Feed-condition line

Note that point 7 can be determined by the intersection of the rectifying operating line and the feed condition line 8-7. 

Fig. 6.15. Operating lines for a complete fractionation column with a feed consisting of a mixture of vapor and liquid. Here (1) is the equilibrium curve, (2) the operating line in the rectifying section, (3) the operating line in the stripping section, and (4) the q or feed-condition line.

The straight line given by Eq. (6.42) with a slope of ql q— 1) is known as the q or feed condition line. Its intersection with the x-y diagonal line occurs at x = Xf where Xp denotes the overall mole fraction of the more volatile component in the feed. The value of q is generally determined from an energy balance around the feed plate. 

The minimum reflux occurs when the operating lines and the feed condition line intersect the equilibrium curve on a McCabe-Thiele diagram. Data for the equilibrium curve can be developed with the aid of Eqs. (6.22) and (6.16). Equilibrium constants are available in Table 6.2. Results are shown in Table 6.5 and plotted in Fig. 6.16. Since the feed to the column is saturated liquid, the slope of the feed condition line is infinite and the line extends vertically at Xp and intersects the equilibrium curve at j = 0.725. A line constructed from this intersection to = 0.95 on the x = y line represents the operating line in the rectifying section of the column under minimum reflux conditions. The slope of this line is given by... 

Since the feed is still saturated, the feed condition line is still a vertical line extending from x =0.5 on the x-y diagonal line. 

The above operating and feed condition lines can now be plotted on an x-y equilibrium diagram for nitrogen and oxygen at 0.101 MPa as shown in Fig. 6.25. Using the procedure of stepping off plates as described in Example 6.8, a little less than six plates is required to accomplish the separation. Therefore, six theoretical plates will be required for the separation, which is identical to that obtained in Example 6.12. 

For certain simplified cases it is possible to calculate directly the number of stages required to attain a desired product composition for a given set of feed conditions. For example, if equilibrium is attained in all stages and if the underflow mass rate is constant, both the equilibrium and operating lines on a modified McCabe-Thiele diagram are straight, and it is possible to calculate direc tly the number of ideal stages required to accommodate arw rational set of terminal flows and compositions (McCabe, Smith, and Harriott, op. cit.) ... 

The point of intersection of the two operating lines is dependent on the phase condition of the feed. The line on which the intersection occurs is called the q line (see Volume 2). The q line is found as follows ... 

In this problem, the y-lines have two widely differing slopes and the effect of the feed condition is to alter the number of theoretical stages as shown in Figure 11m. 

The three sets of vapor-liquid equilibrium data appearing on the x-y diagram show some disagreement, so that great accuracy cannot be expected from determination of tray requirements, particularly at the low water concentrations. The upper operating line in the first column is determined by the overall material balance so it passes through point (0.995, 0.995), but the initial point on the operating line is at x = 0.53, which is the composition of the reflux. The construction is shown for 50% vaporized feed. That result and those for other feed conditions are summarized ... 

The nitrogen oxide reaction gas stream cannot be directly controlled from the steam superheater. Instead the flowrate, temperature and pressure are predetermined by the reactor feed conditions. No direct control exists on this stream as far as the production of steam is concerned, both inlet and outlet lines possess isolation valves for plant shutdown. These lines would be blanked before any platinum recovery work was attempted on the steam superheater. Inlet and outlet linesalsofeature temperature indicators, consistent with the policy of constant monitoring of this parameter throughout the process. 

Shut-down. When the end-of-feed condition occurs for 1AAF, 2AAF or 3AAF, the feed-line to the "high active" feed pump is switched over to the "inactive" feed tank, which can contain simulated HLLW solution, but more normally only HN0 of the appropriate concentration. This solution is used until most of the equipment has been roughly decontaminated. Then all feed-pumps and mixer-settlers are shut off. The mixer-motor units and level transducers are removed from the batteries and the mixer-settlers emptied from solution using a hose and pump attached to a waste tank. 

In Fig. 4.6 we have plotted a typical heat generation expression (curve a) along with the heat removal line, b. In this case the two curves intersect at three locations corresponding to three different reactor conditions that are possible for the same operating parameters and feed conditions. The low-temperature steady state is uneconomical since the feeds are virtually unconverted. The highest-temperature steady state has nearly complete conversion but may be too hot. Under those conditions side reactions may set in or the reactor pressure becomes too high. The middle steady state strikes a good compromise and is where... 

Figure 8.15 shows a possible form of the reaction rate along an adiabatic path. Points B and C ure such that the slope d rjd the curve exactly equals r/, and between these points the stability condition is violated. Since C undoubtedly lies to the left of E where d rfd vanishes, the region of unstable states will lie below the locus It is shown schematically as the cross-hatched region in Fig. 8.13. We notice that the design that minimizes 0 for given feed conditions (problem C, Sec. 8.2) corresponds to point C in Fig. 8.15. Such a reactor would be only marginally stable and the design would not be a good one. We also see from this figure that the problem was probably not particularly well specified. For 0 is the reciprocal of the slope of the line from the origin to a point on the curve. It therefore increases to a local maximum at B, decreases to a local minimum at C, and thereafter...

The separation is specified by fixing the distillate and bottoms compositions, and Xg. The product compositions determine the product rates, which are calculated by material balance. The product compositions are used to locate one end point of each operating line on the Y-X diagram. The feed conditions determine the ty-line (Figure 6.4). 

Effect of feed condition on feed line ra, feed cold liquid rb, feed saturated liquid re, feed partially vaporized rd, feed saturated vapor re, feed superheated vapor. 

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