Naptha cracker unit haldia petrochemicals

1. PREPARED BY:
DEBAJANI DAS
UG-IV,SECTION-A2
CLASSROLL NO.-001910301114
DEPARTMENT OF CHEMICAL ENGINEERING
JADAVPUR UNIVERSITY

2.  Haldia Petrochemicals Ltd., often referred to as HPL is one of
the largest integrated green field petrochemical companies
and 2nd largest among petrochemical industries of India.
 It is a naphtha based project which was set for the first time
in India. It is a polymer industry, producing Linear Low
Density Polyethylene (LLDPE), High Density Polyethylene
(HDPE) and Polypropylene(PP) as main products.

3.  Naphtha is a flammable liquid hydrocarbon mixture.
 The Naphtha that enters the plant from outside the Battery Limit is stored in tanks
before it is supplied to the Naphtha Cracker Unit (NCU).
 There it is cracked so that the bigger hydrocarbons are broken down to smaller ones,
most importantly to Ethylene and Propylene, which are used to produce
polymers,namely, LLDPE, HDPE and PP, the three principal products of HPL.
 In other words, the NCU acts as the most important unit in all of HPL as any carbon atom
in any molecule of product that has been produced from HPL has inevitably passed
through NCU.

4. NCU is a big unit with several operations
continuously going on inside it.
The operations can be broadly grouped into
three sections, namely:
● Heater section
● Compressor section
● Hot and cold section

5.  The main objective of the hot and cold section is to separate
 C1, C2, C3 and C4+ components and produce methane, ethylene
and propylene of required and achievable purity.
 The hot and cold section has four main subsections that separate
the four hydrocarbon components. They are as follows:
 ● Demethanizer
 ● Deethanizer
 ● Depropanizer
 ● Debutanizer

6.  The Demethanizer, the purpose is to separate out C1
components, mainly methane..
 The Demethanizer column is a packed column having
9 beds that separates methane from the heavier bottom liquid.
 The methane overhead splits into two parts. One stream
is mixed with reflux drum liquid and is sent to the cold box
as methane refrigerant.
 The other part is heated, compressed by methane refrigerant
compressor to 39.65 kg/cm²g to liquefy it and then chilled by
overhead vapour and ethylene refrigerant to provide column
reflux and methane refrigerant to the chilling train.
 The bottoms product, containing C2 and above, is pumped to
cold box off gas exchangers no. 3 which preheat the bottoms
before it is sent to the deethanizer.

7.  the Deethanizer is the section that separates the C2 components from
the demethanizer bottoms and provides highly pure ethylene, arguably
the most important product of the naphtha cracker unit.
 The Deethanizer column is a tray column having 69 trays that fractionates
the ethylene rich demethanizer bottoms into two streams. The tower is
pressurized to 21.38 kg/cm²g in order to prevent the boil up of C3’s.
 Feed to the column is in two streams. Both streams have the same
composition but the lower feed is subjected to a higher degree of preheating.
 Preheating and dividing the feeds minimizes the reflux requirements in the
rectifying section and reduces the liquid rates in the stripping section. The
bottoms from the C2 green oil knockout drum is sent on a flow control to
tray 4.
 The deethanizer reboiler utilizes quench water to supply heat to the tower.
The backup steam heated deethanizer steam reboiler is used when there is
insufficient quench water available for reboiling purposes.
 The overhead product, rich in C2’s is fed to the acetylene converters
and the liquid bottoms are pressured under flow control reset by level
control to the depropanizer no. 1

8.  The deethanizer net overhead stream is hydrogenated
in the acetylene converters to convert acetylene to
ethylene and ethane upstream of the ethylene fractionator
 This is a necessary step as acetylene would poison the
catalysts in the polymer units should it reach there with
the ethylene feed.
 This hydrogenation step is done in two stages to improve
the selectivity of the reaction. All the reactions are in vapour
phase.
 The acetylene converter is a reactor system with four beds
provided. Three beds of the reactor will be in service while
the fourth bed will be on standby or regenerating.
 The reactor feed is heated to the reaction temperature
 . It enters the first reactor and flows downward through
the catalyst bed, gets cooled and passes into the second
reactor. Intercooling is provided to remove the heat of
reaction.

9.  The Ethylene fractionator is a fractionating column
having 162 trays, operating at 16.48 kg/cm²g pressure.
 The purpose of this gigantic column is to separate
ethylene and ethane.
 The main feed is hydrogenated C2’s from the ethylene dryer
that enters above tray 116, along with two recycle feeds,
entering at tray 126 and tray 134 respectively. Two reboilers
and one condenser are provided with the column.
 A part of the overhead product is condensed using the
ethylene fractionator reflux drum and refluxed to the
column and the other part is fed as ethylene vent to
the demethanizer column.
 The bottoms is ethane that is recycled to the cracking heaters
and the ethane wash column.
 The main output from the ethylene fractionator column is
collected as side streams from different trays and forms the
desired product, ethylene that is sent to storage and the
polymer units that produce LLDPE and HDPE

10.  The Depropanizer is the part whose purpose is to separate the C3’s from
charge gas that is the bottoms product of the deethanizer column and to
produce propylene, another extremely important product that is essential to the
polymer units.
 There are two Depropanizer columns that serve the purpose of separating
the C3’s in series. The Depropanizer column no. 1and the Depropanizer
column no. 2 are tray columns having 48 trays and 26 trays respectively.
 It has two reboilers and a reflux from the depropanizer no. 1 reflux drum .
 The overhead product of this column passes through the depropanizer no. 1
flash drum where it is divided into two streams, one forming the reflux to
the column and the other forming the feed to the propylene dryers.
The bottoms product of this column still has a considerable amount of
C2’s entrained in it and it is distilled again in the depropanizer column no. 2
 It has two reboilers and a condenser system having the depropanizer no. 2
reflux drum which divides the overhead product from the column into the
column reflux and a recycle feed to the depropanizer column no. 1 , which
exchanges heat with the main feed of this column on its way.
 The bottoms product from the depropanizer column no. 2 containing C4+
is sent to the debutanizer column .

11.  Similar to acetylene, the highly unsaturated
 C3’s,namely the two isomers methyl acetylene
 and propadiene (MAPD) would poison the
 catalysts at the polymer plants if they are
allowed to reach those units mixed with the
propylene feed. Therefore, the dried gas from
the propylene dryer is fed to the MAPD
converters where MAPD is hydrogenated to
propylene and propane.

12.  The Propylene fractionator is a fractionating
 column that is divided into two separate
 columns,50 having 75 trays and 153 trays
 respectively, operating at 19.06 kg/cm²g and
 17.98 kg/cm²g pressures respectively.
 They can be imagined to be the stripping and
 rectifying sections of a single distillation column.
 The two sections are provided in two separate
 towers as a singular propylene fractionator column
 would be excessively high.
 The purpose of these two columns is to separate
 propylene and propane.

13.  The Debutanizer is the final part of the hot and cold section, and it separates
C4 hydrocarbon products from the heavier components. The C4 components
can be used to produce certain useful products so they are separated in the
debutanizer and sent to the BL of the naphtha cracker unit.
 The Debutanizer column is a tray column that has 53 trays and is
operated at 4.53 kg/cm²g pressure. It has two reboilers and a debutanizer
Reflux drum that serves the purpose of a condenser.
 The feed is the bottoms product of the depropanizer column no. 2 and it
enters the column at tray 40. The overhead product from this column is
mixed C4’s that is divided into two streams in the debutanizer reflux drum
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 One stream is sent back to the column as reflux and the other is mixed
C4’s that is sent to the BL.
 The bottoms product of this column is gasoline containing hydrocarbons,
C5 and higher. The bottoms product combines with heavy gasoline and
medium gasoline and forms the raw pyrolysis gasoline (RPG) product that
is sent to the BL.