Efficient In-Situ and Reduced Chemistry Algorithms for Chemical Process Flow Simulation

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The principal objectives of this project are the development and implementation of efficient in-situ and reduced chemistry algorithms for detailed chemical process flow simulation. The current trend in flow simulation in the chemical process industries is towards the application of computational fluid dynamics (CFD) to obtain a more complete descriptions of the flow field and chemical species distribution inside chemical reactors. For chemically reacting flows, treatment of the chemical source terms resulting from complex kinetic schemes (i.e. greater than 10 to 20 species) is often the most computationally intensive part of a flow simulation. Considerable gains in computational efficiency are thus possible by exploiting two common features of complex kinetic schemes, namely, the large separation in chemical time scales (relative to flow time scales), and the compactness of the "accessed region" (i.e., the compositions that actually occur in a particular simulation). Two methodologies that make use of these features will be investigated. The first, in-situ adaptive tabulation (ISAT), is applicable to moderately large kinetic schemes (around 20 chemical species) and, due to its flexibility of implementation, should be powerful for chemical process flow simulations. The second, intrinsic low-dimensional manifold (ILDM) method, is applicable to larger kinetic schemes (provided that the majority of the chemical time scales are smaller than the flow time scales), but computationally more difficult to implement since it requires retabulation after each change in the kinetic scheme or flow parameters. In order to overcome the shortcomings of each individual algorithm, implementations of a combined ILDM-ISAT algorithm will be explored. The algorithms will be implemented in an existing full probability density function (PDF) code designed for turbulent reacting flow simulation. Full pdf simulations of two industrial chemical reaction schemes (thermochlorination of methane and free-radical poly merization of ethylene) will be carried out in order to validate and document the efficiency of the algorithms under a wide range of actual plant reactor conditions.