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BUILDING THE FORMULA FOR CALCULATING THE VAPOR OF THE LPG

LIQUID GENERATING IN THE EXPLOSION RISK OF LPG TANK

Ly Ngoc Minh1; Nguyen Van Quan2; Đinh Xuan Thang3

ABSTRACT:

The paper introduces the way for building of the formula to calculate the vapor of the

Liquefied Petroleum Gas (LPG) generating in the explosion risk of LPG tank.

INTRODUCTION:

Liquid stored under pressure above their normal boiling point temperature present

substantial problems because of flashing. If the tank, pipe, or other containment device

develops a leak or rupture, the liquid will partially flash in to vapor, sometimes

explosively.

When we assessment the risk of the gas explosion from the tank, pipe, equipment

of the LPG, we need to calculate the vapor of the LPG generating from the LPG liquid.

This paper will introduce the way to form the formula to calculating the LPG vapor

generating from the LPG liquid in the explosion.

I.CONDITIONS

LPG equipment place in the atmosphere, pressure is 1 atm (1,01 bar);

Commercial LPG;

Assumes constant physical properties over the temperature range.

Maximum allow working temperature of the LPG tank is 50oC (according to the

Vietnam standard)

II.DETERMINE THE RATE OF LPG LIQUID FLASHING

Flashing occurs so rapidly that the process is assumed to be adiabatic. The excess

energy contained in the superheated LPG liquid vaporizes the LPG liquid and lowers the

temperature to the new boiling point. If LPGLm is the mass of LPG liquid, LPG

atmLpC 1,, the heat

capacity of the LPG liquid (energy/mass.deg.), To be the temperature of the LPG liquid

before depressurization, and Tb is the depressurized boiling point of the LPG liquid, the

excess energy contained in the superheated LPG liquid is given by

1 Hochiminh University of Industry, Vietnam2 Nation Institute of Occupational Safety and Health, Vietnam3 Hochiminh City Institute of Resource and Environment, Vietnam

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LPGatmB

LPG

Co

LPGatmLp

LPGL TTCmQ o 1,50,1,, (a)

This energy vaporizes the LPG liquid. If LPGatmVLr 1, is the heat of vaporization of the

LPG liquid, the mass of LPG liquid vaporized mv is given by

LPG

atmVL

LPGatmB

LPG

Co

LPGatmLp

LPGL

LPGatmVL

LPGVL r

TTCm

r

Qm

o

1,

1,50,1,,

1,

(b)

The fraction of the LPG liquid vaporized is

LPG

atmVL

LPGatmB

LPG

Co

LPGatmLp

LPGL

LPGVLLPG

VL r

TTC

m

mf

o

1,

1,50,1,,

(c)

III.DETERMINE THE LPG VAPOR GENERATING

The vapor of LPG generating is

, .1 0 ,1

,1 1

250 LPG LPG LPG LPGL V p L atm B atmLPG

V LPG LPGL atm atm

m C T TV

r

(d)

IV.CASE STUDY

The tank contents the Propane (C3H8), capacity is the 100 ton. CkgkJC oLPGatmLp /25.21,, ;

CT oMax

LPG 500 ; CT oLPGB 1.42 ; LPG

atmVLr 1, = 427.8 kJ/kg.

Substituting in to Eq. c gives

484.0

8.427

1.425025.2

1,

1,,

LPG

atmVL

LPGB

LPGo

LPGatmLp

LPGL

LPGVLLPG

VL r

TTC

m

mf

That is, only 48.4% of the mass of the original LPG liquid (in this case, propane) is

vaporized.

So, the LPG vapor generating is

3, .1 0 ,1

,1 1

250 250 0.48 100 1023529

510

LPG LPG LPG LPGL V p L atm B atmLPG

V LPG LPGL atm atm

m C T TV

r

m3

V.CONCLUSION AND SUGGESTION

There is only part of the mass of the original LPG liquid is vaporized.

The paper introduces the way to building the formula to can calculate the vapor

generating from the explosion risk of the LPG tank.

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The result of this calculation can use to determine the dispersion of the LPG vapor

in the air when assess the risk of the gas explosion from the tank, pipe, equipment of the

LPG.

Research applying the result of the study to another liquid.