The advantages of a bioscrubber include the
smaller volume of the equipment, better pH control, and more reliability and predictability relative to some other methods. Finally there is lower
occurrence of toxic concentrations in the aqueous
phase. Disadvantages include limited removal
efficiency for some compounds. Moreover the
slowest-growing microorganisms can be washed
out, the disposal of sludge can be difficult, and the
operational cost is high [112].
Gas Phase Advanced Oxidation and
Vapor Recovery
Vapor Recovery
VOCs are among the most common air pollutants
emitted from the chemical sector of industry
[113]. Their emission into the atmosphere and
further reactivity can lead to serious environmental hazards. The realization of VOC’s adverse
effects on human health has brought emissions
regulation and resulted in accelerated advancement in the field of VOC removal. Some of the
techniques for VOC control have been presented
earlier in the sections on oxidation and catalytic
removal. However, in some cases VOCs are of
economic interest. Certain VOCs are valuable
compounds, and their recovery might be more
profitable than removal by destruction
[114]. Therefore, vapor recovery systems have
been designed to deal with the pollution problem
and recover the compounds of interest. Consequently, several advanced separation technologies
for VOC control have been developed. This
includes condensation, adsorption, membranebased recovery, and absorption process covered
in the chapter on scrubbers.
Condensation relies on achieving supersaturation of VOC in the flue gas by a rapid decrease of
temperature or pressurization. The method is most
efficient for VOCs boiling above 50
C at relatively high concentration (above 5000 ppm).
Lower boiling compounds require more energy
for cooling or pressurization. A consideration for
condensation systems is that the high gas concentrations after condensation might exceed the lower
explosive limit (LEL) [113].
Membranes are applicable for relatively high
concentration and low flow rates. The process is
driven by a concentration gradient or pressure
differential between the membrane and flue gas.
The compounds diffuse through the membrane
and can be recovered. Silicon rubber-based membranes are one of the better studied and a quite
efficient technology, but they lack resistance
toward some hydrocarbons such as gasoline
vapors. For this case and others, there is a need
to develop additional, chemically resistant membrane materials. Elastomeric polymers were found
to be versatile materials for membrane production, and their resistance toward organic compounds
has
been
tested
successfully
[115]. Although membrane recovery seems to be
a very promising technique, some problems must
be addressed. Membranes’ lifetime suffers from a
trade-off between permeability and selectivity
[116], and their recovery cycle is considered to
be relatively slow. Furthermore, the membranes
are rather costly, and their sensitivity toward operating conditions (fouling, bacterial growth)
followed by intense maintenance increases their
operating cost significantly. Lastly, the disposal of
used membranes causes a burden on the
environment [113].
Recovery efficiency depends critically on
choosing a suitable technique for the process;
therefore it is of great importance to recognize
and characterize the compounds of interest in
order to fit the method to their properties. First
the source of the compounds must be identified to
characterize the classes of chemicals the recovery
system has to deal with. The chemical properties
(reactivity, toxicity, vapor pressure, solubility,
etc.) must be tabulated. Finally the value of the
compounds must be established, and based on that
knowledge, combined with regulatory demands,
the choice of recovery will be made [114].
The two most common adsorption methods are
temperature swing adsorption (TSA) and pressure
swing adsorption (PSA). The former is achieved
by adsorbing the flue gas at a lower temperature
on an adsorbent bed such as activated carbon
which is regenerated at a higher temperature
(often over 100
C) to recover the material
[117]. The cycle of adsorption, regeneration, and
cooling of the adsorbent bed requires time, and in
502
Industrial Emissions Control Technologies: Introduction
smaller volume of the equipment, better pH control, and more reliability and predictability relative to some other methods. Finally there is lower
occurrence of toxic concentrations in the aqueous
phase. Disadvantages include limited removal
efficiency for some compounds. Moreover the
slowest-growing microorganisms can be washed
out, the disposal of sludge can be difficult, and the
operational cost is high [112].
Gas Phase Advanced Oxidation and
Vapor Recovery
Vapor Recovery
VOCs are among the most common air pollutants
emitted from the chemical sector of industry
[113]. Their emission into the atmosphere and
further reactivity can lead to serious environmental hazards. The realization of VOC’s adverse
effects on human health has brought emissions
regulation and resulted in accelerated advancement in the field of VOC removal. Some of the
techniques for VOC control have been presented
earlier in the sections on oxidation and catalytic
removal. However, in some cases VOCs are of
economic interest. Certain VOCs are valuable
compounds, and their recovery might be more
profitable than removal by destruction
[114]. Therefore, vapor recovery systems have
been designed to deal with the pollution problem
and recover the compounds of interest. Consequently, several advanced separation technologies
for VOC control have been developed. This
includes condensation, adsorption, membranebased recovery, and absorption process covered
in the chapter on scrubbers.
Condensation relies on achieving supersaturation of VOC in the flue gas by a rapid decrease of
temperature or pressurization. The method is most
efficient for VOCs boiling above 50
C at relatively high concentration (above 5000 ppm).
Lower boiling compounds require more energy
for cooling or pressurization. A consideration for
condensation systems is that the high gas concentrations after condensation might exceed the lower
explosive limit (LEL) [113].
Membranes are applicable for relatively high
concentration and low flow rates. The process is
driven by a concentration gradient or pressure
differential between the membrane and flue gas.
The compounds diffuse through the membrane
and can be recovered. Silicon rubber-based membranes are one of the better studied and a quite
efficient technology, but they lack resistance
toward some hydrocarbons such as gasoline
vapors. For this case and others, there is a need
to develop additional, chemically resistant membrane materials. Elastomeric polymers were found
to be versatile materials for membrane production, and their resistance toward organic compounds
has
been
tested
successfully
[115]. Although membrane recovery seems to be
a very promising technique, some problems must
be addressed. Membranes’ lifetime suffers from a
trade-off between permeability and selectivity
[116], and their recovery cycle is considered to
be relatively slow. Furthermore, the membranes
are rather costly, and their sensitivity toward operating conditions (fouling, bacterial growth)
followed by intense maintenance increases their
operating cost significantly. Lastly, the disposal of
used membranes causes a burden on the
environment [113].
Recovery efficiency depends critically on
choosing a suitable technique for the process;
therefore it is of great importance to recognize
and characterize the compounds of interest in
order to fit the method to their properties. First
the source of the compounds must be identified to
characterize the classes of chemicals the recovery
system has to deal with. The chemical properties
(reactivity, toxicity, vapor pressure, solubility,
etc.) must be tabulated. Finally the value of the
compounds must be established, and based on that
knowledge, combined with regulatory demands,
the choice of recovery will be made [114].
The two most common adsorption methods are
temperature swing adsorption (TSA) and pressure
swing adsorption (PSA). The former is achieved
by adsorbing the flue gas at a lower temperature
on an adsorbent bed such as activated carbon
which is regenerated at a higher temperature
(often over 100
C) to recover the material
[117]. The cycle of adsorption, regeneration, and
cooling of the adsorbent bed requires time, and in
502
Industrial Emissions Control Technologies: Introduction