Axial or Mixed Flow Pump?

Overview

A cotton farm on the Darling Downs sought to reduce energy costs associated with its river extraction pump, which supplies irrigation water to a storage dam. The pump’s efficiency and energy usage were evaluated through a Type 3 Energy Audit conducted by Saturn Engineering Group. The audit assessed the farm’s existing axial flow pump and identified opportunities to enhance efficiency and lower operating costs. The assessment answered a key question asked by the farmer: When do I use the axial or mixed flow pump to maximise my energy efficiency?

Challenge

The farm’s axial flow Hoxton Park pump consumed an estimated 81,150 kWh of electricity during the 2023/24 financial year, incurring costs of $31,205.68 under SAC Small Business Tariff 20. Originally installed in the 1970s, the pump had been operating with minimal maintenance, demonstrating inefficiency with an energy usage rate of 6.79 kWh/ML/m head. The pump fell well below modern efficiency benchmarks. This inefficiency, compounded by high electricity consumption and the potential to transition to SAC Large Business tariffs, created financial challenges for the farm.

Proposed Solutions

Upgrading the pump to a more efficient Batescrew 21-24-10.5 axial flow pump was recommended to significantly improve energy efficiency. The proposed upgrade would reduce energy usage from 73.0 kWh/ML to 23.7 kWh/ML, achieving a reduction of up to 67.5%, and bring the energy usage rate to 3.51 kWh/ML/m head, a marked improvement over the current rate of 6.79 kWh/ML/m head.
The upgrade was designed to optimise performance when the storage dam is between empty and three-quarters full (9.0m total dynamic head). Above this level, pump efficiency drops; therefore, management practices were recommended to transition pumping to the mixed flow China pump, which performs better under higher total dynamic head conditions. This coordinated use of the axial and mixed flow pumps would ensure optimal efficiency across all operating scenarios.
The estimated capital cost for the upgrade, including a new electric motor and civil works, was $192,500. The electricity savings from the pump upgrade were estimated to range between 54,804kWh annually, corresponding to a reduction of 67.5% in energy use, depending on seasonal variability and operational factors. This would generate cost savings of $11,273.70 annually and reduce emissions by 48.2 tCO2-e.

The farm’s electricity consumption occasionally exceeded the 100MWh threshold for SAC Small Business tariffs, triggering a transition to SAC Large Business tariffs with significantly higher fixed charges and demand costs. By improving pump efficiency, employing the management practice between axial and mixed flow pumps would maintain annual consumption below 100 MWh, and the farm could avoid these costlier tariffs.

Results

The recommended pump upgrade and management practices offered substantial energy and cost savings, as well as operational benefits:

Efficiency Improvement: Energy usage reduced from 6.79 kWh/ML/m head to 3.51 kWh/ML/m head.
Electricity Savings: 54,804 kWh annually (67.5% reduction).
Cost Savings: $11,273.70 annually.
Emissions Reduction: 48.2 tCO2-e annually.
Operational Strategy: Efficient use of the axial and mixed flow pumps based on total dynamic head conditions ensured sustained efficiency across various water levels.

Conclusion

Through the proposed pump upgrade and improved management practices, the farm could achieve significant energy savings and operational efficiency while avoiding unnecessary transitions to SAC Large Business tariffs. By strategically alternating between the axial and mixed flow pumps based on water level conditions, the farm could optimise performance and reduce energy costs.

Key Takeaway

This case demonstrates the importance of tailored energy solutions and operational strategies in agricultural settings. Upgrading equipment, strategically managing pump operations, and monitoring energy consumption can result in substantial savings and long-term sustainability. Saturn Engineering Group remains committed to supporting farms in achieving efficient and cost-effective energy management practices.