In a recent project in Zimbabwe, fixed cone valves from Glenfield Invicta have been delivered to a new hydroelectric power station.
By Jørn Urup Nielsen, Prosper Shoniwa and Jason Kessell
The customer approached us for a solution to replace the existing energy dissipating valves at the dam bottom outlet. The existing valves were installed in the 1950’s, were not of standard dimensions, and were welded directly onto the pipeline as opposed to i.e. flanged valves.
Harvesting the power in water flow
The complete project entails the construction of a 5MW run-of-the-river hydropower station on the dam; a method that can utilise the water flow to generate power, which will assist in alleviating the power shortage challenges Zimbabwe is currently facing.
The station is added on an existing river dam (for drinking water and irrigation) with no previous hydropower production.
We were tasked to come up with a design and do a value proposition. Jason Kessell, Engineering Manager, and Prosper Shoniwa, Business Development Manager from AVK Valves Southern Africa visited the site in Zimbabwe to familiarise themselves with the old installation. The visit also included officials from Zimbabwe National Water Authority (ZINWA), the EPC contractor and the developer.
The manufacturing process was completed by December 2022, and as agreed we supplied our fixed cone sleeve valves by January 2023.
AVK in Zimbabwe
In Zimbabwe, our first recorded project dates back to 1932-35 at the Khami River Dam in Bulawajo (through our Scottish entity Glenfield Valves). Since then, we have supplied energy dissipating valves to several other projects in Zimbabwe, including the “Pungwe to Matare Christmas Pass” (1997) and the Marovanyati Dam (2021/22). The AVK Group have supplied valves and sluice gates to more than 100 dams and hydropower projects in Africa.
The fixed cone valve: Used for flow control and energy dissipation
The valve provides energy dissipation and flow control at the end of a pipework system. Primarily, it is used in bottom outlet arrangements from dams where it may be necessary to bypass a turbine, provide compensation flow to a river, rapid drawdown, the dam water level or indeed to provide desilting (removal of small solid, dust-like sediment from the water). The valve is designed for operation under high flow rates and velocities.
The energy dissipation is affected by discharging a thin conical curtain of water into the atmosphere where it dissipates most of its energy, falling in droplets onto the suitably sized stilling pond. The flow enters the valve where it is split by means of the internal guide blades, and discharge is over a fixed conical shaped outlet. The flow is induced by retracting the horizontal stainless-steel sleeve which permits the thin, high velocity conical jet to be discharged. The energy break takes place in the atmosphere, and therefore no cavitation is experienced. The sleeve being cylindrical ensures that operation is in hydraulic balance, hence operational forces are minimised.
Products supplied to the project:
Two fixed cone sleeve valves, with the dimensions of DN1100
Dams, Reserviors & Hydropower
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