Predicting the concentration of effluent material within a plume emitted from a tall chimney

Abstract

The rates of formation of aerosols and the visual appearance of chimney plumes (including the effects of condensation of water vapour) both depend upon the dilution of the effluent gases. This dilution differs from that predicted by conventional dispersion formulae in that these latter refer to time mean concentrations, whereas what is required is the dilution at any given instant in time as the plume travels downwind.

The instantaneous dilution near the source depends on the turbulence induced by the plume's movement through the atmosphere, rather than the dispersive properties of the surrounding atmosphere at the plume level.

A theoretical/empirical model, which has been developed to predict the trajectory of hot chimney plumes, also predicts this instantaneous dilution. Dilutions calculated by this method in different conditions of wind speed and atmospheric stability for various plant emission characteristics are tabulated and compared with values obtained from field measurements.