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Microturbines

Microturbines are small combustion turbines that drive a generator and produce between 25 kW and 500 kW of power. Although similar to a genset (a reciprocating engine-driven generator) in that both provide power directly to a facility, the microturbine can generate power continuously with very low emissions.

Compared to a genset, the typical microturbine has relatively few moving parts, higher reliability, significantly longer maintenance intervals, and a longer operating life, offering extended operation of 8,000 hours between scheduled service and an operating life as much as ten times greater than a conventional genset.

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 have reached commercial status. Capstone, for example, has delivered over 3000 microturbines to customers as of 2005.

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.

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.

Microturbines burn a variety of fuels, including natural gas and diesel, to produce clean, reliable, high-quality power that is comparable in every way to the utility electric grid. Microturbines are built for full-time operation to reduce electricity costs, but they can also be operated for peak shaving only during times when utility-grid costs are the highest.

In addition to the microturbine generating electricity, the thermal energy remaining in the exhaust can help heat a facility, provide domestic hot water, drive an absorption chiller, or regenerate a desiccant dehumidifier. The clean exhaust can also be used directly in an industrial drying process. When used for cogeneration of electricity and heat, the overall efficiency of the microturbine is very high.

Microturbines can be placed either inside or outside near a facility and will connect directly to the electrical distribution system. This shift from large, centralized power plants to small, economical on-site generators is especially suited for buildings, retail establishments, and light manufacturing facilities that can benefit from reduced costs, assured availability, and quality electric power.

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Source: Capstone