Design and simulation of a dewatering system for a unit draft tube at Isimba hydro power plant

Abstract

At Isimba Hydro Power Plant, periodic maintenance inspections are scheduled to take place in the draft tube of each unit. The draft tube at any single point contains a substantial amount of water rendering it unsafe for humans to be lowered into it. This presents a need for complete dewatering of the draft tube in order to carry out the required structural inspections. This project set out to develop and evaluate an optimal system for the complete dewatering of the draft tube at Isimba Hydro Power Plant. This entailed determining the current system characteristics whilst highlighting the relevant parameters for the draft tube. After the required parameters were determined, a system design to fit these parameters ensued. Finally, a system simulation was in order for the purpose of evaluating the viability of the proposed system design. The system characteristics which include dimensions of the draft tube, running length from the draft tube to the drainage pit, and water level were acquired during a site visit to the dam. It is imperative to note that when designing it is important to know what exactly is being designed for. In this case that meant the volume of the water to be removed. The volume of water available dictates the required pump and accessories required. The volume of the water in the draft tube was calculated by means of integration and exponential regression. As per the discretion of the design engineer and for purposes of this project the water is set to be removed in 6 hours. With knowledge of the amount of water to be removed from the draft tube, Bernoulli's theorem was used to determine the head required to be overcome by a pump. This concluded the design phase of the project. Solid works fluid flow simulation software was used to evaluate the performance of the system and close correspondence between the simulation results and calculated values was found and therefore rendering the system viable. Further, pump selection ensued based on the determined design values. Finally, a discussion of the results and recommendations for Isimba Hydro Power Plant in regards to the project if it chooses to implement it.