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Aniket Shende 61Rahul Sheth 62

Kunal Shinde 63Advait Soni 64Chaitanya Sudrik 65

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Venting systems include Venting devices, piping or vent header

systems, disposal systems

Vent systems required for Purging, Cleaning Safety Considerations

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Venting devicesValves-PRVs, PSVs

-conventional , balanced

Rupture disks, Breaking PinsPressure Vacuum Vents

Sizing of Relief Valves

3

r

rr

k

k kk

k

1

1

1F

12

2

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Critical flow

4

1

1

cf

1

2

P

P

k

k

k

k

k

M2

1)-TZ(

KPK520

WA

b1d

)PP(MP

TZ

FK735

WA

2112d

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Relief headersWorst case scenarios

Standard pressure drop calculations

Disposal SystemsQuenching, ChillingSeparation of vapors and liquidsFlares- ground, elevated

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No universal method of vent sizing for allsituations

If vent size is too large then the ventingsystem becomes uneconomical

If it is inadequate then it can cause accidents Codes: API 2000 standards NFPA 30 OSHA

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Complex fluid dynamic process Discharge flow, pressure decay depend on

gas properties, vent line configuration, gasflow

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cr

-ce

i

-ce

f

ce

i0f

AA

)P(PPMuVCt

i

foi

c

P

P1

ZRT

VPM

1

i

f

i

c

P

P1

M

M

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Process considerations1)Valve malfunction, equipment failure

2) Sudden rise in feed inlet pressure3) Runaway exothermic reactions4) Process gas exceeding explosion limits5) Dust explosion Fire considerations1) External fire adjacent to pressurized vessels2) External Ignition

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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 vesselrelated to vent area

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Av is area of smallest side For St 2 gas mixtures

F

AP

v

max

F

AK

v

gbar0.2-K25.0Pred

red40P8.0K

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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

The shape factor C is defined as

13

max

5.0

red

3

2

max

4-

P

V)C(P10x2.72F

dt

dP

3

1

2a

bc0.65C

3

2

L

D0.76C

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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

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Put forth by Palmer (1973)

Vent Ratio = Area of Vent

Simplest method for sizing of vents

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Volume of vessel

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Vent ratios for various size ranges provided

Vent ratios on the basis of experiments inHartmann apparatus

The Hartmann apparatus measures themaximum rate of pressure rise in the vesselfor a given size range

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Maximum Rate of Pressure Rise(bar/s)

Vent Ratio(1/m)

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Can be used for vessels of up to 30 cu.m only

For larger vessels, predicted vent size muchgreater than actually required and henceuneconomical

Assumes homogenous conditions and rapidpropagation of flame throughout the reactorconditions 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

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Method developed by Heinrich andBartknetcht

Based on a cubic relation between maximumrate of pressure rise and inverse of thevolume

(dP/dt)max V ^ (-1/3)

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Nomographs are used to determine vent size

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P stat - the vent opening pressure P redreduced 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 graphand intersect it with the appropriate K stvalue

The horizontal axis gives the vent area

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Lowest pressure is 0.2 barg

Vessel volume must be between 1 and 1000cubic m

The vessel Length: Diameter ratio should belesser than 5:1

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Weak vessels- Vent ratio method

Low maximum rate of pressure size-RUSTmethod

Turbulent dust clouds- Vent ratio method

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Vessel Shape- for conical vessels Nomographmethod more suitable

For cylindrical vessels K- factor method moreuseful

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Thank You

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