Particulate Measurement and Control Devices for Hot Mix Asphalt Plants

About the report:

The emission of particulates is the main form of air pollution from hot mix asphalt plants. The measurement of these emissions in the ambient air may be used by the state and the plant personnel to monitor the quality of air in the area of a plant. Source sampling can be used to determine the amount of pollution created by a given source. If the amount of emissions is not in compliance with state standards, control devices must be selected and deployed. The collection of particulates is based on one or more physical laws relating a solid particle to the air stream. The recommended collectors for ambient air measurements are: (1) the high volume sampler, which filters the air; and (2) the dust collector, which collects only the large particles that fall out of the atmosphere due to gravity. Source sampling is done with a "train," which vacuums the air out of the stack into a collection device. These collection devices normally comprise a combination of impingers and filters. Collection for control is normally accomplished by use of a series of devices of successively increasing efficiency so arranged to minimize the load on each device. The primary collectors (cyclones, mechanical collectors, and settling chambers) remove up to 90% of the particles, including all of the large ones, so that the secondary collectors (bag filters, scrubbers, and electrostatic precipitators) may operate at peak efficiency to remove the submicron particles. The degree of efficiency required of the secondary collectors is determined primarily by the stringency of the control standards and costs.

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