Hydro power generation with low water head.
(SL Patent LK/P/1/19066)
The new technology of hydro power generation provides an extension of enclosed pipe in to the head waters from the combination of intake structure, penstock and turbine generator. Idea of providing an extended pipe length is to stream line the flow, that is usually coming without speed.
The hydro power generator illustrated here is intended to use for river current with low hydraulic head and mini hydro power plants to produce electricity. This method is applicable to hydro power plants of higher capacity as well. Conventionally, the hydro power dams are built with its intake bell mouth vertical to the water surface. With the present device bell mouth is place in the horizontal direction inside the water surface. To facilitate the pressure pipeline inside the reservoir, a channel or trench is excavated to extend the pressure pipe line in horizontal direction, if the reservoir bed is steep and intake level is dropped near the dam. This way existing hydro power generators having short penstock lengths can be improved by providing additional pipe length inwards to the reservoir from intake.
Many dam based hydro power generators were built without providing sufficient length in penstock, between intake and turbine. Most low head, low flow hydro power sources are not exploited since standard hydro power generation techniques cannot be employed in such conditions.
Another distinct advantage of this method is that we can find so many new locations for hydro power generation that cannot be utilized by the presently known hydro power generation techniques.
Most current hydroelectric projects require a large hydraulic head to drive power turbines. Required hydraulic head usually created by constructing a dam in a river bed, creating a reservoir. A hydraulic control tower is constructed towards the opposite end of the reservoir and a pressure pipe line (penstock) is drawn to the power house at the other end.
This method can be diversified further to minimize the extending distance from hydropower dam, by giving a spiral shape to the pressure pipe as shown below.
Water entering at intake is having zero velocity and it has to accelerate to gain certain velocity when it reaches turbine blades. If the intake pipe is extended sufficiently the streamline flow can accelerate the flow speed inside the pipe line. Therefore, by extending the pipe line in to intake water source, flow speed increases.
Let us consider the flow of fluid through a pipe having inlet and outlet sectional area are A1, and A2 consecutively. Velocity at two points will be v1 and v2. According to Continuity Equation A1.v1 = A2.v2= Constant
This type of built in pressure pipe is capable of generating a streamline of flow. The sum of dynamic pressure and kinetic pressure will be same at section A-A and section B-B of the streamline flow inside enclosed pipe. Section A-A having a larger area than section B-B. Therefore in this energy system design the speed of flow will increase when it reaches the turbine blades, generating an additional kinetic energy.
Optimization of hydro power for low head turbine
According to present invention, an enclosed penstock (pressure pipe line) is constructed up to the power house, form a suitable distance to generate hydraulic pressure. This hydro power development based on the fact that the flow through closed conduit (pipe) will be greater than flow through an open channel. Water flowing though a closed conduit (pipe) is a lamina flow in a river of a turbulent flow.
Thus, the new technology can be employed to utilize hydro power from rivers having consistency of flow. This technology is inexpensive compared to hydro power projects built with massive hydraulic retaining structures. Sites for this purpose are available in many countries to double the power generating capability of the nation. Therefore this is an affordable and green alternative for small scale waterway sites as well as rivers having large flow without sufficient water head. Also this pressure pipe line optimization technique can be used in existing dams, weirs, waterways and irrigation canals.
Run-off river hydro-electric plants without pond
An application of Pressure pipe optimization technique is illustrated in the run-off river type of hydroelectric power plants is shown below. This construction method based on the fact that water flow though a pipe line will be greater than the free flow of water in a river. Construction of pipe lines to a long distance is highly practical in our times. Thus water of rivers also can be utilize to generate electricity where there is no facility for storing the water. Bringing a part of river flow through the pipeline laid along the river bed would not do any harm to biological inhabitant, chemical characteristics or physical layout of the environment.
Shown above is a longitudinal section and cross section of a river with a consistency of flow where the gradient, conventional hydro power generation methods cannot adopt due the little pressure difference at higher location and the lower location point of the river flow. The water surface pressure at point A and point E are same and equal to atmospheric pressure. River water flow is having some velocity at point "A". Although the point D is a location lower than point "A", velocity of water flow increase by a small value, since it is open channel flow with frictional losses due to uneven surface of river bed and embankments. But the pressure pipe (closed conduit) laid on river bed from point A to point D having reduced in pipe cross section and pressure accumulate at point D that can be applied to generation hydro electric power. The bulb type reaction turbine of Kaplan type is most suitable in such low heads.
Such hydro power generator can be installed at Peradeniya- Sri lanka along Mahaweli River basin without disturbing the environment and without interrupting the natural water flow of the river at the location shown in this picture where 1: Intake point; 3- Pressure pipe line; 2-Bulb type turbine. There's an uninterrupted continues flow along this river though out the year.
The power generator is Shaft-extension type tubular unit.
It requires less space with smaller powerhouse and free discharge without flow interruption due to power house construction. Adjustable Wicket gates are placed at the intake. Runner blades are made adjustable to provide the flexibility to adapt changing head and demand of different power output.
At intake point at "A" trash track, flow control gate and fish screen are introduced. In this typical example the turbine and the generator house are separated constructions. Details shown in Figure. 6 are: 1. Water flow coming through penstock, 2. River water flow, 3. Turbine, 4. Power House & 5. Electricity Generator.
Preferably the generator and turbine are housed inside separate chambers while the elongated turbine shaft drives the generator in the power house. The water flow passes in a radial and axial direction through turbine blades to generate power.
This hydro power generation process result no river flow decrease. Therefore, no impact on aquatic life and water quality: No water impoundment and no flow changes are done. So that, no embankment erosion and loss of land space for storage tanks and reservoirs consuming land space. Such hydro power systems can be installed in association of a bridge across the river.
The designer suggests that maximum of half the river flow to use at any instance. The turbine can be a pit turbine which is a variation of the bulb turbine well suitable for hydropower plants with water head ranging from 2 m to 10 m and unit capacity in the range of 15MW to 30 MW. Also it can be a fixed blade type since expected flow does not vary.
They are suitable for exploitation of tidal power and hydraulic power with low heads such as 2Meters and large flow rates, therefore suitable for generating tidal power as well.
Besides, sending river flow through pressure pipes can prevent flooding in low laying regions.
This method is applicable to reservoirs constructed to use impulse turbine as well.
Impulse turbine Parts : 301-Penstock; 302-Hydraulic accumulator; 303-Injector nozzles; 304-Bucckets connected with the outer drum; 306- Flanges connected the bracket & runner 308- Bracket connectd with the rotor shaft(runner); 309-Runner (Shaft) on bearings
Impulse type turbine applicable with extended tubular passageway is depicted in Figures shown above. This turbine is made to extract energy from jets of water . It defer from the existing impulse type turbines for having the nozzles inject water radially outwards to impel buckets arranged along the outskirt of water wheel circumferentially.
The water carried through extended pipe line integral with penstock 301 is brought to hydraulic accumulator 302 composed of nozzles 303 directed radially outwards. The turbine runner is made integral with arculate buckets 304 concentrically carrying on a wheel around the periphery of a bracket 308 secured to the hub of the runner 309 by flanges 306. The water jets escaping from nozzles impinge on buckets 304 carrying around the periphery of circular bracket 308 and the imparted effect of water jets turns the runner 309 fitted to the turbine shaft 306 mounted on bearings.
Means are provided turbine shaft 306 to couple with electricity generator to produce electrical power. The shape of the buckets ensures that the majority of the kinetic energy is converted into mechanical energy by the turbine. The size of jets is controlled by the needle valves 310 in the center of nozzles303. Means to control the movement of needle are provided from outside. In this design multiple jets of water being directed on to the runner.