StocExpo Conference 2013, Antwerp

Dipl.-Ing. Axel Sommer

Braunschweiger Flammenfilter GmbH

(PROTEGO)

Where Do My Storage Tank Losses Come From ?

Storage Tanks Have to Breath

Why Overpressure Protection ?

• Pressure rise due to filling of

tank (Pump - In)

• Pressure Rise due to

thermal expansion (can be

significant with large tank)

• Pressure rise due to control

valve failure (such as tank

blanketing regulator)

• Pressure rise due to atmospheric

pressure decrease

• Pressure rise due to external

fire

Why Vacuum Protection?

• Vacuum from tank outflow

(Pump - Out)

• Vacuum from cooling

(such as thunderstorm)

• Vacuum from vapour

condensation

• Vacuum from atmospheric

pressure increase

Emission Reduction through breathing loss

minimization (VDI 3479*)

“The Function of the P/V Vent is to keep the vapor space

closed during variations in the atmospheric pressure

and/or temperature decrease in spite of pertinent changes

of gas volume and pressure, until that time when a

technically admissible low or high pressure is reached”

Goal: avoid intake of ambient air and discharge

of product/air mixture

* Forschungsbericht 225 “Kohlenwasserstoff – Emissionen aus Festdachtanks

– Vergleich von Berechnungsformeln unter besonderer Berücksichtigung der

VDI Richtlinie 3479, Hamburg, February 1985

Main influence factor of emission reduction for

hydrocarbon vapors

a) Upper and lower set pressure of vents

(set pressure & set vacuum)

b) Temperature difference within the vapor space

of the tank

c) Hydrocarbon concentration of the

hydrocarbon/air mixture in the vapor space

(vapor pressure)

MAWP

Set Pressure and Vacuum needs to be influenced

(design pressure)

Overall Equation for annual emission of Tank

VD

aBaAVDT mmfm ,,11

1f

aAm

,

aBm

,

= efficiency of p/v-vent

(mainly a function of set pressure to full lift)

= coating factor

= annual emission mass flow of freely vented

tank with fixed roof

(open nozzle, no conservation vent)

= annual emission mass flow of filling

Total Breathing Tanks with Open Vent

wWnnWASSnnSAaAdVcfdVcfm

,,,,,

Af = saturation ratio (existing concentration to

saturation concentration)

c = saturation concentration of hydrocarbons in

vapor space above the liquid surface

d = number of summer/winter days per year

nV = mean volume flow

Is calculated from the following equation: n

V

d

min

tV

T

p

T

p

p

TV

G

n

n

n

3

21

1

nT

np

p

1T

2T

GV

t

= standard temperature

= standard pressure

= atmospheric pressure in mbar

= mean minimum temperature in K in the

vapor space at the morning hours

= mean maximum temperature in K in the

vapor space at the midday hours

= gas volume above the product, in 3m

= reference time, t = 1 d

Finally the average annual emission mass flow

from breathing losses amounts to:

wG

WWn

n

TWA

SG

SSn

n

TSAaA

dVT

p

T

p

p

TMpf

dVT

p

T

p

p

TMpfm

,2,1

8

,

,2,1

8

,,

104.4

104.4

WSTT

,1,1; = mean minimum temperature in K in the

vapor space in summer or winter

= mean maximum temperature in K in the

vapor space in summer or winter

WSTT

,2,2;

Calculation Example 1: Fixed Roof Tank freely vented

(open nozzle, no pressure vacuum vents)

0.62.9

2121720286

1013

278

1013

1013

27368350104.457.0

15317205.303

1013

5.286

1013

1013

27368350104.463.0

8

8

,

aAm

Resulting Vapor Loss: 15.2 tons/year

Total Breathing Fixed Roof Tank with

Pressure/Vacuum Vents

Emission Mass Flow of Total Breathing has to be

multiplied by VD

1

WnWnWASnSnSA

VDWnWnWAVDSnSnSA

VD

VdcfVdcf

VdcfVdcf

,,,,

)(,,)(,,1

tV

T

p

T

p

p

TV G

n

nVDn

1

1

2

1

1)(,

100

%1

1 reoverpressu

pressurelowloperationapressurecatmospheriabsolutep

100

%1

2 reoverpressu

reoverpressuloperationapressurecatmospheriabsolutep

The smaller the

overpressure %

the better the vent

9.78

35.84 %

7.44

51.20 %

5.31

65.17 %

4.32

71.68 %

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

Em

issio

n M

assfl

ow

(t/

yr)

an

d

% o

f E

mis

sio

n R

ed

ucti

on

1 2 3 4

Calculation Example 2: Fixed Roof Tank with Pressure Vacuum Valves

100% 40% 10% 0%

15

Full Lift Pallet - 10% overpressure li

ft [

mm

] -

pre

ss

ure

[m

ba

r]

0

5

10

15

20

25

30

0 5 10 15 20

time [s]

Ventilhub

Tankdruck

valve lift

tank pressure

Vent with 40% overpressure li

ft [

mm

] -

pre

ss

ure

[m

ba

r]

0

5

10

15

20

25

30

0 5 10 15 20 25 30

time [s]

Ventilhub

Tankdruck

valve lift

tank pressure

Vent with 100% overpressure li

ft [

mm

] -

pre

ss

ure

[m

ba

r]

overpressure set pressure mass (opening) mass (reseating) total mass total volume

mbar kg kg kg m³

full lift 10% 20 0,08 0,32 0,40 0,5

modulated 40% 14 0,51 0,66 1,17 1,4

modulated 100% 11 2,31 1,08 3,39 4,1

TÜV-Certified Flow Test Rig

Flow testing of vents according to API 2000/ISO 28300

(TÜV Certified Flow Rig)

L 9

1. test medium supply (e.g. blower or fan)

2. calibrated flow measurement device

3. test tank

4. calibrated measuring device for pressure and vacuum

5. (pressure and vacuum measurement may be achieved with separate instruments)

6. temperature measuring device

7. barometer - measuring device for atmospheric pressure

8. device to be tested

9. pipe-away if fitted

10. atmospheric temperature and dew point measuring device

11. L = length of connecting pipe (straight pipe nipple)

Pset,ERV = 18,2 mbarg

Pset,CV = 14,9 mbarg Pset,N2 = 10,4 mbarg

Best Design Practice: Overpressure 100% versus 10%

Example: API 650 Tank with MAWP of 20 mbarg

Pset,ERV = 10,0 mbarg

Pset,CV = 3,8 mbarg Pset,N2 = 2,6 mbarg

(Considering blow down and leak rate testing)

Blow Down needs to be considered when sizing

4

2d

F

A

Fpset

4

2D

F

A

Fpreseat

d D

d < D

reseatset pp

Benchmark Report on Vents (leak rate)

Why Does A Quality Product Result in Vapor Saving?

Leak rate testing according to API 2521

API calls for leak rate testing at 75% of set pressure

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Tank Pressure oz/sq inch

Le

ak

ra

te [

sc

fh]

Groth

PROTECTOSEAL

PROTEGO

PROTEGO 10%

75 % to set (0.5oz/sqinch)

75 % to set (0.65oz/sqinch)

Point of full open

PROTEGO 6"

PROTEGO 10% 6"

Leak rate testing results

company A

company B

Avoid secondary damage from leaking!

Reduce your Explosion Risk from Leaking!

Thank you for your attention

Questions ?