Zhejiang Zhangzhou Juhua Sulfuric Acid Plant is one of the first key sulfuric acid production enterprises in China, designed, manufactured, and installed domestically. It stands as the largest sulfuric acid production facility in Zhejiang Province. During the sulfuric acid manufacturing process, a water-cooled plate is used for cooling, and the cooling water circulation pump plays a vital role in maintaining the system's efficiency. Traditionally, the pump operated at a fixed speed, with flow and pressure controlled by adjusting the outlet valve. This approach was based on maximum load conditions, leading to significant operational inefficiencies and energy waste. To address this issue and reduce production costs, the company decided to implement variable frequency speed control using the Fengguang JD-BP37 high-voltage inverter. This transformation aimed to optimize energy usage by allowing the pump to adjust its speed according to actual demand, rather than operating at full capacity all the time. The system features three separate circulating pumps, each capable of independent operation. The user’s cooling water circulation pump model is 500S-35, a single-stage double-suction centrifugal pump, with a flow rate of 561 L/s, a speed of 970 r/min, and a head of 35 m. The motor power is 280 kW, with a voltage of 6,000 V and a current of 35.2 A. The motor runs at 985 r/min. The Fengguang JD-BP37 high-voltage inverter uses the latest IGBT technology, featuring a fully digital control system with a color LCD touch screen. It is widely applied across industries such as metallurgy, petrochemicals, power generation, and more. The inverter operates by connecting multiple low-voltage power units in series, enabling direct high-voltage output without the need for additional transformers or filters. It supports 18-phase input, with 36-pulse rectification that minimizes harmonic distortion and meets national standards. Key technical features include a high input power factor, modular design for easy maintenance, fiber-optic isolation between the main circuit and controller, built-in PLC for flexible control, and comprehensive fault detection. The system also includes a color touch screen interface, support for industrial standard signals, and the ability to print operation reports. In the control system, the inverter regulates the speed of the third circulation pump, while the first and second pumps remain open. The main pipe pressure is monitored and adjusted to maintain a target pressure of 0.24 MPa. This setup ensures stable and efficient operation of the cooling system. After implementation in January 2005, the inverter performed reliably, running at around 40 Hz to maintain optimal water temperature. Energy savings data showed a significant reduction in power consumption. Under power frequency operation, the average current was 24.86 A with a power factor of 0.85, whereas under variable frequency operation, the average current dropped to 13.07 A with a power factor of 0.98. This resulted in an annual electricity saving of approximately 718,000 kWh, equivalent to a cost saving of 359,000 yuan. When operating at 35 Hz, the system achieved even greater energy savings, reaching up to 50% in certain seasons. With an estimated annual energy saving of 710,000 kWh, the payback period for the investment was just 1.8 years. In conclusion, the application of the Fengguang high-voltage inverter significantly improved the efficiency of the cooling water circulation system, reduced energy consumption, and lowered maintenance costs. It also enhanced the overall performance of the sulfuric acid plant. As high-voltage inverter technology continues to evolve, it is expected to bring even greater benefits to various industries. The project was successfully executed by Zhejiang Yijia Energy Saving Equipment Co., Ltd., demonstrating their professionalism and expertise in energy-saving solutions.

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