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Sizing of Vents

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Aniket Shende 61 Rahul Sheth 62 Kunal Shinde 63 Advait Soni 64 Chaitanya Sudrik 65 * Prvs rupture disks reactors treat disperse fluids scrubbers flames regular ... – PowerPoint PPT presentation

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Title: Sizing of Vents


1
Sizing of Vents
  • Aniket Shende
    61
  • Rahul Sheth 62
  • Kunal Shinde 63
  • Advait Soni 64
  • Chaitanya Sudrik 65

2
Introduction
  • Venting systems include
  • Venting devices, piping or vent header systems,
    disposal systems
  • Vent systems required for
  • Purging, Cleaning
  • Safety Considerations

3
Venting systems
  • Venting devices
  • Valves-PRVs, PSVs
  • -conventional , balanced
  • Rupture disks, Breaking Pins
  • Pressure Vacuum Vents
  • Sizing of Relief Valves

4
  • Critical flow

5
  • Relief headers
  • Worst case scenarios
  • Standard pressure drop calculations
  • Disposal Systems
  • Quenching, Chilling
  • Separation of vapors and liquids
  • Flares- ground, elevated

6
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

7
Purging Process
  • Complex fluid dynamic process
  • Discharge flow, pressure decay depend on gas
    properties, vent line configuration, gas flow

8
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

9
Methods for vent sizing
  • K- factor Method
  • RUST Method
  • Vent Ratio Method
  • Nomograph or Cubic law Method

10
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

11
  • Av is area of smallest side
  • For St 2 gas mixtures

12
  • Vessel volume between 1 to 1000 m3
  • L/D ratio less than 51
  • Does not account for vent ducts

13
RUST Method
  • Spherical flame front propogation
  • Used for equipments in soap and detergent
    industries
  • Rust equation
  • The shape factor C is defined as

14
  • Limited to maximum rate of pressure rise of 345
    bar /s
  • L/D ratio should be less than 2.51
  • Does not account for vent ducts

15
Vent Ratio Method
  • Put forth by Palmer (1973)
  • Vent Ratio Area of Vent
  • Simplest method for sizing of vents

Volume of vessel
16
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

17
Recommended Vent ratios
Maximum Rate of Pressure Rise (bar/s) Vent Ratio (1/m)
lt345 1/6.1
lt690 1/4.6
gt690 1/3.1
18
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

19
Modifications of Vent Ratio for Larger Vessels
Volume Range (cubic m) Modification
30-300 Vent ratio reduced linearly from 1/6 to 1/25
300-600 1/9.2
gt700 1/3.1
20
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 a V (-1/3)

21
Nomograph or Cubic law Method
  • Nomographs are used to determine vent size

22
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

23
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 51

24
Selection of Vent sizing method
  • Weak vessels- Vent ratio method
  • Low maximum rate of pressure size-RUST method
  • Turbulent dust clouds- Vent ratio method

25
Selection of Vent sizing method
  • Vessel Shape- for conical vessels Nomograph
    method more suitable
  • For cylindrical vessels K- factor method more
    useful

26
  • Thank You
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