Technology
The Plume-RT modelling system combines the CALMET and CALPUFF meteorological and dispersion models with digital terrain data, local meteorology and regional weather forecasts to create realistic on-line animations and reports showing current and predicted ground-level contaminant concentrations. Modelling results are provided for the current hour as well as 24-hour forecasts. All weather and modelling results are stored in a database for reporting.
CALMET is a meteorological model that produces hourly wind and temperature fields on a three-dimensional gridded modelling domain and provides realistic estimates of wind flow accounting for complex terrain features (Earth Tech, 2000a www.src.com). The CALMET model uses ground station meteorological data and the ETA and RUC meteorological upper air data available from the National Centers for Environmental Prediction (NCEP – www.ncep.noaa.gov). From this point, CALMET uses the three dimensional terrain data, local real-time meteorology, and upper air data to produce three dimensional wind and temperature fields over the modelling domain.
CALPUFF is a transport and dispersion model that advects "puffs" of material emitted from modelled sources, simulating dispersion and transformation processes along the way (Earth Tech, 2000b www.src.com). A web-based interface inputs the source characteristics as a gas composition, flare stack location, stack height and inside diameter, flow rate, and elevation. Specific points of interest (landowners, roads, schools, wildlife reserves, etc) can be added to predict ground-level contaminant concentrations at desired locations.
The CALPUFF modelling results are available to the client by email or through a secure web interface as a series of animations and reports:
- Animation of ground level SO2 concentrations
- Maximum SO2 concentration contour plots
- Frequency distribution plots and tables
- Time-series graph for the discrete receptors
All of the data is stored in a Microsoft SQL database and can be queried to produce customized information at the request of the client. This data can also be used to run post-event modelling outside of the Plume-RT system.
The Plume-RT modelling system provides predictions of SO2 concentrations based on the source conditions and meteorological conditions input into the model and assuming that a release is occurring continuously. Model results are available that represent the actual last-hour conditions as well as next-hour forecast conditions (up to a maximum of 24 hours).
The modelling process consists of the following steps:
Step 1: Model Setup
Qualified RWDI personnel set up and configure Plume-RT based on the following information provided by the client:
- Location of the modelling domain
- Size and granularity of the modelling domain
- Inventory of emission sources
- Specific points of interest are identified
Step 2: Capture Weather Information
Plume-RT is then configued to capture local weather information by deploying one or more on-site meteorological towers to locations within the modelling domain. These ground stations send measured weather information to our system at predefined time intervals where it is then stored in the Plume-RT database. RWDI will provide a list of companies that can supply ground stations that have been certified to work with the Plume-RT system.
Regional Weather forecast information is supplied to Plume-RT by the National Centers for Environmental Prediction (NCEP). NCEP provides an 84 hour weather forecast over the modelling domain that is updated every 3 hours. The weather forecast is also stored in the Plume-RT database.
Step 3: Run the Dispersion Model
Once the meteorological data has arrived at the Plume-RT data center the CALMET/CALPUFF dispersion model is executed. The model will use the current ground station meteorological data and the upper air weather forecast information to calculate ground-level SO2 concentrations for the current hour. Plume-RT will then compute ground-level SO2 concentrations for the next 24 hours using the weather forecast information. All modelling results are stored in the Plume-RT database.
Alternatively, "what-if" scenarios may be submitted to the Plume-RT system to predict ground-level SO2 concentrations based on current and forecasted meteorology and alternative release rates, percentage of fuel gas usage and H2S content.
Step 4: Report the Modelling Results
Modelling results are accessible to the client by automatic email or a secure web interface l
The types of reports available are:
- By Email
- Maximum ground-level SO2 concentrations
- Image of the maximum ground-level SO2 concentrations
- Regional Weather forecasts
- Maximum ground-level SO2 animation
- By Web Interface
- Image of the maximum ground-level SO2 concentrations
- Maximum ground-level SO2 animation
- Time-series SO2 at points of interest
- Count of the number of exceedences at the points of interest
- Exceedence count table
As part of the Plume-RT product, RWDI has a 24/7 on-call person that can assist with the interpretation of the modelling results, and flare management plans where the system is being used. This on-call person ensures that the system is running during the work program and can adjust the configuration of the project or add additional scenario configurations at the request of on-site or other designated people.
