Tushar Khandhadia, General Manager – Production, Udaipur Cement Works, discusses the role of grinding in ensuring optimised cement production and a high quality end product.
How does the grinding process contribute to the production of high-quality cement?
The quality of cement depends on its reactive properties and particle size grinding helps to reduce the size of the clinker particles and additives, increasing their surface area and improving their reactivity. Finer particles react more efficiently with water
during hydration, resulting in stronger and more durable cement.
Can you explain the significance of achieving a homogeneous mixture in the raw material preparation stage?
Achieving a homogeneous mixture in the raw material preparation stage is significant in cement production. Here are the key reasons why achieving homogeneity is essential:
• Consistency: A homogeneous mixture ensures consistency in the composition of cement.
It allows for uniform distribution of raw materials, resulting in consistent quality and performance of the final product. Consistency is vital for meeting the required strength,
durability and other specifications of cement in construction applications.
• Quality Control: By achieving a homogeneous mixture, cement manufacturers can exercise better control over the quality of the product. It enables them to monitor and adjust the proportions of raw materials accurately, ensuring that the desired chemical and physical properties are achieved. Consistent quality is crucial to ensure the structural integrity and longevity of constructed buildings.
• Reaction Rate: Cement production involves a chemical reaction known as hydration, where water reacts with the cementitious materials to form a solid matrix. A homogeneous mixture facilitates the uniform distribution of reactive components, promoting a balanced and efficient hydration process. This leads to the development of optimal strength and durability in the final cement product.
Which types of mills are used in your organisation for grinding raw materials?
In Udaipur Cement Works Limited, we use the following types of mills for grinding raw materials and cement:
• Vertical Roller Mill (VRM): We employ the Loesche (LM 38.4) and Gebr. Pfeiffer (MVR 6000C6) technology for raw material and cement grinding respectively. The VRM is a type of grinding mill that combines crushing, grinding, drying, and classification functions into a single compact unit. It operates by rotating a grinding table, equipped with rollers, while the raw materials are fed into the mill from the top. The rollers exert grinding pressure on the material, resulting in comminution and fine grinding. The ground material is then conveyed upwards and collected in a cyclone separator, while the coarse particles are returned to the grinding table for further grinding. The use of VRM technology allows for efficient grinding and improved energy utilisation. We are operating a mill with lowest power i.e., 12.5 KWh/MT with 10 per cent on 90 micron for raw material grinding.
• CPI & LNVT Ball Mill: CPI & LNVT is a renowned manufacturer of grinding equipment for the cement industry. Their ball mills are widely used for grinding cement clinker, gypsum and other materials into a fine powder. The ball mill operates by rotating a horizontal cylinder, filled with steel balls, which impact and grind the material as it rotates. The ground material is discharged through the adjustable central diaphragm, while the coarse particles are returned for further grinding. CPI optimises material flow and thin linear plate, which increases the overall area of grinding also as a high efficient dynamic separator with top feeding.
• Both the VRM and ball mill technologies provide effective grinding solutions for raw materials and cement production, each with its advantages and specific applications. The choice of the grinding mill depends on various factors such as the type of raw materials, desired fineness, production capacity and energy efficiency requirements.
How do you control the fineness of the cement during the grinding process?
Here are some methods employed to control the fineness during the grinding process:
• Adjusting Grinding Parameters: The grinding parameters, such as the grinding pressure, rotational speed, and airflow, can be adjusted to control the fineness of the cement. By modifying these parameters, the residence time of the material inside the grinding mill can be varied, affecting the degree of grinding and thus the fineness of the product.
• Separator Efficiency: A high-efficiency separator is used in the grinding process to separate the ground particles according to their size. The separator ensures that only the fine particles are collected as the final product, while the coarse particles are returned to the grinding mill for further grinding. By optimising the separator operation and adjusting its parameters, such as the rotor speed and air flow, the desired fineness can be achieved.
• Grinding Aid Additives: Grinding aid additives are chemicals added during the grinding process to improve the efficiency of grinding and control the particle size distribution. These additives can enhance the grinding kinetics, reduce agglomeration and modify the cement particle surface characteristics. By using specific grinding aid additives, cement manufacturers can achieve the desired fineness more effectively.
• PSD Analyser: At Udaipur Cement, we have Modern grinding systems often incorporate advanced process automation and control technologies. These systems continuously monitor and optimise the grinding process based on real-time data, including fineness measurements.
By using feedback control mechanisms, the system can automatically adjust the grinding parameters to maintain the desired fineness within the specified range.
What are the challenges faced in maintaining the desired fineness of cement?
Some of the common challenges faced in achieving and maintaining the desired fineness include:
• Raw Material Variability: The fineness of cement can be influenced by the variability of the raw materials used in its production. Changes in the chemical composition, hardness, and grind ability of the raw materials can affect the grinding process and result in variations in fineness. Manufacturers need to carefully monitor and adjust the grinding parameters to accommodate such variations and maintain the desired fineness.
• Grinding Mill Performance: The performance and efficiency of the grinding mill can impact the fineness control. Issues such as wear of grinding media, liner plates, or internal components of the mill can affect the grinding process and lead to deviations in fineness. Regular maintenance, monitoring, and optimisation of the grinding mill are essential to ensure consistent performance and achieve the desired fineness.
• Grinding Aid Compatibility: Grinding aids, which are used to improve the efficiency of the grinding process, can sometimes impact the fineness control. The compatibility between the grinding aid additives and the cement composition must be carefully considered. Incompatibilities can result in unexpected changes in particle size distribution, affecting the desired fineness. Proper selection and testing of grinding aid additives are necessary to mitigate this challenge.
• Separator Efficiency: The performance and efficiency of the separator used in the grinding process play a crucial role in achieving and maintaining the desired fineness. Inadequate separation efficiency can result in coarse particles being carried over into the final product, affecting the fineness. Regular monitoring and optimisation of the separator parameters are necessary to ensure effective particle size classification
and control.
• Process Dynamics: Cement grinding is a dynamic process influenced by various factors such as feed rate, mill ventilation, grinding pressure, and material moisture content. Changes in these process variables can impact the fineness control. Maintaining stable process conditions and effective process control strategies are essential to minimise fluctuations and achieve consistent fineness.
Could you elaborate on any measures taken by your organisation to reduce the environmental impact of the grinding process?
• Energy Efficiency Improvements: Energy consumption during the grinding process is a significant contributor to environmental impact. We focus on improving energy efficiency by adopting various measures. These include using more efficient grinding equipment, optimising grinding parameters, and implementing advanced control systems. By reducing energy consumption, carbon emissions associated with energy generation can be minimised.
• Alternative Raw Materials: Our organisation is increasingly utilising alternative raw materials in the grinding process. Alternative material, such as fly ash, slag and pozzolans, and chemical gypsum reduces the demand for virgin raw materials, conserves natural resources and reduces environmental impact.
• Emission Control Systems: To minimise air emissions during the grinding process, we have installed efficient emission control systems. These systems include bag filters, electrostatic precipitators, and reverse air bag houses that capture particulate matter and control the release of pollutants into the atmosphere. Proper maintenance and regular monitoring of these systems ensure effective emission control and compliance with environmental regulations.
• Environmental Management Systems: Our organisation has adopted environmental management systems, such as ISO 14001, to establish and maintain environmental performance standards. These systems involve regular environmental audits, setting targets for reducing environmental impact and implementing continuous improvement measures. Environmental management systems ensure a structured approach to reducing the environmental footprint of the grinding process.
Are there any innovations or advancements in the grinding process that your organisation has adopted?
Innovations and advancements in the grinding process have significantly contributed to improving efficiency, reducing energy consumption and enhancing environmental sustainability in the cement industry. Here are some notable advancements implemented by our organisation:
• Raw Mill Rotor Blade Modification: In our raw mill, we have replaced the rotor blades with modified angles. This modification has resulted in a reduction in raw mill residue and power consumption. The modified rotor blades enhance the efficiency of the grinding process, ensuring finer grinding and improved control over the particle size distribution of the ground raw materials.
• RABH Purging Sequence Logic Modification: To optimise the performance of our Reverse Air Bag House (RABH) system, we have implemented an in-house modification of the purging sequence logic. This modification has been integrated into the ABB Distributed Control System (DCS) from the central control room (CCR). The revised logic ensures efficient cleaning of the bag filters, reducing pressure drop and maintaining consistent airflow, thereby enhancing overall system performance.
• Intermediate Diaphragm Scoop Opening Optimisation: In our cement mill, we have optimised the intermediate diaphragm scoop opening. This optimisation aims to achieve multiple objectives, including reducing overgrinding in chamber 1 and increasing the material flow out of the chamber. By adjusting the scoop opening, we have improved the classification of grinding media and reduced the residence time of oversized particles, resulting in enhanced grinding efficiency and improved overall performance.
• Replacement of Cement Mill Reject Material Belt: In order to address power consumption and prevent fugitive dust emissions, we have replaced the cement mill’s reject material belt with a closed air slide system. This innovation has resulted in significant power savings
and eliminated the risk of dust emissions during the transportation of rejected materials.
The closed air slide ensures a sealed and controlled environment, enhancing environmental sustainability and reducing energy consumption.
How does the grinding process fit into the overall cement production cycle, and what are its implications on the organisation’s operations and productivity?
The grinding process is a critical stage in cement production and plays a significant role in the organisation’s operations and productivity. Here’s how the grinding process fits into the cement production cycle and its implications:
• Raw Material Preparation: The grinding process occurs after the raw materials, such as limestone, clay, iron ore, and others, are extracted and prepared. These raw materials are crushed, dried, and ground to a fine powder in the grinding mills. The grinding process prepares the raw materials for further chemical reactions in the kiln and ensures their proper blending.
• Cement Kiln: The ground raw materials are fed into a cement kiln, where they undergo a series of high-temperature chemical reactions, known as clinkerisation. In the kiln, the raw materials are heated to a high temperature, resulting in the formation of clinker, which is a nodular material. The grinding process determines the fineness and characteristics of the ground raw materials, impacting the quality of the clinker produced in the kiln.
• Cement Grinding: After the clinker is cooled, it is finely ground with gypsum and other additives to produce cement. The grinding process involves reducing the clinker particles to a specific fineness, typically measured in terms of Blaine specific surface area or particle size distribution. The grinding process significantly influences the cement’s strength development, setting time, and other performance characteristics.
The grinding process is a crucial component of the cement production cycle, impacting the organisation operations, productivity, cost efficiency and product quality. Optimal grinding practices, efficient equipment utilisation and continuous process improvements are vital to enhance overall operational performance and maintain a competitive edge in the cement industry.
–Kanika Mathur
