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). ------- 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 ------- 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. ------- 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 ------- |