Principal reactor types

The three principal reactor types employed in coal gasifier design are the moving packed bed, the entrained flow, and the fluidized bed reactor. In the discussion of gasification principles the moving packed bed (Fig. 3) was used to illustrate steam-oxygen or steam-air gasification of coal. 

There are two principal reactor types that have been used for reactions in SCF, as seen in Figure 3.8. Batch reactors can be readily equipped with a suitable window to assess homogeneity of the reaction mixture and are widely used in academic research. 

This chapter gives a brief account of the nuclear fission reaction and the most important fissile fuels. It continues with a short description of a typical nuclear power plant and outlines the characteristics of the principal reactor types proposed for nuclear power generation. It sketches the principal fuel cycles for nuclear power plants and points out the chemical engineering processes needed to make these fuel cycles feasible and economical. The chapter concludes with an outline of another process that may some day become of practical importance for the production of power the controlled fusion of light elements. The fusion process makes use of rare isotopes of hydrogen and lithium, which may be produced by isotop>e separation methods analogous to those used for materials for fission reactors. As isotope separation processes are of such importance in nuclear chemical engineering, they are discussed briefly in this chapter and in some detail in the last three chapters of this book. 

Figure 1.4 shows typical energy spectnims for the neutron population in the three principal reactor types. The ordinate in these curves gives the relative density of neutrons as a function of their kinetic energy. The intent here is to present some illustrative sketches which will give some idea of the nature of the distribution function. Other than indicating the general shape of these curves, the only feature of interest is the relative sharpness of the spectrum in the thermal reactors. 

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Retrofitting features of the more efficient reactor types have been the principal thmst of older methanol plant modernization (17). Conversion of quench converters to radial flow improves mixing and distribution, while reducing pressure drop. Installing an additional converter on the synthesis loop purge or before the final stage of the synthesis gas compressor has been proposed as a debotdenecking measure. 

For scale-up operations, the selection of the reactor is considered to be the key element in designing SCWO systems. Environmental regulations set the requirement for the destruction efficiency, which in turn sets requirements on the temperature and residence time in the reactor (as an example, the required DRE is 99.99% for principal hazardous components and 99.9999% for polychlorinated biphenyls, PCBs). The reactor parameters for the scale-up designs can be extrapolated from the available bench-scale data. A detailed discussion on available reactor types is given below. 

There are many different types of reactors. In the United States, the majority of the reactors are pressurized water reactors with graphite moderators. The Canadians built the CANDU reactor using heavy water as both moderator and coolant. Naval ship reactors are graphite moderated liquid metal cooled reactors. The detailed differences between the reactor types will not be examined, but the operating principal common to all will be discussed. 

The four principal types of reactors used for bench-scale kinetic studies are batch, continuous stirred-tank (CSTR), tubular, and differential reactors. Which of these to choose is essentially a matter of the reaction conditions, available equipment, and the chemist s or engineer s predilections. The discussion here will focus on facets that pertain specifically to quantitative kinetic studies. A table summarizing the advantages and disadvantages of the different reactor types can be found on page 47. 

We dealt with various polymerization processes in the previous sections. We now consider polymerization reactors. Our treatment of this subject is essentially qualitative the principal focus is to highlight salient features of each reactor type. 

In this section, we have focused our attention on four aspects that are the most important from the industrial perspective— the synthesis and typical industrial recipes adopted principal analytical methods for process control and product characterization main reactor types used, their characteristics, and involved technologies and aspects connected to the safety and hazards in alkyleneoxide processing. 

The principal difference between the three reactor types may be discussed with reference to plots such as Fig. 4. 

II-l. The following diagrams of the RCSASs present the principal components and main functional features of several reactor types in a simplified form. 

Although it appears that methyl ethyl ketone [78-93-3] caimot be the principal product in butane LPO, it has been reported that the ratio of methyl ethyl ketone to acetic acid [64-19-7] can be as high as 3 1 in a plug-flow-type reactor (214). However, this requires a very unusual reactor (length dia = 16, 640 1). The reaction is very unstable and wall reactions may influence mechanisms. 

Chlorination of Hydrocarbons or Chlorinated Hydrocarbons. Chlorination at pyrolytic temperatures is often referred to as chlorinolysis because it involves a simultaneous breakdown of the organics and chlorination of the molecular fragments. A number of processes have been described for the production of carbon tetrachloride by the chlorinolysis of various hydrocarbon or chlorinated hydrocarbon waste streams (22—24), but most hterature reports the use of methane as the primary feed. The quantity of carbon tetrachloride produced depends somewhat on the nature of the hydrocarbon starting material but more on the conditions of chlorination. The principal by-product is perchloroethylene with small amounts of hexachloroethane, hexachlorobutadiene, and hexachloroben2ene. In the Hbls process, a 5 1 mixture by volume of chlorine and methane reacts at 650°C the temperature is maintained by control of the gas flow rate. A heat exchanger cools the exit gas to 450°C, and more methane is added to the gas stream in a second reactor. The use of a fluidi2ed-bed-type reactor is known (25,26). Carbon can be chlorinated to carbon tetrachloride in a fluidi2ed bed (27). 

Pyrometallurgy, the dominant process in chemical metallurgy, uses reactor of different types and designs. In terms of the physical states of the reactants, one generally finds that the different reactions carried out in pyrometallurgy include principally, gas/liquid, liquid/... 

The point is that the same population dynamics are applicable to remediation systems. The principal difference is that in a soil/water system, one has essentially the growth rate of the bacteria as a limiting condition. This is also akin to another type of system known as the Sequencing Batch Reactor or SBR. 

The IWA (International Water Association), formerly known as the IWQA, has had several task forces working on model development for various types of processes. I believe that these reactor models have a good potential application for remedial treatment. The subject of the models is extremely complex and too involved for this discussion, as it is a Master s Level course in Environmental Engineering. However, let me indicate that there are several types of models which may have some application to the bioremediation field. The principal models are... 

In addition to these three principal types of reactor, there is also the semi-batch reactor in which one reactant is added gradually to the others. This is a convenient manner of operation for some highly exothermic reactions since the temperature can be controlled by adjusting the rate of addition. 

A silica-supported Sn—V—P—O catalyst (Sn/V/P = 1/9/3) was investigated by Onsan and Trimm [244]. Working with a flow reactor at about 520°C, a maximum selectivity of 75% to acrylonitrile was reached at a contact time of ca. 230 g sec l-1 and an oxygen/propene/ammonia ratio of 2/1/1.75. The authors assume that the six principal products (acrylonitrile, acetonitrile, HCN, CO, C02, N2) are formed by six parallel reactions and in the first instance apply power rate equations. A more detailed analysis reveals that a Langmuir—Hinshelwood type rate equation, surface reaction being rate-determining, properly describes the production of acrolein plus acrylonitrile from propene, viz. 

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