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Aniket Shende 61 Rahul Sheth 62 Kunal Shinde 63 Advait Soni 64 Chaitanya Sudrik 65. Sizing of Vents. Introduction. Venting systems include Venting devices, piping or vent header systems, disposal systems

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sizing of vents

Aniket Shende 61

Rahul Sheth 62

Kunal Shinde 63

Advait Soni 64

Chaitanya Sudrik 65

Sizing of Vents


Venting systems include

  • Venting devices, piping or vent header systems, disposal systems

Vent systems required for

  • Purging, Cleaning
  • Safety Considerations
venting systems
Venting systems:
  • Venting devices

Valves-PRVs, PSVs

-conventional , balanced

Rupture disks, Breaking Pins

Pressure Vacuum Vents

Sizing of Relief Valves


Relief headers

Worst case scenarios

Standard pressure drop calculations

  • Disposal Systems

Quenching, Chilling

Separation of vapors and liquids

Flares- ground, elevated

methods for vent sizing
Methods for vent sizing
  • 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
purging process
Purging Process:
  • Complex fluid dynamic process
  • Discharge flow, pressure decay depend on gas properties, vent line configuration, gas flow
safety considerations
Safety considerations:
  • 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

methods for vent sizing9
Methods for vent sizing
  • K- factor Method
  • RUST Method
  • Vent Ratio Method
  • Nomograph or Cubic law Method
1 k factor method
1. K factor method
  • Factor K Method by Simmonds and Cubbage
  • For compact rectangular vessels
  • Max. explosion pressure in vented vessel related to vent area

Av is area of smallest side

  • For St 2 gas mixtures

Vessel volume between 1 to 1000 m3

  • L/D ratio less than 5:1
  • Does not account for vent ducts
rust method
RUST Method
  • Spherical flame front propogation
  • Used for equipments in soap and detergent industries
  • Rust equation
  • The shape factor C is defined as

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
vent ratio method
Vent Ratio Method
  • Put forth by Palmer (1973)
  • Vent Ratio = Area of Vent
  • Simplest method for sizing of vents

Volume of vessel

vent ratio method16
Vent Ratio Method
  • 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
drawbacks of vent ratio method
Drawbacks of Vent Ratio Method
  • 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
nomograph or cubic law method
Nomograph or Cubic law Method
  • 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)
nomograph or cubic law method21
Nomograph or Cubic law Method
  • Nomographs are used to determine vent size
nomograph or cubic law method22
Nomograph or Cubic law Method
  • 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
drawbacks of nomograph or cubic law method
Drawbacks of Nomograph or Cubic law Method
  • 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
selection of vent sizing method
Selection of Vent sizing method
  • Weak vessels- Vent ratio method
  • Low maximum rate of pressure size-RUST method
  • Turbulent dust clouds- Vent ratio method
selection of vent sizing method25
Selection of Vent sizing method
  • Vessel Shape- for conical vessels Nomograph method more suitable
  • For cylindrical vessels K- factor method more useful