
4. Dilution Steam
5. Quality of Naphtha
6. Availability of Ethane heater
The NCP is divided into three zones to facilitate easier operation and
understanding. The three zones are:
1. AB Zone: Cracking and quenching, high temperature fractionation
2. C Zone: Compression and refrigeration
3. D Zone: Chilling, cold fractionation and recovery
4.3 NCP FLOW DIAGRAM :-

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FIG – 4.2
4.3.1 PROCESS DESCRIPTION OF A-B ZONE :-

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4.3.1 PROCESS DESCRIPTION OF A-B ZONE :-
1) Naphtha, stored in the floating roof tanks is pumped to the naphtha surge drum.
Naphtha is maintained at 80% of the drum height such that, in case the pumps that pump
naphtha from offsite stop working, the drum is capable of supplying naphtha for the
next 10 minutes.
2) The naphtha surge drum is blanketed with fuel gas. The blanketing is done due to the
following reasons:
 To maintain the drum pressure.
 To avoid any air-entry into the naphtha surge drum.
3) Naphtha from the surge drum enters the Quench Water Pre-Heater, shell side, where it is
heated by quench water, to T=60° C.
4) Then naphtha enters the Quench Oil Pre-Heater, shell side, where it gets heated by
quench oil, to T=116° C.
5) DMDS is added to naphtha before it is sent to the SRT heaters.
100 ppm Sulphur for Naphtha
150 ppm Sulphur for Ethane
DMDS is added to prevent undesired secondary reactions, such as water gas shift
reaction that results in coke-formation.
6) The SRT heater is has two zones- convection and radiation.
 The convection zone is further is divided into 3 sections-top, middle and bottom.
o The naphtha stream first enters the top section of convection zone and gets
heated to T=150° C At this temperature about 95% of the liquid naphtha is
vaporized.
o Dilution steam is mixed with the heated naphtha stream at the outlet of the
top section. The dilution steam is added according to the following ratios.
o 2:5 (wt ratio) for naphtha stream
o 1:3 (wt ratio) for ethane stream

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 Then the mixed naphtha and dilution steam is heated in the bottom section of the
convection zone. Then it is sent to the radiation zone through a crossover.
 The middle section of the convection zone is used for heating Boiler Feed Water
(BFW) from 160° C to 320° C.
 From here, BFW goes to the SHP (super high pressure) Drum.
 After the diluted naphtha stream is heated in the convection zone, it is sent to the
radiation zone through a crossover.
 Crossover temperature for naphtha, T=536° C
 Crossover temperature for co cracking ethane-naphtha, T=549° C
o The radiation zone is where cracking of naphtha takes place.
o The residence time is 0.5 s.
o After naphtha is cracked in the radiation zone, the coil outlet temperature is
T=810°C.
7) The cracked gases now enter the TLEs, where it is cooled. Each heater has two TLE
respectively.
 The cracked gases enter tube side and the cooling water (BFW, from SHP Drum)
enters shell side, both from the bottom of the TLE.
 The temperature of the cracked gases is brought down from 810ºC to 425° C.
 This immediate cooling after the cracking in the SRT heaters is necessary to avoid
polymerization and other side reactions.
8) The cracked gases (T=425°C) now enter the Quench Fitting (QF), where it is mixed with
quench oil to further cool the cracked gases.
 The quench oil is introduced at T=138°C and allowed to mix with the incoming
cracked gases.
 The mixture of cracked gases and the quench oil attains a temperature, T = 178°C.
 It is then sent as feed to the Gasoline Fractionator (GF).
 This temperature of the gasoline feed (T=178° C) is maintained by controlling the
flow of the quench oil that is mixed.
9) The mixture of cracked gases and the quench oil enter the GF from the bottom, at
T=178° C.
 At GF, heavy fuel oil cuts are separated from the bulk of the effluent stream.

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 A part the hydrocarbon stream of 3rd compartment of the Quench Water Settler
(QWS) serves as the reflux to GF.
 The overhead vapors (C1-C8, H2, CO, CO2, H2S), leaving at T=103.4° C, gets
mixed with the stripped lighters of the Gasoline Stripper (GS) and then are sent to
the Quench Tower (QT).
 Liquid oil tapping from GF is taken and sent to Fuel Oil Stripper (FOS). It mostly
contains heavier fractions and CBFS.
 The quench oil left at the bottom is pumped to the LP Steam generator.
 The heat of the quench oil is used to generate LPS, heat naphtha in pre-heater and
also used to wash instrument lines.
 The cooled quench oil is used to cool naphtha at QF.
o At the suction of these pumps, there are two basket-type strainers to filter
out any solid coke particles.
o These filters are changed periodically once in every 5-6 months.
10) The overhead vapors from the GF (T=104.4°C), joined by the stripped lighters of GS,
now enter the bottom of QT.
 The gases are quenched in QT with three streams of quench water coming at
different temperatures - top at T=24°C, middle at T=45°C and bottom at T=54°C.
 The steam and the heavier hydrocarbons settle at the bottom of the QT.
 As they are immiscible, an interface gets created separating the water and the
hydrocarbon phase.
 These two phases of liquid are then led into a horizontal vessel called the Quench
Water Settler (QWS), by the means of two pipelines.
 The overhead gases from the QT (T=28°C, P=0.33 kg/cm2
g) are sent to C-Zone
for compression.
11) At the liquid entry of the QWS, baffle is provided to break the turbulence of the
incoming liquid stream as well as any hydrocarbon water emulsion present.
 The vessel has three compartments.
 Liquid hydrocarbon phase being lighter than the water phase will flow into the
last compartment.

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 The first compartment will have quench water, and thus serves as the suction pot
for quench water circulating pumps.
 The second compartment serves as the suction pot for the Process Water Stripper
(PWS).
 The hydrocarbons settled in the 3rd compartment of the QWS are pumped by 2
pumps. The discharge is distributed into three portions:
o The first portion serves as reflux to the GF.
o The second portion is sent to the Petroleum Resin plant, through a FRC.
o The third portion serves as a feed to the Gasoline Stripper (GS).
12) The 2nd
compartment of QWS has both water and hydrocarbons in it. It is sent to PWS
to strip off hydrocarbons from BFW.
 The feed enters PWS from top.
 The stripping stream, LPS is directly injected at the bottom of the tower.
 The stripped hydrocarbons from the top of the PWS T=109°C is sent to the QT
for recovery.
 The PWS bottom is BFW. It is used for raising dilution steam, which is
distributed to the cracking heater coils.
13) A part of hydrocarbon from the 3rd
compartment to QWS is sent to Gasoline Stripper to
strip off the light gases from the heavy gasoline.
 The stripping stream used is LPS.
 The overhead product joins the overhead of GF and sent to the QT.
 And the heavy gasoline from the bottom is pumped to Pyrolysis Gasoline
Hydrogenation (PGH) unit.
14) Liquid oil tapping from GF is sent to FOS to strip out lighter fuel oil components from
the heavier fractions and CBFS.
 The stripped fuel oil is sent back to the GF for recovery.
 The bottom product is carbon black feed stock (CBFS) and this is cooled in
quench water to 600° C and then it is sent to storage in CBFS tank.
 Need for FOS:

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o Accumulates lighter fuel oil components in the quench oil loop by
stripping the fuel oil with hot heater effluent.
o Enables operation at a higher bottom temperature.
o Revolves reflux by decreasing the bottoms light component requirement.
o Reduces quench oil circulation and less fouling of heat exchangers.
4.3.2 Decoking:
 Required when coil back pressure exceeds allowable pressure (SRT, TLE).
 Outlet temperatures increase as a result of tube fouling due to coke formation.
 It is done every 45 days.
 In radiant coil sections, decoking reaction is done. C is burned with O2 and air is
injected into the heater coils to increase the rate of decoking reaction.
 This reaction is highly exothermic, so COT should be maintained around 810°C by
controlling the air flow rate.
 In TLE, physical removal of coke is done by steam flow.

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FIG – 4.4
4.4 .1 PROCESS DESCRIPTION OF C-ZONE:

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The gases from the QT are now known as the charge gases. They are now at T=28°C and
P=0.33 kg/cm2
g. It contains C1-C6 gases, H2, CO& H2S.The charge gases now enter the
Charge Gas Compressor (CGC) in the C-Zone.
 The function of the CGC is to compress the low charge gases, so that most of it can be
liquefied in series of exchangers and refrigeration cycles that follow. Once liquefied,
the desired separation of the various components can be achieved by normal
distillation process.
 Charge gases coming to the CG Compressor is made from – gasoline fractions in the
QT.
The CGC is centrifugal type, having free modules for 4 stages of operation driven by a
steam turbine.
 Inter-cooling is done in each stage by cooling water and propylene refrigerant.
 Inter-cooling after each compression stage is required to minimize the suction and
discharge temperature, which otherwise leads to polymer formation.
 There is also provision to inject wash oil in the suction of each stage. The aromatic
oil helps in washing polymer wear and also helps in keeping the compressor impeller
clean.
15) STAGE 1:
 The CG (T=28°C, P=0.33 kg/cm2
g) enters the 1st
stage suction drum, after first
neutralizing the ammonia present in it with a corrosion inhibitor.
o The corrosion inhibitor is a mixture of Amines, which has a property of filming.
o It forms an inert film on the inner surface of the pipes of the CG system, which
prevents corrosive effects of acid gases on the inner surface of pipe. The
corrosion inhibitor is injected to the discharge line of 1st
, 2nd
and 3rd
stage as
well.
 The CG is compressed to 2.35 kg/cm2
g and attains a temperature, T = 94°C.
 This 1ststage discharge is then cooled to T=24°C first with cooling water and then
with propylene refrigerant.
 A small cut of the C4 from the butadiene plant joins the first stage discharge.
 Then passes through a Knock Out Pot (K.O. Pot) which is equipped with demister
pads.

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o Here, C5 and C6 fractions condensed previously get separated and are passed
on to the GS.
o Also the water that is condensed is sent to the QWS.
 The CG now free of condensed fractions is ready for the second stage compression.
16) STAGE 2:
 The CG from the 1st
stage (P=2.35 kg/cm2
g, T=24°C) now enters the 2nd
stage of
the CGC.
 Here it is compressed to P=6.31 kg/cm2
g and the corresponding temperature is
94°C.
 It is cooled with cooling water followed by propylene refrigerant such that it attains
a temperature of T=24°C.
 The CG then enters a K.O. Pot, from where two streams go to GS and QWS,
similar to the process described in the 1ststage.
17) STAGE 3:
 The CG from the 2nd
stage (P=6.35 kg/cm2
g, T=24°C) now enter the 3rd
stage.
 Here it is compressed to P=15.23 kg/cm2
g.
 It is cooled with the help of cooling water to T= 56°C.
 Then it enters the 3rdstage discharge drum, having a K.O. Pot.
 Gas from top of K.O. Pot of the 3rd stage discharge drum, enters the Caustic Tower
from the bottom.
18) In the Caustic Tower, CG is scrubbed with caustic soda solution so as to remove CO,
CO2, H2S (formed in the SRT heaters, during the steam cracking). The reasons for .the
removal of the above compounds from the CG are as follows:
o H2S and CO2 contaminate the final product.
o CO2 creates choking in the downstream cold end section of the compressor.
o H2S acts as a poison to the Acetylene Converter catalyst and
o Methanator catalyst.
o Both CO2 and H2S under a highly pressurized environment corrode the
equipment.

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 The CG from the 3rd
stage discharge enters the bottom of the Caustic Tower.
 The tower is divided into 4 sections. The bottom three sections are caustic wash
sections. The top most section is the water wash section where the washing is
done by BFW.
 Top most caustic section has circulation of strong caustic (6-8%), middle section
has intermediate caustic (4-6%) and the last section has weak caustic (3-4%).
 A storage caustic solution of 50% concentration is diluted to 10% concentration
and is injected at the top of the caustic section. The solution overflows into the
bottom 2 sections. Each of the section is provided with bottom low and high level
pumps.
 A split stream from the BFW heater is spread at top of the water wash section. .
 The CO2 and H2S scrubbed hot caustic, is drained from the bottom most section of
the caustic tower.
 The spent caustic's concentration is maintained at 2-3%.
 Wash containing caustic traces is drained from the bottom of the top section.
19) The CG after caustic treatment is cooled by cooling water and propylene refrigerant up to
24°C. It then enters the 4th
stage suction drum at P=15.23 kg/cm2
g and T=24°C.
20) STAGE 4:
 CG is compressed to P=36.70 kg/cm2
g and T=94°C.
 The gas is first cooled by cooling water and then by propylene refrigerant to T=15°C.
 The CG, now at P=36.70 kg/cm2
g, T=15°C is sent to the final zone, D zone for
chilling and cold fractionation.
 Condensed liquid hydrocarbons from the 4th
stage are taken out under level control
through an exchanger where the liquid stream is heated to T=50°C by returning hot
quench water and is pumped to the Condensate Stripper.
21) The stream from the bottom of the 4th
stage suction drum and the heated stream from 21-
11-206 are combined and then fed to the Condensate Stripper.
 The function of the Condensate Stripper is to strip out the C2 and the lighter
hydrocarbon fractions from the condensate coming from the 4th
stage suction and
discharge drum.

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 The reboiling to the stripper is done with LPS in the reboiler. The steam quantity is
adjusted by TRC-FRC.
 The temperature of the stripper is maintained at T=72ºC to prevent the carryover of
any C2 in the bottom product.
 The top vapour of Condensate Stripper is sent to 4th stage suction of CG Compressor.
Any water that is carried out with CG is condensed, and is sent to the QWS manually.
 The bottom product is at T=9ºC. It flows under pressure to the Depropanaizer and the
gases are passed to the dryers to reduce the moisture content.
4.4.2 WASH OIL:
 Provision is made for injection if aromatic oil known as wash oil (usually diesel oil)
into the suction of each stage.
 As substantial quantities of unsaturated C4 and C5 compounds are present in the CG,
the compressor discharge temperature may lead to polymerization which results in
compressor fouling.
 The polymer formation is promoted by sulphurous gases. The lay down of polymer
is highly influenced by pressure and temperature. Polymer formation leads to
increased frictional losses and decreases the compressor efficiency and thus leads to
a rise in the delivery temperature.
 Thus, the horsepower required by the compressor increases for a fixed rate. Also the
polymerization also increases with the rise in delivery temperature.
 Wash oil is added to prevent the polymer build up on the compressor wheel. There is
also provision for injection of wash .oil in case of 4M and 3M (generally not used).
DESCRIPTION OF THE SUPPLY SYSTEM FOR WASH OIL:
 Wash oil stored in tanks which have total capacity of 105 m3
.
 From here it is pumped and injected into various parts of the CG compressor casing
and suction line.
 This pump is called MICROYAL. It has a single plunger.
 The flow of wash oil to each point is indicated by a rotameter and can be
independently varied by adjusting the globe valve located downstream of the
rotameter.

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DESCRIPTION OF THE WASH OIL SYSTEM:
 The MICROYAL are variable stroke and positive displacement pumps.
 They take suction from the tank and deliver the oil to the various injection points.
 There is provision to use one pump for injection wash oil into the compressor
suction line.
 The maximum capacity of the pump is 60-600 lit/hr. Two relief valve setting is 50
kg/cm2
g and discharge pressure is 50kg/cm2
g.
 The wash oil is injected into the four-suction line of the compressor through a
strainer, flow indicator, non-return valve and two injections.
 The non-return valve is designed to withstand any back flow of gases.
 Because of the special isolation valve provided, the injection nozzle can be
withdrawn for cleaning.
 The flow suction line can be independently varied by globe valve.
 Apart from the suction line, provisions are made to inject washed oil casing of 4M &
3M modules. But this is generally not used.
 The 4M casing has two points while the 3M module has 6 points; 3 for each stage.
The flow of the oil through this injection lines will be adjusted by the individual
valve and there is no flow indication for these lines.
4.4.3 REFRIGERATION SYSTEMS AT NCP:
There are two refrigeration systems at NCP:
1. Propylene refrigeration system
2. Ethylene refrigeration system
PROPYLENE REFRIGERATION SYSTEM:
 Basically, four levels of refrigeration can be achieved in this system. They are: 20⁰C,
5⁰C, -20⁰C, -40⁰C.
 Pure propylene is used as a refrigerant.
 The refrigeration compressor is centrifugal compressor, driven by steam turbine.

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 The refrigeration is mostly used in the CG Compressor intercoolers, overhead
condenser and reboiler of the cold fractionators and to the coolers of Depropanizer,
Deethanizer, Ethylene Fractionator, CG chiller.
 As seen before, the minimum temperature that can be achieved in propylene
refrigeration is -40⁰C.
ETHYLENE REFRIGERATION SYSTEM:
 Ethylene refrigeration system can temperatures be used to achieve lower
 Three levels of refrigeration can be achieved in the system. They are – 50⁰C,-75⁰C
and -110⁰C. Pure ethylene used as a refrigerant in this system.
 The refrigeration compressor used here is also a centrifugal compressor, driven by
steam turbine.
 The minimum temp that can be attained here is about -110⁰C.
 The refrigerant is used in the Demethanizer overhead condenser.
Vapour Compression Refrigeration Cycle:
 The refrigeration cycle used in NCP is the vapour-compression type.
 The vapour compression cycle is used in most of the household refrigerators as well
as many large commercial and industrial refrigeration systems. The figure below
provides a schematic diagram of the components of a typical vapour-compression
cycle.

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FIG – 4.5 TYPICAL SINGLE-STAGE
VAPOR COPMRESSION REFRIGERATION
CONDENSOR MAY BE WATER COOLED OR AIR COOLED
STEPS OF A TYPICAL SINGLE-STAGE CYCLE:
 In this cycle, a circulating refrigerant such as ethylene or propylene enters the
compressor as vapour.
 First, the vapour is compressed at constant entropy. It gets superheated.
 Next, the superheated vapour travels through a condenser. The condenser first cools
it and removed the superheat and then condenses the vapour to liquid by removing
heat at constant P, T.
 It is now saturated. Now, the liquid refrigerant goes through expansion valve where
its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of
typically less than half of the liquid. That results in a mixture of liquid and vapour at
lower T, P.
 The cold liquid-vapour mixture then travels through the evaporator coil or tubes and
is completely vaporized by cooling warm air (from the space being refrigerated),
being blown by a fan across the evaporator coil or tubes.
compressor
VAPOR
comp
EVAPORATOR
FAN
CONDENSOR
VALVE
Expansion
LIQUIDLIQUID+VAPOR
WARM
AIR
COLD
AIR

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 The resulting refrigerant vapor returns to the compressor inlet at the original to
complete the thermodynamic cycle.

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FIG – 4.7
4.5.1 PROCESS DESCRIPTION OF D-ZONE:
22) The CG from the CG Compressor of the C-Zone, now at P=36.7kg/cm2
g, T=15ºC.
 This CG has moisture content of about 600 ppm.
 Before it is sent for the cold fractionation, the moisture content needs to be brought
down to 1 ppm or else hydrates will form in the chilling train.
 The removal of moisture from CG is achieved in the molecular sieve dryers.
 Three identical CG dryers are provided.
 Normally, two of them will be in operation as lead and guard.
 The 3rd
dryer will be left for regeneration and after it's regenerated, it is replaced as
the guard dryer.
 The CG dryers have molecular desiccant for the purposes of drying.
 The distinctive advantage of molecular desiccant over drying is that, molecular
desiccant selectively absorbs water molecules and does not absorb hydrocarbons.
 As there is no polymer deposition, there is no consequent fouling of the desiccant.
 Also, since it does not absorb hydrocarbon, it is not necessary to run the molecular
drive dryer to breakthrough while regeneration.
 In case alumina is used, it has to be run through break through during regeneration
since it absorbs hydrocarbons also.
 The inlet temperature of the dryer should not fall below 14ºC as there is possibility
of hydrate deposition.
 Also, if the inlet temperature rises above 15ºC quantity of water vapour in CG will
increase which will reduce its water content by 5%.
 Dried CG from the guard dryer goes to the chill down train via side reboiler of
Ethylene Fractionator (EF), Demethanizer (DM) and Ethane Vaporizer.
4.5.2 DRYER REGENERATION:
 The main steps are: Purging, Heating and then Cooling.
 HP methane (dry), T=200ºC, P=7 kg/cm2
g is used for dryer regeneration.
 HP methane is heated in a steam heater by HP steam.
 It then enters the bottom of the dryer.
 The inlet temp should be maintained at T=200ºC, else, there will be water-built up
which may not be reported by the condensate pot.
 During adsorbtion (drying of CG), the gas flow is from top to bottom.
 During regeneration, the gasflow is from bottom to top.
 Hot gas from the dryer passes through the cooler and most of the liquid is
condensed.

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DRYER CHANGEOVER OPERATION:
 The dryer change over operation is a very important operation. Guard becomes lead
and the regenerated dryer becomes the guard. Dryer bypassing may lead to serious
consequences and is checked by the 12 valves that each dryer has.
23) The main purpose of Chill down train section is to chill the Demethanizer (DM) feed
streams by propylene and ethylene refrigerant and also by heat exchange with cold off gases
Le. H2, CH4 and C2H6 and also by reheating the cooled DM feeds.
 There are six exchangers that form the compact Cold Box.
 The CG coming out of the dryer is then passed through the side reboiler of Ethylene
Fractionator, gets cooled to T= -10ºC.
 It is further cooled in the side reboiler of the Demethanizer to T= -17°C.
 It gets further cooled to T= -23ºC in Ethane Vaporizer by propylene refrigerant.
 It is then sent to Feed Chiller NO.1 of the Cold Box, tube side.
 The CG at T= -23ºC is cooled to T= -37ºC.
 61% (W/W) of the vapor is liquefied.
 Cooling is done by propylene refrigerant, boiling at T= -40ºC.
 It is then led to the first feed separator.
 From the 1st Feed Separator,
o The liquid from this separator is sent as 1st
feed to tray no. 33 of DM.
o The gases overhead of this separator go to a section of the cold box where
its temperature comes down to T= -45ºC and 10% is liquefied.
 Next, it enters Feed Chiller No.2, tube side.
o The gas is cooled to T= -50ºC.
o 48% of the vapor is liquefied.
o Ethylene refrigerant is used for cooling purposes first time in the Chill
Train. It boils at T= -55ºC.
 Next, it enters the Feed ChillerNo.3, tube side.
o It is further cooled down in two ethylene coolers to -70ºC.
o 71% of the vapor is liquefied.
o It is led to the Second Feed Separator.
 From the 2nd Feed Separator,
o The liquid is taken as the 2nd
o The vapor is sent to the Cold Box and gets chilled to -84ºC against the off
gases. 22% of the vapor is liquefied at this stage.
 Next, the process stream is chilled further Feed ChillerNo.4.

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o It is chilled to T= -98ºC.
o 42% is liquefied.
o Ethylene refrigerant boils at T= -101ºC
o It is next led to the Third Feed Separator.
 From the 3rd
Feed Separator,
o The liquid is withdrawn at T= -98ºC.
o This liquid gives refrigeration to the cold box, gets heated to -75ºC and
then it finally goes as the 3rd
o The gases from the 3rd separator are chilled in the cold box to T= -122ºC
and 31% gets liquefied.
 Next, the above process stream is chilled in the Feed Chiller No.5.
o It is cooled to T= -130ºC.
o It is now sent to the Fourth Feed Separator.
 From the 4th Feed Separator,
o The liquid goes to the cold box, gives its cold and gets heated to T= -
103ºC and then goes as 4th
o The gas from the 4th
feed separator goes to the cold box.
 The gas from the 4th feed separator now mainly contains Hydrogen and Methane.
o In gets chilled to -164ºC.
o Such low temperature is achieved by vaporizing LP methane (P=0.l
kg/cm2
g).
o At this temperature most of the CH4 is liquefied and most of the H2
remains as gas. This mixture is now led to the Hydrogen Methane
Separator for.
 At Hydrogen Methane Separator, 95% (V/V) pure H2 is separated from the
condensed CH4.
o The liquid methane at P=32 kg/cm2
g, T= -164ºC separated is called LP
methane.
o It is expanded to a low pressure of P= 0.l kg/cm2
g.
o LP methane gives refrigeration to the Cold Box (21-11-315) and itself
gets heated to T= -30ºC. It is also used to cool the incoming gases.
o Thereafter, it goes to the methane compressor, where it is compressed to
P= 4.65 kg/cm2
g and then it is released to the fuel gas system.
o The gas from the top is 95% (V/V) pure H2 at T= -164*C, P=33.2
kg/cm2
g.
o This hydrogen gas passes through cold box-11-315, 313,311,308,305,
gets heated to T=30ºC.
o It still has 0.5 mol% CO, hence can't be used for hydrogenation
o purposes (BBH, AC, MAPD, and PGH). Thus, it is sent for purification
to Methanator.

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o The purity of H2can be improved by lowering the temperature of the
separator achieved by lowering the temperature of the evaporating
CH4.This in turn can be achieved by either reducing the P of the
expanded CH4or by reducing the PP by injecting a little H2 to the
expanded liquid. Care should be taken in mixing H2 to the expanded
liquid to avoid T going below T= -180ºC which is close to the freezing
point of methane in the expanded mixture.
 At the Methanator, CO contained in the hydrogen stream is removed by catalytic
hydrogenation.
o CO is one of the major impurities that is produced during thermal
cracking as steam is used as a dilution agent.
o CO from Hydrogen Methane Separator contains O.5mol% CO.
o CO poisons the catalyst in the subsequent hydrogenation processes
(MAPD, AC)
o The catalyst used for hydrogenation of CO contains nickel oxide on the
refractory carrier consisting of alumina. This catalyst cannot be
regenerated and the expected life is 3-7 years.
o The hydrogenation reaction is as follows:
o H2 + CO catalys
CH4+ H2O
o H2 from the Cold Box at T=30ºC is heated to the reactor temperature of
T=280ºC in the heat exchangers.
o The inlet temperature of Methanator should never fall bellow
o T=150ºC since the catalyst has a tendency to form nickel carbonate.
o The purified Hydrogen from this section is ready for hydrogenation
purposes at PGH, BBH, AC and MAPD
24) As seen earlier, the Chilling Train provided feed to Demethanizer at 4 points. At DM,
CH4 (containing a little H2) is stripped from C2 & heavies.
 Feed enters tray no. 14, 20 , 28 , and 33 .
 The overhead product is mainly methane, at P=31 kg/cm2
g, T= -96ºC, is partially
condensed with liquid ethylene refrigerant (boils at -101ºC).
o Condensed liquid obtained is MP methane.
o It is partly sent as reflux to DM to maintain the top temperature at T= -
96º C.
o Some liquid CH4, under TRC/3009 flows from bottom of the reflux
drum is sent to the Cold Box for refrigeration recovery where it'
successively gets heated to T=30º C.
o Then this MP methane at P=4.0 kg/cm2
g goes to the fuel gas system.
o Uncondensed overhead CH4 gas from the reflux drum is called HP
methane.
o It is at P=30.6 kg/cm2
g, T= -96ºC.
o It is released at P=8.1 kg/cm2
g and then sent to the Cold Box, where it
gets successively heated to T=30ºC.
o HP methane at P=7 kg/cm2
g is used for regeneration of the dryers-
charge gas dryer, ethylene dryer and hydrogen dryer.
o It is then passed to fuel gas system via a KO Pot.

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 The bottom of the DM is mostly C2 and heavies containing ethylene, acetylene,
ethane, propane, as well as propylene vapors from the propylene refrigeration
system.
o This is sent to the Deethanizer.
o Methane in the bottom product should be kept as low as possible, as the
methane in the bottom stream lands up in the C2 Splitter and will
pollute the final product
o Reboiling is done by condensing propylene and cooling process gases.
25) At the Deethanizer, the DM bottom product, at T= 11ºC is separated into an overhead C2
stream and the bottom stream containing C3 and the heavies.
 The feed enters at tray no. 12
 The Deethanizing action is achieved by LP Steam.
 The system and overhead vapors are condensed at T=12ºC by propylene
refrigerant, evaporating at T= -24ºC.
o The overhead vapors mainly consisting of C2 is sent to Acetylene
Convertor (to convert acetylene) then to the Green Oil Absorber and
then finally to Ethylene Fractionator to get the desired products
(ethane, ethylene).
 The bottom product from the last tray flow to the reboiler.
o The bottom product should have less than 0.01 mol% C2.
o The bottom product at a temperature of T=73ºC is cooled to T=40ºC
by cooling water.
o It is then sent to Depropanizer as feed.
 At the Acetylene Convertor, acetylene present in the C2 stream is converted
to ethane or ethylene by catalytic hydrogenation.
o Acetylene is one of the impurities produced during the steam
cracking.
o Reasons For Conversion of Acetylene:
o It seriously affects the polymerization reaction to produce polyethylene.
o It will not separate from ethylene in any of the distillation column in the
gas separation train.
 Concentration of acetylene is reduced from 0.18% (V/V) to less than 3ppm.
 The catalytic hydrogenation in carried out in a double bed reactor in series.
 The catalyst used is palladium metal on alumina support.
o The catalyst is expected to be on stream for 6 months for
regeneration.
o Thus, two reactors are provided. One is on stream while the other
one is regenerated and kept as standby.

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o Superheated steam and air at T=45ºC in bed accomplishes the
regeneration of the catalyst.
 Each reactor consists of two reactor beds with provision for hydrogen
addition to each bed.
 Inter-cooling is provided between two reactor beds.
o It lowers the temperature of the reaction bed, which enhances the
catalyst selectivity.
o Higher temperature results from the exothermic nature of the
hydrogenation reaction.
 Hydrogen is added in mol ratio of 1.6 : 1 (H2 : C2H2) for 1st bed and 2:1 at
the inlet of the second bed. H2 is added slightly in excess to ensure the
complete conversion of acetylene to ethylene. Adding H2 in too much excess
will lead to the undesirable hydrogenation of Ethylene to Ethane.
 The mechanism of the hydrogenation of Acetylene is discussed at the later
section of the report.
 As the reaction is highly exothermic, the effluent comes out at a temperature,
T=100ºC.
 Incoming feed is heated from T= -17ºC to T=45ºC by the effluent coming out
of the Acetylene Converter.
 The effluent after the heat exchange, attains a temperature of T= -11ºC and
goes to the Green Oil Absorber.
4.5.3 GREEN OIL ABSORBER
 At the Green Oil Absorber, some heavy of C4and green oil is knocked out
by the C2 from the Ethylene Fractionators.
 During acetylene hydrogenation, a small quantity of heavier hydrocarbons (oily
polymers) is formed due to the side reactions.
 This liquid is called the green oil.
 The feed from AC comes at T= -11º C and P=22 kg/cm2
g.
 Green oil is removed by liquid wash of C2stream coming from the EF.
 The bottom wash is sent to the DE, and the green oil finally goes out of the
system along with the pyrolysis gasoline.
 The overhead of the GOA contains some moisture (formed in AC or from the DE
overhead). Thus it is sent to the Ethylene Dryer.
 The overhead vapors from the GOA enter the Ethylene Dryer.
 The dried gas is sent to the C2 Splitter or the Ethylene Fractionator.
 For regeneration, hot HP methane, at T=220º C is used.
 At the Ethylene Fractionator, ethylene and ethane are separated.
 The tower can be mainly divided into 2 sections:
o Enriching Section: Where primary separation of Ethylene and Ethane
takes place.

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o Stripping Section: Where lighter impurities like H2 and CH4 are
removed from ethylene.
 The feed from the Ethylene Dryer comes at T=22º C
 The overhead vapor of the EF leaves at T=-30º C and it is condensed by
propylene refrigerant, boiling at T=-40º C in three parallel condensers.
 It is then transferred to the reflux drum.
o The liquid from the reflux drum is sent back to the column as reflux.
o The vapour containing lighters like methane, hydrogen andethylene is
further chilled in a vent condenser by ethylene refrigerant and sent
back to the CGC 4th stage suction
 Total ethylene product is withdrawn from tray no. 9 and is delivered to the
offsite storage.
 The bottom product is ethane at T= -30⁰C and P=20 kg/cm2
g.
 There are 2 thermosyphon reboilers operating in parallel.
 Bottom reboiler is provided by condensing propylene at P=5.32 kg/cm2
g from
the 3rdstage suction drum
 Side reboiler is heated by CG from the dryer, at T= 15⁰C.
 The bottom product next passes to Ethane Vaporizer, shell side, where it is
evaporated by CG.
 Then this ethane is sent for cracking or to fuel gas.
26) As mentioned earlier, the bottom of the DE is fed to Depropanizer. A separate stream
from the Condensate Stripper is also fed to the DP at a different place.
 At DP, C3 stream is separated from C4 and heavies.
 The DE tower bottom is cooled from T=73⁰C to T=40⁰C and fed to tray no. 20.
This feed has 73.8 mol% propylene.
 To the feed from Condensate Stripper, polymer inhibitor is added to prevent the
formation of polymer in the DP reboiler due to its high temperature. In case, the
reboiler gets clogged due to polymer formation, a spare reboiler is provided
there.
 Liquid from last tray, mainly containing C4 and heavies flows to the
thermosyphon reboiler from where liquid product is withdrawn.
 This is sent to Debutanizer.
 The overhead vapors, mainly containing C3 leave the top at T=16⁰C.
o They are condensed by propylene refrigerant.
o The reflux and distillate product are collected in the reflux drum.
o Reflux at a temperature, T=10⁰C is pumped to the tower at the top.
o They are first sent to the MAPD Convertor and then finally to the
Propylene Fractionator to get the desired products.
 A part of the liquid reflux from the reflux drum of DP and to MAPD Convertor.

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o At the MAPD reactors, methyl acetylene (MA) and propadiene (PD),
both of which are formed during the cracking reaction, are
selectively hydrogenated to propylene.
o Reasons for the MAPD conversion,
 MA and PD pose serious problems in the manufacturing of polymers.
o A concentration of MAPD in any stream above 40% is a serious
threat as it can undergo auto-ignition without any oxygen. Thus
concentration should be kept low in all the fractionators.
o A good quantity of propylene could be saved from down grading to
fuel in the form of mixed C3 from fractionator bottom.
 Feed from DP reflux drum is pumped at P=26/kgcm2
g and T=120⁰C.
 It is then mixed with hydrogen, and then the feed and hydrogen mixture is fed to
the reactor from the top.
 As the feed flows down, selective reaction takes place across the bed.
 The column is operated at P=22.5 kg/cm2
g and T=58⁰C.
 The temperature is controlled by reboiler with quench water as heating medium.
 The vapor from top, containing propylene is condensed and is sent back to the
column.
 MAPD in the feed= 1500 ppm.
 MAPD at the reactor outlet, <300 ppm.
 The converted liquid from column bottom is then sent to Propylene Fractionator.
 At the Propylene Fractionator, propane and propylene are separated.
o The stream from the bottom of MAPD converter enters PF at
T=100ºC.
o The PF's overhead, mainly propane is condensed to T=40⁰C.
o Condensed liquid is sent partly as reflux to PF and partly as the
polymer grade propylene.
o Liquid propylene from 7th tray of PF is obtained which is chemical
grade and is sent to the storage.
o The column is reboiled with quench water.
 The bottom of DP, at T=89⁰C is going as feed to Debutanizer.
27) At the Debutanizer, the bottom from DP containing C4 and heavies is separated into an
overhead mixed C4 stream and a bottom stream containing C5 and the heavies.
 The incoming feed is from the DP bottom at T=89⁰C and fed to tray no. 23.
 The overhead product (mixed C4) of DB leave at T=51⁰C is totally condensed at
by cooling water.
o The distillate product and the reflux are collected in the reflux drum.
o The liquid is withdrawn from the reflux drum at T=43⁰C and P=3.54
kg/cm2
g by pump.
o The discharge is split into two streams.
o One stream is sent back to DB as reflux.

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o Other is withdrawn as product and this mixed C4 is sent to Butadiene
Plant feedback for storage.
 DB is reboiled with LP steam, P= 3.5 kg/cm2
g.
 The bottom product of DB (C5 and heavies) is cooled to ambient temperature by
cooling water and sent to storage in Pyrolysis Gasoline Stripper bottom.
 In order to minimize the polymer formation and thus increase the run length of
the reboiler, the tower is operated at relatively low pressure to aid in reducing the
bottom temperature.
 However, there is provision to introduce a polymer inhibitor due to high
temperature there.
 Spare reboilers have been provided in case the in-line reboiler needs cleaning
due to fouling.
4.5.4 MECHANISM OF CATALYST HYDROGENATION REACTION
(IN MAPD)
Main Reaction
On the surface of the catalyst, acetylene reacts with hydrogen to from ethylene.
C2H2+ H2 = C2H4
Since the amount of C2H2 at the outlet should be less than 1 ppm, hydrogen to acetylene
molar ratio is maintained in excess of stoichiometric requirement.
Because of this excess H2 small amount of total ethylene gets converted to ethane.
C2H4 + H2 = C2H6
Both the above reactions are exothermic in nature.
Formation Of Water
Some of the Coentering the converter leads to the following reaction,
CO + 3H2 = CH4+ H2O
Catalyst Selectivity/Activity
Conversion from acetylene to ethylene should be promoted and complete reaction of ethylene
to ethane should be restricted. The factors that affect the catalyst activity and selectivity are:
1. Temperature: High reaction temperature increases the activity of the catalyst but reduces
the selectivity as with the increasing temperature distillation of ethylene becomes significant.
Thus, keep the temperature as low as desired.
2. CO Concentration: The mechanism by which CO presence affects catalyst selectivity is
not well understood however, it has been confirmed by experiences that for the given
temperature highly active catalyst can become more selective and less active by introducing a
small quantity of CO. Excess of CO are a temporary poison which will deactivate the
catalyst.

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3. Hydrate Action: Excess of hydrate will increase the hydrogenation reaction of ethylene to
ethane, which not only reduces the primary reaction of C2H2 product but also results in the
high heat of reaction which could be dangerous to the equipment. Still slight excess H2 is
required to maintain the desired activity of the catalyst.
4. Catalyst Poison: Activity of catalyst is reduced' by the pressure of sulphur compound.
Increase in CO is more likely to be originated from nickel rich of the furnace tubes.
C2H6+ H2O = 2CO +5H2
The catalyst reaction of nickel is inhibited by the continuous addition of sulfur compound to
the furnace, thereby keeping CO concentration at lower level.

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4.6 EQUIPMENT DESCRIPTION
Naphtha Storage Tanks
 Type: Floating head type roof tank
 Naphtha is stored in 3 floating head type roof tanks:
o 2 tanks- 15000 m3
, height= 12.3 m, diameter =42 m
o 1 tank- 25000 m3
, height=14.05 m, diameter =50 m
 Advantages of floating head type roof tank
o No air will enter
o No formation of vapour
o No losses
 From here, it is pumped by offsite transfer pumps to the Naphtha Surge Drum
Naphtha Surge Drum (21-12-107)
 Capacity=87.9 m3
, Horizontal tank with inlet at top and outlet at bottom.
 Naphtha level is maintained at 80% drum height, by LIVC. There are high level and low
level audio visual alarm provided.
 It is blanketed with fuel gas (T=37ºC, P=0.3 kg/cm2
g):
o To maintain the drum pressure
o To avoid entry of air into the surge drum
 Two PIVC with alarm provided to maintain pressure. One introduces flue gases into the
drum, if drum pressure falls. Other vents out the excess pressure into the wet flare.
 I/L: Naphtha, From floating head type roof tanks
 O/L: Naphtha, Pumped to Quench Water Pre-heater
Pumps (21-15-107/108):
 Two pumps for pumping out naphtha from Surge Drum to the cracking furnace.
 Both of them are centrifugal type.
 One steam turbine driven (21-15-107).
 Other motor driven (21-15-108), which is a standby in case the turbine driven fails. It
starts with auto switch.
 For both pumps:
o Capacity=100m3
/h
o Pressure= 20 kg/cm2
Quench Water Pre-heater (21-11-113):
 Heat exchanger type: Shell & Tube
 Shell side: Naphtha (Cold fluid):
o I/L: T=30ºC, from Naphtha Surge Drum
o O/L: T=60ºC, to Quench Oil Pre-heater
 Tube side: Quench water (Hot fluid):
I/L: T = 68ºC,
O/L: T=45ºC,

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Quench Oil Pre-heater (21-11-114):
 Heat exchanger type: Shell & Tube
 Shell side: Naphtha (Cold fluid):
o I/L T=60ºC, from Quench Water Pre-heater
o O/L T=85ºC -116ºC, to SRT Heater (convection zone)
 Tube Side: Quench Oil (Hot fluid):
o I/L T =160ºC, from LPS Generator
o O/L T =138ºC, to Quench Fitting
Short Residence Time (SRT) Heaters (21-16-101 to 106):
 6 Cracking heaters present
o 5 for naphtha cracking
o 1 for ethane cracking
o Ethane furnace can also be used to crack naphtha at 50% efficiency of other heaters.
o The 2 Naphtha heaters have provision for co cracking ethane.
 Residence time is 0.5 sec
 Skin Temperature =110ºC
 COT= 820ºC (Naphtha Cracking)
 COT= 850ºC (Ethane Cracking)
 The heater can be divided into two zones:
o Convection Zone
o Radiation Zone
 Convection Zone:
o Top section:
o Finned, horizontal, carbon steel tubes interconnected to form 4 coils.
o Naphtha is pre-heated.
o I/L Temp= 116ºC
o O/L Temp= 143ºC
o Dilution steam is added to the naphtha stream at the outlet of this section.
o Middle Section:
o 30 Finned coils
o BFW is heated.
o I/L Temp= 160ºC
o O/L Temp= 323ºC
o Bottom Section:
o 31 tubes (15 finned + 16 non-finned)
o The mixture (naphtha + dilution steam) is heated together and then, it is sent to the
radiation section through a crossover.
 Normal crossover temp:
o 586ºC for Naphtha
o 594ºC for Naphtha + Ethane cracking
 Radiation Section:
o Radiation section of the furnace is fired is fixed by air aspirating gas burners (John
Zink burner), mounted on both walls.
o 56 (7 rows x 8 columns) on each wall, and thus there are 112 burners for each heater.
o 4 coils, each having 8 passes

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o Each pair of coil will be linked to one TLE, thus 2 pairs linked to 2 TLEs
 Each SRT heater has 2 TLEs (Transfer Line Exchanger) and a SHP (super high pressure)
drum.
Transfer Line Exchangers (TLE) (21-11-101 to 112)
 For each SRT heater, there are 2 TLE (north TLE and south TLE).
 Its basic function is to promote heat exchange between BFW and cracked gases, so as to
cool the cracked the gases. It's necessary to cool the cracked gases after cracking, to avoid
side reactions like polymerization.
 Type : Shell & tube type heat exchanger
 Shell Side : BFW
o I/L T=308ºC, from SHP Drum
o O/L T=400ºC, to Superheaters, via SHP Drum
 Tube Side: Cracked Gas
o I/L T=823ºC, from SRT heaters (radiation zone)
o O/L T=375ºC to 450ºC, to Quench Fitting
 Shell side and tube side fluid enter from bottom of the TLE
 Provision for injecting phosphate continuously at the discharge of TLE
SHP Steam Drum:
 The SHP steam drum is horizontal, cylindrical vessel with dished end.
 It is designed to hold binary phase of water & steam.
 Water level is maintained at about 50 mm above middle point level indicated by LIVC.
 Operating Pressure of the SHP drum=125 kg/cm2
g.
 BFW heated from the 2nd
section of convection zone enters SHP drum
 The water from SHP Drum is sent to the TLE.
 The steam from here is sent to the super heater, after letting down its pressure from
125kg/cm2
g to 43 kg/cm2
g.
Super Heaters:
 Flow Rate 54.8 MT / H
 Saturated steam from Pressure Reducing Station enters the convection coils and gets
distributed into 4 coils.
 Each coil has 2 passes of non-finned type and 3 passes of finned type.
 Convection section hooks up with 4 coils in the radiant section of 13 passes each.
 Top most section of the convection section is the BFW pre heater which heats the BFW
coming from the TLE pumps.
Quench Fitting:
 It's a mixing device. Here, the cracked gas is cooled by mixing it with quench oil.
 It is horizontal, cylindrical equipment.
 Diameter = 42 inches.
 Cracked gas enters via two nozzles, which discharges the gas to the centre of quench
fittings.

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 The oil is introduced by two main rings around the mixing chamber having 4 inlet
nozzles. This arrangement is given to ensure complete mixing of cracked gas &quench oil
within a very short time.
 Cracked Gas:
o I/L Temp= 425º C
o From= TLE
 Quench Oil:
o I/L Temp= 138ºC
o From= Quench oil pre-heater
 Mix of Cracked gas and Quench oil
o O/L Temp= 178ºC
o TO= GF
Gasoline Fractionators (21-13-110)
 Feed:
o C1- C8, C9+, H2, CO, CO2, H2S,
o From QF
o T=178ºC
 Overhead Product:
o C1-C8, H2 ,CO, CO2, H2S
o To the Quench Tower
o T=103.4ºC
 Bottom Product:
o C9+, CFBS
o To Fuel Oil Stripper
 The quench oil from bottom of GF is pumped to LPS generators.
 In the suction of these three pumps (two steam and one turbine there are 2 Basket type
Strainers. It is for straining carbon or coke resent in the quench oil. In practice, these
filters are changed periodically once in 5 or 6 months.
Quench Tower:
 18 trays in total.
o Top 11 are double cross flow valve type
o 12th
acts as distributor tray
o 13th -18th
are angles of iron deck type
 Feed:
o Overhead gases from GF + stripped lighters from the Gasoline
o Stripper (GS)
o Temp T=103.4ºC
 The cracked gas is quenched in the quench tower, by three quench water streams.
o Top at T=24ºC
o Middle at T=45ºC
o Bottom at T=54ºC
 Bottom:
Condensed heavier hydrocarbon and steam.

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An interface, separating water and hydrocarbon phases, gets created.
To Quench Water Settler
 Top:
o Uncondensed lighter hydrocarbons
o To CG Compressors of C-Zone
Quench Water Settler:
 At the entrance, a baffle is provided.
o Breaks the turbulence of the incoming liquid
o Breaks any hydrocarbon-water emulsion present
 The horizontal vessel has 3 compartments.
o Compartment l: Suction pot of the Quench Water circulating pumps.
o Compartment 2: Suction pot for the Process Water Stripper feed pumps.
o Compartment 3: Feed for the GS Reflux for the GF To PR
 Operating Temp, T=790ºC
Process Water Striper (21-13-150):
 12 single cross valve trays
 Feed:
From 2nd
compartment of the QWS
 Stripping Steam: Directly injected LPS
 Overhead Product:
o Stripped hydrocarbons
o To QT based recovery
 Bottom Product:
o BFW
o For raising dilution steam
Gasoline Stripper (21-13-130/132):
 12 single cross flow valve trays
 Feed:
o Pumped from 3rd
compartment of QWS
o Pumped by 2 pumps
 Striping steam: LPS steam
 Top:
o Stripped lighter hydrocarbons
 Bottom:
o Heavy gasoline
o To PGH
Fuel Oil Stripper:
 8 single cross valve trays
 Feed from GF bottom

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 Top product sent back to GF and Bottom Product is CBFS, which is cooled to 600ºC and
sent to the storage in CBFS tank.
Charge Gas Compressor:
 To compress the low Pressure gas coming from the pryolysis section, so that most of it
can be liquefied in a series of exchangers and can thus be separated into the desired
products by simple distillation.
 Centrifugal type
 Four stages of operation
 Driven by a steam turbine
First Stage Suction Drum
 CG at the first stage suction has P=0.33kgj/cm2
g, T=28ºC.
 It is then compressed to P=2.35 kg/cm2
g and the outlet temperature is T =94ºC
 It is then passed through cooling water exchanger and C3R. It attains a temperature of
24ºC.
 It is then sent to a Knock out pot.
 In the knock out pot two layers of water and Hydrocarbon separate out.
 The water is sent to the Quench settler
 The Hydrocarbon is sent to the Gasoline stripper.
Second Stage Suction Drum:
 The incoming charge gas is compressed to P=6.31 kg/cm2
g.
 The corresponding temperature is 94ºC.
 It is then sent to a combination of Cooling water exchanger and C3R
 Outlet temperature = 24ºC
 It is then sent to a K.O. pot where water and H/C are separated as in the previous case.
Third Stage Suction Drum:
 The charge gas is compressed to P=15.23 kg/cm2
g.
 Outlet temperature = 90ºC
 Now the Charge gas is cooled to 55ºC by a cooling water exchanger
 Now it is sent to the Knock out pot.
 The gas from the top of the K.O pot is sent to the Caustic Tower
Caustic Tower:
 This tower is divided into 4 sections
 There are 3 caustic sections with 12 valve type trays in each section.
 The top most section is the water wash section.
 Each section is provided with a circulation pump.
 The Strength of the caustic used is 10 % Strength of caustic available at the battery limit
is 20 %.

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 Charge gas is scrubbed with caustic solution between the third and fourth section to
remove CO2 and H2S formed in the SRT heaters during naphtha steam cracking reaction.
 The wash section consists of 3 bubble cap trays.
 In this section BFW at T=50ºC is sprayed to remove any caustic solution getting carried
away.
Fourth Stage suction drum:
 The outlet from the caustic tower is passed through the combination of CW and C3R.
 This is sent to a K.O. pot.
 Here the H/C removed is sent to the Condensate stripper and the water to the Quench
settler.
 At the 4th
stage it is compressed to 38 kg/cm2
g.
 The corresponding temperature is 95ºC.
 The gas stream is now sent through a combination of CW, C3R and C2R.
 The outlet temperature is 15ºC
 This gas stream is now sent to a K.O pot.
 The top gases are sent to the Charge gas dryers in the D-zone.
 The bottom H/C is sent to the Condensate Stripper.
Condensate Stripper:
 The function of the Condensate stripper is to strip off C2S and lighter fractions of the
hydrocarbon condensate coming from the 4th
stage suction and discharge drums.
 The heavies are sent to the depropanizer column
 Consists of 30 valve trays.
 Separates C2s and C3+. .
 Operating pressure: 15.0 kg/cm2
g
 Temperature:
o Top: 32°C
o Bottom: 87°C
Chilling Section:
 Consists of 6 exchangers in a compact arrangement. Also called the Cold Box.
 Exchanger Type: Brazed Aluminium Plate Exchangers
 MOC: Brazed Aluminium
 CG after drying is fed to chilling section.
 Chilling with Ethylene and Propylene Refrigerants and Off-gases.
 Hydrogen is separated at T= -164°C by reducing the partial pressure of LP methane.
Methanator:
 Hydrogen purification by methanation.
 Catalyst: Nickel Oxide
Demethanizer:

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 Consists of 72 cross flow valve trays.
 Separates C is and C2+.
 Operating pressure= 31.3 kg/cm2
g
 Temperature:
 Top:T= -110°C
 Bottom :T= 11°C
 Since the tower is operating at a temp range from -110ºC to 111ºC, different metallurgy is
provided such that the material can withstand the operating temperature.
 The tower is made up of 2 types of materials.
 The top section up to tray no. 32 is made of stainless steel and can be safetly cooled to T=
-15ºC while the carbon steel can be cooled up to T= -45ºC
Deethanizer:
 MOC: Carbon Steel
 Consists of 52 cross flow valve trays.
 Separates C2S and C3+.
g.
 Temperature:
o Top: -17°C
o Bottom: 68°C
Acetylene Convertor and MAPD Reactor
 Acetylene is converted to ethylene by hydrogenation.
 Catalyst used: Pd with Silver
 Exothermic reaction.
 Methyl acetylene (MA) and Propadiene (PD) are converted to Propylene.
 Catalyst: Palladium

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Ethylene Fractionator (21-13-340):
 Separates ethylene and ethane.
 Diameter=2.6m, Height=56.3m
 MOC=Carbon Steel, can be closed up to T= -45ºC only.
 Fitted with 111 valve trays, due to the close boiling points of ethane and ethylene.
 Operating pressure: 19 kg/cm2
g.
 Temperature:
 Top: T= -30°C
 Bottom: T= -5 °C
Propylene Fractionator (21-13-380):
 Separates propylene and propane.
 Diameter=2.6m, Height=64.95 m, MOC=Carbon Steel
 Fitted with 162 valve trays.
 Feed: DP overhead after MAPD conversion T=100ºC
 Temperature:
Top: T=48°C
Bottom: T=62°C
 Operating pressure :19 kg/cm2
g
 Tallest column in Baroda Complex (65 m)
Depropanizer:
 Separates mixed C3and C4and heavies.
 Diameter=l.4m, Height=25.65m, MOC=Carbon Steel
 Fitted with 44 trays.
 Feed:
 Temperature:
o Top: T=11ºC
o Bottom: T=73ºC
g.
Debutanizer:
 Separates mixed C4and pyrolysis gasoline.
 Diameter=1.2m, Height=26.7m, MOC=Carbon Steel
 Fitted with 50 valve trays.
 Feed: DP bottom T=89⁰C
 Overhead: Mixed C4, T=43ºC , P=3.54 kg/cm2
g
 Bottom: Pyrolsis Gasoline ,T=110ºC
g

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5 . UTILITIES
5.1 PROCESS WATER
1) Water
Water is basic requirement for any industry (Big or Small). This water which is
available is seldom used as it is received and requires some treatment, oterwise it will cause
problems. Untreated water contains several impurities such as lower Solubility Dissolved
Gases and Suspended Particulate Matter. These impurities lead to corrosion, scaling and
deposit formation resulting in reduced efficiency of the equipment increased operating cost
and unscheduled down time for repairs and maintenance.
Most of the manufacturers know that such type of problems are caused by the water
they are using but are not aware about the right Treatment for which Chembond Chemicals
has the solution.
2) Sources of water
The sources from which water is available for water supply can be classified as
follows:
(1) Surface water
(2) Underground water
Surface water - Lakes, streams and rivers water
Underground source - Springs, well waters
3) Hard & soft water
A simple test for soft water is that it forms lather or foam with soap. Of course the
foam does not have any cleaning properties and hence some industries produce soap which
does not form foam even with soft water.
Hard water is that which contains objectionable amounts of dissolved salts of calcium
and magnesium. These are usually present as bicarbonates, chlorides or sulphates. The salts
form insoluble precipitations with soap i.e. calcium sulphates, carbonate and silicate, which
form clogging scales with low thermal conductivity in boilers. Magnesium silicate and
calcium carbonate may reduce heat transfer in process heat exchangers.
Hardness is usually expressed in terms of the dissolved calcium and magnesium salts
calculated as calcium carbonate equivalent. Hardness of water is divided into two classes.
4) Temporary Hardness
It is due to presence of calcium and magnesium salts. It can be removed by boiling or
try adding lime to the water.
5) Permanent hardness

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It is due to presence of calcium and magnesium chlorides and sulphates. It can be
removed only by the use of chemical agents.
6) Typical water analysis Parameter
1. pH 8. Chlorides
2. Total Dissolved Solids 9. Silica
3. Total Hardness 10. Sulphates
4. Calcium Hardness 11. Phosphates
5. Magnesium Hardness 12. Iron
6. P-Alkalinity 13. Turbidity
7. M-Alkalinity
7) How to check water analysis
Anion – Cation balance
Total Anions= Total Cations
pH and Alkalinity relation
If pH > 8.3 P-Alkalinity should be present
If pH < 8.3 P-Alkalinity should not be present
Total hardness > Calcium hardness
Calcium hardness = 25-50% of total hardness (Apprx.)
M-Alkalinity > P-Alkalinity
Typical terms used in water Treatment
a) pH
The most important parameter in Cooling Water and is characterized by pH which is a
measure of Hydrogen ion concentration. The scale forming and corrosive tendency depends
upon pH of water.
b) Total Dissolved Solids:
Apart from above, natural water contains salts of Sodium, Potassium in dissolved
form. Total Dissolved Solids are the residues left after complete evaporation of water.
c) Parts Per Million (PPM):
Alkalinity, Hardness, TDS, Chlorides, Iron, etc. are measured as parts per millions
(PPM). 1 PPM = 1 mg/lit.
5.2. COOLING TOWER
Cooling Tower is a familiar sight in all industries. A tower through which water is
circulated to remove the heat generated from various heats generating operations and the hot
water comes back to the Cooling Tower. This water is cooled in the Cooling Tower collected
in the Sump and recirculated, the cycle continues. This is basic definition of Cooling Tower.

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There are three types of Cooling Towers:
1. Natural Draft : Natural re-circulation of air-cools the hot water
2. Forced Draft : Using a fan, air is forced in the cooling tower
3. Induced Draft : Air is sucked through the water shower using a fan
5.2.1 Functioning of Cooling Tower
Water is lost through the Cooling Tower by evaporation during the process of heat
exchange. Fresh water is added to the cooling tower to make up the losses. Evaporated water
leaving along with air is pure water. While incoming water contains Dissolved Solids and
Suspended matters, etc. Therefore there is always a concentration of Dissolved Solids in the
recirculating Cooling Water due to evaporation. This Solids build up in recirculating water
should not exceed certain limits else deposition in Heat Exchanger may take place. In order to
remove such Dissolved Solids, part of water removed periodically or continuously is known
as Blow down (Bleed Off).
Make up water (M) = Water lost by evaporation (E) + Blow down (B)
5.2.3 General Terms Used in Cooling Water Systems
1. Acidity
Presence of acid in water, pH of water less than 7.
2. Alkalinity
Presence of alkali in water, pH of water is more than 7.
3. Hold up capacity of the system
It is an amount of water contained in basin and sump of cooling tower + water
contained in piping and equipment.
4. Blow down
Since pure water is evaporated out of the system, the dissolved and the suspended
solids are concentrated in the circulating water. Beyond certain limit, these solids will cause

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massive scale and corrosion. In order to balance this, a certain amount of water is removed
from the system by blow down.
5. Make up Water
This is the water, which is to be added to replace the water lost by evaporation, blow
down, drift and leakages.
6. Drift
Some water droplets escape alongwith the evaporation. A usual drift loss in
conventional cooling towers is in the range of about 0.05 – 1 % of the recirculation rate.
7. System Losses
Circulating water is lost in the plant through pumps, valves or leakages through
flanges, etc
8. Evaporation Losses
The water lost to the atmosphere in the cooling process is evaporation. The rate of
evaporation depends upon the temperature differential and the circulation rate. It amounts to
about 0.1% of the circulation rate for each 10 of temperature drop.
9. Cycle of Concentration
Due to evaporation of water in Cooling tower the impurities get concentrated in
recirculating water. Number of times the impurities get concentrated in recirculating water is
known as Cycle of Concentration (C.O.C.).
Cycleofconcentration =
Conc.circulating water (for cooling tower)
Conc.in makeup water
=
Conc.Blow down water (for boiler)
Conc.in make−up water
10. Langlier Index (L.I.)
It is a qualitative indication of the tendency of calcium carbonate to deposit or
dissolve.
Langlier Index= pHa – pHs
Where, pHa = pH actual
pHs= pH saturation which is the effectof
pH, calcium hardness,total alkalinity,
dissolved solids and temperature.

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5.2.4 Typical Problems in Cooling Tower
1. Scaling
The salt like calcium carbonate, calcium sulfate and calcium phosphate in the cooling
water have reverse solubility, i.e. at high temperature their solubility decreases. This
causes precipitation and scaling in heat exchange. Cooling water is heated in the heat
exchangers where temporary hardness salts decompose and form scales.
Cooling water is concentrated in the system due to evaporation in tower. Due to
concentration, sparingly soluble salts like calcium sulphate tend to precipitate out and
form scales. Thus scale of calcium carbonate, calcium sulphate and calcium
phosphate are often found in the heat exchanger.
2. Corrosion
Cooling water is corrosive to mild steel, copper, etc. due to higher TDS. More are the
dissolved salts in water more are the corrosiveness. Also various galvanic cells are
formed in the heat exchangers due to differential metal, combination, concentration,
temperature, velocities and stress strain on metal. Corrosion is generally observed all
over the cooling system. But it is more near welding, joints and under the deposition.
3. Microbiology
Cooling water is ideal medium for microbiological growth. It provides optimum
temperature, oxygen, nutrient and sufficient surface area for growth. Algae, bacteria
and fungus are commonly found in cooling system. If not controlled in time,
microbiological growth can be plugged heat exchanger and causes corrosion and
reduce cooling tower efficiency.
4. Bacteria
Bacteria are mainly of two types aerobic and anaerobic. Aerobacter secrets certain
enzymes, which form sticky masses, called as slime. Slime can for on heat transfer
equipment as well as on complete pipelines. Slime attracts other suspended particles
in water to form deposits, which is generally called biofouling.
Anaerobic bacteria e.g. Desulphovibrio desulphuricans (sulfate reducing bacteria)
contains an enzyme, hydrogenous, enables it to reduce sulfate to hydrogen sulphide.
Hydrogen sulphide then reacts with elemental iron to form ferrous sulfide. Sulfate
reducing bacteria (SRB) leads to pitting.
Nitrifying and denitrifying bacteria found particularly in fertilizers cooling water
system. These bacteria converts ammonia to nitric acid by enzymatic action thereby
reduces pH of water, which accelerates corrosion.
5. Algae

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Algae is often visible as green fibrous organisms in internal section of wall and plates
of cooling towers that are wet and exposed to sunlight. Formation of algae on cooling
tower structure causes poor heat removal efficient of tower.
6. Fungi
Cellulolytic fungi attack fibres of cellulose in wooden cooling towers and can destroy
the structure.
7. Fouling
Fouling of system is mainly due to suspended matter in the cooling water. The
suspended matter comes through make up water and by scrubbing of air born dust in
the cooling tower. The suspended dust, dirt may coagulate and accumulate in heat
exchangers. Contaminants like oil, grease, algae also foul the system.
5.2.5 Disadvantages due to above problems in Cooling Water Systems
1) Problems of scale, deposition, fouling leads to maintenance cost for frequent cleaning
of heat exchanger etc.
2) Corrosion can damage heat transfer equipment and thereby leads to replacement cost.
3) Frequent unschedule forced shutdown for cleaning heat exchangers, lines etc. causes
production loss.
4) Scale, deposition, corrosion and fouling in cooling water system forced to run the
system at lower cycle of concentration. Hence water consumption is huge.
5) Energy consumption is more e.g. pumping cost.

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5.3 D.M. PLANT
5.3.1 Equipments of DM plant
(1) Dual media filter:
Capacity- 18 m3
/hr
Working pressure- 6.0 bar g.
 There are two beds of sand and gravels. Dual media filter is a one type of sand filter.
Raw water from the process water storage sump (800 m3 capacity) at 5800-kg/hr-flow
transfer to DMF. Process water pass to DMF to remove suspended solids and
turbidity. Back washing of the filter beds has to be carried out periodically more
frequently if pressure drop across the bed exceeds 0.7 bars and this indicates the
accumulation of the dust in the bed.
 Backwash is taken once in a week.
 There is a pressure control valve to maintain DMF inlet pressure at 6.0 bar g. The
pressure control valve is operated on pressure transmitter, which is located on DMF
inlet line.
(2) Activated carbon filter:
Capacity: 18 m3
/hr
Filter- activated charcoal
The out let water from dual media filter comes in activated carbon filter. Activated carbon
filter if used to remove oil and free chlorine.
3) Strong acid cat ion:
Capacity- 12 m3
/hr
M.O.C----MS rubber lined
Resin----tulsion T-42 (760 liter)
Working pressure-4.0 bar g.
Quantity of resin-660 m3
HCL required- 39.6 kg on 100 % base.

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Output between regeneration- 220 m3
In a cation exchange cation like ca+2
, mg+2
, Na+2
are replaced by hydrogen ion H+
Cacl2 + R-H= R-ca + HCL
Nacl+ R-H= R-Na +HCL
Mgso4 + R-H= R-Mg + H2SO4
CaSO4+ R-H= R-Ca + H2SO4
Periodically we check the quality of the SAC out let water during their service cycle. The
quality of the SAC out let water is as per bellow.
PH- @ 3.0
Sodium-< 300ppb
Free mineral acid-30 ppm
If any of the one parameter gets disturbed we have to do regeneration generally after
18 hrs.
(4) Degasser tower:
Top portion: filled with poly propylene rings.
Bottom portion- storage tank (1600 * 1800)
M.O.C.-M.S
Size- 500 * 2500
Degassor air blowercapacity-212 m3
/hr
Degassor pump- 12 m3
/hr
Water coming from strong acid cation enters in the top portion of the dergassor tower. Air is
blown from the bottom of the toter. Temporary hardness is removed by blowing air through
packing. Air will decompose bicarbonate and co2 will liberate which will be removed from
the top portion of the tower.
(5) Strong base anion:
Capacity- 12 m3
/hr
Moc-M.S rubber lined
Resins-agrion –27 mp

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Work pressure-4.0 bar g
Quantity of resins-780 liters
Output between regenaration-220 m3
NAOH required- 1.2 kg on 100% base
In anion exchange anions like CL, SO4, will be removed with the OH-
hydroxyl ions.
Chemistry of anion exchange
CaSO4 + R-OH= R-SO4 + Ca(OH)2
MgSO4 + R-OH = R-SO4 + Mg(OH)2
Cacl2 + R-OH = R-CL + Ca(OH)2
Mgcl2 + R-OH = R-CL + Mg(OH)2
The anion resins are micro porous resins it will also remove organic matter. The out let water
from the strong base cation is as per following.
PH-8.0 to 9.5
Conductivity-<10 Mmohs/cm2
Silica-<0.2 ppm
(6) Mix Bed:
Capacity-12 m3
/hr
MOC------ms rubber lined
There are both type of resin in it i.e. cation & anion with equal quantity.Whatever ion passed
through cation and anion exchanger will be removed in mix bed. Ion exchange will take place
like cation and anion.
Periodical quality of mix bed outlet is to be analyzed during service cycle.
pH------------------------605 TO 705
Conductivity-------------< 0.2 Mmohs
Silica-----------------------<0.02ppm
Type of resin--------------T-42 + A-27 MP
Quantity of resin----------100 ltr + 100 ltr

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Output between regn-----1320 m3
HCl required---------------4.0 kg on 100% base
NaoH required-------------6.0 kg on 100% base.
Finally Mix Bed outlet called DM water and it will go storage tank. There are two DM
storage tanks in NCPL, 125 m3
, 50 m.3
The process and instrument diagram (P& ID) is
attached here with (fig no C2).
5.3.2 PROCESS OF DEMINERALIZATION
 Demineralization or deionization is the process of removing mineral salt from water by
using the ion exchange process. Demineralization involve two ion-exchange reaction.
Initially, the Cation such as calcium, magnesium and sodium are removed in a
hydrogen Cation exchanger, the exchangeable ion in the resion bed being hydrogen.
The salt are converted to their respective acids. The acidic water is then passed through
an anion exchange where the anions such as sulphates, chlorides, etc. are removed by
exchange of hydroxyl ions.
 Ion exchange is an equilibrium & reversible reaction. In the hydrogen Cation exchange
resins the Cation group shows the greater affinity for other Cation in presence to
hydrogen ions. This process is reversed when the resin bed gets exhausted of hydrogen
ions and it regenerated with a strong acid, the reverse process-taking place because of
hydrogen ions being presented in high concentration in the regenerate acid (either HCl
or H2SO4).
 The anion exchange resin contains activated amine groups and the OH radical replace
the anion like SO4 and Cl2. There are two type of anion exchange resins, strong basic
and weekly basic. The strong basic anion exchange resin is regenerated with Caustic
soda and the weekly basic anion exchange resin is regenerated with Sodium carbonate
or Caustic soda.
 Hydrogen Cation Exchange: -
R.SO3H + NaCl R.SO1Na + HCl
2R.SO3H + CaSO4 (R.SO1) 1Ca + H2SO4
 Weakly basic anion Exchange: -

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RNH1 + HCl RNH1Cl + H2O
 Strong basic anion exchange: -
R4N.OH + H2SIO2 R4N.HSIO2 + H2O
 When the supply of exchangeable ions within the resin is exhausted, the treated water
quality deteriorates and the resins require regeneration.
 The cation exchange resins with mineral acid such as HCl or H2SO4. The strong basic
anion exchange resin is regenerated with Caustic soda and the weekly basic anion
exchange resin is regenerated with Sodium carbonate or Caustic soda.
R.Na + HCL R.H + NaCl
R.Mg + H2SO4 2R.H + MgSO4
R.Cl + NaOH R.OH+ NaCl
R.HCl + NaOH H2O

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5.4.1 STEAM
 Steam is the vaporized form of water. This vapor is commonly visible as a cloud
escaping from the spout of teakettle in which water in the teakettle produces 1600
times more volume in steam form.
 These properties of steam, its ability to carry a large amount of heat and the large
quantity of steam which can be made from a small amount of water, make steam an
ideal substance for transferring heat conveniently and economically to every corner of
the plant. Another property of steam is the way its volume varies with change in
temperature and pressure of the same.
 We take advantage of these properties by generating steam at high pressure to operate
steam turbines, drive generator, compressor and pumps. The low-pressure exhaust
steam from the turbines is then used for process requirements.
 Steam itself will not burn nor will it support combustion and this property of steam is
utilized to purge or remove oil or gas or to extinguish a small fire.
 The intent of the ensuing discussions is to present the fundamentals and precautions
encountered in steam generation. The fundamentals presented touch the basics of heat
transfer and their respective contribution to steam generation, furnace details, material
selection, fuels etc. the precautions mentioned pertain to feed water treatment in areas
of oxygen removal, alkalinity and scale formation.
5.4.2 Principles of steam formation and circulation
 Within the steam generation, steam formation of steam is hinged upon a successful
transfer of heat. Once this transfer is made, steam formation will start. Steam
formation can be described best by use of a simple drum heated from beneath. Steam
forms in bubbles to the surface where the steam is released into the space above. In its
simplest form, three parts of cycle are common to every steam generator.
 There is a drum, which has connected to it a loop of tubing; one of which is heated
and the other is unheated. Steam bubbles form in the heated leg, generally called a
riser. The resulting steam-water mixture is displaced by relatively heavy water in the
un-heated leg or the down-comer and circulation of water is established. Under
operating conditions, there is a continuous flow of water from the drum where steam
releases. The factors influencing circulation is: the column of water in the down-
comer leg weigh more than equal column of steam water mixture in the down-comer
leg. This difference represents the force available to overcome friction and maintain
circulation.
 An actual steam generator consists of many tubular circuits, with a drum or drums
acting as a distributing and collecting device and a releasing point of steam. However,

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actual steam generators are not built up by merely multiplying the number of simple
loops, the circuits are more complex and the number of individual paths for steam
water flow varies from point to point. There are three types of circulation systems
adopted in boilers:
1. Natural Circulation System.
2. Controlled Circulation System.
3. Combine Circulation System.
FIG - 5.2 : Steam Generation plant

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