Temperature forcing, reactors with

Example 5.11 The results of Table 5.1 suggest that scaling a tubular reactor with constant heat transfer per unit volume is possible, even with the further restriction that the temperature driving force be the same in the large and small units. Find the various scaling factors for this form of scaleup for turbulent liquids and apply them to the pilot reactor in Example 5.10. 

In the construction of the wet oxidation unit, several areas of safety were considered. Of utmost importance was that of personal safety. Since this type of operation demands the use of high pressures and temperatures, operator contact with the high pressure vessels had to be limited. To accommodate this criterion, a barrier was constructed to shield the operator from any unforeseen releases from the reactor. This barrier was constructed from 1/4 inch steel and is desig ied in a manner that will fully contain any releases. This barrier is also equipped with two explosion vents to direct the force of any explosions away from the main walls and into a safe area. To further maximize personnel safety, all operator assisted controls are mounted on the outside of the unit. 

With a homogeneous reaction and mechanical equilibrium (VP = 0), consider a reactor consisting of a large number of n subsystems with equal volumes and the same reaction taking place in all subsystems. We assume that the subsystems have a uniform composition and temperature. The reaction flow in subsystem k is Jrk and the driving force is AGk/T. The total system is a nonhomogeneous reactor with variations in temperature and composition... 

Heat is lost from the surface by conduction through the susceptor and mount, by forced convection of gas over the substrate, and by radiation to the reactor walls, provided the temperature of the substrate is sufficiently high. Endothermic chemical reactions also result in heat loss from the film. The substrate temperature is monitored with a thermocouple or an optical pyrometer and controlled using a traditional proportional-integral-derivative (PID) controller and power source. 

Figure 6.2b displays the temperature profile for a 100-zone case that is a tour de force for the optimization routine. The results took less than 20 min of computing time, but the difference in bout between the 10- and 100-zone cases is negligible. These multizone designs give bout = 3.61 compared to 3.59 for the best adiabatic reactor with t = 0.8 h, but multizone reactors would be very expensive to build. Problems 6.11-6.13 suggest practical approaches to achieving a desirable temperature profile. 

Values at the wall, i = /, are determined from the wall boundary condition. Eor concentrations in any reactor with solid walls and for temperature in an adiabatic reactor, there is zero slope at the wall. It would be sufficient to set d/ = d/ i, but this is only a first-order approximation. Fitting a cubic to the points d/, d/ i, d/ 2, and d/ 3 and then forcing the slope to be zero at / = / give a smoother estimate that sometimes improves convergence ... 

There are few investigations of the temperature effect on the dispersion and chemical kinetics in the FIA system. Since an increase in temperature increases molecular diffusion—and thus radial mass transfer—the physical dispersion will decrease with increasing temperature. When the contribution of external forces on the radial mass transfer is minimized, as in straight very narrow tubes, the temperature effect should be greatest, and it should decrease in reactors with progressively distorted geometry. Betteridge et al. have simulated the temperature effect by a random walk... 

Temperature Forcing of Reactors with Catalyst Decay... 

Options are forced draft or induced draft. Use forced draft with louvers when temperature control is critical. Forced draft has less fan power easy access for maintenance easy to use hot air recirculation but has greater susceptibility to air maldistribution and to inadvertent hot air recirculation low potential for natural circulation and the tubes are exposed to the elements. Induced draft high fan power needed, not easy access for maintenance limitation on exit air temperature less chance of air maldistribution or unwanted hot air recirculation better protection from the elements process stream temperatures < 175 °C. Cubic/monoUthic corrosive liquids, acids, bases or used as catalyst/heat exchanger for reactors. Usually made of graphite or carbon that has high thermal conductivity. Area 1-20 m. Ceramic monoliths are used as solid catalyst for highly exothermic gas-catalyst mass transfer[Pg.69]

Under accident conditions such as a loss-of-forced-cooling accident, natural circulation flow of molten salt up the hot fuel channels in the core and down by the edge of the core rapidly results in a nearly isothermal core with about a 50 C difference between the top and bottom plenums. For the reactor with a nominal coolant exit temperature of 1000 C, the calculated peak fuel temperature in such an accident is 1160 C, which will occur at 30 hours with a peak vessel temperature of -750 C at 45 hours. The average core temperature rises to approximately the same temperature as the hottest fuel during normal operations. 

It is not a primary function of the RCCS to ensure that the fuel does not exceed its maximum allowable temperature, but together with the design of the heat transfer path from the fuel to the outer surface of the reactor pressure vessel (RPV), the RCCS is providing a heat sink for continuous removal of heat transferred from the RPV during normal operation, and in a postulated loss of forced cooling event [XIV-4],... 

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