Multiphase_Continuum_Formulation_for_Gas-Solids_Reacting_Flows

Multiphase_Continuum_Formulation_for_Gas-Solids_Reacting_Flows

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Unformatted text preview: 1 Copyright © 2011, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 1 Multiphase Continuum Formulation for Gas- Solids Reacting Flows Madhava Syamlal National Energy Technology Laboratory, USA Sreekanth Pannala Oak Ridge National Laboratory, USA abstract This chapter describes the formulation of multiphase continuum models for gas-solids Fows with chemi- cal reactions. A typical formulation of the equations is presented here, following the equations in the open-source software M¡IX (http://m¢x.netl.doe.gov) so that interested users may look up details of the numerical implementation, study the solutions, or experiment with the numerical implementation of alternative formulations. The authors will ¢rst provide a brief overview of the signi¢cance of gas-solids reacting Fows and the challenges in modeling these systems along with various efforts undertaken by different groups over the last 2–3 decades. They will then summarize the methods used to derive mul- tiphase continuum models and to formulate constitutive equations. They will later provide information on the formulation for mass, momentum, granular energy, energy, and species balance equations for gas and multiple solids phases. They will discuss the constitutive equations required in each of the bal- ance equations; a detailed discussion of certain constitutive equations, such as the gas-solids drag and granular stresses (derived from kinetic theory), will be presented by other authors in later chapters. The authors will point out the differences between different approaches and direct the reader to refer- ences that discuss those approaches in detail. They will end the chapter with the example problem of the simulation of a bubbling Fuidized bed to illustrate some of the modeling options — physical models, numerical discretization schemes, and grid resolution – that need to be considered to accurately simulate gas-solids systems. DOI: 10.4018/978-1-61520-651-3.ch001 2 Multiphase Continuum Formulation for Gas-Solids Reacting Flows 1. intrOductiOn Gas-solids reactors, which are critical components in many energy and chemical conversion processes, cannot be designed reliably using correlation-based scale-up methods, and a physics-based method is needed for increasing the reliability of the design. There are many examples: coal gasifiers that react coal with oxygen and steam to produce synthesis gas (syngas)—a mixture of hydrogen and carbon mon- oxide; circulating fluidized-bed combustors that burn coal to generate heat and electric power; or fluid catalytic cracking (FCC) risers that crack heavy oil with the help of hot catalyst particles, producing light hydrocarbons such as gasoline. Increasing the conversion of the reactants (e.g., coal in a gasifier) or improving the selectivity of the products (e.g., gasoline in FCC) or ensuring the reliability of the reac- tors or reducing the size of the reactors are design objectives that would help increase the profitability...
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Multiphase_Continuum_Formulation_for_Gas-Solids_Reacting_Flows

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