Selectivity feed point

If the selected feed point location produces a region of little or no change in Sp, fewer theoretical stages may be required. If the Sp shows a reversal in the value near the feed stage, a new feed point location should be selected. 

Because of the steep pitch required, slides are limited in application. They are most commonly used to bridge the gap between roller-conveyor systems on two floors, because the roller conveyor can take the container off the slide rapidly and ehminate or reduce the chance for collisions. Slides may also be used when containers can be chuted from an upper floor to a manually loaded carrier. The use of several rollers at the feed point is recommended for easy dehveiy to the sloping section. If the drop is short and containers light, a roller cleanout will prevent backup of containers on the slide. The slope of gravity slides is a function of container weight, size, and friction characteristics and should be selected with care to be sure that containers do not move either too swiftly or not at all. Slides usually use flat steel sheet. 

Since this is a countercurrent operahon, the selective volume of the adsorbent enters the top of this zone containing only desorbent. As the adsorbent passes countercurrent against the feed, it ultimately reaches bottom of the zone which is the feed point. By this time, the adsorbent s selective volume is filled with normal paraffins. This zone may contain as many as eight beds and as few as three. Product purity and recovery requirements dictate how many beds are required. 

The first parameter A represents the selective pore rate (m /h). For a set volume of adsorbent contained in the Sorbex chambers, there is a known selective pore volume. This selective volume quantity is divided equally among the various adsorbent beds. Since Sorbex process simulates a moving bed process where adsorbent moves counter current to the process flow, the selective pore rate represents the quantity of selective volume that moves with every step or index of the rotary valve. One step of the rotary valve indexes the feed point from one bed to the next sequential bed position. 

As can be understood from Figure 11.5, the amount of adsorbate lost in the effluent and the extent of the adsorption capacity of the fixed bed utilized at the break point depend on the shape of the breakthrough curve and on the selected break point. In most cases, the time required from the start of feeding to the break point is a sufficient index of the performance of a fixed-bed adsorber. A simplified method to predict the break time is discussed in the following section. 

For the values selected above B is 1.4 to 2.1 m. This estimate agrees with current commercial practice of spacing feed points at intervals of 1 to 3 m. For our test case, this corresponds to one coal feed point for every 1.8 to 4 MW, or approximately 25 to 55 feed points. The requirement for a large number of feedpoints is one of the shortcomings of AFBC s. Methods of overcoming the problem of multiple feed points include the use of a spreader-stoker to distribute the coal evenly over the surface of the bed or the promotion of lateral mixing by recirculating bed solids. 

The tablet is a small digitizer, perhaps fourteen inches on a side. Using either a stylus or cursor, it can feed back coordinates (within a fixed frame of reference, thus it is an absolute positioning device) to the machine which can be used to select a point of interest or enter data by tracing a curve. Those coordinates must be interpreted by software in terms of the screen coordinate system since is it unlikely that they will match. 

Chemical Reactions Chemical reactions are influenced by the uniformity of concentration both at the feed point and in the rest of the tank and can be markedly affected by the change in overall blend time and circulation time as well as the micro-scale environment. It is possible to keep the ratio between the power per unit volume at the impeller and in the rest of the tank relatively similar on scale-up, but many details need to be considered when talking about the reaction conditions, particular where they involve selectivity. This means that reactions can take different paths depending upon chemistry and fluid mechanics, which is a major consideration in what should be examined. The method of introducing the reagent stream can be projected in several different ways depending upon the geometiy of the impeller and feed system. 

With the proper idlers selected for size and service conditions, the most important step is to locate them properly. For long belts the tension varies considerably, and idlers should be spaced to hold belt sag to reasonable limits along the full length of travel. Too much belt sag can cause a significant power loss, but for most belts of ordinary length it is usually satisfactory to space idlers fairly closely at the feed point and then farther apart and uniformly for the rest of the conveyor length. 

Fig. 3 Impact of different feed positions on the precipitation of barium sulfate. The selectivity to by-product as a percent of reactant is shown for feed into zones of high and low turbulent energy dissipation. The impeller speed and reactant addition time were held constant. More by-product is formed at feed points where the local mixing is slow.

Find the value of the selectivity set point which gives the highest value of the objective function, as defined above with a= 50. Compare the feeding profile found with those found in the previous exercises. 

Figure 18.3 shows examples of applying this procedure to benzene-toluene columns with different feed points and different feed compositions. Accordingly, trays 7,10, and 5 or 10 are the best control trays in Fig. 18.3a, b, and c, respectively. Figure 18.4, based on the column in Fig. 18.3a, shows how a variation in control tray temperature affects product composition with a correctly located and an incorrectly located control tray. When the temperature variation is caused by a change of pressure or in the concentration of a nonkey component, it will produce a steady-state offset in product composition. A disturbance in the material or energy balance will cause a similar temperature variation until corrected by the control action in this case, the offset will only be temporary. Figure 18.4 shows that the offset in either case is minimized when the control tray is selected in accordance with Tolliver and McCune s procedure (403). A dynamic analysis by these authors (403) indicated that the control tray thus selected tends to have the fastest, most linear dynamics. 

When simulating the mold-filling process, the designer of a plastic part must therefore select the feed points such that the flow lines are not within regions of maximum stress load. 

Guideline 11. Select measurement points that are sufficiently sensitive. Consider, for example, the indirect control of the product compositions from a distillation column by the regulation of a temperature near the end of the column. In high-purity distillation columns, where the terminal temperature profiles are almost flat, it is preferable to move the temperature measurement point closer to the feed tray. 

In order to reduce the computational workload, it is often necessary to only select a sample of all extreme points in conv(X) as feed points C[ for use in the DSR integrations. We often also designate specific points to act mixing points C w (j fee(j equilibrium points), since, from Chapter 6, it is known that critical DSR trajectories must be fed with sidestream concentrations that reside on the true AR boundary, which also cannot originate from protrusions (concentrations from PFR trajectories). A trade-off between constmction time and computational accuracy must often be estabhshed when implementing the RCC algorithm in practice. 

In case of heavy solvent, with total reflux and appropriately selected feed flow rate, the feasible EPs from any point in the composition triangle (A) run to a stable node (SN) situated near or on the AE edge. From the neighborhood of this SN point, high purity distillate composition can be reached by rectification profile. 

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