Feed location

Cold feed should be introduced Into the vapor body introducing it at the calandria inlet may result in reduced heat transfer rates. Cold feed should be sprayed Into the vapor body to Improve direct contact heat transfer. 

Flashing feed is often introduced at the inlet of the calandria. The effects of flashing must be evaluated when establishing natural circulation flow rates. It may be advantageous to introduce flashing feed in the vapor body. 

Liquid level in the vapor body is an important variable affecting operation of natural circulation calandrias. Normally units are operated with the evaporator liquid level at the top tubesheet of the calandria. For non-fouling fluids, the liquid level can be lowered to the optimum value in order to minimize heat transfer surface or maximize performance. The optimum value is approximately half the distance between the top and bottom tubesheets of the calandria, and will vary with each system. The liquid level should not be appreciably above the top tubesheet and certainly should not be maintained above the caiandria outlet nozzle. Liquid levels above the vapor return will limit the performance of the calandria and may result in damage to the evaporator. Flow instabilities may also be experienced. 

Internal calandrias present some unusual problems. Understanding the effects of the froth created above the top tubesheet will permit adequate design and operation. Downcomers must be properly sized. However, external calandrias generally are preferred. 

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However, the total number of equilibrium stages N, N/N,n, or the external-reflux ratio can be substituted for one of these three specifications. It should be noted that the feed location is automatically specified as the optimum one this is assumed in the Underwood equations. The assumption of saturated reflux is also inherent in the Fenske and Underwood equations. An important limitation on the Underwood equations is the assumption of constant molar overflow. As discussed by Henley and Seader (op. cit.), this assumption can lead to a prediction of the minimum reflux that is considerably lower than the actual value. No such assumption is inherent in the Fenske equation. An exact calculational technique for minimum reflux is given by Tavana and Hansen [Jnd. E/ig. Chem. Process Des. Dev., 18, 154 (1979)]. A computer program for the FUG method is given by Chang [Hydrocarbon Process., 60(8), 79 (1980)]. The method is best applied to mixtures that form ideal or nearly ideal solutions. 

Optimum feed location (which may or may not reflect the actual location). 

P IDs (piping and instrumentation diagrams) should identify instruments, sample locations, the presence of sample valves, nozzle blinding, and control points. Of particular importance are the bypasses and alternate feed locations. The isolation valves in these hues may leak and can distort the interpretation of the measurements. 

Improper tray spacing at feed location. Premature flooding. Design error. 

The models presented correctly predict blend time and reaction product distribution. The reaction model correctly predicts the effects of scale, impeller speed, and feed location. This shows that such models can provide valuable tools for designing chemical reactors. Process problems may be avoided by using CFM early in the design stage. When designing an industrial chemical reactor it is recommended that the values of the model constants are determined on a laboratory scale. The reaction model constants can then be used to optimize the product conversion on the production scale varying agitator speed and feed position. 

Hn-hp ypTp F=Feed Location between Trays 4 E y8=0verhead Vapors fa = Still Vapors... 

Provide at least three, and perhaps four feed nozzles in addition to the one theoretically calculated to be the optimum location. Select these feed locations approximately two and four trays above and below the design basis or theoretical location. These extra nozzles must be oriented on the column so they have proper feed entry spargers or distributors (entry can be onto the tray or into the downcomer) and can be valved from a feed manifold to select the alternate desired location for testing purposes. 

The entrance of a liqmd-flashing vapor mixture into the distillation column feed location requires a specially designed distribution tray to separate the vapors from the liquid, w hich must drop onto the packing bed for that section in a uniform pattern and rate. 

However, before the above set of equations can be solved, many important decisions must be made about the distillation column. The thermal condition of the feed, the number of equilibrium stages, feed location, operating pressure, amount of reflux, and so on, all must be chosen. 

Finally, the reactor vessel has been assumed to be perfectly mixed. Imperfect mixing and a flow pattern created by different types of agitators, baffles, feed locations and other reactor vessel configurations will cause the performance to be below that indicated by perfect mixing. 

Mechanically stirred gas-liquid reactor performances are affected by the degree of mixing, apparatus geometry, stirring power, flow rate, discharge and feed locations for the gas and liquid. For a correct design, the following requirements must be satisfied ... 

Viswanathan, J. and I. E. Grossmann. Optimal Feed Locations and Number of Trays for Distillation Columns with Multiple Feeds. Ind Eng Chem Res 32 2942-2949 (1993). 

The 23-cm-diameter distillation column under study is used to separate ethanol and water. It contains 12 sieve trays with a 30-cm spacing (Fig. 11) as well as three possible feed locations, an external reboiler, and two condensers, which are used at the bottom and the top of the column. The second condenser is also used as a reflux drum a pump sends the reflux back to the column (tray 1) and the product to the product tank. 

The minimum active volume depends on feed location but not on impeller size. This suggests that the maximum size of deadwater region depends on the geometry of the vessel. 

Above the critical agitator speed, the active volume rises linearly to unity with r.p.m. This rate of rise is a function of impeller blade size (hence energy input) but is independent of feed location (or vessel geometry). 

The application of this technique to talc-reinforced polypropylene has shown that the microstructure of platelets and the resulting physical properties of the moulded composites are markedly affected [171)]. With two live feeds located at either end of the mould cavity, the talc platelets exhibited strong talc platelet alignment throughout the thickness of the moulding in the direction of the ap-... 

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