Gravity liquid separation

Gravity liquid separation uses gravity force to separate the liquid-phase contaminant from water (immiscible with the contaminant) by the force of gravity. 

Crystals suspended in liquors emerging from crystallizers are normally passed to solid-liquid separation devices such as gravity settlers or thickeners that may subsequently feed filters to remove yet more liquid prior to drying. Here the transport processes of particle motion and the flow of fluids through porous media are important in determining equipment size, the operation of which may be intensified by application of a centrifugal force. 

Osborne, D.G., 1990. Gravity thickening. In Solid-liquid separation, 3rd edition. Ed. L. Svarovsky. Oxford Butterworth-Heinemann. 

A liquid-liquid separator used for removing small, usually 2% or less, quantities of one immiscible liquid from another is termed a coalescer. These units are not gravity settlers, but agglomerate the smaller liquid by passing... 

It provides better solids-liquid separation than a gravity thickener. 

In the preceding processes, the particles were separated from the fluid by gravitational forces acting on the particles. Sometimes gravity separation may be too slow because of the closeness of the densities of the particles and the fluid, because of small particle size leading to low settling velocity or, in the case of liquid-liquid separations, because of the formation of a stable emulsion. 

A possible difference in the flowsheet might be the addition of a gravity preconcentration stage for lead. In some cases, the heavy liquid separation is performed prior to lead zinc oxide flotation. 

Waste solids are defined as heterogeneous materials that range from sticky, viscous, or tarry material to dry solid particulates. Special techniques for the treatment of oily, gummy, and adhesive materials (e.g., addition of anhydrous sodium sulfate or silica gel) are specified in the protocol. The gravity phase-separation procedure (24 h at 4 °C) developed by the Environmental Waters and Waste Water Work Group is incorporated by reference to address the removal of liquids from waste solids samples. The waste solids protocol can also be applied to solids partitioned from aqueous or nonaqueous liquids or from gaseous media. 

The majority of the process vessels you see in your plant are gravity, vapor-liquid separators. Their main purpose is to settle out droplets of entrained liquid from the upflowing gas. Factors that affect the settling rate of these droplets are... 

The reflux drum separates liquid and wet gas by gravity settling. A horizontal vapor-liquid separator works in much the same way as the vertical KO drum. 

Time is a critical variable because the magnetite settles if the mixture is held too long in a static condition. Use of hydrocyclones makes possible the separation in a fraction of a minute (21). These devices impart centrifugal force to the system, thereby permitting a separation to be made at a specific gravity less than that required in static, heavy-liquid separations. 

Svarovsky L (2000), Gravity clarification and thickening, In Svarovsky L (ed), Solid-Liquid Separation, Butterworth-Heinemann, Oxford. 

Solid-liquid separation by flotation may be achieved by gravity alone or induced by dissolved-air or vacuum techniques. The mechanisms and driving forces are similar to those found in sedimentation, but the separation rate and solids concentration can be greater in some cases. 

The PAC activated slndge system is a modified activated sludge process. PAC is added to the aeration tank where it is mixed with the biological solids. The mixed liquor solids are settled and separated from the treated effluent in a gravity clarifier. Polyelectrolyte will normally be added prior to the clarification step to enhance solids-liquid separation. If phosphorus removal is necessary, alum is often added at this point. Even with polyelectrolyte addition, tertiary filtration is normally required to reduce the level of effluent suspended solids. The clarifier nnderflow solids are continuously returned to the aeration tank. A portion of the carbon-biomass mixture is wasted periodically to maintain the desired solids inventory in the system. 

FIG. 18-155 Two-phase decanter centrifuge—gravity liquid discharge. Flottweg Separation Technology,... 

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