Partial feed

For the classical SMB process described above, the composition and flow rate of the feed is constant for the whole switching interval. Following the approach by Zang and Wankat (2002) in the Partial-Feed process, two additional degrees of freedom are introduced, i.e. the feed duration and feed time. Figure 5.23a compares the feed flow... 

Fig. 5.23 Flow rates during Partial-Feed operation. (Reproduced from Wankat et al., 2002.)...

Partial-Feed processes switch the feed stream on and off within one time interval while the other inlet and outlet lines are active all the time. ISMB (Improved SMB) processes partition the switching interval in a different way. In the first part of the period (Fig. 5.24a), all external lines (desorbent and feed inlets as well as extract and raffinate outlets) operate. However, in contrast to a classical SMB unit, the outlet of section IV is not recycled during this part of the switching interval and, consequently, the flow rate in section IV is zero. The first. .injection period" is followed by a recirculation period in the second part of the switching interval (Fig. 5.24b). During this time all external ports are closed and recirculation is performed with a constant... 

Fig. 9.23. Steady-state flux and permeate pressure as a function of partial feed pressure for different gases at300K (a) and at673K (b). After Bakker et al. [71 ]. (0) neon, (+) argon, (V) krypton, ( ) methane, (A) ethtine, ( ) n-butane, (A) isobutane, (O) CFC-12.

The above heuristics may produce a feasible but not always optimum sequence. In principle, the sequences can be compared by means of operation and capital costs. The first depends on the total utility consumption, proportional with the vapour rate. The second depends on the number of stages. Glinos Malone (1988) demonstrated that optimal sequencing depends less on the total number of stages, but near-optimum sequences are those minimising the total vapour rate of key components. Therefore, when the relative volatility of keys differs considerably the estimation of total vapour flow based only on partial feeds is in large error. It is worth to mention that the method described before can be used for ranking of sequences, but not to determine the effective optimal vapour flow. 

Partial-Feed, Partial-Discard, and Fractionation-Feedback Concepts... 

Figure 5.20 Flow rates during partial-feed operation (according to Zang and Wankat (2002a, 2002 b).

Another modification of the classical SMB process is the so-called ModiCon approach by Schramm et al. (2003). In contrast to the partial-feed process, where the feed flow rate is varied during one switching interval, in ModiCon the feed concentration is altered instead of the feed flow rate. Figure 5.22 illustrates this variation of the feed concentration during the switching interval tshia- In the example shown, which is suitable for systems with favorable isotherms, at the beginning only pure solvent is fed to the plant while in the second part feed at a rather high concentration is used. The modulation of the feed concentration allows for improved process performance for systems with nonlinear adsorption isotherms. 

Zang, Y. and Wankat, P.C. (2002a) SMB operation strategy - partial feed. Ind. 

Yif Pi being valid for solutions of i. It must be noticed that the activity coefficient Yi f varies with the concentration of i in the feed soluhon. For dilute solutions of i the product Yif P is constant and may be described by the Henry coefficient. Hi. In vapor permeation the value of pn may be increased by compressing the feed vapor before processing it through the membrane unit. If the partial permeate pressure Pi -p of solute i is negligible in view of its partial feed pressure p f (but not necessarily when the total permeate pressure Pt is close to zero, as is often stated in the literature), then it follows that... 

The intensive water-sulfuric acid interaction (fe = 10 1 1/moEs) and substantial thermal effect (q = 196 kilojoules/kg) result in 84 °C adiabatic increase of temperature in an extremely small local area of the reaction volume (L ooi = 10 1 m). In this case, technologically acceptable conditions (reactor temperature does not exceed 70 °C (343 K)) can be achieved in a two-zone operation model with the partial feed of a 90% acid solution into two zones, separated by the cooling area. This approach provides a technologically acceptable temperature mode for the process. In addition, the partial feeding of acid allows a 20% reduction of the device s radius in the first zone (from 0.01 to 0.008 m). It favours both the required level of flow turbulence and the increase of external heat removal output (additional 15-20% decrease of The maximum... 

If ingested at a concentration of 0.15 mg/kg bw/day, DON is able to cause vomiting in swine, while it has been estimated that levels up to 1—2 mg/kg in the diet can cause partial feed refusal in livestock, mainly pigs. Unfortunately, an accurate acute dose—response evaluation in humans has not been reported so far. However, it has been possible to ascribe the induction of acute gastroenteritis to vomiting in both mammals and humans to... 

The effective diffusion coefficients, Da. were calculated from the observed flux, J, versus the partial feed pressure pp and the fiber wall thickness L using Equations 1 and 2 below (2) ... 

The usefiiliiess of partial feed bypass is discussed in more detail in Fromrait, G. F. and Bischoff, K. B., Chemical Reactor Analysis and Design, 2nd edition, John Wiley Sons (1990), Chapter 11, Section 5.5,... 

A plant in Germany was modified to accept ground-up plastic wastes as a partial feed. The plant, originally built to process coal to synthetic fuel, had been converted to oil sludge upgrading. The process has been described as follows [42] ... 

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