Accounting for Moisture Effects in the Prediction of Buoyant Plumes

Abstract

In this paper, the theory of plume rise from stacks with scrubbers is critically evaluated. The significant moisture content of the scrubbed plume upon exit leads to important thermodynamic effects during plume rise which are unaccounted for in the usual dry plume rise theories. For example, under conditionally unstable atmospheres, a wet scrubbed plume treated as completely dry acts as if the atmosphere were stable whereas in reality, the scrubbed plume behaves instead as if the atmosphere were unstable. Even the use of moist plume models developed for application to cooling tower plume rise are not valid since these models employ (a) the Boussinesq approximation, (b) use a number of additional simplifying approximations which require small exit temperature differences between tower exit and ambient, and (c) are not calibrated to stack data.

Although these two theories are often used to predict plume rise from stacks with scrubbers, both theories contain unacceptable assumptions. This paper details the invalid approximations made in each theory. The direction and magnitude of the important errors are estimated for these models when applied to scrubber stack plumes.