Module 3: Characteristics of Particles Particle Formation - Practice Problems

Instructions:: Work these problems on a sheet of paper and check your answers against those provided below.

#1

Describe each of the following particle formation processes.

: Answer: i.; In physical attrition, particles are created as a result of two surfaces rubbing together. The composition and densities of these particles are identical to the parent material.; Answer: ii.; During combustion, most of the organic compounds in the fuel are vaporized and oxidized in the gas stream leaving behind much smaller particles composed of incombustible matter (ash) and char.; Answer: iii.; The process by which vapor-phase materials convert to a particulate form upon reaching their dew points. In homogeneous nucleation, the new particles are composed of one compound.; Answer: iv.; Heterogeneous nucleation is the process by which one or more vapor-phase materials upon reaching their dew points, accumulate on the surfaces of existing particles.; Answer: v.; Droplet evaporation is a particle formation mechanism that can occur in air pollution control systems that recycle solids-containing water from scrubbers to cool gas streams. The small droplets, formed when recycled water streams are atomized into the hot gas streams, evaporate to dryness and release the suspended and dissolved solids as small particles.

#2

Select the particle formation mechanism that would most likely produce the particles described in items (i) through (vii) below.

Particle Formation Mechanisms

Particles resulting from the evaporation of recycled scrubbing liquid used to cool gas streams.
Particles created remain as solids and are identical in composition and density to the material in the process from which they were formed.
Particles created are approximately 500 to 1000 micrometers in size.
Particles that result from burning pulverized coal.
Toxic particles formed by enrichment.
Particles emitted by a stone crusher, coal pulverizer, or oil atomizer.
Previously nonexistent particles formed from mercury vapor as the gas stream is cooled.

: Answer: i. b. 10 - 1000; Physical attrition usually forms particles in the size range from 10 to 1000 micrometers.; Answer: ii. c. 1 - 100; Combustion particle burnout usually forms particles in the size range from 1 to 100 micrometers.; Answer: iii. d. 0.1 - 1; Homogeneous and heterogeneous nucleation usually form particles in the size range from 0.1 to 1 micrometer.; Answer: iv. a. 0.1 - 20; Droplet evaporation usually forms particles in the size range from 0.1 to 20 micrometers.

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Particle Formation

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Collection Mechanisms