c/EPA
United Stales
Environmental Protection
Agency
United States Environmental Protection Agency
August 2013
Renewable Energy Fact Sheet:
Microturbines
DESCRIPTION
This fact sheet describes the use of microturbines
as auxiliary and supplemental power sources
(ASPSs) for wastewater treatment plants
(WWTPs). Microturbines are a new, innovative
technology based on jet engines (more
specifically the turbo charger equipment found
in jet engines) that use rotational energy to
generate power.
Most microturbines have four main components:
compressor, combustion chamber, turbine blades,
and drive shaft. The compressors operate by taking
in the surrounding air at one end of the
microturbine and then condensing the air by
increasing the air's pressure and density. This
air is fed into the combustion chamber where it
is mixed with fuel, and then burned. This
combustion releases enormous amounts of heat
energy and high-pressure exhaust gases. The
exhaust gases are discharged through exhaust
vents into a series of turbine fan blades that
are attached to a central shaft. As the gases are
discharged, they spin the turbine fans, which in
turn spin the drive shaft at high speeds
(100,000 revolutions per minute). The rotational
energy produced by the shaft, spins copper coils,
which excite the electrons in the wire, producing
electricity. The quantity of electricity depends
on how fast the shaft can spin in the
magnetic field, the strength of the magnetic
field, and the quantity and arrangement of the
copper coils. To produce electricity at a
relatively low cost, the shaft must rotate at high
speeds.
Microturbines can run on bio-gas, natural gas,
propane, diesel, kerosene, methane, and other fuel
sources, making them suitable for backup power in
a variety of applications. Since each individual
microturbine produces anywhere from 15 to 300
kilowatts (kW) of energy, they are often grouped
to produce the required energy for a given
application. Most microturbines are about the size
of a refrigerator and have very low nitrogen oxide
emissions.
ADVANTAGES & DISADVANTAGES
There are numerous advantages that make
microturbines appealing. From an economic
standpoint, the microturbine generators are
cheaper to build and run in comparison to larger
conventional gas or diesel powered generators.
The technology is well understood and has been
implemented in many applications throughout
the U.S. They are also relatively inexpensive,
easy to manufacture, and have few moving
parts. These power plants can also use various
types of fuels. Another advantage of
microturbines is durability and reliability; they
function for about 40,000 hours and require little
maintenance. These systems can also be ready
to operate only ten minutes after being turned
on. Microturbines create a large amount of
energy relative to their size. Because of their
size, microturbines can be placed on site, easing
security and maintenance. Microturbines have
the ability to work alone or in groups. If one
microturbine fails while in use, this does not
necessarily mean that the entire system of
microturbines will fail.
Electric Powor
Exhmust
Intake Air
Turbine
Compressor
Figure 1: Microturbine Flow Diagram
(Source: www. wastegaspower.com/images/microturbine.jpg)
From an environmental standpoint, these new
machines pollute less and take up less space. The
increased efficiency means that they use less fuel,
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which means fewer emissions into the air.
Increased efficiency and less fuel also result in a
lower reliance on finding the natural resources
necessary to power the turbines.
One disadvantage of microturbines is a limit on the
number of times they can be turned on.
Microturbines also run at very high speeds and
high temperatures, causing noise pollution for
nearby residents and potential risks for operators
and maintenance staff It may also take several
microturbines set in a series to provide enough
energy to power a small WWTP.
COST
Capstone Microturbine and Ingersoll Rand are two
of the larger microturbine manufacturers. Each
offers different models of microturbines that vary
based on the power output that is needed. Based on
estimates by the Gas Research Institute and National
Renewable Energy Laboratory, the total plant cost
varies from about $2,600 per kW for a 30 kW system
to around $1,800 per kW for a 100 kW system.
Interviews with several municipalities suggested
annual savings of $25,000 to $216,000 through use
of microturbines over conventional gas or diesel
powered engines.
CASE STUDY
The Sheboygan Regional Wastewater Treatment
Plant situated in Sheboygan, Wisconsin has a
permitted flow of 18.4 million gallons per day
(MOD) and an average flow of 11 MOD. In 2006,
as a part of Sheboygan's goal of becoming energy
self-sufficient, a combined heat and power project
consisting of ten 30 kW Capstone microturbines
and heat recovery systems was commissioned.
Using the biogas produced from the WWTP's
anaerobic digesters, the microturbines produced
2,300 megawatts (MW) of electricity annually
which translates to energy cost savings of $78,000.
The microtuines also produced 84,000 therms of
heat, which is equivalent to $60,000 in prevailing
natural gas rates. These turbines were installed at a
capital cost of $300,000. In 2011, the City of
Sheboygan, won the "Wege Small Cities
Sustainability Best Practices Award" from the
Great Lakes and St. Lawrence Cities Initiative, for
being nearly energy self sufficient.
Lancaster Water Reclamation Plant, in Los Angeles
County, California, is a 15 MOD wastewater
treatment facility. The facility's digester
collectively produces about 200,000 cubic feet per
day of biogas that is composed of 55% methane.
To utilize this biogas, a 250 kW microturbine
combined with a waste- heat recovery system was
installed at a total cost of $720,000. The net
design electrical and thermal efficiency is
calculated to be 51%. The annual savings from the
power generation was calculated to be $225,000,
resulting in a payback period of three years.
REFERENCES
1. http://www.energyusernews.com/CDA/Article_
Information/Fundamentals_Item/0,2637,89816,OO.html
2. http://uschpa.admgt.com/TB_Microturbines.pdf
http://www.its.caltech.edu/~sciwrite/journal03/A-
L2/Arcia.html
3. http://www.microturbine.com/onsites/WWTP.pdf
4. http://wwwl.pplweb.com/newsapp/news_releases
.articleview?p_artid=1772
5. http://www.visionengineer.com/mech/microturbi
nes.html
6. Claire Scares P.E., Microturbine Economics and
Market Factors, Microturbines, Butterworth-
Heinemann, Burlington, 2007, Pages 31-36, ISBN
978-0-75-068469-9.
7. Case Study-Sheboygan,WI-Energy Efficiency in a
Wastewater Treatment Plant, American Council for an
Energy Efficient Economy, April 2011.
8. "Microturbines, Gas Engines Link Biogas to the
Grid," BioCycle September 2006, Vol. 47, No. 9, p.59
http://www.jgpress.com/archives/free/001066.html
Mark McDannel and Ed Wheless, The Power of
Digester Gas, Water Environment & Technology, June
2008.
Some of the information presented in this
fact sheet was provided by the manufacturer or
vendor and could not be verified by the EPA.
The mention of trade names, specific vendors,
or products does not represent an actual or
presumed endorsement, preference, or
acceptance by the EPA or federal government.
Environmental Protection Agency
Office of Wastewater Management
EPA 832-F-13-018
August 2013
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