A Validation of Flare Combustion Efficiency Simulations

Our objective is to predict the combustion efficiency of industrial flares by using Large Eddy Simulations (LES). The practical utility of the results of a computer simulation is proportional to the degree to which the error and uncertainty in the simulation results have been quantified by validation with experimental data. The available combustion efficiency data from flare experiments is both expensive and sparse. The International Flare Consortium has recently released experimental data on tests performed at the CANMET wind tunnel flare facility. For this paper we have used experimental data from the 4 inch flare tests for measured outlet species concentrations to obtain combustion efficiency as a function of crosswind velocity. We have also included data from buoyant helium plumes measured by Sandia National Laboratory in the validation hierarchy. We have used this validation process to demonstrate and advocate a validation procedure that is philosophically influenced by the Scientific Method, made quantitatively rigorous by Bayesian Inference, but made simple and practical through the use of a consistency constraint. The consistency constraint requires all experiments and all simulations to be bounded by their individual experimental uncertainty. This approach draws on prior information to exploit the consistency requirement among the available experimental data sets and the simulations of these sets to quantify the uncertainty in model parameters, boundary conditions and experimental error and simulation outputs. The final result is a predictive capability for flare combustion efficiency where no experimental data are available but where the validation process produces error bars for the predicted combustion efficiency.