Can a Centrifugal Pump Function as a Hydro Turbine?

The suitability of a centrifugal pump to function as a hydro turbine is a common inquiry, particularly in the context of small hydroelectric plants. Centrifugal pumps, especially those designed for multi-stage axial Francis or mixed flow impellers, have been employed in some instances to generate power by reversing the flow. However, this application comes with significant challenges and inefficiencies.

Optimization for Pump and Hydro Generation

Specially designed horizontal split case centrifugal pumps with multi-stage axial Francis or mixed flow impellers have been adapted for use in small hydroelectric plants. The flow of water is initially used for pumping to a reservoir and then reversed for power generation during peak demand periods. While the concept is intriguing, the power generated is often significantly lower than the energy consumed, resulting in a net loss that can be upwards of 20%. This inefficiency makes such applications less viable in practical terms.

Design Limitations for Industrial Centrifugal Pumps

Traditional end suction ANSI or ISO configured industrial centrifugal pumps are not suitable for this application due to the excessive overhung load on the impeller shaft when discharging into low or zero heads. The structural integrity of the pump can be compromised. The bolt or nut that locates the impeller is prone to loosening, which can cause the impeller to strike the volute, leading to catastrophic damage to both the impeller and the volute. This highlights the fundamental differences in design and operational requirements between pumps and hydro turbines.

Impeller and Mechanical Differences

The design of the impeller in a centrifugal pump is not structured to function efficiently as a hydro turbine. While it is theoretically possible to flow enough water volume with sufficient pressure to get the impeller to turn, the amount of power derived would be very low. The performance and efficiency of a pump and a turbine are vastly different due to the mechanical elements.

However, in a more limited sense, the impeller can function as either a pumping device or a power generating one. This adaptability is exemplified by the use of specifically designed reversible Francis wheels, which can run as both a pump and a turbine with comparable efficiencies. Such design elements are often found in pumped storage hydro power stations, where the wheel's capability to switch between functions is crucial for optimal performance.

Conclusion

The question of whether a centrifugal pump can function as a hydro turbine is complex and depends on the specific design and operational context. While certain designs can achieve a degree of functionality in both roles, the inherent limitations and inefficiencies make it a less practical solution for most applications. Proper design and adaptation, such as using reversible Francis wheels, can enhance performance but may still not fully compensate for the fundamental differences between pumps and turbines.