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Abstract: This study focuses on the energy-saving and safety control of cooling tower fans, aiming to achieve energy-efficient and safe automated online management of fan operation. Tests based on actual usage show that this control system addresses some of the challenges in fan management, enabling energy-saving and safe automated control of the fans. It has improved economic efficiency and equipment reliability, achieving ideal results, and it also provides new approaches for strengthening the scientific management of equipment. Keywords: cooling tower, fan, energy saving. The cooling tower fan is the core equipment in a circulating water system. The refinery of Beijing Yanshan Petrochemical Company currently has 7 circulating water systems, with a total designed treatment capacity for circulating cooling water of 4.665×104 t/h ； There are 105 cooling tower fans (98 of 4.7m type and 7 of 8.5m type), with a total installed capacity of 4060kW; the maximum daily power consumption when all of them are in operation is 9.74×104kW·h. In terms of the management of circulating water equipment, cooling tower fans account for a significant proportion, whether considered in terms of the number of units, the amount of maintenance work required, or power consumption. The number of fans accounts for 57% of the total equipment in the workshop; maintenance hours account for 60% of the total, while electricity consumption accounts for 22% of the total. To ensure the long-term operation of equipment while saving energy and reducing consumption as well as minimizing the need for labor, it is necessary to apply advanced scientific and technological methods as well as management techniques. Since 1993, our institution has collaborated with the Institute of Engineering Thermophysics of the Chinese Academy of Sciences to develop two monitoring systems for fan energy conservation and automatic control as well as safety control, namely the “KR-933 Fan Energy Conservation Controller” and the “KR-939 Fan Safe Operation Monitor”. At present, this system has been fully implemented in the circulating water workshop and has achieved satisfactory results. 1 Research on fan energy-saving controllers: The purpose of fan energy-saving control systems is to achieve closed-loop automatic control of fan operation. The water supply temperature is preset in advance according to production requirements. The effects of climate and weather conditions on water temperature, as well as changes in the system’s heat exchange conditions, are detected in real time by temperature sensors. Ultimately, the energy consumption of cooling equipment is adjusted to stabilize the water supply temperature, thereby achieving automatic control and energy savings. It is generally believed that “variable frequency speed control technology” is the ideal method to accomplish the above process. However, the use of variable frequency speed control technology in the control of fans in circulating water cooling towers has the following limitations and shortcomings: ① While “variable frequency speed control technology” can achieve high temperature control precision, this is not very important in circulating cooling water systems. ②The energy losses inherent in the inverter itself (with an average operating efficiency of less than 90%) affect the energy-saving effect. ③Variable operation causes a change in the attack angle (angle of incidence) of the fan blades, and operating the fan outside its optimal operating point reduces its efficiency. ④Operation of the motor at low speeds below its rated speed, along with the nonlinear relationship among speed, torque, and power consumption, also significantly reduces the motor’s operational efficiency. ⑤Variable frequency speed control systems are relatively expensive (around 1,000 per kilowatt), requiring significant investment for both new projects and the renovation of existing equipment. ⑥In the design, it is also necessary to take into account the issue of destructive resonance that can occur when the variable frequency drive operates at certain specific speeds, as well as the problem of strong electromagnetic interference generated by the variable frequency drive, which can disrupt other instruments. Given that cooling tower fans typically operate in groups of multiple units connected in parallel, we have proposed an approach that automatically adjusts the number of fans that are turned on or off based on changes in the temperature of the water supply, thereby achieving temperature control and energy savings. It is a simple and inexpensive control method, but it differs from conventional PID analog control approaches. It is a single-variable discrete control closed-loop regulation system that must ensure a certain level of temperature control accuracy, while preventing the fan from starting and stopping frequently ； It is necessary to ensure that the fans can operate individually, while also requiring multiple fans to operate in a balanced manner in terms of timing and the number of starts and stops. In response to the practical problems encountered in the control and management of cooling tower fans, we formulated 18 basic design requirements, including \"temperature measurement range\", \"measurement accuracy\", \"display resolution\", \"measurement upper and lower limits\", \"measurement calibration values\", \"execution cycle\", \"temperature tolerance\", and \"temperature rate tolerance\", and used these to develop the corresponding system. It was first tested in practice at the fans in the third circulating water plant in March 1993; this system was named the \"KR-933 Intelligent Fan Controller\". 2 Research on Fan Safety Monitors: The purpose of fan safety monitoring systems is to automatically detect changes in vibration levels, oil temperature, and oil level, display and record these values. It also alerts and shuts down fans when the detected values exceed acceptable limits, thereby ensuring the safe and stable operation of the fans and reducing or even preventing fan damage incidents. Based on the actual conditions of on-site management, it was determined that the three parameters of “fan vibration,” “lubricating oil temperature,” and “reducer oil level” are the most important operational parameters for ensuring the safety of the fan. A total of 15 design parameters, including “measurement range,” “measurement accuracy,” and “inspection time,” were also determined for research, development, and production. The system was first tested in the circulating water plant in September 1993, and was named the “KR-939 Fan Safety Monitor”. This system utilizes multi-parameter combined probe technology, digital command encoding technology, and computer network management technology. The three-parameter combined probe is installed on the gauge holder of the fan’s reduction gearbox; its probe rod is inserted directly into the lubricating oil, converting the oil temperature, level, and equipment vibration values within the reduction gearbox into electrical signals, which are then transmitted to the fan safety monitor in the control room. Each security monitor can be connected to 8 combined probes via a four-core cable, enabling real-time monitoring of the operating parameters of 8 fans, along with digital display. Multiple functions such as overload alarm and shutdown upon overload. After numerous tests and redesigns, it has now been successfully applied in equipment manufacturing facilities, with all parameters meeting the predetermined design requirements. 3 Implementing computer-based network control: The two monitoring 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 computer. When equipped with the appropriate configured monitoring and management software (DCS-900 software), it can achieve networked control of multiple KR-933 and KR-939 monitors. The fan monitor connected to a computer now has the following additional functions: ① It can monitor the measurement parameters of all controllers on the network simultaneously, enabling comprehensive management. ②Modify the setting parameters of various controllers within the network. ③System optimization management is achieved by adjusting the operating parameters of various controllers. ④Records historical data and charts to assist in analysis and facilitate querying. 4 Effects of fan management research: Since 1993, the Beijing Yanhua Refinery has been conducting experiments on automatic control management for fans, achieving good results, which are mainly reflected in energy savings and safe operation. 4.1 The energy-saving effect of fan operation is significant. Taking the second circulating water plant equipped with KR-933 as an example, the energy-saving results achieved by using the KR-933 energy-saving controller are shown in Table 1. As shown in Table 1, the third circulating water plant, which was the first to trial the KR-933 energy-saving controller on-site, saved 178,533 kW·h in electricity consumption during the months of June, July, August, and September 1993, when the fan load was high. Compared with the corresponding periods in 1991 and 1992, this represented a savings; calculated at 0.45 yuan per (kW·h), the total savings in electricity costs for those 4 months amounted to 79,200 yuan ； The cost of installing an energy-saving controller in the third circulating water plant is only 43,600 yuan; it is evident that the investment can be recouped within just a few months of the equipment being in operation. To date, our factory has successively installed 13 KR-933 intelligent controllers in 4 circulating water plants, controlling a total of 92 fans, thereby achieving significant economic benefits. Table 1: Energy-saving effects of KR-933 4.2 Ensuring the safe operation of fans Through continuous improvements over several years, by 1998 and 1999, the accuracy of the safety monitors improved significantly. Statistics from January 1999 to July 1999 show that the system issued 17 alerts in total, of which 13 cases involved issues with the equipment, resulting in an alert accuracy rate of over 76.5% ； Furthermore, during the equipment inspection, 2 units with serious potential defects were identified, which prevented severe damage to the equipment and yielded good economic benefits. Based on field experience, for fans in good condition, the characteristics of their oil temperature, oil level, and vibration curves are as follows: ① Oil temperature curve: It gradually rises and falls from the moment of startup and shutdown, and after about 1 hour it becomes a smooth curve that is approximately linear. ②Berth curve: It should be approximately a horizontal line, whether the machine is running or not. ③Vibration curve: In the powered-on state, it is an irregular curve that oscillates up and down within a narrow range around a virtual straight line. Since 1994, our factory has installed 13 KR-939 type fan safety monitors in 6 circulating water plants, enabling long-term online monitoring of 86 fans of different types. This has enabled the maintenance of our factory’s fans to shift from being based primarily on the cumulative operating time of the fans for scheduling major repairs, to being based on the measurement data provided by monitors, thus making the maintenance work more scientific and rational. For fans equipped with safety monitors, the maintenance workload has been reduced by about 30% compared to before ； At the same time, it has prevented several serious catastrophic accidents involving the fans; over the past few years, no accidental damage incidents have occurred, resulting in considerable benefits. 5 Shortcomings 5.1 Large fans are not suitable for use with the KR-933 energy-saving controller. In cooling water systems for large-capacity fans with a small number of units, each start or stop of a fan has a significant impact on the water temperature. Therefore, the KR-933 fan energy-saving controller cannot properly and stably control the water temperature. For example, the sixth circulating water plant is equipped with 3 fans with a diameter of 8.53 m and a power output of 160 kW; assuming that energy-saving controllers are installed for these fans, temperature rate tolerances can be set. When it comes to parameters such as temperature tolerance and execution cycle, significant conflicts arise, making it difficult to select appropriate values for these parameters; as a result, the goal of saving energy and reducing consumption cannot be achieved. For fan management in such cases, an automatic variable-frequency speed control system is more suitable for control and management. Preparatory work in this area is also underway currently. 5.2 The oil level measurement technology of the KR-939 safety control system still needs improvement. The KR-939 safety monitor currently has shortcomings, with the main issue being oil level monitoring; due to harsh operating conditions, it is prone to problems such as fouling of the heating wire and wire failure caused by water contamination in the lubricating oil. If the probe is not maintained in a timely manner, manual inspections by climbing the tower are also required for actual measurements. To strengthen the scientific and modern management of fans, continuous improvements should be made on the existing foundation. References: Yang Qin, Yan Xushi. Water Supply Engineering. Beijing: China Architecture & Building Press, 1987. Hu Anding. Guidelines for the Cyclical Operation of Petrochemical Plants. Beijing: Sinopec Press, 2001. ISBN7-80043-499, Procedures for the Maintenance and Repair of Petrochemical Equipment (Volume 9)