Flow mixing vessel

Humphrey DW, Van Ness HC. (1957) Mass transfer in a continuous-flow mixing vessel. AICHEJ, 3 283-286. 

The flow mixing vessel operates from room temperature to 200 °C and for a range of fluid pressure from 0.1 to 20MPa. The fluid flowrates vary from 50 to 1500 p. min that allow to cover a wide range of mixture composition. 

Pickiug up the solids at the bottom of the tank depends upon the eddies and velocity fluctuations in the lower part of the tank and is a different criterion from the flow pattern required to keep particles suspended and moving in various velocity patterns throughout the remainder of the vessel This leads to the variables in the design equation and a relationship that is quite different when these same variables are studied in relation to complete uniformity throughout the mixing vessel. 

FIG. 23-7 Imp ulse and step inputs and responses. Typical, PFR and CSTR. (a) Experiment with impulse input of tracer, (h) Typical behavior area between ordinates at tg and ty equals the fraction of the tracer with residence time in that range, (c) Plug flow behavior all molecules have the same residence time, (d) Completely mixed vessel residence times range between zero and infinity, e) Experiment with step input of tracer initial concentration zero. (/) Typical behavior fraction with ages between and ty equals the difference between the ordinates, h — a. (g) Plug flow behavior zero response until t =t has elapsed, then constant concentration Cy. (h) Completely mixed behavior response begins at once, and ultimately reaches feed concentration. 

Sano, Y. and Usui, H., Interrelations among mixing time, power number and discharge flow rate number in baffled mixing vessels, J. Chem. Eng., Japan, 18 47-52, 1985. 

Wiped film stills in place of continuous still pots —Centrifugal extractors in place of extraction columns —Flash dryers in place of tray dryers —Continuous reactors in place of batch —Plug flow reactors in place of CFSTRs —Continuous in-line mixers in place of mixing vessels... 

We can now return to the problem of the feeding a salt and water to a mixing vessel that initially contains water, and from which the flow is governed by gravity without the... 

The shape, size, and baffling of a specific mixing vessel significantly influences the Reynolds number, flow, and power numbers. 

The mixture of caustic and disulfides is transferred to a settler. From the settler, the treated gasoline flows to a coalescer, sand filter, or wash water tower, before going to storage. The caustic solution is recirculated to the mixing vessel/fiber film contactor. 

For the purpose of paint formulation the most important units of equipment are the laboratory ball mill, bead mills and high speed dispersers. The most common, the ball mill, consists of a cylindrical porcelain vessel a little more than half filled with steel, porcelain balls or pebbles. Pigment, together with sufficient binder and solvent to make a free-flowing mix, is loaded into the mill until it is approximately two-thirds full. The mill is then closed and fixed into a device whereby it is made to rotate about its major axis. Normally, a period of about 16 hours is required for thorough dispersion of the pigment, whereupon the mill-base is emptied out and blended with the remainder of the ingredients. 

Liquid residence-time distributions in mechanically stirred gas-liquid-solid operations have apparently not been studied as such. It seems a safe assumption that these systems under normal operating conditions may be considered as perfectly mixed vessels. Van de Vusse (V3) have discussed some aspects of liquid flow in stirred slurry reactors. 

A qualitative picture of the flow field created by an impeller in a mixing vessel in a single-phase liquid is useful in establishing whether there are stagnant or dead regions in the vessel, and whether or not particles are likely to be suspended. In addition, the efficiency of mixing equipment, as well as product quality, are influenced by the flow patterns prevailing in the vessel. 

Clearly, the flow pattern established in a mixing vessel depends critically upon the vessel/impeller configuration and on the physical properties of the liquid (particularly viscosity). In selecting the appropriate combination of equipment, it must be ensured that the resulting flow pattern is suitable for the required application. 

Figure 2.6. A constant volume continuous flow well-mixed vessel.

Example 2.11 Linearize the differential equation for the concentration in a mixed vessel Wf = Qin(t)Cm(t) - Qm(t)C, where the flow rate and the inlet concentration are functions of time. 

Consider a series of well-mixed vessels (or compartments) where the volumetric flow rate and the respective volumes are constant (Fig. 3.3). If we write down the mass balances of the first two vessels as in Section 2.8.1 (p. 2-20), they are 1 ... 

Mixed-flow Mixed-flow Mechanically agitated vessel 10 0.02-0.2... 

Liquid-liquid extraction is carried out either (1) in a series of well-mixed vessels or stages (well-mixed tanks or in plate column), or (2) in a continuous process, such as a spray column, packed column, or rotating disk column. If the process model is to be represented with integer variables, as in a staged process, MILNP (Glanz and Stichlmair, 1997) or one of the methods described in Chapters 9 and 10 can be employed. This example focuses on optimization in which the model is composed of two first-order, steady-state differential equations (a plug flow model). A similar treatment can be applied to an axial dispersion model. 

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