Computation and optimisation of selected processes and equipment with presence of combustion

report

English

The present research report in the first four chapters briefly surveys the current state of the art in mathematical modelling of gaseous diffusion flames as well as numerical methods used to solve the governing equations. Targeted are namely practically viable options incorporated in major commercial general-purpose computational fluid dynamics (CFD) codes. Three following chapters provide three independent case studies for different devices. First of the case studies is a design optimisation study of an exhaust duct from industrial waste (pulp sludge) incinerator. The problem is described in detail and after that, the adopted modelling approach is presented including simplifying assumptions. An objective function for the design optimisation analysis is proposed and used for evaluation of several design alternatives, which are compared to a baseline (original) configuration. Second is a simulation study of an advanced staged low-NOx burner, where special attention was paid to specification of inlet boundary conditions and prediction of nitrogen oxides including semi-empirical modelling. As the burner geometry is very complex, it was necessary to simulate the flow in the furnace in two independent studies, the first providing an analytical expression for inlet flow rates of primary and secondary combustion air, whereas combustion chamber was modelled in the second study. Various model options were employed and critically evaluated by comparing the predicted data with available measured values. Finally, results of a new semi-empirical modelling approach for predicting nitrogen oxides emissions is presented. Third case study concerns another low-NOx burner, although less complex than the one of the preceding chapter, which has only staged gas supply. Simulations are described and results (namely NOx predictions) show rather worse agreement with the measurements than in the case of the first burner. Reasons for this result and other conditions that influenced the comparison of computations and measurements are discussed. Finally, a simple empirical NOx prediction model is evaluated. Conclusions of the work are summarised and ideas for future work are outlined in a final chapter of the report.

NOx, combustion, modelling, CFD

HÁJEK, J., KERMES, V.

30. 11. 2004

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