Decanters continuous gravity

CONTINUOUS GRAVITY DECANTER. A gravity decanter of the type shown in Fig. 2.6 is used for the continuous separation of two immiscible liquids of differing densities. The feed mixture enters at one end of the separator the two liquids flow slowly through the vessel, separate into two layers, and discharge through overflow lines at the other end of the separator. 

Assume that the heavy liquid, of density p, overflows the dam at radius r, and the light liquid, of density pg, leaves through ports at radius r. Then if both liquids rotate with the bowl and friction is negligible, the pressure difference in the light liquid between fg and f must equal that in the heavy liquid between and (. The principle is exactly the same as in a continuous gravity decanter. 

A continuous gravity decanter is to separate chlorobenzene, with a density of 1109 kg/m , from an aqueous wash liquid having a density of 1020 kg/m. If the total depth in the separator is 1 m and the interface is to be 0.6 m from the vessel floor, (a) what should the height of the heavy-liquid overflow leg be (b) how much would an error of 50 mm in this height affect the position of the interface ... 

AUXILIARY EQUIPMENT. The dispersed phase in an extraction tower is allowed to coalesce at some point into a continuous layer from which one product stream is withdrawn. The interface between this layer and the predominant continuous phase is set in an open section at the top or bottom of a packed tower in a sieve-plate tower it is set in an open section near the top of the tower when the light phase is dispersed. If the heavy phase is dispersed, the interface is kept near the bottom of the tower. The interface level may be automatically controlled by a vented overflow leg for the heavy phase, as in a continuous gravity decanter. In large columns the interface is often held at the desired point by a level controller actuating a valve in the heavy-liquid discharge line. 

Gravity separator for two immiscible liquids. In Fig. 2.2-6 a continuous gravity separator (decanter) is shown for the separation of two immiscible liquids A (heavy liquid) and B (light liquid). The feed mixture of the two liquids enters at one end of the separator vessel and the liquids flow slowly to the other end and separate into two distinct layers. Each liquid flows through a separate overflow line as shown. Assuming... 

Purdue investigations (36) indicate that sulfuric acid separates significantly more rapidly by decanting (or gravity separation) than hydrocarbons from dispersions of sulfuric acid and hydrocarbons. Hence, the relative amount of sulfuric acid in the remaining acid-continuous dispersion decreases to at least 10 90. In some cases, a relative stable acid-continuous froth is obtained after most of the separation occurs such a froth often has ratios of 2 98 or maybe even 1 99. 

Another nickel cataly2ed process is described ia a Tolochimie patent (28). Reaction conditions claimed are 1—2.4 MPa (150—350 psi) at 100°C minimum. The combination continuous stirred reactor and gravity decanter uses density-driven circulation between the two vessels to recirculate the catalyst to the reaction 2one without the use of filters or pumps. Yield and catalyst usage can be controlled by varying the feed rates. 

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. 

No matter what the situation, the specific gravity difference is a very, very important variable. Aerstin Street (6) have published the simple decanting equation with viscosity of the continuous phase in cp and time in hours ... 

A mixture of 118 g. (1 mole) of succinic acid, 188 g. (2 moles) of phenol, and 138 g. (83 ml., 0.9 mole) of phosphorus oxychloride (Note 1) is placed in a 2-1. round-bottomed flask fitted with an efficient reflux condenser capped with a calcium chloride tube (Notes 2 and 3). The mixture is heated on a steam bath in a hood (Note 3) for 1.25 hours, 500 ml. of benzene is added, and the refluxing is continued for an additional hour. The hot benzene solution is decanted from the red syrupy residue of phosphoric acid and filtered by gravity into a 1-1. Erlenmeyer flask. The syrupy residue is extracted with two 100-ml. portions of hot benzene, which are also filtered into the Erlenmeyer flask. The combined benzene solutions are concentrated to a volume of about 600 ml. (Note 4), and the pale yellow solution is allowed to cool, whereupon the diphenyl succinate separates as colorless crystals. It is filtered with suction on a Buchner funnel, washed with three 50-ml. portions of ether, and dried on a porous plate at 40°. The yield of diphenyl succinate, m.p. 120-121°, is 167— 181 g. (62-67%) (Note 5). 

Steady-state control of a continuously fed extraction column requires maintenance of the location of the liquid-liquid interface at one end of the column. The main interface will appear at the top of the column when the light phase is dispersed and at the bottom of the column when the heavy phase is dispersed. If needed, extraction columns can be designed with an expanded-diameter settling zone to facilitate liquid-liquid phase separation by reducing liquid velocities. If sufficient clarification of the phases cannot be achieved, then it may be necessary to add an external device such as a gravity decanter or centrifuge. (See Liquid-Liquid Phase Separation Equipment. ) Sometimes a column is built with expanded ends at... 

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