Flash vaporization, curve

In determining a flash-vaporization curve, a series of runs at different... 

Example 4-5. Estimate of Flash Vaporization Curve. The T.B.P. curve of Fig. 4rl7 has a slope (degrees/per cent) between the 10 and 70 per cent points of... 

According to Fig. 4-18, the slope of the flash vaporization curve will be 6.5 deg/per cent, and the 50 per cent temperature of the flash curve (Fig. 4-19) will be about 64"F below the 50 per cent temperature of the T.B.P. curve ... 

The various curves may be corrected for pressure or vacuum by means of vapor pressures (Figs. 5-25, 5-26, 5-27) applied at the 50 per cent point or at the crossing point of the curves with the T.B.P. curve. However, the flash vaporization curve tends to become horizontal at the critical point or range (Fig. 15-i3) and accoidin y, Edmister suggests an approximate correction based on Fig. 4-22. The method is termed approximate because the focal point pressures of the phase diagrams of petroleum mixtures are not known with accuracy. The estimation of focal points and phase diagrams is discussed on pages 456 to 460. 

Example 4-6. Curvature of Flash-vaporization Curve. The experimental flash-vaporization curve and the ASTM distillation of a pressure distillate are shown in Fig. 4-24. The computed straight-line curve is shown dotted, the triangular points are computed points, and the circular points are experimental ones. 

Edmister, Reidel, and Mervin have determined flash-vaporization curves on three oils up to pressures of 200 psia. They find that the higher the pressure the flatter the vaporization curve, and hence the curves at high pressures should not be drawn parallel to the atmospheric-pressure curve. Obviously, the flash curve should be horizontal at the critical pressure, and hence the slope of the flash curve will be flatter and flatter as the pressure is increased. They find that the 50 per cent atmospheric boiling point should be corrected to the new pressure by using the vapor-pressure relationship of the paraffin hydrocarbons (Fig. 5-27). In practical design computations it is common practice to convert to the new pressure by using any convenient point on the atmospheric flash-vaporization curve. Refer also to Figs. 4-22 and 15-13. 

Fio. 7-21. Carrier distillation curves of a crude oil. Dotted curve shows the vapor temperatures in a T.B.P. distillation of the feedstock curve 1, liquid temperatures in a T.B.P. distillation 2, flash-vaporization curve of the feedstock 3, flash-vaporization curve of feed plus 50 per cent recirculation 4, flash-vaporization curve of feed plus 100 per cent recirculation and 5, flash-vaporization curve of feed plus 200 per cent recirculation. 

Experimental Vaporization Curves. When such complex materials as gasoline and petroleum fractions are dealt with, the application of the aforementioned equilibrium laws is cumbersome. Furthermore, the component analyses of these heavy oils cannot be easily obtained and even if such analyses are-availalUe, accurate vapor-pressure or equilibrium data for the compounds or fractions contained in them are not always available. At present most equilibrium relations are obtained by determining experimental flash-vaporization curves or by computing such curves from the empirical relationships discussed in Chap. 4. Empirical flash curves can be estimated from true-boiling-point or ASTM curves, and with less accuracy from Hempel or Saybolt distillation curves. 

The fiash-vaporization curve at atmospheric pressure will lie across the phase diagram on a constant-pressure line at 14.7 psia. The slope of the straight-line flash-vaporization curve (Fig. 4-18) will be about 1.03, and its 50 per cent temperature... 

Fig. 16-5. ASTM distillation and. flash-vaporization curves of the products used in Examples 16-3 and 16-4.

Vaporizer Temperature. A flash-vaporization curve (Figs. 4-18 and 4-19) is drawn. At atmospheric pressure a vaporizer temperature of 655 F is required to vaporize the 63 per cent of products, and for a tower pressure of 10 psig the vaporizer temperature becomes 695 F (Fig. 5-27). If steam were used in the tower it would reduce the vaporizer temperature (Eq. (15-8)]. 

The extent of vaporization may be estimated by drawing flash-vaporization curves of the stocks (Figs. 4-18 and 4-19) and correcting these curves for pressure by means of Fig. 5-27, but more precise results can be obtained by drawing the phase envelopes of the outlet material and also... 

The distillation and flash vaporization curves were computed for the furnace feed, the effluent, and for the material when it was half cracked, as indicated in Fig. 19-10. In estimating the distillation curves, the mid boiling points of Table 19-16 were used, along with a terminal temperature of 770 F for the recycle stock (see Fig. 19-9), and an initial boiling point of 590 F for the gas oil. It was judged that materi boiling up to 1000°F could be vaporized (into the gas oil) by exposure of the reduced crude oil in vessel A of Fig. 19-7. 

Fig. 19-10. Estimates of distillation and atmospheric-flash cu rves of furnace feed and effluent of Example 19-8, and the equilibrium-flash-vaporization curve of the effluent at 415 psia.

Draw the flash-vaporization curve of the crude oil unless this curve is included in the laboratory analysis (Figs. 4-18 and 4-19). 

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