After more than a decade of rapid development, the cement industry has entered a new historical phase, with production reaching an all-time high. 
How can we achieve market leadership in the new normal of overcapacity and intensely fierce competition? First, we need to become thoroughly familiar with the challenges facing the cement industry! 
You wish to grasp the direction of cement development. 
Maintain the company's profitability. 
Optimize the energy structure, reduce energy consumption per ton of cement, and lower energy costs. 
Improve management levels, enhance production efficiency, and reduce variable costs. 
Extend the lifecycle of fixed investments to dilute the fixed costs per ton of cement. 
Improve product quality to earn market credibility. 
Reduce greenhouse gas emissions, ensure the safety of personnel and the environment, and fulfill corporate social responsibility. 
We can help you achieve your goals. 
As a professional provider of intelligent motor control products, Powtran Technology leverages its expertise in smart manufacturing, power distribution and automation, process control, and energy efficiency management to deliver high-quality, comprehensive solutions for users in the cement industry. 

Not only can it meet your production needs and perfectly address engineering and maintenance challenges, but it also empowers your production with the wings of automation and information technology, making your factory healthier, smarter, and more efficient. This allows you to focus more energy on your core business areas and smoothly achieve your goals. 
 

> 150 More than 150 countries have a cement industry. 
World No. 1 In 2018, China's cement production reached 2.184 billion tons, ranking first in the world and accounting for over 60% of global total production—a staggering 33.5 times the 65.24 million tons produced in 1978! 
Cement System Process Flow and Retrofit Solutions 

1) Introduction to the Cement Production Process 
The production of cement primarily involves several key processes: crushing, storage and pre-homogenization, grinding, homogenization and storage of raw materials, calcination, and final grinding of cement. Grinding is carried out in a metal cylinder equipped with robust internal metal linings; this cylinder is filled with numerous spherical steel balls. As the mill rotates, these steel balls crush the raw materials into fine particles, which are then referred to as raw meal. 

Calcination involves, after homogenization, transporting the raw materials through a cyclone system known as a preheater, where they undergo gradual thermal treatment up to a temperature of 900℃ before entering a rotary kiln, which further cures the materials. The kiln itself is a long cylindrical structure, ranging from 50 to 150 meters in length and with a diameter of 3 to 50 meters. Its inner wall is lined with refractory bricks. The kiln’s rotational motion, combined with its drive mechanism, propels the materials toward the kiln outlet, where the temperature rises to 1,400℃. During this process within the kiln, the raw materials are transformed into hard, granular particles called clinker. Clinker constitutes the primary component of cement; its quality directly determines that of the final product. Cement, as the finished product, is a very fine powder that must meet specific requirements when mixed with clinker, gypsum, and various natural and synthetic materials (such as volcanic ash). The cement mill is similar to the raw-material mill, with strict control and continuous monitoring of material mixing. The type of cement and its most important property—the compressive strength—depend on the chemical composition of the clinker, the duration of grinding, and the addition or omission of various admixtures. The process flow diagram is shown in the accompanying figure. 
 

2) Renovation Plan 
(1) Fan operating status 
The typical adjustment method for low-pressure vertical kiln blowers is damper regulation. For Roots blowers, the air supply can be adjusted either by exhaust-air regulation or by return-air regulation. As for centrifugal blowers, the air supply is regulated via inlet valve adjustment. Under normal operating conditions, the valve opening typically ranges from about 70% to 90%, meaning that a portion of the airflow is wasted. The blower system is designed based on the maximum air demand (the peak operating condition plus a reserve capacity), and the blower operates under similar conditions—i.e., according to the maximum air supply requirement of a single unit. However, in actual operation, there are many instances when the blower needs to be adjusted according to the actual operating conditions. Traditionally, this adjustment is achieved by manually opening and closing dampers. Such a regulation method not only increases throttling losses in the air supply system but also causes inrush currents during blower startup. Moreover, the system’s adjustment process itself is stepwise and relatively slow, with limited ability to reduce losses, leaving the entire system operating in a fluctuating state. By installing an energy-saving device on the blower, however, these issues can be resolved once and for all. This approach ensures smooth and stable system operation and allows for investment recovery through variable-frequency energy savings. 

(2) Based on general operational experience with fans, it is known that in the power-frequency operating mode (AC 380V/50Hz), when using dampers (air valves) to regulate airflow, the fan’s load fluctuates between 15% and 100%. The lower the load, the greater the throttling loss caused by the damper (air valve), and the lower the fan efficiency. By switching to variable-frequency control, however, the throttling loss associated with dampers virtually disappears. Moreover, since the variable-frequency drive employs a soft-start method, there is no inrush current during startup. For factory electrical systems with limited distribution capacity, this approach can also enhance their safety margin. 

(3) The renovated variable-frequency air supply system, while retaining the original air supply system, adds a variable-frequency circuit that operates in parallel with the original circuit, forming a dual-circuit, switchable control system. The speed-regulating device of the frequency converter is installed at the upper part of the kiln, and by adjusting the rotational speed of the motor (fan), the air volume required during sintering can be regulated. Its features are: 

The energy-saving effect is excellent. Since the power consumed by the motor is proportional to the cube of its rotational speed, after the modification, the motor can operate at around 35–43 Hz for most of the time, which is sufficient to meet the air volume requirements, resulting in an energy-saving rate of over 25%. 
Features soft-start functionality, reducing load intensity, extending equipment lifespan, minimizing inrush current, enhancing electrical safety, and reducing grid capacity requirements. 
The air volume adjustment is accurate, timely, and convenient. 

 

Cement powder selection system 
The working principle involves adjusting the rotational speeds of the classifier and the classifier fan according to the different grades of cement produced, thereby selecting cement products with varying degrees of fineness. In older-style classifiers, the number and angle of the fan blades had to be adjusted; after comparative testing, the desired fineness of the classified product was achieved. The newer classification systems consist of two main components: the classifier itself and the classifier fan. The classifier is driven by a slip-ring (electromagnetic speed-regulating) motor, while the classifier fan’s airflow is regulated by adjusting the angle of its damper plates. Both types of systems suffer from drawbacks such as complicated operating procedures, poor adjustment accuracy, and excessive energy consumption. In particular, the slip-ring motor not only consumes a lot of electricity but also has an exceptionally high failure rate due to the severe dust conditions in cement manufacturing environments, leading to frequent and difficult repairs. After the frequency conversion retrofit, whether it’s an older or a newer system, the motors can be precisely adjusted to a specific rotational speed, enabling the selection of particles with the required fineness. This not only saves energy but also ensures that particles of the desired fineness can be consistently selected at a fixed rotational speed. As a result, continuous and automated production is achieved, significantly improving labor efficiency and reducing labor intensity. The comprehensive benefits are evident, as shown in Table 2 following the retrofit at a certain cement plant. 
 

Machine-stand kiln discharging system 
To ensure a balanced operation of feeding, air supply, and discharging during cement sintering, vertical kilns commonly employ slip-ring motors (electromagnetic speed-regulating motors) as the power source for disc-and-tower discharge devices. However, these motors not only fail to meet the required protection ratings for cement production environments but also consume about 20% more power than asynchronous motors under the same output speed conditions. Moreover, when the speed is reduced, the efficiency of slip-ring motors further declines, resulting in even higher power consumption compared to asynchronous motors. Therefore, by replacing the slip-ring speed regulation system with a variable-frequency drive (VFD) system, we have overcome these drawbacks. The VFD system offers significantly superior speed-control performance compared to slip-ring motors, enabling substantial energy savings and greatly reducing maintenance costs. This technology has now been widely adopted across the industry; for instance, companies such as Cement Co., Ltd. have carried out VFD upgrades in their discharge processes. The energy-saving effects are shown in Table 3. 
 

Ball-forming system 
 

The raw material balling process is one of the key procedures affecting the quality of cement clinker sintering. Among these factors, the water-to-material ratio directly influences the quality of the formed balls. After introducing a frequency converter, the rotational speed of the pre-addition water pump for ball formation can be continuously adjusted by tracking the supply rate of raw materials, thereby achieving fully automated closed-loop control. This ensures stable material-water coordination, produces high-quality balls, and significantly improves the quality of cement sintering. 

Raw Material Homogenization Feeding System 
After the system is retrofitted with frequency converters, the feeding motors at all feed ports will be equipped with frequency converters for stepless speed regulation, enabling proportional feeding and improving the homogenization effect. 

Other devices 
After analysis and comparison, dryers, drying fans, crushers, and other slip-ring speed-regulating motors—all can achieve energy savings of over 20% following frequency conversion upgrades. 
The application of variable-frequency technology in the cement industry not only saves energy, reduces maintenance and upkeep efforts, and lowers cement production costs, but also stabilizes the production process, thereby improving cement quality. The widespread adoption of variable-frequency technology in mechanical and electrical equipment and production lines across various industries has become an inevitable necessity for enterprises’ development. An increasing number of companies recognize the competitive advantages that come from implementing variable-frequency technology; thus, they are retrofitting their conventional equipment with variable-frequency drives, which in turn promotes enterprise growth. This approach not only enhances equipment efficiency and meets production process requirements, but also significantly cuts down on equipment maintenance and repair costs, shortens downtime periods, and delivers both direct and indirect economic benefits that are remarkably evident. 
The one-time investment in the equipment can typically be fully recovered within 9 to 16 months of production. 
3) Application of New Dry-Process Cement Production Lines 
In new-type dry-process cement production lines, directly adopting frequency converters or motor energy-saving devices allows for immediate implementation of energy-saving and consumption-reducing measures, yielding remarkably significant results.

Based on a conservative estimate, with a power-saving rate of 25%, an annual production of 300 days, and 24 hours of operation per day, the electricity savings and reduced electricity costs are as follows (assuming normal operation at 80% of rated power): 
Power savings: 1559 × 80% × 25% × 24 = 7,483 (kWh) per day 
7483 × 30 = 224,496 (kWh) per month 
224,486 (kWh) per month × 10 months (300 days) = 2,244,860 (kWh) per year 
Based on a rate of 0.50 yuan per kilowatt-hour, the annual electricity savings would be: 2,244,860 × 0.5 = 1,122,430 yuan—meaning annual electricity savings of 1.1 million yuan. 
The cement industry is characterized by high energy consumption, heavy pollution, and low added value. We offer a wealth of advanced solutions in smart manufacturing that can help you achieve modernization, significantly enhance your competitiveness, and promote sustainable development!