String reactor

Figure 5 Schematic diagrams of reactors used in FIA in order of increasing dispersion (a) single bed string reactor, (b) knitted tube, (c) coiled tube, (d) straight tube, and (e) external mixing chamber with stirring.

Bead-string reactors represent the limit of parallel-passage reactors They contain single-catalyst-particle subunits. Figure 10 gives a schematic representation (25). 

Bead-string reactors have the advantages of lateral-flow reactors but not the disadvantage of the low mass transfer rates in the units of the lateral-flow reactors. 

Figure 10 Schematic (a) and reactor configuration (b) of the bead-string reactor.

Calis HP, Takacs K, Gerritsen AW, Bleek CMvd. Bead-string reactor. In Cybulski A, Moulijn JA, eds. Structured Catalysts and Reactors. New York Marcel Dekker, 1998 355-392. 

Autothermal Methanol Reforming 2 [AMR 2] Micro Structured String Reactor for Autothermal Methanol Reforming... 

Figure 2.15 Schematic and photograph of the microstructured string reactor [39]...

Horny, C., Kiwi-Minsker, L, Renken, A., Micro structured string-reactor for autothermal production of hydrogen, Chem. Eng.J. 2004, 303, 3-9. 

The CNMMR, however, is not always advantageous over the pellet-string reactor. When the membrane tube is wetted only on the external surface and the rate of supply of volatile A from the tube core is very high, depletion of the reactant B occurs within the membrane matrix potentially leading to a lower reaction rate than that of a pellet-string reactor. 

In case methanol is used as an intermediate fuel (e.g. in mobile fuel cells), the cost of methanol production is of interest. Produced from fossil fuels, notably natural gas, at a price of 3 US GJ, reforming or series reactor schemes lead to a methanol production cost estimated around 5.5 US GJ (Lange, 1997). Advanced micro-structured string-reactors for this concept are under development (Homy et ah, 2004). 

H.P.A. Calis, Development of Dustproof Low Pressure Drop Reactors with Structured Catalyst Packings—The Bead String Reactor and the Zeolite-Covered Screen Reactor, Ph.D. dissertation. Delft University, Delft, The Netherlands. 1995. 

In addition to and as an alternative for the existing concepts of low-pressure-drop reactors with structured catalyst packings, discussed in the previous chapters, a new concept is proposed in this chapter the bead-string reactor (BSR). The BSR was invented [1] as an alternative for a parallel-passage reactor (PPR) with extremely thin catalyst beds, viz. beds of only one catalyst-particle-diameter width. 

A. Advantages of the Bead-String Reactor (BSR) and Potential Applications... 

Figure 1 Schematic of the bead-string reactor, (a) Principle of operation (b) artist s impression.

Knowing this, we might expect that a study of the existing literature would be sufficient to allow modeling of mass transfer in a bead-string reactor, because heat transfer relations usually can be translated directly into mass transfer relations, since the governing differential equations are identical. Unfortunately, this is not completely true, for two reasons. 

To assess the feasibility of the BSR as a competitor of the monolithic reactor, the parallel-passage reactor, and the lateral-flow reactor, it is necessary to do case studies in which the performance and price of these reactors are compared, for certain applications. To allow such case studies, two tools are needed (1) mathematical models of the reactors that predict the reactor performance, and (2) an optimization routine that, given a mathematical reactor model and a set of process specifications, finds the optimum reactor configuration. Furthermore, data are needed on costs, safety, availability, etc. In this section, five mathematical models of different complexity for the bead-string reactor (BSR) are presented that can be numerically solved on a personal computer within a few hours down to a few minutes. The implementation of the reactor models in an optimization routine, as well as detailed cost analyses of the reactor, are beyond the scope of this text. 

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