Column & Vessel_NS.pptx

Process Design & Engg Cell

1

Process Design basics of Column

andPressure Vessel

N ShaikhManagerProcess Design Engineering CellIOCL-RHQ


2Process Design Basics of Column

Process Design Basics of

Column

Process Design & Engg CellThe First Distillation Still

Process Design Basics of Column

The First Distillation Still used in Digboi

???

Process Design & Engg CellDistillation History


Early distillation consisted of simple batch stills to produce ethanol. Crude ethanol was placed in a still and heated, and the vapor drawn from the still was condensed for consumption.

Lamp oil was later produced using the same method, with crude oil heated in batch stills.



The next progression in the history of distillation was to continually feed the still and recover the light product

Furnace Condenser

Batch Still Distillation Process



Further advancements include placing the stills in series and interchanging the vapor and liquid from each still to improve recovery. This was the first type of counter-current distillation column that we have today

Still Distillation in Series

Process Design & Engg CellDistillation – Fractionation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will vaporize.

Fractional distillation in a laboratory makes use of common laboratory glassware and apparatuses, typically including a Bunsen burner, a round-bottomed flask and a condenser, as well as the single-purpose fractionating column.


Process Design & Engg CellDistillation vs Other Processes


Distillation is by far the most important separation process in the petroleum and chemical industries. It is the separation of key components in a mixture by the difference in their relative volatility, or boiling points. It is also known as fractional distillation or fractionation.

Distillation can consume more than 50% of a plant’s operating energy cost.

Alternatives to distillation process : Solvent extraction, membrane separation or adsorption process. These processes often have higher investment costs. Therefore, distillation remains the main choice in the industry, especially in large-scale applications.

Process Design & Engg CellDistillation Processes- Types


Variations appear due to difficulty in separation when the physical properties of the components in a mixture are very close to one another, such as an azeotropic mixture.

Fractional Distillation

Extractive Distillation

Reactive Distillation



Fractional Distillation:

It is the separation of key components in a mixture by the difference in their relative volatility, or boiling points.



Extractive DistillationAn external solvent is added

to the system to increase the separation.

The external solvent changes the relative volatility between two ‘close’ components by extracting one of the components, forming a ternary mixture with different properties.

The solvent is recycled into the system after the extracted component is separated from it.



Extractive DistillationAn external solvent is added

to the system to increase the separation.

The external solvent changes the relative volatility between two ‘close’ components by extracting one of the components, forming a ternary mixture with different properties.

The solvent is recycled into the system after the extracted component is separated from it.




A distillation column may also have a catalyst bed and reaction occurring in it. This type of column is called a reactive distillation column. The targeted component reacts when it is in contact with the catalyst, thereby separated from the rest of the components in the mixture.




A distillation column may also have a catalyst bed and reaction occurring in it. This type of column is called a reactive distillation column. The targeted component reacts when it is in contact with the catalyst, thereby separated from the rest of the components in the mixture.




Process Design & Engg CellIndustrial distillation

Process Design & Engg CellIndustrial distillation

Distillation is the most common form of separation technology used in petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.

Industrial distillation is typically performed in large, vertical Cylindrical columns known as "distillation or fractionation towers" or "distillation columns" with diameters ranging from about 65 centimeters to 6 meters and heights ranging from about 6 meters to 60 meters or more.


Process Design & Engg CellDistillation Column/Fractionator


Process Design & Engg CellDistillation Column Internals


Critera of Distillation Column internals :

To provide better mass and heat transfers between the liquid and vapor phases in the column.

Include trays, packings, distributors and redistributors, baffles and etc.

Promote an intimate contact between both Liq and Vap phases.

The type of internals selected would determine the height and diameter of a column for a specified duty because different designs have various capacities and efficiencies.



Column internals:

Two main types

Trays

Sieve Bubble Cap Valve Trays

Packing

Random : Rings, saddles Structure

Distillation Column Internals


Feed : Liquid Vapor Mixture of vapor-liquid

The vapor phase that travels up the column is in contact with the liquid phase that travels down.




Vap- Liq pathways inside the column :

The vapor phase that travels up the column is in contact with the liquid phase that travels down.




Column distillation is divided two stages :

Rectifying stages

Striping stages



Rectifying Stages

The process above the feed tray is known as rectification.

Vapor phase is continually enriched in the light components which will finally make up the overhead product.

A liquid recycle condenses the less volatile components from rising vapor.

To generate the liquid recycle, cooling is applied to condense a portion of the overhead vapor and termed as reflux.




Stripping Stages

The process below the feed tray is known as stripping

Heavier components are being stripped off and concentrated in the liquid phase to form the bottom product.

At the top of the column, vapor enters the condenser where heat is removed.

Some liquid is returned to the column as reflux to limit the loss of heavy components overhead.




CondenserTotal Condenser

All vapors leaving the top of the column is condensed to liquid so that the reflux stream and overhead product have the same composition.

Partial CondenserIn a partial condenser , only a portion of the vapor entering the condenser is condensed to liquid. Condensed liquid is refluxed into the column and the overhead product drawn is in the vapor form.

In many cases only part of the condensed liquid is refluxed. In these cases, there will be two overhead products, one a liquid with the same composition as the reflux stream while the other is a vapor product that is in equilibrium with the liquid reflux.

Distillation Column Overhead


CondenserTotal Condenser

All vapors leaving the top of the column is condensed to liquid so that the reflux stream and overhead product have the same composition.

Partial CondenserIn a partial condenser , only a portion of the vapor entering the condenser is condensed to liquid. Condensed liquid is refluxed into the column and the overhead product drawn is in the vapor form.

In many cases only part of the condensed liquid is refluxed. In these cases, there will be two overhead products, one a liquid with the same composition as the reflux stream while the other is a vapor product that is in equilibrium with the liquid reflux.

Total Condenser

Partial Condenser

Distillation Column Overhead



Distillation Column

Tray ColumnBubble

Cap Tray

Sieve Deck Tray

Dual Flow Tray

Valve Tray

Baffle Tray

Shed Decks Tray

Side to Side Tray

Disk and Donuts Tray

Packed ColumnRandom Packed Column

Structured Packed Column

Grid Packed Column




Tray Column

Utilize a pressure and temperature differential to separate the products.

For most tray columns, the weir holds a liquid level of each tray. Liquid enters from the down-comer of the tray above.

The vapor must overcome this liquid head to move up the column.

On the tray the vapor and liquid are contacted becomes bubble or froth where the mass transfer takes place and then above the tray they are separated where froth flows over the outlet weir and vapor with the light volatile compound is disengaged.



Tray Column-advantages

Tray column performs well in high liquid and vapor loading.

Tray have higher pressure drop than packed.

Tray also have high resistance to corrosion.

Tray Column-TypesFive major types of tray column :

• Bubble Cap• Sieve• Dual Flow• Valve• Baffle

Shed Deck, Side to Side, Disk and donuts

Process Design & Engg CellDistillation Column Tray


Bubble Cap Tray

A bubble cap tray is perforated flat which has a riser (chimney) for each hole cover with a cap mounted.

Equipped with slots to allow the passage of vapor then the vapor will contact with liquid forming bubble on the next tray.

It is able to operate at low vapor and liquid rates (less than 2 gpm per foot of average of flow width).



Bubble Cap Tray






Bubble Cap Tray






Sieve Deck TraySieve deck tray is perforated plate with

holes punched into the plate usually has holes 3/16” to 1” diameter.

Vapor comes out from the holes to give a multi orifice effect.

The vapor velocity keeps the liquid from flowing down through the holes (weeping).

The number and hole size are based on vapor flow up the tower.

The liquid flow is transported down the tower by down-comers, a dam and overflow device on the side on the plate.

Sieve deck tray has a minimum capacity approximately 70%



Sieve Deck TraySieve deck tray is perforated plate with

holes punched into the plate usually has holes 3/16” to 1” diameter.

Vapor comes out from the holes to give a multi orifice effect.

The vapor velocity keeps the liquid from flowing down through the holes (weeping).

The number and hole size are based on vapor flow up the tower.

The liquid flow is transported down the tower by down-comers, a dam and overflow device on the side on the plate.

Sieve deck tray has a minimum capacity approximately 70%



Dual flow trayDual flow is a sieve tray without down comer. The term dual flow comes from the

countercurrent flow of the vapor and liquid through the perforations.

Vapor move up to the tray above through the hole while the liquid turn down in the same hole that result mal distribution and low efficiency.

Typical perforation sizes range between 1/2” and 1” in diameter.

Dual flow trays best suit systems containing a moderate to high solids content or polymerizable compounds.

High open area dual flow trays have a higher capacity and lower pressure drop than comparably spaced fractionation trays.



Valve TrayValve Tray is using valve which is rise as

vapor rate increase and then reduce as vapor rate fails.

This stop the liquid from weeping.

Valve can be round or rectangular, with or without caging structured.

Valve disk rise as vapor rate increase.

Valve tray has minimum capacity approximately 60%.



Valve TrayValve Tray is using valve which is rise

as vapor rate increase and then reduce as vapor rate fails.

This stop the liquid from weeping.

Valve can be round or rectangular, with or without caging structured.

Valve disk rise as vapor rate increase.

Valve tray has minimum capacity approximately 60%.



Baffle TrayBaffle trays are trays of low fouling po

tential, with low efficiency. They have open areas approaching 50%

where a high efficiency tray will have an open area of less than 15%.

The down-comers require a disengaging area to separate the liquid from the vapor.

This area requires a minimum distance that normally sets the tray spacing.

The liquid is required to travel across the deck to the next down-comer.

Baffle tray has three types:Shed Decks TraysSide to Side TraysDisk and Donuts Trays



Baffle TrayBecause of their open design, baffle trays are

used in applications requiring high capacity, fouling resistance and low pressure drop.

Vapor-liquid contacting takes place when the vapor passes through a curtain of liquid falling between trays, or through rivulets of liquid flowing through tray deck perforations.

Tray decks may be level or slightly inclined and typically occupy 40-60% of the tower cross-sectional area. “.

Baffle trays are well suited for heat transfer applications including heavy oil refining and petrochemical oil refining and petrochemical heat transfer services with high solids or petroleum coke content.



Baffle TraySide to side baffle trays

Side-to-side trays are trays that allow the liquid to splash from side to side.

The decks can be sloped.

Fouling potential of this tray is low, as with efficiency.



Baffle TrayDisk and donut trays

Disk and donut trays are slightly sloped trays that allow the liquid to splash from inner circle ring to outer circle ring.

Fouling potential of this tray is low along with the efficiency.



Schematic of a disk and donut baffle tray column for use as a steam condenser











Baffle TrayShed Decks trays

Shed decks are essentially angle iron beams of various sizes from two to ten inches that are placed in rows across the column.

They typically are at on 24 inch tray spacing.

They may be set in overlapping rows or rotated 90 degrees from tray to tray.

Process Design & Engg CellDistillation Column with packing


Packed ColumnPacked column utilize packing to contact between

the phases (liquid-vapor) on the surface. A major advantage to packed columns

is the reduction in pressure across the column. Typically the column pressure drop for a packed column is less than that of a trayed column because of the percent open area.

Typical percent open area of a trayed column is 8 to 15%, whereas a packed column can approach 50%.

Packed column is advantageous than tray for reduced foaming since generates thin films instead of fine droplets for mass and heat transfer.

Packed column is divided by Random, Structured and Grid Packed Columns

Schematic diagram of a typical packed bed absorption column



Packed Column—random packing

Random packing is packing of specific geometrical shapes which are dumped into the tower and orient themselves randomly.

Random packing has more risk than structured packing and less ability to handle maldistributed liquid.



Packed Column-structured packing

Structure Packed column is crimped layers or corrugated sheets which is stacked in the column.

Each layer is oriented at 70° to 90° to the layer below.

Structured packed offers 30% capacities higher than random packed for equal efficiency up to 50% higher at the same capacity.



Packed Column-Grid packing

Grid packed column is systematically arranged packing use an open-lattice structure.

This device is composed of panels that promote mass transfer and enhance entrainment removal.

They have high open area, resulting in high capacity, low pressure drop, and high tolerance to fouling.

Process Design & Engg CellDistillation Column Design


General Considerations

A tower design is normally divided into two main steps a process design followed by a mechanical design.

The purpose of the process design is to calculate the number of required theoretical stages, column diameter and tower height.

On the other hand, the mechanical design focuses on the tower internals and heat exchanger arrangements.



Steps :Determine the separation sequences, which depends on the relative volatility

and concentration of each component in the feed

Performing a material balance for the column

Determining the tower operating pressure (and/or temperature)

Calculating the minimum number of theoretical stages using the Fenske equation

Calculating the minimum reflux rate using the Underwood equations

Determining the operating reflux rate and number of theoretical stages

Selection of column internals (tray or packings)

Calculating the tower diameter and height



The Selection of Column Internals :The selection of column internals has a big impact on the column

performance and the maintenance cost of a distillation tower.

There are several choices of column internals and the two major categories are trays and packing. The choice of which to utilize depends on the

PressureFouling potentialLiquid to vapor density ratioLiquid LoadingLife Cycle Cost



Criteria for Tray Column



Criteria for Packed Column



Important Thumb rule :Tower operating pressure is determined most often by the temperature of the

available cooling medium in the condenser or by the maximum allowable reboiler temperature.

Economically optimum reflux ratio is about 120% to 150% of the minimum reflux ratio.

The economically optimum number of stages is about 200% of the minimum value.

A safety factor of at least 25% about the reflux should be utilized for the reflux pumps.

Reflux drums are almost always horizontally mounted and designed for a 5 min holdup at half of the drum's capacity.



Important Thumb rule :Limit tower heights to 175 ft (53 m) due to wind load and foundation

considerations.

The Length/Diameter ratio of a tower should be no more than 30 and preferably below 20.

A rough estimate of reboiler duty as a function of tower diameter is given by:

Q = 0.5 D2 for pressure distillationQ = 0.3 D2 for atmospheric distillationQ = 0.15 D2 for vacuum distillationWhere,Q : Energy in Million Btu/hrD : Tower diameter in feet.



Important Thumb rule :Overall column height depends on tray spacing. Tray spacing should from 18“ to 24“

(ease of maintenance to be kept in mind).

For tower dia > 4 ft, Tray spacing ~ 24 “ and for tower dia < 4 ft, Tray spacing is ~18”.

Peak tray efficiencies usually occur at linear vapor velocities of 2 ft/s (0.6 m/s) at moderate pressures, or 6 ft/s (1.8 m/s) under vacuum conditions.

A typical pressure drop per tray is 0.1 psi (0.007 bar).

Tray efficiencies for aqueous solutions are usually in the range of 60-90% while gas absorption and stripping typically have efficiencies closer to 10-20%


58

Process Design Basics of

Pressure Vessel


59

Process Vessel --- why required???

Hold up time of fluid

Phase-Separation-separation between various phases of mixed process stream

a. Liquid-Liquidb. Vapor-Liquid

c. Vapor-Liquid-Liquid

Process Design Basics of Pressure Vessel

Process Vessel are necessary for providing:


60

Process Vessel --- types ???

Vertical

a.Knockout drums (except flare knockout drums) b.Flash drums c.Blowdown drums d.Driers

Horizontal

a. Distillate drums – reflux vesselsb. Surge vesselsc. Steam drums d.Settling drumse.Flare knockout drums


Process Vessel can be classfied as :


61

Advantages of a vertical vessel are:

A smaller plot area is required (critical on offshore platforms)

Large Vapor throughput with small liquid hold up

Generally the vessel volume is smaller

Advantages of a horizontal vessel are:

It is easier to accommodate large liquid flow

Less head room is required

The downward liquid velocity is lower, resulting in improved de-gassing

and foam breakdown

Additional to vapor / liquid separation also a liquid / liquid separation can

be achieved (e.g. by installing a boot).

Vertical vs. Horizontal Vessels



62

Application Preferred OrientationReactor Effluent Separator (V/L)

Vertical

Reactor Effluent Separator (V/L/L)

Horizontal

Reflux Accumulator Horizontal

Compressor KO Drum Vertical

Fuel Gas KO Drum Vertical

Flare KO Drum Horizontal

Condensate Flash Drum Vertical

The preferred orientation for a number of typical vapor / liquid separators

Vertical vs. Horizontal Vessels--services


63

Drum sizing- Vapor/Liquid Separation



64



N6

MINN3

MIN

MIN

`

6 Inch (min)

VO

RT

EX

BR

EK

ER

N4

N7

5 ft

N1

3AN

13BN

9

10+3 THK CLAD(MIN)

HIL 2 FT

NIL 1 FT

LIL 1 FT

4.16 ft

VORTEX BREKER

2:1 ELLIPSOIDAL HEAD10+3 THK CLAD (MIN.)

AFTER FORMING (TYP.)

12

165

STIFFENER RING-1 NOAT CENTER

20012

1:120

2 NOS. EARTHING LUGS

SADDLE 2 NOS.

M2

12.5

ft

N8

WEARPLATE



N1

MIN

150

MM

MIN

IMU

M (H

HLL

TO

BO

TT

OM

OF

PIP

E)

900 S

HO

RT

RA

DIU

S E

LB

OW

HHLL 10 FT

HLL 9 FT

LLL 3 FT

NLL 6 FT

N2

MIN

17+

3 T

HK

CLA

D(M

IN.)M

1

M1

6

M1

1

M5

M1

0

M1

8

M17

NAMEPLATE

N12A

N14A

N12B

N14B

N15A

41.5 ft

LLLL 10 Inch

4 ft.

2 ft.


65




66

Major steps for Vapor/Liquid vessel sizing

Step 0: Assume L/D ratio and % vapour area

Assume L/D ratio

Assume % Vapour area from the standard




67

Major steps for Vapor/Liquid vessel sizing

Step 1: Calculate Minimum allowable vapor area

For both Horizontal & vertical vessels

Area =flow volume per second/ allowable velocity per second

The allowable vapor velocity (VA) is obtained by applying a factor to the critical velocity (Vc - maxm allowable design velocity).

VA = Factor x Vc

VC = 0.15



1G

L


68



ALLOWABLE VELOCITY FACTORS Drum Type Factor Vertical knockout drum without internals 1.0 Vertical knockout drum with baffles

1.5 Vertical knockout drums with horizontal crinkled wire mesh pad. (Pad at least 4 inches (10 centimeters) thick) 2.0 Horizontal drums (With or without crinkled wire mesh pad) 1.7


69



Step 2: Calculate Liquid Space

a. Liquid Surge Volume (LLL-HLL) -- guidelines for liquid surge time

Service Surge Time, Minutes Feed to Tower or Furnace Drum Diameter, feet Below 4 20 4 to 6, inclusive 15 Above 6 10 Reflux to Tower 5 Product to Storage 2 Flow to Heat Exchanger 2 Flow to Sewer or Drain 1 In case surge must be provided for both product and reflux, the larger volume is used, not the sum of the two volumes. When the discharge rate is unimportant, a nominal surge (or holdup) time of approximately two (2) minutes is provided.


70




b. Surge Volume (BTM-LLL) – Locating LLL

Without Water Settling

For guidance, the following minimum levels may be used: Horizontal drums 6 inches (15 centimeters) above bottom Vertical drums 6 inches above lower tangent line

With Water Settling Provide five (5) minutes holdup at the total hydrocarbon rate below the low liquid level for the “settling out“ of water.

In case no pot is employed, holdup for the water itself must also be provided in the bottom of the drum.


71




b. Surge Volume (BTM-HLL) – Locating HLL

Following minimum distance are maintained above HLL

Horizontal Drums Minimum 20% of the drum diameter or 12 inches (30 centimeters) or clearance for feed inlet device, whichever is greater, to top of drum.

Vertical Drums 1'-0" to the bottom of the inlet arrangement (bottom of nozzle, elbow, or impingement baffle) when vapor is present. If no vapor is present, 15% of the drum diameter or 12 inches (30 centimeters) or clearance for feed inlet device, whichever is greater, to the upper tangent line


72




c. Total Liquid Volume

Volume (LLL-HLL ) + Volume (BTM-LLL)

Step 3: Drum Dia and Length calculation

Lx

4

2dπ x % of Total Drum Volume Occupied by Liquid

= Total Volume of Liquid

“D” and “L” is calculated from above assuming L/D ratio


73

Length to Diameter (L/D) ratio:

Design Pressure, in Psig Length to Diameter Ratio (L/D)

50 and less 2:1 to 3:1

greater than 50 4:1 to 5:1

Note: 3.5 kg/cm2 gauge is equivalent to 50 psig

Vessels - Important guidelines



74



Check A: Vapor Space Check

a. Check that height of Vapor area >=0.20 x Drum Dia

% of Total vapor area= (Minimum vapor area (step-1)/ Total area )x100 Height of vapor area can be calculated from the standard chart

b. Vapor space check w.r.t.feed inlet device

Take the larger height of the check “a” and “b”


75




76



Nominal Elbow

Diameter, Inches

Vertical Drums Horizontal Drums

High Liquid Level to Nozzles Centerline, Inches

High Liquid Level to Top of Drums, Inches

ShortRadius Elbow

Long Radius Elbow

Short Radius Elbow Long Radius Elbow

Minimum Recommended Minimum Recommended

1 13 14 4 10 5 10

1 ½ 14 15 5 11 6 11

2 14 15 6 11 7 12

3 15 17 7 13 8 14

4 16 18 9 14 11 16

6 18 21 12 17 15 20

8 24 28 15 20 19 24

10 30 35 18 23 23 28

12 36 42 21 26 27 32

14 42 49 23 29 30 36

16 48 56 26 32 34 40

18 54 63 29 35 38 44

20 60 70 32 38 42 48

24 72 84 38 44 50 56

Required Distance for 900 Elbows


77



Step 4: Height (BTM-LLL) calculation

Area (BTM-LLL) =Volume (BTM-LLL ) / Length

% Area (BTM-LLL) = Area (BTM-LLL) / Total Area

Height (BTM-LLL) can be calculated using the chart

Step 5: Height (BTM-HLL) calculation

Volume (BTM-HLL)= Volume (BTM-LLL ) +Volume (LLL-HLL)

Area (BTM-HLL) =Volume (BTM-HLL ) / Length

% Area ( BTM-HLL) = Area (BTM-HLL) / Total Area

Height (BTM-HLL) can be calculated using the chart


78



Step 6: Locating Normal Liquid Level

NLL = (LLL+HLL)/2


79

Drum sizing- Vapor/Liq/Liq Separation


Water Settling (Draw off Pots) --- Boot Calculation

MAXIMUM POT DIAMETER Drum Diameter Max. Pot Diameter Below 60 inches (150 centimeters) 1/2 drum diameter

60 inches and larger 1/3 drum diameter Increase the water velocity as required up to 10 inches per minute (25 centimeters per minute) to avoid exceeding these values.


80Process Design Basics of Pressure Vessel

Water Settling (Draw off Pots) --- Boot CalculationMINIMUM POT DIAMETER Drum Diameter Pot Diameter Feet Centimeters Inches Centimeters Below 5 Below 150 12 30 5 to 8 150 to 240 18 45 inclusive inclusive Above 8 Above 240 24 60 If extremely low water velocities, less than 0.10 inches per minute (0.25 centimeters per minute) are obtained with the above diameters, do not provide a pot. Instead, extend the hydrocarbon outlet above the bottom of the drum to provide disengaging.




Water Settling (Draw off Pots) --- Boot Calculation

Step1 : Consider boot diameter as per the guideline

Step2 : Consider boot liquid hold-up time of ~ 10 mins between LIL & HIL

Step3: Calculate Length of boot

Step 4: Check Min. length of 3 ft betn. HIL & LIL for controller connection

Step5 : Keep minimum distance of 1 ft betn. LIL & BTL of Boot



82



N6

MINN3

MIN

MIN

`

6 Inch (min)

VO

RT

EX

BR

EK

ER

N4

N7

5 ft

N1

3AN

13BN

9

10+3 THK CLAD(MIN)

HIL 2 FT

NIL 1 FT

LIL 1 FT

4.16 ft

VORTEX BREKER



12

165

STIFFENER RING-1 NOAT CENTER

20012

1:120

2 NOS. EARTHING LUGS

SADDLE 2 NOS.

M2

12.5

ft

N8

WEARPLATE



N1

MIN

150

MM

MIN

IMU

M (H

HLL

TO

BO

TT

OM

OF

PIP

E)

900 S

HO

RT

RA

DIU

S E

LB

OW

HHLL 10 FT

HLL 9 FT

LLL 3 FT

NLL 6 FT

N2

MIN

17+

3 T

HK

CLA

D(M

IN.)M

1

M1

6

M1

1

M5

M1

0

M1

8

M17

NAMEPLATE

N12A

N14A

N12B

N14B

N15A

41.5 ft

LLLL 10 Inch

4 ft.

2 ft.


83




84

Slop for Horizontal vessel:

1 inch in 10 feet down towards the outlet or low point drain so that the vessel may be completely drained during shutdown.

This slope is equivalent to a slope of 1:120.




85

Location of Feed Inlet Nozzle




86

Feed Inlet

Inlet Nozzle

The feed nozzle is normally sized to limit the momentum of the feed.

The limitation depends on whether or not a feed inlet device is installed.

Inlet device

Impacts vapor / liquid separation that can be achieved

Some Typical Inlet Device are as follows:

A Deflector Baffle

Slotted Tee

Half Open Pipe



87

Feed Inlet device



Table 3


88

Feed Inlet device



Table 3


89

Vortex Breaker

Vessels - Internals



90

Vessel Internals-Wire Mesh

Vapor + Liquid

Feed Inlet Vapor (Entrained Liquid)

Wire Mesh

Vapor (Liquid Free)

Liquid


91



92



93

They are used for two reasons:

To minimize entrainment

Suction drums for reciprocating compressors are the most notable examples

To reduce the size of a vessel

The allowable vapor velocity in a drum can be increased significantly by using a wire

mesh demister.

So, when sizing is governed by vapor-liquid separation criteria, this will result in a

smaller diameter of the vessel

Major disadvantage of wire mesh demisters is:

They are not suitable for fouling services



94

Inlet / Outlet Nozzle sizing guideline




95

Inlet / Outlet Nozzle sizing guideline




96

Vapor Nozzles sizing guideline




97




98



PARAMETER LOWER LIMIT UPPER LIMIT

Vessel Diameter, ft (m) 0.7 (0.2) 25 (7.6)

Vapor Density, lb/ft3 (kg/m3) 0.005 (0.08) 5 (80)

Liquid Density, lb/ft3 (kg/m3) 20 (320) 80 (1280)

Surface Tension, dynes/cm or mN/m 2 75

Liquid Viscosity, cP or mPa•s 0.05 2

CWMS Liquid Loading, gpm/ft2

(dm3/s•m2)0.0 (0.0) 20 (13.6)

Foaming Tendency NONE, except for Crude Flash Vessels

TYPICAL LIMITS FOR VAPOR-LIQUID SEPARATOR



Drum sizing- Liquid/Liquid Separation







Major steps for Liquid/Liquid vessel sizing

Step1. Liquid /Liquid Separators are generally horizontal

L/D ratio ~ 4:1 or 5:1

Step2. Calculate Rising Rate (V) of Light Liquid through Heavy Liquid

---Calculation require droplet diameter

DROPLET SIZES Droplet Diameter System Inches Centimeters Caustic - 0.85 specific gravity oils 0.005 each phase 0.012 each phase Water - Naphtha or heating oils 0.005 each phase 0.012 each phase Propane - oil deresining 0.004 each phase 0.010 each phase




Step3. Calculate Rising Rate (V) of Light Liquid through Heavy Liquid

a. Calculate Rising Velocity

Stokes’ law (Reynolds number less than 1)

V = 8.3 x 105 x d2 x Δ S / uc

Intermediate law (Reynolds number between 1 and 1,000) V = 1.04 x 104 x d1.14 x Δ S0.71 / ( Sc0.29 x uc

0.43 )

Newton’s law (Reynolds number between 1,000 and 200,000) V = 2.05 x 103 (d Δ S)0.5 / ( Sc )

Where the Reynolds number = 10.7 d V Sc / uc





V = settling rate in each phase, inches per minute d = droplet diameter, inches S = droplet specific gravity Sc = continuous phase specific gravity Δ S = specific gravity differential between phases uc = continuous phase viscosity, centipoise

b. Select Rising velocity based on Re value from point “a”. But if rising velocity exceeds 10"/min then take 10”/min.




Step4. Calculate Settling Rate (V) of Heavy Liquid through Light Liquid

a. Calculate Settling Velocity

Stokes’ law (Reynolds number less than 1)

V = 8.3 x 105 x d2 x Δ S / uc

Intermediate law (Reynolds number between 1 and 1,000) V = 1.04 x 104 x d1.14 x Δ S0.71 / ( Sc0.29 x uc

0.43 )

Newton’s law (Reynolds number between 1,000 and 200,000) V = 2.05 x 103 (d Δ S)0.5 / ( Sc )






V = settling rate in each phase, inches per minute d = droplet diameter, inches S = droplet specific gravity Sc = continuous phase specific gravity Δ S = specific gravity differential between phases uc = continuous phase viscosity, centipoise

b. Select Settling velocity based on Re value from point “a”. But if settling velocity exceeds 10"/min then take 10”/min.




Step5. Calculate Vessel Diameter

D= 2 +1.7 (flow rate / V) ½

“flow rate“ = that of light phase, cubic feet per minute

V= settling rate of heavy droplet,inches/min

D = drum diameter, feet

Step6. Calculate “L” Keeping L/D ratio 4:1 to 5:1




Step6. Calculate Low & High Interface levels

a. Bottom Tangent Line (BTL) to Low Interface Level (LIL)-----Recommended 12 inches minimum

(i) Calculate Height (BTL-LIL)/Radius of Drum(ii) Calculate % Area occupied by BTL-LIL from chart---y

b. Bottom Tangent Line (BTL) to High Interface Level (HIL)

Low Interface level (LIL) to High interface level (HIL)-----Recommended 14 inches minimum(i) Calculate Height (BTL-HIL)/Radius of Drum(ii) Calculate % Area occupied by BTL-HIL from chart-----x


108






Step7. Residence time of Heavy Liquid settling through Light Liquid

a. Area between high and low interfaces =(x-y)*0.01*cross sectional area of vessel

b. Residence time of Heavy Liquid between high and low interface level=area in”a”*L/Heavy Liquid volume flow

CHECK: Residence time should be more than 2 min




Step8. Light phase space settling time

a. Distance Heavy Liquid must fall from top of drum to High Interface level=Vessel dia - Height(BTL-HIL)

d. Heavy Liquid settling time (between top of drum and high interface level) required for separation

= Distance “a”/ Heavy Liq settling velocity




Step9. Light phase space residence time

a. Light Space Area=(100 - % area occupied below HIL)*Vessel cross sectional area*0.01

b. Light Space volume= Light space area*L

c. Light phase Space residence time= Light space volume/Light Liq flow rate

CHECK : Light phase space residence time

> Heavy Liquid settling time through Light phase




Step10. Heavy phase space rising time

a. Distance Light Liquid must travel from bottom of drum to low Interface level =Height (BTL-LIL)

d. Light Liquid rising time (between bottom of drum and low interface level)

required for separation = Height (BTL-LIL) /Light Liq rising velocity




Step11. Heavy phase space residence time

a. Heavy Space Area=( % area occupied below LIL)*Vessel cross sectional area*0.01

b. Heavy Space volume= Heavy space area*L

c. Heavy phase Space residence time= Heavy space volume/Heavy Liq flow rate

CHECK : Heavy phase space residence time > Light Liquid rising time through Heavy phase






Drum sizing- Vertical Flash Drum





117


Vapor + Liquid

Feed Inlet Vapor (Entrained Liquid)

Wire Mesh

Vapor (Liquid Free)

Liquid


118

They are used for two reasons:

To minimize entrainment

Suction drums for reciprocating compressors are the most notable examples

To reduce the size of a vessel

The allowable vapor velocity in a drum can be increased significantly by using a wire

mesh demister.

So, when sizing is governed by vapor-liquid separation criteria, this will result in a

smaller diameter of the vessel

Major disadvantage of wire mesh demisters is:

They are not suitable for fouling services





Major steps for Vertical Flash Drum Sizing

Step1. Vessel with CWMS or without CWMS

a. The use of a crinkled wire mesh pad or screen would not permit a large reduction in vessel size for vessels lower than 4 ft in diameter, and since a crinkled wire mesh pad or screen is fairly expensive, it is not used much in diameters less than 4 ft. When used, it would be to prevent large slugs of liquid from going to the compressor.

Step 2: Calculate with Crinkled Wire Mesh Screen

a. Calculate critical vap velocityb. Calculate allowable vap velocity ( with CWMS, allowable factor – 2.0)c. Calculate min vap area (Vap Flow rate/allowable vap velocity)d. Calculate minimum diameter




Step3. Calculate without Crinkled Wire Mesh Screen

a. Calculate critical vap velocity

b.Calculate allowable vap velocity ( without CWMS, allowable factor – 1.0)

c. Calculate min vap area (Vap Flow rate/allowable vap velocity)

d.Calculate minimum diameter

Step4. Liquid surge volume and height calculation

a.Consider liquid hold–up time (between LLL-HLL) as per standard

b.Calculate LLL-HLL height




Step5. Drum height

a. Height of CWMS (if there)

b. Height of inlet +elbow - min recommended 2.5 ft

c. Height (Vessel top tangent line to top of inlet nozzle) - min recommended 2.5 ft

d. Height HLL to bottom of Inlet nozzle – min recommended 1 ft

e. Height (LLL to Bottom Tangent line)– min recommended 0.5 ft

f. Height (HLL-LLL)

f. Total Drum Height Calculated

g. Check L/D - as per previous table. If L/D is not OK, calculate with new Dia



Drum sizing- Vertical KOD




Major steps for Vertical KOD Sizing

Step1. Vessel with CWMS or without CWMS

a. The use of a crinkled wire mesh pad or screen would not permit a large reduction in vessel size for vessels lower than 4 ft in diameter, and since a crinkled wire mesh pad or screen is fairly expensive, it is not used much in diameters less than 4 ft. When used, it would be to prevent large slugs of liquid from going to the compressor.

Step 2: Calculate with Crinkled Wire Mesh Screen

a. Calculate critical vap velocityb. Calculate allowable vap velocity ( with CWMS, allowable factor – 2.0)c. Calculate min vap area (Vap Flow rate/allowable vap velocity)d. Calculate minimum diameter




Step3. Calculate without Crinkled Wire Mesh Screen

a. Calculate critical vap velocity

b. Calculate allowable vap velocity ( without CWMS, allowable factor – 1.0)

c. Calculate min vap area (Vap Flow rate/allowable vap velocity)

d. Calculate minimum diameter

Step4. Liquid surge volume and height calculation

a.Consider liquid hold–up time (between LLL-HLL) – min recommended 24 hrs

b.Calculate LLL-HLL height

– min recommended 1.5 ft




Step5. Drum height

a. Height of CWMS (if there)

b. Height of inlet +elbow - min recommended 2.5 ft

c. Height (Vessel top tangent line to top of inlet nozzle) - min recommended 2.5 ft

d. Height HLL to bottom of Inlet nozzle – min recommended 1 ft

e. Height (LLL to Bottom Tangent line)– min recommended 0.5 ft

f. Height (HLL-LLL) – min recommended for KOD is 1.5 ft

g. Total Drum Height Calculated

h. Check L/D - typical L/D for KOD is 2:1


126

Drum sizing- Flare KOD



127



Typical Flare KOD


128




129



Major steps for Flare KOD Sizing

Step1. Drum sizing based on maximum single risk vapor load condition

a. Sp. Garvity of HC liq from chart at 3200F and 19 psiab. Dropout Velocity(VD) -- Critical velocityc. Allowable Velocity (VA) – Generally 1.0 for conservative cased. Assume vapor space Height (HLL-top of drum)e. Liquid space Height (BTL-HLL)- Generally zero(0)f. Residence time – Vapor Space height / Allowable velocityg. Find vapor volume = maxm vap Flow rate/residence time

= drum volumeh. Drum Dia = maxm vap space height i. Find drum lengthj. Check L/D ratio– within 3:1 to 5:1


130




131



Step2. Check Drum sizing based on maximum liquid relief condition

a. Maximum liquid relief load after flash at operating condn – generally 3200F and 19 psia

b. Liq flow time – Generally 2 hrs recommendedc. Pump capacity for liquid outd. Net Liq fill up flow = “a*b” – “c”e. Net liq fill up volume= “d” * “b”f. Find Drum volumetric capacity = 3.14*0.25*D2*L

( using D & L calculated in Step-1)

CHECK: Net Liq Fill up Volume (for maxm liquid relief condition) <= 50% of Drum Volumetric capacity( for maxm vapor load condition)

If not satisfied, recalculate



Drum sizing- Vapor/Liq/Liq SeparationExample



































144

Documents

Column & Vessel_NS.pptx