ACERC
Abstracts - 1993 |
ACERC
Abstracts - 1993 |
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Thrust Area 5: Comprehensive Model Development |
Brewster, B.S.; Hill, S.C.;
Radulovic, P.T. and Smoot, L.D.
Chapter 8, Fundamentals of Coal Combustion: For Clean and Efficient Use,
(L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded
by ACERC.
This chapter treats comprehensive modeling of combustion and gasification systems. Entrained, fluidized and fixed bed models are considered. Single and multidimensional models are reviewed. Developing comprehensive computer models to help design combustors and gasifiers for clean and efficient utilization of coal and other fossil fuels is a primary objective of ACERC. Such models provide not only a framework for effectively integrating combustion-related technology from a wide array of disciplines, but a vehicle for transferring this technology to industry. In order to be useful, these models must satisfy at least three criteria: First, the input and output must be easily accessible (user-friendly graphics must play a role here). Second, the computer algorithms must be robust and computationally efficient. And third, the models must be thoroughly evaluated to demonstrate applicability to industrial processes and to justify confidence in their predictions. Developing and implementing user-friendly, robust, efficient, applicable, accurate models requires significant, on-going effort that is reviewed herein.
Radulovic, P.T. and Smoot,
L.D.
Chapter 1, Fundamentals of Coal Combustion: For Clean and Efficient Use,
(L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded
by ACERC.
This chapter discusses current coal combustion and gasification processes and technologies, with emphasis on clean and efficient use. Entrained, fluidized and fixed beds together with MHD generation and fuel cell cycles are treated. Coal is the world's most abundant fuel. Most of the coal presently being consumed is by direct combustion of finely pulverized coal in large-scale utility furnaces for generation of electric power, and this is likely to remain the way through the end of this century. However, many other processes for the conversion of coal into other products or for the direct combustion of coal are being developed and demonstrated, including various coal combustion and gasification processes. Several other processes and technologies such as underground coal gasification, magnetohydrodynamic generators, and fuel cells are also being developed, as discussed herein. Increasing the use of coal presents many technical problems, particularly in protecting environment while maintaining or increasing efficiency. In order to solve these problems and increase the use of coal, the USA and many other countries in the world are supporting research and development of clean coal technologies that are summarized in this chapter.
Fletcher, T.H. and Hill,
S.C.
Energy & Fuels, 7, (6):870-873, 1993. Funded by ACERC.
A major objective of the Advanced Combustion Engineering Research Center (ACERC) is the development of comprehensive combustion models to help in the solution of critical national combustion problems. Computer models incorporate research and technology results from center projects and from external research programs. The synergistic integration of scientific knowledge that is expected from the NSF engineering research centers is demonstrated to a great extent at ACERC by the development of these software tools. The transfer of technology from ACERC to industry is also accomplished in part by the implementation of the models at industrial firms. The effort to develop such products requires significant integration and development, together with fundamental research. The development of comprehensive models also produces personnel and technology able to help address the challenge of synergistic cross-linkage among thrust areas within ACERC and provides an important means of transferring this technology to industry. This article is an overview of the purpose, accomplishments and goals of research at ACERC in comprehensive modeling. (Thrust Area 5.)
Zundel, A.K.; Saito, T.;
Owen, S.J.; Sederberg, T.W. and Christiansen, H.N.
Energy & Fuels, 7 (6): 891-896, 1993. Funded by ACERC.
This paper presents some tools that have been developed to aid in visualizing the analysis results obtained from the simulation of coal combustion furnaces in the particular and other computational fluid dynamics problems in general. These tools have been implemented into a visualization software package called CQUEL.BYU. This paper presents an overview of the general capabilities of CQUEL.BYU that are pertinent to the coal combustion community. It then presents some new algorithms for visualizing gas flow, particulate motion, and scalar fields using animation techniques. Specifically, many kinds of flow features, such as vortex formation and velocities at each point, can be conveyed effectively in both animation and still images by means of cyclic particle animation and oriented motion blur. Implementation of these capabilities into a software package that runs on most general purpose, low-cost workstations is discussed.
Sikorski, K.; Ma, K.-L.;
Smith, P.J. and Adams, B.R.
Energy & Fuels, 7 (6):902-905, 1993. Funded by ACERC.
This paper reports research in progress. Two types of domain decomposition have been used in distributed computing with networked workstations for the numerical modeling of full-scale utility boilers. The numerical model is a three-dimensional combustion code that couples turbulent computational fluid dynamics with the chemical reaction process and the radiative heat transfer. Two approaches, here called microscale parallelism and macroscale parallelism, are proposed to study the intrinsic parallelism of typical combustion simulations. We describe the implementation of the microscale parallelism as well as its performance on networked workstations.
Sikorski, K. and Ma, K.-L.
Energy & Fuels, 7 (6):1993, 897-902, funded by ACERC.
The Navier-Stokes equations are central to applied scientific research. The complete set of three-dimensional Navier-Stokes equations is very complex and thus requires a substantial amount of computer time as well as memory in order to obtain an accurate solution. The scalability in both processing power and memory space of distributed-memory parallel computers give promise of solving large-scale three-dimensional scientific problems based on these equations. In this paper, we describe the implementation and performance of a distributed three-dimensional Navier-Stokes solver in Parasoft's Express. We have run the solver on both the IBM Victor Computer (a 256-node transputer based system) and a token ring networked IBM RS/6000-520 workstation. Our test results demonstrate that distributed multiprocessing allows researchers to solve large-scale computational fluid dynamics problems and can improve their productivity with reducing turn around time.
Brewster, B.S. and Smoot,
L.D.
Energy & Fuels, 7 (6):884-890, 1993. Funded by US Department of Energy.
Flame data from a near-laminar coal jet have been compared with model predictions. Inclusion of gas turbulence with laminarization was necessary for adequately predicting the upper-flame and postflame regions and for predicting particle dispersion. Dispersion of gas and particles was insensitive to inlet turbulence intensity. Gas buoyancy induced radially inward flow that opposed particle dispersion. Gas temperature was predicted too high near the coal nozzle, perhaps due to neglecting finite-rate mixing of volatiles with the bulk gas and chemical kinetics effects. Single-particle burning effects were important in the flame zone, as evidenced by the sensitivity of particle temperature to direct enthalpy feedback from volatiles combustion. Particle burnout was insensitive to enthalpy feedback, heterogeneous CO2 formation, and chemistry/turbulence interaction.
Hill, S.C. and Smoot, L.D.
Energy & Fuels, 7 (6):874-883, 1993. Funded by ACERC.
A generalized, three-dimensional combustion model has been developed to simulate large-scale, stead-state, gaseous and particle-laden, reacting and nonreacting systems. The model, which is based on an earlier two-dimensional model, has been applied to turbulent, combustion systems, including pulverized-coal systems. It uses an Eulerian framework for the gas phase and a Lagrangian framework for the particles. The code assumes equilibrium gas-phase chemistry and couples the turbulent flow field with the chemical reactions by integrating the equations over a probability density function. The model uses advanced numerics and a differencing scheme capable of solving the large computational meshes required to simulate practical furnaces. Convective and radiative heat transfer are also modeled. Radiative heat transfer is modeled using the discrete ordinates method. The model has been evaluated by comparison of predictions with experimental data from a large-scale 85-MEe coal-fired utility boiler. The data include furnace profile measurements obtained with intrusive and laser-based optical probes. These comparisons show qualitative agreement of model predictions with observed trends, and indicate that the model can be used to provide insights into boiler operation.
Smith, J.D.; Smith, P.J.
and Hill, S.C.
AIChE Journal, 39, (10):1668-1679, 1993. Funded by Combustion Laboratory
Consortium through Brigham Young University.
Parametric sensitivity of a two-dimensional pulverized-fuel (PF) combustion model is studied extensively for the effect of parametric uncertainty on model predictions. Results show that error in coal devolatilization/oxidation parameters has the dominant effect on predicted burnout, NOx formation, local gas temperature, and coal-gas mixture fraction. Uncertainty in the turbulent particle dispersion parameters appears to have a secondary effect, while error in the particle-gas radiation parameters has little impact on model predictions. Regions of the computational domain exhibiting sensitivity to specific parameters are identified. Specific parameter sensitivity implies the relative importance of various mechanisms in the overall process. Turbulent particle dispersion seems to be important early in the reactor with kinetic processes dominating at and following the predicted ignition point. Radiation appears to be of minor importance. These results indicate the need for a better method of predicting the overall volatiles yield and further understanding of the devolatilization/oxidation mechanism and its role in the overall PF combustion process. The study provides fundamental direction for future comprehensive model development and focuses on experimental work to better quantify critical input parameters.
Ghani, M.U.; Radulovic,
P.T. and Smoot, L.D.
American Chemical Society, Division of Fuel Chemistry, 38: 1358-1369,
1993. Funded by US Department of Energy, Morgantown Energy Technology Center
and ACERC.
An advanced, one-dimensional fixed-bed coal gasification and combustion model is presented. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on functional groups and depolymerization, vaporization and cross-linking, oxidation and gasification of char, and partial equilibrium in the gas phase. The model is described by 191 highly non-linear, coupled, first order differential equations. Due to the countercurrent nature of the gas and solids flow the system of equations constitutes a split-boundary value problem that is solved by converting it to an initial value problem. This paper presents a split back-and-forth shooting technique that exactly satisfies conditions at both the upper and the lower boundary and provides significant improvements in the predictions. Comparisons of the predicted and experimental results for an atmospheric, air-blown Wellman-Galusha gasifier fired with Jetson bituminous coal are presented.
Sikorski, K.; Tsay, C.W.
and Wozniakowski, H.
Journal of Complexity, 9: 181-200, 1993. (Presented at NATO Advanced
Studies Institute Conference, II Ciocco, Italy, September 1993. Also presented
at the International Conference on Interval Methods, Lafayette, LA, February
1993.) Funded by IBM and ACERC.
We consider the problem of approximating fixed points of contractive functions with using the absolute error criterion. It was proven in (A.S. Nemirovsky, 1991, J. Complexity 7, 121-130) that it is impossible to essentially improve the efficiency of the simple iteration whenever the dimension of the domain of contractive functions is large. However, for a moderate dimension we exhibit a fixed-point ellipsoid algorithm which is much more efficient than the simple iteration for midly contractive functions. This algorithm is based on Khachiyan's construction of minimal volume ellipsoids used for solving linear programming.
Ma, K.-L. and Smith, P.J.
Proceedings of the Visualization 93 IEE/ACM SIGGRPHY Conference:253-259,
San Jose, CA, October 1993. Funded by IBM and ACERC.
This paper describes a highly interactive method for computer visualization of simultaneous three-dimensional vector and scalar flow fields in convection-diffusion systems. This method allows a computational fluid dynamics user to visualize the basic physical process of dispersion and mixing rather than just the vector and scalar values computed by the simulation. It is based on transforming the vector field from a traditionally Eulerian reference frame into a Lagrangian reference frame. Fluid elements are traced through the vector field for the mean path as well as the statistical dispersion of the fluid elements about the mean position by using added scalar information about the root mean square value of the vector field and its Lagrangian time scale. In this way, clouds of fluid elements are traced not just mean paths. We have used this method to visualize the simulation of an industrial incinerator to help identify mechanisms for poor mixing.
Ma, K.-L.; Painter, J.S.;
Hansen, C.D. and Krogh, M.F.
Proceedings of the 1993 Parallel Rendering Symposium, San Jose, CA, 15-22,
October 1993. Funded by IBM and ACERC.
This paper presents a divide-and-conquer ray-traced volume rendering algorithm and a parallel image compositing method, along with their implementation and performance on the Connection Machine CM-5 and networked workstations. This algorithm distributes both the data and the computations to individual processing units to achieve fast, high-quality rendering of high-resolution data. The volume data, once distributed, is left intact. The processing nodes perform local raytracing of their subvolume concurrently. No communication between processing units is needed during this locally ray-tracing process. A subimage is generated by each processing unit and the final image is obtained by compositing subimages in the proper order, which can be determined a priori. Test results on the CM-5 and a group of networked workstations demonstrate the practicality of our rendering algorithm and compositing method.
Brewster, B.S.; Boardman,
R.D.; Huque, Z.; Berrondo, S.K.; Eaton, A.M.; Smoot, L.D.; Zhao, Y.; Solomon,
P.R.; Hamblen, D.G.; Serio, M.A.; Charpenay, S.; Best, P.E. and Yu, Z.-Z.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel
Research/Brigham Young University Final Contract Report, Vol. II, 1993.
Funded by US Department of Energy and Morgantown Energy Technology Center.
A two-dimensional, steady-state model for describing a variety of reactive and non-reactive flows, including pulverized coal combustion and gasification, is presented. Recent code revisions and additions are described. The model, referred to as 93-PCGC-2, is applicable to cylindrical, axi-symmetric systems. Turbulence is accounted for in both the fluid mechanics equations and the combustion scheme. Radiation from gases, walls, and particles is taken into account using a discrete ordinates method. The particle phase is modeled in a Lagrangian framework, such that mean paths of particle groups are followed. A new coal-general devolatilization submodel (FG-DVC) with coal swelling and char reactivity submodels has been added. The heterogeneous reaction scheme allows for both diffusion and chemical reaction. Major gas-phase reactions are modeled assuming local instantaneous equilibrium, and thus the reaction rates are limited by the turbulent rate of mixing. A thermal and fuel NOx finite rate chemistry submodel is included which integrates chemical kinetics and the statistics of the turbulence. A sorbent injection submodel with sulfur capture is included. The gas phase is described by elliptic partial differential equations that are solved by an iterative line-by-line technique. Under-relaxation is used to achieve numerical stability. Both combustion and gasification environments are permissible. User information and theory are presented, along with sample problems.
Solomon, P.R.; Hamblen,
D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel
Research/Brigham Young University Final Contract Report, Vol. I, 1993. (Also
presented at the Coal-fired power systems 93 Conference, Morgantown,
WV, June 1993.) Funded by US Department of Energy and Morgantown Energy Technology
Center. (This report is available from Advanced Fuel Research, Inc.)
This project included research in the following areas: (1) fundamental high-pressure reaction rate data; (2) large particle oxidation at high pressures; (3) SOx-NOx submodel development; (3) integration of advanced submodels into entrained-flow code, with evaluation and documentation; (4) comprehensive fixed-bed modeling, review, development, evaluation and implementation; (5) generalized fuels feedstock submodel; (6) application of generalized pulverized coal comprehensive code and (7) application of fixed-bed code.
Ghani, M.U.; Hobbs, M.L.;
Radulovic, P.T.; Smoot, L.D.; Hamblen, D.G. and Zho, Y.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel
Research/Brigham Young University Final Contract Report, Vol. III, 1993.
Funded by US Department of Energy and Morgantown Energy Technology Center.
A generalized, one-dimensional, heterogeneous, steady state, fixed-bed model for gasification and combustion of coal is presented. The model, referred to as FBED-1, is a design and analysis tool that can be used to simulate a variety of fixed or moving bed gasification, combustion, and devolatilization processes. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, depolymerization, vaporization and crosslinking, oxidation and gasification of char, and partial equilibrium in the gas phase. The conservation equations and boundary conditions are formulated for gas and solid overall continuity, gas and solid energy equations, and gas and solid species or elemental continuity equations. Plug flow is assumed in both the solid and the gas phase with variable axial velocities. Gas phase pressure drop is calculated with the Ergun equation for packed beds. Large coal particle devolatilization is allowed to occur simultaneously with char oxidation and gasification. A generalized, coal devolatilization submodel, FG-DFC, is an important part of the model. Shell progressive or ash segregation, shrinking core char submodel describes oxidation and gasification. Turbulence is not treated formally in the slowly moving bed with low gas velocity, but is included implicitly through model correlations such as the effective heat transfer coefficient. A split, back-and-forth iteration and a Livermore solver for ordinary differential equations, LSODE, are used to solve a highly non-linear, stiff system of differential governing equations. Model formulation and solution method are presented, along with user and implementation guides and a sample problem.
Smithson, T.G.
Intuitive Modeling of the ACERC Three-Dimensional Mesh, M.S./BYU, April
1993. Advisor: Sederberg
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