Reactor Control Methods

In practice, one can impose a condition such as (5.159) upon the multiplying system by external means and thereby exercise control over the neutron population. This is the basis of all reactor control methods (see Sec. 1.3b). 

We are also purchasing a new pilot reactor which we intend to automate using the same tools we are using in the lab this reactor will facilitate scale-up, and will allow us to demonstrate the control methods we evolve on a more nearly production-scale system. 

The micro reactor properties concern process control in the time domain and process refinement in the space domain [65]. As a result, uniform electrical fields are generated and efficiency is thought to be high. Furthermore, electrical potential and currents can be directly measured without needing transducer elements. The reactor fabrication methods for electrical connectors employ the same methods as used for microelectronics which have proven to satisfy mass-fabrication demands. 

Cuthrell, J. E., and Biegler, L. T., Simultaneous optimization and solution methods for batch reactor control profiles, Comp, and Chem. Eng. 13(1/2), 49-62 (1989). 

In conclusion, a complete analysis of a complex mixture can require very long times (from a few minutes up to many hours) thus, such a measuring apparatus is not suited for online measurements to be used in reactor control. On the contrary, in the laboratory, chromatography is very often the preferred method of analysis of complex mixtures, since these more accurate data can be used to identify the reaction mechanism and the relevant kinetic parameters. 

A variety of methods and configurations can be used for heat transfer. These are described in Section 1.5. Since heat transfer is one of the key issues in reactor control, the CSTR is usually more easily controlled than a tubular reactor. It is physically difficult to adjust the heat removal down the length of a tubular reactor. 

The second item is the concentration of the reactant in the feed. We considered the case in which the feed is pure reactant A and found a heat removal rate for a given conversion and reactor temperature. However, suppose that the feed were a mixture of reactant A and product B. Now for the same feedrate and conversion, there is less of A to react so the heat transfer requirements are lower. This indicates one method of improving reactor controllability, which is to reduce reactant feed composition by diluting the feed with some nonreactive component. Of course, the downside of this approach is that there must be more material to recycle, which increases capital and energy costs. 

The catalyst activity is assumed to be constant. Because of excellent temperature control achievable in tube-wall reactors, thermal sintering of the catalyst is less likely than in a fixed-bed reactor. Some methods of avoiding catalyst deactivation or reducing the deactivation rate for methanation are described by Mills and Steffgen (7). 

The measurement of compounds in bioprocesses, including fermentations, using conventional laboratory techniques such as HPLC, TLC or calorimetric assays is often tedious, invasive, requires sample handling and difficult to do in real time. For a bioprocess where it is important to gain information about the reactor status for feedback control, methods enabling rapid and reliable measurement of components are desirable. 

A typical setup for kinetic measurements is given in Fig. 8. Basically a feed, a reactor and an analysis section are required. Nowadays mass flow controllers for both liquid and gas result in stable molar flowrates, ideally for kinetic studies. Pressure controllers maintain a constant feed pressure for the flow controllers, while backpressure controllers maintain the pressure in the reactors. Various methods of product analysis are available and depend highly on the system under investigation. 

Step 3 is next because the reactor is typically the heart of an industrial process and the methods for heat removal are intrinsically part of the reactor design. So it is usually not optional what degrees of freedom can be used for exothermic reactor control. When the heat generated in an exothermic reactor is used within the process via energy integration, we must ensure that the energy is dissipated and not recycled. Hence we examine process-to-process heat exchangers and... 

Implementation of the method of Spent Nuclear Fuel (SNF) unloading from unwatered NS reactors represents a crucial solution of the nuclear safety challenge because removal of moderator eliminates the risk for reactor core to attain critical condition under any design-basis/beyond-the design-basis operations with reactor control systems. 

This paper presents an on-line model based level control of a batch reactor with reaction rate uncertainties. The analyzed chemical batch process is catalyzed by a catalyst which decomposes in the reactor therefore it is fed several times during the batch. The chemical reaction produces a vapour phase by-product which causes level change in the system. The on-line control method is based on the shrinking horizon optimal control methodology based on the detailed model of the process. The results demonstrate that the on-line optimization based control strategy provides good control performance despite the disturbances. 

In contrast to the requirements for homopolymerisation processes, the parameters needed to fully describe copolymerisation processes are more numerous. Molecular features such as the copolymer composition, composition distribution and chain sequence structure and their variation with conversion are compounded with those of copolymer MW and MWD. To understand copolymerisation processes, it is desirable to decouple as many of these molecular parameters as possible and study the influence of polymerisation reactor conditions on each. As yet there have been relatively few reports on the detailed behaviour of copolymerisation reactors (6-9 ). This work forms part of a wider range of investigations which are being carried out in our laboratories of control methods for the production of speciality polymers. 

Early emission control methods were based on the use of a thermal reactor for hydrocarbon and carbon monoxide oxidation, combined with exhaust gas recirculation (EGR) for reduction of nitrogen oxide emissions (Fig. 3.2a). Hydrocarbons and carbon monoxide in the hot exhaust fed to the reactor, once heated, were rapidly oxidized to carbon dioxide and water by the additional pumped air which was fed to the reactor (e.g., Eqs. 3.3 and 3.4). 

A way to further minimize corrosion is by adding base to the feed or reactor, so dial acids formed during the oxidation reaction are immediately neutralized. However, one must then deal with the resulting salts. Whether formed during reaction or already contained in the feed, salts will quickly precipitate in supercritical water. As these salts tend to adhere to and accumulate on the reactor walls and other surfaces within the reactor, they can inhibit and ultimately block process flow unless they are removed or their accumulation is controlled. Nonsalt solids (e.g., metal oxides, grit), by contrast, have little tendency to stick to process surfaces but can be a problem with respect to erosion and system pressure control. Methods that have been developed to manage and/or minimize the impact of corrosion, salt precipitation/accumulation, and solids handling are discussed in Sections 6.5 and 6.6. 

There is another chemical method for evaluating the temperature control ability of a reactor the method uses thermal decomposition of radical initiators. Let us briefly touch on this method (Figure 6.19). 

Problems in Choice of a Reactor. When a process engineer is faced with the problem of designing a commercial or semicommercial unit, he must first choose the reactor to be used. The type of reactor (tube, tower, or tank), the type of operation (batch, continuous, recycle, or once-through), and the means of temperature control (isothennal or adiabatic) may depend on the type of reaction involved. In order to choose the best reactor and method of operation, the specific type of reacting system must be considered. 

Comparison of Temperature-control Characteristics of Various Types of Reactors. Several methods of heat removal are used in the various reactors. Heat removal for the most part may be considered to take place either directly, as in the oil- or gas-cooled systems where the catalyst surface is in contact with the cooling medium, or indirectly, as in the fixed or fluid beds where heat must be transferred through the bed to a cooling surface. Admittedly this is an oversimplification, especially in the case of the fixed and fluid beds where some direct heat transfer occurs. 

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