I
Emission Factors for a Feed Mill or Grain Elevator

The primary pollutant of concern for grain elevators and feed mills is particulate matter (PM). In general, these emissions are like those shown in Figure 4-2. The entrainment of PM in air is a consequence of pneumatic conveying and ventilation systems designed to prevent grain dust explosions by reducing concentrations of grain dust. Typically, controls are installed to reduce PM emission rates. The mass emission rate (Mi) for each exhaust i is determined by its PM concentration (Ci) (measured by source sampling) and its flow rate (Qi) as follows:

Mi = Ci × Qi,

where the terms in the equation have units shown in parentheses: Mi (mass per unit time), Ci (mass per unit volume), and Qi (volume per unit time).

An emission factor (EFi) is determined from Mi and the processing rate (PRi):

where EFi is a dimensionless number (mass of pollutant per mass of feed or grain processed) and PRi has units of mass per unit time.

Source sampling for PM10 from an emission point is accomplished using pre-collectors in series with a filter. The pre-collector for PM10 sampling will typically have a fractional efficiency curve that is log normal with a 50 percent



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OCR for page 226
Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs I Emission Factors for a Feed Mill or Grain Elevator The primary pollutant of concern for grain elevators and feed mills is particulate matter (PM). In general, these emissions are like those shown in Figure 4-2. The entrainment of PM in air is a consequence of pneumatic conveying and ventilation systems designed to prevent grain dust explosions by reducing concentrations of grain dust. Typically, controls are installed to reduce PM emission rates. The mass emission rate (Mi) for each exhaust i is determined by its PM concentration (Ci) (measured by source sampling) and its flow rate (Qi) as follows: Mi = Ci × Qi, where the terms in the equation have units shown in parentheses: Mi (mass per unit time), Ci (mass per unit volume), and Qi (volume per unit time). An emission factor (EFi) is determined from Mi and the processing rate (PRi): where EFi is a dimensionless number (mass of pollutant per mass of feed or grain processed) and PRi has units of mass per unit time. Source sampling for PM10 from an emission point is accomplished using pre-collectors in series with a filter. The pre-collector for PM10 sampling will typically have a fractional efficiency curve that is log normal with a 50 percent

OCR for page 226
Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs collection efficiency (cut-point) of 10 ±1 μm aerodynamic equivalent diameter and a slope (d84.1/d50) of 1.5. This relatively flat penetration curve results in significant PM10 concentration measurement errors, which will ultimately result in incorrect emission factors.