environment, destroying aqueous habitats and
damaging tree foliage and crops [7]. Combustion
of sulfur-containing fossil fuels, especially for
electricity production, is the main cause of SO 2
formation today [105]. Energy generation (51%)
and energy use in the industrial sector (20%) are
the major contributors to EU-28 emissions of SO x
[18]. Therefore, power plants are encouraged to
find an effective way to reduce emissions to comply with National Emissions Ceilings (NEC)
Directive (2016/2284/EU). In recent years, thanks
to the new European air quality standards and caps
on NO x and SO x emissions, acid rain in Europe is
slowly declining, and forests, lakes, and natural
habitats are showing signs of recovery [18]. SO x
emissions can be reduced in many ways, including the removal of sulfur before combustion, during combustion, or post-combustion.
Desulfurization before combustion is done by
selection of low sulfur fuels or by fuel desulfurization, e.g., physical preparation of coal. This
method, although quite effective (sulfur reduction
of 30%), is not economical and, if applied, would
significantly increase the market coal prices
[106]. Combustion controls are primarily used in
coal-fired plants and work by adding the SO 2
sorbent to the furnace. The post-combustion process focusses on removing SO x from the flue gas
and is referred to as flue gas desulfurization
(FGD). Post-combustion desulfurization can be
carried out with multiple methods. Currently, the
most common processes available on the market
include wet scrubbers, spray dry scrubbers, sorbent injections, and combined SO 2 /NO x removal
processes. The desulfurization technology can be
also classified roughly into regenerable and
throwaway, depending on how the sorbent is
treated after the process.
In throwaway technology, the used sorbent is
disposed of or utilized as a by-product. The sorbent can also be regenerated, and the SO 2 released
from it can be further processed to sulfuric acid or
elemental sulfur. The latter method produces
almost no waste, but the cost of a regenerable
FGD is also much higher.
The mechanism of desulfurization in dry and
wet scrubbers was described previously; here we
will focus on the materials used in those processes
and their by-products. The sorbent of choice for
most of the scrubbers are limestone (CaCO 3 ) and
lime (CaO). Wet scrubbers, using those materials,
can achieve a removal efficiency of up to 99%.
Limestone is a common, naturally occurring mineral, and its chemical composition can vary
greatly from source to source and has a significant
effect on product (e.g., gypsum) quality. Lime is
produced by calcination of limestone. It is a
highly reactive material, and its storage requires
special attention due to its irritant properties. The
sludge created after the process of desulfurization
using limestone can either be disposed of or, with
the right technology, can be transformed to low
cost, easily available, marketable gypsum
(CaSO 4 Á 2H 2 O) by the following reaction:
SO 2 þ CaCO 3 þ 2O 2 þ 2H 2 O
! CaSO 4 Á 2H 2 O þ CO 2
The gypsum created during the absorption of
SO 2 must be then separated from the water, its pH
adjusted and stored. Water used in the process can
be purified and reused. The value of produced
FGD gypsum depends highly on used technology,
the composition of the fuel, and limestone. In
Europe it’s successfully used as a cement additive,
plaster products, etc. [107]. Additionally, ammonia can also be used in the process of desulfurization, and its by-product ammonium sulfate is used
worldwide as an agricultural fertilizer [107].
CO 2 Removal
Carbon dioxide is the largest of the anthropogenic
climate forcing agents that cause global warming.
Anthropogenic emissions of CO 2 contribute significantly to climate change and have become a
serious global problem. 40% of total CO 2 emissions come from fossil-fueled power plants
[108]. Since the Kyoto Protocol came into force,
signatories of the treaty are obligated to reduce
GHG emissions. Carbon capture and storage
(CCS) comprises techniques which trap CO 2
from exhaust and store it and hence mitigate climate change. CSS quickly became a priority for
environmental agencies around the world. The
EU countries have managed to successfully
500
Industrial Emissions Control Technologies: Introduction
damaging tree foliage and crops [7]. Combustion
of sulfur-containing fossil fuels, especially for
electricity production, is the main cause of SO 2
formation today [105]. Energy generation (51%)
and energy use in the industrial sector (20%) are
the major contributors to EU-28 emissions of SO x
[18]. Therefore, power plants are encouraged to
find an effective way to reduce emissions to comply with National Emissions Ceilings (NEC)
Directive (2016/2284/EU). In recent years, thanks
to the new European air quality standards and caps
on NO x and SO x emissions, acid rain in Europe is
slowly declining, and forests, lakes, and natural
habitats are showing signs of recovery [18]. SO x
emissions can be reduced in many ways, including the removal of sulfur before combustion, during combustion, or post-combustion.
Desulfurization before combustion is done by
selection of low sulfur fuels or by fuel desulfurization, e.g., physical preparation of coal. This
method, although quite effective (sulfur reduction
of 30%), is not economical and, if applied, would
significantly increase the market coal prices
[106]. Combustion controls are primarily used in
coal-fired plants and work by adding the SO 2
sorbent to the furnace. The post-combustion process focusses on removing SO x from the flue gas
and is referred to as flue gas desulfurization
(FGD). Post-combustion desulfurization can be
carried out with multiple methods. Currently, the
most common processes available on the market
include wet scrubbers, spray dry scrubbers, sorbent injections, and combined SO 2 /NO x removal
processes. The desulfurization technology can be
also classified roughly into regenerable and
throwaway, depending on how the sorbent is
treated after the process.
In throwaway technology, the used sorbent is
disposed of or utilized as a by-product. The sorbent can also be regenerated, and the SO 2 released
from it can be further processed to sulfuric acid or
elemental sulfur. The latter method produces
almost no waste, but the cost of a regenerable
FGD is also much higher.
The mechanism of desulfurization in dry and
wet scrubbers was described previously; here we
will focus on the materials used in those processes
and their by-products. The sorbent of choice for
most of the scrubbers are limestone (CaCO 3 ) and
lime (CaO). Wet scrubbers, using those materials,
can achieve a removal efficiency of up to 99%.
Limestone is a common, naturally occurring mineral, and its chemical composition can vary
greatly from source to source and has a significant
effect on product (e.g., gypsum) quality. Lime is
produced by calcination of limestone. It is a
highly reactive material, and its storage requires
special attention due to its irritant properties. The
sludge created after the process of desulfurization
using limestone can either be disposed of or, with
the right technology, can be transformed to low
cost, easily available, marketable gypsum
(CaSO 4 Á 2H 2 O) by the following reaction:
SO 2 þ CaCO 3 þ 2O 2 þ 2H 2 O
! CaSO 4 Á 2H 2 O þ CO 2
The gypsum created during the absorption of
SO 2 must be then separated from the water, its pH
adjusted and stored. Water used in the process can
be purified and reused. The value of produced
FGD gypsum depends highly on used technology,
the composition of the fuel, and limestone. In
Europe it’s successfully used as a cement additive,
plaster products, etc. [107]. Additionally, ammonia can also be used in the process of desulfurization, and its by-product ammonium sulfate is used
worldwide as an agricultural fertilizer [107].
CO 2 Removal
Carbon dioxide is the largest of the anthropogenic
climate forcing agents that cause global warming.
Anthropogenic emissions of CO 2 contribute significantly to climate change and have become a
serious global problem. 40% of total CO 2 emissions come from fossil-fueled power plants
[108]. Since the Kyoto Protocol came into force,
signatories of the treaty are obligated to reduce
GHG emissions. Carbon capture and storage
(CCS) comprises techniques which trap CO 2
from exhaust and store it and hence mitigate climate change. CSS quickly became a priority for
environmental agencies around the world. The
EU countries have managed to successfully
500
Industrial Emissions Control Technologies: Introduction