Ashok Kumar Dembla, President and Managing Director, KHD Humboldt Wedag India, discusses the advancements in grinding solutions that focus on low energy consumption, dust free circuits and low maintenance.

Tell us about the role of your grinding solutions in the cement industry?
We all know that grinding constitutes about 65-70 per cent of electrical energy consumption of cement manufacturing. Any saving in grinding energy can be good for operating cost reduction. Also, energy cost is increasing with time, therefore cement manufacturing companies are looking for new technologies for low electrical energy consumption. In the past few years, KHD has worked extensively in the field of grinding to reduce electrical energy consumption in the cement industry, which also helps in reduction in carbon footprints. We at KHD provide all kinds of grinding solutions be it raw material grinding, cement grinding or slag grinding.

How do you customise your grinding solutions to fit the requirements of distinct cement plants?
Based on the cement manufacturers requirement, we offer customised solutions for various grinding circuits. Every cement plant has specific requirements. Like some focus on low-cost solutions, some focus on energy efficiency whereas some focus on operational excellence. The input material hardness, moisture, abrasively, feed size and product requirement decide what solution is to be offered for achieving a cost effective and energy efficient solution. We have various sizes of roller presses, various types of roller surfaces, types of rollers and arrangement of roller presses in the circuit like roller press in semi-finish mode, roller press in finish mode, size of ball mill in semi-finish mode, location of static separator in process circuit, etc. So, based on all the factors, we decide what is to be offered.

How do your grinding solutions help cement plants achieve energy efficiency?
Latest developments related to raw material grinding in finish grinding in roller press have paid dividends even for soft and medium to hard material. Hard raw materials are giving higher bonus factor in finish grinding roller press systems and cement manufacturers are getting 2-4 Kwh/t saving in electrical energy in raw material grinding itself by using this technology as compared to vertical mill technology. Typical circuit offered by KHD for raw materials grinding in ComFlex Grinding circuit has advantages to process raw materials with high moistures with incorporation of V-Separator below the roller press and use of hot gases to dry the raw materials.
With the focus of the industry towards WHR systems, roller press grinding has further received acceptance as it uses no water for bed stabilisation and uses minimum hot gases as compared to other contemporary technologies.
In case of cement grinding, two technologies are being accepted, either vertical roller mill or roller press in semi-finish or finish grinding. Roller press in finish grinding has the advantage of further saving of 3-4 Kwh/t as compared to semi-finish grinding and vertical mill technology. With more acceptance of blended cements like PPC, PSC and composite cements, roller press in finish grinding is accepted as advanced technology in cement grinding. Typical finish and semi-finish grinding circuits offered by KHD are very popular in the cement industry. which includes use of roller press alone or in combination of roller press and ball mill respectively.
In the case of slag grinding, acceptance of roller press in finish grinding is well recognised. It offers a distinct advantage of saving of about 6-7 Kwh/t as compared to the vertical roller mill at 4200 Blaine. The advantage comes due to the hardness of slag and pressure grinding in roller press instead of attrition and low pressure in vertical roller press. Moisture issue is also tackled with the problem of coating by incorporating a V-separator below the roller press.

Tell us about the role of separators in the grinding process? How do they help achieve cost efficiency?
The basic role of a separator is to separate the feed material entering into it after grinding into two products i.e., coarse and fine. While fine is normally the final product in case of dynamic separator and is intermediate product in case of V-Separator. Dynamic separators have also gone through various technological developments, and we are offering 4th generation high efficiency separators now-a-days. These separators offer sharp cut point and minimum bypass (particle below 3 microns). This leads to less recirculation of fines thus improving the availability of the system and in turn efficiency of the system. V-separator is an excellent pre-separator cum dryer (in case of wet material) which is used for pre-separating the roller press throughput before the second separation in a dynamic separator. Two stage separation in the roller press circuit makes it energy efficient and ensures proper product quality.

Materials used for the manufacturing of cement are evolving every day. How does your machinery adapt to this change at the cement plants?
With the trends more on low clinker to cement ratio, today the Indian cement industry is moving very fast toward this aspect. PSC, PPC, composite cements are going up the curve. The cement industry is well versed with the utilisation and manufacturing of blended cement. KHD is one of the key suppliers for providing energy efficient technologies viz roller press grinding for the production of blended cement.
It is estimated that decreasing the clinker ratio in production of cement contributes to nearly 37 per cent of targeted CO2 reduction. By promoting PPC and PSC cement in India, more than 85 per cent cement is produced as blended cement or composite cement (which has come into existence during the last 3-5 years). PPC allows 35 per cent fly-ash usage at present, whereas PSC allows 55 per cent to 65 per cent granulated slag in clinker. Increase of Pozzolana (fly-ash) usage in PPC, up to 45 per cent can reduce the carbon footprint further which has a permissible limit of up to 55 per cent in some European countries. Our roller presses are well versed to take care of all these materials smoothly.

What role does technology play in designing and executing your grinding circuit at the cement plants?
It’s mainly the technology that has promoted the roller press circuits for grinding over VRM technology. Our technology takes into consideration the lowest energy consumption, dust free circuits, nil water consumption, lower maintenance and more in terms of availability and reliability. So, all the systems are based on technology to address all these points. For example, roller press surface plays an important role regarding maintenance requirements. Stud surface of roller press can provide continuous availability of roller press for 4-5 years without any welding requirement. Welded surfaces also have less than half the requirement of welding as compared to VRM, which has the attrition principle of grinding in addition to pressure grinding.

What are the major challenges in curating and executing grinding solutions?
Over the years we have done intensive work in the field of grinding solutions. We don’t foresee any major challenge now as we have already achieved lower power consumption, dust free circuits, more reliability, environmentally friendly grinding. However, we are on the track of continuous improvements to even achieve better because we believe that nothing is impossible, and we are always bound to reach new heights. With use of blended cements and LC3 Cement in coming future in India we are expecting higher blain requirement in final product which may see some technological advances in secondary grinding i.e., ball mills may be replaced by special mills however roller press shall continue in semi-finish and finish grinding applications.

Tell us about the innovations by your organisation in the near future that the cement industry can look forward to.
At present, the focus is to use roller press in finish grinding to get maximum energy advantage as compared to ball mill grinding especially for blended cement. Apart from electrical energy, the focus is also on roller press surfaces, which has minimum wear and offers trouble and maintenance free operation. Stud technology has proven to be a boon for the industry. Tungsten Carbide Studs are fixed on the roller surface by pressing in pre-drilled rollers, which offers autogenous grinding and minimum wear. Life expected out of these roller surfaces varies from 25,000-40,000 hours of operations without any surface maintenance.
Apart from this, developments are focussed on optimising the process circuit for energy efficient and pollution free operation. Developments in actuated dosing gate for feeding material to roller press and online monitoring of roller press surface are also worth noticing. There shall also be developments related to use of digital technology to monitor the performance of these grinding systems, which can contribute towards optimised production and increased availability due to timely signals regarding maintenance requirements.

-Kanika Mathur

Dr SB Hegde, Professor, Jain University and Visiting Professor, Pennsylvania State University, United States of America, gives a detailed account of the use of waste glass as Pozzolana, a sustainable solution for cement production, in a two-part article.

The increasing demand for cement, coupled with growing environmental concerns, has led to a search for alternative materials that can reduce the carbon footprint of cement production. Waste glass, a significant environmental concern itself, has emerged as a promising alternative due to its pozzolanic properties.
This paper delves into the concept of utilising waste glass as a pozzolanic material in cement production, highlighting its benefits, challenges and potential for sustainable development based on the research and development work carried out by the author. This is part one of the study; part two will be featured in the consecutive issue of the magazine.

Generation and Availability of Waste Glass
On a global scale, this only amounts to a recycling rate of less than 35 per cent. Worldwide, around 130 million tonnes (Mta) of glass are currently produced annually.
India alone produces three million tonnes of glass waste annually, of which only 35 per cent is recovered, and the rest often ends up in landfills or down cycled into construction material aggregates. Glass is found in municipal solid waste (MSW), primarily in the form of containers such as beer and soft drink bottles; wine and liquor bottles; and bottles and jars for food, cosmetics and other products. India is one of the largest consumers of glass in the world, and as a result, it also generates a significant amount of waste glass. Waste glass, also known as cullet, can come from various sources such as bottles, jars, containers, windows and other glass products.
The availability and generation of waste glass in India depend on several factors, including population, consumption patterns, recycling infrastructure and waste management practices. Glass waste can be generated from residential households, commercial establishments and industries as well as construction and demolition activities. In recent years, there has been growing awareness about the importance of recycling glass waste in India. Recycling glass has several environmental benefits, such as reducing the consumption of raw materials, saving energy and reducing landfill waste.

Infrastructural requirement
To effectively use waste glass as a pozzolanic material in a cement plant, certain facilities and processes can be implemented. Here are some key facilities that can be created:

1. Glass Sorting and Preprocessing: A facility for sorting and preprocessing waste glass is essential to segregate glass by colour and removing contaminants such as paper, plastics and metals. Crushing or grinding equipment can be used to reduce the glass to a suitable particle size.
2. Glass Storage and Handling: Adequate storage facilities should be established to store the sorted and processed glass. It is important to protect the glass from moisture and other environmental factors that can affect its quality.
3. Glass Dosing System: A dosing system should be set up to accurately measure and control the amount of waste glass being added to the cement production process. This can involve automated feeders or other equipment to ensure a consistent and controlled addition of glass.
4. Glass Grinding or Milling Equipment: Depending on the desired fineness of the waste glass, a grinding or milling unit may be required to further reduce the particle size. This equipment can include ball mills, vertical roller mills, or specialised glass grinding mills.
5. Blending and Mixing Facilities: Cement plants typically have blending and mixing facilities where various supplementary cementitious materials, including waste glass, can be combined with other raw materials. This ensures homogeneity and uniformity in the cement production process.
6. Quality Control and Testing: Facilities for quality control and testing should be in place to assess the chemical and physical properties of the waste glass, as well as the performance of the cementitious mixtures incorporating the glass. This can include laboratory testing equipment and personnel trained in relevant testing methods.
   It’s important to note that the specific facilities required may vary depending on the scale of the cement plant and the volume of waste glass being processed. Detailed engineering studies and consultations in cement production and waste management can help determine the optimal design and layout of these facilities within a cement plant. Additionally, it is advisable to comply with relevant environmental regulations and obtain any necessary permits or approvals from statutory bodies in that particular country for handling and using waste glass within the cement plant.

The Fineness of Waste Glass
When waste glass is used as a supplementary cementitious material in cement production, it is important to consider the fineness or particle size distribution of the glass. The fineness of waste glass affects its reactivity and compatibility with
cement, which can impact the performance of the cementitious mixture.
The specific fineness requirements for waste glass can vary depending on the specific application, the type of cement being used, and the desired properties of the final concrete or mortar. However, in general, the waste glass particles should be finely ground to ensure effective pozzolanic or latent hydraulic reactions with the cement.
Here are some common guidelines for the fineness of waste glass used in cement:
• Particle Size Distribution: The waste glass particles should have a range of sizes to ensure good packing and fill the voids between cement particles. A typical particle size distribution for waste glass in cement applications is similar to that of cement, with a majority of particles passing through a 325 mesh (45 microns) sieve.
• Blaine Fineness: The Blaine fineness test is often used to measure the specific surface area of cementitious materials. The waste glass should generally have a Blaine fineness similar to or higher than that of cement. Typical values can range from 300 to 500 m²/kg or higher, depending on the application.
• Grinding or Milling: Waste glass may require grinding or milling processes to achieve the desired fineness. The grinding method can vary depending on the available equipment and the specific glass composition. Ball mills, vertical roller mills or specialised glass grinding equipment can be used.
• Gradation Control: It is important to control the gradation of waste glass during the grinding process. A well-controlled gradation can improve the flowability and workability of the cementitious mixture.
It is worth noting that the precise fineness requirements may vary depending on the specific standards, specifications, or guidelines established by statutory bodies of the particular country.

Attributes of Waste Glass as Pozzolana
Based on research and development investigations the following avenues are investigated for utilisation of waste glass.
• Pozzolanic Properties of Waste Glass: Pozzolanic materials, when combined with calcium hydroxide in the presence of water, react to form cementitious compounds. Waste glass, rich in amorphous silica, exhibits excellent pozzolanic properties. Through a process called pozzolanic reaction, waste glass can contribute to the strength, durability, and chemical resistance of cementitious materials.
• Environmental Benefits: Incorporating waste glass as a pozzolanic material in cement production offers significant environmental advantages. Firstly, it reduces the need for virgin raw materials such as limestone, thus conserving natural resources. Additionally, it mitigates the environmental impact associated with glass waste disposal, diverting it from landfills or incineration.
• Improved Concrete Performance: The use of waste glass as a pozzolanic material enhances the performance of concrete. Due to its pozzolanic activity, waste glass reacts with calcium hydroxide in the cement matrix, resulting in denser and more durable concrete. This leads to improved mechanical strength, reduced permeability, and increased resistance to chemical attack.
• Supplementary Cementitious Material: Waste glass can be used as a supplementary cementitious material (SCM) in cement production. When properly ground and processed, waste glass can replace a portion of cement without compromising the desired concrete properties. This substitution not only reduces cement consumption but also lowers the carbon dioxide emissions associated with cement production.
• Sustainable Development and Circular Economy: Utilising waste glass as a pozzolanic material aligns with the principles of sustainable development and the circular economy. It promotes resource efficiency, reduces waste generation, and contributes to a more sustainable construction industry. The integration of waste glass into cement production presents opportunities for collaboration between cement manufacturers, waste management companies, and regulatory bodies to develop innovative and eco-friendly solutions.

References

1. Utilisation of Waste Glass Powder in Concrete by P. Manoj Kumar,
   K. Sreenivasulu, and M. Srinivasulu Reddy, International Journal of Innovative Research in Science, Engineering and Technology, 2013.
2. Recycling of Waste Glass as a Partial Replacement for Fine Aggregate in Concrete Mix by W. A. Rahman, M. A. S. Al-gahtani,
   and M. A. K. El-Kourd, Journal of King Saud University – Engineering Sciences, 2010.
3. Mechanical and Durability Properties of Concrete Containing Glass Powder as Partial Replacement of Cement by A. Shayan and R. Xu, Construction and Building Materials, 2004.
4. Properties of Glass Concrete Containing Fine and Coarse Glass Aggregates by Z. Feng, S. Xie, and Y. Zhou, Journal of Materials in Civil Engineering, 2011.

ABOUT THE AUTHOR
Dr SB Hegde, Professor, Jain University and Visiting Professor, Pennsylvania State University, United States of America.

Teijin Group provides innovative solutions for enhanced quality of life

As climate change has a large impact on the global society and economy, industry, governments and academia are making efforts to reduce environmental impact including greenhouse gas (GHG) emissions through energy conservation, green energy and lifecycle assessment (LCA).

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