Microturbines

Microturbines are small combustion turbines that produce between 25 kW and 500 kW of power. Microturbines were derived from turbocharger technologies found in large trucks or the turbines in aircraft auxiliary power units (APUs). Most microturbines are single-stage, radial flow devices with high rotating speeds of 90,000 to 120,000 revolutions per minute. However, a few manufacturers have developed alternative systems with multiple stages and/or lower rotation speeds. Microturbines are nearing commercial status. Capstone, for example, has delivered over 2,400 microturbines to customers (2003). However, many of the microturbine installations are still undergoing field tests or are part of large-scale demonstrations.

Photo Source: Capstone

Microturbine generators can be divided in two general classes:

• Recuperated microturbines, which recover the heat from the exhaust gas to boost the temperature of combustion and increase the efficiency, and
• Unrecuperated (or simple cycle) microturbines, which have lower efficiencies, but also lower capital costs.

While some early product introductions have featured unrecuperated designs, the bulk of developers' efforts are focused on recuperated systems. The recuperator recovers heat from the exhaust gas in order to boost the temperature of the air stream supplied to the combustor. Further exhaust heat recovery can be used in a cogeneration configuration. The figure below illustrates a recuperated microturbine system.

Source: EPRI