MICROTURBINES are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts. They are also known as "turbo alternators", or "gensets". Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor. Microturbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. They are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants. Microturbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator.Typical micro turbine efficiencies are 25 to 35 percent. When in a combined heat and power cogeneration system, efficiencies of greater than 80 percent are commonly achieved.
Microturbines are a new type of combustion turbine being used for stationary energy generation applications. They are small combustion turbines, approximately the size of a refrigerator, with outputs of 25kw to 500kw, and can be located on sites with space limitation for power production. Microturbines are composed of a compressor, combustor, turbine, alternator, recuperator, and generator. Waste heat recovery can be used in combined heat and power system to achieve energy efficiency levels greater than 80%. In addition to power generation micro turbines offer an efficient and clean solution to direct mechanical drive markets such as compression and air conditioning. Since making their commercial debut a mere five years ago, microturbines have installed with considerable success in office and apartment building, hotels and motels. Supermarkets, school and college, office and industrial parks, small industries, and numerous other facilities both in the US and abroard.They provide not only electricity, but the thermal energy to provide for all heating and cooling needs.
WHAT IS A MICROTURBINE?
Microturbines are small combustion turbines approximately the size of a refrigerator with outputs of 25kw to 500kw. They evolved from automotive and truck turbochargers, auxiliary power units for airplanes, and small jet engines and are comprised of a compressor, combustor, turbine, alternator, recuperator, and a refrigerator. The engine itself is about the size of a beer keg. The most popular models have just one moving parts—a shaft with a turbine wheel on one end , a permanent magnet generator on other end, and an air compressor wheel in the middle. This assembly rotates at up to 96,000 rpm. At that speed, traditional oil-lubricated bearings are severely challenged. Accordingly the most popular micro turbine engines use air bearing to float the shaft.
Not only is the turbine turning at high rpm, so is the generator. The generator in turn produces a high frequency electrical output, which is then converted by power electronics unit to grid –compatible 400-to-480-volts alternating current, 10-to-60 hertz.3phase power.
Microturbine offer a number of potential advantages compared to other technologies for small-scale power generation. These advantages include a small number of moving parts, compact size, light-weight, greater efficiency, lower emission, lower electricity cost, and opportunities to utilize waste fuels. They have the potential to be located on sites with space limitation for the production of power. Waste heat recovery can be used with these systems to achieve efficiencies greater than 80%.
There is very definitely a trend toward installing microturbine system onsite—not only for generating electric power. But also for meeting site heating and cooling needs. Such microturbine configuration are called combined heat and power, or combined cooling, heat and power (cogeneration) system. The core idea is this: when burning a fuel in a micro turbine unit, don’t just use the resulting heated gases to spin a turbine and generate electricity. There is still a huge amount of thermal energy in the turbine exhaust. Don’t waste that valuable energy to the atmosphere—which is what they do in most central power plants (because there is no use for the heat in remote areas).
Instead, use a heat exchanger to capture much of that thermal energy and use it to meet all the heating and cooling needs of the site. When a microturbine unit is arranged in CHP or CCHP mode, heat from the turbine stack is captured and used to meet some or all the heating and cooling needs of the facility. This makes for much more efficient fuel use. Instead of just using 35% of thermal energy released during fuel combustion (as with a traditional central power plant), with CHP and CCHP one would be using 65% or more of the fuels thermal energy. This realization is a major reason the federal Department of Energy has been strongly encouraging the advance of onsite power generation with CHP and CCHP.
The 30-kilowatt model of Microturbine is very versatile, being able to burn several gaseous or liquid fuels—natural gas, propane, biogas, diesel, and kerosene.