In industry, there are terms and elements that play a crucial role in the operation of various installations. One of these essentially important concepts is the “plume”. However, to understand what plumes are in industry, we must first have a prior understanding of the role played by industrial chimneys.
Industrial chimneys are structures that have the specific purpose of providing an outlet for gases generated during combustion processes, chemical reactions or drying processes, among others.
These gases, called tail gases, have contaminants that require removal. Although an attempt is made to purify these gases as much as possible before releasing them, a certain concentration inevitably remains.
The direct release of these pollutants at ground level would be very harmful, as the pollutants would reach the earth’s surface in a concentrated form. For this reason, chimneys play a key role, since, thanks to their great height, these structures ensure that gases are dispersed at an adequate elevation.
And it is the visual result of this process that we call the plume. This smoke plume, which is transported in the atmosphere, is a phenomenon that depends on both the emission conditions and the nature of the receiving atmosphere .
Plumes can have different shapes and sizes, reflecting the different conditions of origin and the atmospheric variables that influence their formation.
What are the phases of plumes in the industry?
Plumes in the industry are formed by different phases, which depend on the emission conditions and the receiving atmosphere. These phases are:
Issuance phase
This first phase occurs when the combustible material comes into contact with air and an exothermic reaction takes place. This phase depends on the superelevation, i.e. the difference between the air temperature and the temperature of the combustible material. If this difference is large, the combustible material burns faster and generates more gases and particles that can form the plume.
The exit velocity and temperature of the gases also influence the emission phase. If the gases exit very fast or have a very high temperature, they can create turbulence that favors the dispersion of smoke in the atmosphere.
Transition phase
In this phase, the plume changes its direction and temperature due to the action of the air, until it stops ascending.
This occurs because, upon contact with the atmospheric temperature, the plume cools and loses buoyancy, that is, the ability to stay aloft.
Developed plume stage
In its last phase, the plume has a more defined shape and its composition and trajectory can be better appreciated. It rotates in the direction in which the wind blows and with the wind speed, which determines its horizontal dispersion.
In addition, the plume has a higher concentration of combustible material than the circulating air, as it comes from upstream pollutants, which determines its vertical dispersion.
However, as mentioned above, the shape of the plume developed depends on the characteristics of the atmosphere in which it is emitted, such as temperature, pressure, humidity and stability. Therefore, according to these characteristics, the following types of tufts can be distinguished:
Conical plume
It originates when both the air and the plume have the same temperature. In this case, the plume does not experience any force that drives it in a vertical direction, either upward or downward.
Its movement is due solely to the inertia of the source, adopting a conical shape and being distributed uniformly in all directions.
Source: https://www.euskadi.eus/gobierno-vasco//contenidos/informacion/com_turbulencias/es_7764/es_turbulencia.html
Serpentine plume
It forms when the atmosphere is unstable, which means that there are conditions that favor vertical mixing. In this case, the plume follows a path with turbulent variations over time due to these conditions.
Source: https://www.euskadi.eus/gobierno-vasco//contenidos/informacion/com_turbulencias/es_7764/es_turbulencia.html
Tubular plume
They appear when the environment is stable. That is, when the temperature changes smoothly with altitude and there is no turbulence caused by the wind. Under these conditions, if the density of the plume is not very different from that of the surrounding air, the plume moves with the wind at a constant altitude.
Source: https://www.euskadi.eus/gobierno-vasco//contenidos/informacion/com_turbulencias/es_7764/es_turbulencia.html
Fumigant plume
A fumigant plume may originate due to certain thermal inversion conditions. This situation occurs when there is a stable layer of air located a short distance above the emission source, while below the plume there is an unstable layer. This combination results in the formation of a plume that will move over the ground surface.
Antifumigant plume
In this case, the thermal inversion is the opposite of the previous one. It occurs when the inversion layer is located below the plume, and the unstable layer is located above it.
This results in a plume that acts as a barrier, preventing significant concentrations of contaminants from reaching ground level.
Conclusion of plumes in the industry
Industrial plumes, those columns of smoke rising from smokestacks, are the result of complex processes involving the emission of gases and interaction with the atmosphere. Their shape, color and size vary according to environmental conditions, making them visual indicators of air quality.
The best way to treat plumes is to prevent them from forming, for which there are techniques such as the hygroscopic cycle, which considerably reduces emissions in industrial processes, while recovering water and part of the energy emitted into the atmosphere.
