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. ------- 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 & - ^ I *^r* 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 ------- |