Reactor kinetic devices

Level 3 includes the first elements of the flowsheet structure. The central issue is the cost of recycles. However, only some elements can be expressed quantitatively. The easiest is the cost for recycling fluids, as gases via compressors. Because the recycle flow rate varies inverse proportionally with the conversion, the cost of recycling fluids introduces the first element setting a lower bound for conversion. The next element is the cost of the reactor, including devices for feed conditioning. Because kinetic information is hardly available in an evaluation project, the reactor cost can be estimated only loosely. The cost of separations that deliver the recycle streams is yet not known. Hence, the formula for computing the Economic Potential at the Level 3 is ... 

We consider the TAP reactor as a basic kinetic device for systematic studies of reaction-diffusion systems. In this chapter, we are going to (i) present and analyze models of different TAP configurations with a focus on their possibilities with respect to characterizing active materials and unraveling complex mechanisms, and (ii) demonstrate relationships between TAP models and other basic reactor models, that is, models for the ideal continuous stirred-tank reactor (CSTR), batch reactor (BR) and plug-flow reactor (PER). In some situations, the TZTR can be considered a simple building block for constracting the various models. 

For each class of PIE it may be sufficient to analyse only a limited number of bounding initiating events that can then represent a bounding response for a group of events. The basis for these selected bounding events should be described in this section. Those plant parameters important to the outcome of the safety analysis should be identified. These would typically include reactor power and its distribution core temperature cladding oxidation and/or deformation pressures in the primary and secondary system containment parameters temperatures and flows reactivity coefficients reactor kinetics parameters and the worth of reactivity devices. 

It has also been recognized that micro-structured components, because of their low mass and thermal inertia, are able to offer short response times for unsteady state periodic operations. Micro-reactors have been used successfully for fluorination, oxidations and both heterogeneous [63-65] and homogeneous hydrogenations [66]. A review on gas-liquid micro-structured reactors has been published [67]. The very small material inventory when using micro devices offers another advantage, notably as a laboratory tool for screening applications, kinetics determination and process data acquisition, where the main concern is... 

Markov chains theory provides a powerful tool for modeling several important processes in electrochemistry and electrochemical engineering, including electrode kinetics, anodic deposit formation and deposit dissolution processes, electrolyzer and electrochemical reactors performance and even reliability of warning devices and repair of failed cells. The way this can be done using the elegant Markov chains theory is described in lucid manner by Professor Thomas Fahidy in a concise chapter which gives to the reader only the absolutely necessary mathematics and is rich in practical examples. 

Various devices can be used to determine the kinetics and rates of chemical weathering. In addition to the batch pH-stats, flow through columns, fluidized bed reactors and recirculating columns have been used (Schnoor, 1990). Fig. 5.15a illustrates the fluidized bed reactor pioneered by Chou and Wollast (1984) and further developed by Mast and Drever (1987). The principle is to achieve a steady state solute concentration in the reactor (unlike the batch pH-stat, where solute concentrations gradually build up). Recycle is necessary to achieve the flow rate to suspend the bed and to allow solute concentrations to build to a steady state. With the fluidized bed apparatus, Chou and Wollast (1984) could control the AI(III) concentration (which can inhibit the dissolution rate) to a low level at steady state by withdrawing sample at a high rate. 

Continuous operation In flow-type reactors, e.g., loop reactors, the space velocity of the reaction is determined through the installed static mixing device that is used to generate the dispersion, together with the velocity of the circiflating medium (catalyst- and substrate/product phase). Knowledge of these parameters allows one to set up a kinetic model for the investigated reaction. 

The experimental batch reactor is usually operated isothermally and at constant volume because it is easy to interpret the results of such runs. This reactor is a relatively simple device adaptable to small-scale laboratory set-ups, and it needs but little auxiliary equipment or instrumentation. Thus, it is used whenever possible for obtaining homogeneous kinetic data. This chapter deals with the batch reactor. 

The experimental strategy in studying catalytic kinetics usually involves measuring the extent of conversion of gas passing in steady flow through a batch of solids. Any flow pattern can be used, as long as the pattern selected is known if it is not known then the kinetics cannot be found. A batch reactor can also be used. In turn we discuss the following experimental devices ... 

Because of the ease in interpreting its results the mixed flow reactor is probably the most attractive device for studying the kinetics of solid catalyzed reactions. 

Real kinetics data To date, almost all the kinetics data on reaction systems in liquid phase or multiphase with liquid as the continuous phase have been measured in traditional stirred tank reactors. From the results reported in this chapter, it is likely that significant deviations exist in the existing kinetics data. On the other hand, the LIS device cannot yet be considered as absolutely ideal for kinetics investigation, not least because its micromixing time, tM, is not zero. What then is the ideal equipment and conditions for obtaining real kinetics data ... 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

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