How can we predict flue gas dispersion?Author Timo Kulju
When designing a new energy production plant, it has become increasingly important to pay attention to the effects the plant operations will have on the surrounding environment. This is partly due to the fact that it is already required by law. It is, however, also a good idea to conduct such studies in order to gain general acceptance for the operations. One aspect that needs to be clarified in such studies is how flue gas disperses into the surrounding environment.
The most harmful components in flue gas to human health and the environment are nitrogen oxides, sulphur dioxide and particle matter. Concentration levels of these elements are limited at the emissions source by Finnish legislation (e.g. PIPO or SUPO decrees). Emissions concentration levels in the environment, on the other hand, are regulated by air quality legislation (e.g. decree 79/2017).
Already while designing a new plant computational fluid dynamics (CFD) can be used to study how emissions will spread into the environment. With the aid of modelling very accurate predictions can be obtained quickly, which aids in gaining support for the operations from surrounding communities.
Local wind conditions, the location of the emissions source and surrounding flow barriers (buildings, trees) are significant factors in emissions’ spread as they affect air flows and, therefore, the movement of emissions. All these factors can be taken into consideration in modelling. This allows emissions dispersion to be modelled under different conditions and plant environments.
If modelling reveals that emissions concentration levels are too high, appropriate preventative actions can be taken. These include, for example, dimensioning the height of chimneys or changing their location. The goal is to find a solution that allows emissions to disperse at sufficient heights so that the fallout on the ground remains below levels required by legislation. This also promotes the general acceptance of plant operations.
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