Concept
The difference between axial and radial turbines consists in the way the air flows through the components (compressor and turbine). Whereas for an axial turbine the rotor is 'impacted' by the air flow, for a radial turbine, the flow is smoothly orientated at 90 degrees by the compressor towards the combustion chamber and driving the turbine in the same way water drives a watermill. The result is less mechanical and thermal stress which enables a radial turbine to be more simple, more robust and more efficient (in a similar power range as axial turbines). When it comes to high power ranges (above 5 MW) the radial turbine is no longer competitive (heavy and expensive rotor) and the efficiency becomes similar to that of the axial turbines.
Advantages against Axial turbines
Thanks to lower thermal and mechanical stress on the turbine tips, it is possible to boost power quite significantly by increasing the turbine entry temperature (increasing fuel input) which results in an improved mechanical efficiency. The lower mechanical stresses also enable radial turbines to handle single stage compression and expansion. As a result, the radial turbine does not need to be air cooled, which means that all the air entering the compressor is used only to drive the turbine which gives the radial design a strong advantage for cogeneration applications. Another result of avoiding air cooling is that power and efficiency are kept almost constant during the lifetime of the radial turbine whereas an axial gas turbine needs to be washed often to maintain ISO performance standards. The other advantage of such a simple rotor is that the bearings can be placed at the front, in the cold part, so less lubrication oil is needed, and there are no thermal losses due to lubrication of the hot parts of the rotor.
Constructors
The first company to produce radial turbines for power generation was Kongsberg Våpenfabrikk, a Norwegian company founded by Jan Mowill. The turbine had a unique, all radial configuration, originally rated at 1200 kW. The turbine proved very successful and was generally sold in electric generating packages. The major markets for the units were in the maritime, offshore oil and gas and communications industries. During the following years, more than a thousand units were delivered world wide. Kongsberg Våpenfabrikk was privatized, split up and sold off in the late nineteen eighties and development of the original turbine business was discontinued under the new ownership. Mr Mowill then founded OPRA in the beginning of the 1990s which leaded to the manufacturing of a the OP16 advanced radial gas turbine in 2003, rated at 1900 kW.
