Pseudo-moving bed

The system proposed by Freund et al. contained all the essential properties of the modern moving bed, or pseudo moving bed chromatographic systems. The procedure was extended by Scott [6], in 1958, to gas/liquid chromatography and... 

A pseudo moving bed system was described by Barker [8,9] who simulated the process by employing a column in circular form. A diagram depicting this wheel concept is shown in Figure 13. 

Discussion. Fixed bed cracking reactors as well as commercial moving bed reactors operate under steady state or pseudo-steady state conditions ( ). Observed selectivity (eg., ratio of yield of branched to n-paraffin) in a steady state catalytic reactor is independent of space velocity (1, 17). The selectivity depends on intrinsic rate constants and diffusivities of the reacting species which depend on temperature. Thus, the selectivity observations reported here are applicable to commercial FCC units operating at space velocities different from that employed in this study. 

Some work has already been done on the simulation of transient behavior of moving bed coal gasifiers. However, the analysis is not based on the use of a truly dynamic model but instead uses a steady state gasifier model plus a pseudo steady state approximation. For this type of approach, the time response of the gasifier to reactor input changes appears as a continuous sequence of new steady states. 

The pseudo-simulated moving bed process - the JO process of Japan Organo Co. [28, 29] - has been successfully applied to the separation of a ternary mixture. The process cycle is divided into two steps (Fig. 3.4-14). In step 1, feed and eluent streams are introduced into the system, equivalent to a series of preparative chromatographic columns, and the intermediate component is produced. In step 2, similar to an SMB, there is no feed and the less-adsorbed species is collected in the raffinate while the more-retained species is collected in the extract [30]. 

The choice of a model to describe heat transfer in packed beds is one which has often been dictated by the requirement that the resulting model equations should be relatively easy to solve for the bed temperature profile. This consideration has led to the widespread use of the pseudo-homogeneous two-dimensional model, in which the tubular bed is modelled as though it consisted of one phase only. This phase is assumed to move in plug-flow, with superimposed axial and radial effective thermal conductivities, which are usually taken to be independent of the axial and radial spatial coordinates. In non-adiabatic beds, heat transfer from the wall is governed by an apparent wall heat transfer coefficient. ... 

Consider, then, a section of a chromatographic column (pseudo-homogeneous fixed bed) as shown in Figure 9.8. Here Fj and Fn represent volume fractions of the moving (fluid) phase and the stationary (adsorbent/adsorbate) phase, respectively, a is an appropriate mass-transfer coefficient between phases, and is a Henrys law constant. One can see that this is not too removed from several models we have considered before, such as that of Section 9.2. Here, though, our interest is in the separation of two or more fluid-phase components, not just the adsorption wave of a single species. Nonetheless, let us look at the balances referred to an individual component with concentration Q. We will write separate balances for phases 1... 

Fixed bed decoking involves time-dependent profiles of the oxygen concentration and the carbon load both within the particles (pore diffusion) and within the fixed bed (moving reaction zone). The reaction zone migrates through the reactor, which may lead to overheating of the catalyst, if the velocity of the zone is too fast. To model the coke burn-off process in the adiabatic fixed bed the so-called one-dimensional pseudo-homogeneous reactor model can be used. 

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