Abstract: This paper studies the energy saving and safety control of cooling tower fans to realize the energy saving and safety automation online management of fan operation. Through the actual use effect investigation, it is shown that the control system solves some problems in fan management and realizes the energy saving and safety automation control of fans. It improves economic benefits and equipment reliability, achieves ideal results, and provides a new idea for strengthening the scientific management of equipment. Keywords: Cooling tower fan, energy saving Cooling tower fan is the core equipment of the circulating water system [1]. Beijing Yanshan Petrochemical Company Refinery currently has 7 sets of circulating water devices, with a total designed cooling water treatment capacity of 4.665×104t/h; 105 cooling tower fans (98 of which are 4.7m and 7 of which are 8.5m), with a total installed power of 4060kW. The maximum daily power consumption under the condition of simultaneous operation is 9.74×104kW·h. In terms of the management of circulating water equipment, cooling tower fans account for a large proportion in terms of the number of equipment, maintenance workload, power consumption, etc. The number of fans accounts for 57% of the total number of equipment in the workshop, maintenance hours account for 60% of the total, and electricity consumption accounts for 22% of the total. How to ensure the long-term operation of equipment while saving energy and reducing labor is necessary to apply advanced scientific and technological methods and management methods [2]. Since 1993, our unit has cooperated with the Institute of Engineering Thermophysics of the Chinese Academy of Sciences to jointly develop two sets of monitoring systems for fan energy saving and safety control, namely "KR-933 type fan energy saving controller" and "KR-939 type fan safety operation monitor". At present, the system has been fully applied in the circulating water workshop and has achieved ideal results. 1 Research on fan energy saving controller The purpose of proposing fan energy saving control management is to realize closed-loop automatic control of fan operation. The water supply temperature is preset according to the production needs. The influence of climate and meteorological environment on water temperature and the influence of changes in system heat exchange conditions on water temperature are reflected in time by the measured value of temperature sensor. Finally, the water supply temperature is stabilized by regulating the energy consumption of cooling equipment to achieve automatic energy saving. It is generally believed that "variable frequency speed regulation technology" is the ideal method to complete the above process. However, the application of variable frequency drive (VFD) technology in the control of circulating water cooling tower fans has the following limitations and defects: ① While VFD technology can achieve high temperature control accuracy, this is not crucial in circulating cooling water systems. ② The energy loss of the VFD itself (average operating efficiency less than 90%) affects energy-saving effects. ③ Variable speed operation alters the fan blade angle of attack (windward angle), causing the fan to operate outside its operating point and reducing efficiency. ④ Low-speed operation of the motor, away from its rated speed, and the nonlinear relationship between speed, torque, and power consumption also significantly reduce motor efficiency. ⑤ VFD systems are relatively expensive (around 1000 RMB per kilowatt), requiring substantial investment for both new projects and retrofitting existing equipment. ⑥ The design must also consider the destructive resonance problem of the VFD operating at certain specific speeds and the interference of strong electromagnetic pollution generated by the VFD on other instruments. Given that cooling tower fans often operate in a group of multiple units connected in parallel, we propose an automatic adjustment of the number of fans on and off based on changes in the measured supply water temperature to achieve temperature control and energy saving. This is a simple, easy-to-implement, and low-cost control method, but it differs from conventional PID analog regulation. It is a single-variable discrete control closed-loop system that must ensure a certain level of temperature control accuracy while preventing frequent fan start-stops; it must ensure that a single fan can operate while requiring multiple fans to operate in a balanced manner in terms of time and number of start-stop cycles. Addressing the practical problems encountered in cooling tower fan control and management, we developed and manufactured a system based on 18 basic design requirements, including "temperature measurement range," "measurement accuracy," "display resolution," "measurement upper and lower limits," "measurement calibration value," "execution cycle," "temperature tolerance," and "temperature rate tolerance." This system was first tested on-site at the third circulating water plant in March 1993 and named the "KR-933 Fan Intelligent Controller." 2. Research on Fan Safety Monitoring Devices The purpose of proposing the safety monitoring and management of the fan is to automatically detect changes in vibration, oil temperature and oil level, display and record them, and alarm and shut down the fan if the detected value exceeds the limit, so as to achieve the goal of safe and stable operation of the fan and reduce or even eliminate the occurrence of fan damage accidents. According to the actual situation of on-site management, the three parameters of "fan vibration", "lubricating oil temperature" and "gearbox oil level" were determined to be the most important operating parameters to ensure the safety of the fan [3]. A total of 15 design parameters, including "measurement range", "measurement accuracy" and "inspection time", were also determined for research and development. The system was first tested in the circulating water field in September 1993 and named "KR-939 Fan Safety Monitor". This system utilizes multi-parameter combined probe technology, digital instruction encoding technology, and computer network management technology. The three-parameter combined probe is installed on the gauge mount of the wind turbine gearbox, with its probe rod directly inserted into the lubricating oil. It directly converts the oil temperature, gauge position, and equipment vibration values ​​within the gearbox into electrical signals, which are then transmitted to the wind turbine safety monitor in the control room. Each safety monitor can connect eight combined probes via a four-core cable, enabling real-time monitoring of the operating parameters of eight wind turbines and simultaneous digital display. It includes multiple functions such as over-limit alarms and over-limit shutdowns. After numerous trials and redesigns, it has been successfully applied in the equipment production site, and all parameters have met the predetermined design requirements. 3. Achieving Computer Network Control The two measurement and control systems described above can be connected to a management computer via a four-core communication cable (RS-422 standard serial interface). The computer can be a general-purpose PC or an industrial control computer. When equipped with the corresponding configurable monitoring and management software (DCS-900 software), it can network with multiple KR-933 and KR-939 monitors for control. The fan monitor connected to the computer adds the following functions: ① Simultaneously monitors the measurement parameters of all controllers within the network for comprehensive management. ② Modifies the setting parameters of each controller within the network. ③ Optimizes system management based on changes in the operating parameters of each controller. ④ Records historical data and graphs for analysis and easy retrieval. 4. Effects of Fan Management Research Since 1993, Beijing Yanhua Refinery has conducted fan automatic control management experiments, achieving good results, mainly reflected in energy saving and safe operation. 4.1 Significant Energy Saving Effect in Fan Operation Taking the second circulating water field equipped with KR-933 as an example, the energy saving effect of using the KR-933 energy-saving controller is shown in Table 1. As shown in Table 1, the third circulating water plant, where the KR-933 energy-saving controller was initially tested on-site, saw energy savings of 178,533 kWh compared to the same period in 1991 and 1992 during the four months of June, July, August, and September of 1993, when the fan load was relatively heavy. At a cost of 0.45 yuan/(kWh), this translates to a total saving of 79,200 yuan in electricity costs over those four months. The cost of installing the energy-saving controller at the third circulating water plant was only 43,600 yuan, demonstrating that the investment could be recovered within just a few months of equipment operation. Currently, our factory has successively applied 13 KR-933 intelligent controllers to 92 controlled fans in four circulating water plants, achieving considerable economic benefits. Table 1: Energy Saving Effect of KR-933 4.2 After several years of continuous improvement, the accuracy of the safety monitoring system was significantly improved in 1998 and 1999. Statistics from January to July 1999 show that the system triggered 17 alarms, identifying 13 units with problems, achieving an alarm accuracy rate of over 76.5%. Furthermore, during equipment inspections, two units with serious potential hazards were discovered, preventing severe damage and achieving good economic results. Based on field experience, the characteristics of the oil temperature, oil level, and vibration curves of a wind turbine in good condition are as follows: ① Oil temperature curve: Gradually rises and falls from the start-up and shutdown times, becoming a smooth, approximately straight curve after about one hour. ② Oil level curve: Approximately a horizontal straight line regardless of whether the turbine is running. ③ Vibration curve: In the running state, an irregular curve exhibiting narrow-amplitude oscillations around a virtual straight line. Since 1994, our plant has installed 13 KR-939 type fan safety monitors in 6 circulating water systems, conducting long-term online monitoring of 86 fans of different types. This has changed our fan maintenance strategy from primarily relying on cumulative operating time for major overhauls to basing maintenance on the monitor's measurement data, making fan maintenance more scientific and rational. After the installation of the safety monitors, the workload for fan maintenance has decreased by approximately 30%; simultaneously, it has prevented several serious fan-related accidents, and in recent years, there have been no unexpected damage incidents, achieving considerable benefits. 5. Shortcomings 5.1 Large fans are not suitable for the KR-933 energy-saving controller. In circulating water systems with high-power, few-unit fans, the start-up and shutdown of each fan significantly impacts water temperature. Therefore, the KR-933 fan energy-saving controller cannot stably control the water temperature. For example, in the sixth circulating water system, there are three fans with a diameter of 8.53m and a power of 160kW. If an energy-saving controller is installed, significant contradictions will arise when setting parameters such as temperature rate tolerance, temperature tolerance, and execution cycle, making it difficult to select appropriate parameter values ​​and ultimately failing to achieve energy saving and consumption reduction. In this situation, an automatic variable frequency speed control system is more suitable for fan management. Preparations for this are currently underway. 5.2 The oil level measurement technology of the KR-939 safety control system needs improvement. Currently, the KR-939 safety monitor still has shortcomings, primarily in oil level monitoring. Due to harsh conditions, hot wire scaling and water in the lubricating oil can easily lead to wire breakage. If probe maintenance is not timely, manual on-site inspection and measurement are still required. To strengthen the scientific and modern management of fans, continuous improvement should be made on the existing basis. 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