Industrial Air Pollution and Cotol

Question 1

Primary industries

Answer 1

Provide raw material - diary, beef and sheep farming, forestry, fisheries and horticulture, coal mining, aggregate /mineral mining quarry’s

Question 2

Secondary industries

Answer 2

Manufacturing products out of raw material - heat and dairy export, fish and other food products, timber and concrete, coal power (for local use).

Question 3

What major industries are dust emitting

Answer 3

Coal miring, aggregate mineral mining, timber and concrete, coal power

Question 4

4 major air polluting industries

Answer 4

Coal power plant, cement, mining, waste incineration (global)

Question 5

Flue gas

Answer 5

Gas stream that carries the fire particles → need to separate these particles from the gas stream

Question 6

Particle collection mechanism

Answer 6

An external force must be applied to enable the particle to develop a velocity that will displace it and for direct it to a collection or retrieval area. The particles should be retained in this area with forces strong enough to prevent re-entrainment. Collected recovered particles should be subsequently removed. These particles should be disposed recovered or reused.

Question 7

Forces that can be used for particle recovery and collection / mechanisms to separate fine particles from flue gas streams.

Answer 7

Gravity (gravity settler), wet scrubbing (wet scrubber), filtration (bag filter), centrifugal action (cyclone separater), electrostatic attraction (electrostatic precipatator).

Question 8

Gravity settler

Answer 8

Low efficiency, usually below 50%, effective for larger sized particles > 50 um. Low power requirement as it uses gravity for separation. Large space required as the separating chambers can be bulky.

Question 9

Horizontal flow settling chamber

Answer 9

When gas stream enters the expansion section of the duct, the expansion of the gas stream causes the gas velocity to be reduced, and particles are separated by the force of gravity. Low velocity and law pressure drop maintained.

Question 10

Multiple (Howard) tray settling chamber

Answer 10

Shortens the length of the settling path and improves collection efficiency. Diffulcut to clean and not suitable for high temperature applications.

Question 11

Baffle chamber (inertial separator)

Answer 11

Baffles within the chamber enhance particle separation and collection. This happens by changing the direction of the gas velocity and imparting a downward motion to the particle. Particles as small as 20-40 um can be collected.

Question 12

4 types of wet scrubber

Answer 12

Tray scrubber, packed tower, Venturi scrubber, quencher (spray tower)

Question 13

Wet scrubber

Answer 13

Moderate efficiency 50-99%, works for fine and course particles 0.5 - um. Moderate to high power requirement, requires energy for pumps and fans.

Question 14

Filter bag house

Answer 14

99%+ efficiency, effective for particles <10 um, high power requirement, fans and cleaning systems require energy, large space requirement.

Question 15

Impaction and interception

Answer 15

Force applied in a bag filter to separate particles from gas stream

Question 16

Important process variables for bag filters

Answer 16

Particle characteristics, gas characteristics, fabric properties. The most important design parameter is gas to cloth ratio. Most important operating parameter is the pressure drop across the filter (important to clean filter)

Question 17

Types of filter bags cleaning

Answer 17

Shaker cleaning, reverse flow type

Question 18

Cyclone separator

Answer 18

Moderate efficiency 70 - 90% effective for particles >10 um, low power requirement. The shape / curvature of the collector causes the gas stream to rotate in a spiral motion. Larger heavy particles are pushed outwards, pressure drop created, particles loose their kinetic energy and are separated from the gas stream. Clea air enters a second spiral movement and exit from the top.

Question 19

Particle cut diameter

Answer 19

Size of a particle that you can collect with 50% efficiency using a cyclone separator e.g. 1 um 50% efficiency is really good.

Question 20

Types of cyclone separators

Answer 20

High efficiency- have the highest pressure drop but fine particles are collected. High throughput - designed to treat large volumes of gas with a low pressure drop. Fine particles can escape

Question 21

Electrostatic precipitator

Answer 21

Uses electrostatic attraction, charged particles migrate to an oppositely charged collection surface. Very efficient, > 99% efficiency, captures PM I0 and PM 2.5 fine particles takes up lots of space

Question 22

Summary particle collection efficiency

Answer 22

Electrostatic precipitators and filter bag houses offer the highest efficiency, while gravity settlers have the lowest

Question 23

Summary power requirement

Answer 23

Gravity settlers and cyclone separators generally have lower power demands compared to electrostatic precipitators and filter bag houses,

Question 24

Summary space requirement

Answer 24

Gravity settlers and electrostatic precipitators usually require the most space due to their size and design, whereas wet scrubbers and cyclone separators are more compact