How to Benefit from CFD Simulation

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Siemens Industry Software GmbH Digital Factory Division

Gas Phase Reacting Flow Models

The most basic types of flow models are for gas phase reacting flows where the different species (feedstocks) enter the reactor non-premixed, completely mixed or partly premixed. For each category, a host of models are available to simulate the reaction (table 1).

Some of these are regarded as tabulated chemistry models to reduce computation times, while others make use of detailed chemistry using DARS.

DARS (Digital Analysis of Reacting Systems) is a standalone gas phase detailed chemical kinetics modeling tool. It can be used for simulating ideal (simplified) reactor models, to develop and import reaction mechanisms to perform sensitivity analysis, validate experimental data, and simplify the reaction mechanisms for use in CFD simulations.

Modeling Process for Heaters and Crackers

In process heaters and naphtha crackers, reactants pass through a tube while heat is supplied by combustion outside the tube. “STAR-CCM+” provides a simplified way to simulate these reactions by modeling the tubes as 1D plug flow reactors — an idealized model used to describe chemical reactions in continuous, flowing systems of cylindrical geometry — while the external combustion is modeled in 3D. This approach is much less computationally expensive than simulating the whole system in 3D.

On the outer tube wall, conduction, convection and radiation are modeled in 3D, while inside the tube, heat transfer via convection is modeled in 1D. Then the two simulations are coupled at the junction of the tube wall. This allows the designer to look at how mass fractions of species behave inside the tubes, and at the same time look at heat transfer and temperature profiles outside the tubes in the furnace.

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