Reboiler space requirement

The design of a distillation column requires a reboiler operating at 2.23 psia (vapor space above bottom liquid). The heat duty is 1,528,600 Btu/hr. The properties of the acrylonitrile mixture have been calculated to be... 

A centrifugal pump is required to circulate a liquid of density 800 kg/m2 and viscosity 0.5 x 10 3 Ns/m" from the reboiler of a distillation column through a vaporisor at the rate of 0.004 m3/s, and to introduce the superheated vapour above the vapour space in the reboiler which contains a 0.07 m depth of liquid. If smooth-bore 25 mm diameter pipe is to be used, the pressure of vapour in the reboiler is 1 kN/m2 and the Net Positive Suction Head required by the pump is 2 m of liquid, what is the minimum height required between the liquid level in the reboiler and the pump ... 

When alloy piping or large bore piping is required, the associated equipment is located together as much as possible to keep the pipe runs short, preferably nozzle-to-nozzle by avoiding the piperack. Items such as elevated overhead condensers are located near the source and destination. Similarly, theonosyphon reboilers need to be placed adjacent to the column they reboil. Where gravity flow is required, these lines must be kept short and sloped. Space allocation for future additions must also be considered. 

Selection A Karbate column of 8 in. nominal diameter will be used. Four bubble cap plates and a reboiler will be furnished. Using a plate spacing of 18 in. requires a column height of 12 ft. 

In large-diameter packed colxunns where I-beams support the packing support plate, a larger space between the reboiler return nozzle and the packing support plate may be required. The prime consideration here is allowing sufficient open area between the bottom of the beam and the high liquid level for adequate vapor distribution. Detailed discussion is in Sec. 8.2. 

Figure 8-7 shows the characteristic pattern of distillation curves for ideal or close to ideal VLE with no azeotropes. All of the systems considered in Chapters 5. 6, and 7 follow this pattern. The y-axis (Xg = 0) represents the binary A-C separation. This starts at the reboiler (x = 0.01 is an arbitrary value) and requires only the reboiler plus 4 stages to reach a distillate value of x = 0.994. The x axis (x = 0) represents the binary B-C separation, which was started at the arbitrary value Xg = 0.01 in the reboiler. The maximum in B concentration should be familiar from the profiles shown in Chapter 5. Distillation curves at finite reflux ratios are similar but not identical to those at total reflux. Note that the entire space of the diagram can be reached by starting with concentrations near 100% C (the heavy boiler). 

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