process design_some practical tips
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Process Design: Some PracticalTips
P.K.Mukhopadhyay
Indian Oil Corporation Ltd.
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Points to be covered
Basics of Fractionation column Design
Crude Oil Distillation : Atmospheric & Vacuum
Distillation of components defined by narrow cutse.g. Naphtha Stabilization & Naphtha Splitter
Energy Improvement Opportunities & Heat ExchangerNetwork design in Process plants
Case Studies
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SOME BASICS
Section above feed point - Rectifying /Enrichment section.
Section Below feed - Stripping section.
Reflux ratio R = Flow returned as reflux
Flow of top product distillate
Minimum reflux Rmin
:- Reflux below which stage
required is infinity.
Optimum reflux ratio typically lies between 1.2 to 1.5
times the minimum reflux ratio
Relative Volatility ij = Pi / Pj = Ki / Kj
y = x /(1+ (1)x) for construction of y-x diagram
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McCabe Thiele B-T
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Stage 30,feed stage 12, QR=16.4 Gcal/ hr; Qc =15.2 Gcal/hr; Feed Temp = 80 Deg C
McCabe Thiele B-T
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Tray Number0 6.0 1 2.0 18.0 24.0 30.0
S
epa
ration
F
actor
1E-2
1E-1
1E0
1E1
1E2
1E3
COLUMN T1
BENZENE/ TOLUE NE
Stage 30,feed stage 12, QR=16.4 Gcal/ hr; Qc =15.2 Gcal/hr; Feed Temp = 80 Deg C
Feed Tray Location for separation of B-T-PX
Separation Factor Vs stage
Separation Factor defined as Log XLK/XHK
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Tray Number
0 6.0 12.0 18.0 24.0 30.0
Fract
ion
0
0.20
0.40
0.60
0.80
1.00
COLUMN T1
Liquid Fraction of BENZENE
Liquid Fr action of TOLUENE
Liquid Fr action of PXYLENE
Feed Tray Location
Composition Vs Stage (Feed At 12th Stage)
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Better Feed Tray Location for separation of
B-T-PX
Separation Factor Vs stage
Tray Number
0 6.0 12.0 18.0 24.0 30.0
Separati
on
Factor
1E-2
1E-1
1E0
1E1
1E2
1E3
COLUMN T1
BENZENE / TOLUENE
Stage 30,feed stage 18, QR
=13.26, Qc=12.03; R/R= 1.64 Feed Temp = 80 Deg C
Separation Factor defined as Log XLK/XHK
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Composition Vs Stage (Feed At 18th Stage)
Tray Number
0 6.0 12.0 18.0 24.0 30.0
Fraction
0
0.20
0.40
0.60
0.80
1.00
COLUMN T1
Liquid Fraction of BENZENE
Liquid Fr action of TOLUENE
Liquid Fr action of PXYLENE
Better Feed Tray Location for separation of
B-T-PX
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What is Crude Oil?
Crude is a mixture of hydrocarbons mainly.
Characterized by narrow cuts.
The mid point of the cuts is used to determinethe average boiling point of the cut.
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Crude Oil Distillation
Crude oil distillation is an open art technology .
The crude oil is distilled at atmospheric
pressure and separated into various fractions as
desired in Crude oil distillation unit .
The reduced crude oil is further fractionated
under vacuum to produce vacuum gas oil
(VGO)as a feed to Hydrocracker or FCCU in a
Fuel type Vacuum Unit , or distilled to produce
Lube oil feed stock in a Lube type Vacuum
Unit.
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Basic Process and Fractions
SEPERATION BY BOILING POINT DIFFERENCE.
CRUDE ASSAY/TBP PROVIDES ESTIMATES OF VARIOUSPRODUCTS OBTAINABLE FROM A PARTICULAR CRUDE.
TYPICAL PRODUCTS OF CRUDE OIL FRACTIONATION:
UNSTABILIZED NAPHTHA : IBP 1200C
HEAVY NAPHTHA : 1200 1400C
KEROSENE : 1400- 2700CLIGHT GAS OIL : 2700-3200C
HEAVY GAS OIL : 3200- 3700C
REDUCED CRUDE OIL : 3700C +
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Basic Process and Fractions
RCO is further fractionated into (Fuel Type)
Gas Oil
VGO ( 370oC 550oC) VR ( 550oC + )
Lube Type Gas Oil
Spindle Oil
Light Oil Inter Oil
Heavy Oil
VR
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Distillation Column Design
The design of distillation column can be divided into the following steps
Specify the degree of separation : Set product specification.
Select the operating conditions : Operating pressure and temperature.
Determine the stage and reflux requirement : the no. of equilibrium stages.
Select the type of contacting device : Plates or packing.
Size the column : Diameter, number of actual trays.
Design the column internals : Plates, distributors, packing supports etc.
Mechanical Design : Vessels and internal fittings.
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Separation Criteria
DEGREE OF SEPARATION :
DIFFERENCE BETWEEN ASTM 5 % POINT OF
HEAVIER DISTILLATE & ASTM 95% POINT
OF LIGHTER DISTILLATE.
DEGREE OF DIFFICULTY OF SEPARATION :
DIFFERENCE BETWEEN ASTM 50% POINT OFTHE DISTILLATE FRACTIONS IN QUESTION.
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Separation Criteria
It can be derived from the above.
FOR A FIXED NUMBER OF TRAYS TO GET
DESIRED DEGREE OF SEPARATION, REFLUX
REQUIREMENT IS DIRECTLY PROPORTIONAL
TO THE DEGREE OF DIFFICULTY OF
SEPARATION.
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Manual computation Method
Mark the cut points in the TBP curve of the crude and notethe yields.
Consider defined ASTM GAP/ Overlap as basis to
develop TBP/ASTM of each fraction by modification ofthe tail.
Convert ASTM Gap/Overlap to TBP GAP/Overlap with
reference of charts.
Superimpose the TBP GAP/Overlap using parallelogrammethod.
The TBPs of each fraction is now available.
Convert them to ASTM.
The EFV can also be drawn.
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Manual computation of cut points
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SELECTION
OF
COLUMN PRESSURE
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Selection of column pressure
Pressure to be adequate that dew point (for the composition of top
product) is more than cooling hot water temperature , to be around
450C + T(15 0C) = 600C with cooling water inlet temperature of
330
C with condensate temperature of 400
- 450
can be obtainedwith consideration of 100 150 T . The column pressure to be
adequate that bubble point of the top product is 400- 450.
n
KiXi =1 at column pressure and drum temp of 450.
i=1
or n
Pt = pii=1
pi calculated at 450C for all components
pi = xi.Pi or yi Pt = xi Pi.
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For crude distillation columnThe top product is a mixture of light end and top Naphtha (C5-1400).
The naphtha TBP is subdivided 10 0C or 200C cuts e.g. 700-800, 800-900,900-1000 etc.and midpoints are tabulated .
Kvalues are estimated from De Priester chart
Comp./Cut range(TBP) B.P.T Ki at 450,1.6 Kg/cm2g Xi Ki Xi
C1 B1 K1 X1 K1 X1
C2 B2 K2 X2 K2 X2
C3 B3 : : : :
C4 B4 : : : :
C5 B5 : : : :
700- 900 800 : : : :
900-110 0 1000 : : : :
1100-1300 1150 : : : :
1300-1500 1400 Kn Xn Kn Xn
n
Ki X i =1i=1
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It KiXi =1 then the pressure is O.K.
if not 1 then repeat trial with another value of pressure till KiXi is 1.
Same method is applied for discrete components and mixture of pure component
and fixes the reflux drum pressure.
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Typical calculation for top pressure determination
11-V-02 pr. Deternination [ Determination of Bubble point process]11-V-02 liq. Temp. assumed 450C =1130F
Pr. assumed 450C =28.4 pisa = 2 Kg/cm2 abs
Components ormal Boiling pt 0 Ki Xi x 100 K X i
C2 20 0.79 15.8
C3 8.5 5.54 36.01
iC4 2.8 3.73 10.444
nC4 2 12.69 25.38
45-55 122 0.46 9.75 4.485
55-65 140 0.3 7.74 2.322
65-75 158 0.23 7.42 1.7875-85 176 0.17 6.77 1.151
85-95 194 0.12 6.11 0.733
95-105 212 0.079 6.41 0.506
105-115 230 0.056 6.86 0.384
115-125 248 0.04 6.42 0.257
125-135 266 0.027 6.22 0.168
135-145 284 0.017 5.33 0.091145-155 302 0.013 4.49 0.058
155-165.5 322.25 0.008 3.73 0.03
99.589100
Trial assumed found O.K.
For K determination [ Pcv = 3100 psia]
Defference API Data BookSo 11-V-2 Pressure = 2 Kg/cm2(abs)
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Components Normal Boiling pt 0F Yi x 100
Ki @
2480F&
29.3 psia
100 x Xi =
(Yi x 100)/
Ki
C2 0.79 38 -
C3 5.54 17 0.3
iC4 3.73 10 0.4
nC4 12.69 8 1.6
45-55 122 9.75 2.5 3.9
55-65 140 7.74 2.2 3.5
65-75 158 7.42 2 3.7
75-85 176 6.77 1.7 4
85-95 194 6.11 1.15 5.3
95-105 212 6.41 1.05 6.1
105-115 230 6.86 0.8 8.6
115-125 248 6.42 0.63 10.2
125-135 266 6.22 0.5 12.4
135-145 284 5.33 0.35 15.2
145-155 302 4.49 0.258 17.4155-165.5 322.25 3.73 0.225 16.6
x i =106.5
Trial assumed O.K.
Top temp of the column =1200C
Top per =1.5 Kg/cm2(g)
Typical calculation for top temperature determination
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Kirkbride equation is used for feed tray location.
log [Nr/ Ns] = 0.206 log [(B/D) ( x f. LK / x d.HK )2] (Kirkbride equation )
where Nr = number of stages above the feed, including any partial
condenser,
Ns = number of stages below the feed, including the reboiler.
B = molar flow bottom product.
D = molar flow top product.
xf. HK
= concentration of the heavy key in the feed.
x f. LK = concentration of the light key in the feed.
x d. HK= concentration of the heavy key in the top product.
x b. LK = concentration of the light key in the bottom product.
In simulation method is known as short cut method.
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Configuration
There are several configuration commonly deployed in Crude
Distillation Unit.
Without pretopper.
With a pretopper. With a preflash drum.
The unit with Pre-topper is sometimes more energy efficient
than the conventional (with only Topper and Pre-flash drum)
as Pre-topper is operated at lower reflux ratio than Topper and
Pre-topped Naphtha alone is fed to stabilizer resulting in lower
requirement of its re-boiler duty so this configuration calls forlower heat requirement.
Typically, the Crudes having higher Naphtha yield needs
pretopper to limit the topper diameter and stabilizer diameter.
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Configuration contd
Adding a Pre-topper is a best configuration for
debottlenecking /revamping of Crude Distillation Unit
as this configuration reduces the diameter requirement
of topper and stabilizer.
Additionally, if furnace mass velocity is limiting,
installation of Pre-topper or Pre-flash drum helps indebottlenecking the same.
The other configuration deployed is an Atmospheric
& Vacuum Unit combined (AVU). Wherein the RCOis fed directly to the Vacuum Furnace then to the
Vacuum Column. This is considered to be the most
energy efficient configuration.
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Heat integration Opportunity inCrude distillation unit
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Heat integration in crude distillation unit:
The basic art of a Crude Distillation Unit lies not only in designing theunit for desired products with desired separation but also for better Heat
exchanger synthesis and heat integration for achieving maximum heat
recovery from hot products. Crude units having integration with Vacuum
unit is a heat surplus environment. The heat supplied by two Furnacesare available to crude.
Maximum preheat attainable with this configuration on gulf crude is
around 2950
C-3000
C. Rest of the heat is typically utilized for utilityheating/steam generation.
It is often felt that crude with low RCO yield would result in much lower
preheat. But often recoverable heat from pumparounds are high, and this
provides opportunity to the designer to configure the heat exchanger
train to recover full potential of pumparound heat. Traditionally, Gujarat
ANK/SG (with RCO yield ~20%) processing used to deliver a preheat
of~2300C but with reorientation of the train along with maximization of
PA, preheat can be enhanced to 2750C in one revamped crude unit.
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Overhead heat integration
Options:-
Introduce a Top Pump around in Topper.
Integrate Pre-topper Overhead along with crude
Integrate Topper Overhead along with crude.
It is worth mentioning that,
o Introducing a top pump around is the easiest and cheapestway to integrate Overhead heat. This is achieved byreducing the reflux ratio; thereby lowering heat rejection
to Overhead Condenser/ coolers.
o A Pre-topper Overhead integration is also a good optionand safe from the point of view of corrosion.
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Overhead heat integration- Contd
o The Overhead integration of topper is somewhat cumbersomefrom the viewpoint of corrosion as Overhead System willcontain Cl- and H2S. H2S is known as chloride corrosion
accelerator as it combines with Iron Chloride (a product ofcorrosion) to produce FeS and regenerate HCl for furtherattack.
2 HCl + 2 Fe + 2 H2O FeCl2 + Fe (OH) 2 + H2FeCl2 + H2S (Vapor phase) FeS + 2 HCl
Introduction of a Top PA in the column design and integrating it
with crude for heat recovery can be a preferred option when the
unit does not have a Pre-topper in its configuration.
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AVU contd.This configuration is most energy efficient
where in RCO from Crude Column is fed
directly to Vacuum heater then to Vacuum
Column, as no heat of RCO is lost in air
cooler/tempered water coolers.
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CASE STUDIES
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Case Study-1
Capacity Augmentation of a Crude unit:
Often, when Pump around duties need to be
increased with augmentation of throughput; two
Pumparounds can be configured instead of one. An
example is the revamp configuration envisaged for
AU-5 of Gujarat Refinery. In the existing unit thereis single Topping column having provision for three
side cuts, viz., Heavy Naphtha, Kerosene, Gas Oil
and correspondingly three pumparounds, viz., TopPA, SK PA, GO PA.
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Case Study-1 Contd.The same column thus could be used with splitting of
Pumparound & Product draws as per above arrangement.
The old train of 3.0 MMTPA has been retained by
allocating Pump-arounds & products of similar flows in the
train.
A new parallel train was added to take the heat duties of
additional Pump-around & products.
Also RCO stream was split into two. One part routed the
old train the balance routed to the new train.
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Case Study-2 Contd
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Case Study 2 Contd
One very old crude unit was in operation abroad. The unit wasoriginally designed by Foster Wheeler Corp. This had a pre-flash
drum, and had a unique configuration of Naphtha splitter located
upstream of stabilizer. The off gas was being compressed and put to
the fuel gas system.
On simulation it was found that no gas is bled at operating pressure of
the crude column. The gas and LPG components were getting
released from Naphtha splitter top and being compressed and put in
fuel gas system.
The Pre-flash drum was operating at low temp of around 90
0
C due tolow heat pick up and not vaporizing enough hydrocarbons. Thus,
mass velocity through the feed furnace was high and at its limit.
Consequently, the pressure drop through furnace was high and
increasing throughput was not possible.
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Original configuration of the unit
Stabilizer
Stab Naphtha
Pre
Flash
Drum
Atm.
Column Nap.
Splitter
Comp
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Case Study-2 Contd
The heat exchanger train was reorganized and
pre-flash drum temperature increased toaround 2000C to separate Naphtha and thus
reduce the feed to the furnace and maintain the
Mass velocity stipulation through it and
allowed capacity augmentation. Further, the
stabilizer was placed upstream of Naphtha
splitter and the compressor was eliminated.
Vacuum Distillation Unit:
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Vacuum Distillation Unit:
The primary objective of a vacuum distillation is to
produce either feedstock for FCCU or HCU. This type
of vacuum distillation units are termed as Fuel Type
Vacuum Unit. The other kind of vacuum distillation
unit is a Lube Type Vacuum Unit and deployed for
production of fractions for Lube Oil Base stocks.
In a Fuel Type Vacuum distillation Unit the VGO
TBP cut point is controlled for Maximizing
profitability while containing the level of
contaminants acceptable by downstream secondary
Units.
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5500
5300VGO Cut Point
100 %0
Vol %
Temp 0C
Vacuum Distillation Unit- contd:
TBP Crude
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Different Configuration of Vacuum Column contd:
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Different Configuration of Vacuum Column - contd:
* The first one operates typically at 8-12 mm Hg (a) at top. The
vapour directly goes to ejectors.
* The second type operates at 60-70 mm Hg (a) at top and havea precondenser, the non-condensable are pulled by ejector.
* The third type of operation is done at 18-25 mm Hg (a) at top.
Without stripping steam has a booster ejector followed bycondenser.
* This fourth type again operates with a top pressure of 18-25
mm Hg (a) and uses stripping steam and Coil steam both. This typeis considered best to increase cut point of VGO limiting the
contaminants like V, Ni etc. in VGO with same number of stages in
wash section as compared to other configurations.
Revamp of Vacuum Distillation Unit (VDU):
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Case Study-3
In Fuel type vacuum column, revamp design for capacity
augmentation can be undertaken by
- increasing number of side products
- introducing additional pumparound(s)
Outcome!
Increased heat recovery in feed resulting in higher
preheat
Capacity increase limited by Fired heater Mass
velocity criterion
Revamp of Vacuum Distillation Unit (VDU): -
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Revamp of Vacuum Distillation Unit (VDU): Case Study-3
One very old fuel type Vacuum unit having a capacity of 0.8
MMTPA was revamped to 1.2/1.5 MMTPA. The unit was operating
with 3 side cuts namely Heavy Diesel,VGO, Vacuum Slop and with
two Pumparounds, viz., Heavy Diesel PA and VGO PA. In revamp a
fourth draw HVGO was introduced along with Pumparound and good
amount of heat in Heavy Diesel PA which was getting rejected to
water cooler has been shifted to LVGO/ HVGO Pumparoundsmaking them recoverable to preheat the feed.
In wash section Mellagrid packing equivalent to two stages has been
installed. As a result of this modification, the preheat temperature gotincreased from 2500C to 3150C and VGO cut point increased
considerably. Besides, improvement in quality and yield of VGO,there was reduction in P of column to a level of 8 to 10 mm Hg.
Case Study-3 contd:
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Hvy Diesel
VGO
Slop
VDU:- Old Configuration
VR
Feed
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Case Study 4
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Case Study-4
FPU-2(Hydrocracker Feed Preparation Unit):
Capacity revamp of a Vacuum Distillation unit generating
VGO for Hydrocracker feed is constrained by feed qualityrequirement w.r.t Ashphaltene, metals, N.
Higher load in wash zone makes the washing poor.
Introduction of extra heavy VGO (HHVGO) draw will
relieve the wash section and hence quality of VGO.
However, this approach is successful if the refinery has a
FCC, which take this HHVGO with higher Ashphaltene,
metals and N.
Case Study-4 contd:
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Typically, two stages are provided in vacuum tower wash zone. Often
three stages are also provided in wash section to improve the quality ofVGO. This would need higher amount of wash oil so that bottom of the
wash bed dont get dried and form coke. A minimum wash oil rate
required is 0.5 M3/hr per M2 of the column at the bottom of the wash
bed. The wash oil flow at the top of wash bed should be adequate to
ensure a wash rate of 0.5 M3/hr per M2 of cross section of the column at
bottom of the bed to avoid coking of wash bed. This is best measured by
vacuum slop draw rate.
Thus, the wash oil flow & vacuum slop flow are very important for
maintenance of the health and operation of a Vacuum tower.
Pressure drop measuring devices are provided across each bed to
indicate the performance with respect to flooding /coking etc. Typically,
Vacuum tower internals are either random or structured packing.
Case Study-4 Contd
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y
The FPU-2 was originally designed to produce feedstock forHydrocracker (HCU) and had a capacity of 2.5 MMPA. Design
preheat was 2980C. It was observed that the asphaltene and N
content of VGO used to go up often with change in feedstock. The
HCU was originally designed to process a VGO feed stock having
asphaltene content of maximum 100 ppm (n-Heptane insoluble
Chevron method) and N content of 800 ppm max.).
It was desired to augment the unit capacity beyond 2.5 MMTPA
to the maximum level feasible without any change in the existing
charge heater. The study showed that there was requirement of
preheat increase to process more feed within designed furnaceduty. So emphasis was given to enhance preheat and increase
VGO cut point maintaining the asphaltene & N content within
stipulated level.
Case Study-4 Contd:
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A third VGO withdrawal as HHVGO below HVGO draw off zone wasintroduced in the revamp. The routing envisaged was:
VGO (LVGO + HVGO) HCU Feed
HHVGO FCCU Feed
Wash section was located below HHVGO tray. Thus, it was possible tocontain VGO asphaltene & N within stipulated limit and reduce VR by
pulling HHVGO. High N content of HHVGO was getting diluted by
VGO obtained from RCO of HS origin (low in Nitrogen) from other
Vacuum Unit. Thus, it helped in increasing distillate (LVGO+HVGO+HHVGO) cut point and reduction of VR from vacuum column.
The preheat could be increased to ~ 3200C by splitting of RCO train
and recovering HVGO rundown product heat in feed which in earlierconfiguration was used for LP steam generation.
The unit operates at 3.3 MMTPA delivering the revamp objectives.
Case Study-4 contd:
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Heavy Diesel
LVGO
Vacuum Slop
Old Configuration
VR
Feed
HVGO
Case Study-4 contd:
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Heavy Diesel
LVGO
Vacuum slop
New Configuration
VR
Feed
HVGO
HHVGO
Design deficiency : Case of Two column Atmospheric
Distillation
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Distillation
Original configuration: Fractinator Column, Stabilizer
Revamp Configuration: Prefractionator, Fractionator, Stabilizer
Crude Distillation Unit Configuration Change in
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revamp:
- Single column Configuration:
Sub-cooled Reflux at 450
C for minimum Fractionator pressure
- Two Column Configuration:
Pre-fractionator reflux to be sub-cooled for minimum pressureoperation
Fractionator reflux to be at bubble point otherwise reflux drum is
likely to be under vacuum. Fuel gas make up required for positivepressure, that makes overhead Naphtha unstable requiring its
processing in Stabilizer Extra energy consumption
Two column Atmospheric Distillation Design mistakes
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Modification of Fractionator overhead system
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Case study -5
Preheat improvement of HR CDU-1
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63
Design Basis:
Crude TPut 3.5 MMTPA
Crude Considered:
HS : Basra Light
Naphtha Splitter idling
Preheat improvement of HR CDU-1
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Preheat improvement of HR CDU-1
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Preheat improvement of HR CDU-1
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Preheat improvement of HR CDU-1
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Preheat Improvement Study:
Present Preheat temperature of CDU-1 (Actual) 265 Deg C
Achievable Preheat with Present configuration 272 Deg C
Achievable preheat by idling of Naphtha Splitter 282 Deg C
and adding exchangers in Gas oil/Crude circuit
Naphtha Splitter cannot be idled at present due to surface area
limitations in existing preheat exchangers 11-E-05 A-D Two new exchangers in Gasoil/crude service also required.
Benefit : Savings of 2.9 Gcal/h
Preheat improvement of HR CDU-1
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NAPHTHA SPLITTING UNIT CONFIGURATION
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MR PX-NSU ENERGY OPTIMIZATION STUDY
PX feed preparation unit consists of two column arrangement withoverhead vapor heat of Second column ( HP) supplying part heat tothe re-boiler of the first column( LP) ( Heat Coupling Arrangement).
Required C8 specified in PX feed : 60 % purity of C8 with min 85%recovery
Both single column and two column configuration were studied toachieve the desired specification with minimum energy
consumption, minimum outage of unit with easy execution.
Case study- 6
MR PX-NSU EXISTING CONFIGURATION
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MR PX-NSU SINGLE COLUMN WITH SIDE CUT
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MR PX-NSU:TWO COLUMN TCDS ARRANGEMENT
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Case of salt deposition in reactor effluent cooler and
corrosion in top section of Stripping column in aDHDT unit:
DHDT units typically are with two separator drums
CHPS & CLPS
Energy reduction endeavor pushes designers to
adopt 4-drum system HHPS,HLPS,CHPS &
CLPS
HHPS temperature is critical as Rx effluent contains
NH4CL and NH4HS chances of solidification
Case study-7
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DHDT UNIT : EXISTING UNIT CONFIGURATION(FEED + EFFLUENT CIRCUIT+ STRIPPER)
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79 2013 Indian Oil Corporation Ltd.
All rights reserved
28
27
30
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C 8:
ISOM Unit Isomerate Yield Problem Case study-9
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ISOm unit of an Indian refinery experienced Isomerate RON drop
from design number because of change in feed characteristics
Limitation in OH condenser of DIH column was experienced
Necessity of performance improvement of DIH column to
alleviate the problem
Feed Quality:
Present operation, wt% Design, wt%
Naphthenes, MCP,CH ~ 35 ~12
C5 / C6 Paraffin ratio ~ 0.9 ~0.42
Iso Pentane 13-14 ~8.0
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ISOM Unit Problem Contd
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Higher Naphthene content in feed to Rx inhibits isomerizationreaction of n-C5 / n-C6 and affects RON
Higher C5/C6 ratio in feed lowers Isomerate RON
Higher i-Pentane in feed reduces n-Pentane conversion
DIH recycle stream Quality:
High MCP, CH content in feed increases Naphthene load in DIH
recycle thus resulting in poor conversion in Rx
Effect is lowering Isomerate RON
Present operation, wt% Design, wt%
2- Me Pentane 33.9 18.4
3-Me Pentane 21.2 13.5
N-Hexane 14.5 11.1
Total 69.6 43.0
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CASE STUDY-9
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88
2009 Indian Oil Corporation Ltd. All rights
reserved 88
2009 Indian Oil Corporation Ltd. All rights
reserved
TROUBLESHOOTING OF CRUDECOLUMN INTERNALS FOR
PREHEAT IMPROVEMENT
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250 .
AF .
.
AF
.
2007 /D,
AF ,
.
B A
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B A:
&
E A C
C D A
F C D
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AF AF C
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AF AF C &
& ( 1)
Inadequate cross section of the central channel may obstruct theliquid Flow path as chimney length was oriented in the direction ofwithdrawal channel
D A , C
The obstruction to liquid flow path may result in very high liquidgradients
Open segmental weir for internal reflux may result in
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Open segmental weir for internal reflux may result inpossibility of Inadvertent high flow of IR from the
chimney tray from side down comers from both sides
10%
D
75%
B
)
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, ( )
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.
Sealing of the down comer and provision of piped down
comers
,
.
()
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, ) DEC
2009
A ,
()
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C 10 C
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C 10 C.
4800 F /
9.3 C /.
B AF
1.5 % AF .
D
Conclusion: -
The basic configuration adopted during the design of a Unit plays
major role in efficient & trouble free operation of the unit.
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j p
During operation maintaining column top temperature to avoid
water dew point corrosion needs to be continuously monitored.
Further ensuring prescribed wash oil reflux to wash section is the
key to trouble free and efficient operation of crude & vacuum
distillation units.
Energy improvement design study needs to be done in conjunction
with the process optimization to achieve most optimal solution
With new feed to the unit, Simulation may be carried out todetermine the most optimum operating condition and the unit needs
to be operated in accordance to the same.
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