Special-Purpose Reactors

In this section we briefly discuss the use of mechanically agitated reactors in the electrochemical, photochemical, and chemical vapor deposition industries. While the use of mechanical agitation is not very common in the reactors used in these industries, it does provide special advantages in specific instances. 

Explorations of new electrochemical routes to traditional as well as specialty chemicals via electro-organic synthesis have given rise to a search for more efficient electrochemical reactors. The radial flow reactors or cells show promise compared to the conventional parallel plate configurations. A typical radial flow reactor is schematically shown in Fig. 39, which includes the 

Schematic of radial flow electrochemical cells, also showing the enclosed boundary for flow simulation. (Reprinted with permission from Chem. Eng. Sci. 43,2013, F. B. Thomas, P. A. Ramchandran, M. P. Dudukovic, and R. E. W. Jansson, Copyright 1988, Pergamon Press pic.) 

The effectiveness of RE and PC electrochemical reactors for methoxylation of furan was examined by Thomas et al. (1988). The performance of various types of reactors is compared in Table XXIX. As shown, both RE and PC with cathode spinning gave better performance than a capillary gap cell. For the pump cell, the results differ depending on whether the cathode is spinning or 

Thomas et al. (1988) also showed that for both CGC and RE, the velocity profiles become fully developed after a certain radial entry length. The fully developed velocity profile has a parabolic shape for the CGC and the shape of two wall jets with a nearly stagnant region in between for the RE. For the pump cell, no asymptotic velocity profile is reached. The fluid continues to accelerate in the radial direction near the spinning electrode, while significant reverse flow is obtained near the stationary electrode. 

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The high cost of constructing a modem nuclear power plant— three to four billion dollars, in the U.S.— reflects in part the wide range of safety features needed to protect against various possible mishaps, especially those which could release to the environment any of the plant s inventory of radioactive substances. (Small special-purpose reactors, such as those used to power nuclear submarines or aircraft carriers, have different costs and technical features from the large, land-based reactors used to supply electrical grids.) Some of those features are incorporated into the reactor core itself. Eor example, all of the fuel in a reactor is sealed in a protective coating... 

AChE-biotests are located in a special column-reactor connected with the peristaltic pump and the incubation is done in flowing conditions. For this purpose special flowing, termistatic column-reactor is used (described in Supplement 2). 

More exotic reactor types for special purposes have also been described [7, 12], Table 1 gives a generalized comparison of the various reactor models. 

In this section, we first evaluate the design of conventional nonaerated and aerated stirred slurry reactors. Since the design of mechanically agitated gas-liquid reactors has already been discussed in Section II, here the main emphasis is placed on the effects of solids on the design parameters. We subsequently illustrate some special-purpose slurry reactors used in the chemical and petrochemical industries. Novel slurry reactors used in biological or polymeric industries are discussed in Sections VI and VII, respectively. 

Although the fission products could be recovered as byproducts from the waste from spent nuclear reactor fuel, special-purpose neutron irradiation of highly enriched uranium (isotopically separated uranium-235) followed by chemical separation is the normal production method. The major products, molybdenum-99 and iodine-131 with fission yields of 6.1 and 6.7 percent, respectively, have important medical applications. Mo-99,... 

Plant cells or tissues may be fermented like micro-organisms in the submerged fermenter if grown on the surface of carrier beads or are kept in suspension. There is also experience in the operation of special membrane reactors for this purpose [13]. 

Use Special-purpose alloys, cementation of iron, neutron absorber in reactor controls, oxygen scavenger for copper and other metals, fibers and filaments in composites with metals or ceramics, semiconductors, boron-coated tungsten wires, rocket propellant... 

Important process units such as a reactor or a non-standard separation unit (e.g., a crystallizer) are often modeled by means of special-purpose packages. 

Boron Boron, metallic EINECS 231-151-2 HSDB 4482. Nonmetallic element. Used in special-purpose alloys cementation of iron neutron absorber in reactor controls oxygen scavenger for copper and other metals fibers and filaments in composites semiconductors rocket propellant mixtures, mp = 2200" insoluble in H2O. Atomergic Chemetals Noah Chem. 

In the past, there was no need for small-scale (< 1 MW) distributed hydrogen production from hydrocarbons where such reactors would likely be first employed. In any case, unsupported palladium membranes have required too much expensive metal to be economically feasible for all but special purposes. The potential availability of cost effective, high hydrogen permeance, palladium membranes supported on porous, stainless steel, tubular substrates combined with the advent of stable, high volumetric activity WGS catalysts is the driving force behind the system modeling... 

The high impedance is usually a resistance chosen to limit the earth current to about 20 mA. A current detector is used in conjunction with the resistance to raise an alarm if a line-to-earth fault occurs. A zig-zag transformer, or reactor, is sometimes used with three-wire supplies such as used in drilling rigs and emergency systems. It is specially designed and internally connected to create a very low zero sequence impedance to earth currents. Therefore, the current is limited only by the resistance of the neutral earthing resistor. Some special purpose earth current alarm systems are available that inject a small DC current into the three-phase system, which is used to identify the actual location of the fault. 

Local pressure drop in the subassemblies (for instance that due to spacing elements) can make significant contribution to the total pressure drop [6.7, 6.8]. It is unlikely, that spacing elements used in the fuel subassemblies of sodium cooled reactors (wire, etc.) could be applied for lead cooled reactors. Therefore, if the new spacers are designed, the available data cannot be applied. This would require special-purpose experiments not only for determining hydrodynamics, but to test structure for vibration and attrition. 

The seismic analysis of the core is performed with the two-dimensional special purpose computer codes CRUNCH-2D and MCOCO, which account for the non-linearities in the structural design. Both CRUNCH-2D and MCOCO are based on the use of lumped masses and inertia concepts. A core element, therefore, is created as a rigid body while the element flexibilities are input as discrete springs and dampers at the corners of the element. CRUNCH-2D models a horizontal layer of the core and the core barrel structures (Figure 3.7-7). The model is one element deep and can represent a section of the core at any elevation, MCOCO models a strip of columns in a vertical plane along a core diameter and includes column support posts and core barrel structures (Figure 3.7-8). The strip has a width equal to the width of a permanent reflector block. Both models extend out to the reactor vessel,... 

Tracers have also been used to mark some special-purpose or special-quality materials, like stainless-steel alloy tubes for the heat exchangers of nuclear reactors. 

Therefore, after drying, the catalyst powder has to be passivated by controlled oxygen exposure under temperature control. Vacuum chambers or special chemical reactors are required for this purpose. During the preparation step, the absorbed hydrogen is removed, and the catalyst surface is subsequendy oxidized and will be... 

The furnace process involves spray injection of a low end fraction of crude oil into a heated chamber. The temperature, shape of the iujectors of the oil, rate of injection, shape of the reactor, and other factors are controlled to produce carbon black fillers of different particle sizes and structures. The particle size and structure control and the reinforcing character of carbon black are the bases of their classification system (Table 8). There are approximately 30 common grades of carbon black used iu the rubber iudustiy. There are also numerous specialty grades produced for use in plastics, conductive applications, and proprietary grades produced for use in tires and other special-purpose products (14). 

Like every system operating under steady-state conditions, an FCC unit must stay in heat balance at all times. However, because catalyst circulation between the regenerator and the reactor serves the dual purposes of providing reaction activity and the heat requirement to the reactor, the heat balance in the FCC process has special purposes that other processes do not have. Thus, heat balance is the key to better understanding of how different variables interact with one another in the FCC unit. 

In 1953, studies were conducted by the U.S. Atomic Energy Commission (AEC) to show the technical and economic feasibility of constructing a dual-purpose reactor capable of producing SNM for weapons and research and steam for electricity. In 1957, Congress authorized the AEC (now a part of DOE) to build a special reactor on the Hanford Site. Construction of the New Production Reactor, now simply called N Reactor, began Nay 1, 1959. It took 4.5 years to complete initial criticality was achieved December 31, 1963. Table 4-1 provides an overview of significant dates for major activities occurring at 100-N. 

Nfointenance facilities for NSSS components are provided within the Reactor Building within the transfer corridor and, if necessary, within a specially constructed off-island building. New or replacement reactor components can be delivered to the transfer corridor for movement to the reactor. Transfer of activated and contaminated components from the reactor building or transfer corridor to any off-island facility and vice versa will be within a transit flask, and in conjunction with a special purpose transport system. 

The effluent stream from the reactor could be either sent to a wet-test meter, or diverted to the vent. Provisions were also made for sampling of the product stream in a gas chromatograph during the steady-state runs or the collection of an effluent sample in a special purpose collection chamber during the cyclic runs. Similarly there was a by-pass arrangement for the analysis of the reactants stream for the steady-state runs and a reactant collection chamber for the cyclic runs. 

In addition, thermal energy generated by the reactor may be used for seawater and brackish water desalination provided that special-purpose equipment is added to the mix of NHP components. 

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