Fractional conversion profiles, simulate

To quantify the effect of the incomplete mixing on reaction rates in the front of the reactor channel, this same simulation was repeated assuming second order kinetics (first order in each of the two components) and Cjj = C2j = 100 mol m. A rate constant of 1.0 X 10 m moh s was used to give an intermediate level of conversion (near 25%). This case can be compared with a simulation in which the inlet boimdary conditions were changed to assume complete mixing (50 mol m of each component across the entire inlet cross section). The axial fractional conversion profiles for these two cases (unmixed and premixed feeds) are shown in Fig. 13.4, where the unmixed feed curve is the average of the calculated values for the two components. The computed conversions for the two components were... 

Equation 6-74 is a first order differential equation substituting Equations 6-70 and 6-78 for the temperature, it is possible to simulate the temperature and time for various conversions at AXa = 0.05. Table 6-4 gives the computer results of the program BATCH63, and Figure 6-7 shows profiles of both fractional conversion and temperature against time. The results show that for the endothermic reaction of (+AHR/a) = 15.0 kcal/gmol, the reactor temperature decreases as conversion increases with time. 

At the conditions reported in this paper where the total pressure is closer to 1000 psig and the feed gas to the FDP reactor is an approximately equimolar mixture of hydrogen and methane, the total carbon conversions are closer to the fraction of carbon that instantaneously reacts and kinetic interpretation is even more difficult. Therefore the kinetic analysis is not yet complete. However for the purposes of FDP reactor simulation, a mathematical model was used that assumed all the carbon reacts at a rate dictated by Equation 1 rather than assuming a portion of this carbon reacts instantaneously. This assumption is felt to be conservative because it does not allow for the fraction of carbon that may react at a considerably faster rate than the final amount of carbon conversion which was used to evaluate the rate constant k. The temperature dependency of k used for our initial reactor simulation studies (11) has been reported (I). While the more detailed kinetic analysis may result in a modified rate equation, the results of our simulation study (11) indicate that radiant heat transfer plays a dominant role in small FDP reactors such as the one used in this study. Because the effect of radiant heat transfer from the reactor walls diminishes as the diameter of the reactor increases, temperature profiles in commercial reactors will be considerably different from those existing in our present 3-inch id FDP reactor this indicates the necessity of using larger diameter pilot plants to obtain reliable scaleup data. 

The simulation results of the one-dimensional model were found to be in fair agreement with the two-dimensional model considering the chemical conversion of the reactor, as is also utilized by the Kunii-Levenspiel type of modeis [85]. Moreover, with extended conductive fluxes, fair temperature profiles can be predicted with the one-dimensional model. On the other hand, the flow pattern, i.e., the phasic fractions and gas phase velocity, were associated with the largest uncertainty in the current model. However, the internal flow details did not have signiflcant influence on the chemical process performance. Thus, the current one-dimensional model was considered to have good potentials for further CEB model developments in order to study interconnected fluidized bed reactors with a dynamic solid flux transferred between the reactor units. 

The velocity profiles and the axial distribution of volume fraction of solid particles are shown in Fig 4.12. The solid velocity pattern did show a non-axial symmetric behavior. The axial distribution of the solid phase was close to uniform. Figure 4.13 displays the outlet fractions of hydrogen, methane, and CO2 in the gas phase as achieved for the SMR and SE-SMR processes operated in a BFB reactor. In the SMR results, the outlet molar fraction of H2 is only 75 %, thus a considerable amount of CO2 and CH4 are emitted out of the reactor. In the SE-SMR process results, both the conversion of methane and the adsorption of CO2 are larger than 99 %. The simulation results show that the integration of CO2 sorption in the SMR process can enhance the methane conversion to hydrogen to near the equilibrium composition in the BFB reactor. 

---