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Waste to Energy to Wealth

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Handling of waste; be it hazardous, industrial or domestic was never so challenging in the earlier years. However cement industry offers an easy solution with minimal cost that needs to be utilised fully.

Rapid urbanisation and industrialisation and increasing household income are leading to higher waste volumes in India. The safe and effective disposal of this increasing level of waste generation is a key concern for authorities at local, State and Government level. One way forward is the promotion of large-scale co-processing in the cement industry, and to create a more conducive regulatory environment.

The increased use of waste as alternative fuel and raw material (AFR) in cement kilns can make a considerable contribution to effective and safe waste disposal efforts. In addition, this will not only help with the Indian cement industry become more competitive on a global stage, but is also in line with Prime Minister Modi’s "Swachh Bharat Abhiyan"(Clean India campaign), which has been launched throughout the country as a national movement. It has become necessary in the present situation of Covid-19 pandemic, we revisit "Swachh Bharat Abhiyan."

While the domestic cement industry has made significant strides in terms of enhancing energy efficiency and optimising productivity, the use of AFR is still a major area that can be developed. Thermal substitution of coal remains low compared to the European average of 40 per cent and varies dramatically from plant to plant. While some leading facilities report substitution rates of between 15 to 20 per cent, most achieve less than three per cent.

Challenges faced by Indian cement industry
The slow pace of revision of waste management rules to keep pace with current advancements in waste management approaches-i.e. co-processing and the absence of a proper waste hierarchy that recognises waste stream suited for co-processing?has been a long-standing barrier for co-processing in the country. Limited waste availability,the level of co-processing depends on the plant location and available surrounding waste market.

At present, obtaining a regular supply of homogeneous waste is asignificant challenge for cement plants as detailed information on quality, quantity and the type of waste generated is not readily available in the public domain. Since data on the quantity and quality of waste is minimal or outdated, cement producers have to spend a considerable amount of time and resources in exploring the availability of different types of AFR, thus weakening the business case for waste utilisation.

Lengthy permit process
The long permit processes further compounds the issue. To initiate co-processing, cement plants must conduct trial runs to obtain clearances from local and pollution control authorities, which is not only a lengthy process but also cost intensive. Although state regulatory bodies are working to simplify procedures, an approach based on the infrastructure, and measuring, reporting and verification (MRV) system in place at co-processing sites would be more appropriate than a trial-based one. Moreover, the inter-state movement of waste (except agricultural waste) comes with its own challenges.

The inter-State movement of hazardous waste in India is not usually encouraged, requires additional permissions and is marred by the lack of certified transporters who can safely move materials from waste generators to cement plants. Permitting the inter-state movement of waste would certainly support the uptake of waste utilisation in the cement industry. However, clearly-defined responsibilities for each stakeholder in terms of collection, packaging, transportation, handling and storage, etc would go some way to helping authorities in their decision-making process. Similarly, the development of operational guidelines with built-in safety features for the aforementioned associated-activities will aid safe and environmentally sound co-processing.

The expert group is also examining various kinds of incentives that can be accorded to both waste generators and waste users that pursue co-processing opportunities. Incentives could be, for instance, financial, government recognition, or faster approval process, etc. The co-processing movement has received further stimulus from the Clean India Mission, as the government is currently working on the revision of various waste management rules.

The initiative recognises co-processing as one of the approaches for waste management, as well as emphasises the importance of segregation of waste at source which will help ensure the homogeneous supply of waste for co-processing. Though India still has a long way to go in terms of forming a comprehensive co-processing system, now is an opportune time for domestic cement industry to focus on how co-processing can help increase its competitiveness on a global stage, and assist with the disposal of the country’s every-increasing volumes of waste.

What is the circular economy?
Taking as an example the cyclical nature pattern, circular economy is presented as a system of resources utilisation where reduction, reuse and recycling of elements prevails: minimise production to a bare minimum, and when it’s necessary to use the product, go for the reuse of the elements that cannot return to the environment.

That is, the circular economy promotes the use of as many biodegradable materials as possible in the manufacture of products -biological nutrients- so they can get back to nature without causing environmental damage at the end of their useful life. When it is not possible to use eco-friendly materials-technical nutrients: electronics, hardware, batteries-the aim is to facilitate a simple uncoupling to give them a new life by reintroducing them into the production cycle and compose a new piece. When this is not possible, it will be recycled in a respectful way with the environment.

Circular economy is a substantial improvement common to both businesses and consumers. Companies that have implemented this system are proving that reusing resources is much more cost effective than creating them from scratch. As a result, production prices are reduced, so that the sale price is also lowered, thereby benefiting the consumer; not only economically, but also in social and environmental aspects.

The main objective of the circular economy is to make economic systems and industrial processes more environmentally friendly and sustainable. Shifting to a circular economy is not a straight forward process and requires substantial changes in the value chain, such as; adapted design, better waste and water management, greater recycling and re-use of products. European Union has done much more work than any other such body.

Based on the data of 2015, turning waste into a resource – only around one-third was recycled and the rest incinerated or landfilled. Estimated additional potential for reuse/recycling is up to 600 MT. If this material is lost then growth, job creation and competitiveness will be compromised and negative environmental impacts generated. The main objective is to recycle more in order to have more "waste" which can be used as a resource. Recycling is a pre-condition for the circular economy.

However, it is important to be aware that there are two problems connected to the topic:
The "legal" base is missing: Currently, there is an action plan which is still under discussion at the EU commission. Final recycling targets are still to be fixed, as well as the methods of calculation to be used. It will take some time until the action plan has been formally finalised by the EU and it will require more time to transfer the amended EU laws into national laws- However, we should remain prepared as these implementations are clearly approaching.

The comparison of data from the different countries has not proved easy so far; with each EU country applying different methods for the counting of waste streams and the calculation of recycling targets, which has rendered the data from different countries more or less incomparable. One target of a circular economy is to harmonise these methods of definition and calculation.

Are we in India prepared for a circular economy?

– VIKAS DAMLE

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Concrete

Innovations in Sustainability

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Dr SB Hegde, Professor, Jain University, Bangalore, and Visiting Professor, Pennsylvania State University, USA, discusses how the cement sector is battling substantial carbon emissions and resource depletion, and embracing advanced technologies to mitigate its environmental impact.

In the relentless pursuit of urbanisation and infrastructure development, the cement industry finds itself at a pivotal intersection of ambition and responsibility. This foundational sector has long been synonymous with progress and growth, providing the bedrock for modern cities and industries. Yet, beneath its seemingly unyielding façade lies a profound challenge – the environmental footprint it leaves behind. Cement production, for its high carbon emissions and resource consumption, is now compelled to rewrite its narrative. The cement industry needs to become more sustainable using advanced technology. In this article, we will explore the world of cement production and discover new solutions that can change its future.

Considering traditional cement production is a major emitter of CO2, accounting for around 8 per cent of global greenhouse gas emissions. It consumes a vast amount of limestone, a finite resource, and contributes to deforestation and habitat destruction in limestone-rich regions.

Supplementary cement materials (SCMs) and creative ideas like Calcined Clay Clinker (LC3) are making a big difference. These different materials are transforming the way things are done. For example, in India, where the cement industry is one of the largest carbon emitters, LC3 technology, which incorporates calcined clays into cement, has been demonstrated to reduce CO2 emissions by up to 30 per cent and substantially decrease energy consumption during the clinker production process. By 2050, it is estimated that the implementation of such alternative materials could help the cement sector reduce its global CO2 emissions by up to 16 per cent.

The cement industry because of its energy-intensive processes, consuming approximately 5 per cent of the world’s total energy and contributing significantly to greenhouse gas emissions.

Waste heat recovery systems, a pivotal technology, are setting an example for sustainability. A case study from a cement plant in Germany showed that waste Innovations in Sustainability Dr SB Hegde, Professor, Jain University, Bangalore, and Visiting Professor, Pennsylvania State University, USA, discusses how the cement sector is battling substantial carbon emissions and resource depletion, and embracing advanced technologies to mitigate its environmental impact. heat recovery reduced energy consumption by approximately 20 per cent and cut CO2 emissions by 1.6 million tons annually. This not only demonstrates the environmental benefits but also underscores the economic advantages of such innovations.

Furthermore, the industry is adopting alternative fuels, often derived from waste materials. Lafarge Holcim, one of the world’s largest cement producers now utilizes alternative fuels in 37 per cent of its cement plants. This has resulted in an estimated reduction of 2.2 million tonnes of CO2 emissions annually, showcasing the transformative potential of sustainable fuel sources.

The electrification of kiln systems is a transformative step towards sustainability. While the shift to electrification is in its nascent stages, there are promising examples. Heidelberg Cement, a global leader in building materials, has set ambitious targets to electrify its cement production processes. By leveraging renewable energy sources, such as wind and solar, the company aims to reduce CO2 emissions by 30 per cent within the next decade. These concrete numbers underscore the industry’s commitment to low-carbon electrification.

Hybrid and flash calcination technologies offer compelling statistics as well. For instance, a pilot project using flash calcination technology in the Netherlands yielded a 25 per cent reduction in CO2 emissions compared to traditional rotary kilns. These numbers highlight the potential of disruptive technologies to reshape the cement industry.

This article is like a clear road map with real examples, explaining how the cement industry is becoming greener and more sustainable. By using technology, the cement industry wants to find a balance between moving forward and taking care of the environment. It’s showing how an industry can change to become more sustainable, strong and responsible for the future.

CURRENT TECHNOLOGIES


1. Alternative raw materials: The cement industry’s traditional reliance on limestone as a raw material is undergoing a transformation. The incorporation of alternative materials like fly ash, slag or pozzolans is a sustainable approach. For example, the use of fly ash in cement production can reduce CO2 emissions by up to 50 per cent compared to traditional Portland cement.

2. Energy efficiency: Improving energy efficiency is crucial. Waste heat recovery systems can significantly reduce energy consumption. For instance, waste heat recovery in cement plants can lead to a 20-30 per cent reduction in energy consumption.

3. Carbon Capture and Storage (CCS): CCS is a promising technology. In Norway, the Norcem Brevik cement plant has successfully demonstrated the capture of CO2 emissions, which are then transported and stored offshore. This technology can capture up to 400,000 tonnes of CO2 annually.

4. Use of alternative fuels: The shift towards alternative fuels can significantly reduce carbon emissions. For example, the use of alternative fuels in the European cement industry results in an average substitution rate of about 40 per cent of conventional fuels.

5. Blended cements: Blended cements, combining clinker with supplementary cementitious materials, can lead to lower emissions. For example, the use of slag and fly ash can reduce CO2 emissions by up to 40 per cent.

INNOVATION FOR THE FUTURE
1. Carbon Capture and Utilisation (CCU): CCU technology is still emerging, but it shows great potential. Innovations like carbon mineralisation can convert CO2 into stable mineral forms. Carbon Engineering, a Canadian company, is working on a direct air capture system that can capture one million tons of CO2 annually.

Feasible CCS technologies for the cement industry include:

a. Post-combustion capture: Capturing CO2 emissions after combustion during clinker production using solvents or adsorbents.
b. Pre-combustion capture: Capturing CO2 before combustion, often used with alternative fuels.
c. Oxy-fuel combustion: Burning fuel in an oxygenrich environment to facilitate CO2 capture.
d. Chemical looping combustion: Using metal oxides to capture CO2 during the calcination process.
e. Carbonation of alkaline residues: Capturing CO2 using alkaline residues from other industrial processes.
f. Integrated Carbon Capture and Storage (ICCS): Directly capturing CO2 from the cement production process.
g. Underground storage: Transporting and storing CO2 underground in geological formations.
h. Enhanced Oil Recovery (EOR): Injecting captured CO2 into depleted oil reservoirs.
i. Mineralisation: Converting CO2 into stable mineral forms for potential use or storage.

The cement industry can reduce emissions by adopting these technologies, but cost, energy, and infrastructure challenges must be addressed for widespread implementation. Collaboration among stakeholders is crucial for successful CCS integration.
2. Biomimicry in cement design: Researchers are exploring biomimetic materials inspired by nature. For example, a company called BioMason uses microorganisms to grow cement-like building materials, reducing energy use and emissions.
3. 3D printing of cement: 3D printing technology offers precise and efficient construction, reducing material waste. In a study, 3D-printed concrete structures used 40-70 per cent less material compared to traditional construction methods.
4. Blockchain for supply chain transparency: Blockchain technology ensures transparency and traceability. It is already being used in supply chains for various industries, including cement. By tracing the origin of raw materials and tracking production processes, it ensures sustainability compliance.

EVALUATING AND IMPLEMENTING SUSTAINABLE TECHNOLOGIES
1. Life Cycle Assessment (LCA): LCAs assess environmental impacts. For instance, a comparative LCA study found that geopolymer concrete (an alternative to traditional concrete) had 36 per cent lower carbon emissions compared to Portland cement.
2. Cost-benefit analysis: Considerations of initial investments and ongoing operational costs are paramount. Studies show that the implementation of waste heat recovery systems can pay back their initial costs in as little as two years, leading to long-term savings.
3. Regulatory compliance: Stricter emissions standards are being enforced globally. The European Union, for instance, has set ambitious emissions targets for the cement industry, mandating a 55 per cent reduction in CO2 emissions by 2030
4. Scalability: The scalability of technologies is critical for industry-wide adoption. Technologies like blended cements and waste heat recovery systems are already scalable, with global cement companies actively implementing them.
5. Stakeholder engagement: Engaging stakeholders is essential. For example, Holcim, a leading cement manufacturer, has partnered with NGOs and local communities to ensure sustainable practices and community involvement in their projects.

In conclusion, the cement industry is on a transformative path towards sustainability, driven by technological innovations. By embracing alternative raw materials, enhancing energy efficiency, and exploring cutting-edge solutions like carbon capture and utilization, the industry is reducing its environmental impact. The future holds even more promise, with biomimetic materials, 3D printing and blockchain enhancing sustainability.

Evaluating and implementing these technologies necessitates comprehensive assessments, cost-benefit analyses, regulatory compliance, scalability and stakeholder engagement. The industry’s commitment to sustainability not only addresses environmental concerns but also aligns with societal values and expectations, setting the stage for a greener and more responsible future for cement production.

REFERENCES:
1. NIST. (National Institute of Standards and Technology) Role of NIST in Sustainable Cements.
2. International Energy Agency. Cement Technology Roadmap 2018.
3. Gassnova. Longship – CO2 Capture, Transport, and Storage.
4. European Cement Association. Cembureau.
5. CSI. (Cement Sustainability Initiative) Slag Cement and Concrete.
6. Carbon Engineering. Direct Air Capture and Air To Fuels.
7. The University of New South Wales. Alternative Cement Discovery Set to Reduce Carbon Emissions.
8. BioMason. BioMason Technology.
9. NCCR Digital Fabrication. DFAB House Project.
10. IBM Blockchain. IBM Blockchain Solutions for Supply Chain.
11. ScienceDirect. Life Cycle Assessment of Geopolymer Concrete.
12. Energy.gov. Heat Recovery Technologies.
13. EU Climate Action. EU Climate Action: Climate Targets for Cement Industry.

ABOUT THE AUTHOR:


Dr SB Hegde is an industrial leader with expertise in cement plant operation and optimisation, plant commissioning, new cement plant establishment, etc. His industry knowledge cover manufacturing, product development, concrete technology and technical services.

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Concrete

Stud technology has proven to be a boon for the industry

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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

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Concrete

Waste Glass as Pozzolana

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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.

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