addition the material has a limited throughput
defined as the space velocity or ratio of the flow of
air that can be treated with a given volume of
adsorbent. Altogether, for high throughput a large
bed is required [114]. PSA on the other hand has a
much shorter cycle time and hence can achieve high
throughputs even for a small adsorption bed. PSA is
performed by cycling the pressure between flue gas
and adsorbent bed. Adsorption occurs at a pressure
higher than atmospheric, and the regeneration process occurs at atmospheric pressure. This is in contrast to vacuum swing adsorption (VSA), another
pressure-dependent technique which desorbs at
lower pressure, with adsorption occurring at atmospheric pressure. PSA, due to its lower energy
requirement, shorter regeneration cycle, and higher
regeneration rate, has been established as a superior
method over TSA [114, 116, 117]. Furthermore,
some recent studies suggest that the recovery rate
can be improved by combining thermal and vacuum
techniques in a hybrid technology [118]. Electrical
swing adsorption (ESA) is currently one of the most
promising new methods. Heat is generated via current passing through the adsorbent, without heating
the surroundings. Thus, the techniques offer several
advantages due to improved energy efficiency, faster
regeneration cycles, and better desorption
kinetics [117].
Various adsorbent materials can be used for
vapor recovery. One of the most popular adsorbents is activated carbon (AC) [114, 116,
117]. AC is very effective at adsorbing VOCs
and CO 2 but is not very selective, and the use of
more complex multilayer adsorbent beds can be
necessary if recovery of individual compounds is
desired. A molecular sieve, thanks to its great
selectivity and versatile application, is often a
good alternative. If high flue gas humidity is a
concern, zeolites can be considered, due to their
superior hydrophobic properties [114].
Vapor recovery is applied for environmental
protection by emissions control and for recovery
of expensive or tradable compounds. Regulations
on gasoline vapor emissions in the EU and USA
have accelerated innovation in the field of VOC
recovery and resulted in the successful application
of vapor recovery systems in fuel dispensers
[119]. Installation of vapor recovery systems in
service stations can significantly reduce personal
exposure to harmful emissions, in addition to
improving regional air quality [120]. Furthermore,
vapor recovery is an important process in chemical industry. It not only decreases the emission of
environmentally hazardous substances but significantly reduces the expense of solvent recovery
and in some cases can bring profit from the recovery of tradable components. Industrial processes
such as drying, coating, and gluing produce an
immense amount of solvent vapor which can be
either destroyed or reused [121]. Vapor recovery
is also one of the CCP methods mentioned in the
section on scrubbers. It can be used to reduce CO 2
emissions from large stationary sources such as
fossil-fuel plants and also for direct capture from
ambient air, achieved economically with, e.g.,
moisture swing sorbents [122]. The CO 2 captured
by an adsorbent can be later recovered and find its
place in a variety of applications.
Gas-Phase Advanced Oxidation (GPAO)
Gas-phase advanced oxidation (GPAO) is an
emissions control method based on the mechanisms that remove pollution from the Earth’s
atmosphere [123]. In the system, pollutants are
oxidized, and their oxidations products are
removed as particles [124].
The GPAO process is shown in Fig. 12. Polluted air enters the system and is mixed with
ozone. UV-C light photolyzes the ozone to produce O(
3 P), O(
1 D), HO 2 , and the OH radical. The
OH radical is the main driver of the oxidation
process and oxidizes pollution, in many cases a
VOC compound. SOA forms from VOC oxidation products and is removed by an electrostatic
precipitator (ESP) or another particle removal
technique. As a part of the ESP, the particles are
first charged by a high-voltage (HV) electrode and
then collected. The remaining unreacted ozone is
finally removed by a MnO 2 catalyst, and the clean
air leaves the system [124, 125].
The OH radical can initiate oxidation of a wide
range of pollutants [123], and in the atmosphere,
all air pollution is removed by a variety of mechanism (oxidation, photolysis, deposition). In low
NO x conditions, HO x is formed by the photolysis
of ozone by UV-C light, which produces O(
1 D).
O(
1 D) reacts with water vapor to produce OH
Industrial Emissions Control Technologies: Introduction
503
defined as the space velocity or ratio of the flow of
air that can be treated with a given volume of
adsorbent. Altogether, for high throughput a large
bed is required [114]. PSA on the other hand has a
much shorter cycle time and hence can achieve high
throughputs even for a small adsorption bed. PSA is
performed by cycling the pressure between flue gas
and adsorbent bed. Adsorption occurs at a pressure
higher than atmospheric, and the regeneration process occurs at atmospheric pressure. This is in contrast to vacuum swing adsorption (VSA), another
pressure-dependent technique which desorbs at
lower pressure, with adsorption occurring at atmospheric pressure. PSA, due to its lower energy
requirement, shorter regeneration cycle, and higher
regeneration rate, has been established as a superior
method over TSA [114, 116, 117]. Furthermore,
some recent studies suggest that the recovery rate
can be improved by combining thermal and vacuum
techniques in a hybrid technology [118]. Electrical
swing adsorption (ESA) is currently one of the most
promising new methods. Heat is generated via current passing through the adsorbent, without heating
the surroundings. Thus, the techniques offer several
advantages due to improved energy efficiency, faster
regeneration cycles, and better desorption
kinetics [117].
Various adsorbent materials can be used for
vapor recovery. One of the most popular adsorbents is activated carbon (AC) [114, 116,
117]. AC is very effective at adsorbing VOCs
and CO 2 but is not very selective, and the use of
more complex multilayer adsorbent beds can be
necessary if recovery of individual compounds is
desired. A molecular sieve, thanks to its great
selectivity and versatile application, is often a
good alternative. If high flue gas humidity is a
concern, zeolites can be considered, due to their
superior hydrophobic properties [114].
Vapor recovery is applied for environmental
protection by emissions control and for recovery
of expensive or tradable compounds. Regulations
on gasoline vapor emissions in the EU and USA
have accelerated innovation in the field of VOC
recovery and resulted in the successful application
of vapor recovery systems in fuel dispensers
[119]. Installation of vapor recovery systems in
service stations can significantly reduce personal
exposure to harmful emissions, in addition to
improving regional air quality [120]. Furthermore,
vapor recovery is an important process in chemical industry. It not only decreases the emission of
environmentally hazardous substances but significantly reduces the expense of solvent recovery
and in some cases can bring profit from the recovery of tradable components. Industrial processes
such as drying, coating, and gluing produce an
immense amount of solvent vapor which can be
either destroyed or reused [121]. Vapor recovery
is also one of the CCP methods mentioned in the
section on scrubbers. It can be used to reduce CO 2
emissions from large stationary sources such as
fossil-fuel plants and also for direct capture from
ambient air, achieved economically with, e.g.,
moisture swing sorbents [122]. The CO 2 captured
by an adsorbent can be later recovered and find its
place in a variety of applications.
Gas-Phase Advanced Oxidation (GPAO)
Gas-phase advanced oxidation (GPAO) is an
emissions control method based on the mechanisms that remove pollution from the Earth’s
atmosphere [123]. In the system, pollutants are
oxidized, and their oxidations products are
removed as particles [124].
The GPAO process is shown in Fig. 12. Polluted air enters the system and is mixed with
ozone. UV-C light photolyzes the ozone to produce O(
3 P), O(
1 D), HO 2 , and the OH radical. The
OH radical is the main driver of the oxidation
process and oxidizes pollution, in many cases a
VOC compound. SOA forms from VOC oxidation products and is removed by an electrostatic
precipitator (ESP) or another particle removal
technique. As a part of the ESP, the particles are
first charged by a high-voltage (HV) electrode and
then collected. The remaining unreacted ozone is
finally removed by a MnO 2 catalyst, and the clean
air leaves the system [124, 125].
The OH radical can initiate oxidation of a wide
range of pollutants [123], and in the atmosphere,
all air pollution is removed by a variety of mechanism (oxidation, photolysis, deposition). In low
NO x conditions, HO x is formed by the photolysis
of ozone by UV-C light, which produces O(
1 D).
O(
1 D) reacts with water vapor to produce OH
Industrial Emissions Control Technologies: Introduction
503