Preliminary designs example

For example a process flow scheme for crude oil stabilisation might contain details of equipment, lines, valves, controls and mass and heat balance information where appropriate. This would be the typical level of detail used in the project definition and preliminary design phase described in Section 12.0. 

The detailed design of solid bed dehydrators. should be left to experts. The general rules of thumb presented in this chapter can be used for preliminary design as shown in the following example ... 

Though Kern s method does not take account of the bypass and leakage streams, it is simple to apply and is accurate enough for preliminary design calculations, and for designs where uncertainty in other design parameters is such that the use of more elaborate methods is not justified. Kern s method is given in Section 12.9.3 and is illustrated in Examples 12.1 and 12.3. 

A comprehensive review of the methods available for predicting convective boiling coefficients is given by Webb and Gupte (1992). The methods proposed by Chen (1966) and Shah (1976) are convenient to use in manual calculations and are accurate enough for preliminary design work. Chen s method is outlined below and illustrated in Example 12.9. 

Make a preliminary design for a vertical thermosyphon reboiler for the column specified in Example 11.9. Take the vapour rate required to be 36 kmol/h. 

If the piping layout is known, then the above correlations can be used to estimate the pressure drop through the pipes. This might be the case, for example, in a retrofit situation. In preliminary design, it might be necessary to make some allowance for a cost of pumping and compression without... 

For preliminary design purposes, we shall calculate the conversions for two situations and compare the results. Only one of the situations will be presented in detail in this example. The other is given as a problem on the CD-ROM, but the answer will be used in the comparison. 

Predesign cost estimation, 5 Preferred stock, dividend rates on, 248-249 Preliminary designs, 14,16-18 example of 22-34,... 

In this example, we illustrate the use of preliminary design tools in exploring design options efficiently. The design problem is represented schematically in Fig. 5. 

This example follows the procedures in Section III.B.2 quite closely, with some judgment being exercized in the selection of the appropriate worst-case scenarios. This application is fairly typical of preliminary designs in that good... 

Example 1—Preliminary Design of the Minimum Solvent Flow Rate and Number of Extraction Stages... 

Based upon product batch requirements, preliminary vessel dimensions are listed in Table 6. Gas flow rate (ACMM) is determined to obtain the mass transfer required by reaction kinetics. A ring sparger is selected as discussed in conjunction with Fig. 8. Table 7 summarizes the calculation of the required specific power and gas holdup based on mass transfer and the desired oxygen concentration in the liquid. It must be confirmed that vessel dimensions accommodate the aerated liquid height. An appropriate agitation drive system is recommended in Table 8. Fig. 9 is a schematic of the reactor in this design example. 

The following example illustrates the development of an economic model for the NPV, rate of return, and economic price using a preliminary design of a process to produce 100 million pounds per year of aniline from the reaction of phenol and ammonia. The following information has been developed. 

To illustrate the preliminary design formulae and the time saved by using the standard form sheets, an example is worked out on the Vessel Calculation Form. Following the example, the derivation of the formulas is given. The forms may be used for horizontal vessels if the beam bending stress is used instead of wind stress and for riveted vessels if proper efficiencies are used for the joints. 

They are readily computed for a given cell geometry and are very useful for preliminary design. They have a direct impact on physical properties and converter performance. For example, the substrate strength O3 is proportional to the product of MIF and wall strength <5,, i.e. 

In discussing the preliminary design of fixed bed reactors in Sec. 11.3 we mentioned that adiabatic operation is frequently considered in industrial operation because of the simplicity of construction of the reactor. It was also mentioned why straight adiabatic operation may not always be feasible and examples of multibed adiabatic reactors were given. With such reactors the question is how the beds should be sized. Should they be designed to have equal ATs or is there some optimum in the AT s, therefore in the number of beds and catalyst distribution In Section 11.3. this problem was already discussed in a qualitative way. It is taken up in detail on the basis of an example drawn from SOj oxidation, an exothermic reversible reaction. To simplify somewhat it will be assumed, however, that no internal gradients occur inside the catalyst so that the effectiveness factor is one. 

It will be assumed that bubble growth occurs close to the distributor, so that a single effective bubble diameter for the entire bed can be assumed. This is a contentious assumption, and several studies accounting for bubble size distribution and other hydrodynamic features of the bed have been reported, for example. Van Deemter (1961, 1967), Partridge and Rowe (1966), Toor and Calderbank (1967), Kato and Wen (1969), Fryer and Potter (1972, 1976), Jayaraman et al. (1980), Chen et al., (1982), Werther (1977), Werther and Schoessler (1984), Grace (1982, 1986). However, we persist with the constant bubble size assumption because it is sound enough for a preliminary design. 

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