Packing Hydraulics: Flooding and Pressure Drop

Vocabulary flashcards covering packed column hydraulics, pressure drop calculations, loading, flooding, and empirical design correlations.

Pressure Drop

The reduction in pressure as gas travels up a column, caused by packing and column internals interrupting gas flow and creating turbulence.

Specific Pressure Drop

The pressure drop per unit height of packing, represented as $\frac{\Delta P}{Z}$.

Superficial Velocity

The velocity of a single phase traveling through a column calculated as if there were no obstructions present in the vessel.

Loading Point

The operational point where a packed column begins to transition from normal operation, liquid holdup starts to increase, and specific pressure drop rises steeply.

Flooding Point

The condition where superficial vapor velocity ($u_v$) becomes high enough to push liquid upward, filling the column and disrupting operation.

Percent Flood

The operational ratio comparing actual superficial gas velocity to gas velocity at flooding ($u_v / u_{v,\text{flood}}$), typically targeted between $60\,\%$ and $80\,\%$ flood by adjusting column diameter.

Liquid/Gas Kinetic Energy Ratio ($F_{LV}$)

A dimensionless factor indicating the relative amount of liquid carried relative to gas, defined by $F_{LV} = \left(\frac{L M_L}{V M_V}\right) \left(\frac{\rho_V}{\rho_L}\right)^{0.5}$.

Capacity Factor ($F_C$)

A dimensionless factor used in generalized pressure drop correlations that represents the effective gas momentum in a packed column.

Packing Factor ($F_P$)

A unique empirical constant for a specific packing type and size, used in generalized pressure drop correlations to determine column hydraulic capacity.

Flooding Pressure Drop Correlation

An empirical relation $\Delta P_{\text{flood}} = 0.115 F_P^{0.7}$ applicable to modern packings with $9 < F_P < 60\,\text{ft}^{-1}$, where flooding pressure drop is generally $\le 1.5\,\text{in.}\,\text{H}_2\text{O/ft}$.

Generalized Pressure Drop Correlation Chart for Random Packing

A design correlation chart (Figure 6.36) relating Capacity Factor ($F_C$) and Liquid/Gas Kinetic Energy Ratio ($F_{LV}$) across curves of constant specific pressure drop $\Delta P$ for random packing.

Generalized Pressure Drop Correlation Chart for Structured Packing

A design correlation chart (Figure 6.37) relating Capacity Factor ($F_C$) and Liquid/Gas Kinetic Energy Ratio ($F_{LV}$) across curves of constant specific pressure drop $\Delta P$ for structured packing.

Liquid Holdup ($h$)

The volume of liquid per unit volume of packing ($\text{m}^3/\text{m}^3$), which is constant below the loading point and depends on liquid rate ($u_L$), packing type, liquid viscosity, and liquid density.

Stichlmair Model Equations

A general model used to predict pressure drop and hydraulic capacity in countercurrent packed columns using parameters like dry bed pressure drop ($\Delta P_{\text{Dry}}$), gas Reynolds number ($\text{Re}_g$), liquid Froude number ($\text{Fr}_L$), and liquid holdup ($h$).

Gas-Phase Number of Transfer Units ($N_{OG}$)

A parameter estimated from phase compositions and top/bottom driving forces via $N_{OG} = -\frac{1}{\ln(\text{mean ave}(\Delta Y_{\text{top}}, \Delta Y_{\text{bot}}))}$, where $\Delta Y_{\text{top}} = Y_1 - K_1 X_{\text{lean solvent}}$ and $\Delta Y_{\text{bot}} = Y_{\text{lean gas}} - K_n X_n$.