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Module 6: Air Pollutants and Control Techniques - Particulate Matter - Formation Mechanisms
Lesson Material
Practice
Problems
Objective
- Describe four basic mechanisms of particle formation.
The manner in which particles are formed determines the size and composition of particles. The four main mechanisms of particulate matter formation described in Module 3 are listed below.
- Physical attrition
- Combustion particle burnout
- Homogeneous nucleation and heterogeneous nucleation of vapor phase
compounds in hot gas streams
- Release of solids during the evaporation of solids-containing droplets
in hot gas streams (Droplet evaporation)
Physical attrition occurs when two surfaces rub together. The composition and density of the particles formed are identical to the parent material and range in size from less than 10 micrometers to almost 1,000 micrometers.
Combustion particle burnout occurs when fuel particles are injected into the hot furnace area of a combustion process and, as the combustion progresses, are reduced to ash and char particles that are primarily in the 1- to 100-micrometer size range.
Homogeneous nucleation and heterogeneous nucleation involve the conversion of vapor phase materials to a particulate form. Homogeneous and heterogeneous nucleation generally create particles that are very small, often between 0.1 and 1.0 micrometer.
Droplet evaporation is caused by air pollution control systems that use solids-containing water recycled from wet scrubbers to cool the gas streams. The water streams are atomized during injection into the hot gas streams and, as these small droplets evaporate to dryness, the suspended and dissolved solids are released as small particles.
For more information on these formation mechanisms, refer to the lesson on Particle Formation in Module 3.
Practice Problems
Particulate Matter - Formation Mechanisms
- Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.