Research and Application of Pump Frequency Control Technology
**1. Introduction**
The Daqing Petroleum Administration Water Supply Company consumes approximately 30% of the total cost of water supply in terms of electricity annually. Of this, about 70% is attributed to the transmission and distribution of electricity. Therefore, optimizing daily pump operations to maintain a more economical balance between water and electricity usage has become a key focus for energy conservation. The company has actively explored various methods, conducted thorough research, and implemented effective measures to address this challenge.
**2. Problem Statement**
The Longhu Bubble Water Plant, located on the northern bank of the Dragon and Tiger River, has a water intake capacity of 500,000 cubic meters per day. Originally designed with long-term planning in mind, it features two pumps: one with a motor of 1400 kW at 10 kV, and another with a 900 kW motor at 10 kV. These pumps are designed to operate under high head conditions (62 meters), but due to declining external water demand from the oilfield, the actual daily water supply has dropped to 250,000–300,000 cubic meters. This means the system operates at a much lower flow rate than originally intended, leading to inefficient pump operation. To manage pressure, the outlet gate is frequently adjusted, which causes significant energy loss and increases the risk of pump failure. Over the past two years, maintenance costs have exceeded 100 million yuan, highlighting the urgent need for technical upgrades.
**3. Frequency Conversion Transformation Plan**
Under normal operating conditions, pumps are designed to work at their optimal efficiency point. However, when flow decreases, the pump must work at higher pressure, leading to excessive energy waste through valve throttling. By implementing frequency conversion technology, the pump speed can be adjusted to match the system's requirements. This results in a proportional reduction in both flow and pressure, significantly lowering energy consumption. For example, reducing the speed of a 900 kW pump from 748 rpm to 500 rpm would decrease power consumption by nearly 57%, as shown in detailed calculations. This transformation not only improves energy efficiency but also extends the lifespan of the equipment.
**4. Energy-Saving Estimates**
Assuming a reduction in pump pressure from 5.8 kg to 2.5 kg while maintaining the same flow, the theoretical energy savings could reach 57%. Based on current electricity rates of 0.41 yuan per kWh, and considering an annual operational period of 330 days, the original annual electricity cost was estimated at 478 million yuan. After the frequency conversion, this cost would drop to around 205.54 million, resulting in an annual saving of over 272 million yuan. These figures demonstrate the substantial economic benefits of the project.
**5. Implementation Plan**
After careful evaluation, the decision was made to install a frequency control system using the 6# pump. The system allows for independent operation of the second phase pipeline, with the ability to switch back to power frequency if needed. A bypass cabinet enables manual switching, and electrical interlocks ensure safe operation. Additionally, constant pressure control, automatic valve linkage, and cooling water protection features were incorporated to enhance reliability and safety.
**6. Trial Operation Results**
On January 6, 2002, the frequency control device for the 6# pump was commissioned. During the trial, the 3# and 7# pumps were gradually phased out, and the 6# pump operated at 37 Hz. After stabilization, the second-stage outlet valve was opened to 70%, and the system ran smoothly without issues. The frequency converter proved stable, efficient, and user-friendly, meeting all operational requirements.
**7. Post-Transformation Energy-Saving Test**
Energy-saving performance was measured using power meters before and after the transformation. Data showed that the unit power consumption dropped from 0.21 kWh/m³ to 0.14 kWh/m³, representing a significant improvement. Based on these results, the annual energy savings were calculated to be around 604 million kWh, translating into a cost saving of 2.878 million yuan.
**8. Process Improvements**
The frequency conversion system brought several operational improvements, including enhanced automation, reduced mechanical stress, and improved control accuracy. It also allowed for remote monitoring and centralized management, increasing overall system efficiency and reliability.
**9. Conclusion**
The frequency conversion project at the Longhu Bubble Water Plant has proven successful, delivering substantial economic and environmental benefits. It reduces energy consumption, enhances system flexibility, extends equipment life, and improves working conditions. As a high-tech solution, this technology holds great potential for future applications in the water supply industry and beyond.
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