Drums, Vessels, & Storage Tanks

Design Considerations

The Equipment List

� Vessels, including Reactors

� Towers

� Storage Tanks

�See User Added Equipment

Equip # Type Tray Dia Tray Spacing Ideal TraysReal Trays Op. Pressure Max Op. Pressure

mm m ft mm number number m ft KPA bar (guage)

TOWERS

Tower Dia Length or Height

VESSELS

Equip # Name Type Op. PressureMax Op. PressureOrientationMat'ls of Construction CAPCOSTBase

m ft m ft KPA bar (guage) horiz/vert vessel demister Equip# Cost

Diameter Length or Height

Vessels - General

�Wall Thickness

�determined by required pressure

� Process Engineer Determines Design Pressure

�See Web Notes

Normal Op. Pressure (Pro II)

Maximum Op. Pressure (Controls, S/U , S/D ...)

Design Pressure (Relief Valve Set Pressures,

Minimum Required Metal Thickness) Process Engineer

Maximum Allowable Working Pressure

(MAWP)- Actual Metal Thickness Used Fab Shop

Design Pressure

� Excessive design pressure causes equipment to be more expensive than is required

t = metal thickness, P = Design Pressure

Cc = Corrosion Allowance, Ej = Joint Efficiency 5

for cylindrical shells

tP ri⋅

S EJ⋅ P−Cc+

Vessels - General

General - Design Temperatures

� Allowable Stress Values are dependant on Temperature

� Temperature at Design Pressure must be stated

�Materials become brittle below certain temperatures - minimum design metal

temperature

Reflux Drums

Reflux Drum Sizing

� Assume a length to diameter Ratio of 3

� Therefore:

� Solve for diameter

vol πdia

2

2

⋅ 3 dia⋅( )⋅

diavol

π

4

3⋅

1

3

Reflux Drums (PRO II)

� The Volume - Method 1

�Determine Liquid Rate Into the Drum -

Careful of your simulator flows

�Give 20% excess for start-up

�Size for 5 to 10 min @ half full TRAY NET VAPOR RATES AND DENSITIES

--------------- RATES ---------------

TRAY MW ACTUAL DENS Z FROM NORMAL ACTUAL

KG/M3 DENSITY K*KG/HR K*M3/HR K*M3/HR

---- -------- ------------ -------- ----------- ----------- -----------

1 43.543 4.23300 0.95990 5.097E-02 2.624E-02 1.204E-02

2 42.180 4.05470 0.95259 4.412 2.345 1.088

3 40.722 3.91766 0.95369 4.302 2.368 1.098

General - Tanks/Vessels

� Method 2 - Hold Up Time (at half full)

� 2 to 32 minutes depending on quality of control for each outgoing stream

� 5 to 10 minutes is sufficient with modern control systems to handle minor upsets

� 30 minutes provides a 99% probability that an operator can determine cause of failure

� Engineering Judgement !

11

Vessels - Safety

� Vessel that can be isolated require Relief Valves

Vessels - Relief Valves

Vessels (Reactor)

� Sized on processing requirements

�Agitated vessels usually have L/D ~ 1

�Non agitated L/D ~ 3

�Superficial velocities

important?

�Fluidization of contents?

�Internal coils, external

jackets

Vessels (Reactor)

� Plug Flow Reactor Issues

�Residence Time / Volume - Pro II

�Pressure Drop - packed beds - ergun eqt.

(Perry’s)

�Back Mixing - Testing, CFD - L/D > 5

General - Tanks/Vessels

� Horizontal vs. Vertical

� Vertical preferred when:

�small liquid load

�limited plot space

�ease of level control is desired

12

�Horizontal preferred when:

�large liquid loads are involved, consequently hold-up will set the size �three phases are present

General - Tanks/Vessels

Mesh

Entrainment

Separator

36” + 1/2

feed nozzle

OD (48”

min)

12” + 1/2

feed nozzle

OD (18”

min)

Vertical Separator 13

General - Tanks/Vessels

� Liquid levels

� norm liq level at 50%

� show low liq level at 25%

� provide low, low liq level for pump shut offs

� Vapour Disengagement (vertical flash vessel)

� Diameter Calcs; v = ft/ sec; density = lb/ft3

� No Mesh k=0.16; Mesh Separators k = 0.35

� Length to Diameter Ratio - 3 to 5 for Economical Design - but not a necessity

Vallowable kρL ρv−

ρ v⋅:= Vdesign 75 %⋅( ) Vallowable⋅:=

13

Mesh Separator

Codes Stds’ - ASME

�ASME - American Society of Mechanical Engineers

�Section I - Fired Heaters

�Section VIII - Pressure Vessels

�Other Sections (Plastic / Fiberglass /

nuclear)

14

Auxiliaries

�Manholes / inspection ports

�ASME Code has minimum requirements for

these based on vessel size - See Section 8 UG-46

� Nozzles - velocities

�max v=100/√ρ , ft/sec

�min v= 60/√ρ , ft/sec

� Non-tangential inlet for easier level control

14

Auxiliaries

� Thermowells

� Steamouts

�Maintenance blinds

� Drains

� Level Gauges

12 ft

36 inLow Liq Level= 6”

Norm Liq Level = 12”

High Liq Level = 18”

M

V

X

Y U

R

D

Towers

� Diameter - Pro II

� Tray Section Height

�Number of Real Trays

�Ideal Trays / 0.6 * 1.1

�Height = 24” x # trays

�Remember - subtract condenser & Reboiler

� Additional Height for Reboiler

� Additional Height for V/L Separation at top

� Double Tray Spacing at Feed

Towers

6 ft

4 ft

Double Tray

Space

Towers - Diag

Valve Trays

Towers

� Tray Flows

VIDEO

Towers

� Packing

�Random

�Structured

Field Fabricated Vessels/Tanks

� Fabricate in field if shipping is impractical

� Typically large atmospheric tanks

� Tank Types

�Cone,

�floating roof,

�sphere,

�hemispheroid

� Codes & Std’s – API, ASME

Storage Tanks Design Pressures < 15 psig

Tank Farm

Tanks - Cone Roof

� Typically Design Pressure < 2 psig, but usually 2.5 Inches Water gauge

� Ensure Vapour Pressure of Liquid is sufficiently low (suggest < half D.P.)

Storage Tanks - Cone Roof Conservation Vent

Tanks - Floating Roof

� Suitable for fluids with vapour pressures up to about 8 psig

pontoons Edge Seal

Floating Roof

Tanks - Spheres

� Suitable for Design Pressures of

�2 to 15 psig

�30 to 220 psig (Ludwig)

Tanks - Bullet Tanks

� Any Pressure

Workshop

vol πdia

2

2

⋅ 3 dia⋅( )⋅

diavol

π

4

3⋅

1

3

Vallowable kρL ρv−

ρv⋅:=

Vdesign 75 %⋅( ) Vallowable⋅:=

� Size the Flasher

Vap Rate:

Liq Rate:

Vap Density:

Liq Density:

Size 50% Liq Hold-up for 10 min

36” + 1/2 feed

nozzle OD (48”

min)

12” + 1/2

feed

nozzle OD

(18” min)

end

questions

� types of trays

� horiz vs vertical reactors

� lifter roof?

�Margin of error on flows

Reflux Drums (HYSYS)

� The Volume

�Liquid Rate Into the Drum - Careful of your

simulator flows

�Give 20% excess for start-up