POWER March 2013 - 76

COMMENTARY
Biogas: An Alternative
Energy Source
By Sarah K. Walls
ost professionals in the energy industry know about biomass;
fewer of us are conversant with biogas. This commentary
explains the basics of biogas, with a focus on its
current use and future potential as a source of electrical power.
M
What Is Biogas?
Biogas is produced from anaerobic digestion of biodegradable organic
matter, or " biomass. " Bacteria present in, or added to, the
biomass ferments it anaerobically (without oxygen), through biochemical
reactions. The constituents of biogas include methane
(60% to 80%), carbon dioxide (20% to 40%), and trace amounts
of hydrogen sulfide, nitrogen, and other impurities. Cleaning to
remove impurities and moisture is necessary before biogas can
be used as an energy source for certain alternatives, such as
compressed natural gas. This purification is known as " upgrading "
the biogas. Rendering biogas to be at least 98% methane
produces a product known as " biomethane. " Biomethane performs
identically to conventional fossil fuel natural gas, with all
the same benefits and uses, and is one of the cleanest and most
efficient alternative energy sources.
Major sources of biogas include municipal wastewater treatment
plants, industrial waste treatment facilities, landfills, and
agricultural sources such as manure and energy crops. In the past,
such facilities used anaerobic digestion for stabilization, pathogen
reduction, and volume reduction of wastes prior to disposal or
land application. In many cases, biogas was simply flared.
Biogas now is developing into a significant alternative energy
source. Using biogas to produce electricity satisfies several regulatory
concerns at once. Greenhouse gas emissions are reduced,
because the release of methane is prevented; green and renewable
energy is produced; volumes of waste requiring storage and
disposal are reduced.
Uses of Biomethane
Advantageous uses of biomethane include combined heat and
power (CHP), boiler fuel, and injection into natural gas pipelines,
along with use of compressed biomethane and liquefied
biomethane for vehicle fuels. CHP systems, which produce both
mechanical and thermal energy, can use biogas to produce electricity.
The electricity produced can be used on-site, which reduces
the facility's electrical costs, or fed into mainstream power grids.
CHP uses for biogas include internal combustion engines, combustion
gas turbines, microturbines, fuel cells, and steam turbines.
In other countries, especially in Europe, where the cost of
electricity is much higher than in the U.S., anaerobic digestion
for biogas production is used widely. Anaerobic digestion facilities
utilizing " energy crops, " such as corn, are already built or
in progress in Germany, Sweden, Poland, Hungary, and Denmark.
These facilities produce biogas, whereas in the U.S., energy crops
are being used for production of fuel alcohol or ethanol. The
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production of biogas from energy crops is much more energyefficient
than the production of ethanol: For the same quantity
of energy crop converted to alternative energy, the net energy
value produced is greater with biogas.
The Kyoto Protocol has pushed other countries to establish
renewable energy targets and promote development of renewable
energy technologies. Germany was the first nation to enact
feed-in-tariff (FIT) laws promoting biogas. The FIT legislation
requires utilities to buy the electricity produced by biogas generators.
Even German farmers can generate electricity from biogas
and sell it to the grid.
Slow Start in the U.S.
Certain barriers have prevented broader use of biogas in the U.S.
These barriers include less-than-favorable economics, lack of
capital, technical complications, and air permitting delays. However,
while the up-front capital investment necessary is high,
benefits over the entire life cycle can exceed the initial costs.
The Village Creek Water Reclamation Facility in Fort Worth,
Texas, is a prime example of using biogas to produce electricity.
This cutting-edge municipal facility uses low-Btu methane biogas
generated as a by-product of its anaerobic sludge digesters,
six of which have been upgraded to take in high-strength liquid
industrial wastes to supplement biogas production. The raw, untreated
biogas, combined with biogas contributed by a nearby
landfill, passes through a dehydrator prior to being burned as
fuel in two 5.2-MW combustion turbines. The waste heat from
the engines is combined with additional biogas in a duct burner
to fire boilers, which produce steam. The steam is used to operate
two steam turbines that operate two of the 1,000-horsepower
blowers, which provide aeration for the activated biological
treatment part of the facility. Once all units are operating, the
facility will produce more biogas than is needed for its own operation
and will have additional electricity to sell to the grid or
trade for uses at other facilities.
Bright Future in the U.S.
The future of biogas in the U.S. will depend to a large extent
upon the price of natural gas. Last year, President Obama's Executive
Order 13624 recognized the barriers that have led to
under-investment in CHP and directed certain agencies and executive
departments to convene stakeholders with the goal of
accelerating investment in industrial energy efficiency, and in
CHP in particular. A national goal was set of 40 GW of new, costeffective
CHP by the end of 2020-a 50% increase from today.
Biogas has much potential, and there has never been a better
time for owners, state and federal government leaders, lenders, and
utilities to work together to accomplish this challenging goal. ■
-Sarah K. Walls (swalls@canteyhanger.com) is a partner with
Cantey Hanger LLP.
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POWER March 2013

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