Problem
With over 70 ethanol plants under construction, there is a need
for quality pollution control.
Originally published in the July 2007 issue of Pollution
Engineering Magazine.
By Scott W. Golla, QEP, MBA, senior consultant for
Malcolm Pirnie, and Richard Grzanka, BSME, MBA, regional vice
president for Anguil Environmental Systems
Solution
Recent increases in ethanol production and trends in
plant design
In an effort to reduce the world's dependence on fossil fuels,
there has been a major push towards alternatives. Ethanol has been
at the forefront of this movement because it reduces greenhouse gas
emissions from automobiles and its production has a positive net
energy balance. The homegrown fuel also reduces the need for
imported oil from sometimes unfriendly and unreliable supplier
nations.
The Energy Policy Act of 2005 required the blending of 7.5
billion gallons per year of renewable fuels with gasoline by 2012.
According to the Renewable Fuels Association, that threshold should
be met sometime this summer, on a capacity basis. Ethanol plants
are expanding and being developed at a significant rate in North
America and throughout the world. There are currently over 70
ethanol production plants under construction in the United States
alone. Washington is talking about a goal of 25 percent of our
transportation fuel supply from renewable biofuels by 2025. This
ethanol development has expanded to nearly all regions of the
country; suffice it to say there is a boom going on the ethanol
industry and it is expected to continue for some time.
There are currently over 70
ethanol production plants under construction in the United States
alone.
Ethanol is produced by fermenting and distilling starch,
creating a 200-proof alcohol suitable for combustion in a vehicle.
When processing corn, only 70 percent of the kernel is made into
ethanol; the remaining fats, proteins, fiber, oils and minerals are
referred to as distiller's grain (DG). If a production plant is not
very proximate to dairy operations or other significant livestock
feeding needs, it will have to dry the DG in order to prevent
spoilage during transport to more distant regional markets.
Operating restrictions, penalties and fines, as well as community
pressures, are forcing many plants to strive for the lowest
possible emission levels from their dryers, enabling future
capacity expansions.
Since air permits are granted on a facility-wide basis, when
developing, designing and permitting ethanol production facilities,
selecting the most appropriate process equipment as well as air
pollution control equipment is critical. Some unique DG dryer
designs are steam-heated or compressed air-based, but the vast
majority of installed dryers are heated with natural gas.
Regardless of the dryer type, volatile organic compounds (VOCs),
odors and aerosols are emitted from the drying activity. By far the
most commonly installed technology for this critical emissions
source is some form of efficient thermal oxidation. Most of the
major ethanol design firms incorporate thermal oxidation of this
exhaust stream into their plant designs, and most state air
permitting agencies require it.
Process configurations & air permit
implications
Selecting a dryer technology and its corresponding pollution
control equipment often is the underlying decision for determining
air permitting major source status. Prevention of significant
deterioration (PSD) thresholds are now 250 tons per year (tpy) per
pollutant facility-wide, since the EPA changed its interpretation
of PSD rules for ethanol plants, in 72 FR 24060, on May 1,
2007.
In some non-corn-belt areas of the country where ethanol plants
are now being proposed, such as those in ozone non-attainment areas
or transport regions, major source thresholds are as low as 50 or
even 25 tpy of VOCs to trigger non-attainment New Source Review
(NNSR) permitting. When combustion emissions from boilers,
emergency generators, fire water pump engines and load-out flares
are added to those from the dryer and thermal oxidizer, one can
envision why these decisions are critical.
NNSR permitting involves determining and installing lowest
achievable emissions rate (LAER), control technology, obtaining
emissions offsets, and analysis of alternatives for the entire
development project. PSD permitting involves dispersion modeling,
best-available control technology (BACT) determination and
commitment, and other impact analyses. Both NNSR and PSD permitting
involve additional expense and longer permitting timelines, neither
of which finds fondness with ethanol developers. Efficient,
properly tuned thermal oxidizers are generally considered to meet
BACT and LAER requirements, but there is surprisingly little
history in the EPA's RACT/BACT/LAER Clearinghouse database[1],
since most ethanol developers to date have sought to avoid NNSR and
PSD permitting by maintaining emissions below the threshold
levels.
Abatement equipment selection
Some ethanol facilities in the upper Midwest were originally
constructed without thermal oxidizers. However, odor complaints and
EPA consent orders forced the installation of oxidizers, and hence
some form of thermal oxidation is now a part of any new ethanol
plant design involving a dryer. Certain plants with solid fuel
boilers (often major sources) may vent the dryer exhaust into the
boiler for thermal destruction. Others may recover some energy from
direct-fired thermal oxidizers by generating steam.
In general, the following two technology solutions have been
considered preferred for the ethanol plant DG dryer emission
control:
Regenerative thermal oxidizer (RTO):
- Destruction Efficiencies of 98 to 99 percent for VOCs,
hazardous air pollutants (HAPs) and CO
- Designed to handle a wet air stream with some particulate.
- Pre-filters available for higher levels of particulate.
- Thermal energy recovery of 95 percent insures low fuel usage,
and low NOX production.
- Fuel injection system further lowers NOX.
Direct-fired thermal oxidizer/waste heat
boiler:
- Designed to oxidize 99+ percent of VOCs, HAPS, CO and organic
particulate without obstructions, eliminates the potential for
plugging.
- Generates steam for use in the process.
- Can reduce overall capital cost of plant and air
emissions.
- Optional turbine produces power for driving electric motors or
for distribution within the plant.
A natural gas RTO may have the highest efficiency,
the lowest emissions and a lower total installation cost versus
other options. A natural gas RTO may allow a larger capacity plant
to be constructed (greater than 100 MGY) while remaining a minor
source, but most other options will trigger major source
permitting. Tradeoffs are between capital expenditures and
operating expenses, as well as a shorter timeline to construction,
versus potential future competitive advantages. A good natural gas
supply deal is a must, with some portion of the net input reserved
for hedging on the spot market.
An ethanol developer's speed-to-market, permitting timeline and
expenses, material logistics, feedstock, energy source, and
selected co-products all relate to the dryer type and air pollution
control technology decisions.
Several other parameters need to be considered to evaluate the
selection and design of a fully integrated air abatement system,
including regulatory requirements and emission characteristics for
VOCs, NOX, CO and HAPs. Other parameters include the following
process characteristics:
- New or existing plant
- Airflow requiring treatment
- Steam requirements and cost to produce
- Power availability and cost to distribute
Environmental impact
According to the Department of Energy's Argonne National
Laboratory, ethanol-blended fuels reduced CO2-equivalent greenhouse
gas emissions by 7.8 million tons in 2005, which had the equivalent
effect of removing the annual greenhouse gas emissions of over 1
million automobiles from the road. Many agree that ethanol is a
cleaner-burning fuel than gasoline. With state-of-the-art control
technology in place at ethanol plants, it can be ensured that
production does not counteract the positive impact of this
alternative fuel.
Scott W. Golla, QEP, MBA, is a senior consultant in Malcolm
Pirnie's Pittsburgh office. He assists new energy development
clients with permitting and strategy, and can be reached at (724)
934-4112.
Richard Grzanka, is regional vice president - sales for
Anguil Environmental Systems, and holds a BSME, and an MBA. He has
been active in heat recovery and thermal oxidizer applications for
25 years, and can be reached at (973) 543-8923 or visit www.anguil.com.
- Visit http://cfpub1.epa.gov/rblc/htm/bl02.cfm to learn more
about the RACT/BACT/LAER Clearinghouse.
Visit www.pollutionengineering.com and electronically
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