DOUBLE FEED

The extractive column must be a double-feed column, with the solvent feed above the primary feed the column must have an extractive section. 

Baldyga, J., Podgorska, W. and Pohorecki, R., 1995. Mixing-precipitation model with application to double feed semibatch precipitation. Chemical Engineering Science, 50, 1281-1300. 

Two experimental rigs were used for this study. The first rig comprised a double-feed hopper arrangement to ensure a virtually constant mass flow rate of powder during each test. The hopper arrangement was mounted on a frame that could be raised or lowered to change drop height and was suspended on cables connected to three load cells to enable the mass flow rate to be recorded. The bulk material dropped through a hole in a shelf above the stockpile and air was extracted from underneath the shelf at a rate such that the air pressure under the shelf was kept exactly equal... 

Try this for yourself using DODS-SiCo and the TT design option, find a combination of product distribution for a set a that will result in the double-feed pinch. 

The double-feed pinch case occurs only at a specific selection of product purities. Although it may seem like a trivial ccmdition, the double-feed pinch scenario... 

FIGURE 5.29 Illustration of minimum reflux increase for a given feed and for product specifications laying either side of the double feed pinch product ecifications. 

Notice that in finding / a3min and /Jasmin that there was only one possibility in which the TTs could touch one another since the Xa s of the respective CSs were fixed. In the case of CS2 and CS4 however, the difference points are variable and hence it is necessary to take account of aU three of these pinching scenarios. Since a double-feed pinch case is merely the special condition where cases (a) and (b) in Figure 7.31 meet, there are essentially only two cases of minimum reflux across the feed. In order to find the minimum reflux for the CSs across the feed, it is thus necessary to consider both these cases. Holland et al. [27] treated this problem by evaluating the eigenvectors at the feed for liquid feeds only, but we will treat the general case here for any quality feed. 

No.20, 1998, p.4915-21 MATHEMATICAL MODELLING OF THERMOPLASTIC NATURAL RUBBER MELT FLOW IN A DOUBLE FEED EXTRUSION SYSTEM... 

A mathematical model was presented for studying the melt flow behaviour of thermoplastic natural rabber (TPNR) in a double feed extrusion system. The model predicted the processing parameters in the feed and main extruders, from which the optimum processing conditions for TPNR were obtained. The double feed system enabled better mixing to occur in the main extruder. 20 refs MALAYSIA... 

The ETBE reactive distillation column studied by Al-Arfaj and Luyben is a double-feed system with pure ethanol fed to stage 6 at the top of the reactive zone and a mixed C4 stream fed to stage 20 at the bottom of the reactive zone. The C4 feed is 40 mol% isobutene and 60 mol% w-butene. The column has 4 stripping trays, 15 reactive trays, and 4 rectifying trays, which are shown in Figure 9.18. 

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