Optimisation of Furnace Design for In-Furnace NOx Reduction: Project Summary

Abstract:

<p>The objectives of this project are: <bl> <li>To determine the optimum burner size relative to furnace dimensions</li> <li>To determine the minimum acceptable pitch between adjacent burners and between the wing burners and furnace side walls</li> <li>To investigate the effect of interleaving the burner pitches in opposed wall fired plant in order to increase furnace utilisation and improve the turndown characteristics of the plant</li> <li>To investigate whether biasing of fuel or air across a burner row offers significant improvements in NO_x levels without adversely affecting carbon burnout</li> </bl></p> <p>Retrofit installations of low NO_x systems are often constrained to some extent by the configuration of the existing plant. These practical constraints can be avoided in the design process for new plant. Factors such as the size, number and pitching of burners are selected to optimise furnace performance in terms of heat input, residence time, corrosion, pollutant formation and economics. The identification of optimum burner size and pitch with particular regard to NO_x emissions and carbon burnout is of significant interest.</p> <p>The typical burner size employed in existing front and opposed wall fired furnaces, of 300 and 500 MWe, is between 40 and 60 MWth. A non-dimensionalised horizontal, vertical and wall clearance pitch of 2.75d was deemed to be representative of all units studied. However, several units feature tighter pitches.</p> <p>Comparison of physical model data with predictions from a CFD model of the physical model showed reasonable agreement. Mathematical modelling, for the prediction of the flow field within a multi-burner furnace, can therefore be applied with confidence.</p> <p>For lower NO_x emission, with no carbon burnout penalty, fewer larger burners are preferable to more burners of a lower thermal heat input. Employing larger burners is also economically advantageous.</p> <p>Modelling predictions were found to be consistent with previous research by IFRF into the effect of burner scaling technique on NO_x emission. When considering constant-velocity scaling, flame chemistry becomes dominant over mixing as scale is reduced and so a higher NO_x emission results from rapid fuel and air mixing.</p> This profile contains information on the project's: <bl> <li>Objectives</li> <li>Summary</li> <li>Cost</li> <li>Duration</li> <li>Contractor</li> <li>Collaborators</li> <li>Background</li> <li>Furnace Review</li> <li>Physical Modelling and CFD Validation</li> <li>Model Definition</li> <li>Burner Versus Furnace Size</li> <li>Air Biasing</li> <li>Burner Pitching</li> <li>Burner Interleaving</li> <li>Burner Arrangement and OFA Injection</li> <li>Conclusions</li> </bl>

Author(s):

DTI