POWER December 2014 - 28

TOP PLANTS
Hometown BioEnergy, Le Sueur,
Minnesota
Owner/operator: Minnesota Municipal Power Agency/Avant Energy Inc.
Courtesy: Avant Energy Inc.
Using agricultural and food-processing waste products, Hometown BioEnergy is
helping the Minnesota Municipal Power Agency meet state-mandated renewable
energy standards while also providing a valuable fertilizer for area farmers and solid
biomass as a fuel for other facilities.
Aaron Larson
W
e've all heard the phrase " one
man's trash is another man's treasure. "
Hometown BioEnergy
(HTBE) offers a case in point. The plant uses
vegetable-processing waste and livestock
manure in an anaerobic digestion process to
produce biogas for use in engine generator
sets. The agricultural trash is a real treasure
for the company.
Avant Energy Inc.-the energy management
company that developed, oversaw construction,
and continues to manage operation
of the plant for Minnesota Municipal Power
Agency (MMPA)-sees tremendous opportunities
to redefine the term " waste. " It
believes bioenergy can help utilities, large
waste producers, food processors, and communities
create value from waste streams and
reduce overall energy costs. Its development
team supports clients in the planning, design,
and construction of both conventional and renewable
power generation facilities.
While some people may think that the
plant is utilizing vital resources that could
otherwise be used to fertilize area farmland,
it actually increases options for the agricultural
industry. Not only does it help manage
disposal of the waste, but its biological pro28
cess
also produces a liquid fertilizer-rich in
nutrients such as nitrogen, phosphorus, and
potassium-that is then sold back to local
farmers to spread on their land. In addition,
undigested biomass is dried to create a solid
fuel, which can be sold to other biomass and
coal-fired facilities to fuel their boilers.
A Flexible Design
Variety may be the " spice of life, " but it
doesn't always make for the best " seasoning "
at biomass plants. When dealing with
agricultural waste products, though, variety
is also a fact of life. Materials are frequently
exposed to weather, which means rain, sun,
and wind will all significantly affect moisture
content. If waste is stockpiled for any length
of time prior to delivery, quality can degrade.
Farm management practices-such as cleaning
schedules, herd size, square footage per
animal, and base bedding material-can also
affect waste quality.
One of Avant's key objectives when designing
the HTBE facility was maintaining
flexibility in the allowable feedstocks. Tolerating
variety enables the plant to manage
large seasonal changes in waste volumes
from suppliers in the region. In addition, it
www.powermag.com
allows the company to accept wastes that
become available on a sporadic basis with
fewer operational challenges.
The process begins with feedstock delivery.
The mixture of local agricultural and
food processing waste includes sweet corn
silage, food waste, livestock waste, and
waste oils (all sourced from within a 60-mile
radius). The material is transported to HTBE
via truck and delivered to the plant's receiving
hall. The biomass is weighed, mixed, and
heated in feeding modules to prepare it for
the anaerobic digestion process.
" The percentages of each type of material
varies; however, on average, the plant sees
approximately 50% higher solid wastes and
50% liquid wastes, " said Kelsey Dillon, vice
president BioPower for Avant Energy.
Inside the digesters, bacteria work together
in the absence of oxygen to decompose
organic material and produce biogas. Biogas
typically contains about 55% to 70% methane,
30% to 45% carbon dioxide, and trace
amounts of other gases, including sulfur in
the form of hydrogen sulfide (H2S). As H2S
is corrosive, it must be removed before combustion.
At HTBE, the H2S is removed from
the biogas through microbial processes in gas
POWER | December 2014
http://www.powermag.com
POWER December 2014

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