Multiple inlets

There are seven commercial processes in operation six operate in the vapor phase. The Universal Oil Products process operates in the Hquid phase and is unique in the simulation of a moving bed. The adsorption unit consists of one vessel segmented into sections with multiple inlet and oudet ports. Flow to the various segments is accompHshed by means of a rotary valve which allows each bed segment to proceed sequentially through all the adsorption/desorption steps. 

Unlike the momentum equation (Eq. [6-11]), the Bernoulli equation is not easily generahzed to multiple inlets or outlets. 

The need for and use of multiple inlets/oudets for centrifugal compressors becomes apparent when balancing process flow and pressure requirements. See the later discussion, and also refer to Figures 12-40B and 12-40D. 

The use of inert tracer experiments to measure residence time distributions can be extended to systems with multiple inlets and outlets, multiple phases within the reactor, and species-dependent residence times. This discussion ignores these complications, but see Suggestions for Further Reading. ... 

Light emission from a multiple inlet combustor under (a) stable and (b) unstable operation. (From Poinsot, T.J., Trouve, A.C., Veynante, D.P., Candel, S.M., and Esposito, E.J., /. Fluid Mech., 177,265,1987. With permission.)... 

It should be emphasized that the enthalpy change includes not only sensible heat effects but also a heat-of-reaction term and in some cases pressure effects. If there are multiple inlet and outlet streams, appropriate averaging techniques must be used to employ this equation. 

The Molex process developed by U.O.P. is unique not only in its liquid-phase operation but also in its adsorption system (1-8). Its adsorption system consists of a single adsorption tower with multiple inlet-outlet points and a special rotary valve. The adsorption tower has many smaller adsorption chambers interconnected in series, and it operates under the so-called simulated moving bed operation. Instead of moving the adsorbent bed, the simulated moving bed operates by simultaneously advancing inlet-outlet points periodically. At any time, the adsorber has four zones—viz., adsorption, primary rectification, desorption, and secondary rectification zones, and these zones advance simultaneously as the rotary valve turns periodically. Desorption of n-paraffins is achieved by displacement. 

In large gas ducts or large diameter pipes carrying liquids it may be necessary to use multiple probes (Fig. 6.59/) or long probes with multiple inlets. ASTM Standard D4177(82) specifies sampling procedures required to obtain representative samples of petroleum and petroleum products and similar methods can be employed in sampling most non-corrosive liquid industrial chemicals. 

In conclusion to this section, research in the RTD area is always active and the initial concepts of Danckwerts are gradually being completed and extended. The population balance approach provides a theoretical framework for this generalization. However, in spite of the efforts of several authors, simple procedures, easy to use by practitioners, would still be welcome in the field of unsteady state systems (variable volumes and flow rates), multiple inlet/outlet reactors, variable density mixtures, systems in which the mass-flowrate is not conserved, etc... On the other hand, the promising "generalized reaction time distribution" approach could be developed if suitable experimental methods were available for its determination. 

This technique (Fig. 3.8), which is examined in greater detail in connecdon with the upgrading of aromatic Cs cuts, is based on the use of a pseudo-countercurrent between the liquid feedstock and the adsorbent bed. The displacement of the solid is in fact simulated by means of a rotary valve with multiple inlets and outlets, which causes a gradual change ih the injection and collection points of the liquid streams in the molecular sieve placed in a rould-stage column. 

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