1. Existing Problems Our plant's circulating water system has three cooling tower fans, using a dual-phase full-pressure start-up system (forward and reverse rotation). In summer, the fans operate in forward rotation, and the airflow is adjusted by changing the number of motors running to control the circulating water temperature. In winter, they operate in reverse rotation for defrosting. The following problems exist: 1) The cooling tower fans cannot be adjusted during operation; they can only operate at a constant speed. This cannot meet the requirements for fine-tuning the airflow. 2) The cooling tower fan motors have a capacity of 160kW and a rated current of 282A. The full-pressure starting current is close to 2000A, causing fluctuations in the low-voltage electrical system and severe impact damage to mechanical and electrical equipment, resulting in frequent maintenance of the motors and equipment. 3) To adjust the airflow, only coarse adjustments can be made by changing the number of motors, wasting a significant amount of electrical energy. 4) The cooling tower fan motor protection only provides conventional short-circuit and overload protection, which cannot meet the requirements for comprehensive motor protection. 2. Improvement Methods: 1) Replace the original contactor with an FRN160P11s-4cx frequency converter to control the fan speed (wiring diagram shown in the attached diagram). Dual-location control (control room/front-end) is used, with manual speed adjustment from the control room. Considering uninterrupted fan operation during frequency converter fault repair, a frequency converter cabinet with a maintenance bypass is used. 2) Replace the original full-pressure start and inertial stop with the frequency converter's soft-start/soft-stop function. The optimal acceleration time is set to 15 seconds, and the optimal deceleration time to 20 seconds. This reduces the damage to the equipment caused by starting current and mechanical shock. 3) Utilize the frequency converter's energy-saving function to achieve fan energy savings. Because the fan's airflow is proportional to the first power of its rotational speed, the pressure is proportional to the second power of its rotational speed, and the shaft power is proportional to the third power of its rotational speed, a 15% reduction in fan speed will reduce energy consumption by nearly 40%. It is evident that there is a huge potential for energy saving by using frequency converter speed regulation. 4) Utilize the complete protection function of the frequency converter to achieve comprehensive protection of the motor. The frequency converter has protection functions such as overcurrent, overvoltage, undervoltage, and motor overload. 3 Application effect After improvement, the cooling tower fan has been running continuously to this day, with significant energy savings. The starting current and running current have been significantly reduced; the speed regulation is simple and practical, the speed adjustment is flexible, and the data recording is accurate; soft start/soft stop has been achieved, and the speed regulation is smooth and stable. It reduces the impact on the low-voltage system and extends the service life of the equipment. 4 Economic benefits (1) Direct economic benefits After the frequency conversion modification of the cooling tower fan, the various operating data records are shown in the attached table. The frequency of operation after the frequency conversion modification is in the range of 35 to 45 Hz. According to the annual average operation of 40 Hz, the modified fan is calculated based on 320 days of operation per year. The annual power consumption of the three fans is 1,359,360 kW-h, the unit electricity cost is 0.4 yuan/kW-h, and the annual electricity cost is 543,700 yuan. Before the frequency conversion, the operating current of the motor was 189 A and the operating power consumption was 112 kW. The annual operating power consumption of the three motors was 2,580,480 kW·h, and the unit electricity cost was 0.4 yuan/kW·h, with an annual electricity cost of 1,032,200 yuan. It can be seen that the frequency conversion has saved 488,500 yuan in electricity costs annually. After deducting the investment cost of 540,000 yuan, the investment was basically recovered in one year and two months. In the future, the annual electricity cost will be saved by 488,500 yuan, indirectly saving more than 10,000 yuan in motor maintenance costs and extending the service life of the motor. (2) Indirect economic benefits The low failure rate of the cooling tower fan ensures the high quality of the circulating water used by the three production units of the entire chemical plant. It ensures the safe, stable, high-quality, and high-load production of the production units. Practice has proved that the application of frequency converters in circulating water cooling tower fans is a good solution with high returns for enterprises and an essential way for chemical plants to achieve energy conservation.