CFD Simulation for Exhaust Gas Dispersion to Control Industrial Emissions
Posted by: Mehul Patel | Posted on: December 20th, 2014
Exhaust gas streams emitting from industrial process plants consist of harmful pollutants, which are carried away for sufficiently large distances from the source. The control of these pollutants dispersion is mandatory to avoid spreading of toxic gases into urban areas nearer to plant locations.
There are several regulations issued by government and environment protection agencies that define the pollutant concentration limits in the ambient air or in gaseous emissions. As such, predicting the exhaust gas dispersion into atmosphere is essentially required in order to tune the equipments and exhaust systems, so that the pollutant concentrations remain at an acceptable level.
The utilization of CFD remains a versatile solution to simulate the pollutant dispersion into the ambient atmosphere. There has been a wide research in development of mathematical models to simulate particle dispersion, plume visibility, and odor. However, establishing a CFD model requires comprehensive understanding about the parameters that affect the gas dispersion.
Developing the CFD Model:
CFD simulation requires setting up of physics, boundary conditions and meshing, in order to obtain meaningful results. For a case of exhaust gas dispersion from industrial stacks, it is important to define the geometry and develop an atmospheric domain to capture the flow emitting from the stack. It is also required to select the flow model, which in this case is usually compressible governed by conservation of energy, momentum and species.
To successfully simulate the plume and its visibility, it is also required to select appropriate turbulence models. The use of standard k-ε turbulence model is capable to capture the flow consisting of low turbulence; however, for cases involving high turbulence flows, SST k-ω provides more detailed solution on the effect of turbulence and its dissipation.
Since the exhaust gas stream will also consist of particle dispersion, a separate model is also required to simulate this effect. The discrete phase model is required in this case to determine particle trajectories considering the inertia and drag forces. Also, the dispersion of the gas into the atmosphere will largely depend on the wind profile.
As such, it is required to setup the profile using empirical relations based on logarithmic scales. Apart from the requisites mentioned, the inlet and outlet flow conditions are required to define the boundary conditions.
Visualizing the Results:
The results obtained through CFD simulations can be visualized by plotting different parameters such as velocity distribution, temperature distribution and pollutant concentration. Visualizing the plume and particle concentration can be plotted by using empirical relations available such as PPMV (parts per million by volume), which is a usual measure for air pollutant concentration. Depending on the results, the industrial equipments responsible for the exhaust emission can be tuned, or the pollution control systems can be altered subsequently.
While CFD results provide an approximate information on the dispersion phenomenon, it is always better to perform experimental tests to validate the CFD data, and later implement design changes.
About Author: Mehul Patel specializes in handling CFD projects for Automobile, Aerospace, Oil and Gas and building HVAC sectors. He works as a CFD consultant with Hi-Tech CFD for the past 5 years and has successfully executed numerous CFD projects of high complexities. He is an expert in turbo-machinery, gas dynamics, Combustion, Fluid Dynamics, multiphase flow analysis, computational fluid dynamics etc.