Simplified flare combustion model for flare plume rise calculations

摘要

The dispersion of plumes released from stacks depends on wind speed, plume emission rate, stack height, and other meteorological and stack variables. Plume rise is an important aspect of plume dispersion because it increases the apparent release height, which leads to lower ground-level concentrations. Plume rise linked with flare combustion has received only minimal attention in the literature to date, despite its importance. This study develops a numerical model of plume rise with flare combustion based on material, heat, mass, and momentum balances. The basis of the model is a numerical plume rise model used in CALPUFF to model plume rise of large buoyant area sources, and is also used in PRIME (plume rise model enhancements), which models building downwash. The proposed model considers the reaction kinetics. The competition between CH4 and CO combustion causes a modification of the temperature profile of up to 3% in comparison with an instantaneous reaction model. Moreover, emissivity, which plays an important role in the heat conservation equations but which was only parameterized in an earlier work, is calculated more directly to increase the accuracy of the model. It was found that soot is the main contributor to flame emissivity. Finally, the air dispersion model CALPUFF was run according to the proposed flare model and an empirical flare model by Beychok to compare results of the models. This new flare method is sufficiently simple to be embedded into air dispersion modelling software such as CALPUFF.