High-Speed Technology Research
Turbo-compressors, small gas turbines and other small power plants, and high pressure pumps all use high rotational speeds. In general, energy and speed changes are performed by using traditional electric machines and gearboxes.
High-speed technology removes the need to use a gearbox: for a high-speed electrical machine, one shaft is connected to all the major parts including the turbine, compressor, or pump rotor itself.
The rotational speeds used are typically between 20,000 and 200,000 revolutions per minute. The use of gas, magnetic or oil-free bearings give high-speed machines the added advantages of being completely oil free and fully hermetically sealed.
High-Speed Technology Towards A Green Future
High-speed technology has been researched at LUT since 1981. In the research work, numerous prototypes and pilot plants have been built. In addition to its related publications, the research has produced a number of licentiate and doctoral theses. High-Speed Technology research is also conducted in the department of LUT and LUT Mechanical Engineering.
In autumn 2010, LUT released a comprehensive report on high-speed technology research in Finland: Low resolution pdf, 6 MB
As a result of the research work conducted in cooperation with LUT and the Helsinki University of Technology, Sulzer Pump Solutions Finland (formerly HST) has since 1996 manufactured commercial, high-speed technology-based compressors at its plant in Lappeenranta. The company currently employs 30 personnel. Each year, the company manufactures approximately one hundred high-speed compressors, which are mostly for export.
Key Areas Of Research In High-Speed Technology
ORC power plants
An ORC cycle is a means of implementing the Rankine cycle (used for power production), using a suitable organic fluid in the circulation instead of water. Because the relative latent heat of an organic liquid is much lower than water, the single-stage ORC process can achieve the same or better efficiency than a two-stage steam process, e.g. by using the flue gas heat of a diesel engine.
This makes it possible to utilise low temperature waste heat with the ORC process, which is usually not profitable with the steam process.
Also, the drop in the specific enthalpy of organic fluids in the turbine is much smaller than that of steam, which also makes it possible to make the ORC process efficient at low power.
BioCHP (combined heat and power generation using biofuels)
LUT has developed power plants using biofuels since 2004 for combined heat and power production. The Fluid Dynamics Laboratory has designed a steam turbine, a feed pump, and machine cooling for power production.
Reverse gas turbines
The inverse gas turbine process does not contain a combustion chamber, so the turbine temperature is not great enough to compensate for compressor power requirements. The resulting electric motor-driven machine and process is used for air drying, heat pump processes, and refrigeration. Because the machine works on air and requires very low levels of maintenance, its environmental footprint is very low. In 1991, LUT began to consider applications for the process with the company HST, leading to the construction of two prototypes.
The first prototype was made mostly using traditional technology. The power consumption of the first re-wound motor running at 20,000 rpm was 12 kW. Based on these positive results, a second prototype was designed that was based entirely on high-speed technology with a resulting power requirement of 2 kW.
Traditionally used CFC refrigerants have been shown to be harmful to the ozone layer. New refrigerants do not harm the ozone layer, but they are associated with other problems. Conventional compressors require a refrigerant fluid that works with the lubricating oil, and this restricts the choice of process fluid.
If a high-speed compressor using magnetic or gas bearings is used, then the need for lubricating oil is removed. In this case, it is possible to choose a truly environmentally friendly refrigerant that is best suited for each purpose.
The cooling process can also be fully implemented without any need for refrigerants in the inverse gas turbine process. In this case, the cooling agent used is simply air alone.
The refrigeration machines project was the first high-speed technology project and is still ongoing. The research started at LUT in 1981. During this period, two refrigeration machine prototypes have been designed and built.
Many of the laboratory facilities have been equipped with axial turbines at LUT.
Two-stage ORC turbine, 30 kW
The turbines are a part of subsea equipment that was tested at a depth of 5 km. The first stage was supersonic, with an achieved design efficiency of 80%.
One-stage RBC turbines, 10 kW and 2 kW
These air turbines were designed for an inverse gas turbine. The larger turbine (1993) produced 10 kW, the outer diameter was 150 mm, the speed was 20,000 rpm, and the mass flow was 0.4 kg/s. The turbine was measured separately and its efficiency was 86%.
The left turbine (1994) produced 2 kW, the outer diameter was 45 mm, the speed was 87,300 rpm, and the mass flow was 0.06 kg/s. The turbine efficiency rate was measured to be 72%.
The pump type developed at LUT produces very high pressure, so there is very little chance of cavitation. The pump also works at very low specific rotational speed with good efficiency.
High pressure pumps
Water jet cutting, paint removal and water hydraulics require small amounts of water with very high pressure. Traditionally this has been produced using piston pumps, which are short-lived because of the poor lubricating properties of water. In a high-speed pump with water bearings, the low viscosity of water is in fact beneficial: the bearing capacity is sufficient because of the high speed, and the friction losses remain reasonable.
High-speed pump control
Thanks to a high-speed motor and frequency converter, it is possible to use variable rotational speed control in the pumps. The Fluid Dynamics Laboratory pump test station has researched the optimal control and drive methods for a variety of high-speed pumps.
Fuel cells and micro turbines
LUT had already designed a 250 kW electric power gas turbine in the 1980s. The gas turbine used peat gas as its primary fuel gas. The turbine construction consisted of an individual gas turbine with a radial compressor and turbine on the same shaft.
Because the turbine produces only the power required by the compressor its pressure ratio is lower and the remaining expansion work can be carried out by the power turbine. For the production of electricity a high-speed generator coupled to the same shaft as the power turbine was designed.
Small-sized micro gas turbines, below 50 kW and using natural gas as fuel, are becoming more common. They are characterized by their small size, high-speed of rotation and integrated structure. High-speed electrical motors and maintenance-free bearings have made the technology commercially viable.
Fuel cell micro turbines
Electricity generation using high-temperature fuel cells is expected to become increasingly more common and it is believed that electricity will be produced using this technology in a more energy friendly and efficient manner. By connecting a gas turbine into the fuel cell process up to approximately 70%, electrical generation efficiency can be achieved.
LUT has also researched the optimisation and design of fuel cell gas turbines based on high-speed technology. In the project, gas turbine units with an electrical output of 50 kW and 250 kW have been designed, with the 50 kW unit selected for more detailed development.
The gas turbine is equipped with a frequency converter and active magnetic bearings, which have been used with great success in high-speed technology. Equipment with oil-free bearings requires very little maintenance and is environmentally friendly.
Anode gas recirculation fan
Solid oxide fuel cells (SOFC) enable power generation with different fuels at high levels of efficiency and with low levels of emissions.
The most effective pre-treatment for hydrocarbon fuel for the fuel cell is by implementing a steam reforming process for the fuel. In the steam reforming process, water can be used. This forms an oxidisation reaction in the fuel cell, where part of the outgoing flow from the anode is recycled and mixed with fuel which is fed into the system. At the same time, the fuel efficiency rate for the whole system is improved.
During the anode gas recycling phase, an adjustable parameter is the gas mixture's oxygen-to-carbon ratio to be fed into the reformer.
The recycling can be implemented with different technologies, but a motor-driven compressor provides the O/C control and flexibility required and allows sufficient pressure adjustment for the anode gas to be made, which is needed to make necessary pressure adjustments for the reformer, fuel cell and other system components in the fuel line.
Depending on the topography of the system, the anode gas recirculation fan must be able to typically recycle steam, carbon dioxide, hydrogen and carbon monoxide-containing gas mixtures at remarkably high temperatures (up to 600˚C).
The anode gas recycling fan consists of the fan on the same axle as the electric motor and the size of the parts corresponding to the main bearings. Equipment cooling is carried out by an external fan. Due to the temperature and composition of the gas, it is necessary to make the impeller and its surrounding materials out of heat-resistant metal.
In connection with the anode recirculation fan designed at LUT, active magnetic bearings were chosen with gas bearings as second choice in conjunction with magnetic thrust bearings. The fan was selected for the solid rotor induction electric motor (750 W, 73000 rpm) manufactured by LUT Energy and for the Mecos Traxler AG produced permanent magnet synchronous motors with magnetic bearings (max 500 W, 60000 rpm).
Currently, there is a scaled-up version of the fan, which is in operation at the Saimaa University of Applied Sciences.