Abstract
The dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions.
Highlights
Plume dispersion has been a significant field of study to understand and monitor the effects of air pollution [1, 2]
The effect of the stack configuration and the negative atmospheric temperature gradient upon the plume rise and dispersion have been enlisted below: 1. At a given atmospheric temperature gradient, the inline configuration shows the highest plume rise compared with the 45° layout and the non-inline
This is because of the shielding of the downwind jet, by its upwind counterpart which allows slower cooling of the plumes emitted by the downwind plume and allows for higher plume rise
Summary
Plume dispersion has been a significant field of study to understand and monitor the effects of air pollution [1, 2]. Some of the major pollutants present in flue gases are carbon monoxide, sulphur dioxide, nitrogen monoxide and nitrogen dioxide. They are emitted after combustion from various industries into the atmosphere. The pollutant dispersion is affected by various factors like flue stack height, plume exit velocity from the stack, atmospheric conditions, the distance between the flue stack exits, wind velocity and direction and stack layout. The temperature gradient is −0.6 K/100 m altitudinal increase in a large-scale normal atmosphere. In the region close to the ground due to convection (i.e. less than 500 m), the temperature gradient variation is highly dependent on the several local meteorological
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