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Heavy-duty trucks and buses account for about one-third of NOx emissions and one-quarter
of PM emissions from mobile sources. In some urban areas, the contribution is even
greater. The fine particles in diesel exhaust (known as particulate matter) can
penetrate deep into the lungs and pose serious health risks including aggravated
asthma, lung damage, and other serious health problems. In addition, diesel exhaust
is a likely human carcinogen. Children are more susceptible to air pollution than
healthy adults because their respiratory systems are still developing and they have
a faster breathing rate. Diesel exhaust also has environmental impacts. PM from
diesel engines contribute to haze, which restricts visibility. In addition, diesel
exhaust contributes to ozone formation (a component of smog), acid rain, and global
climate change. [N]
Diesel engines, which provide fuel economy and durability advantages for large heavy-duty
trucks, buses and nonroad equipment, emit significant amounts of oxides of nitrogen
(NOx),
particulate matter
(PM), and hydrocarbons (HC) that contribute to acid rain, ground-level ozone,
and reduced visibility. In addition, there is concern about the adverse human health
effects related to exposure to diesel exhaust such as lung damage, respiratory problems,
and premature death. Increasing evidence also suggests that diesel exhaust can cause
cancer in humans. The severity of air quality issues vary greatly with the region
of the U.S. and level of urbanization. Current estimates indicate that emissions
from such engines in the Northeast States account for roughly 33 percent of the
nitrogen oxides (NOx) and 80 percent of the particulate matter (PM 10) emitted by
all mobile sources. [N]
There are new EPA emission standards to dramatically reduce pollution from new engines
beginning in 2004, "New Emission Standards for Heavy-Duty Diesel Engines Used in Trucks
and Buses. [N]
However, the diesel engines currently on the road pollute at much higher rates.
They can run for 1,000,000 miles and last for 20 to 30 years. Several strategies
are being pursued to make existing diesel engines cleaner. In addition to efforts
to optimize fuel delivery and air intake systems, after-treatment devices such as
particulate traps and catalytic converters offer ways to prevent dangerous emissions
from entering the air. Particulate traps collect and burn away particulate emissions.
Catalysts convert damaging pollutants to less-harmful products. There are also efforts
to improve the emission characteristics of diesel fuel by modifying fuel properties
such as sulfur content and through the use of fuel additives. EPA has a fact sheet
on Emissions
Control Potential for Heavy Duty Diesel Engines that explains the potential
for control of pollution from Heavy-Duty Diesel Engines. [N]
EPA has issued emission standards for new, nonroad diesel engines, such as construction
equipment, but engines within the existing fleet will not be subject to the new
regulations, yet may remain in operation for another 25-30 years. Therefore, state
DOTs with who are taking seriously stewardship with respect to air quality are retrofitting
existing diesel vehicles with pollution controls, implementing emission testing
programs for diesel vehicles, creating and implementing anti-idling programs, and
promoting cleaner fuels like ultra-low sulfur diesel and compressed natural gas.
[N]
Idling Reduction
The Environmental Protection Agency is working with the trucking industry, manufacturers
of idle control technologies, various states, and other partners to help save fuel
and reduce air pollution from idling trucks. EPA is conducting emissions testing
on idling trucks under various conditions, surveying trucking fleets to learn more
about idling times, implementing demonstration projects to test idle control technologies,
and holding workshops to educate affected communities. Truck drivers idle their
engines during their rest periods to provide heat or air conditioning for the sleeper
compartment, keep the engine warm during cold weather, and provide electrical power
for their appliances. Trucks consume up to one gallon of diesel fuel for each hour
at idle, using as much as 2,400 gallons of fuel every year per truck. This totals
1.2 billion gallons of diesel fuel consumed every year from idling, costing $1.8
billion (at $1.50 gallon/diesel). On average, each idling truck produces about 21
tons of carbon dioxide (C02) and 0.3 tons of nitrogen oxides (NOx) annually totaling
over 11 million tons and 150,000 tons, respectively. Diesel exhaust also contains
particulates, sulfur dioxide, carbon monoxide, hydrocarbons, and various air toxics.
Idling emissions can contribute to premature mortality, bronchitis (chronic and
acute), hospital admissions, respiratory symptoms (upper and lower), and asthma
attacks. The vast majority of fuel consumed during long-duration idling can be saved
and air emissions reduced by installing one of several idle control technologies
that provide heat, air conditioning, and electrical power. These technologies include
auxiliary units and truck stop electrification. A list of the currently available idle technologies can be found on-line
at EPA. [N]
Strategies for reducing idling include:
- Auxiliary units: These are small, diesel-powered engines (5 to10 horsepower)
that are installed on the truck They range in cost from $1,500 for direct-fired
heaters (providing heat only) to $7,000 for auxiliary power units (combined cab
heat/AC, electric power, and heat to engine and fuel).
- Truck stop electrification: This technology involves modifications to the truck
and to the truck stop parking space to provide electrical power, heat and air conditioning.
An advanced truck stop electrification product is also available as a rental without
modification to the truck. Costs to implement truck stop electrification vary depending
on the company modifying the truck and installing the electrification technology
used.
Diesel Engine Retrofits through Fleet Management
Fleet upgrades are a major capital investment for a DOT. For example, NJDOT's Capital
Investment Strategy FY 2003-2007 allocated approximately $ 21.5 million to NJ Transit
towards clean air programs, emission control and rebuilt engines on fleet."
[N]
- An engine "retrofit" includes but is not limited to
- Addition of new/better pollution control after-treatment equipment to certified
engines.
- Upgrading a certified engine to a cleaner certified configuration.
- Upgrading an uncertified engine to a cleaner "certified-like" configuration.
- Conversion of any engine to a cleaner fuel.
- Early replacement of older engines with newer (presumably cleaner) engines (in
lieu of regular expected rebuilding).
- Use of cleaner fuel and/or emission reducing fuel additive (w/o engine conversion).
Fleet owners should consider the cost and benefits of each of these options. Potential
Funding Sources are available for projects meeting certain criteria. It is also
helpful to work with air quality planners to calculate the tons of emissions reductions
the project can generate. EPA has created an Emissions Reductions Calculator that facilitates investigation
of various retrofit scenarios. Recommended practices include the following:
- Consider alternatives with the most advanced emission control systems available
in new vehicle purchases. Such alternatives include those equipped with devices
that minimize idling and warm-up time automatically, and those that run on cleaner
fuels like compressed natural gas.
- Identify and characterize the fleet. EPA's Fleet Assessment web page can assist fleet managers in determining
the fleet information needed for proper description.
- Understand which retrofit technologies are good choices for the engines in the
fleets.
EPA's
Verified Technology List provides a table all retrofit technologies verified
to produce measurable emissions reductions. New technologies are added to this list
periodically.
- Review the
New York City Transit Authority or Massachusetts Big Dig retrofit project case studies to
note some of the details of existing retrofit projects. Some details of the latter
are reviewed in the next section.
- Understand the
In-Use Testing Requirements for which retrofit manufacturers are responsible.
A retrofit device manufacturer may request that some of the retrofitted engines
be tested in the future to confirm that the retrofit technology is performing properly.
- Review EPA's
Tampering Concerns web page to understand EPA's policies regarding changes
to certified engines.
EPA also maintains lists of Retrofit Manufacturers web page and applicable Engine Manufacturers and additional maintenance requirements,
installation procedures, or other factors that may be associated with a retrofit
project.
Use of Clean Fuels
Ultra-Low Sulfur Diesel (ULSD) improves the performance of after-treatment technologies
such as a particulate matter (PM) filter. The combination of a PM filter and ULSD
can reduce emissions of PM by 90 percent. The quantity of emissions reductions from
the use of ULSD alone will vary depending on the application, level of sulfur reduction,
and other fuel characteristics of the replacement fuel (e.g., cetane number, aromatics,
PNA). Some case studies suggest that the use of ULSD alone can reduce emissions
of PM between 5 and 9 percent. While ULSD-only emission reductions for PM are relatively
modest on a per-vehicle basis compared to aftertreatment retrofit, the emission
reductions can be significant if an entire fleet is fueled with ULSD. ULSD will
be available nationwide in June 2006, but currently is available in certain parts
of the country. The price differential between ULSD and regular diesel fuel varies
by location but currently ranges between 8 and 25 cents more per gallon. In 2006,
when ULSD is available nationwide, the cost differential will be much less.
"The joint announcement, by the New Jersey Department of Transportation and
the New Jersey Department of Environmental Protection, in 2002, to purchase 60 million
gallons of Ultra-Low Sulfur fuel for New Jersey Transit (NJ Transit) fleet made
NJ Transit among the first transit agencies in the nation to have a full fleet using
environmentally-friendly fuel." [N]
Biodiesel is a domestically produced, renewable fuel that can be manufactured from
new and used vegetable oils and animal fats. Biodiesel has several advantages over
petrodiesel. It has greater lubricity, so it reduces wear between contacting metal
engine parts. This attribute will be of greater importance as the levels of sulfur
in diesel fuel are lowered from 500 ppm to 15 ppm in 2006. All diesel engines will
need lubricity-enhancing agents, and biodiesel is a proven choice in this regard.
Also, biodiesel's higher cetane content gives it a higher flash point and greater
resistance to premature ignition - a plus for many applications. Perhaps most
important, though, is that pure biodiesel reduces sulfates by 100 percent, carbon
dioxide lifecycle emissions by 78 percent, and carbon monoxide by 44 percent, due
to the higher oxygen level in the fuel. It also reduces particulate emissions by
40 - 80 percent and cuts unburned hydrocarbons by 68 percent. Blends of 20 percent
biodiesel with 80 percent petroleum diesel (B20) can be used in unmodified diesel
engines. B20 reduces emissions of PM by about 10 percent. However, B20 also increases
NOx emissions by approximately 2 percent. The B20 blend costs about 15 to 30 cents
per gallon more than regular diesel fuel. Biodiesel can be used in its pure form
(B100), but may require certain engine modifications to avoid maintenance and performance
problems. Pure blends of biodiesel may not be suitable for cold climates. B100 reduces
emissions of PM by roughly 40 percent and costs about 75 cents to $1.50 more than
regular diesel fuel.
Emulsified diesel is a blended mixture of diesel fuel, water, and other additives
that reduces emissions of PM as well as NOx. Emulsified diesel can be used in any
diesel engine, but the addition of water reduces the energy content of the fuel,
so some reduction in power and fuel economy can be expected. Emulsified fuel will
stay mixed for a fairly long time. However, if a vehicle sits dormant for months
at a time the water can settle out of the fuel and possibly cause problems.
Compressed Natural Gas (CNG), perhaps the most commonly known "clean fuel,"
is a gaseous fuel that is a mixture of hydrocarbons, mainly methane, and is produced
either from gas wells or in conjunction with crude oil production. More information on alternative fuels is available online.
Sample Diesel Emission Controls: The Boston Central
Artery/Tunnel (CA/T )and New Haven Harbor Crossing
The diesel emission control programs with the Central Artery/Tunnel (CA/T) Project
in Boston, Massachusetts, and the I-95 New Haven Harbor Crossing Improvement Program
(I-95 NHIP) in Southern Connecticut entailed add-on pollution control devices with
the option of cleaner diesel fuels. Initially started as a pilot program, the CA/T
retrofit program was then expanded to include all off-road equipment on more than
20 remaining construction contracts. Based on EPA certification data, it was anticipated
that oxidation catalysts would achieve at least 20 percent reductions for PM 10,
40 percent reductions for CO, and 50 percent reductions for HC in all heavy-duty
engines. The results of the evaluation for 88 pieces of equipment retrofitted during
the year 2000 indicated emission reductions of approximately 90 Kg/day of CO, 30
Kg/day of HC, and 7.4 Kg/day of PM 10. The cost of these catalysts ranges from $1,000
to $3,000 per unit, depending on the engine horsepower (HP) rating of the unit being
retrofitted. The average cost for the CA/T project was $2,500. [N]
The CA/T project had also explored the possibility of lowering diesel emissions even
further by replacing the diesel fuel with a cleaner alternative, using a low NOx
emission blend of diesel fuel consisting of a mixture of diesel fuel, water, and
an additive to maintain stability of the emulsified mixture. Demonstration projects
have achieved 10-30 percent NOx reductions and 10-50 percent PM reductions. A test
performed on one of the CA/T contracts using a Caterpillar excavator for a period
of three weeks indicated that this fuel, PuriNOx TM, reduced NOx emissions up to
30 percent, and smoke up to 96 percent when compared to No. 2 diesel fuel; however,
PuriNOx TM was not applied due to needed reductions in project costs. [N]
To help improve air quality in Greater New Haven, the Connecticut Department of Transportation
(ConnDOT) is implementing new methods for reducing emissions during the I-95 New
Haven Harbor Crossing (NHHC) Corridor Improvement Program. During construction on
the I-95 NHHC Corridor Improvement Program, equipment used on highway contracts
will be part of a pilot emissions reduction program for the State of Connecticut.
ConnDOT is requiring all contractors and sub-contractors to take part in the Connecticut
Clean Air Construction Initiative. The following contractor requirements apply:
[N]
- Emission control devices (such as oxidation catalysts) and/or clean fuels (such
as PuriNOx) are required for diesel-powered construction equipment, with engine
horsepower (HP) ratings of 60 HP and above, that are on the project or assigned
to the contract in excess of 30 days. Based on the CA/T experience PuriNOx TM was
considered a good alternative to the use of retrofit equipment to reduce NOx and
PM 10 emissions. The cost of PuriNOx TM was estimated to be 16 cents per gallon
above the cost of N o2 diesel fuel in the Northeast. The cost of B-20 Blend was
estimated between 15 to 30 cents per gallon above the cost of N o2 diesel fuel.
[N]
- Truck staging zones will be established for diesel-powered vehicles waiting
to load or unload materials. The zones will be located where diesel emissions will
have the least impact on abutters and the general public.
- Idling is limited to three minutes for delivery and dump trucks and other diesel-powered
equipment (with some exceptions).
- All work will be conducted to ensure that no harmful effects are caused to adjacent
sensitive receptors, such as schools, hospitals, and elderly housing. Diesel-powered
engines will be located away from fresh air intakes, air conditioners, and windows.
- Initial and monthly reporting by contractors will ensure the proper implementation
of the Connecticut Clean Air Construction Initiative. Non-compliance will be enforced
with a 24-hour notice to the contractor to improve a vehicle or remove it from a
project.
The cost of retrofitting equipment or using clean fuels was included in the general
cost of the contract, as bid by each contractor. Whereas a contractor who owns equipment
may be more likely to install the retrofit apparatus, one who rents equipment may
opt to use clean fuels.
To introduce the program to area contractors including clean fuel vendors and equipment
manufacturers, ConnDOT three informational meetings regarding clean fuels and equipment
retrofitting were conducted in August and September 2001, which were attended by
clean fuel vendors and equipment manufacturers. On Boston's "Big Dig",
no adverse operational problems or additional maintenance costs have been reported
for construction equipment retrofitted with oxidation catalysts. With proper installation,
and as long as a system is not stressed beyond its design limitations, equipment
warranties are not affected by installation of retrofit products. It has been estimated
that on Boston's "Big Dig," emission reductions amount to 36 tons/year
for carbon monoxide, 12 tons/year for hydrocarbons, and 3 tons/year for fine particulate
matter. Estimates for reduced emissions during the I-95 NHHC Corridor Improvement
Program are 20 tons/year for carbon monoxide and two tons/year for fine particulate
matter (with clean fuels or oxidation catalysts) and eight tons/year for hydrocarbons
(with oxidation catalysts only).
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Dust or particulate matter (small airborne particles) is a major form of air pollution
and can constitute a health hazard and create unsafe driving conditions. Airborne
particulate pollution arises from a number of sources, including manipulation of
the surface soil during construction activities, bulk material operations on construction
sites, and traffic on paved and unpaved roadways. Maintenance activities such as
sweeping, sand or chip sealing, ditch cleaning, foreslope shaping, roadside repairs,
and sanding for snow or ice conditions present possible sources of fugitive dust.
While dust control is an issue on many construction sites, particularly in arid
areas, it has become an even more important issue in metro areas with serious non-attainment
area designation for both the annual and 24-hr. PM10 National Ambient Air Quality
Standards. The Arizona Department of Transportation (ADOT) completed an investigation
into construction project PM10 source emissions in 1994, and recommended a variety
of control measures for future projects; however, many of these measures are not
having the anticipated impacts to address the particulate matter pollution issue,
leading to another study underway as of this writing, focusing on development of
a project manual to be used for education and outreach.
Wind erosion controls consist of applying water, other dust palliatives or covering
material as necessary to prevent or alleviate dust nuisance. Dust control practices
should be implemented on disturbed soils subject to wind erosion (including Shoulder
Grading, Roadside Stabilization and Minor Slides and Slipouts Cleanup/Repair).
Dust control practices are typically implemented on all exposed soils subject to
wind erosion. Covering of small stockpiles or areas is an alternative to applying
water or other dust palliatives. Dust abatement involves application of a dust palliative
to non-paved road surfaces to temporarily stabilize surface soils, leading to a
reduction of dust during the dry season. Palliatives are applied in liquid form
and can include water or calcium magnesium acetate, magnesium chloride, emulsified
asphalts, or lignon sulfonates. Wind erosion controls should be implemented for
stockpiles of loose materials.
DOT recommendations for dust control include the following:
- Evaluate suspending work under windy conditions when loose materials are prone
to erosion.
- Materials applied as temporary soil stabilizers also provide wind erosion control
benefits.
- Water is applied by means of pressure-type distributors or pipelines equipped
with a spray system or hoses and nozzles that will ensure even distribution.
- All distribution equipment is equipped with a positive means of shutoff.
- Unless water is applied by means of pipelines, at least one mobile unit should
be available at all times to apply water or dust palliative to the project or maintenance
activity site.
- Only potable and nonpotable (uncontaminated) water should be used. If reclaimed
waste water is used, the sources and discharge should meet state and local water
reclamation criteria. Nonpotable water should not be conveyed in tanks or drainpipes
that will be used to convey potable water, and there should be no connection between
potable and nonpotable supplies. Nonpotable tanks, pipes, and other conveyances
should be marked as non-potable and not for drinking.
- Do not apply excess water. Non-stormwater discharges are prohibited.
- Never use oil to control dust
- During preparation for application of dust palliatives, gravel berms should
be constructed at the low shoulders of the roadway to inhibit liquid palliatives
from entering waters of the State or waters of the U.S.
- Dust palliatives are not be applied during rain.
- Methods or materials are applied in a manner that is not detrimental to either
water or vegetation.
- Carry adequate spill protection.
- Use environmentally sensitive cleaning agents.
- Dispose of excess materials at appropriate sites.
- Maintenance: inspect protected areas to ensure proper coverage.
- All methods and devices employed to minimize dust pollution are subject to the
daily approval of the Resident Engineer.
Model Air Monitoring and Dust Control Practices
on Boston 's Central Artery Project
To minimize air quality dust impacts from CA/T construction activities, the project
developed Construction Dust Control Specification 721.561. Before any work can begin
on a CA/T site, a contractor must first develop and submit for approval a "Dust
Control Plan" which follows the requirements of the dust specification. The
requirements contractors followed to control construction generated dust included:
[N]
- Wet suppression alone, or with approved binding agents, to be used on-site on
a routine basis using a water truck.
- Wet spray power vacuum street sweeper to be used on paved roadways.
- Use of calcium chloride instead of wet suppression when freezing conditions
exist.
- Use of windscreen fabric or solid wood barriers around the perimeter of construction
sites.
- Use of wheel-wash stations or crushed stone at construction ingress/egress areas.
- Covering active stockpiles with plastic tarps, and seeding or using approved
soil stabilizers on inactive stockpiles.
- Covering dump trucks during material transport on public roadways.
Due to the unique characteristics of each contract in terms of location and scope
of work, particular methods to control dust in addition to the dust control specification
were implemented. These methods included: [N]
- Reducing the number of truck entrances and exits from a site within the contract;
- Providing a crushed stone base for the dump truck in the on-site loading area;
- Creating embankments between stockpiles and haul roads.
These particular measures were implemented to manage and reduce the dirt that was
tracking off work sites and onto city streets. To evaluate the effectiveness of
the dust control measures, a PM 10 monitoring and field dust inspection program
was implemented in 1997. The program measured PM 10 levels and inspected nuisance
dust at close to 20 sidewalk locations along the alignment during the summer months
for the past five years. The results from the monitoring program indicated that
the highest PM 10 levels decreased almost 50 percent once dust control efforts were
implemented. [N]
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At the plant, minimize air emissions by employing the following environmental stewardship
practices: [N]
- Select plant mixing temperature by:
- Contacting the asphalt supplier.
- Using the chart on the back.
- Do not use laboratory mixing temperature as plant mixing temperature.
- Make sure RAP and aggregates are dry.
- Do not use RAP containing coal tar.
- Do not expose RAP to flame.
- Do not over-heat RAP.
- Look for other sources of fumes such as:
- Slag aggregate
- Shingles
- Crumb rubber mixtures
- Other products from construction and demolition waste
- Read the Material Safety Data Sheet (MSDS) for all materials.
- Regularly calibrate thermocouples and other sensors.
- Tune up the burner.
- Contact the manufacturer and find out the limits on CO and O 2.
- When the stack is tested, compare the plant's thermocouple reading to the tester's
thermocouple.
- Gather data on aggregate moisture content and fuel usage. If fuel usage goes
up for the same or less moisture, find the reason.
- Have stack gases tested to see if they are in limits. If not, contact manufacturer
to make adjustments.
- Compare mix temperatures with plant temperatures. Look for changes over time.
- Measure and record the pressure drop in the baghouse. Look for changes over
time.
- Keep a record of fuel usage over time. Find the reason for any big changes.
- Keep track of this information and discuss it with co-workers and the manufacturer.
- Do not use diesel fuel and kerosene as release agents.
At the plant, minimize air emissions by employing the following environmental stewardship
practices:
- Try increasing the mat lift thickness before calling for a higher plant temperature.
Do not use diesel fuel and kerosene as release agents.
- Maintain engineering controls on paving equipment.
Guidance for Plant Mix Production and Field Compaction
Temperatures of HMA
High temperatures may cause several problems to occur, including damage of the asphalt
binder, generation of unnecessary fumes and odors, and excessive asphalt drain-down
may occur with some mix types. [N]
At this time, a reliable test does not exist for measuring the emissions potential
for a given asphalt binder. Research is underway to establish a test to indicate
emissions potential for a given asphalt and establish a maximum temperature that
will prevent unnecessary emissions generation. Until this research is completed,
the following procedure is recommended for selecting the starting point for plant
mixing and field compaction temperatures: [N]
- Contact the asphalt supplier, describe the mix type, and request the plant mixing
temperature recommendations.
- Consider previous field experiences with this asphalt binder grade from this
asphalt supplier and current project conditions. Project conditions could include
weather or seasonal conditions, lift thickness, haul distance, and mixture considerations.
Adjust the supplier's recommended temperatures to suit project conditions.
- Consult the chart "Typical Binder Temperatures" listed by PG Grade.
- Select a plant mix temperature starting point based on the information obtained
in items above.
- The starting point should be close to the middle of the range of temperatures
for the PG vender grade being used.
- Construct a test strip and monitor both densities and temperatures in accordance
with an approved Quality Control plan.
- Determine the laydown temperature at which specification density can be achieved.
- Use available software or graphs to estimate the heat loss during mix transport
and laydown, taking into consideration haul distance, ambient temperature, wind
conditions and mat thickness.
- Add this temperature loss to the targeted mix temperature obtained from the
test strip and this will yield a starting point for plant mixing temperatures at
the HMA plant.
- Adjust this temperature as necessary during normal production.
Aggregate, RAP, and Anti-Stripping Environmental
Stewardship Practices
- Do not use materials for RAP containing coal tar or other questionable material.
- Do not over-heat.
- Do not expose RAP to burner flame
High moisture contents in aggregate and RAP introduced into the HMA production process
may cause unnecessary fumes, emissions, and odors. Further, high moisture contents
can waste fuel in the drying process and negatively impact the quality of the HMA.
Therefore, to minimize these moisture contents, best management practices should
include the following:
- Paved stockpile areas graded to enhance drainage.
- Stockpiling techniques to allow materials to shed rain.
- Use of covered stockpiles in areas of high annual rainfall.
- Procedures to use the driest portion of a stockpile.
- Flighting in the dryer configured to optimize retention time and drying efficiency
while at the same time minimizing exposure of RAP and asphalt to the hot air stream.
In addition, anti-stripping additives should be used to enhance mixture durability
only when test results indicate the need for them. The antis-tripping additive must
be uniformly blended into the asphalt. Non-uniform blending may contribute to unnecessary
emissions. To minimize emissions:
- Use "low-odor" formulations of anti-stripping additives. Manufacturers
have developed blends that have reduced odor potential.
- Determine the optimal percentage of anti-stripping additive to use. Dosages
exceeding 0.5 percent (by weight of asphalt cement) are rarely needed. If high concentrations
are required, consider using a higher efficiency formulation. Note that the dosage
rate is expressed as a percentage of the weight of asphalt - not the weight
of the mixture.
- Control the temperature of the asphalt binder and the antistripping additive
at the lowest temperatures that produce satisfactory results. Do not overheat since
excessive heating may generate unnecessary emissions.
HMA Facility Burner Operation and Maintenance Practices
for Reducing Emissions
An HMA facility has the potential to emit various emissions, and it should not operate
outside its permit limits. Carbon Monoxide (CO), nitrogen oxides (NOx), sulfur oxides
(SOx), and volatile organic compounds (VOCs) are found in the exhaust gas stream.
The concentration level of each of these gases indicates the efficiency of the combustion
process. It is important to know the burner system specifications and capacities,
along with the concentration level of each of these gases. [N]
Implementation of a burner maintenance program is necessary to achieve optimum performance
of a burner system. Daily monitoring of burner performance is an integral part of
effective burner operation. Fuel usage should be tracked in relation to aggregate
moisture, mix temperature, and baghouse temperature to create and maintain a database.
Then daily burner operation parameters can be compared to this database to indicate
when burner efficiency has diminished, and burner maintenance is required. Flighting
in the combustion zone should be checked for wear and proper combustion space. In
parallel flow plants, particular attention should be given to obtain the proper
cigar-shaped flame.
Best practices for reducing emissions in facility burner operation and maintenance
include the following mechanisms: [N]
- Counter-flow mixing equipment technology can reduce emissions since it keeps
the RAP and binder separate from the drying area and flue gases.
- Sealed silo tops and sealed load-out areas may reduce fugitive emissions especially
when tied into fugitive emission recapture and destruction systems.
- An asphalt storage tank fugitive emission capture system may reduce fugitive
emissions from the vent.
- Exhaust fans should be kept running efficiently.
- Calibration of the thermocouples and other sensors are essential in monitoring
plant conditions and mix temperatures.
- Properly maintained engineering controls on the paver will help reduce emissions
in the work zone.
- Elimination of the use of diesel fuel and kerosene as release agents throughout
the hot mix asphalt production and construction process.
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