Concrete
Environmentally Speaking
Published
2 years agoon
By
adminSustainable mining is the buzzword for all industries depending on mined raw materials, especially the cement sector. It is, therefore, imperative that we take a closer look at its economic and environmental impact.
The focus on mining in the context of cement has more than one reason to be at the top of the agenda on sustainability. With the sheer growth of this sector as an extractive process that touches many aspects of the environment on the one hand, and leaves the livelihoods of the people associated in a state of quandary on the other, given that the life of the mine and that of the prosperity of the people get intertwined.
The narratives have changed from the mere lifecycle of the mineral deposit to the complete sustainability that includes an integrated and holistic approach to preclude economic, environmental and social value from mining and allied operations and supply chains for a large number of stakeholders.
Economic Repercussions
The prelude to this narrative is the understanding of stakeholder responsibilities at a time when some parts of the world, where the global extractive process for limestone, the key mineral for producing cement, has seen capacities being ramped up to serve the burgeoning rise of cement demand. As ballpark estimates suggest, for a 4 billion tonne cement output of the world, the limestone requirement stands at close to 2.8 billion tonnes, which is the highest mineral ore extracted every year from the deposits of the world, which happens to be the top cover of the earth’s surface.
Most of these deposits occur closer to forests, biodiversity and tribal populations, essentially places where economic progress has been slow. If one looks at the total extractive mineral output, one would be seeing a three-fold increase over the last four decades. From 1970 to 2017, the annual global extraction of materials tripled and the global use of materials is expected to more than double from 79 Gt in 2011 to 167 Gt in 2060. Minerals that are non-metallic, such as construction material, e.g., sand and gravel, represent more than half of the total use of materials by weight and their use is expected to grow rapidly in the coming years (from 35 Gt in 2011 to 82 Gt in 2060). Cement industry, coupled with the concrete that needs aggregates and sand, is a part of the extractive mining industry landscape, and thus the environmental and social impact of mining becomes a very important subject, if one adds these supply chains as well.
On the one hand, mining as an economic activity could be encouraging for the populace, it could end up with the ‘Resource Curse’ as well, as mines reach the end of cycle of the deposits. Thankfully at least for cement, we have a burgeoning downstream, mostly closer to the mining operations, where a vibrant downstream operation is established that employs larger sections of people and thus livelihoods are intertwined on a bigger scale through supply chains that crisscross. Apart from the building and construction industry, which requires 80 per cent of the extraction, we still have steel, agriculture and chemical Industries needing limestone mining for a number of reasons.
Keeping Track of Sustainability
Sustainability reporting, which is mostly voluntary reporting, is at the core of the sustainable initiatives, sometimes prompted by the Country Reporting guidelines and Environmental and Sustainability Goals (ESG) of 2015 or the Global Reporting Initiative (GRI). The investors also demand more disclosure on Sustainability Initiatives with clear mandates that can be verified through trends and data. However, the 2018 Responsible Investing Survey and the 2020 Responsible Mining Index cites lack of quantity and quality in the reporting so far. Stakeholders increasingly require information on the environmental and social impacts of mining at the mine-site level, and presented in the local context. Sometimes there is little use to look at headline numbers aggregated over many sites across countries. Focus on site level reporting that gives periodic data on a host of environmental and social impact of mining becomes the important indicator of progress.
Some of the sustainability indicators at the site level include:
- Impact on biodiversity: Number/percentage of sites with biodiversity management plans
- Description of significant impacts on biodiversity: Amount of land disturbed or rehabilitated and information on the use of biodiversity offsets
- GHG emissions and energy use: Amount of CO2e GHG emissions and mitigation measures and energy consumption and reductions
- Water management: Amount of water withdrawal by source and water sources significantly affected by withdrawal of water
- Health and safety: Number of accidents/deaths, information on training on health and safety management security / human rights and rights of indigenous peoples
- Number/percentage of reserves in or near areas of conflict: Number/percentage of reserves in or near indigenous lands and engagement processes in place
- Processes in place to prevent child or forced labour and impact on local communities and local community engagement
- Number of operating sites where resettlement took place, number of households resettled in each site and information on how their livelihoods were affected in the process
- Number/percentage of operations with local community engagement (including minority groups such as women), and/ or environmental/social impact assessments
- Number/percentage of operations with significant negative impacts on local communities – Proportion of spending on local suppliers
Apart from these, water and air quality and gender diversity in mining operations have become important pointers as well. For mining operations in cement, site remediation and rehabilitation become an area of focus as many mines have reached their end of life. One of the ways to enforce this has been to enforce some of these at the inception of the Environment Impact Assessment and Mining Permit stage itself. With the lack of site-specific reporting as evidenced in almost 90 per cent of the mining sustainability reporting, corporate level reporting is only a high-level aggregation of most of data, masking site level inadequacies, which has been pointed out in both the Responsible Investing Survey and Sustainable Mining Index 2020.
If one looks at the expansion of the scope for the building and construction industry, where only a smaller part is covered under the cement-limestone mining operations and the larger part falls under aggregates and sand mining operations, which remains uncovered by sustainability reporting as most of these fall under small scale industry structure,
absolving them of the detailed disclosure requirements. It is therefore to be concluded that for most developing nations, we still have a long way to progress as far as sustainable mining operations are concerned. The entire supply chain of mining operations for concrete / building and construction industry must be looked at where the suppliers of sand, gravel and aggregates must be brought under the same purview and this leaves a lot to be desired as these
supply chains have third party sourcing activities lacking the rigour of the bigger corporate entities like cement companies.
-Procyon Mukherjee
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Concrete
JSW Cement aims to launch Rs 4,000-crore IPO in Jan 2025
SEBI had put the IPO on hold in September.
Published
15 hours agoon
November 22, 2024By
adminJSW Cement plans to launch its Rs 4,000-crore initial public offering (IPO) in January 2025, according to JSW Group chairman Sajjan Jindal. The Securities and Exchange Board of India (SEBI) had previously paused the IPO in September 2023.
The IPO will consist of two parts: a fresh issue of equity shares worth Rs 2,000 crore and an offer-for-sale (OFS) of Rs 2,000 crore by existing shareholders. Under the OFS, AP Asia Opportunistic Holdings Pte. Ltd and Synergy Metals Investments Holding Ltd will each sell shares worth Rs 937.5 crore, while the State Bank of India (SBI) will divest shares valued at Rs 125 crore.
The company intends to use Rs 800 crore of the proceeds from the fresh issue to help finance the establishment of a new integrated cement plant in Nagaur, Rajasthan. An additional Rs 720 crore will be allocated for debt repayment, with the remaining funds earmarked for general corporate purposes.
JSW Cement, which currently has a manufacturing capacity of 19 million tons per annum (MTPA), aims to increase this to 60 MTPA. Its existing manufacturing units are located in Vijayanagar (Karnataka), Nandyal (Andhra Pradesh), Salboni (West Bengal), Jajpur (Odisha), and Dolvi (Maharashtra). Additionally, through its subsidiary Shiva Cement, the company operates a clinker unit in Odisha.
JSW Group has a diverse business portfolio spanning sectors such as steel, energy, maritime infrastructure, defense, B2B e-commerce, real estate, paints, sports, and venture capital. The group’s last IPO was that of JSW Infra.
ICR discusses India’s rapid advances in renewable energy, on track to exceed its 2030 targets, even as the rising energy demands challenge complete reliance on sustainable sources.
The cement industry, a cornerstone of infrastructure development, has long been associated with high emissions, particularly of CO2. This sector alone is responsible for approximately 8 per cent of global carbon dioxide emissions, primarily due to the energy-intensive processes of clinker production and calcination. Beyond carbon emissions, cement production also generates particulates, nitrogen oxides (NOx), sulphur oxides (SOx), and other pollutants, contributing to environmental degradation and health risks. With the global push towards sustainable practices and carbon neutrality, addressing emissions in the cement industry has become imperative.
According to Climate Change Performance Index, India ranks 7 in 2024. India receives a high ranking in the GHG Emissions and Energy Use categories, but a medium in Climate Policy and Renewable Energy, as in the previous year. While India is the world’s most populous country, it has relatively low per capita emissions. Data shows that in the per capita GHG category, the country is on track to meet a benchmark of well below 2°C.
India’s situation underscores the complexity of transitioning to sustainable energy systems in the face of rising and fluctuating energy needs. International support is crucial for India to access advanced technologies, financial resources, and best practices that can accelerate its transition to a sustainable energy future. Our analysis shows that with current policies, India will overachieve its conditional NDC targets of achieving 50 per cent non-fossil capacity by 2030, so it could set stronger targets. India has ambitious renewable energy plans as outlined in the National Electricity Plan 2023 (NEP2023) aiming for a share of installed capacity of 57 per cent and 66 per cent in 2026-27 and 2031-32, respectively. Share of renewable energy capacity in India reached 44 per cent, ranked fourth in the world in renewable energy capacity installations in 2023, after China, the US and Germany. The NEP2023 is reflected in the lower bound of our current policy and action pathway.
India has seen a steady increase in renewable energy deployment, including both utility-scale and rooftop solar, leading to the share of coal capacity dropping below 50 per cent for the first time. However, this increase in renewable energy capacity is barely able to keep up with the surging demand. As a result, the electricity generation share of renewable energy, including large hydro, remains at around 18 per cent, showing no improvement since last year. Investment in renewable energy projects in India are projected to increase by over 83 per cent to around USD 16.5 bn in 2024, with fossil fuel companies also diversifying their investments into the renewable sector. Despite this, India has not committed to phasing out coal power or fossil gas.
The National Electricity Plan indicated a temporary halt in coal capacity addition, but current under-construction capacity exceeds the threshold stated in these plans. While new gas power projects have been abandoned, the utilisation of existing gas power plants has increased to meet energy demand driven by severe heat stress.
Understanding Emissions in Cement Production
Primary Sources of Emissions: Cement production emissions stem mainly from three sources: calcination, fuel combustion, and electricity use. During calcination, limestone is heated to produce clinker, releasing CO2 as a by-product. This process alone accounts for roughly 60 per cent of emissions in cement manufacturing. The remaining emissions result from burning fossil fuels in kilns to achieve the high temperatures needed for calcination and from electricity consumption across production stages.
Raju Ramchandran, SVP Manufacturing (Cluster Head – Central), Nuvoco Vistas, says, “We consistently track air emissions from fuel combustion in our cement manufacturing and power generation operations. The burning of fossil fuels releases pollutants such as Oxides of Sulphur (SOx), Oxides of Nitrogen (NOx), and Particulate Matter (PM), which require stringent monitoring.”
“We ensure compliance with regulatory standards by using the Continuous Emission Monitoring System (CEMS) to monitor these emissions. For the FY 23-24, both our stack and fugitive emissions have stayed within the permissible limits set by Pollution Control Boards. Moreover, our ongoing monitoring of fugitive emissions ensures that we meet the prerequisite air quality standards,” he adds.
In addition to CO2, the cement industry releases various pollutants that pose risks to air quality and public health. These include particulate matter, NOx, and SOx, which can lead to respiratory and cardiovascular issues, acid rain, and ecosystem imbalances.
Governments worldwide are setting increasingly stringent regulations to curb industrial emissions. Standards such as the EU Emissions Trading System and India’s National Action Plan on Climate Change encourage cement manufacturers to adopt cleaner technologies. Many countries now impose limits on NOx, SOx and particulate emissions, with the aim of minimising the industry’s environmental impact.
Challenges in Reducing Emissions
High carbon intensity of cement production: Cement’s high carbon intensity largely stems from the chemical reactions involved in transforming limestone into clinker, making emissions difficult to reduce without altering core processes. Additionally, achieving the necessary kiln temperatures requires significant energy, often derived from coal or natural gas.
Operational limitations: Altering the traditional cement production process can compromise the quality and durability of the end product. Adapting existing production lines for lower emissions involves extensive R&D and technical trials to ensure the finished cement meets industry standards.
Financial constraints: The cost of implementing green technology is high, creating economic challenges, particularly for smaller cement manufacturers. Equipment upgrades, energy-efficient kilns, and carbon capture facilities require considerable investment, which many companies find difficult to justify without strong financial incentives.
Balancing market demands and environmental goals: With global infrastructure demands rising, the cement industry faces pressure to meet growing production needs while simultaneously working to reduce emissions. Balancing these competing demands requires innovation, efficient resource management, and support from stakeholders.
Technological Innovations for Emission Reduction
Alternative fuels and energy sources: One of the most effective ways to reduce emissions is by replacing fossil fuels with alternatives like waste-derived fuels, biomass, or biofuels. Some manufacturers are incorporating solar and wind energy to power auxiliary processes, further reducing reliance on traditional energy sources.
Sudhir Pathak, Head- Central Design & Engg (CDE), QA, Green Hydrogen, Hero Future Energies, says, “The cement industry is one of the largest consumers of grid power (Scope 2) and also a guzzler of in-process fossil CO2 (Scopem1) including process-based CO2 through limekilns. Decarbonisation can be achieved only up to 50 per cent to 60 per cent through plain hybrid solar and wind. However, for achieving balance 40 per cent, storage is essential, be it chemical or mechanical. Today, HFE is ready to provide such bespoke storage solutions as is evident through several complex RTC tenders that we have won in the last 6-8 months floated by agencies like SECI, NTPC and SJVN. These include tenders for FDRE projects, peak power, load following, etc. Further, regarding green hydrogen and its derivatives, we are ready to apply these for decarbonising industrial heating and mobility.”
Carbon Capture and Storage (CCS): CCS technology captures emissions at the source, storing CO2 to prevent it from entering the atmosphere. Recent advancements in CCS technology make it a viable option for large-scale cement plants, although high costs and infrastructure requirements remain obstacles to widespread adoption.
Clinker Substitution: Reducing clinker content is a promising method for emission reduction, achieved by using supplementary cementitious materials (SCMs) such as fly ash, slag, and calcined clay. These materials not only reduce CO2 emissions but also enhance the durability and performance of cement. SCMs are gradually becoming industry-standard components, especially in eco-friendly and green cement products.
Rajesh Kumar Nayma, Assistant General Manager – Environment, Wonder Cement, says, “The use of AFR plays a critical role in our strategy to reduce the environmental footprint of cement production. By substituting traditional fossil fuels with waste-derived alternatives like biomass, refuse-derived fuel (RDF) and industrial by-products, we significantly lower CO2 emissions and reduce the demand for natural resources. The utilisation of supplementary cementitious materials (SCMs), such as fly ash, helps in reducing clinker consumption, which is a major source of carbon emissions in cement production. This not only decreases our reliance on energy-intensive processes but also promotes waste recycling and resource efficiency. AFR adoption is an integral part of our commitment to the circular economy, ensuring that we minimise waste and optimise the use of materials throughout the production cycle, ultimately contributing to a more sustainable and eco-friendly cement industry.”
“WCL is exploring transitioning from fossil fuels to cleaner alternatives like biofuels or hydrogen or RDF/plastic waste/other hazardous waste. Till date, 5 per cent TSR has been achieved, while the intent is to achieve more than 20 per cent TSR. WCL is utilising the hazardous and other waste as an alternative fuel or raw material. We have used more than 3 lakh metric tonne of hydrogen waste and other waste in FY-2023-24,” he adds.
Improving energy efficiency is critical for emissions reduction. Technologies like high-efficiency kilns, heat recovery systems, and process optimisation techniques are helping manufacturers achieve more output with less energy. These measures reduce the carbon footprint while lowering operational costs.
The Role of SCMs
SCMs serve as partial replacements for clinker, providing a dual benefit of reduced carbon emissions and improved product resilience. The use of materials like fly ash and slag also helps mitigate industrial waste, contributing to a circular economy. Fly ash, slag, and silica fume are among the most widely used SCMs. Each has unique properties that contribute to cement’s strength, workability, and durability. By incorporating SCMs, manufacturers can produce cement with a lower environmental footprint without compromising quality.
While SCMs are effective, several obstacles hinder their widespread adoption. Supply chain constraints, material variability, and lack of technical standards are challenges that manufacturers face. Additionally, geographic limitations impact access to certain SCMs, creating disparities in their usage across regions.
Policy and Industry Collaboration
Policies play a critical role in driving green transitions within the cement industry. Carbon credits, tax incentives, and funding for R&D are some measures governments have introduced to support emission reduction. India’s Perform, Achieve, and Trade (PAT) scheme is an example of a policy incentivising industrial energy efficiency.
Collaborations between government entities, private corporations, and research institutions foster innovation and accelerate the adoption of sustainable practices. Partnerships can also help address funding gaps, allowing companies to explore new technologies without bearing the full financial burden.
International frameworks such as the Paris Agreement and industry-led efforts like the Global Cement and Concrete Association (GCCA) are setting targets for sustainable cement production. These initiatives encourage the sector to adopt environmentally friendly practices and set a roadmap toward achieving net-zero emissions.
Towards a Net-Zero Future
Reaching net-zero emissions is an ambitious but necessary goal for the cement industry. Realistic targets, set with interim milestones, allow companies to gradually transition to greener processes while maintaining production efficiency. Continued investment in R&D is crucial for discovering new methods of emission reduction. Emerging technologies such as carbon-negative materials, alternative binders, and low-carbon clinkers hold promise for the future, potentially transforming cement production into a more sustainable process.
Increasingly, consumers and investors are prioritising sustainability, placing pressure on companies to reduce their environmental impact. This shift in consumer sentiment is driving the cement industry to adopt green practices and focus on transparency in emissions reporting.
Conclusion
The journey toward reducing environmental impact in the cement industry is complex and multifaceted, requiring a combination of innovation, policy support, and industry collaboration. By adopting alternative fuels, implementing carbon capture technology, integrating SCMs, and improving energy efficiency, the industry can take significant strides in minimising its carbon footprint. Achieving sustainability in cement production is essential not only for the industry’s future but also for the planet’s well-being. Together, industry players, policymakers, and consumers can support the transition to a net-zero future, ensuring that cement remains a vital yet sustainable component of global infrastructure.
– Kanika Mathur
Concrete
Maximising AFR in Cement Manufacturing
Published
20 hours agoon
November 22, 2024By
adminShreesh A Khadilkar, Consultant and Advisor, and Former Director Quality and Product Development, ACC Ltd Thane, discusses the importance of optimising the use of alternative fuel and raw materials (TSR percentage) in cement production without affecting clinker quality, in part one of this two-part series.
Over the past decade or so, the Indian cement industry has made significant progress in terms of improvement in energy efficiency and productivity. However, the use of alternative fuel and raw material (AFR) to replace coal for thermal energy needs, remains an area where the Indian cement industry is yet to catch up with global benchmarks. Though a few cement plants co-process large quantities and varieties of AFR in their kilns, and are reported to reach a level of around 40 per cent Thermal Substitution Rate (TSR), many plants are still at much lower levels of TSR percentage.
Most of the cement plants have now installed co-processing facilities or are on the verge of having one. Some of the plants also have pre-processing facilities, which could include shredding, segregation, impregnation, foreign body removal etc., while some others source a pre-processed solid AFR (RDF, MSW, Industrial waste sludges, agro wastes etc.).
This article shares important aspects such as assessment of clinker quality in plant clinker quality optimisation, influence of alkalis, chlorides and SO3, effects of some important minor constituents and subsequently discusses the concept for maximising AFR (TSR percentage) without affecting clinker quality through with or without use of XRD technique for in process control. The author further recommends bi-hourly quality and in process dashboard for consistent kiln performance and consistent clinker quality.
Assessment of Clinker Quality
The clinker quality assessment can best be done by Lab Ball Mill grinding of day average clinker with mineral gypsum (with SO3 of the lab ground cement targeted at 2.2 to 2.4 with fixed grinding time to achieve Blaine’s of around 300-320 M2/kg with the residue on 45 microns of the cement in range of 18 per cent to 20 per cent, at this fineness, the clinker is observed to clearly depict changes in clinker reactivity in terms of changes in 1 Day strengths of cements (± 3 to 5 MPa). At lower grinding Blaine’s (of around 250 M2/kg), which is presently being practiced by many cement plants, one does not observe the changes in clinker reactivity, as the difference of 1 Day compressive strengths is only ± 1 MPa, which does not show the changes in clinker reactivity.
Typically, clinkers with good reactivity are observed to show 1 Day strengths in lab ground cements of 30 to 35 MPa. Higher values being observed when clinker alkali sulphates are high (especially with Petcoke as fuel), the achieved Blaine’s and quantity of nibs removed from the lab ground cement, in the fixed grinding time is also indicative of clinker grindability. Judicious raw mix optimisation with existing or alternative corrective materials (with the fuel mix used by the plant) can be attempted so as to have a clinker with improved reactivity/hydraulic potential. In a running plant the approach has to be by attempting small gradual changes to clinker composition and assessing the impact of the changes, on kiln performance and clinker quantity.
The changes to be attempted could be indicated through data analysis.
In each plant, the QC and process has detailed analysis data of the day average clinkers along with its lab ground cement test results. It is also suggested to test at least one spot clinker per day for chemical parameters and physical tests of lab ground cement. From the analysis data it could be observed that on some days the lab ground cements show much higher strengths. Why on some days or in some spot clinkers, the clinker reactivity is suddenly very good? Such clinkers should be preserved and evaluated by XRD, so as to identify the optimum clinker composition which shows higher reactivity. Such an evaluation could also indicate at times the impact of changes in fuel / sources of coal / proportions of coal and Petcoke (even source of Petcoke) / solid AFR usage levels.
Typically, the target clinker composition to give a good hydraulic potential would be with LSF of 93 to 95 with a bogues potential C3S of >55 per cent clinker (especially with Petcoke as main fuel in fuel mix), with C3A (6.5 per cent to 8.5 per cent) if the clinker is used for PPC/PSC and also for OPC (especially if OPC is supplied to RMX customers) and SM 2.2 to 2.4 A/F 1.2 to 1.4. In plants where clinker MgO is higher (> 4.5 per cent), besides having the LSF target of around 93 to 95, the minimum clinker lime targeted should be such to have C/S ratio of 2.95 to 3.1 for having good clinker reactivity in spite of high clinker MgO.
Co-Processing of AFR (Liquid AFR /Solid AFR)
The properties of AF(R) co-processed in the calciner have an impact on environment, health and safety, plant operations and product quality as shown in Table 1:
- Alkalis without sulphidisation: Formation of orthorhombic C3A, fast setting
- Alkali sulphates (Na2SO4, K2SO4, 2CaSO4.K2SO4 or even Ca-langebnite): Increased early strength, usually shows decrease of later age strengths. Changes must be accounted for in gypsum optimisation
- Excess of sulphur over alkalis
- Integration of SO3 in C2S and/or formation of CaSO4
- Possible reduction of final strength could be observed
- Reduces the CaO availability for C3S formation
- The clinker could be harder to grand
- Changes the Clinker Liquid Characteristics which affects the phase formations
- Chlorides tend to be higher in AFR liquid/solid, the control on chlorides is necessary to prevent inlet/cyclone jamming and to have < 0.06 per cent in clinker, so that the OPC has <0.04 per cent chlorides and is suitable for
- RMC/structural concrete. To avoid problems of kiln inlet and cyclone jamming caused by SO3 and Cl. Preferably maintain the Hot Meal (2 Cl + SO3) < 3.5. The threshold value for a given plant needs to
be assessed.
If the value goes above the plant threshold value, immediate actions of adding caustic soda for 2 to 3 shifts (in small polyethene bags) should be done to remove the depositions and avoid kiln stoppage.
Effects of some minor constituents on the clinker quality
Effects of ZnO
- Zinc in clinker nearly distributes evenly between the silicates ad matrix phases (with preference to ferrite), trigonal C3S and ß C2S is stabilised by zinc.
- Presence of zinc reduces the amount of aluminates in favour of alumino ferrite.
- Each 1 per cent zinc reduces aluminates by
1 per cent and increases alumino-ferrites by
2 per cent. - Zinc is very effective flux and mineraliser, it lowers clinkerisation temperatures and accelerates lime combination. Knofel reports increased comp. strengths by up to 20 per cent and above at early ages.
Effects of TiO2
- The clinker TiO2 should be <0.7 per cent, it should be noted that TiO2 is a viscous flux like Al2O3 and so for understanding the clinker liquid property for good C3S formation and based on the kiln conditions adjust the clinker Fe2O3 contents accordingly.
- At higher TiO2, contents for improved kiln conditions the clinker Fe2O3 content needs to be much higher which is aggravated if clinker SO3 is higher (which also affects the viscosity of clinker liquid)
- At high total liquid the clinker becomes silica deficient and so free lime tends to be higher (with clinker balls with calcined un sintered material inside)
- In plants that use red mud especially with petcoke due to its higher alkalis, many sources of red muds also have TiO2, the plant should target Al2O3 + TiO2 as the viscous flux and then adjust the clinker Fe2O3 to get good kiln conditions as indicated above. Targeting higher liquid only increases the limestone LSF from mines and also affects clinker grindability.
Effects P2O5 sources
- Many types of agriculture waste, biowastes, phosphate sludge, paint sludges, medical waste, RDF/municipal solid waste, expired detergent, cow dung cakes, etc.
- Under Indian conditions of clinker phase composition, any increase of P2O5 contents can substantially affect clinker quality.
- When higher P2O5 are present, the dicalcium silicate (C2S) is stabilised and inhibits formation of alite (C3S) i.e can decrease the percentage of C3S although bogue may show high percentage C3S.
- When P2O5 present exceeds 0.4 per cent in the clinker it reduces the percentage of C3S by 10 per cent and 1 Day Comp. Strengths by around 5-6 MPa with negative effects on clinker reactivity and setting of cement.
- Use of wastes containing phosphates in controlled manner so that P2O5 in the clinker (maximum limit in clinker is 0.25 per cent) can enhance the use of agricultural waste or use of other wastes with P2O5. It may be noted that in some regions limestone and laterite also have shown P2O5 contents.
- In some plants up to 5 to 7 per cent TSR there is no impact observed on quality or productivity, however as the TSR/AFR percentage is increased say above >8 per cent to 10 per cent, the kiln conditions get frequently disturbed with a very high dust generation and there is a drop in clinker reactivity/quality.
In the plants a judicious study of process conditions and understanding the burnability of kiln feed could help achieve productivity without affecting the clinker quality with increased AFR/TSR.
In one of my consultancy visits to an integrated plant, similar observations as above were reported. In a brainstorming discussions with the plant process, production and QC teams, it was noted that:
- There was substantial variation in calciner outlet/kiln inlet material/C6 material temperature it fluctuated from around 920oC to as low as 860oC, these changes in temperatures nearly corresponded with the fluctuation in percentage of moisture and feed rate of solid AFR (SAFR), RDF and other solid wastes.
- The kiln torque decreased below the desired levels, when the calciner outlet and kiln inlet material temperatures (in this case C6 material temperatures) were less than 890oC and the kiln performance showed high dust recirculation/generation.
- The bi-hourly XRF analysis of clinker showed lower LSF/high free lime. The decrease in clinker LSF was understandable as the SAFR ash showed a higher percentage of ash.
It was decided to collect hot meal samples 900oC to 910oC and 920oC to 930oC and also corresponding clinker samples collected after 40 minutes of the sample collection time of hot meal samples. The hot meal samples were analysed for XRD and clinker samples for XRF (Chemical analysis with free lime) and XRD (for clinker phase formation).
The XRD analysis of hot meal samples is shown in Table 2.
The XRD analysis indicates that:
- The calcination percentage is much higher than the convention DOC of hot meal samples.
- The un-combined CaO decreases with increase in temperature of collected sample.
- The total belite increases with increase in temperature.
It was observed in the plant that when attempts were made to maintain the kiln inlet material temperature at 910oC to 920oC, the kiln torque showed an improvement and the kiln performance improved. The clinker quality showed improvements with lower free lime. However due to the fluctuations in ash percentage content of SAFR the clinker LSF showed lower values during the day. As a corrective action, lime sludge (available at the plant) was added on the SAFR conveyor. These corrective actions helped achieve a consistent improved clinker quality.
About the author:
With an MSc in Organic Chemistry from Jodhpur University (now JNV University), Shreesh Khadilkar joined ACC’s Organic Chemical Product Development Division in 1981 and later transitioned to the Cement R&D Division as a technical assistant. He took over as VP of R&D (Quality and Product Development Division) and retired as Director of the department in 2018, with over 37 years of experience in cement manufacturing and cements/cementitious products.