Air Pollution is an ever rising threat to the health of planet earth. This presentation illustrates some of the methods that are used to decrease the pollutants emitted from industrial complexes.
2. Type Of Systems
Absorbing units
1. The technology is
based on the removal of
air pollutants by inertial
or diffusional impaction
or absorption into liquid
solvent.
2. Objectionable
components, are
transferred to the liquid
phase.
Adsorbing units
1. Adsorption is defined
as the collection and
concentration of a
substance onto a solid
surface from a gas .
2. The equilibrium
relationships associated
with adsorption,
3. The adsorption
process is exothermic.
Thermal oxidization
In this gases are
oxidized by burning
them at high
temperatures.
Harmful gases like
CO are oxidized in
their higher forms.
3. Packed Bed
Scrubbers
a chamber containing layers of
variously shaped packing
material, such as Whig rings,
spiral rings, that provide a large
surface area for liquid-particle
contact. The liquid coats the
packing and establishes a thin
film.
4. Packed Bed Scrubbers
โข Gases Removed
โข Removal of inorganic fumes, vapors, and gases (e.g., chromic
acid, hydrogen sulfide, ammonia, chlorides, fluorides, and
SO,); volatile organic compounds (VOC);
โข Achievable Limits
โข Inorganic Gases: Control device vendors estimate that
removal efficiencies range from 95 to 99 % .
โข VOC: Removal efficiencies for gas absorbers vary for each
pollutant-solvent system and with the type of absorber used.
5. Packed Bed Scrubbers
โข Parameters
โข Air Flow: gas flow rates for packed-bed wet
scrubbers are 0.25 to 35 standard cubic
meters per second (sm3/sec)
โข Temperature : 4 to 38 อฆC for gas absorption
applications,
โข Pollutant Loading: Typical gaseous pollutant
concentrations range from 250 to 10,000
ppmv.
6. Create liquid disposable
problem
High maintenance cost
Particulate materials may
block the bed
Capable of achieving high
Mass transfer efficiencies
Low capital cost
Small space required
7. Adsorbing systems
Bulk
gas
1. Mass
transfer
from bulk
to outer
surface
2. diffusion through
the passages within
the particle
3. adsorption on the
internal particle surfaces
1
2
3
Adsorbent
Three stage process
NOTE :Often, one of the transfer processes will be significantly slower than
the other two, and will control the overall transfer rate
8. Adsorbing Systems
โข Types Of Adsorbent Systems
โข Fluidized bed system - the combination of high gas
rate and small adsorbent particle size results in
suspension of the adsorbent, giving it many of the
characteristics of a fluid
โข Continuous moving bed system- adsorbent
mechanically falls by gravity through the rising stream
of gas
โข Unsteady state fixed bed system ( simple, economical
and most widely used)- adsorbent spread over fixed
bed and gas passed over it. Unsteady because conc. of
pollutant in effluent changes drastically.
9. Adsorbing systems
โข Types Of Adsorbents
โข Activated Carbon โ used mainly for removal of
volatile organic compounds (V.O.C)
โข Siliceous adsorbent- Silica Gel
โข Metal oxides โ Alumina (gas drying purposes)
10. Thermal Oxidization
โข Organic Loading
โข Measurable unit - The LEL( lower explosive limit)
of a stream is the lowest organic concentration in
a stream that would, in the presence of an
ignition source, yield a combustible mixture.
โข For example benzene, which at 12,000 ppm, is
100% LEL. The National Fire Protection
Association (NFPA) states that equipment can
operate, without LEL monitors or controls, if the
LEL is less than 25% LEL. For benzene then, 25%
LEL is equal to 3,000 ppm.
11. Thermal Oxidization
1. Catalytic recuperative oxidizers
2. Thermal recuperative oxidizer : burning of gases
by providing sufficient retention time at specific
temp. (usually 1/2 second)
Gas is
pressurized
Heat exchanger
(heated)
Reaction
chamber
