Type of DG: Micro Turbines
Micro Turbines or Turbogenerators are very small combustion turbines with outputs of 30 kW to 200 kW. Individual units can also be packaged together to serve larger loads. Turbogenerator technology has evolved from automotive and truck turbochargers, auxiliary power units for airplanes, and small jet engines used for unmanned military aircraft. Micro Turbines are nearing commercial status. Capstone, for example, has delivered over 1700 Micro Turbines to customers (as of October 2001). However, many of the Micro Turbine installations are still undergoing field tests or are part of large-scale demonstrations.
Recent development of these Micro Turbines has been focused on this technology as the prime mover for hybrid electric vehicles and as a stationary power sources for the DG market. In most configurations, the turbine shaft spins at up to 100,000 rpm and drives a high speed generator. This high frequency output is first rectified and then converted to 60 Hz (or 50 Hz). The systems are capable of producing power at around 25-30% efficiency by employing a recuperator that transfers heat energy from the exhaust stream back into the incoming air stream. Like larger turbines, these units are capable of operating on a variety of fuels, including natural gas, sour gases (high sulfur, low Btu content), and liquid fuels such as gasoline, kerosene, propane and diesel fuel. The systems are air cooled and some even use air bearings, thereby eliminating both water and oil systems. Low-emission combustion systems are being demonstrated that provide emissions performance comparable to larger GTs (gas turbines). The following diagrams provide an overview of currently available Micro Turbine system and component design.
Commercially Available MTG Unit and Fuel Storage
Representative MTG Combustion Module Structure
Turbogenerators are appropriately sized for commercial buildings or light industrial markets for cogeneration or power-only applications.