8. GAS STREAM CONDITIONING
8.4. Gas Preheaters
The temperature of the emission gas stream can be increased by using a gas
preheater. Increasing the temperature of the emission gas stream reduces the likelihood
of condensation. In fabric filters, condensation can plug or blind fabric pores. Additionally,
condensation can increase the corrosion of metal surfaces in a control device. To
overcome these problems, a gas preheater can be used to increase the temperature of
the emission gas stream above the dew point temperature. Three methods are
commonly utilized to raise the gas emission temperature: direct-fired afterburners, heat
exchangers, and stream tracking. Direct-fire afterburners preheat the gas stream by
using a flame produced from burning an auxiliary fuel. Additionally, the flame also
combusts organic constituents in the emission gas stream that might otherwise blind the
filter bags in a downstream control device. An shell-and-tube arrangement is used by a
heat exchanger to preheat the gas emission stream. The stream-tracking method runs
an emission gas stream line inside of a steam line to preheat the emission stream. This
method is typically only employed when a steam line is available at the site.
8. GAS STREAM CONDITIONING
8.4. Gas Preheaters
When the emission streams contain HAPs, the preheating of the stream should
be raised to only 50–100ºF above the dew point temperature to minimize the vapor
components of the HAP. This allows the downstream control devices, such as a bag
house or an electrostatic precipitator, to control the HAP as effectively as possible.
Emission stream parameters must be recalculated using a standard industrial equation
when the temperature of the gas stream is preheated, because when the gas stream
temperature increases, it increases the actual gas flow rate of the emission stream.
9. AIR QUALITY MANAGEMENT
9.1. Recent Focus
9.1.1. Emission Sources
A recent focus of air quality management (12,18–61) has been on reducing
natural and man-made airborne contaminants from various sources:
(1) point source hazardous air emissions,
(2) non-point-source fugitive hazardous emissions,
(3) greenhouse or global warming gases,
(4) ozone-depleting gases,
(5) indoor emissions that release asbestos, microorganisms, radon gases, VOCs, lead,
and so forth,
(6) odor emissions,
(7) vehicle emissions,
(8) wildfire emissions, and
(9) terrorists’ emissions of airborne infectious and/or toxic contaminants.
9. AIR QUALITY MANAGEMENT
9.1.2. Airborne Contaminants
Of various airborne contaminants, organic gaseous emissions are the most
important recent focus. Air emission standards have been developed by the US Office of
Air Quality Planning and Standards (OAQPS) to address organic emissions from several
waste-management sources. The unit operations and processes for removing organic
airborne contaminants include wet and dry scrubbing, condensation, flare, thermal
oxidation, catalytic oxidation, gas-phase carbon adsorption, gas-phase biofiltration, and
so forth presented in Chapters 5–12.
Waste-management sources also contribute other types of air emission such as
inorganic gaseous (metals) and particulate matter (PM), which are subject to federal
regulation under other programs. This can be illustrated by the program developed by the
US Office of Solid Waste (US OSW), which has standards for metal emissions from
industrial boilers and furnaces. At landfills and hazardous waste-treatment, storage and
disposal facilities (TSDFs), US OSW has general requirements that limit blowing dust
(particulate matter). Additionally, the US EPA has developed the following document that
deals with the control of emissions from TSDFs: Hazardous Waste TSDF—Fugitive
Particulate Matter Air Emission Guidance Document EPA- 450/3-89-019 (22)
9. AIR QUALITY MANAGEMENT
9.1.2. Airborne Contaminants
Fabric filtration (Chapter 2), cyclones (Chapter 3), electrostatic precipitation
(Chapter 4), and wet scrubbing (Chapter 5) are the processes for removal of PM and
inorganic contaminants (metals). The readers are referred to ref. 59 dealing with the
following important subjects for removing inorganic and PM contaminants:
1. Atmospheric modeling and dispersion
2. Desulfurization and SO x/H2S emission control
3. Carbon sequestration
4. Control of nitrogen oxides during stationary combustion
5. Control of heavy metals in emission streams
6. Ventilation and air conditioning.
Infectious airborne pollutants are various pathogenic microorganisms, including
bacteria, virus, and fungus, and can be present indoors (39–41), or both indoor and
outdoor when there is a bioterrorist’s attack (49–52). Finally, radon gases are radioactive
airborne pollutants, and noise is transmitted through air. The solutions to the problems of
airborne infectious bacteria, virus, fungus, radon, and noise can be found elsewhere (59).
9. AIR QUALITY MANAGEMENT
9.2. Ozone
9.2.1. Ozone Layer Depletion and Protection
Depending on what part of the atmosphere contains ozone, it can either benefit
or harm human health and the environment. Figure 15 illustrates this relationship. Ozone
occurs naturally in the upper (stratosphere) and the lower atmospheres (troposphere).
Ozone in the stratosphere protects us from the sun’s radiation; ozone in the troposphere,
however, can have adverse health effects and other negative environmental impact. The
greenhouse gases are CO2, H2O, CH4, NO2, and chloroflurocarbons (CFCs), the
concentrations of which are increasing and causing global warming. CFC gases destroy
the ozone in the stratosphere, thus reducing the ozone layer’s radiation protection effect
(20).
9. AIR QUALITY MANAGEMENT
9.2. Ozone
9.2.1. Ozone Layer Depletion and Protection
9. AIR QUALITY MANAGEMENT
9.2. Ozone
9.2.1. Ozone Layer Depletion and Protection
As illustrated in Fig. 15, the stratospheric ozone, which provides protection from the sun’s
radiation, is the “good ozone,” whereas the tropospheric ozone, which is detrimental to
human health and welfare, is the “bad ozone.” For our health or long-term survival, we
must protect the stratospheric ozone in the ozone layer. CFCs are the major ozone-
depleting substances. Other ozone-depleting substances that also reach the
stratospheric ozone layer include carbon tetrachloride, methyl chloroform, and halons.
Recent major scientific findings and observations (37,38) include the following:
(1) Record ozone depletion was observed in the mid-latitudes of both hemispheres in
1992–1993, and ozone values were 1–2 % lower than would be expected from an
extrapolation of the trend prior to 1991;
(2) the Antarctic ozone “holes” of 1992 and 1993 were the most severe on record, and a
substantial Antarctic ozone “hole” is expected to occur each austral spring for many
more decades;
(3) ozone losses have been detected in the Arctic winter stratosphere, and their links to
halogen chemistry have been established;
(4) the link between a decrease in stratospheric ozone and an increase in surface
ultraviolet (UV) radiation has been further strengthened; (5) the ozone depletion
potential (ODP) for CFC-11 is designated to be 1, and the ODP for methyl bromide is
calculated to be about 0 6; (6) methyl bromide continues to be
9. AIR QUALITY MANAGEMENT
9.2. Ozone
9.2.1. Ozone Layer Depletion and Protection
(5) the ozone depletion potential (ODP) for CFC-11 is designated to be 1, and the ODP for
methyl bromide is calculated to be about 0.6;
(6) methyl bromide continues to be viewed as another significant ozone-depleting
compound;
(7) stratospheric ozone losses cause a global-mean negative radiative forcing; the ozone-
depleting gases (CFCs, carbon tetrachloride, methyl chloroform, methyl bromide, etc.)
have been used extensively in industrial applications, including refrigeration, air
conditioning, foam blowing, cleaning of electronic components, and as solvents;
(8) many countries have decided to discontinue the production of CFCs, halons, carbon
tetrachloride, and methyl chloroform, and industry has developed many “ozone-friendly”
substitutes for protection of the stratospheric ozone layer; and
(9) in the domestic refrigeration industry, HFC134A and HFC152A have been used as the
substitutes for CFC; in commercial refrigeration industry, HFC134A, HCFC22, HCFC123,
and ammonia have been used as the substitute for CFC; and in mobile air conditioning
systems, only HFC134A is recommended as the substitute for CFC.
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
The formation of ozone in the troposphere (lower level) is simplistically
illustrated in Fig. 16. The primary constituents are nitrogen oxides (NOx), organic
compounds, and solar radiation. Nitrogen oxide emissions are primarily from combustion
sources, including both stationary and nonstationary types. Coal-burning power plants
are the major stationary source for NOx, whereas transportation modes, such as
automobiles, trucks, and buses, are the major nonstationary source for NOx. Another
source for organic compounds is waste-management operations.
When nitrogen oxides and organic compounds are exposed to sunlight, a series
of complex chemical reactions occur to form two principal byproducts: ozone (O3) and an
aerosol that, among other things, limits visibility. This mixture of ozone and aerosol is
described as photochemical smog. The respiratory system can be negatively affected
when humans are exposed to ozone. Possible effects include inflammation of the lungs,
impaired breathing, reduced breathing capacity, coughing, chest pain, nausea, and
general irritation of the respiratory passages. The long-term exposure to ozone could
result in increased susceptibility to respiratory infections, permanent damage to lung
tissue, and severe loss of breathing capacity.
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
The effects of ozone are more severe on the very young, elderly, and those with
pre-existing respiratory conditions than on the normal, healthy, adult population. It has
been shown, however, that young, healthy individuals who exercise outdoors can also
exhibit negative health effects when exposed to ozone.
Urban areas can be subjected to an oxidizing type of pollution, which is the result of a
chemical reaction of NO x and HC in sunlight and produces O3, PAN, and other complex
compounds. This pollution is described as ozone and referred to as photochemical
oxidants. Because this pollution is considered a secondary pollutant, transport is a
concern. Ozone is a regional concern because it can impact an area 250 km from the
source.
Researchers showed the existence and the extent of impact of ozone on human
health. In 1998, a study examined several hundred deceased persons in Los Angeles
who were victims of automobile accidents but were otherwise healthy. It was found that
about half had lesions on their lungs, which is a characteristic of lung disease in the early
stages. One of the causes for the observed lesions was attributed to the victims’
exposure to the levels of ozone in the Los Angles area.
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
Other negative impacts are associated with ozone exposure, such as materials
sustaining damage from ozone exposure. The useful life of synthetic and rubber
compounds become significantly shorter when they are exposed to ozone-laden
environment. Additionally, reduction in crop fields, lower forest growth rate, and
premature leaf droppage may occur from ozone exposure. The US EPA has estimated
that the damage to commercial crops and forests resulting from ozone exposure ranged
between 2 and 3 billion dollars. Reduction in visibility by photochemical smog can also be
considered as a negative impact on society.
As established under the Clean Air Act (CAA), the air quality standards for air
pollutants including ozone are the responsibility of the US EPA. To illustrate the extent of
the ozone problem in the United States, one can compare the health-based ambient air
quality standard with the air-quality-monitoring data reported for areas throughout the
United States. Based on an hourly average not to be exceeded more than once annually,
the national ambient air quality (NAAQ) standard for ozone is 0.12 ppm.
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
When this ambient air standard is compared to historical monitoring data, over
60 areas nationwide have routinely exceeded this standard. It is estimated that over 100
million people live in these areas. However, recent data have indicated that ozone levels
have shown some improvement in these areas, but the ambient air quality standard for
ozone is still being exceeded in many areas that contain a significant portion of the total
population of the United States. It has been determined that some these areas may not
attain the ambient air quality standard for many years. To address these “nonattainment”
areas, Congress amended the CAA in 1990. These nonattainment areas do not attain the
ambient air quality standards for several criteria pollutants, include ozone.
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
9. AIR QUALITY MANAGEMENT
9.2.2. Photochemical Oxidants
The amendment requires that areas with extreme ozone nonattainment
problems have 20 yr to achieve the ozone ambient air quality standard. For the more
sensitive populations, a more stringent standard for ozone has been requested.
These nonattainment areas include the largest urban areas, such as the Los
Angeles area, Chicago, Houston, and the Northeast corridor. These areas are classified
as “hot spots” for ozone, but there are many areas across the United States that have
ozone problems. It has been observed in some of the national parks, for example, that
the ozone levels occasionally exceed the ambient air quality standard.
The US EPA considers VOCs one of primary ingredients for the formation of
ozone. Figure 17 shows the relative contribution of various source categories to total
nationwide emissions of VOCs. As shown in Fig. 17, one significant source for VOCs is
hazardous waste TDSFs, which contribute about 8% of the total VOC emission in the
United States.
9. AIR QUALITY MANAGEMENT
9.3. Air Toxics
Air toxics are described as air pollutants that cause cancer or other human
health effects. The CAA amendments of 1990 specifically identify 190 compounds as air
toxics. As required by the CAA, the US EPA must investigate and potentially regulate
these air toxics. Air toxic compounds include radon, asbestos, and organic compounds.
Radon is a naturally occurring, colorless, odorless gas formed from the normal
radioactive decay of uranium in the earth’s rocks and soils. Exposure to radon through
inhalation has been demonstrated to increase risk for lung cancer. Radon gas typically
enters buildings via soil or groundwater migration. The best technology for radon gas is
activated carbon adsorption (27,32,36).
Generally, the inhalation of asbestos is from occupational exposure to asbestos
when asbestos material is being applied, as well as its manufacturing and the demolition
of buildings. Exposure to asbestos through inhalation has shown a higher than expected
incidence of bronchial cancer. Various technologies for the control of airborne asbestos
have been reported in US EPA Report No. TS-799 (28), a United Nations report (27), and
elsewhere (29–32).
.
9. AIR QUALITY MANAGEMENT
9.3. Air Toxics
Air toxics emit from existing point and area sources. Large point sources
include chemical plants, petroleum refineries, and power plants. The small point sources
of air toxic emission, such as dry cleaners, are more widespread than large point sources.
Air toxics emissions are also attributed to waste-management sources; the US EPA OSW
has shown that there are 2600 to 3000 potential TSDFs.
Acute (short-term) or chronic (long-term) exposure to an air pollutant has
characteristic health effects. The neurological, respiratory, and reproduction systems can
be affected by exposure to air toxics. Exposure to benzene, for instance, can result in
cancer. The US EPA has developed two methods to identify or quantify the impact of
carcinogenic air toxics: individual risk and population risk. Individual risk is expressed as a
statistical probability to show an individual’s increased risk of contracting cancer when
exposed to a specific concentration of a pollutant over a 70-yr lifetime. Population risk,
which is expressed as number of cancer incidences per year expected nationwide,
shows the risk as result of exposure to a pollutant.
.
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.1. Industrial Ecology
Industrial ecology seeks to balance industrial production and economic
performance with the emerging understanding of both local and global ecological
constraints. As a result, industrial ecology is now a branch of systems science for
sustainability, or a framework for designing and operating industrial systems as
sustainable and interdependent with natural systems (33).
9.4.2. Global Warming
Over the past 50 yr, global warming has been attributed to greenhouse gases,
such as carbon, water vapor, methane, nitrogen dioxide, CFCs, and so forth. It has been
projected that average temperatures across the world could climb between 1.4ºC and
5.8ºC over the next century. A major cause for this projected global warming is the
increased carbon dioxide emission by industries and automobiles. At the source, carbon
dioxide emission can be easily removed from industrial stacks by a scrubbing process
that utilizes alkaline substances. The long-term effect of global warming, projected in the
UN Environmental Report released in February 2001, may cost the world about $304
billion (US) a year down the road. This projected cost is based on the following
anticipated losses: (1) human life loss and property damages as a result of more frequent
tropical cyclones; (2) land loss as a result of rising sea levels; (3) damages to fishing
stocks, agriculture, and water supplies; and (4) disappearance of many endangered
species (33)
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.2. Global Warming
According to a 2001 Gallup poll, 57% of Americans surveyed stated
that where economic growth conflicts with environmental interests, the interest of the
environment should prevail. On the other hand, the same survey discovered that only
31% of those polled think global warming would pose a serious threat to themselves or
their way of life. The results of this poll indicate that both environmental and economical
interests are important to Americans. Some of the existing removal processes, although
very simple in theories and principles, are considered to be economically unfeasible by
industry and government leaders. For example, carbon dioxide could be easily removed
by a wet scrubbing process, but the technology is not considered cost-effective, because
the only reuse is the solution in the process. In response, President Bush decided not to
regulate carbon dioxide emission at industrial plants. He also rejected the Kyoto
international global warming treaty, but US EPA Administrator Christine Todd Whitman
stated: “We can develop technologies, market-based incentives and other innovative
approaches to global climate changes.”
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.3. Carbon Dioxide Reuse
An industrial ecology approach to carbon dioxide has been extensively
studied (decarbonization) by Wang and his associates (25,26,33) at the Lenox Institute of
Water Technology in Massachusetts. Their studies showed that decarbonization is
technically and economically feasible when the carbon dioxide gases from industrial
stacks are collected for in-plant reuse as chemicals for tanneries, dairies, water-
treatment plants, and municipal wastewater plants. It is estimated that tannery
wastewater contains about 20% of organic pollutants. Using the tannery’s own stack gas
(containing mainly carbon dioxide), dissolved proteins can be recovered from the tannery
wastewater. Recovery of protein can also be accomplished at a dairy factory. By bubbling
dairy factory stack gas containing mainly carbon dioxide through dairy factory
wastewater stream, about 78% of the protein in the stream can be recovered. Stack gas
containing mainly carbon dioxide can be used at a water-treatment softening plant as a
precipitation agent for hardness removal. Neutralization and warming agent can be
accomplished at a municipal wastewater-treatment plant by using stack gas containing
carbon dioxides. At plants that produce carbon dioxide gas, a large volume of carbon
dioxide gases can be immediately reused as chemicals in various in-plant applications,
which may save chemical costs, produce valuable byproducts, and reduce the global
warming problem.
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.4. Vehicle Emission Reduction
A second industrial ecology approach is to develop a new generation of vehicles
capable of traveling up to 80 mpg while reducing nitrogen oxides, carbon dioxide, and
hydrocarbon levels. Specifically, a “supercar” is to be developed to meet the US EPA’s Tier
2 emission limits (33). There are growing health concerns about persistent bio-
accumulative toxics that are produced from the combustion of coal, wood, oil, and
current vehicle fuels (46).
The issues of energy versus environment have been continuously discussed by
many scientists and policy-makers (44–46). In the United States, automakers are racing
to build hybrid vehicles and fuel-cell vehicles (53). On January 29, 2003, President George
W. Bush announced a $1.2 billion Freedom Fuel Program to speed the development of
hydrogen-powered vehicles in 17 yr using fuel-cell technology (58,61,65). Fuel cells
create energy out of hydrogen and oxygen, leaving only harmless water vapor as a by-
product of the chemical process. For automobiles, this would end their damaging air
pollution and eliminate American dependence on foreign oil. Menkedick discusses the
energy and the emerging technology focus (46).
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.4. Vehicle Emission Reduction
9. AIR QUALITY MANAGEMENT
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach
9.4.5. Planting Fast-Growing Trees
A third industrial ecology approach is to plant Loblolly pines (Pinus taeda) in
areas with high CO2 concentrations. These faster-growing trees will respond more to
elevated CO 2 levels than will slower-growing hardwoods, because of faster
photosynthesis and plant growth. The Loblolly pine is the species most frequently grown
for timber production in the United States. Its wood has a wide range of uses, such as
building material pulpwood and fuel (33).
9.5. Environmental Laws
As required by the Superfund Amendments and Reauthorization Act (SARA),
Section 313, major US industries began reporting the amounts of toxic chemicals they
released into the air, land, and water. In 1987, industries reported that about 2.4×109 lb of
toxic pollutants were released into the air. The US EPA has estimated that air toxics
accounted for between 1600 and 3000 cancer deaths per year, and the average urban
individual lifetime risk of contracting cancer as a result of exposure to air toxics is
estimated to be as high as 1 in 1000 persons.
Air toxics emissions from TSDFs have been preliminarily estimated to have a
national population risk of about 140 cancer cases per year. Exposure to these air toxics
from TSDFs has also been estimated to have a maximum individual risk of 2 in 100
persons contracting cancer.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Figure 18 shows the top 14 VOCs and air toxics, which are referred to as
hazardous air pollutants (HAPs) on a mass emission basis. During the examination of air
emission, the toxicity of each compound and degree of exposure that occur must be
considered (e.g., time and concentration). The most emitted VOC is toluene, but this is
less toxic than benzene, a carcinogen linked to leukemia.
Several major environmental laws have been established to address organic air
emissions. The CAA was created to address major air pollution problems in the United
States. Additional environmental laws include RCRA, amended by the Hazardous and
Solid
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Waste Amendments and the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) as amended by SARA.
Most of the new air emission standards, discussed in this chapter, are being developed
under RCRA. As required under Section 3004(n), the US EPA Administrator is directed to
protect public health and welfare by establishing the standards for monitoring and
controlling the air emission from TSDFs. The implementation of these standards is
conducted under RCRA’s permitting systems for hazardous waste-management units.
The US EPA is developing the RCRA 3004(n) air standards under a three-phase
program, as shown in Table 7. Phase I develops the organic emissions standards from
process vents associated with specific noncombustion waste-treatment processes (e.g.,
stream stripping and thin-film evaporation units). Additionally under this phase, organic
emissions standards are developed for equipment leaks from pumps, valves, and pipe
fittings. On June 21, 1990, the final standards for these sources were promulgated. See
Subparts AA and BB in the Code of Federal Regulations (CFR), Title 40, Parts 264 and 265
(40 CFR 264 and 265). Under Phase II, the organic emission from tanks, surface
impoundments, containers, and miscellaneous units are established.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
The proposed standards for these sources were proposed in July 1991 and
published in (new) Subpart CC in 40 CFR, Parts 264 and 265. Even after the
implementation of Phase I and II organic standards, current analyses indicate a potential
residual risk problem. As a result, Phase III will develop individual constituent standards
as necessary to bring the residual maximum individual risk to within acceptable range (10
-6 to 10-4). Proposed Phase III standards are planned to be concurrent with promulgation
of Phase II standards.
Also established under RCRA is the Corrective Action Program, which requires
solid-waste-management units to go through a site-specific facility evaluation. Air
emissions must also be included in the site-specific evaluation and risk assessment.
Additionally, air emissions are affected by the land disposal restrictions (LDR), which
were promulgated under RCRA. Unless certain treatment requirements are met, LDR
prohibits the depositing of hazardous waste on or into land disposal sources such as
landfills, surface impoundments, and waste piles. When the hazardous waste is treated
to meet LDR requirements, air emission may result if the treatment process is not
properly controlled. To prevent cross-media pollution, the RCRA 3004(n) air standards
work in concert with the LDR .
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Another RCRA program establishes location standards for the siting of new
facilities. These standards also require consideration of air emissions.
Figure 19 shows an overview of hazardous waste management. After a hazard is
generated, it may go through a series of different processes and waste-management
units before disposal. For example, hazardous waste may be stored or treated in tanks
and containers. Various types of containers can be used for storage, including 55-gal
drums, dumpsters, tank trucks, and railcars. Treatment of the hazardous waste to meet
LDR can occur early in the waste-management process, or just prior to disposal.
Additionally, hazardous waste management can occur at the generator site (on-site) or at
commercial TSDF (off-site). A storage and transfer station may be used to handle waste
off-site prior to its being transported to another location for final treatment and disposal.
As shown in Figure 19, the coverage of the Phase I and II RCRA air standards is
overlaid onto the hazardous-waste-management units. As required in Phase I standards,
organic air emissions from process vents from treatment units specifically identified in
the standards are limited. Additionally, Phase I limits the air emission from equipment
leaks at waste-management units.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
To address organic air emissions from tanks, surface impoundments, and
containers, coverage of the RCRA air standards would be expanded by Phase II
standards. These standards are designed to contain (or suppress) potential organic
emissions from escaping prior treatment. As dictated by the standards, operators would
be required, for example, to cover open tanks containing organic waste unless it can be
demonstrated that the concentration of organic material in the waste is below a specific
level. Because the control requirements are initiated by the organic concentration of the
waste in the container, these standards are described as “waste-based” rules. According
to the Phase II RCRA air standards, waste treatment is not required; however, treatment
is required under LDR. For benzene waste, the national emissions standards for
hazardous air pollutants (NESHAP) require containment-type control prior to treatment.
This requirement is similar to requirements under Phase II RCRA air standards.
Additionally, NESHAP requires waste containing benzene to meet treatment
requirements.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Table 8 lists the major regulatory programs established under the CAA. These
programs address organic air emissions, ozone precursors, and air toxics. The US EPA, as
discussed previously, establishes the NAAQS for “criteria” pollutants. States are then
required to set standards to attain and maintain NAAQS. Because ozone is a criteria
pollutant, states regulate VOCs (ozone precursors) on a source-by-source basis.
Additionally, Section 111 of CAA sets new source performance standards (NSPS) for
emissions of criteria pollutants. These sources include new, modified, or reconstructed
stationary sources. Other pollutants may also be addressed by NSPS. These pollutants
are classified as “designated pollutants.” Designated pollutants are noncriteria pollutants
that are identified by the US EPA for regulation under CAA Section 111(d) based on
impact on health and welfare. Total reduced sulfur (TRS) and sulfuric acid mist are
examples of designated pollutants (66).
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Section 112 of the CAA establishes the NESHAP standards, which identify and
limit hazardous pollutant emissions from both existing and new stationary sources. The
1990 CAA amendments substantially change Section 112. Prior to 1990, Section 112
required the US EPA to first list the pollutant as hazardous and then to establish
standards to protect public health “with an ample margin of safety.” The amended
Section 112 requires the US EPA to establish technology-based standards for the sources
of 190 hazardous pollutants listed in the new law. Additionally, the law requires further
action by US EPA to establish a more stringent standard, if a risk assessment at later
time indicates that technology-based standards are not adequately protective.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Recently completed was the NESHAP for benzene waste operations. This was
the last NESHAP set under the “old” Section 112. In March 1990, it was promulgated and
codified in 40 CFR 61, Subpart FF. It applies to the following emission sources: chemical
plants, petroleum refineries, coke by-product recovery facilities, and TSDFs. The rule
establishes a compliance deadline of March 7, 1992 for which existing facilities must
install the required control.
The Comprehensive Environment Response, Compensation, and Liability Act
mandates the cleanup of inactive contaminated sites. Table 9 indicates that CERCLA has
several aspects that provide control of organic emissions. The process required for a
Superfund site cleanup is a site-specific risk analysis conducted prior to a removal and
remediation action. Under this analysis, consideration of air emissions resulting from the
cleanup must be incorporated in the cleanup. This is illustrated by a cleanup of
groundwater contaminated with organics. This cleanup could use a groundwater
stripping process to remove the organic contaminants, which would result in a potential
cross-media problem if air emissions created by this process were not controlled. The
cleanup process (removal and remediation) is also required to comply with applicable
rules and requirements (ARARs). Additionally, for some cleanup operations under the
Superfund, Phase I RCRA air standards may be ARARs.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Another important tool used to address air toxics is toxic release inventory,
required by SARA Title 313. Generally, this inventory assists in improving US EPA’s
knowledge of the sources of air toxics. Recently, the US EPA reviewed this inventory to
identify sources of the 190 toxic pollutants listed under the CAA of 1990.
Figure 20 shows the overlap of statutory coverage of air emission sources with
various laws. This overlap may in some instances result in the same source being subject
to regulations with different control requirements. This conflict is the result of regulations
being developed under laws with different mandates. For example, CAA requires
technology-based standards for NSPS, whereas RCRA 3004(n) air standards are risk
based. Compliance under this circumstance must be demonstrated with all applicable
rules. The US EPA will try to make consistent and complementary control requirements
of rules that apply to the same sources. This overlap is illustrated in Fig. 20 for the
coverage of air emissions from storage tanks in waste management. For example, three
separate rules may cover storage tanks containing benzene waste located at chemical
plants, petroleum refineries, coke by-product plants, and certain TSDFs.
First, NESHAP regulations, as described in 40 CFR 61 Part FF, would apply.
9. AIR QUALITY MANAGEMENT
9.5. Environmental Laws
Second, NSPS regulations, as described in 40 CFR Part 60, Subpart Kb, would
apply to new, modified, or reconstructed tanks containing volatile organic liquids (VOLs)
and tanks above a certain size limits.
Third, Phase II air standards, as described in RCRA, would apply to tanks in
which organic hazardous waste is managed. Therefore, depending on the particular
physical characteristics of the tank, these standards could be covered by the benzene
waste NESHAP, the VOL storage NSPS, and RCRA Phase II air standards. This overlap
would have minimal ramifications on owner/operators because control requirements
would be the same for all three. Readers are referred to the literature for the additional
discussions on the US Clean Air Act compliance (47,48,56,66).
10. CONTROL
In the subsequent chapters of this volume, the ways in which emissions diffuse
and become diluted in the atmosphere and methods for controlling air pollution
emissions are discussed. Once the basic diffusion mechanisms and their theory of
control are mastered, it is important to understand how to implement this information
effectively in real situations (23,24). When determining the control option to meet a
specific regulation, there will always be several available alternatives. One must consider
factors such as adverse environmental impact, economics, and effect on the process
(27,33,34,63,64). The following discussion illustrates how these factors may influence
the choice of control devices.
One must remember that the improper control of air pollutants can result in
other environmental problems. For example, the by-product discharge from a control
system can create odors and other varieties of air pollution, water pollution, or solid-
waste disposal problems. As a result, it may be necessary to provide auxiliary facilities to
dewater or even completely dry the slurries, deodorize wastes, and cover dry discharges
to prevent the escape of fugitive dust. Incorporation of air pollution control systems is
often a convenient method of “closing the loop” in a process, and recycling the by-product
of the control system should be examined.
Economic considerations are linked closely to the end use of the byproduct.
When considering recycling of the by-product, one needs to examine the potential market.
10. CONTROL
It has been shown that fly ash, for example, can be used in construction
material (lightweight strong building blocks, concrete, and asphalt) and the demand in
some markets has exceeded the supply.
The economical analysis of control system must include both capital and
operational costs. Significant factors in this economical analysis include the cost of
money (interest rate), the age of the existing process facilities, and/or the expected life of
the processing system with pollution controls. Additionally, both the capital and
operational costs must be examined. The operating cost for a control system is often
related to the cost of purchase and installations of the control equipment. Often, control
equipment with a high-cost capital has a low operational cost. Conversely, it is also true
that control equipment with a lower capital cost has a high operational cost. The gas
pumping system (blowers, etc.) is the single largest energy-related operating expense for
a control system. Therefore, a control system that requires a high-pressure gas pumping
system will have high energy demands that result in high operating expenses.
Another economical consideration is the actual operation and maintenance
procedures, which can influence the operating costs significantly. Control equipment
requires frequent and periodical preventive maintenance care and inspection to ensure
the useful life of control equipment. This work will be performed by either the operator or
the maintenance personnel.
10. CONTROL
For example, blowers, pumps, and other parts in a control unit require routine
lubrication, adjustment of belts and seals, and inspection. Periodically, a control unit
requires complete inspection of the entire unit. Additionally, some control units may also
require a complete shutdown in order to purge the system so that it can be entered for
inspection.
To maintain performance and assist in the maintenance of the equipment,
provisions should be made for obtaining sample measurements, including the building in
of sample and velocity ports and pressure taps into equipment. Routine measurement of
pressure drop across the control unit, pressure in the system, and gas and liquid flow
rates are minimal requirements for ensuring proper operation of control equipment. It is
important during the startup of the control that baseline information on the control
equipment be taken and recorded. This information should include measuring and
recording the outlet and inlet static pressures at the blower and current draw from the
blower motor. These startup measurements are compared to the regularly made
pressure drops and current draws to help in troubleshooting.
To handle the maximum process emission rate without inducing adverse
pressure (negative or positive) on the process, the control system must be sized properly.
Important considerations in sizing control equipment are temperature fluctuations and
humidity changes.
10. CONTROL
Changes in the temperature and humidity of the emission can significantly
affect the volume of gas required for treatment by a control unit. Section 6 presented the
calculation procedures for estimating the effects of these changes. Quantitative gas
stream calculations were presented in Section 7.
12. EXAMPLES
12.1. Example 1
12. EXAMPLES
12.1. Example 2
