How to Control Temperature in Cement Mill Operation

Why is it essential to control temperature in cement mill operation?

In cement mill operation, the temperature of the inlet, interior, and discharge all need to be taken into consideration. Temperature control is critical for preventing dehydration of gypsum, ensuring cement quality, protecting cement grinding equipment, etc. Improper temperature may lead to reduced output, decreased grinding efficiency, deterioration of cement performance, equipment wear, etc.

Key influencing factors of cement mill temperature

In the operation of a cement mill, temperature is not an isolated variable but is affected by multiple combined systematic factors. The following are several key factors that play a decisive role in the temperature changes inside the mill.

Raw material temperature and moisture content

The initial temperature and moisture content of the feed directly determines the starting point of heat exchange in the mill. High-temperature raw materials will increase the temperature rise in the mill, especially in hot seasons or when the heat recovery system at the kiln tail is not isolated. High-moisture raw materials may evaporate and produce a large amount of steam during the grinding process, causing the humidity inside the mill to rise, indirectly affecting temperature control, and may also cause agglomeration or adhesion.

Retention time of materials in the mill

The longer the material stays in the cement mill, the more friction and collision time there is, the more heat is generated, which causes the temperature inside the mill to rise. If the residence time is too short, it may lead to insufficient grinding, and the fineness of the output material may not meet the standard.

1. Efficiency of ventilation and cooling systems

Reasonable ventilation can remove the heat inside the mill in time and is one of the most direct means of temperature control. If the ventilation volume is insufficient, the heat cannot be discharged in time, causing the temperature inside the mill to rise rapidly. If the ventilation volume is too large, it may carry away the fine materials that have not been ground yet, affecting the quality of the finished product. In addition, some systems are equipped with external cooling fans or air heat exchangers to control systemic heat accumulation.

2. The setup and operation of the water sprinkler system(for ball mills)

Many ball mills are equipped with a water spray system to spray cold water at key locations to lower the local temperature. The spray location is generally set at the feed end of the hollow shaft. If the water spray is insufficient, the temperature is difficult to drop. If the water spray volume is too large, it may cause agglomeration or wet grinding in the mill.

3. Setting of operation parameters

Operation parameters, including rotating speed, feeding speed, and loading capacity, directly affect the mechanical energy consumption and heat release per unit of time. High speed or high loading will increase the frequency of media impact, thereby increasing the temperature inside the mill. Unstable feeding speed may lead to fluctuations in system temperature, which is not conducive to the stable control of the back end.

4. Environmental temperature and seasonal differences

The temperature of the external environment also has a significant impact on the operation of the system. In summer, the air temperature is high, the cooling air entering the system has weak heat-carrying capacity, and temperature control is more difficult. In winter, on the contrary, the mill is prone to overcooling, which affects the grinding efficiency.

Common methods of temperature control in a cement mill

In cement mill operation, effective temperature control can not only improve grinding efficiency but also extend the service life of grinding equipment and improve cement quality. The following are some common and practical methods of temperature control.

Implement a water spray system

A water spray system is one of the most common and direct methods of temperature control in cement mills, especially when a dramatic temperature rise happens.

Working principle: By spraying atomized water at the feed end or hollow shaft, excessive heat is absorbed, and heat dissipation is promoted.

Application: The water spray system is suitable for closed-circuit grinding systems or ball mills operating under high temperatures.

Advantages: Quick effect, simple structure, and low maintenance cost.

Matters need attention: The amount of water spray should be controlled within a range that does not cause” wet grinding” or “adhesion”. The nozzle should be positioned away from high-impact areas to prevent wear or clogging. The water should be clean to avoid the impurities clogging the nozzle.

Tips: It is recommended to use a temperature feedback closed-loop control system to adjust the spray volume automatically.

Improve ventilation

Ventilation is one of the basic means of controlling the temperature in the mill. By adjusting the air volume and speed, heat and steam can be quickly discharged from the system.

Install high-efficiency induced draft fans, and regularly clean the air ducts, filters, and dust removal system to prevent blockage. Install temperature and pressure composite sensors at key nodes to realize intelligent control.

Advantage: Evenly cool the entire system to help stabilize material flow.

Tips: In summer, you can consider introducing low-temperature ambient wind. In winter, you need to avoid cold winds that may cause sudden cooling of materials and condensation.

Equip external cooling devices

Some advanced factories will equip the ball mills or discharge elevators with cooling or heat exchange devices to enhance the heat dissipation capacity. Common external cooling devices include: an air-water heat exchange cooler, an air-cooled discharge belt, a liquid cooling ring, or a sandwich cooling pipe.

Application: Processes with high requirements on discharge temperature, such as the production of high-performance cement or special cementitious materials.

Advantage: The cooling effect is long-lasting and can be linked with the finished product temperature control system.

Optimize grinding media and loading method

The distribution of different particle sizes will affect impact frequency and friction heat release. A reasonable configuration can effectively control the heat load inside the mill.

• Use a multi-level ball diameter distribution to reduce high-intensity impact.
• Control the filling rate in the mill to avoid “over-filling,” which causes local heat.
• Regularly adjust the liner and partition plate to maintain grinding efficiency.
• Combined with a real-time grinding sound analysis system, it can be determined whether the ball-to-material ratio needs to be adjusted.

Material pre-treatment before feeding

Adjusting the temperature and moisture content of raw materials before entering the mill can help lower the starting point of temperature rise in the mill.

• Set up raw material pre-drying equipment(such as a rotary dryer and hot air furnace).
• Avoid mixing high-temperature clinker directly into the mill.
• Ensure continuous and stable material feeding to avoid sudden high-temperature and high-humidity materials entering the system.

It should be noted that raw material pretreatment should be coordinated with an overall energy-saving strategy of the grinding system, and energy-consumption equipment should not be set up separately.

Introduce an intelligent control system

Adopt a PLC+SCADA or DCS integrated control system to achieve intelligent adjustment by a temperature sensor, frequency conversion fan, and water pump controller. It is evolving towards “unmanned operation+intelligent maintenance”, which is especially suitable for large-scale clinker production lines or high-standard environmental protection projects.

• Real-time temperature data collection and trend analysis
• Trigger temperature alarm or automatic water spraying/exhaust
• Automatically adjusting air volume and water supply according to load

How to implement temperature monitoring and regulation at the operational level

The temperature control of a cement mill depends not only on the equipment configuration but also on the daily monitoring ability and response skills of the operator. Through a reasonable temperature monitoring system and operating system, most of the temperature rise risks can be controlled in the embryonic stage.

Install and correctly use temperature sensors

Modern cement mill systems are usually equipped with multiple temperature sensors. Reasonable points should be selected and calibrated regularly to ensure that the temperature readings are true and effective.

Recommended monitoring points:

• Grinding mill feed port

• The middle and tail of each bin

• Grinding outlet or the bottom of the elevator

• Near the water spray inlet (if any)

Sensor type: It is recommended to use high-temperature thermocouples or infrared sensors with good dust and earthquake resistance.

Operation suggestions: Record the temperature of each point during daily inspections and report any abnormal fluctuations immediately.

Set up a temperature alarm mechanism and emergency response

Establishing a reasonable temperature warning and shutdown mechanism will help avoid the expansion of accidents.

Set the upper and lower limits of temperature: For example, the temperature out of the mill should not exceed 120°C, and the temperature at the end of the mill should trigger an alarm if it exceeds 150 °C;

Alarm classification:

Level 1 warning: It is recommended to adjust the operation (such as increasing air or spraying water)

Level 2 alarm: It is recommended to suspend feeding or shut down for inspection

Emergency plan: Prepare a high-temperature emergency handling process in advance, such as artificial ventilation, auxiliary cooling, or emergency water injection.

Supplementary measures: Some companies are equipped with red light + buzzer alarm devices, which provide visual and auditory reminders.

Establish a temperature data recording and trend analysis mechanism

Not only look at the temperature value at a certain time, but also pay attention to its fluctuation trend and periodic changes.

Daily record sheet: Synchronously record the temperature of each point with related parameters (feeding amount, current, water spraying amount);

Trend analysis: Compare data in different periods through chart software or DCS system to find potential anomalies;

Seasonal comparison: Comparison of temperature control strategies in summer and winter helps to optimize operating parameters continuously.

Recommended tools: Excel or SCADA system with built-in reporting function; if conditions permit, it is more efficient to connect to the cloud platform for multi-site comparison.

Dynamic adjustment of operating parameters

Through dynamic management of key operating parameters, the temperature change in the mill can be “actively affected”.

Feeding rate: Adjusting the speed can directly affect the material retention time and temperature rise rate;

Air volume: Control the fan speed through the inverter to adjust the cooling capacity in the mill;

The switching frequency and pressure of the water spray system: According to the real-time temperature changes, manual or automatic adjustments are made in time.

Key points of operation: Temperature control should be aimed at “gentle and slow change” to avoid frequent adjustments that cause system instability.

On-site inspection and abnormal identification experience accumulation

The operator’s experience and judgment are still an important guarantee for the safe operation of the system.

Common visual signals:

White smoke coming out of the mill tail: it may be that the material is too wet + the temperature is too high;

Cement agglomeration: It is mostly caused by excessive water spraying or repeated temperature changes.

Muffled grinding sound and increased current of the main motor: it may be that the temperature rise in the mill causes the material to agglomerate, and the grinding efficiency decreases.

Recommended inspection frequency: no less than 2 full-line temperature checks per shift, and more frequent inspections during key periods.

Recommended establishment: Add a “temperature inspection standard table” to the job operation manual to strengthen the training of new employees.

Typical problems and solutions