United States
Environmental Protection
Agency
Auxiliary and Supplemental Power
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 condensing it 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.
Microturbine Schematic
turbine Exhaust
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.
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From an environmental standpoint, these new
machines pollute less and take up less space. The
increased efficiency means that they use less fuel,
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.
addition to saving in peak energy demand charges,
The San Elijo Joint Power Authority also received
a $76,000 rebate check from the San Diego Gas and
Electric's Self-Generation Incentive Program.
I & - ^
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Large Scale Microturbine Application
COST
Capstone Mictroturbine and Ingersoll Rand are two
of the larger microturbine manufacturers. Each
offer different models of microturbines that depend
on the power out put that is needed. Costs for these
units can range from $30,000 to $250,000,
installed, depending on the unit. Interviews with
several municipalities suggested annual savings of
$25,000 to $216,000 through use of microturbines
over conventional gas or diesel powered.
CASE STUDY
In 2000, microturbines were installed at San Elijo
Joint Powers Water Reclamation Facility. San
Elijo is a small (3 MOD) WWTP. Instead of just
burning the excess gas, San Elijo now uses its bio
gas from their digesters to fuel the microturbines.
Three microturbines were installed, producing 80
kW of energy. The system produces approximately
15% of the plant's demand. The exhaust from the
microturbines was captured and used to heat water
at the reclamation facility. This process is known
as combined heat and power (CUP). One generator
system uses one fuel source to yield two usable
energy outputs with very high fuel efficiency. The
plant experienced a decline in electricity costs
estimated at $4,000 per month and expects a
payback on their investment in 3-4 years. The
microturbine exhaust is also lower in methane and
NOx than emissions from flaring digester gas and
substantially less that those from conventional
reciprocating engine driven generator sets. In
REFERENCES
http: //www. energyuserne ws. com/CD A/Arti cl e_In
formation/Fundamentals_Item/0,2637,89816,OO.h
tml
http://uschpa.admgt.com/TB_Microturbines.pdf
http://www.its.caltech.edu/~sciwrite/journal03/A-
L2/Arcia.html
http://www.microturbine.com/onsites/pdf/WWTP
.pdf
http://wwwl.pplweb.com/newsapp/news_rel eases
. articleview?p_artid= 1772
http://www.visionengineer.com/mech/microturbi
nes.shtml
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U. S. Environmental
Protection Agency.
EPA832-F-05-014
Office of Water
March 2005
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