Model Studies and the Prediction of Full Scale Levels of Stack Gas Concentration

The scaling requirements and experimental procedures for modeling the diffusion of stack plumes during conditions of neutral atmospheric stability are presented. Wind during neutral conditions is modeled by a turbulent boundary layer developed naturally over a long fetch of upstream terrain. Both the inertia and buoyancy properties of the plume are simulated; the latter is achieved by using an air helium mixture. The helium is also used as a tracer gas for measurements of model concentrations resulting from the stack operation. Some illustrative experimental measurements are presented.

The methodology developed at the Boundary Layer Wind Tunnel Laboratory for providing predictions of full scale stack gas concentrations is summarized. In this approach wind tunnel derived measurements of stack gas concentration at particular down wind locations, wind speeds, wind directions, and power plant operating conditions can be combined with the statistical description of the local wind climate to arrive at predictions of the exceedance of particular full scale SO₂ concentrations. Ground level SO₂ concentrations predicted to be exceeded during particular proportions of time are compared with data derived from analysis of full scale SO₂ observations.