4. LIQUID-LIQUID SEPARATOR
Separating liquid-liquid dispersions can be difficult depending on the physical properties of the two liquid phases. The specific gravity, viscosity and interfacial tension (IFT) of the two liquid phases are important parameters in determining how easily the two liquids can be separated. In liquid –liquid separator interface position can be fixed at the desired level by fixing the difference in elevation ΔH between liquid phase overflow and heavy phase under flow. The high specific gravity liquid prevents the light phase from leaving the separator via the bottom outlet. The position of interface in the liquid-liquid separator depends upon the difference in the elevation ΔH between the light and heavy phase (figure 5.4). Pressure change in the separator can affect the static pressure difference between the two layers and this change in the pressure affects the interface position in the separator.
Size of this type of separator depends upon the retention time needs for each phase to settle within the separator. Horizontal unit is most popular to carry out the separation process efficiently and avoids the mixing of the two phases (light and heavy). If the phases can be easily separated, vertical unit also shows good performance.
Figure 5.4 : Two phase (Liquid-Liquid) separator
Let ρL ; ρh specific gravity of light and heavy phase respectively ( also refer the figure given in the example 5.2 )
H1 and H2 height of heavy and light phase
C – Distance from the bottom of the separator to the reference line
X – light phase liquid head in the separator
Y – heavy phase liquid head in the separator.