Variability of Natural Dust Erosion from a Coal Pile

Abstract

A study of fugitive dust emissions from a pile of crushed coal revealed that, in addition to dust being emitted into the atmosphere during periods of pile-management (human) activity, it is also emitted during periods without human activity. This ''natural'' emission in itself is not surprising given past work on wind erosion of particulate matter from aggregate piles. However, hourly downwind measurements of fine particle (PM 10 ) mass concentrations at two sites revealed that excessive dust was present in the air even when wind speeds were below the erosion threshold estimated from nearby wind speed measurements and regulatory guidance on coal pile aerodynamic characteristics. During periods of natural emissions with higher wind speeds, downwind concentrations were strongly associated with m 2 -the squared excess of 1-min maximum wind speed above the erosion threshold-consistent with previous work on wind erosion potential. However, 88% of hourly concentrations coincided with lower winds for which wind speed was not a good predictor of airborne dust levels. Evidence was found that natural low-wind PM 10 concentrations varied significantly with relative humidity, air temperature, and turbulence parameters (s u and s w ). Smoke from coal combustion was ruled out as a significant factor in PM 10 levels, but statistical evidence along with visual observation suggests that microscale turbulent airflows, including dust devils, were a significant source of PM 10 during low wind speeds over the pile. The localized behavior of the turbulence makes it very difficult to develop a strong statistical model of natural downwind concentrations on the basis of off-pile meteorological measurements.

Evaluación del CALPUFF para Estimar Concentraciones Ambientales de PM 10 de una Cantera en Terrenos Complejos

“…Las mayores emisiones se realizan durante horas solares en operaciones normales de la cantera, en horas nocturnas las emisiones están limitadas a pilas de almacenamiento y áreas expuestas a erosión. Para emisiones de PM10 por procesos naturales, erosión en pilas y áreas expuestas, las velocidades del viento debe superar la velocidad umbral de fricción (Mueller et al, 2015). Las emisiones por procesos naturales son insignificantes comparadas con las actividades de operaciones de la cantera.…”

Emission factors for fugitive dust from bulldozers working on a coal pile

“…(i.e., the time period experiencing the lowest amount of natural emissions). Consequently, most hours experiencing bulldozer activity coincide with the midday maximum for natural emissions or the late afternoon/evening period when higher wind speeds made it more likely that wind erosion contributed to dust emissions from the pile (Mueller et al, 2015). The highest observed PM 10 concentrations were near or above 1000 µg m −3 and were typically associated with bulldozer activity.…”

“…The preponderance of nonzero C xs * for hours without activity implies a "natural" source of particle emissions. Mueller et al (2015) identified wind erosion and the action of microscale turbulence (a smaller scale form of wind erosion) on the coal pile as the most probable sources of natural fugitive emissions. AP-42 lists three different values for friction velocity (u*) erosion thresholds associated with coal: 0.55 m s −1 for ground coal, 0.62 m s −1 for scraper tracks on a coal pile, and 1.12 m s −1 for an uncrusted coal pile.…”

“…Natural dust emissions are described at length by Mueller et al (2015) for this site. Their primary finding was that natural processes at the study site produced significant downwind particulate concentrations that could not be ignored when using ambient measurements to determine fugitive emissions from anthropogenic activity.…”

Reducing Environmental Impact of Coal-Fired Power Plants by Building an Indoor Coal Storage: An Economic Analysis

“…Furthermore, they examined the influence of wind speed, humidity, air temperature, and turbulence on the concentration of dust. Similarly, Muller et al [18] examined the effect of the bulldozer movement, which is a representative human activity in a coal yard, on coal dust emissions.…”