Gravity settling liquid, density

Equation (2.17) is analogous to Eq. (2.14) for a gravity settling tank. It shows that ) (, the radius of the neutral zone, is sensitive to the density ratio, especially when the ratio is nearly unity. If the densities of the fluids are too nearly alike, the neutral zone may be unstable even if the speed of rotation is sufficient to separate the liquids quickly. The difference between and pg should not be less than approximately 3 percent for stable operation. 

Gravity settling For immiscible liquids the density difference may yield sufficient separation Oil-water separation... 

Descriptions and discussions of gravity sedimentation in textbooks (and this one is no exception) are usually dominated by water treatment and mineral processing applications. One must not lose sight, however, of the many chemical, pharmaceutical, nuclear, petrochemical or petroleum applications where gravity settling is used to resolve emulsions or to separate other liquid-liquid dispersions. As the density difference in such cases is nearly always low, the benefits of coalescence are usually sought. The present book, as per its title, is concerned primarily with solid-liquid systems and a reader interested in separation of liquid-liquid dispersions is referred to an excellent review of such applications (and of electrostatic coalescence)... 

V = settling rate g = gravity constant r = particle radius dj = particle density d = liquid density p = liquid viscosity... 

Solid partieles in liquids generally tend to settle to the bottom of a vessel under gravity due to their exeess density. To maintain a suspension, some form of agitation is normally provided together with wall baffles to prevent vortex formation in the swirling flow (Figure 2.14). 

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. 

Vapor-Liquid Gravity Separator Design Fundamentals The critical factors in the performance of a horizontal separator are the vapor residence time and the settling rate of the liquid droplets. However, two other factors enter into the design—the vapor velocity must be limited to avoid liquid entrainment, and there must be sufficient freeboard within the vessel to allow for a feed distributor. For vertical separators, the design is based on a vapor velocity that must be less than the settling velocity of the smallest droplet that is to be collected, with due allowance for turbulence and maldistribution of the feed. The vapor residence time is a function of the vapor flow rate (mass), vapor density, and volume of vapor space in the separator, based on the following ... 

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