v>EPA
United States Environmental
Protection Agency
Office of Air and Radiation
(6202J)
EPA430-F-02-012
October 2002
LANDFILL METHANE
OUTREACH PROGRAM
POWERING MICROTURBINES
WITH LANDFILL GAS
Microturbines are an emerging
landfill gas (LFG) energy
recovery technology option,
especially at smaller landfills where
larger electric generation plants are not
generally feasible due to economic
factors and lower amounts of LFG.
Several LFG microturbine projects have
come on line recently, demonstrating
both the risks and benefits of these
small-scale applications. Microturbines
may play an important role in future
LFG project development, if the technical
and economic hurdles facing them can
be overcome.
This fact sheet provides an overview
of microturbine technology and its
applications, as well as the economic
considerations and benefits of powering
microturbines with LFG.
Overview
Microturbines are a recently commer-
cialized distributed generation (DG)
technology. Like other DG technologies,
such as fuel cells, wind turbines, and
photovoltaic cells, microturbines are
generally best suited to relatively small
applications (i.e., less than 1 megawatt
[MW]) and are designed to produce
electricity for onsite energy needs and for
end users in close proximity to the gener-
ation site. As a point of reference, the
output of a 50 kilowatt (kW) microtur-
bine can power a 40 horsepower motor
or satisfy the electricity needs of about
20 homes.
Internal combustion engines have
traditionally been the choice for LFG
projects 800 kW and larger, and conven-
tional turbines are generally considered
only for projects 5 MW and larger.
However, with individual unit sizes in
the 50 to 100 kW range and the ability to
group these units into larger sets,
microturbines can fill an important
niche. They can be used at landfills
where the gas output is too low for larger
engines and conventional turbines or
where excess gas or onsite energy needs
exist. (As an example, microturbines
could be used to power blowers in a gas
collection system.)
To date, most microturbines on the
market are powered using natural gas.
However, they can also be operated using
LFG or other waste fuels, such as oilfield
flare gas and wastewater treatment plant
Several LFG microturbine projects have
come on line recently, demonstrating
both the risks and benefits of these
small-scale applications. Microturbines
offer another option to generate
electricity at sites ranging from older
closed landfills with low-methane gas
and low flow, to smaller, more rural
landfills where larger generation
technology is not usually feasible.
digester gas. At the time of publication
of this fact sheet, several companies
are manufacturing and distributing
microturbines or are expected to do so in
the near future. These include: Bowman
Power (Southampton, England);
Capstone Turbine Company (Chatsworth,
California); Elliott Energy Systems
(Jennette, Pennsylvania); Ingersoil-Rand
(Portsmouth, New Hampshire); and
Turbec (Malmo, Sweden).
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Nearly 100 microturbine projects
operating on waste fuels are already
operational, and additional projects are
expected to be operational soon. In the
past two years, microturbines operating
on LFG have come on line at at least
three landfills in the United States, and
additional LFG projects are in the plan-
ning or construction stages.
Microturbine
Technology
Microturbine technology is based on
the design of much larger combustion
turbines employed in the electric power
and aviation industries. Microturbines
generally work as follows:
• Fuel is supplied to the combustor
section of the microturbine under
70 to 80 pounds per square inch
gauge (psig) of pressure.
• Air and fuel are burned hi the
combustor, releasing heat mat causes
the combustion gas to expand.
• The expanding gas powers the gas
turbine that in turn operates the gen-
erator; the generator then produces
electricity.
• To increase overall efficiency, micro-
turbines are typically equipped with
a recuperator that preheats the
combustion air using turbine exhaust
gas. A microturbine can also be fitted
with a waste heat recovery unit to
heat water.
A general schematic of the microtur-
bine process (illustration at upper right)
as well as a cross-section of one
microturbine that is currently available
for LFG application (lower illustration)
are shown to illustrate how a microtur-
biue operates.
Microturbmes differ from traditional
combustion turbines in that they spin at
much faster speeds. Those currently on
the market are equipped with air bear-
ings rather than traditional mechanical
bearings in order to reduce wear. A typi-
cal LFG-fired microturbine installation
has the following components:
Exhaust
wwv
AAAAA
Heat To Users
Recuperator
Potential
Waste-Heat
Recovery
Compressor
Air Inlet
To Plant Utility
or Grid
Turbine
Microturbine process schematic.
Exhaust Outlet
Generator Cooling Fins
Recuperator
Generator
Combustion Chamber
Compressor
Recuperator Housing
Air Bearings
Turbine
Cross-section of a microturbine.
LFG compressor(s)
LFG pretreatment equipment (for
moisture, siloxanes, and particulates
removal)
Microturbine(s)
Courtesy of Capstone Microturbines
Motor control center
Switchgear
Step-up transformer
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The extent of fuel pretreatment steps
required depends on the characteristics
of the LFG and varies by microturbine
manufacturer. In some instances, the
gas is chilled to remove moisture and
condensable impurities and is then
reheated to supply fuel above dew
point temperature to the microturbine.
In addition to moisture removal,
some manufacturers recommend an
adsorption step using activated carbon
to remove virtually all impurities.
Applicability
Microturbines provide unique advan-
tages over other electrical generation
technologies for landfills in cases where:
• LFG flow is low (or excess flow from
an existing project is available).
• LFG has low methane content.
• Air emissions, especially nitrogen
oxide (NOX), are of concern (e.g., in
NOX nonattaimnent areas where the
use of reciprocating engines might be
precluded).
• Electricity produced will be used
for onsite facilities rather than for
exporting power.
• Electricity supply is unreliable and
electricity prices are high.
• Hot water is needed on site or nearby.
Econpmic
Considerations
Microturbine heat rates are generally
14,000 to 16,000 Btu/kWh. The total
installed cost for a LFG microturbine
project is estimated to be $4,000 to
$5,000 per kW for smaller systems
(30 kW), decreasing to $2,000 to $2,500
per kW for larger systems (200 kW and
above). Non-fuel operation and mainte-
nance costs are about 1.5 to 2 cents
per kWh.
LFG microturbine projects are most
economical under a retail deferral
scenario. (Retail deferral is the replace-
ment of purchased electric power by
self-generated power.) In many cases,
the cost to generate electricity with
microturbiues will be higher than the
price for which it can be sold to utilities.
Benefits
LFG microturbines offer the following
advantages when compared to other
types of LFG utilization technologies:
• Portable and easily sized,
Microturbines are modular and
available in incremental capacities for
multiple-unit stacks, so that single
or multiple microturbines can be
configured to adapt to gas flow and
satisfy onsite power requirements.
They can then be moved to another
project site when gas production
ceases.
• Flexibility. Microturbines may be a
more viable option at smaller and
older landfills where LFG quality and
quantity would not support more
traditional LFG electric power
generation technologies. They may
also be feasible at larger LFG projects
that have excess unutilized gas.
• Compact and fewer moving parts.
Microturbines are approximately the
size of a large refrigerator and require
minimal operation and maintenance.
The use of air bearings coupled w^ith
an air-cooled generator eliminates
the need for lubrication and liquid
cooling systems.
• Lower pollutant emissiojis.
Microturbines burn cleaner than
comparable reciprocating engines.
For example, NOX emissions levels
from microturbines are typically less
than one-tenth those of the best per-
forming reciprocating engines and
lower than those from a LFG flare.
• Capable of combusting lower-methane-
content LFG. Microturbines can
operate on LFG with 55 percent
methane content and perhaps as low
as 50 percent.
• Ability to generate heat and hot water.
Most microturbine manufacturers
offer a hot water generator as a
standard option to produce hot water
(up to 200°F) from wraste heat in the
exhaust. This option can replace rela-
tively expensive fuel, such as propane,
needed to heat water in colder
climates to meet space-heating
requirements. The sale or use of
microturbine waste heat can signifi-
cantly enhance project economics.
Concerns with LFG
Microturbines
Reciprocating engines are a widely
proven, mature technology in the LFG
power generation industry, especially for
800 kW and larger units. In contrast, the
long-term reliability and operating costs
of microturbines have yet to be con-
firmed. Disadvantages of inicroturbtnes
as a LFG utilization option include:
• Microturbines have a lower efficiency
than reciprocating engines and
other types of turbines, and they
consume about 55 percent more fuel
per kWh produced.
• Microturbines are sensitive to
siloxane contamination, and LFG
supplied to microturbhies is
generally expected to require more
pretreatment than LFG used to
power conventional turbines or other
electric generation sources.
• Currently, few low-flow, high-
pressure compressors are available
that meet the needs of microturbhies
without high equipment modification
costs; a suitable solution would need
to be identified to permit cost-effective
delivery of LFG to microturbines
without significantly increasing the
parasitic load.
• Information needs to be gathered
about the long-term reliability and
operation and maintenance costs of
LFG microturbines.
To learn more about the potential
concerns of running microturbines on
LFG, a pilot test of a 50 kW unit was
conducted at the Puente Hills Landfill in
Los Angeles County, California.
Microturbines that were operated for
over 2,000 hours on LFG developed
some wear and tear, potentially from
abrasives (such as siloxaiies) in the LFG.
A second pilot project was launched
in June 2001 to learn more about and
eliminate these problems.
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Development Potential
At present, principal hurdles in the
development of LFG microturbine tech-
nology are the lack of information on
long-term reliability, unclear estimates
of operation and maintenance costs aris-
ing from extensive LFG cleanup
requirements, and high capital costs.
The microturbine projects that are cur-
rently in operation or under
development are attempting to address
these concerns by:
• Obtaining extended-term operation
and maintenance cost guarantees
from equipment manufacturers, based
on agreed upon fuel specifications.
• Applying aggressive LFG pretreat-
ment (e.g., refrigeration, activated
carbon treatment).
• Emphasizing projects with relatively
rapid projected paybacks.
Microturbines offer another option to
generate electricity at sites ranging from
older closed landfills with low-methane
gas and low flow, to smaller, more
rural landfills where larger generation
technology is not usually feasible.
While the future of microturbines that
run on LFG is uncertain, additional
research is essential to gain a better
understanding of the long-term viability
of this technology.
Sources of Additional
Information
While limited research has been con-
ducted to date on powering
microturbines with LFG, some sources
of information include:
1) "Landfill Gas Fueled Microturbines
Are Here," George Wiltsee, Capstone
Turbine Corporation, and Paul
Wintheiser, EMCON-IT Group, 5th
Annual LMOP Conference and
Project Expo, December 15-14, 2001,
Washington, DC. (Contact LMOP at
888-STAR-YES or visit
www.epa.gov/lmop.)
2) "Demonstration Test of the Capstone
Microturbine on Landfill Gas," Ed
Wheeless, Sanitation Districts of Los
Angeles County, California, and
George Wiltsee, Capstone Turbine
Corporation, 24th Annual Landfill
Gas Symposium, March 19-22, 2001,
Dallas, TX. (Contact SWANA at 800-
GO-SWANA.)
5) "Microturbine Distributed
Generation Using Conventional and
Waste Fuel," Jeff Pierce, SCS
Engineers, The National Defense
Industrial Association's 28th
Environmental and Energy
Symposium and Exhibition,
Charleston, South Carolina, March
25-28, 2002. (Contact Mr. Pierce at
562-427-0805.)
4) U.S. Department of Energy, Office of
Distributed Energy Resources,
Microturbines Program. (Visit
www.eren.doe.gov/der/microtur-
bines/microturbines.html.)
The Landfill Methane Outreach Program (LMOP) is a
voluntary program that assists project developers, utili-
ties, landfill owner/operators, energy users, and
communities to encourage new landfill gas use projects. The
U.S. Environmental Protection Agency has developed a vari-
ety of tools (e.g., profiles, fact sheets, project development
manuals, and software) to facilitate the development of LFG
use projects. For more information, please contact LMOP at:
U.S. Environmental Protection Agency
Landfill Methane Outreach Program
Climate Protection Partnerships Division
1 200 Pennsylvania Avenue, NW (6202J)
Washington, DC 20460-0001
www.epa.gov/lmop
Phone: 888-782-7937
Fax: 202-775-6680
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