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September 28, 2020
Hydro turbines are considered as a heart of hydro power plants, it almost all the time represents the highest investment in the entire project. After the electric engine hydro turbine got the highest efficiency, plus the fact that it is the most applied RES system, even slightest possibility to higher this effectiveness could make major differences.
The fact that hydro turbines are already mastered technology comes from the vast history of applications that will not be discussed in detail due to large volume of information, however it is important to mentioned that water wheel as the "proto-machine" using water power was one of the technical inventions that anticipated the 1st Industrial Revolution. As a matter of fact the power of water was among the early types of energy human masters to be the engine of his ideas along with all its variations like horizontal or vertical axis wheel from Hellenic Greece, further derived water mill, gristmill, vertical shaft Norse mill, Cornwall stamp mill,
sugar and steel mill, hullers, Portuguese tide mills, irrigation water rising wheels, Roman reversed overshot wheels for mines(mentioned in Marcus Vitruvius Pollio´s treatise De architectura / Ten Books on Architecture) or hydro turbine which could be find in roman ruins in Tunisia where it serves most likely as a mill.
Nowadays hydro turbines are subject for high precision anufacturing based on ISO´s standards attained by CAD drawing softwares e.g. Autodesk Inventor. The feasibility of design is later tested by Computational Fluid Dynamics CFD e.g. Autodesk CFD - Fluid Flow & Flow. Further manufacturing processes use CNC technologies, usually multi axis milling machine. Turbine runners and blades are special parts which are either milled, casting or forging. In case of R&D a digital manufacturing technologies might be applied. All these processes result in precise calibration and balance for securing ideal working surfaces hence the highest energy conversion efficiency of the modern water turbine.
3.1 Turbines division according to environment and applied medium There is vast number of hydro system which application depends on the physical conditions of the given environment (development site) mostly represented by water discharge versus net head in contrast to desired demands.
Generally the overwhelming majority of applied micro hydro systems broadly applied in SHP using concept with diversion weir followed by inflow pipe or penstock leading directly to the power house. This configuration could use high or low head and low or high flow volume and is largely connected with the application of all types of micro turbines from slower reaction types with high torque like Francis or Kaplan in bulb, PIT, “S” and “Z” (Saxo) turbine configuration or high pressured and speed, but lower torque impulse types like single, double-nozzle "Pelton" turbine, alternatively single-nozzle "Turgo" turbine or OssbergerBanki-Crossflow turbine. All depends on given environmental conditions. Of course large and multipurpose installations are more complex thus they could not be mass produces.
Two common schemes of hydro power systems harvesting energy from waste water treatment process in case sufficient flow volume and head is present. Scheme A the water that enters turbines is fully treated by combination of sedimentation and separation systems and WWTP itself, hence the turbine works with clean water that returns back to the biothope.
However in scheme B the waste water is just acquitted from solid and large particles, but not the chemicals that are treated in WWTP after they went through the hydro power system.
Another condition for hydro systems typology is the construction which is specified by the type of the intended medium. There is hard water and salty water causing sedimentation of the minerals (water stone, limestone) on the surface of turbine blades and within pipelines, which might results in change of the hydrodynamic profile of the turbine blades and smaller the flow volume. Further in case of wetlands, sewers and waste Water treatment plants(WWTP) applications where the hydro turbine is exposed to the most aggressive environment consists of various rigid debris, chemical combinations of acid and alkaline water e.g. H2S - Hydrogen sulfide which causes serious corrosion and has the capability of destroying carbon steel within weeks. The mentioned salts or solid particles can also pose a threat to the turbine blades degradation which may results in unbalance of the entire runner.
Generally hydro turbines applied in this kind of conditions could be divided into systems applied before the treatment processes and those placed after. The various combinations could be observed in the Fig. 5. Both systems no matter applied in front or rear of the WWTP are subject for special anticorrosion treatment like highly valuable Duplex stainless steel and adequate ceramic coating, alternatively if more cost-effective solutio cost-effective solution with less efficiency is acceptable an application of a simple systems like reversed Archimedes screws or water wheels are suggested.
Ultimately the water with high portion of sand and small rocks - sediment-laden water, causing erosive and abrasive wear visible especially on turbine blades which results in efficiency reduction and extensively shorten the overall life span of the turbine.
The last but not least there is new generation of hydro turbines applied in specific installations and working under versatile conditions like reversible types not only applicable in PS hydro systems, but also in wave, ocean current or tidal energy harvesting technology which has been in research for the past decades. Interesting is also application in osmotic installations where turbines could also operate reversibly. These and many more just prove the versatility of hydro turbine as a viable RES system and secure energy back up technology.