Heavy phase

Equation 10 estimates the flow or throughput rate, above which particles of size d are less than 50% sedimented, and below which over 50% are mostly coUected. Equations 10 and 11 are also appHcable to the light particles rising in a heavy phase Hquid, provided that and are interchanged in equation 11. 

Tank bottom slope is important because sediment, water, and heavy phases settle at the bottom. Corrosion is usually the most severe at the bottom, and the design of the bottom can have a significant effect on the life of the tank. In addition, if the Hquid stock is changed, it is usually desirable to remove as much as the previous stock as possible. Therefore, designs that allow for the removal of water or stock and the ease of tank cleaning have evolved. In addition, specialized tank bottoms have resulted from the need to monitor and detect leaks. Tank bottoms in contact with the soil or foundations are one of the primary sources of leaks from aboveground tanks. 

Gravity Settlers Decanters These are tanks in which a liqmd-liquid dispersion is continuously settled and coalesced and from wriich the settled liquids are continuously withdrawn. They can be either horizontal or vertical. Figure 15-24 shows some typical horizontal decanters. For an uninstrumented decanter the height of the heavy-phase-liquid leg above the interface is balanced against the height of the hght-hquid phase above the interface, Eq. 15-50. 

When a small quantity of a second liquid phase is present, a drawoff pot (commonly called a bootleg) is provided to make separation of the heavy liquid (frequently water) easier. The pot diameter is ordinarily determined for heavy phase velocities of 0.5ft/min. Minimum length is 3 ft for level controller connections. Minimum pot diameter for a 4 to 8 foot diameter reflux drum is 16 inches. For... 

Area of interface, assumes flat horizontal, sq ft Cross-sectional area allocated to heavy phase, sq ft... 

Cross-sectional aiea allocated to light phase, sq ft Area of particle projected on plane normal to direction of flow or motion, sq ft Cross-sectional area at top of V essel occupied by continuous hydrocarbon phase, sq ft Actual flow at conditions, cu ft/sec Constant given in table Volume fiaction solids Overall drag coefficient, dimensionless Diameter of vessel, ft See Dp, min Cyclone diameter, ft Cyclone gas exit duct diameter, ft Hy draulic diameter, ft = 4 (flow area for phase in qiiestion/wetted perimeter) also, D in decanter design represents diameter for heavy phase, ft... 

Volumetric flow rate, heavy phase, cu ft/sec Volumetric flow rate, light phase, cu ft/sec Vessel radius, ft... 

V = Settling velocity for hindered uniform spherical particle, ft/s or m/s Wi= Width of rectangular cone inlet duct, ft Z], = Heavy phase outlet dimensions of decanter measured from horizontal bottom, shotvn on Figure 4-12... 

Figure 3.48. Combined plug-flow and well-mixed flow representation for the heavy phase settler flow.

The model equations for the heavy phase settler region then become for the well-mixed region... 

X is the equilibrium mole ratio in the heavy phase, corresponding to light phase mole ratio Y (kmol solute/kmol water). 

Pl is the density of the solute-free heavy phase (kmol/m ). 

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