Biomass: A Sustainable
Alternative?
Given the current concern about
global warming and the desire to become
more energy independent, many states
in the U.S. are reviewing their approach
to renewable energy. In fact, about half
already have enacted renewable portfolio
standards (RPS). While these standards
vary widely from state to state, in general
they all require that electrical providers
within a state obtain a minimum percentage of their power from renewable
energy resources by a certain date.
California, not unexpectedly, leads the
charge with a target of 20 percent of its
energy portfolio from renewable resources
by 2010. However, the state may be stymied
by the limitations associated with the
available renewable energy technologies,
including solar, wind and geothermal
energy – in particular, the limitations
associated with the availability of these
energy sources due to geographic location and local climate.
Counterpoint
District Energy magazine is a publication of the International District Energy
Association. All articles are screened, reviewed and checked by an editorial committee and editorial staff. While we feel this article is of interest to our readers, we
did want to include commentary from Anthony Mirabella, PE, technical editor,
who provided the following observations after conducting his review.
From District Energy’s technical editor:
It is hard to disagree with the main premise of this article that energy prices are
going up and that biomass fuels may be an attractive alternative energy source
for some district energy facilities. District Energy St. Paul is the premier example
of this technology in the U.S. However, I disagree with the argument that the
U.S. is running out of natural gas, domestic and imported. Proven natural gas
reserves have increased 26 percent over the past 10 years. In other words, we
know of more gas in the ground today than we did 10 years ago, in spite of the
fact that we have been using gas at a record pace. Higher prices for natural gas
have encouraged more drilling and have shifted the politics toward more offshore exploration. The U.S. Department of Energy forecast for production and
consumption of natural gas through 2030 shows a 20 percent increase.
Biomass supplies almost five
times the energy output of
solar, wind and geothermal
energy sources combined.
Biomass energy may offer a feasible
alternative for district energy facilities.
Biomass currently supplies 14 percent
of the world’s energy needs and accounts
for 4-1/2 percent of total U.S energy
production, according to the U.S. Department of Energy. In fact, biomass supplies
almost five times the energy output of
solar, wind and geothermal energy sources
combined. Yet few district energy facilities
have explored this alternative.
As for LNG imports, on April 15, 2008, the first LNG tanker arrived at the new
LNG terminal in Freeport, Texas. Three days earlier an LNG tanker made its
first delivery to the new Sabine Pass River LNG terminal in Cameron Parish,
Louisiana. These terminals are owned by Cheniere Energy. Cheniere will open
two more terminals in Texas and Louisiana in 2010 and 2011. There are 13
other LNG terminals that have been approved by U.S., Mexican, Canadian,
and Bahamian government agencies and are in various stages of permitting.
According to the trade publication Natural Gas Intelligence, there are another
25 projects, with 27. 75 billion cu ft per day of proposed peak sendout, on file
with regulators in Canada, the United States and Mexico. Another 21 projects,
with 17. 3 BCF/d of expected peak sendout, are in the planning stages.
Tony Mirabella, PE, may be reached at tonymirabella@comcast.net
From Waste to Energy
Biomass is an organic material, normally a waste or byproduct of an industrial or agricultural process, with little
or no commercial value. Often biomass
ends up in the industrial waste stream
and is landfilled. Yet it is a potentially
valuable source of energy for steam and/or
electrical generation in a central plant.
Some forms of biomass, such as
wood chips, can be burned convention-
ally in a solid fuel boiler such as a coal
burner. Other forms of biomass do not
directly combust easily, but they can be
converted to a fuel gas through the
process of gasification. These include
rice hulls, corn stover (leaves and
stalks), chicken litter and undigested
sewage sludge from the wastewater
treatment process. Biomass gasification
combines heat, oxygen and the fuel
source in a closed vessel. The products
of gasification are fuel gas, composed
primarily of carbon monoxide and
hydrogen, and ash. The fuel gas can be
used in a reciprocating engine generator
to generate electricity and/or burned in
a boiler to generate steam. Alternatively,
human or animal waste can be converted
to fuel gas using the process of digestion,
a biological process using microorganisms
to break down organic waste. Digestion
can take place in the presence or absence
of oxygen, i.e., aerobic and anaerobic,
respectively. Larger wastewater treatment
plants use anaerobic digestion, as do
septic tanks. The primary constituents
of digester gas are methane and carbon
dioxide.
How Feasible is
Biomass Gasification?
There are pros and cons to biomass
gasification. The biggest plus is the economic incentive; in fact, producers of
waste streams that are inconvenient to
dispose of, such as chicken litter or
