You're having the evening meal at a fast food restaurant. As you munch on the burgers and fries you look around, idly speculating on the power consumption of the business. It must be huge - all of those lights, the HVAC (heating, ventilation, cooling) system, the computer monitors that each assistant is using, the background music.... Just as you've finished totting up a power estimate of 30 or 40 kilowatts, you notice that a mains power failure has occurred in the suburb. The highway lights have gone out, the nearby residential area is now dark and gloomy.
But inside the restaurant, all is as it was before.
"Aaah", you nod wisely, "this place's got a back-up generator."
But you can't hear the thump of a diesel, and the transition to the back-up power was absolutely seamless - no flickering of lights, no sudden distortion in the electronically amplified calls for "More fries!" The store manager wanders by - looking unconcerned - and you accost her.
"Tell me - what sort of back-up power system d'you have?" you ask.
"No sir," she replies, "we don't have back-up power - we're on it all of the time. It's our micro gas turbine generator."
"Ohhhh... of course," you reply lamely.
Micro gas turbine? What the hell?
The stuff of fantasy? Not at all - even as you read this, a McDonald's store in Bensenville, Illinois, USA is being fully powered by its 75kW Parallon? micro gas turbine electrical generator. But isn't that a rather expensive way of providing an uninterruptible power source?
Not according to owner/operator Dennis Stabile. "We've already seen some cost savings from the Parallon 75 turbogenerator. And now we can keep our doors open, no matter what is happening outside. We're thrilled to be the first commercial operation in the world to reap the real benefits of this technology."
And in addition to the Parallon? models which are manufactured by Honeywell Power Systems Inc, the Capstone Turbine Corporation is also producing micro gas turbine generating systems designed to fully power small and medium sized businesses.
Micro Gas Turbines
AlliedSignal - now owned by Honeywell - has a 40-year history of manufacturing gas turbines and automotive turbochargers. In June, 1997 they formed a subsidiary called AlliedSignal Power Systems Inc to develop and market the TurboGenerator?, a gas-powered turbine electric generating system capable of developing 75kW of electrical power as an individual unit, and as much as 1MW with multiple units linked together. Those tiny gas turbine generating sets are now a reality.
Comprising a package the size of an industrial airconditioner, the generator has a footprint of 2.3 x 1.3 metres and a height of 2.1 metres. The core of the unit is a 66kg gas turbine-generator rotating assembly. Air is drawn into the compressor and then passes through a 'recuperator' (heat exchanger) positioned on the exhaust of the turbine. Combustion occurs in a catalytic combustor, with the burning gases expanding through the turbine. Positioned on the main shaft in between the compressor and the turbine is a permanent magnet generator. The shaft is supported on air bearings, a major factor in its ability to operate continuously for long periods.
All operations of the Parallon? 75 are automatic - it works completely unattended. Start-up, synchronisation with the electricity grid (if required), dispatch and shutdown are all automatic. When the unit is being installed for the first time, all that the technician needs to do is connect the gas pipe and wire the unit to the main circuit breaker. The Parallon? 75 is normally connected to the electricity grid and it can even be programmed to automatically start up when it can generate electricity at a lower cost than that is provided by the utility!
The table below shows the specifications of the Parallon? 75.
Maximum Power |
75kW continuous rating |
Thermal to Electrical Efficiency |
28.5 per cent guaranteed minimum with appropriate gas fuel |
Voltage Output |
Options for 120/208, 120/240, 230/400, 240/415, 277/480, 360/600 - all 3 phase, 50 or 60Hz |
Dimensions |
2334 L x 2163 H x 1219 W (mm) |
Mass |
1295kg |
Fuel Pressure |
75-85 psi (optional integral gas compressor available) |
NOX Emissions at 15 per cent O2 |
25 ppm standard, <9 ppm using natural gas |
Noise Output |
65dB(A) at 10 metres |
Design Life |
40,000 hours minimum |
The Capstone MicroTurbine? uses a similar design, although the components are arranged in a different manner and the maximum power outputs are much lower. The induction air is drawn past cooling fins that surround the generator, before flowing to the compressor. The air is then forced into the stainless steel recuperator where it is pre-heated to 600 degrees C before it enters the combustion chamber. Fuel is added and the mixture expands through the turbine, driving the compressor and generator at speeds of up to 96,000 rpm. The combusted air is finally exhausted through the recuperator.
The high-speed generator delivers power at up to 1600Hz, with a sold state Digital Power Controller converting this to 400-480V AC at either 50 or 60Hz. The Digital Power Controller also provides the controls, protection systems and communications for the unit. If the MicroTurbine? is connected to the grid, it uses mains power for starting purposes; when used as a standalone unit it requires battery power to start. As with the Honeywelll design, the MicroTurbine? supports its shaft on air bearings.
In addition to producing electricity, the MicroTurbine? also produces useable heat. The oxygen-rich exhaust can be utilised directly without any cleaning - it has emissions of less than 9 ppm of oxides of nitrogen and "very low" levels of carbon monoxide and total hydrocarbons.
Capstone currently produce models that will run on low or high pressure natural gas, high pressure propane, and high pressure sour gas. The specifications for the low pressure natural gas design are shown below:
Maximum Power |
28.2kW |
Thermal to Electrical Efficiency |
24.9 per cent |
Voltage Output |
400 - 480 V AC 3-phase |
Dimensions |
1344 L x 1900 H x 714 W (mm) |
Mass |
490kg |
Fuel Pressure |
5 or 15 psi |
NOX Emissions at 15 per cent O2 |
<9 ppm |
Power Stations Everywhere?
So we will see the use of lots of micro gas turbines generating electricity? Honeywell's Tony Prophet has declared that his company's small TurboGenerators? could "change the electric power industry as significantly as the personal computer changed the computing industry."
He continues, "Our TurboGenerator? uses clean-burning fuels and has just one moving part, so it offers extremely low emissions, dramatically increased reliability and reduced maintenance costs over current distributed generation systems. It will enable users to safely and efficiently generate electricity at the point of use."
Honeywell has signed up distributorships around the world, including in Africa. In rural Third World villages, a single unit can provide power for approximately 200-250 dwellings. Compared with conventional distributed power generation sources like diesel generator sets, the TurboGenerator? is expected to achieve greater reliability and reduced maintenance costs "at a competitive price".
Commercially available micro gas turbines have been available for only a short time; time will tell if they prove a success.
But one thing's certain - wouldn't you just love to have your own micro gas turbine out the back generating mains power for your house or business?
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It Was Developed For a Tank!
So where did the powerplant used in the Honeywell Parallon 75? micro turbine come from? In the mid 1990s, under a Defense Advanced Research Projects Agency contract, AlliedSignal Aerospace Systems developed a compact 17kW turbogenerator as an auxiliary power unit (APU) for the M1A1 Abrams battle tank. As part of Phase II of this project, AlliedSignal also began R&D testing of a 50kW turbogenerator for automotive use. The AlliedSignal system had many attractive features, including a waste heat recuperator; a system of air bearings, which eliminated the need for an oil-based lubrication system; and a new catalytic combustor to reduce NOx emissions. In 1997 it had become apparent that micro turbines showed promise for stationary applications. AlliedSignal used the tank's core engine (and accessories that had been further developed under a Department of Energy Hybrid Vehicle Program) as the basis for the 75kW TurboGenerator? Power Systems electric generator. In 1997, AlliedSignal formed AlliedSignal Power Systems Inc and marketed the TurboGenerator? as a self-contained power source for commercial and industrial applications. With the merger of AlliedSignal and Honeywell in 1999, Honeywell Power Systems Inc took over the marketing of the micro turbine, now called the Parallon 75?.
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