Reactor Start-Up

The slurry reactor starts up relatively easily by feeding catalyst to the loop containing isobutane under the preset polymerization conditions. Ethylene 

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Steady state analysis explicitly evaluates model parameters, Dynamic simulations predict reactor start-up transients. 

N umerical simulations of reactor start-up were programmed, predicting monomer and initiator concentrations, total polymer concentration, weight and number average molecular weights, viscosity and population density distribution dynamics. The following two relationships obtained from steady state observations were utilized in the simulation. 

Reactor start-up simulations require initial values of A., T(n,t) and T. be zero. Monomer... 

Dynamic simulations for an isothermal, continuous, well-mixed tank reactor start-up were compared to experimental moments of the polymer distribution, reactant concentrations, population density distributions and media viscosity. The model devloped from steady-state data correlates with experimental, transient observations. Initially the reactor was void of initiator and polymer. 

It was also established that the distribution of the liquid phase in the reactor depends on the reactor start-up procedure. When the flow rate of liquid AMS is reduced from 1.47 x 10 1 g s 1 (Figure 5.4.6, images 43 and 45) down to 2.96 x 10-2 g s 1 (images 85 and 87), the distribution of the liquid phase hardly changes and the catalyst bed contains a substantial amount of liquid. At the same time, if... 

For a single continuous reactor, the model predicted the expected oscillatory behaviour. The oscillations disappeared when a seeded feed stream was used. Figure 5c shows a single CSTR behaviour when different start-up conditions are applied. The solid line corresponds to the reactor starting up full of water. The expected overshoot, when the reactor starts full of the emulsion recipe, is correctly predicted by the model and furthermore the model numerical predictions (conversion — 25%, diameter - 1500 A) are in a reasonable range. 

The reactor start-up was performed by feeding a water-free mixture of methane and air with an O2/CH4 molar ratio of 1.36 and by inducing for few seconds the voltaic arc between the spark plugs. When the mixture is ignited, the temperature on the SiC foam suddenly (1 min) reaches around 1000 °C. Furthermore, due to the heat transfer, the temperature in the catalytic zone reaches in about 2 min the light-off value with full reactants conversion. The whole start-up phase is no longer than 3 min. 

Figure 26 shows the predicted axial gas temperature profiles during reactor start-up for standard type I conditions with varying numbers of axial collocation points. Eight or more axial collocation points provide similar results, and even simulations with six collocation points show minimal inaccuracy. However, reducing the number of collocation points below this leads to major discrepancies in the axial profiles. 

To investigate the behaviour of the present reactor, a series of steady state and dynamic experiments were performed, consisting of reactor start-up, step changes in feed composition and ramp changes in feed and jacket temperature. Heat transfer experiments without reaction were also performed. Some of the results are compared with model simulations, using, whenever possible, a priori values of model parameters. 

Through the use of the auto transformers, one was able to override the system control and thus line out the temperature profile. Figure 3 depicts a typical reactor start up for a fresh bed. 

Figure 3. Thermal unsteady response of the apparatus during reactor start-up 1, sand in preheater 2, pebble distributer 3, catalyst...

Additionally, the packing media need to be able to withstand thermal shock or fatigue due to, for example, reactor start-up and shut-down cycles, and, in those cases involving ceramic membranes, absorb mechanical shock from the operation of the unit. Due to their relatively brittle nature, for example, commercial ceramic membranes currently often use some flexible materials, such as polymers, for the connectors to adsorb mechanical vibration. 

Quality variations in the polymer produced in bstch reactors are often caused by slight variations in the reactor start up procedure. Furthermore, the polymerization rate may change considerably during the batch and this may give tempetature variations that are difficult to reproduce causing batch-to-batch variations in quality. These problems would be minimized with CSTRs if the continuous reactor system could be operated for at least several weeks before wall fouling and coagulum buUd up become critical and require reactor shutdown for cleanup. If an effective start-up procedure for a continuous reactor train is not available, the costs associated with offspec material could make continuous operation uneconomical. In addition, with a continuous reactor system one loses the flexibility of batch reactors when a multiproduct operation, with its short productions runs, is involved. 

We will then discuss reactor start-up, falling off the upper-steady state, the control of chemical reactors, and multiple reactions with heat effects. 

The validated model was applied to simulation of typical transients occurring during the operation of industrial SCR monolith reactors. Simulation of reactor start-up and shutdown showed in all cases that the change in NO outlet concentration is considerably... 

Am is a source of alpha particles in neutron sources for laboratory experiments and for reactor start-up. It is alloyed with beryllium to form AmBeia, vriiich produces high-energy neutrons by (a, ri) reactions. 

Figure 5. Equihbrium modeling of carbon formation for various fuels and conditions. The dashed conditions ate potential start-up scenarios, depending upon whether water is available during reactor start-up.

Stream. The heat released due to reaction in the inner region is used to heat the feed in the outer region. When the reactor is operating at steady state, no external heat is required to preheat the feed. Of course, during the reactor start up, external heat must be supplied to ignite the reactor. 

The two frequency functions shown In the bottom two frames of Figure 7 correspond to different steady-state populations growing at approximately the same overall population growth rates as those shown In the two middle frames. These different steady states were achieved by different start-up procedures of the reactor and seem to be connected with some unusual cell clumping phenomenon when reactor start-up Initiates with a significant glucose limitation of growth. Additional Information on this multiple steady-state phenomenon and on Its manifestation In other types of measurements Is available elsewhere (9). 

The two first events are associated with the reactor start-up tests. However, the two last ones, although they initiated an emergency shut-down thank to the "fail-safe" design of the reactor protection system, present the problem of its reliability. 

The objective of this stage is to obtain the SUJB permission for the reactor start-up after refueling as per the provisions of 9(l)e) of the Atomic Act, which at the same time will include the SUJB consent to the operation of the refurbished I C systems important to safety implemented during the current implementation phase. Hence, this phase will also be repeated as many times as is the number of outages necessary for the completion of the refurbishment at the subject plant unit. The safety case will again be a kind of an update of the preceding phase 3B safety case, and will in addition include ... 

The excess reactivity in a zero power critical condition was measured at the reactor start-up of each operational cycle. Measured data were compared with the MAGI calculated values that included the bias factor (C-E) correction obtained for the previous cycle. The comparison of calculated and measured values is shown in Table 3. 

The isothermal temperature coefficients were measured by taking the difference of reactivity at approximately 250 and 370°C during reactor start-up. The measured isothermal temperature coefficients were constant through the MK-II operation because they were determined mainly by radial expansion of the core support plate, which is independent of bumup. However, when the core region was gradually extended from the 32 cycle, the isothermal temperature coefficients were decreased as predicted with the mechanism. Table 4 shows these values. 

The power coefficients were measured at the reactor start-up and shutdown in each operational cycle. Figure 5 shows that the measured power coefficients decreased with increasing core bumup. 

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