37 Questions
What is the principal motivation for the control of dust emissions mentioned in the text?
Environmental and health concerns
Which of the following operations is NOT mentioned as a potential source of high dust concentrations?
Melting
What has become of prime importance since the Health and Safety at Work Act became law?
Avoidance of excessive environmental pollution
What type of product would require extreme measures to prevent its escape from the plant?
Toxic or explosive
What is the primary function of extractor hoods in industrial environments?
Capture dust from external forces and collect dust that would not enter it
What is the primary function of gravity chambers in industrial environments?
Separate solid material from a gas stream by reducing velocity and increasing residence time for particles to fall out under gravity
What is the most common type of cyclone used to separate particles from a gas stream?
Cone-shaped reverse-flow cyclones
What factors affect cyclone efficiency?
Particle density, size, separator's geometry, and pressure drop
What is pressure drop in the context of cyclone separators?
The amount of energy required to move gas through the separator, influenced by gas flow rate, density, and geometry
What is a disadvantage of large cyclone separators?
Lower efficiency rating and lower pressure drop
What is an advantage of cyclones as dust control equipment?
Low maintenance, suitability for high temperatures and liquid mists, and minimal space requirement
What is the primary function of wet scrubbers in industrial environments?
Remove particulate matter from gas streams by capturing them in liquid droplets, which are then collected by absorption
When is absorption in wet scrubbers effective for controlling pollutant gases?
In substantial concentrations and dilute concentrations when the gas is highly soluble in the absorbent
What is a disadvantage of wet scrubbers as dust control equipment?
Increased operating costs with high pressure drops
What are wet scrubbers feasible for in terms of controlling pollutant gases?
Dilute concentrations when highly soluble in the absorbent
What are the three major hazards posed by dust emission in mining environments?
Respiratory effects, skin and eye effects, and fire and explosion
Which type of dust particles are the most hazardous for the lungs?
0.2 - 5 um in diameter
How can dust enter the body, leading to various health issues?
Inhalation, skin absorption, and ingestion
What influences dust deposition in the lungs?
Size of particles and their biological action
How are dusts classified based on their biological action?
Inert, toxic, allergenic, and fibrogenic
What are the defined limits for dust concentration?
Time-weighed average, short-term exposure limit, and threshold limit ceiling
What is the best solution to the problem of dust in manufacturing processes?
Dust suppression and elimination
What is 'dustability' as mentioned in the text?
The tendency of particles to become airborne
Which operations contribute to dust generation in mining environments?
Crushing, grinding, and pneumatic conveying
What is essential to keep dust away from personnel and prevent its escape into the environment?
Methods of controlling dust dispersion
What are effective approaches for controlling dust dispersion, especially in environments presenting an explosion hazard?
Total enclosure or partial enclosure with an exhaust system
What is the purpose of wet washers or scrubbers in air cleaning?
To use water as an absorbent for air cleaning
When are non-aqueous liquids used for air cleaning?
For gases with low water solubility, such as hydrocarbons or hydrogen sulfide
What is the purpose of electrically augmented scrubbers in air cleaning?
To reduce high-power usage of wet dust collectors
How do filters depend on particle size for collection?
Using screens or fabric filter bags
What is the function of electrostatic precipitators in air cleaning?
To remove particles using a high-voltage field
What is the relationship between the area of the collecting electrodes and collecting efficiency in electrostatic precipitators?
Collecting efficiency varies exponentially with the area of the collecting electrodes
What is the trend of capital cost for an electrostatic precipitator with respect to its size?
The capital cost increases with size
What are the conditions required for a dust explosion to occur?
A suspension of combustible dust, an ignition source, and sufficient oxygen
What can ignite dust clouds?
Temperatures as low as 200°C
How can the disastrous effects of a dust explosion be avoided?
By dividing the plant into small separate volumes to prevent the propagation of explosions
What is the range of topics covered in the course?
Topics such as the generation of dust, hazard associated with dust emission, dust suppression, and air cleaners
Study Notes
Industrial Air Cleaning and Dust Explosion Hazards
- Wet washers or scrubbers are commonly used for air cleaning, using water as an absorbent, which may contain other chemicals to react with the gas being absorbed.
- Non-aqueous liquids may be used for gases with low water solubility, such as hydrocarbons or hydrogen sulfide.
- To reduce high-power usage of wet dust collectors, electrically augmented scrubbers, two- or three-stage venturi scrubbers, and bubble foam scrubbers are used.
- Filters depend on particle size for collection, using screens or fabric filter bags, and require regular cleaning for improved collecting efficiency.
- Electrostatic precipitators involve passing dusty gas through a high-voltage field to remove particles, with collecting efficiency varying exponentially with the area of the collecting electrodes.
- The capital cost of an electrostatic precipitator is high and increases with size, but the operating costs are relatively small.
- Dust explosions result from high concentrations of combustible dust particles suspended in the air, which can be ignited by a spark or other ignition source.
- A wide range of particulate solids pose an explosion hazard, and three conditions must exist before an explosion can occur: a suspension of combustible dust, an ignition source, and sufficient oxygen.
- Minimizing the hazard involves eliminating dust clouds and sources of ignition, but complete elimination of ignition sources is impossible.
- Dust clouds can be ignited by temperatures as low as 200°C, and high temperatures and open flames encountered in processing operations or during maintenance can ignite dust clouds.
- To avoid the disastrous effects of an explosion, the plant should be divided into small separate volumes to prevent the propagation of explosions.
- The course covers topics such as the generation of dust, hazard associated with dust emission, dust suppression, elimination of dust, dust dispersion control, air cleaners, and dust explosion.
Test your knowledge of industrial air cleaning and dust explosion hazards with this quiz. Learn about wet washers, non-aqueous liquids, filters, electrostatic precipitators, and the conditions required for dust explosions. Explore ways to minimize the hazard and prevent the propagation of explosions in industrial settings.
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