Reactor Design and Flow Characterization

The fluidized bed reactors can roughly be divided into two main groups in accordance with the operating flow regimes employed. These two categories are named the dense phase and lean phase fluidized beds. 

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Reactor Design and Flow Characterization 873 10.3.1 Dense-Phase Fluidized Beds... 

Micro reactors permit high-throughput screening of process chemistries imder controlled conditions, unlike most conventional macroscopic systems [2], In addition, extraction of kinetic parameters from sensor data is possible, as heat and mass transfer can be fully characterized due to the laminar-flow condihons applied. More uniform thermal condihons can also be utilized. Further, reactor designs can be developed in this way that have specific research and development funchons. 

In general, each form of ideal flow can be characterized exactly mathematically, as can the consequences of its occurrence in a chemical reactor (some of these are explored in Chapter 2). This is in contrast to nonideal flow, a feature which presents one of the major difficulties in assessing the design and performance of actual reactors, particularly in scale-up from small experimental reactors. This assessment, however, may be helped by statistical approaches, such as provided by residence-time distributions. It... 

Flego [1] recommends the use of micro devices for automated measurement and microanalysis of high-throughput in situ characterization of catalyst properties. Murphy et al. [5] stress the importance of the development of new reactor designs. Micro reactors at Dow were described for rapid serial screening of polyolefin catalysts. De Bellefon ete al. used a similar approach in combination with a micro mixer [6], Bergh et al. [7] presented a micro fluidic 256-fold flow reactor manufactured from a silicon wafer for the ethane partial oxidation and propane ammoxidation. 

Instead of accepting the random and chaotic behavior of classical reactors, one can attempt to design and build reactors that are characterized by regular spatial structures. Such structures may be designed in full detail up to the local surroimdings of the catalyst. This opportunity offers control of the local enviromnents, allowing simplification of the fluid mechanics to well-understood behavior, such as laminar flow. The engineer can then easily direct the interaction of transport phenomena and reaction. 

Boyle [15] and Huff [16] first accounted for two-phase flow with relief system design for runaway chemical reactions. A computer simulation approach to vent sizing involves extensive thermokinetic and thermophysical characterization of the reaction system. Fisher [17] has provided an excellent review of emergency relief system design involving runaway reactions in reactors and vessels. Fauske [18] has developed a simplified chart to the two-phase calculation. He expressed the relief area as ... 

In a general sense, the characterization of the performance of the microtechnology-based equipment is not a process analytical problem and is the responsibility of the hardware developer since there are many variables that need to be characterized for proper design and operation of the device. These include flow distribution to the multiple channels, chemical component mixing and heat transfer rates, to name just a few. For example, Schouten has demonstrated the care needed to characterize and model gas-phase reactor systems that he and his colleagues design (e.g. [6]). 

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