Abstract: This paper introduces the energy-saving prediction and practical application of frequency converters (VDCs) in the speed regulation and energy saving of Roots blowers in cement plants, based on the widespread application of high-power VDCs in this field. In operation using power frequency drives, excessive air pressure and insufficient damper adjustment lead to complex production operations and energy waste, thus creating a practical need for VDC speed regulation. The paper also predicts the benefits of speed regulation. After the VDC is put into operation, the improvement in operating conditions and energy savings are measured and summarized. Keywords: Frequency converter, energy saving, Roots blower I. Historical Reasons and Current Status of Cement Plant Construction Due to historical and economic reasons, cement plants built in the 1990s and earlier used AC motors and slip-ring motors for their water supply, coal supply, and ventilation systems. To ensure sufficient power, all components are designed for maximum demand (with a 20% power margin for slip-ring motors). AC motors, fans, and water pumps operate at maximum capacity. To accommodate changes in demand, the ratio of airflow to supply is adjusted using Roots blowers to regulate the opening of air dampers and dampers; water supply is regulated using return valves; and air pressure, airflow, water pressure, and water flow are adjusted by starting and stopping the motors. Electrical control employs star-delta direct starting (or transformer step-down starting). Frequent starts and stops, and the impact of 4-6 times the starting current on grid stability and motor overheating, increase motor maintenance costs and shorten motor lifespan. Simultaneously, frequent opening and closing of dampers and regulating baffles increases air resistance and pipe vibration, generating noise; deteriorating water and air supply quality accelerates equipment aging, and a significant amount of electrical energy is wasted in the regulation process. II. The Positive Significance and Practical Necessity of Technological Transformation In the process of enterprise survival, development, and continuous growth, "maximizing profits" is the eternal theme and pursuit of the enterprise. Increasing corporate profits by reducing raw material consumption and lowering labor costs is widely recognized. However, increasing profits by reducing energy consumption through technological upgrades is often overlooked due to a lack of professional personnel or the increased costs of purchasing, updating, and upgrading related equipment. In fact, saving energy, reducing energy consumption, and rationally utilizing resources not only increase corporate revenue but are also crucial means to change the direction of economic growth. It is a great undertaking that benefits the present, future generations, and all. China is rich in resources, but its per capita resource availability is below the world average, classifying it as a relatively resource-poor country. Since the reform and opening up, my country's rapid economic growth has come at the cost of consuming large amounts of energy. According to relevant statistics, the energy consumption of domestic enterprises is more than 40% higher than the average level of similar foreign enterprises, and my country's energy consumption per 10,000 yuan of GDP is three times the world average. III. Effective Methods and Approaches Following the overall requirement of "reducing energy consumption per unit of output by 20%" in the CPC Central Committee's "Suggestions on Reforming the Eleventh Five-Year Plan for Economic Development,"... my country's economic development model urgently needs to change; it must transform the current "extensive" approach that relies on consuming large amounts of energy to achieve rapid economic growth. One fundamental way to achieve this strategic transformation is to comprehensively analyze and upgrade the current situation of electric motors, which account for 60% of total electricity consumption in industrial production, using advanced frequency conversion technology to achieve energy conservation and consumption reduction. Research shows that, in different application areas, installing advanced, stable, and powerful frequency converters on electric motors is one of the most direct and effective methods. Without reducing functionality and efficiency, the direct benefit to enterprises is a significant reduction in huge electricity bills and production costs. The indirect social benefit is the reduction in the construction of power plants, effectively reducing the burning of water, electricity, and coal, allowing our future generations to live happily on a green planet. IV. Case Study Analysis Due to work reasons, I recently had the opportunity to participate in the demonstration, testing, and acceptance of the equipment upgrade project at Yun'an Dongfeng Cement Plant in Yunyang County, Chongqing. Adhering to the principle of "stability, reliability, and absolute safety," after comparing numerous well-known domestic and international brands of frequency converters with high sales volume and cost-effectiveness in China, they ultimately chose the SY6000 series frequency converter from Shanghai Shanyu Electronic Equipment Co., Ltd. as their first choice for the renovation project. The SY6000 series frequency converters produced by Shanyu use major electronic components from internationally renowned manufacturers, ensuring superior performance. The company's frequency converters use third-generation products from Mitsubishi Electric Corporation of Japan, a preferred choice for many well-known international brands; they offer stable performance and reliable quality. This series of frequency converters features an advanced design concept, comprehensive functions, excellent control characteristics, and robust protection functions. The peripheral system design is simple; it also incorporates PID, PLC, and 485 communication interfaces, enabling remote control, PC central control, and host computer control for remote automatic control. It supports multiple analog and digital input/output channels, high-speed input/output, terminal control program operation, oscillation operation, and other operating modes. It receives feedback control from various physical quantities to form a closed-loop automatic control system. Soft start and soft stop, no inrush current, stepless speed regulation avoids mechanical resonance frequency, reduces noise, extends the service life of mechanical and electrical systems, and achieves optimal control. It can supply water at constant pressure and in a quantitative manner; and deliver air on demand. High (low) voltage, phase loss, overcurrent, and overload protection; comprehensively ensures the safe operation of the motor, with automatic fault reset and sleep/wake-up functions. The company has strong technical capabilities. Its service is comprehensive, timely, and considerate. More than 40 offices are located throughout the country. The original air supply systems of the two blast furnaces at the Yun'an Dongfeng Cement Plant in Yunyang County, Chongqing, used 250KW and 180KW three-phase AC 6-pole motors respectively to drive the Roots blower system. The traditional mechanical adjustment method, which adjusts the ratio of vented air to used air (i.e., adjusting the air volume utilization rate) by adjusting the opening degree of the Roots blower's air vanes, was used to meet the different air volumes required during sintering. The disadvantages of the traditional Roots blower air supply method were: serious energy waste, poor air volume adjustment accuracy, large starting inrush current of the motor, high noise, serious dust pollution, and reduced mechanical life of the motor and blower. Upgrading using the Shanyu SY6000 frequency converter is simple: the original star/delta starting devices in the starter cabinet are removed, and the frequency converter is installed in their place. Other devices in the original cabinet remain in use, and power cable wiring is unchanged. A new frequency converter control loop is added in parallel with the original control system, forming a dual-loop control system. Its advantages include no changes to the original Roots blower system, minimal engineering modifications, low costs, and minimal downtime (approximately 1 hour). The dual-loop system ensures efficient production operation. Because the SY6000 frequency converter has a soft-start function, there is no large current surge during motor startup, reducing equipment maintenance frequency and extending equipment lifespan. The frequency converter can arbitrarily adjust the blower motor speed, thus accurately adjusting the airflow according to the required volume, eliminating the need for bypass ventilation, reducing cement dust pollution, and significantly saving energy. V. Energy-Saving Principle of Fan Speed ​​Regulation Operation 5.1 Fan Operating Characteristics Fans are square torque type loads. The characteristic curves of the fan operating at rated speed are shown in Figure 1. [align=center] Figure 1 Fan Characteristic Curves (β=900)[/align] HQ Curve: When the speed is constant, it represents the relationship between air pressure and air volume. PQ Curve: When the speed is constant, it represents the relationship between power and air volume. η-Q Curve: When the speed is constant, it represents the efficiency characteristics of the fan. 5.2 Determination of Fan Flow Rate When a fan is running, the amount of medium passing through a cross-section per unit time when the centrifugal pressure generated by the fan at a certain speed acts on it is the flow rate. When the fan is running, a stable flow output appears due to the combined effect of the fan pressure and the pipeline resistance, which is called the operating point. Its characteristic curve is shown in Figure 2. [align=center] Figure 2 Fan operating point[/align] M —— Operating point R —— Pipeline resistance curve H —— Fan pressure curve 5.3 Fan flow rate adjustment method (1) Adjusting the fan output by changing the pipeline resistance When the pipeline resistance changes, the fan speed remains unchanged, the air pressure rises accordingly, the fan operating point will change, and the fan output flow rate will change accordingly. Its characteristic curve is shown in Figure 3. [align=center] Figure 3 Fan flow rate characteristic curve when pipeline resistance changes[/align] In actual operation, this is achieved by adjusting the opening of the baffle. When the opening of the baffle decreases, the pipeline resistance increases accordingly. The three openings of the baffle correspond to the three resistance conditions R1, R2, and R3. When the fan speed remains unchanged, the three operating points M1, M2, and M3 appear respectively with the fan pressure characteristic curve. The three flow rates Q1, Q2, and Q3 corresponding to the three operating points are the flow rates corresponding to the three baffle openings when the speed is constant. Adjusting the baffle opening can adjust the amount of the fan output flow. (2) Changing the fan speed to adjust the fan volume When the fan speed is changed, the fan pressure characteristic curve changes accordingly. When the pipe network resistance is constant, its characteristic curve is shown in Figure 4. [align=center] Figure 4 Characteristic curve of changing fan speed[/align] When the fan speed is set to n1, n2, and n3, each speed corresponds to its corresponding pressure characteristic curve. When the pipe pressure resistance R is constant, the operating points change to M1 and M2, and the corresponding flow rates are Q1 and Q2. In practice, the frequency converter method can be used to adjust the fan speed, thereby adjusting the flow rate when the pipe network resistance is constant. 5.4 Comparison of Constant-Speed ​​and Variable-Speed ​​Fan Operations for the Same Output Airflow When the fan's rated speed is n1, the fully open damper pressure is R1, and the rated flow rate is Q1, the output flow rate is changed to Q2 by adjusting the network pressure and fan speed. The difference in operating conditions is shown in Figure 5. [align=center] Figure 5 Difference in Operating Points When Network Resistance and Fan Speed ​​Adjustment Flow Rate[/align] As can be seen from Figure 5, under the condition of the same output flow rate, the operating point using damper adjustment is M3, with operating pressure H3 and Hf. The operating point using speed adjustment is M2, with operating pressure H2. Difference in energy consumption between the two airflow adjustment methods: As can be seen above, the biggest difference between adjusting the damper and adjusting the speed lies in the air pressure. The difference in shaft power consumed by the fan between the two operating methods is: Q＊△H △P=- 102ηTηF. Based on the similarity theory of fan power consumption, it is concluded that: Comparing adjusting airflow by damper and adjusting airflow by speed, as the difference between the actual output flow and the rated flow of the fan increases, the difference in energy consumption also increases proportionally to the square. Comparison of 180KW usage before and after modification: Before modification: Starting current, transformer step-down starting current 1000A, Operating current 332A, Operating voltage 380V, Airflow regulation quality, high vibration, high noise, slow response, poor air supply quality, Labor intensity, 2 people to operate, Daily power consumption 5244 kWh After modification: Starting current, frequency converter soft start 0-350A, Operating current 150-300A, Operating voltage 380V, Airflow regulation quality, low vibration, low noise, fast response, high air supply quality, Labor intensity, 1 person to operate, Daily power consumption, Average power consumption 3791 kWh. Since the on-site fan operates 24 hours a day, the average daily power saving after the modification is 1453 kWh. Calculated at 0.57 yuan per kWh, the daily savings are approximately 830 yuan, which is quite considerable. The results of a 6-month trial run proved that the system upgrade plan was correct. The selected Shanyu SY6000 series frequency converters and the air supply system operated stably and reliably, achieving optimal control effects. They combined soft start, soft stop, closed-loop automatic control with manual intervention. No faults were found during the 6-month trial period, significantly reducing system maintenance frequency and workload, ensuring optimal air supply effects, saving 50% on maintenance costs, increasing production efficiency by 10%, and achieving approximately 40% energy savings per unit. The electricity savings in six months were equivalent to the entire upgrade cost. The factory is now preparing to fully upgrade the entire plant's Roots blower air supply system, pelletizing pre-watering system, raw material homogenization feeding system, cement powder classifier system, and main kiln unloading system using Shanyu brand frequency converters and soft starters. VI. Conclusion: The trial use of frequency converters in the cement plant's air supply system revealed the significant difference in power consumption between frequency converter-controlled operation and the original Roots blower's constant-speed operation via valve adjustment. This highlights the alarming energy waste caused by the original Roots blower. Currently, domestically produced frequency converter technology is quite mature and has been widely used in various industries. With the development of power electronics technology and the further development of high-power IGBT modules, their prices are gradually becoming more reasonable, indicating that frequency converter products will be widely used in my country's energy-saving field.