gas. The targeted pollutants are removed from the
gas and attach to the liquid due to its chemical
composition. As the gas is passed through the
cleaning mist, the remaining contaminants are
attracted to the mist and left behind [102]. The
removal efficiency increases by increasing residence time and surface area of the scrubber
solution.
Advantages of the wet scrubber include the
small space requirements for the setup. The scrubber has a high collection efficiency and collects
both gases and PM. It’s robust and can handle
high humidity and high temperature. On the
other hand, the technology requires high maintenance, which increases the operating cost significantly. The wet scrubber creates wastewater and
wet residuals, presenting a disposal issue.
Dry Scrubbers
Dry scrubbers remove pollutants from the exhaust
gas by using a sorbent. A sorbent is a material that
absorbs/adsorbs gases or liquids. Dry scrubbers
are primarily used for acidic gases from combustion (SO 2 and HCl) and for removal of odorous
and corrosive gases from wastewater treatment
plants. Dry scrubber technologies have different
systems, but common to them all is that the device
has an acid gas sorbent material going into the gas
stream and a control device to remove reaction
products [103].
The system operates by first cooling the gas.
The emission gases are cooled to make it easier to
remove pollutants and other toxins from the gas.
Next, a collection of dry reagents is sprayed into
an exhaust stream. These chemicals can react
differently depending on which material they are
specifically targeting for removal. These materials
neutralize the harmful pollutants in the gas stream
through a chemical reaction, while others cause
the material to react and turn into a different
substance. The product falls out and is collected
and disposed of [9].
The two well-known dry scrubbers are dry
sorbent injection and spray dryer absorbers,
which remove acid gases such as HCl, SO 2 ,
SO 3 , and HF.
The dry sorbent injection includes the addition
of alkaline material into the gas stream to react
with acid gases. The reaction occurs and forms
solid salts, which are collected in a particulate
collection device. This method is effective at capturing HCl (90%) but less so for SO 2 (50%). The
ratio of alkali added is 1:2, so the method is
limited to small facilities. The effectiveness of
the technology can be improved by increasing
the flue gas humidity and recycling the reaction
products.
The process of dry sorbent injection is as follows: Flue gas enters the cooling tower where
water is sprayed on the gas to lower the temperature. The dry reagent is mixed into the flue gas and
reacts with it. In the end, it is removed at a dust
collector [9].
Spray dryer absorption combines a spray dryer
with a dust collector. In the process flue gas enters
the spray dryer and comes in contact with a cloud
of finely atomized droplets of reagent. The flue
gas with decreased temperature and increased
humidity reacts with acid gases and is collected.
This method has a very high removal efficiency
for acid gases HCl (99%), SO 2 (95%), SO 3 (99%),
and HF (95%).
The advantages of dry scrubbers are that the
technology produces much less waste material
compared to wet scrubbers and is less expensive.
Some of the disadvantages are that the removal
efficiency is lower, and dry scrubbers can have a
difficult time removing several pollutants at once.
Residual waste is toxic and must be handled by
experts [9, 103].
NH 3 Removal
Livestock production and animal and human
waste emit NH 3 and odorous gases. Atmospheric
NH 3 damages the natural ecosystem and contributes to particle formation. Ammonia removal can
be achieved using an acid scrubber. Acid scrubbers are also used for other basic compounds and
many odorants [104].
SO x Removal
Sulfur dioxide emission is known to have severe
effects on human health and the environment.
Sulfur emissions lead to sulfate aerosols that
impact climate and health. Sulfate deposition
(acid rain) leads to acidification of the
Industrial Emissions Control Technologies: Introduction
499
gas and attach to the liquid due to its chemical
composition. As the gas is passed through the
cleaning mist, the remaining contaminants are
attracted to the mist and left behind [102]. The
removal efficiency increases by increasing residence time and surface area of the scrubber
solution.
Advantages of the wet scrubber include the
small space requirements for the setup. The scrubber has a high collection efficiency and collects
both gases and PM. It’s robust and can handle
high humidity and high temperature. On the
other hand, the technology requires high maintenance, which increases the operating cost significantly. The wet scrubber creates wastewater and
wet residuals, presenting a disposal issue.
Dry Scrubbers
Dry scrubbers remove pollutants from the exhaust
gas by using a sorbent. A sorbent is a material that
absorbs/adsorbs gases or liquids. Dry scrubbers
are primarily used for acidic gases from combustion (SO 2 and HCl) and for removal of odorous
and corrosive gases from wastewater treatment
plants. Dry scrubber technologies have different
systems, but common to them all is that the device
has an acid gas sorbent material going into the gas
stream and a control device to remove reaction
products [103].
The system operates by first cooling the gas.
The emission gases are cooled to make it easier to
remove pollutants and other toxins from the gas.
Next, a collection of dry reagents is sprayed into
an exhaust stream. These chemicals can react
differently depending on which material they are
specifically targeting for removal. These materials
neutralize the harmful pollutants in the gas stream
through a chemical reaction, while others cause
the material to react and turn into a different
substance. The product falls out and is collected
and disposed of [9].
The two well-known dry scrubbers are dry
sorbent injection and spray dryer absorbers,
which remove acid gases such as HCl, SO 2 ,
SO 3 , and HF.
The dry sorbent injection includes the addition
of alkaline material into the gas stream to react
with acid gases. The reaction occurs and forms
solid salts, which are collected in a particulate
collection device. This method is effective at capturing HCl (90%) but less so for SO 2 (50%). The
ratio of alkali added is 1:2, so the method is
limited to small facilities. The effectiveness of
the technology can be improved by increasing
the flue gas humidity and recycling the reaction
products.
The process of dry sorbent injection is as follows: Flue gas enters the cooling tower where
water is sprayed on the gas to lower the temperature. The dry reagent is mixed into the flue gas and
reacts with it. In the end, it is removed at a dust
collector [9].
Spray dryer absorption combines a spray dryer
with a dust collector. In the process flue gas enters
the spray dryer and comes in contact with a cloud
of finely atomized droplets of reagent. The flue
gas with decreased temperature and increased
humidity reacts with acid gases and is collected.
This method has a very high removal efficiency
for acid gases HCl (99%), SO 2 (95%), SO 3 (99%),
and HF (95%).
The advantages of dry scrubbers are that the
technology produces much less waste material
compared to wet scrubbers and is less expensive.
Some of the disadvantages are that the removal
efficiency is lower, and dry scrubbers can have a
difficult time removing several pollutants at once.
Residual waste is toxic and must be handled by
experts [9, 103].
NH 3 Removal
Livestock production and animal and human
waste emit NH 3 and odorous gases. Atmospheric
NH 3 damages the natural ecosystem and contributes to particle formation. Ammonia removal can
be achieved using an acid scrubber. Acid scrubbers are also used for other basic compounds and
many odorants [104].
SO x Removal
Sulfur dioxide emission is known to have severe
effects on human health and the environment.
Sulfur emissions lead to sulfate aerosols that
impact climate and health. Sulfate deposition
(acid rain) leads to acidification of the
Industrial Emissions Control Technologies: Introduction
499