Shifted compositions

Figure 6.15 The utility target can be determined from the msiximum overlap between the shifted composite curves.

The initial setting for the heat cascade in Fig. 6.18a corresponds to the shifted composite curve setting in Fig. 6.15a where there is an overlap. The setting of the heat cascade for zero or positive heat flows in Fig. 6.186 corresponds to the shifted composite curve setting in Fig. 6.156. 

Such an iterative procedure has been worked out in detail by Drouen et al. [576]. Refinements of the method using the phase selection diagram discussed above include the use of normalized resolution products (see section 4.3.2), shifted compositions and confidence ranges. 

The use of shifted compositions encourages a good distribution of the experimental data over the parameter space. The optimization procedure directs the search to a certain area in the parameter space (around the predicted optimum), but the use of shifted compositions ensures that the maximum amount of new information is obtained from each next data point. The shift in composition (for a one-parameter optimization problem) can be described by... 

In Figure 5.32 the optimum composition predicted from a combination of all three phase selection diagrams is a mixture that contains 10.4% methanol and 33.6% THF (x = 0.84). Eqn.(5.18b) then prescribes a shifted composition of 19.5% methanol and 28% THF (x = 0.7). Obviously, this composition does not fall within one of the (small) confidence regions, and therefore an experimental chromatogram is recorded at the shifted composition. This chromatogram is shown in figure 5.33 (chromatogram d). 

These results provide insight into the potential biogeochemical and trophic impacts of shifting compositions and quantities of new N compounds impHcated in marine eutrophication. Both the amount and makeup of new N play critical roles in determining the magnitude and composition of primary producers. Structural and functional modifications of the primary producer community strongly influence... 

In the /3-hydrides with low susceptibihty, explicit temperature effects are probably unimportant. Indeed, all four pressure/NMR shift isotherms taken on the Pd black between 273 and 350 K give the same composition/NMR shift relationship (64) Equation (21) with 5(0) = -34 ppm and 5i = 85 ppm (0.60 < X < 0.75). The NMR isotherms have also been studied in a 0.2-ixm powder at temperatures between 273 and 383 K (66). Only the two lowest temperature isotherms yield a common shift/composition relationship, with 5(0) 76 ppm and 5, 152 ppm. The results for the Pd black... 

The problem of high amounts of substance needed in flow cells in a single pass mode can be circumvented using recirculation techniques. However, the recirculation can cause problems in studies of chemically reactive systems if an ongoing chemical reaction in the recirculating stream leads to shifting compositions of the evaporator feed, so that no steady state is reached. 

Beside the composite curve, another pinch tool that can be used for assessing process changes is called the grand composite curve (GCC), which can be constructed based on the composite curves. The first step is to make adjustments in the temperamres of the composite curves in Figure 11.3a to derive the shifted composite curves of Figure 11.3b. This involves increasing the cold composite temperature by one half ATimn and decreasing the hot composite temperature by one half... 

If included in the SAR, detailed OLCs for operation should contain numerical values of limiting parameters and operability conditions of systems and components. The corresponding requirements for surveillance, maintenance and repair to ensure that these parameters remain within acceptable limits and that systems and components are operable should also be specified and, where appropriate, justified by means of a PSA. The actions to be taken in the event that operational limits and conditions are not fulfilled should also be clearly established. In some cases, essential administrative aspects, such as the minimum shift composition and the frequency of internal reviews, are also covered by these conditions. Reporting requirements for operational events should also be covered. Further discussion on matters to be covered in this chapter of the SAR is provided in Ref. [39]. 

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