min purge gas rate
DESCRIPTION
purge rateTRANSCRIPT
US Customary Units:
where:Q = pure gas rate, SCFHD = flare stack diameter, inch
Hydrogen: K = +5.783Helium: K = +5.078Methane: K = +2.328Nitrogen: K = +1.067 (No wind)Nitrogen: K = +1.707 (Wind 15 to 20 MPH or 6.7 to 8.9 m/s)Ethane: K = -1.067Propane: K = -2.651
C4+: K = -6.856Note that steam or other condensable is not a suitable purge gas
SI units:
where:
D = flare stack diameter, m
Note: Lower oxygen concentrations should be used for certain flared gases such as hydrogen
US Customary Units:
Husa correlation should be used to calculate minimum purge gas flow rates for gases lighter than air. If purge gas is heavier than air, purge rate based on nitrogen should be used. Husa correlation is expressed as below:
y = stack column depth at which the oxygen concentration (O2) is to be predicted, ft
O2 = oxygen concentration, volume percent
Ci = Volume fraction of ithcomponent
Ki = Constant for component i. Typical values for Ki are:
CO2: K = -2.651
Q = pure gas rate, m3/h
y = stack column depth at which the oxygen concentration (O2) is to be predicted, m
O2 = oxygen concentration, volume percent
Ci = Volume fraction of ithcomponent
Ki = Constant for component i (see above)
These equations can be simplified using the standard criteria of limiting the O2 concentration to 6% by volume, 25 ft (7.62 m) down the flare stack.
Simplified equation considering O2 volume percent as 6% and at a depth of 25 ft (7.62 m) of the flare stack
Q = 0.0035283*D3.46*K
Q = 0 . 07068 × D3.46× (1/y ) × ln (20 . 9/ O 2 ) × [∑i
n
Ci0.65× K i ]
Q = 190 .8 × D3.46× (1/y ) × ln (20 . 9/ O 2 ) × [∑i
n
Ci0.65× K i ]
where:Q = purge gas rate, SCFHD = flare stack diameter, inch K = constant (see above)
SI units:
where:
D = flare stack diameter, m K = constant (see above)
where:
Q = 31.25*D3.46*K
Q = purge gas rate, Nm3/h
Values of Ki for gases lighter than air are determined from
Ki = exp(0.065*(29 - MWi))
Values of Ki for gases heavier than air are determined from an amended Husa correlation where (MWi - 29) is substituted for MWi as follows:
Ki = exp(0.065*(MWi - 29))
MWi = molecular weight of the ith component of n components
Note: Husa correlation is generally applicable for no wind to wind speeds up to 30 MPH (13 m/s). Where prevailing wind speeds are higher, higher purge rates may be required.
Note: Lower oxygen concentrations should be used for certain flared gases such as hydrogen
Husa correlation should be used to calculate minimum purge gas flow rates for gases lighter than air. If purge gas is heavier than air,
concentration to 6% by volume, 25 ft (7.62 m) down the
volume percent as 6% and at a depth of 25 ft (7.62 m) of the flare stack
for gases heavier than air are determined from an amended Husa correlation where (MWi - 29) is substituted for MWi as
Note: Husa correlation is generally applicable for no wind to wind speeds up to 30 MPH (13 m/s). Where prevailing wind