Flooding point determination

Second, flood point data are easy to find, while maximum operational capacity data are less abundant. Generating maximum operational capacity data requires expensive efficiency measurements, while flood-point determination requires far less expensive tests. 

Pressure drop measurements across various column sections are the primary tool for flood point determination, particularly in superat-mospheric and high-liquid-load columns. 

The problem of "undershooting the flood point is just as common. Its occurrence depends on the dynamics of the column. For instance, in the above example, increasing reboil can displace some liquid from the trays. This liquid increases the internal liquid flow rate on the tray below, and it may flood prematurely. When this occvu-s, the flood point determined will be lower than the actual one. 

Although results of the preliminary test may suffer from overshooting or undershooting, they are likely to determine the flood point within 10 percent, and often within 5 percent. The results of this test are used to determine a good starting point for the slow test. The preliminary test technique was found effective both for improving accuracy and reducing time requirements for flood point determination (186). 

Accurate material and energy balances are important for flood point determination, and these should close within 3 and 5 percent, respectively (2, 186) and be checked prior to the test and during the test. There is generally no need for accurate component balances. Several of the key guidelines described in Sec. 14.3, particularly those pertaining to material and energy balances, are also useful for flood testing. Note, however, that flood tests are far less sensitive to analytical errors than efficiency tests, and therefore require a much lower level of effort. 

A discussion of the techniques for measuring the flood conditioa has been givoi by Silvey and Keller, as one considers making such a measuremern he or she soon realizes that the flood point determination is influenced by the measuremern approach and that it is really not a "poim" but a fairly narrow range of values. Even so, methods for milking an esrimate of the flood point are useful and are outlined in the following section dealing with pressure drop. 

It is important to ascertain the liquid hold-up hL throughout the entire operating range of a packed column, both for the prediction of the pressure drop and for the constructive design of a packed column. The liquid hold-up at the flooding point determines the constructive design of the column support, while hL under operating conditions determines... 

A typical form of flooding-point curve for spray towers is shown in Figure 13.35 where values of udf are plotted against ucf. The limiting values of each flowrate as the other approaches zero may be determined readily from equations 13.34 and 13.35. Thus, when... 

To use the flooding point diagram, first it is necessary to decide whether the drops produced in the extractor are circulating or oscillating. The mean diameter di,2 (see Eq. 9.1) is used for the characteristic drop size. If the flow rate ratio is known from the thermodynamic design, the superficial velocities of both phases can be determined at the flooding point. The minimum column cross-sectional area and diameter necessarily follows directly from the superficial velocity at the flooding point with Eq. 9.19. 

The method of calculation introduced in this chapter not only allows an exact determination of the column diameter for nonpulsed sieve tray columns, but also allows a good estimation of the diameters of pulsed and stirred extractors. For the latter, however, more exact specific equations exist for the flooding point, see for example [1,4]. 

Preselection of a suitable extractor type on the basis of available information and testing at pilot scale Establishment of suitable operating conditions as, for example, the pulse intensity of pulsed extractors or the speed of rotation of centrifugal extractors Determination of the flooding point... 

Kamei et al. (K6), 1954 Experimental determination of flooding points in wetted-wall columns of i.d. 1.89-4.91 cm., using various liquids and air counter-flow. 

The design of a multi-purpose plant for the continuous extraction of liquids with supercritical fluids is presented. To provide flexibility in order to treat different feedstocks, a modular concept was developed based on experience gained in the operation of bench-scale and pilot plants. Four test systems were chosen in order to determine the proper dimensions for the equipment. Based on experimental data, e.g. measurements of flooding points and maximum flows for various column internals, the design pressure and temperature and heat exchange requirements were determined. The plant was built by a German manufacturer and was operated successfully by a Canadian company in Edmonton, Alberta. 

Packings and Flooding As pointed out above, optimized mass and heat balances have been derived from a combination of experimental results with a con uter simulation of the process. The optimized balances can be used for the layout of a production plant A multi-purpose plant should be able not only to produce samples, but also to determine scaleup parameters. The scaleup parameters depend on the type of packing and its specific flooding point The ability to measure flooding points or to test different packings is restricted mainly by the range of flow rates. 

For sizing the gas circulating pump, feed pump and reflux pump the results of the optimizations were used. TTie determination of the maximum flows was based on a flooding point diagram. As an example, the optimization of the Monoglyceride process required a gas flow of the regenerated C02/C3Hg mixture of... 

The upper limit of the velocity in a sieve-tray column is determined by the flooding point or by the velocity at which entrainment becomes excessive. Flooding occurs when the liquid in the downcomer backs up to the next plate, and this is determined mainly by the pressure drop across the plate and the plate spacing. Near the flooding point, most of the pressure drop comes from the term in Eq. 

For example, the cost of a distillation column can be assembled from the cost of elements vertical cylindrical vessel, plus internals (trays or packing), reboiler, condenser, and reflux drum. The height of the shell can be determined from the number of trays and inter-stage height. The column diameter can be found by hydraulic calculations based on the flooding point. In this way, the volume of the cylindrical part can be easily evaluated. The volume of auxiliary vessels, as drum and reboiler, can be estimated from the residence time, typically of 10 minutes. 

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