Air Pollution Control

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Air Pollution Control
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Indoor Air Quality Model

• Read pages 509 535 Textbook

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Indoor Air Quality Model

• The following balance on a room in a house or
  office building can be used to evaluate the air
  quality.

Volume V Concentration C
Q, Ca
Q, C
Decay rate, -k
Emission rate, E
Source
Sink
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Indoor Air Quality Model
C pollutant concentration in/out of the room,
g/m3 Q infiltration rate of air into and out of
the room, m3/s Ca pollutant concentration in
outdoor air, g/m3 E emission rate of pollutant
into room from indoor source, g/s k pollutant
reaction rate, s-1
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Indoor Air Quality Model
The general solution
The steady state solution
If the pollutant is conservative and does not
decay with time or have significant reactivity
(e.g. k 0), or if the ambient concentration is
negligible and the initial indoor concentration
is zero then the following equation can be
derived.
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Indoor Air Quality Model
Conservative pollutant
Example 6.6 A non-vented kerosene heater is
operated for one hour in an apartment having a
volume of 200 m3. The heater emits SO2 at a rate
of 50 ?g/s. The ambient air concentration (Ca)
and the initial indoor air concentration (Co) of
SO2 are 100 ? g/m3. If the rate of ventilation
is 50 L/s, and the apartment is assumed to be
well-mixed, what is the indoor air concentration
of SO2 at the end of one hour?
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Indoor Air Quality Model
Example 6.6 - Solution The concentration may
be determined using the general solution form of
the indoor air quality model. The decay rate for
SO2 from Table 6-8 is 6.39x10-5 s-1 and 50 L/s is
equivalent to 0.05 m3/s.
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Treatment of Emissions

• Air Control Processes
• Particulate Materials
• Cyclone
• Bag filters
• Spray Towers or Scrubbers

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Treatment of Emissions

• Air Control Processes
• Gaseous Removal Processes
• Wet Scrubbers
• Adsorption Processes
• Incineration or flaring Processes

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Treatment of Emissions

• Cyclones

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Treatment of Emissions

• Cyclone
• Dirty air containing the particulates is sucked
  in the side of the cyclone. The particle
  velocities are reduced due to friction at the air
  wall interface causing the particles to settle
  out.
• Good for particles 10.0 ?m

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Treatment of Emissions

• Cyclone Standard proportions for a reverse flow
  cyclone

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Treatment of Emissions
The efficiency of this cyclone can be described
mathematically using the following expression and
graph Lapple (1951)

• d0.5 cut diameter, the particle size for which
  the collection efficiency is 50, ?m.
• dynamic viscosity of gas, Pas
• B entrance width, m
• H height of entrance, m
• ?p particle density, kg/m3
• Qg gas flow rate, m3/s
• ? effective number of turns made in traversing
  the cyclone as defined in the following equation
  

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Treatment of Emissions
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Treatment of Emissions

• ?, the effective number of turns made in
  traversing the cyclone as defined in the
  following equation

Where L1 and L2 are the length of the cylinder
and cone, respectively.
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Treatment of Emissions
Example 6-9. Determine the efficiency of a
standard cyclone having the following
characteristics for particles 10 ?m in diameter
with a density of 800 kg/m3. Cyclone barrel
diameter 0.50 m Gas flow rate 4.0 m3/s Gas
temperature 25oC
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Treatment of Emissions
Example 6-9. Solution From the standard
cyclone dimensions we can calculate the
following B (0.25)(0.50 m) 0.13 m H
(0.50)(0.50 m) 0.25 m L1 L2 (2.00)(0.50 m)
1.0 m
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Treatment of Emissions
Example 6-9. Solution From the gas temperature
and Table A-4 of Appendix A, the dynamic
viscosity is 18.5 ?Pas. The cut diameter is
then
The ratio of particle sizes is
From Figure 6-32 we can find the collection
efficiency is about 95 .
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Treatment of Emissions

• Bag Filters

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Treatment of Emissions

• Bag Filters
• The filter bags are about 10 ft long and 8 inches
  in diameter and hung in a chamber. Dirty air
  containing the ash or dust moves up through the
  bag and traps the particles. Periodically the
  bags are shaken to remove the particles. Good
  particle removal in submicron range.

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Treatment of Emissions

• Spray Tower or Scrubber

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Treatment of Emissions

• Spray Tower
• Counter current process where the air moves up
  and a fine spray is introduced into the column
  which absorbs the particles and the dirty water
  is removed at the bottom of the column. Can
  remove submicron particles.

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Treatment of Emissions

• Electrostatic precipitator

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Treatment of Emissions

• Electrostatic Precipitators
• Used mostly in power plants because requires much
  power. Particles are negatively charged through
  a high voltage electrode and collect on the
  positive electrode. Effective in removing
  submicron particles.

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Treatment of Emissions

• Adsorption Process

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Treatment of Emissions

• Adsorption Process
• Gases or volatile organic pollutants in air are
  fed through a column filled with granular
  adsorbent. The pollutants diffuse from the gas
  stream to the adsorbent surface where they are
  adsorbed within the adsorbent particles.

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Treatment of Emissions

• Incineration Process

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Treatment of Emissions

• Incineration Process
• A fuel like natural gas is fed with air and the
  organic pollutants into a combustion chamber
  where the pollutants are oxidized to carbon
  dioxide and water. A catalyst can also be used to
  increase the combustion efficiency and reduce
  fuel costs.

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Comparison of Treatment Efficiencies
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Treatment of Emissions

• Sulfur Dioxide Control
• Primarily for coal fired power plants. Two
  methods for sulfur control
• 1) Change to low sulfur coal
• 2) Desulfurize the coal remove the iron pyrite
  (FeS2) by washing the coal. Removal of organic
  sulfur by gasifying the coal before combustion.

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Treatment of Emissions

• Sulfur Dioxide Control
• Flue-Gas Desulfurization is where the flue gas
  containing the sulfur oxides is contacted with
  powdered lime in the gas stream forming

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Comparison of Particle Removals