Ball Mill Enhancements

In the global economy, the only product more consumed than concrete is water. As one of the primary inputs for concrete production, cement is also among the most consumed materials worldwide. It is estimated that approximately 4.1 billion t of cement must be produced annually to meet current societal demands, making the energy and environmental impact of its production process highly significant on a global scale.

According to the International Energy Agency, the average thermal energy required to produce 1 t of clinker – the main raw material for cement – is 3.4 GJ, with most of the energy used (97%) coming from fossil fuels. Meanwhile, the average electrical energy consumption for producing 1 t of cement is around 85 kWh (or 0.3 GJ), with most of this energy being consumed in grinding processes. Thus, cement production is a highly energy-intensive process, both in terms of thermal and electrical energy, with total carbon emissions corresponding to about 8% of the global total.

The principles of cement grinding have remained largely unchanged since their inception, based on a balance between crushing and shearing forces to break particles and increase the material’s specific surface area. The main modifications to the process over time have come from improvements in available production technologies.

Ball mills, a prevalent grinding system worldwide, have undergone significant technological development, sparking divided opinions over time. What began as a simple tube shell consisting of a single chamber filled with grinding media of variable shapes and sizes in wet processes has evolved in the cement sector into far more complex dry process circuits. One of the first significant design modifications from the original process was the division of the tube shell into multiple chambers (typically two) using slotted walls called diaphragms, in order to separate the ball charge into different diameter ranges and to apply specific liners in each chamber to boost a specific grinding effect – crushing or shearing. The crushing effect is enhanced by using larger diameters and liners that pull the grinding media up, increasing the impact force from the media to the material. The shearing effect, on the other hand, requires that the media rolls onto the material instead of impacting it, making liners that can ensure a gradient of diameter sizes throughout the chamber (or classifying effect) more important than lifting the grinding media. Today, multiple chambers have become close to a standard for cement grinding, with the technology paired with other supporting equipment to create a complete grinding circuit, which ranges from basic 'open circuits' – where the ball mill receives the raw material and grinds it directly into the finished product at discharge – to 'closed circuits' that incorporate an additional separator. The separator allows for more efficient grinding by separating a fraction of the ground material as the finished product while returning the remaining fraction for further grinding in multiple passes.

Although advancements in the original ball mill circuit design have significantly improved system performance, the circuit has a lower maximum throughput and may appear less efficient compared to other available technologies, such as when combined with roller presses or the use of single vertical roller mills. Nevertheless, ball mills offer undeniable advantages, such as more accurate product quality control, easier troubleshooting, lower maintenance costs, and, depending on circumstances, even better overall specific energy consumption. While vertical roller mills for cement grinding have been the 'trend' of the last decade, ball mill circuits have consistently proven to be a more reliable means of production and are now resurfacing as the preferred grinding technology.

As with any industrial process, ball mill circuits must be routinely assessed and optimised to maintain peak performance. Key actions to preserve circuit efficiency include preventive maintenance, weigher calibration, topping up the ball charge to compensate for grinding media wear losses, internal inspections, material sampling throughout the circuit and inside the mill (known as axial sampling), airflow measurements, constant troubleshooting, and investments in the best available equipment technologies. To achieve optimal results, partnering with experienced suppliers ensures the selection of solutions tailored to specific mill configurations and operational requirements.

While optimisation actions and investments in the separator circuit are widespread, the possibilities and advantages of optimising the grinding process inside the mill itself are often overlooked. However, achieving optimal grinding performance inside the mill is the foundational step to truly optimising circuit performance. A common issue encountered in ball mills for cement grinding is the wear and inefficiency of intermediate diaphragms. The metal slotted plate walls that divide the grinding chambers inside the mill shell do more than just separate between grinding media diameters to enhance the grinding effect – they play a crucial role in ensuring effective grinding by also maintaining optimal material flow and level on each chamber, stopping nibs from reaching the next chamber and optimising mill ventilation. Over time, diaphragm components can degrade, leading to poor material flow and ventilation, which bottleneck the system, increase energy demands to achieve the desired product fineness, reduce production rates, and cause operational disruptions along with increased maintenance costs.

To address these challenges, innovative solutions are needed to enhance the performance and durability of intermediate diaphragms while minimising downtime and operational costs.

Introducing a high-performance solution

Replacing traditional intermediate diaphragms with advanced designs such as Christian Pfeiffer’s design offers a promising solution to some of the challenges faced in cement grinding. High-performance diaphragms, engineered with modern materials and innovative configurations, address inefficiencies and deliver long-term benefits that far outweigh initial investment costs. Adopting advanced diaphragm designs not only improves operational efficiency but also supports broader industry objectives, such as cost reduction and environmental stewardship.

Key features of these advanced diaphragms include:

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