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PROCESS DESIGN > Storage Tank Design > Flashcards

Storage Tank Design Flashcards

1
Q

Define ‘Flash Point’

A

The lowest temperature where vapours form an ignitable mixture given an ignition source.

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2
Q

Name the 3 main types of storage tanks.

A

1) Fixed roof
2) Internal floating roof
3) External roof

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3
Q

When is a fixed roof storage tank suitable? Give 2 examples.

A

Very high flash points - must not ignite.

eg. water & fuel oil

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4
Q

When is an internal floating roof storage tank suitable? Give 2 examples.

A

Low flash points. Has fixed & floating roof suitable for countries with lots of rain.
eg. gasoline, ethanol

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5
Q

When is an external floating roof storage tank suitable? Give 2 examples of suitable fluids.

A

Medium flash points. No fixed roof suitable for dry countries.
eg. naptha, kerosene

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6
Q

What is the purpose of a floating roof?

A

It sits directly on top of the fluid to prevent vapour escaping.

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7
Q

When is a spiral staircase required on a storage tank?

A

If the tank is more than 4m tall.

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8
Q

What determines whether a roof is self-supporting or supported? What quantities are used for each?

A

Roof pitch slope must be sufficiently steep to support itself. A 1:5 pitch can be self-supported. A 1:12 pitch uses a roof support

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9
Q

Name 10 features on a fixed roof storage tank.

A

1) Roof manhole
2) Shell manhole
3) Dip-tube (sample)
4) Pressure/vacuum vent
5) Staircase
6) Gauge float/liquid level indicator
7) Inlet nozzle
8) Outlet nozzle
9) Railing (if > 4m tall)
10) Fixed roof

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10
Q

What is the purpose of the pressure/vacuum vent? What vacuum does it operate at?

A

It prevents build up of vapour & relieves internal pressure build up. It operates at a slight vacuum of 0.19kPa.

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11
Q

What is the conversion for barrel (bbl) to m3?

A

1 bbl = 0.1637 m3

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12
Q

How do you calculate volume in a cylindrical tank?

A

V = (pi x D^2)/4 x L

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13
Q

When are short, fat tanks & tall, thin tanks used?

A

Short, fat = used in windy or seismically active areas & where soil bearing strength is low.
Tall, thin = ground space available small & soil bearing strength higher

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14
Q

What is the wall & bottom surface area (SA) of a cylinder?

A

SA wall = pi x D x L

SA bottom = (pi x D^2)/4

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15
Q

What is the surface area (SA) of a conical roof?

A

SA = (pi x D)/2 x s

where s = slope.

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16
Q

Derive the formula for the slope of a conical roof assuming a self supporting roof?

A

Self-supporting r:h = 1:5.
s^2 = h^2 + r^2
s = sqrt [(13D^2)/50]

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17
Q

Derive the formula for the slope of a conical roof assuming a supported roof?

A

Supported r:h = 1:12
s^2 = h^2 + r^2
s = sqrt [(145D^2)/576]

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18
Q

What L/D ratio does the minimum SA occur for a flat roof?

A

L/D = 1

19
Q

What L/D ratio does the minimum SA occur for a self-supporting conical roof?

A

L/D = 1.01

20
Q

List 8 features on a external floating roof tank.

A

1) Rim-seal
2) Access hatch
3) Open top
4) Deck leg (pontoon & centre)
5) Solid guidepole
6) Vacuum breaker
7) Rim vent
8) Overflow drain

21
Q

What is the purpose of a solid guidepole on an external floating roof tank? How many are usually required?

A

Allows floating roof to move up & down without spinning, reducing build up of static which could cause an explosion. Only 1 is usually needed.

22
Q

What is the purpose of the deck legs?

A

Holds up the floating roof allowing for maintenance so it doesn’t slam down.

23
Q

What is the purpose of the rim seal? How is it different in an external & internal floating roof?

A

Stops vapour escaping between joints while allowing roof to move up & down. External roof uses rim-seal around edge of floating roof to prevent rain water entering. Internal roof uses around edge of floating roof, fixed roof & roof columns.

24
Q

What are the 3 types of floating roof?

A

1) Single deck
2) Double deck
3) Single deck with central deck buoyancy compartments

25
Q

List 8 features of an internal floating roof storage tank.

A

1) Rim-seal
2) Vacuum breaker
3) Deck legs
4) Access hatch
5) Fixed roof support column(s)
6) Fixed roof centre vent
7) Peripheral roof vents
8) Gauge float

26
Q

How can the fixed & floating roof be accounted for in tank volume?

A

Effective tank volume should be reduced by adding 0.3m to the L/D ratio to allow space for both roofs when volume is full.

27
Q

What are the 3 main types of external floating roof seals?

A

1) Mechanical
2) Liquid filled
3) Vapour/liquid mounted resilient foam-filled seals

28
Q

How much of a safety margin does the design liquid level provide?

A

Allow 10% ullage to tank volume.

V (tank) + 10% ullage = V (total)

29
Q

How much space should be left be in the non-working capacity between the tank bottom & outlet nozzle?

A

10 inches.

30
Q

How do you calculate the required height of the bund wall?

A

V (tank) + 10% ullage = V (total) = V (bund)

V (bund) = h x L^2

31
Q

What are variable space vapour tanks used for? Give 2 examples & describe how they work.

A

Used for storing vapours in an expandable vapour reservoir. eg;

i) Lifter roof tanks - telescoping roof fits loosely around main tank wall closed by wet seal.
ii) Flexible diaphragm tanks - flexible membrane provides expandable volume.

32
Q

What is the capacity for a horizontal tank?

A

75,000 L

33
Q

What is the L/D range for a horizontal tank?

A

4 < L/D < 6

34
Q

List 4 types of head that can be used on horizontal tanks. What is the benefit to using these types compared to flat head?

A

1) Dished
2) Torispherical
3) Ellipsoidal
4) Hemispherical
No sharp edges or weak points allows for stronger construction

35
Q

List 5 features of horizontal tanks.

A

1) Pressure/vacuum vents
2) Sample/dip tube
3) Manhole
4) Gauge hatch
5) Backfill & Concrete pad (if underground)

36
Q

What are pressure tanks used for? What counts as high pressure & what shape vessel is most suitable?

A

Used for storing organic liquids & gases with high vapour pressure.
High pressure > 1 bar - spherical tanks are most suitable as there are no sharp edges so no weaknesses.

37
Q

How is a pressure/vacuum vent set in a pressure tank?

A

Set to a point to prevent loss from boiling & breathing from daily temperature & pressure changes.

38
Q

What does the HAZChem label include?

A

Fire fight code, substance number & telephone number.

39
Q

What are the 4 key risks that need managing with storage tanks? Give an example for each.

A

1) Containment - eg. flammable liquids
2) Separation - eg. recommended distance
3) Ventilation - eg. vapours disperse quickly
4) Ignition - eg. sources controlled

40
Q

What do each of the zones mean when managing storage tank risk?

A

Zone 0 - explosive gas mixture continuously present.
Zone 1 - explosive gas mixture likely present in normal operation.
Zone 2 - explosive gas mixture not likely to occur in normal operation.

41
Q

How big is a manhole?

A

2ft wide.

42
Q

What is the surface area (SA) of a domed/hemispherical head?

A

SA = (pi x D^2)/2

43
Q

What L/D ratio does the minimum surface area (SA) occur for a domed/hemispherical head?

A

L/D = 1.5

44
Q

What L/D ratio does the minimum surface area (SA) occur for a supported (1:12) conical roof?

A

L/D = 1.002

PROCESS DESIGN (6 decks)

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