WetPlume
A model for simulating the formation, size, timing, and direction of visible plumes from high-moisture emissions.Plumes emitted by plants such as cooling towers, dryers, and desulphurization units can contain a high amount of water vapor. Under suitable meteorological conditions, that vapor condenses and the plume becomes visible.
WetPlume is an Enviroware model for simulating visible plume formation and size. It estimates the size distribution and the monthly and hourly time distribution of visible plume events, supporting visibility impact studies and comparisons among operating scenarios.
The model is written in Fortran and is used from the command prompt. Its hourly output describes plume properties and is typically evaluated with dedicated post-processors.
Directional distribution of visible plume lengths, shown with a rose-style chart.
Why a specific wet plume model is needed
Stack flue gas is usually warmer and more humid than ambient air. As the plume rises and bends with the wind, it entrains ambient air, dilutes, cools, and may reach saturation. When condensation occurs, the liquid water content can make part of the plume visible.
Classical dry-plume-rise algorithms do not include the thermodynamics needed to represent condensation and latent heat release. At the same time, many wet-plume models were developed for cooling towers and include assumptions that are not always suitable for stack emissions, where exit velocity, temperature difference, stack diameter, and plume buoyancy can be very different.
WetPlume was developed for moist stack plumes and is used to support visibility impact assessments, including cases where the study must compare alternative operating conditions such as flue-gas water content, exit temperature, or exit velocity.
Input data
Source
- Stack coordinates, height, and diameter
- Exit velocity and exit temperature
- Water content of the flue gas, expressed as g H2O per kg of flue gas
Meteorology
AERMOD format
- Wind speed and wind direction
- Ambient temperature
- Relative humidity
- Atmospheric pressure
Visibility assessment studies
WetPlume can be applied to determine the distribution of visible plume length and height, the average percentage of visible-plume occurrence by month and hour of the day, and the possible occurrence of plume-induced fogging or icing when the visible plume reaches the ground.
These indicators can be evaluated for different emission scenarios to identify operating conditions that reduce the number of visible events and the size of the visible plume.
Results
WetPlume results are commonly summarized in Excel workbooks and charts. Typical outputs include the main input and output data, the statistical distribution of visible plume events by month and hour, and the distribution of visible plume lengths.
Percentage of hours with visible plume for each month.
Hourly distribution of visible plume events.
Distribution of visible plume lengths.
Section of the visible plume for a specific hour.
Plume centerline temperature as a function of downwind distance.
Example summary of main input and output data.
Sensitivity examples
The visible portion of a moist plume is strongly influenced by ambient humidity, flue-gas exit temperature, and flue-gas specific humidity. WetPlume can be used to compare these effects while keeping the other environmental and release parameters fixed.
Effect of ambient relative humidity on the visible plume.
Effect of flue-gas exit temperature on the visible plume.
Effect of flue-gas specific humidity on the visible plume.
Reference
The model formulation and validation are described in Presotto L., Bellasio R. and Bianconi R. (2005), Assessment of the visibility impact of a plume emitted by a desulphuration plant, Atmospheric Environment, 39(4), 719-737.