Modification, simulation and demonstration of laboratory scale Pelton Turbine for waterfall hydropower plant

Abstract

To demonstrate the concepts of using waterfall hydropower to generate energy, a Mini-Laboratory Pelton Turbine (MLPT) was designed and simulated. The principle of energy conversion from potential energy of water at high elevation to kinetic energy at lower elevation through gravity fall was used. To achieve relative continuity of supply as in waterfall, a centrifugal pump was used to deliver water into a set of three reservoirs positioned at different heights. Water from the reservoirs through pipes of different diameters was used to drive the pelton Wheel turbine. A pipe matrix that allows combination of water from two or three sources at different heights and different pipe diameters was designed to demonstrate principle of conservation of flow at a junction. In the laboratory scale design, a power of 750 W was targeted. The required flow rates from different heights of reservoirs to deliver the power were used to establish nozzle diameters, rotor size, rotational speeds and power coupling ratios. A simulation of the model was conducted with different heights, pipe diameters and flow combinations using pipe matrix, were conducted using Matlab Simulink environment. The results showed that the velocity of flow under gravity increases with height of water and the force and torque associated with the flow rate increase with flow area and height of water. The sum of flows from matrix pipes was always found to be conserved with a variance of 0.27. For water heights of 7, 9 and 11 m, the nozzle diameter was found to be 19.0, 25.4, and 38.1 mm and the corresponding jet velocities were 11.2, 12.5, and 13.8 m/s. The flow rates for the scenarios were 0.0026, 0.0046 and 0.0103 m3/s. The optimum wheel diameter was 313 mm with a power coupling of 5.6:1. Compared to other models [27, 35] from the direct use of jets from pumps, the results have similar characteristics and geometric profiles. The average velocity is lower but, flow rate is higher due to the influence of larger cross sectional area. Thus, it is possible to produce the same power output using lower pressure heads when flow rate is optimized using nozzle diameter to compensate loss in velocity. Such systems can be used to harness most of the low head waterfall in Nigeria. However, the possibility of harnessing waterfalls to generate electricity for low energy demand such as recreation centers and farm settlements is faced with problem of hard-to-reach water source due to topographic complexities.