Flow and reactions

An analytical model of the process has been developed to expedite process improvements and to aid in scaling the reactor to larger capacities. The theoretical results compare favorably with the experimental data, thereby lending vahdity to the appHcation of the model to predicting directions for process improvement. The model can predict temperature and compositional changes within the reactor as functions of time, power, coal feed, gas flows, and reaction kinetics. It therefore can be used to project optimum residence time, reactor si2e, power level, gas and soHd flow rates, and the nature, composition, and position of the reactor quench stream. 

Solution The initial liquid-phase concentration of oxygen is 0.219mol/m as in Example 11.1. The final oxygen concentration will be 1.05 mol/m. The phase balances. Equations (11.11) and (11.12), govern the dynamic response. The flow and reaction terms are dropped from the liquid phase balance to give... 

Fluid flow and reaction engineering problems represent a rich spectrum of examples of multiple and disparate scales. In chemical kinetics such problems involve high values of Thiele modulus (diffusion-reaction problems), Damkohler and Peclet numbers (diffusion-convection-reaction problems). For fluid flow problems a large value of the Mach number, which represents the ratio of flow velocity to the speed of sound, indicates the possibility of shock waves a large value of the Reynolds number causes boundary layers to be formed near solid walls and a large value of the Prandtl number gives rise to thermal boundary layers. Evidently, the inherently disparate scales for fluid flow, heat transfer and chemical reaction are responsible for the presence of thin regions or "fronts in the solution. 

For the catalytic oxidation of malonic acid by bromate (the Belousov-Zhabotinskii reaction), fimdamental studies on the interplay of flow and reaction were made. By means of capillary-flow investigations, spatio-temporal concentration patterns were monitored which stem from the interaction of a specific complex reaction and transport of reaction species by molecular diffusion [68]. One prominent class of these patterns is propagating reaction fronts. By external electrical stimulus, electromigration of ionic species can be investigated. 

Wells, J.T. and Ghiorso, M.S. (1991) Coupled fluid flow and reaction in midocean ridge hydrothermal system The behaviour of silica. Geochim. Cosmochim. Acta, 55, 2467-2481. 

In a final example, we consider a similar problem in two dimensions. Water containing 1 mg kg-1 benzene leaks into an aquifer for a period of two years, at a rate of 300 m3 yr-1. Once in the aquifer, which is 1 m thick, the benzene migrates with the ambient flow, sorbs, and biodegrades. We model flow and reaction over 10 years, within a 600 m x 60 m area, assuming a dispersivity ay along the flow of 30 cm, and a-y across flow of 10 cm. All other parameters, including the flow velocity, remain the same as in the previous calculation. 

Phillips, O. M., 1991, Flow and Reaction in Permeable Rocks. Cambridge University Press. 

A material balance analysis taking into account inputs and outputs by flow and reaction, and accumulation, as appropriate. This results in a proper number of continuity equations expressing, fa- example, molar flow rates of species in terms of process parameters (volumetric flow rate, rate constants, volume, initial concentrations, etc.). These are differential equations or algebraic equations. 

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