Small Hydroelectric Plants: The Hydraulic Auger
Sustainable Development and Planning VI551Small hydroelectric plants: the hydraulic augerG. PerilloDepartment of Technology, Naples Parthenope University, ItalyAbstractSmall-scale hydroelectric plants are an important source of renewable energy andcan actively contribute to the sustainable development of the local area, whilealso being cost-competitive with other renewable energy sources. This paperpresents the application of a hydraulic auger used for flow rates up to 5–6 m3/sand heads up to 10 m. Unlike other turbines, this equipment works by gravitywith water producing torque on a transmission driving a generator connected tothe auger in order to produce electricity. We present a case study on a plantlocated at an existing dam where, by evaluating the river’s mean daily flow, wehave obtained duration curves that make it possible to determine the power andannual energy production obtainable from the plant. This is then compared withthe energy that can be obtained from a plant equipped with a Banki-Mitchellturbine, highlighting that, at equal flow rates, the annual production obtainablefrom the two systems is nearly the same, confirming the effectiveness of theinverse auger in the energy production process. The economic aspects are thenanalyzed by comparing the plant construction costs with revenues from energysales.Keywords: hydroelectric plants, hydraulic auger, turbine comparison.1 IntroductionThe use of hydraulic energy dates back to ancient times and, ever since itsorigins, hydro-electricity has been the most widely used source of renewableenergy after biomass.The first dam known to mankind was built around 4000 BC in Egypt, itspurpose being to divert the flow of the Nile and establish the city of Memphis onthe reclaimed land. Many ancient dams, including those built by theBabylonians, were part of complex irrigation systems which transformed barrenregions into fertile plains. The main ‘inanimate’ source of energy in the ancientWIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)doi:10.2495/SDP130461
552 Sustainable Development and Planning VIworld was the so-called Greek mill, comprising a vertical wooden plank withsmall blades on the lower end submerged in the water, which was mainly used togrind wheat.The Romans used hydraulic energy to till their fields instead of using horsesand, by 85 BC, the kinetic energy of a river or the potential energy of a waterfallwere exploited to power simple machines. A type of watermill with a horizontalaxis and a vertical wheel was designed by the military engineer Vitruvius in the1st century BC and mills of noteworthy dimensions were built in the RomanEmpire from the 4th century AD.In the Middle Ages, the Islamic world made important contributions tohydraulics. In the geographical area where the first Islamic civilizationsdeveloped, important work to reclaim land and distribute water was carried out.Between the 9th and the 10th centuries, the need to find an energy sourcealternative to muscle power led to the considerable technical development ofwater-powered machines. In England, the Doomsday Book (the record of acensus commissioned by William I in 1086) reported the presence of 5,624 watermills. This number gradually rose to 20,000 but the power generated by thesewater mills rarely exceeded 10 kW. In 1770, the French engineer Bernard Forestde Bélidor wrote the book “Architecture Hydraulique” in which he describedhydraulic machines with horizontal and vertical axes.The first important attempt to formulate a theoretical basis for the design ofwater wheels was carried out in the 18th century by the British civil engineerJohn Smeaton, who was the first to build large, cast-iron water wheels. TheFrenchman Jean-Victor Poncelet came up with the idea of an underwater wheelwith curved blades, which increased efficiency by 70%.Another French engineer, Claude Burdin, invented the term “turbine”,introducing it into a theoretical relationship in which he highlighted theimportance of the rotation velocity; Benoit Fourneyron designed and builtimpellers for the French ironworks which reached speeds exceeding 60 RPM andgenerated power up to 50 HP. It was the British-American engineer James B.Francis who, in 1849, designed a turbine with a centripetal flow, i.e. in which theflow was directed inwards.The first hydroelectric plant was built in Northumberland in 1880. In 1858Antonio Pacinotti built the first dynamo and in 1860 the first direct currentelectric engine. In 1895 Le Blanch experimented with the brushed DC electricmotor to be inserted in cascade with an induction motor. The combination ofhydraulic turbines and electric current gave birth to the use of hydroelectricenergy on an industrial scale, based on a technology that has remained almostunaltered to the present day [1–3].According to the classification adopted by UNIDO (United Nations IndustrialDevelopment Organization), hydroelectric plants can be classified on the basis oftheir rated power as follows: Micro hydroelectric plant P 100 kW; Mini hydroelectric plant P 1.000 kW; Small hydroelectric plant P 10.000 kW; Large hydroelectric plant P 10.000 kW.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
Sustainable Development and Planning VI553It is worth remembering that, in terms of power classification, the term ‘SmallHydro Power’ (SHP) refers to hydroelectric plants capable of producing amaximum of 10 MW (10,000 kW).2 Current world situationHydraulic energy amounts to a quarter of the total energy produced in the worldand its importance has been increasing in recent years.Hydroelectric power production was prominent at the beginning of the 1960swhen, due to the progressive use of available hydraulic resources, it stabilized ataround 40–50 billion kWh per year, with oscillations caused mainly by thedifferent hydraulic conditions over the years. In percentage terms, hydroelectricproduction, which in the 1960s constituted 82% of the total power production,fell to 25% in the 1980s, while thermoelectric production increased in the sametime frame from 14% to 70%.Today, over 20% of the world’s energy production comes from hydroelectricpower plants, for a rated power of 870 GW.The market for large hydroelectric plants is almost saturated, especially inEurope, so increasing importance is being attributed to smaller plants.Furthermore, while large hydroelectric plants require large surface areas, whichcauses a considerable environmental and social impact, a smaller plant willintegrate itself perfectly into the local ecosystem, since it exploits the flow of theriver directly [4, 5]. Such plants have a number of advantages: Their installation is very straightforward and can be carried out in shortconstruction times; They require only a limited water supply to generate electricity; The plants are usually located near the users, which minimizes energyloss due to electricity transport; They occupy less space.There is no specific law concerning the classification of small hydroelectricplants, however the literature offers the following definitions: micro-turbines, machines with P 100 kW; mini-turbines, machines with power between 100 kW and 3 MW; small turbines, machines with power between 3 MW and 12 MW.Various turbines are present on the international market, a brief description ofwhich is given below [6–8].2.1 Pelton TurbineThe Pelton Turbine was invented by the carpenter Lester Allen Pelton in 1879,and to this day it is still the most efficient turbine and very simple to operate. Theway it works resembles the classic mill wheel, but revised and corrected toincrease efficiency. This type of turbine is generally used for large heads(between 20 and 200 m) and modest flow rates Q.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
554 Sustainable Development and Planning VI2.2 Turgo turbineThe Turgo turbine is an impulse turbine. It works with heads between 10 and300 m and has a maximum output of 5MW. It differs from the Pelton turbine inthat the blades have a different shape and arrangement and the jet hits several ofthem at the same time. The smaller diameter of the Turgo turbine makes itpossible to have a higher angular velocity, so there is no need for a gearboxcoupled to the generator. This reduces costs and increases the mechanicalreliability of the system.2.3 Francis turbineThe Francis turbine is a reaction turbine developed in 1848 by James B. Francis,a British engineer who moved to the United States. The Francis Turbine makesuse of lower heads and considerable water flow rates; it is suitable for headsbetween 10 and 350 m and generates power between 0.2 MW and a maximum of10MW.2.4 Axial flow turbine (Kaplan)In the Kaplan turbine (or similar) the water runs through the wicket gate with aflow normal to the machine’s rotation axis; therefore, the water will have tomove through about 90 to run axially over the runner, which obviously causesloss. In order to reduce this drawback, tubular axial turbines (TAT) have beenbuilt and patented for fairly large heads (up to 30–40 meters) and generatingpower from 0.3 MW up to 10 MW.2.5 Bulb turbineThe bulb turbine is a reaction turbine which has both a generator and a gear box,if present, inside a watertight, bulb-shaped housing submerged in water. Thebulb turbine, like all tubular axial turbines, is not equipped with a spiral casesupplying the runner and is inserted directly inside the penstock. This allows forconsiderable engineering savings and simplifies routine maintenance operations.Water flow variation is much lower than in normal axial tubular turbines, even ifthe axis is horizontal.2.6 Banki-Mitchell turbineThis kind of turbine is not suitable for use in large plants, but only in small-scaleones. It is well adapted for medium-low heads (from a few meters up to200 meters) and for low power production, and hence also low flow-rate, below700–800 kW. This impulse turbine is also called the Cross Flow or Ossbergerturbine, after the factory that has manufactured it for over 50 years. It is a twostage machine, which allows a double action of the water on the blades.Although its efficiency is less than 87%, it remains constant when the flow-ratefalls as low as 16% of the nominal flow and can, in theory, operate with aminimum flow rate 10% lower than that envisaged in the design specifications.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
Sustainable Development and Planning VI555Figure 1 shows a diagram from which the applicability field of the abovementioned turbines can be determined, at least in a first approximation.2.7 Inverse hydraulic augerThe hydraulic auger employs the same principle as the Archimedes’ screw, usedby the ancient Egyptians to transport water for irrigation.Figure 1:Performance curve of the hydraulic auger (red line) compared.According to this principle, the energy is transferred to a shaft/rotor and thewater is transported upwards. A power-generating machine can be made byusing this principle in the inverse way. Unlike the above-mentioned turbines, thehydraulic auger harnesses gravity to work, i.e. water flows downwards from thehigher chambers to the lower ones. In so doing, the falling water generates atorque on the transmission shaft. Since the auger must extend from the upperwater surface to the lower one, it can only be used for short heads. The designflow determines the angle of incidence of the helix, the number of revolutionsand the external diameter, while the head determines the length of the auger. Theauger is manufactured by welding an optimized-flow helix onto a stiffenedhollow shaft. The motor assembly comprises elastic joints, support frames, gearbox, generator and, if needed, a transmission belt.These augers can be used to harness hydraulic energy at flow rates between0.2 and 5.5 m3/s and for a maximum head of 10 m.Hydraulic augers do not require the fine-mesh grills used in turbines andwater wheels to prevent flotsam and fish from entering the machinery. Thismeans that there is no loss of energy due to head reduction or a fall inperformance because of the grills.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
556 Sustainable Development and Planning VIFigure 2:Inverse hydraulic auger.The wide-mesh grill (10–20 cm) greatly reduces the formation of debris, andhence lowers costs for cleaning and related disposal operations, as any flotsamentering the plant is transported downstream. Variations in flow rate have anegligible impact on performance and do not affect the operation and service ofthe hydraulic auger. Very low flow rates do not damage the hydraulic auger andhydroelectric power plants fitted with them are therefore more feasible thantraditional turbine-driven plants. As can be seen in the figure reported below, theperformance of hydraulic augers can be as high as 90% and is, in any case, highin a range from one third of the flow rate to the maximum flow rate. This meansthat hydraulic augers achieve a high performance even when water supply is low.Moreover, dams and turbines generally represent a major obstacle and a threatnot only for fish heading upstream but also for migratory fish. Hydroelectricplants of any kind also constitute an obstacle for fish migrating to lay eggs.Experts’ tests on hydraulic augers, on the other hand, have shown that both smallfish (longer than 8 cm) and large fish (up to 58 cm) can pass through the plantunharmed, making the inverse hydraulic auger ‘fish-sustainable’ [9].3 Case studyThe study focuses on the possible installation of an inverse auger hydroelectricplant at the Persano dam (figure 3) situated between the Picentini and theAlburni mountains (Italy) at an elevation of 52.10m asl and measuring 158.80 min length.The foundations of the dam comprise layers of cemented large conglomerateover an impermeable concrete diaphragm covering 2500 square meters. The damhas four gates in line between five concrete piles (figure 2). The dam continuesonto the left bank with a masonry structure. The gates have a 17m aperture andare 6m in height and are balanced with counterweights set in shafts inside thepiles and are opened/closed by acting on the water level in the shafts. Obviouslythe speed with which the gates can be opened or closed depends on the quantityof water evacuated from or diverted into the shafts housing the floats.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
Sustainable Development and Planning VIFigure 3:557Aerial image of the dam.Plant maintenance can be performed by diverting the course of the river to aspillway located along the left bank at 38.20 m asl. This spillway also has a gatemeasuring 4.8m x 4m and can divert a flow of about 50 m3/s. The dam greatlyreduces the river flow velocity, which results in the depositing of large quantitiesof silt and sand both at the mouth of the spillway and in the shafts housing thefloats that operate the gates. These areas therefore need to be dredgedperiodically to ensure efficient plant operation. This dam has raised the riverlevel by 6m (from 40.50 m to 46.50 m) and created a reservoir in a large bend inthe river Sele which is also supplied by its tributaries (the Tanagro and theTenza).Figure 4:Frontal view of the dam.The main data for the reservoir are as follows: maximum reservoir height:maximum regulation height:minimum regulation height:46.50 m asl.46.50 m asl.43.50 m asl.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
558 Sustainable Development and Planning VI freewater surface1. at maximum reservoir height:0.6 km22. at maximum regulation height:0.6 km23. at minimum regulation height:0 km2 total reservoir volume:1.5 x 106 m3 regulation working volume:1 x 106 m3 lamination volume:0m3 directly subtended basin surface area: 2336km2.The first step was to calculate the confined flow from the gates; as alreadymentioned, these are 17m in length and are regulated automatically. Raising thegates allows the water to flow into the afterbay. System operation is similar tothat of a sluice, as the entire aperture is below the freewater surface.The data provided by the Bonifica Destra Sele Consortium for the period2003–2009 made it possible to calculate the river’s mean daily flow rate. Thecalculations performed made it possible to obtain the duration curves for everyyear from 2003. Of course, the measured flow rates vary from day to daybetween a maximum and a minimum.The inverse auger plant was located on one of the two diversion channels onthe hydraulic right which are used for irrigating the fields in the Sele valley. Thewater from the reservoir is diverted into these channels only during the irrigationseason (essentially from June to September). In our case, as the aim is to site theproduction plant on the diversion works and as it would be necessary to have aconstant supply throughout the year, it was decided that the augers should beinstalled immediately downstream of the diversion works with a spillwayimmediately downstream of the turbines to channel the water back into the riverwhen irrigation is not required. The Bonifica Destra Sele Consortium hasprovided us with the data necessary for our case study. Specifically: the diverted flow varies between 4 m3/s and 8 m3/s; the bottom of the diversion tunnel is at an elevation of 43.70 m asl; the reservoir elevation is, as already mentioned, 46.50 m asl andmaintains this level for most of the year.4 Assessment of the power and energy producedPlant power can be obtained from the formula:g H Q pPkW 1000where: (1)g is the acceleration of gravity 9.81 m2/s;ρ is the water density 1000 kg/m3;η is the plant efficiency;H is the net head reservoir height – height of the tunnel bottom,assumed to be 2.80 m;Qp is the projected flow.WIT Transactions on Ecology and The Environment, Vol 173, 2013 WIT Presswww.witpress.com, ISSN 1743-3541 (on-line)
Sustainable Development and Planning VI559The available data shows that the maximum flow rate obtainable from thediversion works is 8 m3/s, which is greater than the maximum flow that the augercan manage. It was therefore initially decided that the power should be assessedwith the plant operating at Qp 5.5 m3/s, which is the maximum flow rate atwhich an auger can operate. Thus we calculated the percentage ratio between Qpand Qmax (maximum flow that the plant can manage) which, in this case is 100 %and, using the graph shown in figure 6 with the abscissa value known, the augerperformance was calculated.Figure 5:Auger performance curve (in red) compared.We thus have all the data needed to calculate the power. The plant can beused with a flow rate which is at least 10%–12% of the maximum flow. Forvalues below 10 % of this figure, machine efficiency falls to zero. Adding theflow Qp to the DMV (3.7 m3/s) yields the minimum flow in the river bed neededto ensure a flow to the auger of Qp. At this point, it was possible to evaluate thenumber of days for which the flow rate in the river bed (specifically 9.2 m3/s) isreached or exceeded.Looking at the number of hours during which a flow rate of 5.5 m3/s isguaranteed then makes it possible to calculate the obtainable energy:E P n kWh (2)Obviously the plant will also work for Qp flows below the maximum rate. In asecond stage this value was reduced in steps of 0.5 m3/s and the previouslyanalysed calculations were repeated. For every step, therefore, it was possible toevaluate the power and the energy obtainable from the plant. The calculationsthen make it possible to evaluate the energy obtainable
Hydro Power’ (SHP) refers to hydroelectric plants capable of producing a maximum of 10 MW (10,000 kW). 2 Current world situation Hydraulic energy amounts to a quarter of the total energy produced in the world and its importance has been increasing in recent years. Hydroelectric power production was prominent at the beginning of the 1960s
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