Chemical Engineering July 2012 - 15

Newsfront
THE BIOGAS BOOM
I
New technologies are increasing
production efficiencies, making this
renewable energy source even more popular
t probably isn't going to solve all
the world's energy needs, but producing
biogas from waste can help
slash the energy bills at some
production plants, sewage-treatment
plants and even farms. And for those
companies offering biogas technology,
business is booming.
For example, Eisenmann Anlagenbau
AG & Co. KG (Böblingen, Germany;
www.eisenmann.com) has been
active in the biogas market since
2003, and the company says that international
demand has grown considerably
in recent years. More than
90 plants of very different designs of
Eisenmann are currently in operation,
including 20 biogas plants in Italy.
Germany is the undisputed biogas
champion, with over 7,100 of the estimated
10,000 biogas plants in Europe.
These facilities account for 11% of
the electricity generated in Germany
by renewables, according to BioPro
Baden-Württemberg GmbH (Stuttgart,
Germany; www.bio-pro.de).
The U.S. has over 2,200 sites producing
biogas, according to the American
Biogas Council (Washington, D.C.;
www.americanbiogascouncil.org), including
186 anaerobic digesters on
farms, 1,500 at wastewater treatment
plants and 576 landfill-gas projects.
Anaerobic digestion
Most of the thousands of operating
biogas plants are using conventional
digestion systems, which are basically
large towers or tanks designed
to process dry compost or wet sewage
sludge and industrial wastewater
by anaerobic fermentation. In these
warm, sealed airless containers, bacteria
metabolize organic matter into
biogas, a mixture of carbon dioxide,
Biothane Systems
International
FIGURE 1. The Memthane process features an anaerobic membrane bioreactor,
which increases the biogas yield in a much smaller footprint compared to conventional
anaerobic digesters
methane and small amounts of other
gases (H2O, H2S and NH3). Depending
on the feedstock, the methane content
will vary from 30-40 vol.% (for sewage
sludge and manure) to as much as 80
vol.% (fats and oils). The biogas can be
used - sometimes directly - as a fuel
for heating, burned in a gas engine to
generate electricity and heat (in combined
heat and power (CHP) systems),
compressed for operating vehicles, or
cleaned up for injection into naturalgas
pipelines.
In Spain, for example, Sener Ingeniería
y Sistemas, S.A. (Madrid, Spain;
www.sener.es) developed its Valpuren
process specifically for treating pig
manure. This waste is normally used
as a fertilizer, but in some rural areas,
the livestock density is so large that
the amount of manure is too much
for this disposal option - the nitrogen
levels in ground water can exceed
E.U. Directives.
The Valpuren process uses an anaerobic
mesophillic (30-35°C) biodigestion
of the manure to make biogas,
which is used for cogeneration of heat
and electricity, as well as a fertilizer
in a form that can be stored (dry pellets).
Biogas yields are increased by
co-digestion with other waste feeds,
such as those from food processors or
slaughterhouses. Since the process
was commercialized in 2001, five industrial
plants are now processing
100,000 ton/yr of pig manure and generating
16 MW of CHP.
Eisenmann recently designed a new
composter with a biogas plant to convert
an existing biomass-composting
plant of the Swedish waste-utility
Västblekinge Miljö AB (Mörrum, Sweden),
enabling the company to convert
20,000 ton/yr of regional biowaste into
1,500 tons of fuel. When the facility
starts up later this year, it will feature
two horizontal plug-flow digesters,
each with a capacity of 800 m3. These
digesters are made of precast, reinforced
concrete and equipped with special
horizontal agitators. Operating at
temperatures of 55°C (thermophillic),
the system almost completely digests
the feedstock within 25-30 days, while
destroying potentially harmful pathogens
in the process, says Eisenmann.
Another biogas plant featuring thermophillic
fermentation - one of the
largest in Europe - has been designed
CHEMICAL ENGINEERING WWW.CHE.COM JULY 2012 15
http://www.eisenmann.com http://www.bio-pro.de http://www.americanbiogascouncil.org http://www.sener.es http://WWW.CHE.COM
Chemical Engineering July 2012

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