United States Environmental
Protection Agency
Office of Air and Radiation
October 2002
                      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.
                 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).

  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 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

   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:
                                     Heat To Users
               Air Inlet
                                                          To Plant Utility
                                                             or Grid
Microturbine process schematic.
                      Exhaust Outlet
    Generator Cooling Fins
                                                    Combustion Chamber
                                                        Recuperator Housing
                Air Bearings
Cross-section of a microturbine.
   LFG compressor(s)

   LFG pretreatment equipment (for
   moisture, siloxanes, and particulates

             Courtesy of Capstone Microturbines

       Motor control center


       Step-up transformer

  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.
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

  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.
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.

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

  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 200F) 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
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.

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
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

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-

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

4) U.S. Department of Energy, Office of
   Distributed Energy Resources,
   Microturbines Program. (Visit
          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
      Phone: 888-782-7937
      Fax: 202-775-6680