Cutting time

If liquids are controlling, the residence time varies from 2.5 to 5 min, half full, depending on water content. With this vessel design parameter In mind, reference should be made to the expected production decline and produced water cut time profiles. A decision can then be made based on calculation of residence times If 75% or 50% unit trains should be designed For the problem illustrated, 2 x 73% units would be selected to permit flex iblllty (Table 4). 

Note to avoid abortion of batches during trial experiments (if carried out in an actual plant with large throughput) it is recommended to stop the batch when the distillate composition drops below or the top tray temperature goes above the specification. This will avoid any possible loss of revenue. Also note that, whether it leads to optimal operation or not, the industrial operators decides the cut time based on the above criteria. 

Note Safrit and Westerberg observed that the optimal operation policies (cut time and water flow rate) are quite sensitive to the sales value of the products and the cost parameters of steam and cooling water. Please refer to the original reference... 

Table III lists the material balances for the preparative separations. These are the percent weight recoveries for either asphaltene or maltene defined, using the sulfur balance for an example, as the sum of the amount of sulfur in each cut times the cut weight percent divided by the total sulfur. In general, the balances are in the 80-120% range, which is reasonable considering the amount of sample handling involved. The recoveries are out of line only in a few cases, most notably the Prudhoe Bay maltene nickel balance. In addition, a comparison of the calculated elemental values for the total residua differ somewhat from the raw total values for several residua. These discrepancies are probably attributable to the small samples, multiple sample manipulations, and compounding of individual errors when the asphaltene and maltene data are summed. The data-fitting routine described in the next section was used to obtain a set of best fit data, which were used in the subsequent size calculations.

The Fokker-Planck equation is based on a clear-cut time-scale separation between the variable of intoest and its heat bath. In the linear case this is an exact equation even when ffioite correlation times are considered. 

The results in terms of optimum number of stages, vapour load, reflux ratio, cut time, etc. are summarised in Table 1 for both columns. The results also show the operating cost per batch, annualised capital cost, profit per batch and per year. For MultiVBD column the total number of stages required is 40% more than that required for the conventional column CBD). However, the vapour load for the MultiVBD column is about 25% lower compared to CBD and the operating cost (a measure of energy cost) is 30% lower. Finally, the overall profit realised by MultiVBD column is about 3% more that that by CBD column. The product demand and qualities (purities) of each main-cut and off-cut are achieved to the given specifications. Figure 4 shows the product quality at the end of the batch ior MultiVBD column in each vessel. 

In this chapter, we define two cut times, fc,l tcfi/ arid three fractions for a binary mixture (however, four cut points could also be considered, as shown in the Figure, at the front of the first peak and end of the second one). The first fraction contains the pmified first component, a mixed fraction follows, and the third fraction contains the pmified second component. The production rate for... 

Sc, Rc, calculated data for the maximum production rate of the enantiomer. Se, Re, experimental data corresponding to the same cut times. 

Sharma, S.K., Mittal, G.S., and Hill, A.R. (1994). Effect of milk concentration, pH and temperature on K-casein hydrolysis at aggregation, coagulation and curd cutting times of ultrafiltered milk. Milchwissenschaft 49,450-453. 

As for the four cut times, the end of fraction product fraction B, tg2, is selected as the end of the chromatogram - for example, based on a low threshold concentration. If the initial slope of the isotherm of the stronger adsorbing component is known, Equation 7.65 might be used instead ... 

Figure 7.14b shoivs an overlay of the elution profiles of 50 SSR cycles performed using the cut times determined in Figure 7.14a, ivhich is the reason why the elution profiles of the first cycle (largest concentrations) are identical to those in (a). The process reaches a steady state after about 10 cycles. Note that the second fraction is virtually invariant from cycle to cycle, while the purity for fraction A is fulfilled only after the process, which was started here with a full injection of fresh feed, reaches steady state. The purity requirement on A can be fulfilled also during start-up if the process is initiated using a lower injection concentration. However, the most elegant option is to eliminate the start-up completely, as shown in Figure 7.14c. As proposed by Bailly and Tondeur (1982), this is achieved when using for the first few injection(s) a prepared mixture that corresponds to the steady-state injections, and switching to the fresh feed after these eluted from the column.

The design method was extended to processes with an additional solvent removal in the recycle (Siitonen, Sainio, and Kaspereit, 2011). Furthermore, although it does not directly apply to SSR processes operated in closed loop mode, it can be used to obtain initial guesses on cut times and performance of such process. 

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