1. SAFETY AND LOSS PREVENTION ERT 322
SOURCE MODEL
Prepared by;
Mdm. Syazwani Mahmad Puzi
School of Bioprocess Engineering

2. INTRODUCTION
Most accidents in chemical plants result in spills of toxic, flammable and explosive materials.
Accidents begin with an incident, which usually results in the loss of containment of material from the process.
The material has hazardous properties, that might include toxic properties and energy content.

3. Typical incidents might include the rupture or break of a pipeline, a hole in a tank or pipe, runaway reaction or fire external to the vessel.
Once the incident is known, source models are selected to describe how materials are discharged from the process.

4. What are source models?
Constructed from fundamental/empirical equation representing the physicochemical process occuring during release of materials.
Sometimes, we modified the original models to fit the specific situation
Only can be applied once the incident has been identified
Provide technical information;
Rate of discharge
Total quantity discharged
State of discharge
Dispersion Model – to describe how the material is transported downwind and dispersed to some concentration levels.
Fire & Explosion Model – to convert the source model information into energy hazard potentials (eg. Thermal radiation, explosion overpressure etc.)
Effect Model – to evaluate potential loss/damage on people, properties and environment

5. Limited aperture release
Mode of release
Wide aperture release
Limited aperture release
-Releasing a substantial amount of material in a short time
-Large hole developing in process unit
slow release of material that causing non immediate effect to upstream
Example: overpressure explosion, explosion of a storage tank
Example: leaks in flanges, valves and pumps; ruptured pipes, cracks and relief system

6. Source Models - Liquid
Flow of liquid through a hole
Flow of liquid through a hole in a tank
Flow of liquids through pipes

7. Flow of liquid through a hole
A mechanical energy balance describes the various energy forms associated with flowing fluids:
P pressure (force/area)
 density (volume/mass)
ū average velocity of the fluid (length/time)
α velocity correction factor, dimensionless
g acceleration due to gravity (length/time2)
gc gravitational constant (length mass/force time2)
z height above datum (length)
F net frictional loss (length force/mass)
Ws shaft work (force length)
mass flow rate (mass/time)
Equa. 1

8. Liquid flowing through a hole
Liquid pressurized within
process unit
External surroundings
P = 1 atm
ū2 = ū
A = leak area
P = Pg
ū1 = 0
∆z = 0
Ws = 0
 = liquid density
Equa. 2
Equa. 3
Co Discharge coefficient

9. Discharge Coefficient Value
Event Co
Sharp-edged orifices, Re > 30,000
0.61
Well-rounded nozzle
~1.0
Short section pipe attached to a vessel (L:D  3)
0.81
Unknown/uncertain
1.0

10. Problem 4.1
A 0.20-in hole develops in a pipeline containing toluene. The pressure in the pipeline at the point of the leak is 100- psig. Determine the leakage rate. The specific gravity of toluene is

11. Flow of liquid through a hole in a tank
Equa. 5
= liquid density
A = leak cross sectional
area hL
ū2 = ū
P = 1 atm
ū1 = ū
Ws = 0
If the vessel is at atmospheric pressure Pg=0
Equa. 4
Equa. 6

12. Example 4-2
A cylindrical tank 20 ft high and 8 ft in diameter is used to store benzene. The tank is pedded with nitrogen to a constant regulated pressure of 1 atm gauge to prevent explosion. The liquid level within the tank is presently at 17 ft. A 1-in puncture occurs in the tank 5 ft off the ground because of the careless driving of a forklift truck. Estimate (a) the gallons of benzene spilled, (b) the time required for the benzene to leak out, and (c) the maximum mass flow rate of benzene through the leak. The specific gravity of benzene at these condition is

13. Flow of liquid through pipes
Mechanical energy balance for the flow of incompressible liquids through pipes, (density is constant) Frictional loss, F
Equa 7
Equa. 8
Kf excess head loss due to the pipe/fitting, dimensionless
u fluid velocity (length/time)

14. The frictional loss, F represent the loss of mechanical energy resulting from friction and includes loss of friction and loss from flow through length of pipe, fitting, such as valve, elbows, orifice, and pipe entrances and exits.

15. For fluids flowing through pipes the excess head loss, Kf f fanning friction factor, dimensionless L flow path length d flow path diameter
Equa. 9

16. Determination of Kf 2 methods
Computational method based on Fanning friction factor
2-K method

17. Event
Formula
Laminar flow
Turbulent flow in rough pipes
Smooth pipes, Re < 100,000

20. 2-K Method Excess Head Loss, Kf
K1 & K∞ 2-K constants for loss coefficient, dimensionless
ID internal diameter
Pipe entrances/exit
Equa. 10
Equa. 11

21. Discharge coefficient, Co for liquid flow through a hole;
For a simple hole in a tank with no pipe connections and fittings, the friction is caused only by the entrance and exit effects of the hole.
For Re > 10,000, Kf entrance = 0.5 and, Kf exit = 1.0, thus ∑Kf = 1.5. Solve Equa. 12, Co = 0.63
Equa. 12

23. Problem 4.11
Compute the pressure in the pipe at the location shown on Figure below. The flow rate through the pipe is 10,000 L/h. the pipe is commercial steel pipe with an internal diameter of 50mm. The liquid in the pipe is crude oil with density of 928 kg/m3 and a viscosity of kg/m.s. The tank is vented to atmosphere.

24. Flashing liquid
Flashing normally occurs when a liquid stored under pressure above their normal boiling point is experiencing sudden ambient environment causing the liquid flash to vapor, sometimes explosively.
If the tank develops a leak, the liquid will partially flash into vapor.
The process is rapid and assumed to be adiabatic
Excess energy, Q contained in the superheated liquid is given by;
m is the mass of the liquid, Cp is the heat capacity of the liquid (energy/mass deg), To temperature of liquid before depressurization and Tb is the depressurized boiling point of the liquid.
Equa. 13

25. constant physical properties over the temperature range To to Tb
Q is the energy that vaporizes the liquid.
let ∆Hz is the heat of vaporization of the liquid, now, the mass of liquid vaporized, mv is given by;
Fraction of the liquid vaporized, fv is given by;
Equa. 14
Assumption:
constant physical properties over the temperature range To to Tb
Equa. 15

26. For liquid stored at their saturation vapor pressure, P = Psat, mass flow rate is given by;
Equa. 16

27. Example 4.8
Propylene is stored at 25°C in a tank at its saturation pressure. A 1-cm diameter hole develops in the tank. Estimate the mass flow rate through the hole under these conditions for propylene: ∆Hv = 3.34 x 105 J/kg Vfg = m3/kg Psat = 1.15 x 106 pa Cp = 2.18 x 103 J/kg.K

28. Liquid Pool Evaporation or Boiling
Mass flow rate
Heat flux from the ground
Rate of boiling
Equa. 17
Equa. 18
Equa. 19

29. Problem 4.35
Estimate the vaporization rate resulting from heating from the ground at 10 s after the instantaneous spill of 1500 m3 of liquefied natural gas (LNG) into a rectangular concrete dike of dimensions 7 m by 10 m.
αs = 4.16 x 10-7 m2/s
ks = 0.92 W/m.K
Tliq = 109 K
Tsoil = 293 K
∆Hv = 498 kJ/kg at 109 K