Process Design_Some Practical Tips

8/10/2019 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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62

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



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67

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



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68



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70

NAPHTHA SPLITTING UNIT CONFIGURATION


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71

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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72

MR PX-NSU SINGLE COLUMN WITH SIDE CUT


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73

MR PX-NSU:TWO COLUMN TCDS ARRANGEMENT


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76

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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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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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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Process Design_Some Practical Tips

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