Aniket Shende 61
Rahul Sheth 62
Kunal Shinde 63
Advait Soni 64
Chaitanya Sudrik 65
Venting systems include
 Venting devices, piping or vent header
systems, disposal systems
Vent systems required for
 Purging, Cleaning
 Safety Considerations
Venting devices
Valves-PRVs, PSVs
-conventional , balanced
Rupture disks, Breaking Pins
Pressure Vacuum Vents
Sizing of Relief Valves

k 1


2
k
 k  k 1  r 
F2  
r 
1 r 
 k 1 


3

Critical flow
Pcf  2 

P1  k  1
A
W
520 K d P1K b
A
W
735K d F2
k
k 1
T Z(k -1)
2Mk
TZ
MP1 (P1  P2 )
4
Relief headers
Worst case scenarios
Standard pressure drop calculations

Disposal Systems
Quenching, Chilling
Separation of vapors and liquids
Flares- ground, elevated

5







No universal method of vent sizing for all
situations
If vent size is too large then the venting
system becomes uneconomical
If it is inadequate then it can cause accidents
Codes:
API 2000 standards
NFPA 30
OSHA
6


Complex fluid dynamic process
Discharge flow, pressure decay depend on
gas properties, vent line configuration, gas
flow
Cf V0 Mu Pice (Pf-ce  Pi-ce )
t
A r Ac

M c
 Pf  
Pi Vo 




1 
P  
ZRT 
 i  


M c   Pf
 1  
Mi
  Pi




1






7
Process considerations
1)Valve malfunction, equipment failure
2) Sudden rise in feed inlet pressure
3) Runaway exothermic reactions
4) Process gas exceeding explosion limits
5) Dust explosion
 Fire considerations
1) External fire adjacent to pressurized vessels
2) External Ignition
•

K- factor Method

RUST Method

Vent Ratio Method

Nomograph or Cubic law Method
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
Factor K Method by Simmonds and Cubbage

For compact rectangular vessels

Max. explosion pressure in vented vessel
related to vent area
Av
Pmax 
F


Av
K
F
Av is area of smallest side
For St 2 gas mixtures
Pred  0.25K - 0.2 barg
K  0.8  40Pred

Vessel volume between 1 to 1000 m3

L/D ratio less than 5:1

Does not account for vent ducts
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


Spherical flame front propogation
Used for equipments in soap and detergent
industries
Rust equation
2
3
2.72 x 10-4 C(Pmax V)  dP 
F
 
0.5
Pred
 dt  max

The shape factor C is defined as
 bc 
C  0.65 2 
a 
1
3
D
C  0.76 
L
2
3
13

Limited to maximum rate of pressure rise of
345 bar /s

L/D ratio should be less than 2.5:1

Does not account for vent ducts
14

Put forth by Palmer (1973)

Vent Ratio = Area of Vent
Volume of vessel

Simplest method for sizing of vents
15

Vent ratios for various size ranges provided

Vent ratios on the basis of experiments in
Hartmann apparatus

The Hartmann apparatus measures the
maximum rate of pressure rise in the vessel
for a given size range
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Maximum Rate of Pressure Rise
(bar/s)
Vent Ratio
(1/m)
<345
1/6.1
<690
1/4.6
>690
1/3.1
17
•
Can be used for vessels of up to 30 cu.m only
•
For larger vessels, predicted vent size much
greater than actually required and hence
uneconomical
•
Assumes homogenous conditions and rapid
propagation of flame throughout the reactor
– conditions true in case of smaller vessels
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Volume Range (cubic m)
Modification
30-300
Vent ratio reduced linearly from 1/6 to 1/25
300-600
1/9.2
>700
1/3.1
19

Method developed by Heinrich and
Bartknetcht

Based on a cubic relation between maximum
rate of pressure rise and inverse of the
volume

(dP/dt)max α V ^ (-1/3)
20

Nomographs are used to determine vent size
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




P stat - the vent opening pressure
P red – reduced pressure from P max
First determine the P red
From the volume of the reactor and P red
draw a horizontal line onto the second graph
and intersect it with the appropriate K st
value
The horizontal axis gives the vent area
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
Lowest pressure is 0.2 barg

Vessel volume must be between 1 and 1000
cubic m

The vessel Length: Diameter ratio should be
lesser than 5:1
23

Weak vessels- Vent ratio method

Low maximum rate of pressure size-RUST
method

Turbulent dust clouds- Vent ratio method
24

Vessel Shape- for conical vessels Nomograph
method more suitable

For cylindrical vessels K- factor method more
useful
25
Thank You
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