Concrete
Bartin Cimento Meets Guarantees
Published
8 years agoon
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adminIn April 2012 Belim Makina completed the installation of a new 3000 t/d kiln line of Bartin Cimento, Turkey. Just one month later during a 48 hours test run at full production all parameters met the guarantees of IKN, who had provided the design of the complete pyro line. In addition, IKN had supplied key components like ID fan, valves, dampers, kiln drive, girth gear, kiln roller stations and the clinker cooler.
Bartin Cimento, a member of Sanko Holding, in 2010 decided to replace its old wet kiln line with state-of- the-art equipment, in order to increase production to 3.000 t/d and reduce energy consumption to the best possible level. The new line was to be placed adjacent to the existing wet kiln, which had to be maintained in operation. Upon stable production of the new line the old kiln was to be dismantled. The customer as well as Belim Makina, who was selected as EPC contractor, knew IKN well from earlier projects in Turkey and accepted its proposed solution for the pyro line as it promised operational reliability in combination with attractive process parameters. In particular, the decision to select IKN as supplier for the complete pyro line was based on process guarantees and mechanical warranties. The final solution comprised a six-stage LUCY type preheater with inline calciner, a conventional 4.2x62m 3-pier kiln and a Pendulum Cooler, which is known for its linear pendulum suspension and horizontal aeration. The calciner and kiln burners were designed for burning a mixture of pet coke and coal. In addition a modern multi-channel burner was required for the use of heavy fuel oil as an alternative during start-up.
Preheater LUCY
LUCY stands for low under pressure cyclones, a development of IKN’s sister company PSP of Czech Republic. The six-stage preheater tower rises 100 meters above ground level and accommodates amply two top cyclones followed by a single string of cyclones. The raw meal enters the preheater at the riser duct between the two top cyclones of 6 m diameter. It passes the cyclone stages C2 to C6 which are 7.5m in diameter. In line with the LUCY concept, the pressure drops and the corresponding degrees of raw meal separation decrease towards the hot gas inlet. The separated raw meal leaves the cone of the respective cyclone through steep and wide raw meal chutes equipped with flaps designed for continuous release of the meal at minimal counter flow of hot gas.
Calciner
Between cyclones C5 and C6 an inline calciner type KKN-AS with low NOx duct is installed. The preheated raw meal enters the calcining channel just above the location where the burner pipes and tertiary air ducts are attached. The lower part of the calciner has a width of 4.35m square. It ensures an efficient mixing of 4.35 m square. It ensures an efficient mixing of meal and fuel with the oxygen-rich tertiary air. The upper part of the calciner has a diameter of 4.1m. It ends in a swirl head followed by a down comer duct to the C6 inlet. Initial mixing in the bottom part and repeated mixing by the swirl head together with specified retention time care for complete fuel combustion at low oxygen surplus. Parallel to the calciner channel a so-called low NOx duct bypasses oxygen-rich tertiary air to the swirl head so that the calciner duct generates CO, which reduces a good portion of nitrogen oxides summarized as NOx. Combustion is completed in the swirl head and the down comer duct of the calciner in an oxygen rich atmosphere. The calciner burner is designed to burn any combination of petcoke or coal.
Kiln
For the production of 3.000 t/d a 62m long and 4.2m shell inner diameter rotary kiln of 3 per cent inclination supported by three piers was selected. Its diameter and volume allows for a reserve in gas volume along with higher production or along with alternate fuel combustion. The 12 radial roller bearings of the kiln supplied by IKN have spherical seats for the bushes, which tolerate bending of the roller shafts and render overheating less likely. They are equipped with an oil and water distribution system for lubrication and cooling. Temperature of oil and thrust ring are monitored by thermocouples. Adjustment boxes on the frame serve for horizontal alignment during operation. For uniform wear of rollers and tires regular axial shifts of the kiln take place. A shift to its upper position is performed by a single hydraulic thrust roller pushing against the tire of bottom pier #1. The kiln is then allowed to travel down by gravity against the thrust roller, which has meanwhile returned to its lower position. The axial shifts are programmed in regular intervals of 5 – 8 hours. Shell temperatures and tire slips are monitored by scanners. Combined with proven shell materials and statics, forced axial kiln shifts and spherical roller bearings provide optimal protection against mechanical kiln failures.
The inlet and outlet seals are air cooled double lamella types, which are easily maintained.
The 55MW thermal capacity multi-channel burner is designed to burn 100 per cent pet coke, 100 per cent coal or a mixture of both. For start-up heavy fuel oil can be used through a separate fuel lance of 5.280 kg/h capacity.
Cooler
The clinker cooler still is the key to the availability and heat efficiency of the pyro line. IKN’s Pendulum Cooler has an aerated surface of 68m2. Availability is assured by a single stage, single hydraulic cylinder drive located at the front end, by Linear Pendulum Supports (LPS) with no lubricated parts within the confined area of the under grate housing, by minimal number of movable parts of the grate surface, by a slow motion roller crusher capable of handling chunks up to a size passing the kiln burner pipe and by a minimal number of 7 fans connected to 7 compartments of the 21m long grate.
Heat efficiency equal to secondary and tertiary air of high and stable temperature is assured by the clinker inlet distribution system KIDS, which with regard to the width of the 3.2m wide grate generates a clinker bed of uniform resistance against the passage of air, and by air distribution to all clinker voids by gentle horizontal COANDA aeration. Named after Henry Coanda of Romania, this effect creates horizontal air jets which are aerating the clinker bed and by keeping adjacent to the grate surface provide an efficient cooling of the grate itself. Safe cooler operation is simply limited to the observance of a pre-set bed pressure drop of the first air compartment, which is controlled by the speed of the hydraulic cylinder. Rather than close automated control, which is provided as well, IKN recommends a fixed grate speed allowing for a pre-set range of bed pressure variation. In most cases – including Bartin Cimento – fixed grate speed comes along with stable kiln operation.
Thanks to the accuracy of the grate alignment and the minimal gaps between moving and fixed parts of the grate, the amount of clinker falling into the under-grate compartments is minimal. The dust could be evacuated during annual shut downs. For comfort and safety, a tube chain conveyor is installed for the extraction of any clinker dust to the clinker discharge. Typically, the tube extractor is operated once a day for a couple of hours.
Installation
Installation of the pyro line took place from September 2011 until April 2012. During this period IKN delegated various experts for inspection of local manufacturing based on its detail drawings and for assistance of Belim Makina for speedy identification and installation of parts. The cooperation with Belim Makina was excellent as the company had earlier experience with IKN equipment.
A highlight and challenging task was the installation and alignment of the kiln girth gear. Using a crane, both halves of the girth gear were wrapped around the kiln and firmly bolted together. Upon measurements of an acceptable run-out, the crew installed the auxiliary drive, adjusted the rollers to their final position, and finalized the gear alignment. auxiliary drive, adjusted the rollers to their final position, and finalized the gear alignment. For cooler grate surface installation, preassembly tools specifically designed for this project were used, which reduced installation time and which made sure that all parts fitted easily into their position. For LPS alignment a laser-light theodolite was used and the reference points marked on the kiln foundation were protocolled for later verification.
Finally, the six-stage preheater at Bartin is the new landmark which represents the latest technology in cement production in the area.
Commissioning/Testing
In May 2012 the new pyroline was started up. Within the two days performance test the same month all relevant technical parameters were measured during operation and a protocol was signed.
Conclusions
The performance of the new pyro line at Bartin Cimento confirms that the combination of IKN Pendulum Coolers with a state-of-the-art pyro system provides excellent results. The combination leverages the IKN cooler performance to an over-all plant performance which in this case benefits Bartin +Cimento. It confirms further that for new pyro lines and refurbishment projects, excellent process know-how, in-house manufacturing capability coupled with thorough design experience provides superior results in terms of time, efficiency, and cost.
by Frank Lichomski, IKN GmbH, Germany
Design Parameters:
Capacity |
3.000 tpd |
---|---|
Preheater | 6 stage single string type LUCY with inline calciner (KKN-AS) |
Calciner burner | "for 100% petcoke, 100% coal or mixture of both alternatively 100% HFO" |
Kiln | 4,2m x 62 m |
Kiln Burner | "for 100% petcoke, 100% coal or mixture of both alternatively 100% HFO" |
specific heat consumption | <688 kcal/kg |
Cooler | "single stage with single hydraulic cylinder drive suspended by Linear Pendulum Support (LPS) aerated surface: 67 m2 installed cooling air: 2,1 Nm3/kg clinker" |
cooler discharge clinker temperature | 65?C above ambient |
Roller crusher | Roll crusher with 3 rolls, width: 3m |
Exhaust fan | 245 Nm3/h |
Concrete
JSW Cement aims to launch Rs 4,000-crore IPO in Jan 2025
SEBI had put the IPO on hold in September.
Published
2 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
Shreesh 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.