Return to ACERC Capabilites Page OBJECTIVES
A primary objective of ACERC is the development of comprehensive computer models that can aid in the solution of complex combustion problems. PCGC-3 is a three-dimensional, multiphase combustion computer code that has been developed under the auspices of ACERC to help achieve this objective.
DESCRIPTION
PCGC-3 is a generalized, three-dimensional, steady-state analysis tool that can characterize a variety of reactive or non-reactive fluid flows with entrained particles when these flows can be described locally by general momentum, energy and chemical element conservation equations. Particular emphasis has been placed on pulverized coal combustion and gasification. A combination of several advanced, state-of-the-art numerical and computational techniques have been assembled to solve the conservation relations as a set of fully-coupled equations.
GAS FLUID DYNAMICS
The gas flowfield is assumed to be a three-dimensional mildly compressible turbulent, reacting or non-reacting Newtonian fluid. PCGC-3 solves for this flowfield within an Eulerian framework using a finite-difference formulation of the Navier-Stokes equations coupled with the energy conservation equation.
TURBULENCE
To account for the turbulent transport processes, the Reynolds stresses that result from the time-averaged form of the momentum equations are approximated in PCGC-3 using the Boussinesq assumption. Effective or "eddy" fluid properties are used to relate the Reynolds stresses to the time-averaged flow-field variables. Effective properties are calculated using the two-equation turbulence models. The user may choose between the standard k-epsilon model or a non-linear k-epsilon model that is designed for highly anisotropic turbulent flows.
PARTICLE MECHANICS
To predict the transport of the entrained particles, PCGC-3 uses a Lagrangian model that calculates trajectories of discrete particles through the gas continuum. The particles may be reacting or non-reacting, and particle-particle collisions are neglected. Both the gas and particle conservation equations include source terms for addition and loss of mass, momentum and energy due to interactions between the two flow phases. Turbulent dispersion of the particles is accounted for using an effective turbulent diffusivity based on experimental observations and related to the gas continuum turbulence characteristics.
GAS PHASE REACTIONS
A fundamental assumption used in PCGC-3 is that the gaseous reactions are limited by mixing rates for the major species and not generally by the reaction kinetics. In other words, the reaction kinetics are very fast compared with the time for fuel and oxidizer to mix together at the molecular level. With this assumption, the chemical reaction process can be calculated using locally instantaneous equilibrium based on the degree of mixing of the species.
MIXING AND GAS PROPERTIES
The extent of turbulent mixing between inlet gas streams as they proceed through the flow domain is described in PCGC-3 using a conservative scalar variable called the mixture fraction, which is the local ratio of mass from the primary inlet flow stream to the total mass flow from both the primary and secondary gas flow inlet streams. All other conserved scalars can be calculated from the local value of the mixture fraction. The fluctuating nature of the mixture fraction is modeled using a probability density function (pdf). In PCGC-3, the pdf has the form of a clipped Gaussian distribution adjusted to account for turbulent intermittency.
PARTICLE PHASE REACTIONS
The particle-phase reaction model in PCGC-3 applies to particle reactions that are present in coal combustion and gasification processes. Such particles are considered to consist of four components: liquid, coal, char and ash. The characterization of the coal reaction process comprises several submodels, including liquid vaporization, coal devolatilization, char oxidation and gas-particle interactions, that are based on correlations of extensive experimental observation. The resulting model describes the response of a coal particle to its thermal, chemical, and physical environment.
HEAT TRANSFER
In addition to convective and conductive heat transfer between gases, particles and reaction chamber walls as part of the energy equation solution, PCGC-3 includes a radiative heat transfer submodel. Contributors to radiation include entrained particles and the gas continuum. Radiation calculations are based on performing an energy balance on a beam of radiation passing through a volume element containing an absorbing-emitting medium. A discrete ordinates model is used in PCGC-3 for performing these calculations.
USER REQUIREMENTS
PCGC-3 is a stand-alone computer code that represents the state-of-the art in multi-dimensional combustion-flow modeling. Its use is recommended for those technical specialists with expertise in comprehensive combustion code modeling.
PRE- AND POST PROCESSING
While PCGC-3 is a standalone computer program, the complex nature of 3-D turbulent reactive flowfields requires adequate pre- and post-processing capabilities to prepare input data to review the results of analyses. Such tools have been developed for ACERC computer codes using sophisticated graphical interfaces in a workstation environment. These tools requires X-window graphics capabilities.
SYSTEM REQUIREMENTS
Every effort has been made to maintain ANSI FORTRAN 77 coding standards in the development of PCGC-3. As such, the code can be ported to several different computer platforms. 3-D problems are memory and CPU intusive however. About 1MB of core memory is required to each 1000 nodes in the computational mesh.
AVAILABILITY AND USER SUPPORT
93-PCGC-3 is available to Associate members of ACERC for a one-time licensing fee of $500; to Affiliate members for $10,000; to Supporting members for $13,000; and to other interested parties for a one-time fee of $15,000. Universities interested in using 93-PCGC-3 for research purposes may be able to obtain the code for reduced. Please note however, that code availability and licensing fees are subject to change without notice.
In addition to source code, an extensive user manual detailing code theory and use has been prepared for distribution with 87-PCGC-2. Participation in a user's group and workshops on training in use of the code are also available.
For more information about code availability, licensing fees, or to obtain a copy of the code, contact:
Research and development are being actively pursued at a high level of effort to improve existing submodels in PCGC-2 and add additional features, including new or improved submodels for NOx formation, fouling/slagging, SOx capture, coal-general capabilities and pre- and post-processing packages. Future versions of PCGC-3 will be available at special rates and times that favor ACERC Associates and Affiliates.
ACKNOWLEDGMENTS
The work was sponsored by the Advanced Combustion Engineering Research Center. Funds for the Center are received from the National Science Foundation, the State of Utah, 30 industrial participants and the U.S. Department of Energy.
Key contributors to this development include Dr. Scott C. Hill, Research Associate at BYU, Drs. Subrata Sen and Steve Barthelson, BYU Post-doctoral Associates, and Dr. Andrew M. Eaton, BYU Software Specialist.
REFERENCES
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