Allowable Gas Velocity Through Gas Separator

The allowable gas velocity through a gas separator is the maximum speed at which gas can pass through the separator without causing inefficient separation or operational issues, such as liquid carryover.  Exceeding the allowable velocity leads to poor separation performance, causing entrainment or carryover of liquids. 

The Gas Velocity Depends on Several Factors

Separator Type  -  Different types of separators (horizontal, vertical, two-phase, three-phase) have varying designs that affect the allowable gas velocity.
Droplet Size  -  Larger droplets are easier to separate than smaller ones.  The allowable velocity must be low enough to ensure that liquid droplets can settle or be captured by the separator's internals (mist eliminators).
Operating Pressure and Temperature  -  Higher pressure typically allows for higher gas velocity, while lower temperature can increase gas density, impacting separation efficiency.
Gas and Liquid Densities  -  The density difference between the gas and liquid phases influences how well the separator can handle different velocities.
Vessel Size  -  The cross-sectional area of the separator affects how much gas can flow through at any given velocity.

The design parameter, \(K_s\), in the Souders-Brown equation is an empirical parameter and is a key factor for the sizing the gas-liquid separators vessel diameter as well as for determination of the mist extractor diameter.

 

Allowable Gas Velocity Through Gas Separator formula
\( v \;=\;   K_s \; ( \rho_l - \rho_g \;/\; \rho_g )^{0.5}  \)
Symbol	English	Metric
\( v \) = Allowable Gas Velocity Through Gas Separator	\(ft\;/\;sec\)	-
\( K_s \) = Empirical Gas Constant (Constant that Depends on the Type of Separator and Internals)	\(ft\;/\;sec\)	-
\( \rho_l \) = Liquid Density	\(g\;/\;cc\)	-
\( \rho_g \) = Gas Density	\(g\;/\;cc\)	-

 

Maximum Allowable Gas Velocity Through Gas Separator formula
\( v_{gmax} \;=\;   K_s \; \sqrt{ \rho_l - \rho_g \;/\; \rho_g }  \)
Symbol	English	Metric
\( v_{gmax} \) = Maximum Allowable Gas Velocity Through Gas Separator	\(ft\;/\;sec\)	-
\( K_s \) = Empirical Gas Constant (Constant that Depends on the Type of Separator and Internals)	\(ft\;/\;sec\)	-
\( \rho_l \) = Liquid Density	\(g\;/\;cc\)	-
\( \rho_g \) = Gas Density	\(g\;/\;cc\)	-

 

Minimum Vessel Diameter formula \(F_g = 1\;\) for vertical separators and is a function of liquid height for horizontal separators.
\( D_{min} \;=\;  \sqrt{ [\; (4 \;/\; \pi )\; Q_g \;] \;/\; [\; F_g \; v_{gmax}\;]  }  \)
Symbol	English	Metric
\( D_{min} \) = Minimum Vessel Diameter	\(ft\)	-
\( \pi \) = Pi	\(3.141 592 653 ...\)	-
\( Q_g \) = Gas Flow Rate at the Actual Flowing Condition	\(ft^3 \;/\; sec\)	-
\( F_g \) = Fraction of Area Cross-section Available for Gas Flow	\(in^2\)	-
\( v_{gmax} \) = Maximum Allowable Gas Velocity Through Gas Separator	\(ft\;/\;sec\)	-