ISSN:0010-2202    

DOI:10.1080/00102208808923952

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A general combustor prediction method is here applied to the problem of a corner-fired power station combustion chamber. The balance equations for mass, momentum, energy and the mixing of the primary and secondary streams are solved numerically. The effects of the turbulence are stimulated by the k-ε model, while the radiation transfer is handled by the flexible and economic “discrete transfer” approach. The particulate phase is treated by a Lagrangian calculation scheme which allows for particle well interactions. Result of calculations are presented for the combustor aerodynamics. where they are compared with data, for the heat transfer and temperature distributions in a gas-fired combustor and for the particle trajectories in a coal-fired unit.

ISSN:0010-2202    

DOI:10.1080/00102208808923953

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A mathematical model for pulverized fuel flame predictions has been applied to pulverized coal and peat flames. This paper presents the mathematical model used and the evaluation of the model for a pulverized coal flame. The coal flame is generally well predicted. even in the ignition part of the flame. Differences between peat and other pulverized fuels are discussed. The peat contains more volatile matter and has a higher oxygen content, which has to be considered in the modelling of devolatilization. Some measurements of temperature and incident radiation in two pulverized peat flames are compared to the predictions. It is concluded that the ignition phase in the peat flames is not as well predicted as for the case of the coal flames. The devolatilization model used for the predictions is found to work well for the coal flame, but less satisfactorily for the peat flames.

ISSN:0010-2202    

DOI:10.1080/00102208808923954

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The turbulent flow field in large utility boiler furnaces is strongly affected hy heat release from combustion and by the heat extracted from the furnace through the boiler tube walls. To describe and predict these effects with reasonable engineering accuracy, a mathematical model termed COMpac has been developed at the University of Stuttgart. The series of codes is based on a finite difference solution of the turbulence-modelled Navier-Stokes equations in axisymmetric and in fully three-dimensonal coordinates. Radiative heat transfer is presently predicted using flux method approximatians. A simplified mechanism of pulverized coal combustion is described in a Eulerian framework for both the gaseous and particulate phase. In the present work, validation studies are reported and discussed. The combustion model has been tested for single enclosed flames where detailed measurements were available. Prediction results for three-dimensional furnace flows are compared with velocity data from an isothermal perspex model. Finally, the complete furnace code has been applied to predict a 300 MW brown coal fired furnace both under isothermal and fully reacting conditions.

ISSN:0010-2202    

DOI:10.1080/00102208808923955

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Research efforts with comprehensive computer models that have tried to predict the performance of coal combustors have either neglected the effect of the turbulence on the mean chemical properties or have used one of two approximate methods. This paper focuses on the impact of the turbulence on the chemical reactions of the volatile products of coal combusion processes. It is shown that by ignoring the effect of the turbulence on mean combustion properties significant differences occur as compared to experimental data and as predicted hy both of the more rigorous models. The first method (Lockwood, Salooja and Syed, 1980), the volatile reacted ness model, is an extension of an approach for premixed gaseous combustion presented by Magnussen and Hjertager (1976). The second method (Smoot, Hedman and Smith, 1984), the statistical. coal-gas mixture-fraction model, is an extension of gaseous diffusion flame approaches. These two methods are examined.analyzed and evaluated by comparing predictions from each method with experimental data from three laboratory furnaces. It is shown that while the first method takes only half as much computational time,the second method is required if species and temperatures in zones containing other than mixtures of pure fuel, pure oxidant and pure stoichiometric product are needed. The distribution of eddy mixtures as formulated in the second method is shown to bemore consistent with existing limited experimental data.

ISSN:0010-2202    

DOI:10.1080/00102208808923956

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Results of a theoretical-experimental study of the contribution of radiation to the ignition of coal-water fuel (CWF) flames are reported. The calculation of radiation absorbed by the fuel spray is based on detailed radiation measurements in the ignition zone of three CWF–flames.A simple model to calculate the ratio of radiative to convective heal transfer (11) to the particles in a coal-water slurry fuel spray during its heat-up to ignition is presented. Input data for the model were provided by in–flame measurements and by an ignition model (Walsh et al., 1984).Two limiting cases were calculated for the theoretical heat transfer ratio. 11. the upper limit being the hemispherical radiation incident on a single particle, and the lower limit the narrow angle radiation incident on a cloud of particles. These values of II were then compared with those calculated from experimental data on the absorption of radiation by the fuel spray.The influence of the fuel particle size, the temperature of the gas entrained into the fuel spray, and of the particle temperature history (heat-up, vaporization, ignition times), upon the ratio of radiative to convective heat transfer to the fuel spray is discussed.

ISSN:0010-2202    

DOI:10.1080/00102208808923957

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A methodology for computing steady turbulent combusting flow in combustors of complex shape is presented. Included is discussion of fully- or partially-equilibrated chemical kinetic models, the interaction of turbulence and combustion, grid systems, discretization operators and solution procedures for recirculating flows. Examples that demonstrate the influence of these issues are reviewed. A package of three-dimensional codes for grid generation and flow analysis-developed in the course of these studies-is applied to the flow in a sector of a modern annular gas-turbine combustor. Results are compared with available data. The study demonstrates the utility of modern computational methods and indicates directions for future work

ISSN:0010-2202    

DOI:10.1080/00102208808923958

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Abstract-The task of the combustion engineer is reviewed in the light of available numerical methods,and it is demonstrated how these numerical methods have influenced this task. Examples are shown of application to combustor pattern factor improvement, to diffuser flow and loss optimisation, and to cooling device design improvement. The power of a coupled mesh technique and the flexibility of a boundary fitted orthogonal mesh system are demonstrated to be essential features in the success obtained in applying a single code to all these combustor problems.

ISSN:0010-2202    

DOI:10.1080/00102208808923959

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Turbulent reacting flows with and without swirl are calculated using fast and finite-rate chemistry models and closure is effected by extending constant-density turbulence models to reacting flows. Three experimental combustor flow fields are compared with the calculations: one is a premixed, opposed-jet combustor and the other two are non-premixed, sudden-expansion combustors with and without swirl. The results indicate that an isotropic eddy viscosity model based on the turbulence kinetic energy (k) and its dissipation rate (ε) is sufficient to represent turbulence in non-swirling, reacting flows, whereas an algebraic stress model provides a better overall mean field prediction for reacting flows with swirl. However, flow expansion due to heat release during combustion is only fairly well represented by the submodels used. A finite-rate chemistry model is found to be superior to the fast chemistry approximation in the non-premixed combustor and a two-step global reaction mechanism gives an adequate description of flame stabilization in the premixed combustor. Unfortunately, neither model provides a realistic flame structure. Therefore. further development of finite-rate chemistry models with a suitable coupling of the heat release effects on the turbulence field are needed to improve reacting flow models.

ISSN:0010-2202    

DOI:10.1080/00102208808923960

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The design of a fast, automatic solver for homogeneous, gas-phase chemical kinetic equations requires understanding the physical and numerical sources of computational inefficiency. Several inefficiency sources are reviewed and specific techniques for improvement are recommended (and some advised against). It is argued that exponentially-fitted integration algorithms are inherently more accurate for chemical kinetics modeling than classical, polynomial-interpolant methods for the same computational work.

ISSN:0010-2202    

DOI:10.1080/00102208808923961

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor