Cross-flow turbines are suitable for use in power generation at low head heights of 2 to 70m. Our cross-flow turbine was developed in cooperation with Mr. Univ. Prof. Krešimir Franjić, who lectured in Zagreb at University of Mechanical Engineering and Naval Architecture (dep. of Energy, Power engineering and environment, R&D of Turbomachinery). Mr. Franjić developed with the assistance of his daughter, Ms. GE Katarina Franjić the corresponding calculation software. The whole project, as usual with neromylos, received a Greek name: OBELIXX.
Neromylos OBELIXX turbines are equipped with a flap control system which moves eccentrically over the turbine runner, contrary to the usual cross-flow turbines (Bánki system with 2/3 to 1/3 flap control in the flow duct). The advantage lies in the fact that the entire blade width is flowed evenly and the driving water does not have to move laterally before generating the rotational energy at the rotor. Since there are no disturbing flap parts (like Bánki) in the inlet channel, the inlet flow losses are minimized. The flap is moved digitally with a stepper motor in the hundredth of a millimeter range and the amount of water is thus optimally converted to rotary motion at the turbine blades. This results in a fine controllability of the turbine and an increased efficiency of about 84.5% (about 79% with conventional Bánki) over the entire available water supply. Only a water supply of less than 18% of the reference amount results in lower efficiencies.
The sealing of all rotating parts is done by highly wear-resistant Simmerings, as they are also used in the automotive industry. The bearings are from well-known manufacturers, such as FAG and SKF and can be equipped with a central lubrication unit. The runner is made of high-strength stainless steel on waterjet cutting machines in the thousandths of a millimetre range and then the inlet and outlet angles are attached to the blades. The drive shaft, bearing shaft, sides and support plates are thereafter welded around by means of special welding. The rotor-bearings unit can be removed as a whole unit from the housing and hereby reducing possible repair times and simplifying maintenance work.
The housing is made of thick-walled, coated steel with separation edge between housing and rotor, made of CNC milled and screwed segments. This has the advantage that the components of cutting blades, which are considered to be wearing parts, can be replaced quickly and efficiently (usually after approx. 5 years of continuous operation).
Neromylos tends to the fact, that every single case and case of application is calculated and constructed separately. Subsequent production on our most modern CNC machines guarantees the accuracy of the components in the thousandth of a millimetre range. Through this special processing, we are able to produce parts in recurring quality, with one blade of the other, like an egg to the other. This results in only minor corrections during the subsequent balancing of the impeller. Here, we do not use balancing weights that could fall over time. Instead, we determine the location and size of the drills at the computer-controlled balancing machine, which removes material where it is required and thus lead to the optimal balancing and concentricity results. Each impeller is provided with a documented balance certificate. The impeller consists of 21 to 32 blades. Another advantage of the OBELIXX turbine is that they can operate with relatively high speeds, with no intermediate transmission required. Possible speeds 500 to 1000 rpm. Due to its simplicity and robustness, the cross-flow turbine can also be used for slightly contaminated water.
Stainless steel is the mostly used material in cross-flow turbines (also suitable for use in potable water power plants).
Advantages of neromylos cross-flow turbines:
individual production and design
own blade geometry, CNC milled
use of bearing parts from well-known manufacturers such as FAG, SKF
turbine sealing system based on standard seals
silky smooth and quiet running of the entire turbine (example: 83 dB at 1m distance from the turbine housing)
extremely low vibration due to special and precisely fitting component configuration
even blade inflow distribution results in higher efficiency
high efficiency up to 84,5%
turbines up to 4 MW individual power
special venting valve in the turbine housing, to regulate the water level in the intake manifold
rotary damper actuators electric with emergency buffering and emergency stop function
no use of hydraulic oil at systems up to 4 MW (no environmental pollution due to leakage)
longevity of the components due to special steel selection
runners extremely resistant to abrasion (measured on turbines, during operation)
high availability in daily use, since extremely low maintenance
optimum price/performance ratio