Optimization of Reactor Flows using Discrete Tangent based Sensitivity Analysis

Reactors and flow processes involving chemical reactions are often governed by many operating parameters such as the inlet and exit flow rates, compositions, reaction mechanisms, rate constants, pressures, and temperatures. In most systems many of these parameters influence the system in complicated and interconnected manner. It often requires generating, gathering, and analyzing design data from a large number of simulations or experiments to determine and quantify the critical parameters that govern the performance and their range of influence.

CFD simulations have become a vital tool to study, design, and optimize the equipment and processes concerned with reactive flows. These analyses provide details spatial and temporal detail of the conditions in the system helping to make informed decisions regarding improving or optimizing the performance. However, CFD simulations usually are also time consuming and expensive to perform especially when a large number of parameters are involved.

The work presents investigation of a Plug Flow Reactor (PFR) system and an industrial tubular reactor having multiple inlet streams using Discrete Tangent based method which provides solution and gradients of all variables in the system with respect to input and/or operating parameters. This rich data from a single simulation is useful identifying the strongest parameter which influence the performance both in overall terms and in detail. It will quantify the degree of influence of a parameter on the system and map the spatial influence of the parameter.

The Eddy-Dissipation Model (EDM) and the Eddy Dissipation Concept (EDC) models are used to compute the reaction rates, and the k-epsilon model is used to model turbulence. The results for the sensitivity of the flow and temperature profiles and the outlet stream concentration to input parameters such as the inlet flow rate, the inlet feed composition and the inlet temperature are presented. Results include the solution fields (or derived quantities) at the specified value of the sensitivity parameter (computed value), the gradient of the solution field with respect to this sensitivity parameter (derivative), and the extrapolated value of the field about the specified value of sensitivity parameter. The sensitivity results will be compared with results obtained from multiple single-point simulations using traditional simulators. The work also quantifies the time saved to obtain the range of sensitivity data for this demonstrative reactor flow compared to the conventional methods.