(129h) Effect of Scale up Process on Reactor Performance within Riser: Simulation Using Ozone Decomposition

Circulating fluidized beds (CFB) are widely used in chemical and energy fields because of the high mass and heat transfer rate, significantly reduced back mixing. Successful commercialization of CFBs relies on the ability to scale up the reactors from lab to industrial scale especially for the risers. To apply fundamental knowledge from pilot scale risers into a commercial riser, it is necessary to achieve a clear understanding of the scale-up effects. The scale up effect on the hydrodynamics within riser reactors has been investigated in many aspects, such as solids concentration distribution, particle velocity, solids flux distribution, flow development and regime transition. On the other hand, scaling laws are put forward in order to ensure the hydrodynamic similarity within riser during the scale up process. The scaling laws are deduced by the dimensional analysis of the momentum balance on a particle. The cluster features would change with the variation of particle properties during scaling process and have an influence on the hydrodynamics similarity. In general, recently researches about riser scale up process are focus on the aspect of hydrodynamics. However, the chemical similarity in terms of conversion and selectivity also has to be considered during the scale up process of chemical reactor. The chemical conversion and selectivity depend on the interactions of mass transfer, kinetics, and hydrodynamics, the research results of bubbling fluidized bed have shown that a scale change will always directly influence the ratio of these interactions. Therefore, the effect of scale up process on reactor performance within riser should be investigated.

The reactor performance within riser is always evaluated by the detection of ozone decomposition. Researchers have investigated the local reactor performance and the effect of operation condition, internal structures, new type structures on the reactor performance. The axial and lateral ozone concentration distribution are the most common used to analyze reactor performance.

CFD simulation has shown to be an effective tool in the evaluation of scaling rules with the consideration of cluster effect for risers, since the simulation method offers the advantage by facilitating evaluation of these scaling parameters with fewer requirements of extensive physical experiments. Meanwhile, the ozone decomposition process is also could be realized by the CFD simulation method. Therefore, the effect of scale up process on the reactor performance is investigated by the simulation of ozone decomposition process in the scaling risers with the guide of scaling rules.

Glicksman’s full and simplified sets of scaling parameters are used to build two 1:3 scaled-up risers, which is the same as the previous research. The energy minimization multiscale (EMMS) drag model is used to describe the gas solids momentum interaction, since it can capture the effect of clusters on the gas solids interaction. The EMMS drag force coefficient for each case coupled with the two-fluid models and kinetic temperature granular flow model (KTGF) is used to simulate the flow structures in two-dimension risers. The ozone decomposition was realized within the risers through the coupling with a user defined function (UDF) which describe the ozone decomposition reaction rate equation. The effect of scale up process on the reactor performance especially for the gas solids contact efficiency was analyzed by the comparison of dimensionless axial and radial ozone concentration distribution and corresponding solids concentration profiles between two scales. Furthermore, the cluster characteristics in each case were used to explain the variation of reactor performance during scaling up process.

Conclusions

Ozone decomposition in the riser is simulated with CFD in order to explore the scale up effect on the chemical reaction performance. The variation of gas solids contact efficiency is revealed by the comparison of cluster effect in each set up. The ozone decomposition is effect by the solids volume fraction and gas phase residence time at the same time. The ozone decomposition degree in the scaling riser with full set scaling rules is higher than the small riser, while the ozone decomposition degree in the scaling riser with simplified rules is lower than the small riser. The radial ozone uniformity becomes worse during the scale up process. The overall gas solids contact efficiency is improved during the scale up process with full set scaling rule. The effect of scale up on the gas solids contact efficiency in the core region is not obvious, while the effect of scale up on the gas solids contact efficiency in the wall region is related to the variation of cluster effect during scale up process.