Countercurrent moving-bed

A countercurrent moving-bed adsorption column is used to remove benzene from a gaseous emission. Activated carbon is employed as the adsorbent. The flowrate of the gas is 1.2 kg/s and it contains 0.027 wt/wt% of benzene. It is desired to recover 99% of this pollutant. The activated carbon entering the column has 2 X 10 wt/wt% of benzene. Over the operating range, the adsorption isotherm (Yaws et al., 1995) is linearized to... 

A simulated countercurrent moving bed reactor for oxidation of CO at low concentration over P1/A1203... 

Fig. 1 Concentration profiles of CO, Oj and Hj inside a countercurrent moving bed reactor.

In this study, a simulated countercurrent moving bed reactor (SCMBR) with four parts by switching the inlets and outlets of the parts cyclically is employed in order to avoid abrasion occurring from the movement of a solid catalyst. Based on the above concepts, we focused on the performance of a SCMBR for the oxidation of CO at low concentration in absence of H2 over Pt/AlaOs catalyst adsorbent. For the first stqj of the overall nractor draign, the performance of a SCMBR is experimentally investigated and compared with that of a PBR for the reaction. 

Performance of a simulated countercurrent moving bed reactor, SCMCR is experimentally investigated for oxidation of CO at low concentration in the absence of hydrogen over Pt/AljOs catelyst/adsorhent. The time-average conversion of CO obtained in the SCMBR was higher than the conversion of CO obtained from a conventional PBR for all over the tested range (period = 2-15 min). For the next step, the effects of operating variables on its performance are planed for both CO oxidation in the absence of H2 and Hz-rich gas system. 

Activated carbon adsorption may be accomplished by batch, column, or fluid-ized-bed operations. The usual contacting systems are fixed-bed or countercurrent moving beds, as shown in Figure 8.2. The fixed beds may employ downflow or upflow of water. The countercurrent moving beds employ upflow of the water and downflow of the carbon, since the carbon can be moved by the force of gravity. Both fixed beds and moving beds may use gravity or pressure flow. 

In a typical countercurrent moving-bed carbon column employing upflow of the water, two or more columns are usually provided and are operated in series. The influent contaminated groundwater enters the bottom of the first column by means of a manifold system that uniformly distributes the flow across the bottom. The groundwater flows upward through the column. The unit hydraulic flow rate is usually 2 to 10 gpm/ft2. The effluent is collected by a screen and manifold system at the top of the column and flows to the bottom manifold of the second column. The carbon flow is not continuous, but instead is pulsed. 

Another approach to continuous reaction chromatography is the countercurrent moving-bed chromatographic reactor (CMCR). In this type of reactor the stationary (solid) phase travels in the opposite direction to the liquid phase. In practice this is performed by introducing the stationary phase from the top of the reactor. The stationary phase flows downwards under the influence of gravity while the liquid phase is pumped upwards from the bottom. A schematic presentation of such a system is shown in Fig. 7. Depending on the adsorption characteristics of the different components, they can travel in the direction of the liquid or the solid phase resulting in their separation. 

Fig. 7. Schematic presentation of a true countercurrent moving bed chromatographic reactor. (Reprinted with permission from [151])...

Another study was performed on a catalytic hydrogenation of 1,3,5-trimethyl-benzene to 1,3,4-trimethylcyclohexane, which is a typical first-order reversible reaction [168]. By optimizing various operating conditions it was possible to achieve a product purity of 96% and a reactant conversion of 0.83 compared to a thermodynamic equilibrium conversion of only 0.4. The results were successfully described with a mathematical model derived by the same authors [169]. Comparison to a real countercurrent moving bed chromatographic reactor yielded very similar results for both types [170]. 

The MMP Sorbex process has many similarities but also some differences when compared to the detergent Molex process. As with all of Sorbex processes, the MMP Sorbex process operates in the Uquid phase, employing suitable conditions (pressure, temperature) to overcome any diffusion constraints to achieve target performance. Table 8.4 highlights and contrasts the different characteristics of the detergent Molex and MMP Sorbex processes. The process was successfully demonstrated in a continuous countercurrent moving bed separation pilot plant using commercial n-paraffin-depleted kerosene (Molex raffinate) feedstock. A typical gas... 

The spreader stoker operated as a continuous system, with ash removal doors. The conversion concept corresponds to updraft-downfeed (countercurrent), moving bed. Secondary air (overfire air) entered at 42 inches above the grate. The overfire air ports were directed slightly downward (12°). 

The fuel bed (300 mm deep) was ignited either on the top (overfired), simulating cocurrent moving bed combustion, or in the bottom (underfired), simulating countercurrent moving bed combustion. The igniting source was sawdust soaked in... 

Figure 29 shows the three different categories of updraft moving beds, namely cocurrent moving bed (Figure 29A), countercurrent moving bed (Figure 29B) and crosscurrent moving bed (Figure 29C). This is analogous for updraft mixed beds. [12,38]...

Figure 12-21 Countercurrent moving bed and rotating annulus reactors. Chromatographic separation of spedes in a continuous chemical reactor can be accomplished with a moving bed tubular reactor or a rotating aimulus reactor that separates A, B, and C by carrying a product species counter to the flow direction because it is...

An analysis of the countercurrent moving bed reactor (with S. Viswanathan). SIAM-AMS Proc. 8, 99-124 (1974). 

The simulated countercurrent moving bed chromatographic reactor A novel reactor-separator (with A.K. Ray and R.W. Carr). Chem. Eng. Sci. 49, 69-480 (1994). 

M. C. Bjorklund and R. W. Carr, Enhanced methanol yields from the direct partial oxidation of methane in a simulated countercurrent moving bed chromatographic reactor. Indust. Engng. Chem. 

Z. Y. Zhang, K. Hidajat, A. K. Ray, Application of simulated countercurrent moving-bed chromatographic reactor for MTBE... 

Previous studies of direct reduction on iron ore pellets have been reviewed by Themelis(1), Bogdandy(2) and Huebler(3). Work on reduction by mixtures has been reported by Szekely(4) and Hughes et al(5). Modelling studies on countercurrent moving bed systems have been reported by Spitzer(6) for isothermal reduction in hydrogen, by Miller(7) for non-isothermal reduction in carbon monoxide and more recently by Tsay et al(8) and Kam and Hughes(9) for C0/H2 mixtures. However, since iron is known to be a catalyst for the water gas shift reaction, this reaction will influence the gas composition and therefore the extent of reduction. None of the previous analyses have considered this aspect and the objective of the present paper is to account for the overall reduction by inclusion of this reaction. 

Figure 4. Units combining reaction and separation (a) reactor with countercurrent moving bed, (b) simulated moving-bed reactor with four catalyst layers (bold lines show gas streams during a quarter of cycle), (c) pressure-swing adsorption reactor separator (on the left i given time dependency of pressure during a cycle)...

A modification of this technique, the simulated countercurrent moving-bed chromatographic reactor [35], comprises several catalyst beds (Fig. 4(b)). The locations of inlet and outlet ports between the catalyst beds are changed sequentially, thus the countercurrent movement of solid and gaseous phases is simulated in a discrete manner. Such an operation avoids the technical difficulties (catalyst attrition, nonuniformity of solid flow, etc.) associated with solid-phase movement. Part of the reactor sections can be purged by the carrier gas. To increase the separation effect, a bed of adsorbent can be added in each section. 

Problems in the Design of the Countercurrent Moving-Bed Catalytic Reactor... 

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