Plume Visibility and Icing Study for Mechanical Draft Cooling Towers at a 600 MW CoalFired Power Plant

摘要

Under the requirements of the New Source Review (NSR) regulations1, all power generation facilities in the U.S. Must conduct emissions modeling studies to demonstrate compliance with applicable ambient air quality standards and increments. Emissions modeling often results in adjustments to stack and building parameters such as stack height, exit temperature, stack location, and building orientation in order to avoid or minimize air quality impacts. Modeling of cooling tower particulates, along with other particulate emission sources, is required to assess localized impacts of PM10 and PM2.5 emissions. Additional modeling is also required to assess the impairment to visibility at critical locations (e.g. Class I areas). In order to address public concerns, it is becoming more common to include an evaluation of localized condensed cooling tower plume visibility impairment and icing to existing roadways. Modeling for singlephase pollutant emissions is straightforward with U.S. EPA’s AERMOD dispersion model2, but no similar model exists for the twophase emissions (vapor and liquid water) from a cooling tower. In order to predict and understand the potential fogging and icing impacts of a cooling tower at a facility in the development stages, a new modeling methodology was developed. This paper presents the fourphased approach for cooling tower modeling. The four phases consisted of: (1) Meteorological data preprocessing to determine typical ambient cases (temperature and relative humidity), which were utilized to develop cooling tower performance operating scenarios (temperature and exit velocity); (2) Modeling of cooling tower water vapor for the various scenarios using the widely recognized AERMOD atmospheric dispersion model; (3) Use of postprocessing algorithms to predict visible fog formation at roadway receptors taking into account the hourbyhour ambient conditions, the interaction of the plume with the ambient atmosphere, the conversion of water vapor to liquid water, and, the dispersion of both the water vapor and liquid water content of the plume; and, (4) Calculation of deposition rates and ground temperatures to quantify the potential for ice formation. The results of the modeling were used to assess frequency and duration of fogging and icing events in comparison to normal fogging/icing events in the absence of the facility.