| 1. |
- Aguirre Castillo, José, et al.
(författare)
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Impact of solid alternative fuels on cement kiln operation
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Cement production involves preparing a raw material mix that is burned at 1450 ⁰C in a direct-fired rotatory kiln to produce cement clinker. In this paper, a stable kiln operation has been referred to as a stable burning and constant high product quality. For the burning, conventional fuels such as coal and petcoke are partially replaced with alternative fuels. Properties of alternative fuels like water content, particle size and higher heating value in RDF (Refuse derived fuel), TDF (Tyre derived fuel) and MDM (Meat and bone meal) disturb the establishment of an ideal flame, which affects the burning and product quality. The chemistry of the fuels also influences the product quality as the ash is incorporated in the cement clinker. Evaporation and heavy condensation of volatiles from alternative fuels hinder the streams of gas and material in the kiln system. This paper summarises some experiences cement manufacturers can consider when operating with alternative fuels.
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| 2. |
- Aguirre Castillo, José, et al.
(författare)
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Phase evolution and burnability of cement raw meal
- 2023
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Ingår i: Advances in Cement Research. - : ICE publishing. - 0951-7197 .- 1751-7605. ; 35:12, s. 577-587
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Tidskriftsartikel (refereegranskat)abstract
- The use of high-temperature X-ray diffraction (HT-XRD) to study the mass transfer of raw meal constituents towards forming clinker phases and the occurrence of free lime (calcium oxide), also known as burnability, was assessed. A measuring strategy with temperature ranging from 1000°C to 1450°C was developed and compared with a conventional burnability method. The free lime determined by the methods showed that HT-XRD produced good results for the evaluation of burnability. In addition, HT-XRD revealed the formation of intermediate phases, providing insight into early reactions in a cement kiln. The particle size of quartz was found to affect crystal expansion of the phase at a high temperature, subsequently affecting the formation of silica polymorphs. The different raw meals used in this study also indicate that the formation of different silica polymorphs affects the formation of C2S. The lack of knowledge regarding the influence of β-quartz on the reduction of free lime is highlighted.
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| 3. |
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| 4. |
- Brihuega, Alberto, et al.
(författare)
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Linearizing Active Antenna Arrays: Digital Predistortion Method and Measurements
- 2019
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Ingår i: 2019 IEEE MTT-S International Microwave Conference on Hardware and Systems for 5G and Beyond, IMC-5G 2019.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we provide a novel framework for efficient digital predistortion (DPD) based linearization of active antenna arrays with multiple and mutually different nonlinear power amplifiers. The proposed method builds on the use of a combined feedback signal essentially characterizing the observable nonlinear distortion at the receiving end. The proposed method is validated with extensive over-the-air RF measurements on a 64-element active antenna array transmitter operating at 28 GHz carrier frequency and transmitting a 200 MHz wide 5G New Radio (NR) waveform. The obtained results demonstrate the excellent linearization capabilities of the proposed solution, which allows for a very efficient implementation in practical systems.
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| 5. |
- Brihuega, Alberto, et al.
(författare)
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On the Power and Beam Dependency of Load Modulation in mmWave Active Antenna Arrays
- 2020
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Ingår i: 2020 50TH EUROPEAN MICROWAVE CONFERENCE (EUMC). - 2325-0305.
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Konferensbidrag (refereegranskat)abstract
- Linearization of active antenna arrays is gaining increasing interest due to their wide applicability in 5G New Radio (NR) networks. As direct access to the output ports of the power amplifiers (PAs) in highly integrated millimeter-wave (mmW) active arrays is difficult, different over-the-air (OTA) digital predistortion (DPD) solutions have been recently proposed. Large majority of such solutions build on the assumption that the nonlinear behaviors of the parallel PA units are independent of the beam direction. However, in this paper, we show through comprehensive OTA measurements on a commercial 64-element active array operating at 28 GHz, that the nonlinear distortion characteristics and the involved load modulation phenomenon largely depend on the beam direction as well as on the considered transmit power, and also that the beam-dependence increases with increasing transmit power. The findings of the measurements are also connected to the state-of-the-art PA models, paving the way towards the development of more efficient DPD solutions and the associated parameter learning methods for mmW active antenna array transmitters.
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| 6. |
- Brihuega, Alberto, et al.
(författare)
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Piecewise Digital Predistortion for mmWave Active Antenna Arrays: Algorithms and Measurements
- 2020
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 68:9, s. 4000-4017
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we describe a novel framework for digital predistortion (DPD)-based linearization of strongly nonlinear millimeter-wave active antenna arrays. Specifically, we formulate a piecewise (PW) closed-loop (CL) DPD solution and low-complexity gradient-adaptive parameter learning algorithms, together with a region partitioning method, which can efficiently handle deep compression of the PA units. The impact of beamsteering on the DPD performance is studied, showing strong beam-dependence, thus necessitating frequent updating of the DPD. In order to facilitate fast adaptation, an inexpensive, noniterative, pruning algorithm is introduced, which allows us to significantly reduce the number of model coefficients. The proposed methods are validated with extensive over-the-air RF measurements on a 64-element active antenna array transmitter operating at 28-GHz carrier frequency and transmitting a 400-MHz 5G new radio (NR) standard-compliant orthogonal frequency-division multiplexing waveform. The obtained results demonstrate the excellent linearization capabilities of the proposed solution, conforming to the new 5G NR requirements for frequency range 2 (FR2) in terms of both in-band waveform quality and out-of-band emissions. The proposed PW-CL DPD is shown to outperform the state-of-the-art PW DPD based on the indirect learning architecture, as well as the classical single-polynomial-based DPD solutions in terms of linearization performance and computational complexity by a clear margin.
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| 7. |
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| 8. |
- Cwik, Katarzyna, et al.
(författare)
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Thermal decrepitation and thermally-induced cracking of limestone used in quicklime production
- 2022
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- To produce quicklime, high calcium carbonate rocks, including limestone, are burned in industrial kilns at 1100–1450 °C. As a consequence of the high temperatures, the carbonate rock can break and decrepitate into fine material, causing operational problems and material losses. In the present paper, an industrial case study on thermal decrepitation was performed on Boda Limestone from the Jutjärn quarry in Dalarna, Sweden. We analyzed 80 limestone samples for thermal decrepitation; furthermore, the correlation with chemical composition was statistically analyzed. The experiments were complemented by a detailed analysis of thermally-induced cracking at a range of temperatures (ambient, 500 °C, 800 °C, and 1150 °C) for two limestone samples with similar chemical compositions but with very different decrepitation behaviors. Decrepitation was analyzed by an in-house method, the chemical composition by XRF, and the thermally-induced cracking was investigated by SEM and image analysis. No strong correlation was found between thermal decrepitation and the chemical composition of the limestone. For the sample with low thermal decrepitation, a dense narrow network of fractures was found after full calcination; however, this network was not observed in the sample with high thermal decrepitation. A plausible explanation for the different decrepitation behaviors is that this fracture network releases internal stress and stabilizes the calcined rock. The obtained results can help in predicting limestone thermal decrepitation, enabling increased resource efficiency in quicklime production.
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| 9. |
- Eriksson, Matias, 1976-
(författare)
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Characterization of kiln feed limestone by dynamic heating rate thermogravimetry
- 2016
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Ingår i: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 147, s. 31-42
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Tidskriftsartikel (refereegranskat)abstract
- Quicklime is a product rich in calcium oxide produced in industrial kilns. The process involves thermal decomposition of minerals with high content of calcium carbonate. The kiln feed properties vary with the geological formation from where the mineral is quarried or mined. Characterization of feed properties is necessary to achieve an optimized kiln production. In this work the decomposition of four different types of calcite ore was investigated by comparing conventional constant heating rate and dynamic heating rate thermogravimetric methods. The conclusion of this work is that the conventional method always "overshoots" the calcination temperature when continuously heating during calcination compared to the dynamic rate method that resembles the kiln by holding temperatures constant during the calcination event. This justifies the used of the dynamic rate method. By a correct experimental parameter setup the dynamic rate method can be adapted for individual kilns and feed fractions, giving new additional value to the kiln operator and increasing the high value use of limestone deposits. This new method to characterize calcination properties of kiln feed materials can be utilized in normal kiln operations and when developing new mixes of different quality limestone. The results show differences when comparing the methods and different materials even though CaCO3 is present only as calcite. In addition, the dynamic rate method is faster than the conventional method. Besides quicklime production the method can also be applied in other industries calcining limestone, such as cement clinker production.
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| 10. |
- Eriksson, Matias, et al.
(författare)
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Characterization of ring deposits inside a quicklime producing long rotary kiln
- 2019
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 33:11, s. 11731-11740
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Tidskriftsartikel (refereegranskat)abstract
- Ring deposits are common problems in rotary kiln operations. The ring is constantly subjected to thermal and mechanical wear counteracting the growth of the ring. If the ring hardens or if the growth of the ring is too rapid the kiln needs to be shut down and the ring removed, reducing the operational time and profitability of the process. In the present study, ring deposits from a limestone fed long rotary kiln producing quicklime was sampled and characterized in detail by SEM-EDS, dynamic rate TG and XRD. This work identifies three hardening mechanisms active in the kiln, an increased densification of the ring deposits near the refractory surface, the formation of calcite and spurrite through carbonation of the ring deposits, and the intrusion of molten fuel ash and product into the refractory, resulting in a strong attachment of the deposit to the refractory surface. The work also concludes that a significant part of the ring deposit has its origin in the fuel ash, contributing to deposit mass and increasing ring growth rate.
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| 11. |
- Eriksson, Matias, et al.
(författare)
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Impact of limestone surface impurities on quicklime product quality
- 2024
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).
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| 12. |
- Eriksson, Matias, et al.
(författare)
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Oxyfuel combustion in rotary kiln lime production
- 2014
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Ingår i: Energy Science & Engineering. - : Wiley-Blackwell. - 2050-0505. ; 2:4, s. 204-215
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this article is to study the impact of oxyfuel combustion applied to a rotary kiln producing lime. Aspects of interest are product quality, energy efficiency, stack gas composition, carbon dioxide emissions, and possible benefits related to carbon dioxide capture. The method used is based on multicomponent chemical equilibrium calculations to predict process conditions. A generic model of a rotary kiln for lime production was validated against operational data and literature. This predicting simulation tool is used to calculate chemical compositions for different recirculation cases. The results show that an oxyfuel process could produce a high-quality lime product. The new process would operate at a lower specific energy consumption thus having also a reduced specific carbon dioxide emission per ton of product ratio. Through some processing, the stack gas from the new process could be suitable for carbon dioxide transport and storage or utilization. The main conclusion of this paper is that lime production with an oxyfuel process is feasible but still needs further study.
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| 13. |
- Eriksson, Matias, 1976-
(författare)
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Sustainability measures in quicklime and cement clinker production
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates sustainability measures for quicklime and cement clinker production. It is the aim of this thesis to contribute to the effort of creating a more sustainable modus of industrial production.The methods used comprises process simulations through multicomponent chemical equilibrium calculations, fuel characterization and raw materials characterization through dynamic rate thermogravimetry.The investigated measures relate to alternative fuels, co-combustion, oxygen enrichment, oxyfuel combustion, mineral carbonation and optimizing raw material mixes based on thermal decomposition characteristics.The predictive multicomponent chemical equilibrium simulation tool developed has been used to investigate new process designs and combustion concepts. The results show that fuel selection and oxygen enrichment influence energy efficiency, and that oxyfuel combustion and mineral carbonation could allow for considerable emission reductions at low energy penalty, as compared to conventional post-combustion carbon dioxide capture technologies. Dynamic rate thermogravimetry, applied to kiln feed limestone, allows for improved feed analysis with a deeper understanding of how mixing of different feed materials will affect the production processes. The predictive simulation tool has proven to be of practical value when planning and executing production and full scale campaigns, reducing costs related to trial and error.The main conclusion of this work is that several measures are available to increase the sustainability of the industry.
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| 14. |
- Eriksson, Matias, et al.
(författare)
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The Effects of Oxygen Enrichment and Fuel Composition on Rotary Kiln Lime Production
- 2015
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Ingår i: Journal of engineering technology. - : American Society for Engineering Education. - 0747-9964. ; 32:1, s. 30-43
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Tidskriftsartikel (refereegranskat)abstract
- This article discusses the impact of oxygen (O2) enrichment on rotary kiln lump lime production. A predictive simulation tool is utilized to investigate the effect of O2 enrichment on the following key parameters of the lime process: kiln temperature profile, product quality, specific energy consumption and kiln production capacity. Three fuel mixes - 100% coal, 90% coal and 10% waste derived fuel oil, and 90% coal and 10% sawdust - are simulated at three oxygen levels. The oxygen levels represent three scenarios: no enrichment (21% O2), moderate enrichment (23% O2), and moderate-to-high enrichment (25% O2). This work is a part of the on-going efforts to reduce the environmental impact of industrial production. Reducing emissions, utilizing biofuels and waste derived fuels, full utilization of raw materials, and energy efficiency are areas of importance for industry. In the long term, oxyfuel technology, i.e., combustion with recirculated kiln gases and pure oxygen, could allow for near-zero emission production and carbon sequestration from industry and power production. In the short term, emission reductions in lime production must be achieved through other means, such as energy efficiency. As a step on the path to a near-zero emission lime plant, this paper describes an investigation of the influence of oxygen enrichment in rotary kiln lime production. The simulated results show positive effects of O2 enrichment, and the simulation results have been used by the kiln operator for in-house training. Results indicate that oxygen enrichment applied to lime production can reduce energy consumption and emissions.
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| 15. |
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| 16. |
- Hökfors, Bodil, 1971-, et al.
(författare)
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Improved Process Modeling for a Lime Rotary Kiln Using Equilibrium Chemistry
- 2012
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Ingår i: Journal of engineering technology. - : American Society for Engineering Education. - 0747-9964. ; 29:1, s. 8-18
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Tidskriftsartikel (refereegranskat)abstract
- This article describes an improved process model for simulation of the manufacturing process of lime in a rotary kiln. The model simulates ideal behavior of complex chemical systems with an assumed homogenous mixing without time-dependent factors. It is a totally predictive model that excludes the empirical parameters. The model is a chemical phase equilibrium model that calculates the final product in a non-equilibrium mode, according to established methods. The phase chemistry is among the most complex found in the literature for lime manufacturing. The thermodynamic data used in the model is based on 11 components (Ca, Si, Al, Fe, K, S, Cl, C, H, O and N). The fuel has an important role in the lime manufacturing process. Special attention is required since it is fed directly into the process via the burner and can influence the process and final product. In the model, the fuel is defined in order to have it behave in a realistic way, and operational data from a full scale lime plant verify the simulation results. The simulated amounts of gas and solids correlate well with operational data. The predicting chemical composition of the product needs improvement by adding more system components and their related compounds to the thermodynamic database. Simulation results from co-combustion of coal and processed waste based fuel oil that it is a versatile tool for predicting product quality and amount, temperature profiles of the rotary kiln, and exhaust gas composition and amount.
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| 17. |
- Hökfors, Bodil, 1971-, et al.
(författare)
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Modelling the cement process and cement clinker quality
- 2014
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Ingår i: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 26:6, s. 311-318
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a recently developed simulation model that can be used as a tool for evaluating sustainable development measures for cement and lime production processes. Examples of such measures are introducing new combustion technologies such as oxy-fuel combustion, using biomass fuel and using alternative materials in the raw material feed. One major issue when introducing process changes is the need to maintain product quality. In some ways, oxygen-enriched air combustion resembles oxy-fuel combustion. The model results were validated and found to be consistent with full-scale operational data for normal running conditions and for a full-scale test with oxygenenriched air. The model shows, for example, that with an additional 1500 m3/h of oxygen, fuel addition at the calciners can increase up to 108% and the raw material feed rate can increase up to 116% for a process with a raw meal feed of 335.5 t/h.
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| 18. |
- Hökfors, Bodil, 1971-, et al.
(författare)
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Simulation of oxy-fuel combustion in cement clinker manufacturing
- 2015
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Ingår i: Advances in Cement Research. - Thomas Telford : ICE Publishing. - 0951-7197 .- 1751-7605. ; 27:1, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- A thermodynamic process model is used as an evaluation tool. Full oxy-fuel combustion is evaluated for circulation of 20–80% of flue gases to the burn zone of a rotary kiln. The full oxy-fuel combustion simulations exhibit altered temperature profiles for the process. With 60% recirculation of flue gases, the temperature in the burn zone is comparable to the reference temperature, and carbon dioxide concentration in the flue gases increases from 33 to 76%. If water is excluded, carbon dioxide concentration is 90%. The partial oxy-fuel combustion method is evaluated for 20 and 40% recirculation of flue gases from one cyclone string to both calciners. Fuel and oxygen feed to the burning zone and calciners are optimised for the partial oxy-fuel scenario. The lowest specific energy consumption is desired while maximising the amount of carbon dioxide theoretically possible to capture. By introducing partial oxy-fuel combustion with 20% recirculation of flue gases in the carbon dioxide string, total carbon dioxide emissions increases by 4%, with 84% possible to capture. Within the limits of the model, the introduction of full oxy-fuel and partial oxyfuel combustion is possible while maintaining product quality. When simulating partial oxy-fuel combustion, the energy consumption will increase even when no power consumption for the production of oxygen is included.
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| 19. |
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| 20. |
- Kumar Wagri, Naresh, 1988-
(författare)
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Assessment of bio-based fuel ash effects on magnesia refractory materials in quicklime production kilns
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Limestone is calcined into quicklime in lime kilns at temperatures above 1000°C. Heat is supplied through combustion inside the kilns, which are insulated with a lining of refractory bricks to mitigate heat loss and to protect the kiln from the hot, chemically aggressive, and mechanically abrasive environment. While magnesia bricks have proven to be effective lining materials, they are still susceptible to extensive wear in lime kilns, especially in the burn zone. Refractory corrosion, in particular, can occur when melted fuel ash infiltrates the refractory materials through pores and small cracks. This resultant wear can lead to high maintenance and operational costs, often due to unplanned kiln shutdowns.To reduce the release of fossil-based carbon dioxide into the atmosphere from lime production kilns, there is a growing interest in introducing bio-based fuels with only relatively minor modifications to the process. Biomass fuels can be sourced from bio-based waste streams from industries or be specifically cultivated for combustion. However, the ash content and properties of bio-based fuels tend to be problematic from an ash chemistry perspective. Therefore, before introducing a new fuel source, it is essential to investigate its potential effects on the kiln lining material. In this thesis work, the interactions between melted olive pomace ash and coal ash with commercially available magnesia refractory materials, primarily composed of periclase (MgO) with minor amounts of spinel (MgAl2O4), were studied. A procedure for quantifying the intrusion depths was described. Refractory samples were exposed to the fuel ashes under a simulated lime kiln atmosphere with high CO2 levels at 1200 and 1400°C for 15 and 60 minutes. Cold crushing strength tests were conducted on refractory samples exposed to coal and olive pomace ash, along with CaO powder, at 1400°C for 96 hours. Additionally, postmortem analyses of spent MgO-based refractory bricks were carried out to investigate their chemical characterization and resistance to slag attack after serving as part of the lining in a quick lime rotary kiln for six months.The morphology and elemental compositions of the exposed samples were examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystalline phases were investigated with powder X-ray diffraction. Thermodynamic equilibrium calculations were performed to further investigate the ash’s melting behavior in contact with the refractories.The results indicated that the potassium-rich olive pomace ash exhibited a greater tendency to infiltrate compared to the silicon-rich coal ash, while the latter formed a glassy melt layer on top of the refractory samples. The ash slags primarily infiltrated through the porous matrix and grain boundaries of the refractory materials. Also, refractory phases were observed in both types of ashes, indicating migration of refractory constituents. K2MgSiO4 phase was found in the olive pomace ash residues on top of the samples, both for the 1200°C and 1400°C exposures. Similarly, Al6Si2O13 phase was dominant in the residual coal ash, in both the 1200°C and 1400°C exposed samples. None of these phases were present in the original ashes.The results of the postmortem analysis revealed that there was no potassium (K) from the fuel ash present on the hot side of the refractory bricks. However, some K was detected in the middle and back parts of the bricks. On the other hand, some phases, possibly connected to degradation, could be found on the hot side of the bricks, where most of the wear was observed.The crushing strengths increased after exposure for all samples, except for those exposed exclusively to coal ash. One possible explanation for this is that the refractory materials exhibited a sintered structure, as a result of their interaction with the ashes and CaO. However, in the samples exposed to coal ash, forsterite (Mg2SiO4) was identified, which can be considered a corrosion product.
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| 21. |
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| 22. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between coal ash and MgO-based refractories in lime kiln conditions
- 2023
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 342
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium oxide (MgO)-based refractories are commonly used in quicklime and cement rotary kilns. At the high temperatures in the kiln burn zone, the infiltration of molten fuel ash into the refractory can occur. Subsequent chemical interactions can cause refractory wear that inflicts high maintenance costs and loss of production. To improve refractory reliability, it is necessary to increase the understanding of the interactions between fuel ash slag and refractory liner materials. Three commercially available MgO-based refractory materials were exposed to coal ash at 1200 °C and 1400 °C for between 15 and 60 min under a CO2-rich gaseous environment. Hot slag from the coal ash infiltrated the refractories and the infiltration depths were estimated with scanning electron microscope with energy dispersive X-ray spectroscopy. Based on detailed elemental and microstructure analyses, the interactions between ash and refractory were examined. Molten silicates infiltrated the refractory through grain boundaries and pores into depths of up to 2.8 mm. Powder X-ray diffraction of the exposed refractory samples indicated that MgO grains reacted with SiO2-containing phases to form Mg2SiO4. This was identified as a corrosion product whose formation was supported by thermochemical equilibrium calculations. Elevated Mg content was found in the ash residue on top of the samples, indicating the dissolution or dislocation of refractory components. In addition, phases such as MgO were identified in the ash residue.
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| 23. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between K-rich biomass ash and MgO-based refractories
- 2023
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 43:8, s. 3770-3777
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Tidskriftsartikel (refereegranskat)abstract
- MgO-based refractories are used in lime kilns to withstand the high temperature and chemical environment. Efforts to reduce CO2 emissions have led to an increased interest to use bio-based fuels as alternatives to traditional fossil sources. The potential for refractory corrosion from a potassium-rich biomass ash was investigated by studying the infiltration of olive pomace ash into magnesia/spinel refractories. Refractory samples were exposed to the ash at up to 1400 °C for 15–60 min in a CO2–rich atmosphere. Molten ash infiltrated the refractories through pores and grain boundaries to a depth of up to 9.6 mm, which was quantified with a new systematic procedure. The phase KAlO2 was identified inside the refractories after exposure, indicating an attack of spinel components by potassium. Phases found in the ash residues also indicated the migration of refractory constituents. Thermochemical equilibrium calculations were also used to investigate the ash/refractory chemistry.
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| 24. |
- Kumar Wagri, Naresh, et al.
(författare)
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Interaction of olive pomace ash and coal ash with magnesium oxide based refractories
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In quicklime production, limestone is calcined at temperatures above 1000°C, depending on the desired product quality. Heat is supplied to the process from combustion inside the kilns that are insulated to reduce heat loss. The kilns are lined with insulating refractory bricks to withstand the hot, chemically aggressive, and mechanically abrasive environment. Magnesia bricks have emerged as well-performinglining materials, but they are still prone to extensive wear in kilns that are operated at higher temperatures. In particular, refractory corrosion can be caused by fuel ash infiltration that results inmaterial wear, which can incur high maintenance and operational costs through unplanned shutdowns of the kilns. At the same time, to reduce the release of fossil-based carbon to the atmosphere, it is of interest to introduce bio-based fuels into the kilns with only relatively small modifications to the process. Biobased waste streams from existing industries are preferable rather than biomass grown with the sole purpose of combustion. The ash content and properties of these types of waste residues do, however, tend to be problematic from a fuel ash chemistry point of view. Therefore, before introducing a new fuel, their potential effects on kiln lining material should be investigated. In this study, the infiltration of olivepomace ash and coal ash into commercially available refractory materials composed of mainly periclase(MgO) with minor amounts of spinel (MgAl2O4) were compared. They were exposed to the fuel ashes under a simulated lime kiln high CO2 atmosphere at 1200 and 1400°C for 15 and 60 minutes. The morphology and elemental composition of the exposed samples were investigated with scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Ash-forming elements infiltrated the porous parts of the materials. The analytical results are complemented with thermodynamic equilibrium calculations to investigate the ash melting behavior. Crystalline phases in the residual ashes were investigated with X-ray diffraction. Refractory phases could be found in both ashes, indicating migration of refractory constituents. Olive pomace ash formed new crystalline compounds together with the refractory components whereas this was not observed for the coal ash, indicating that the former is more of a risk for material failure.
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| 25. |
- Romão, Inês, et al.
(författare)
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Carbon dioxide storage by mineralisation applied to a lime kiln
- 2012
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Ingår i: PROCEEDINGS OF ECOS 2012. - Firenze : Firenze University Press. - 9788866553229 ; , s. 226-1-226-13
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Konferensbidrag (refereegranskat)abstract
- This paper describes a design, for a pilot-scale application, of a two-staged process that is under study at Åbo Akademi University (ÅA), for Carbon dioxide Storage by Mineralisation (CSM). The ÅA route implies the production of brucite (besides Ca- and Fe- based by-products) from a magnesium/calcium silicate rock, using recoverable ammonium sulphate (AS), followed by carbonation of the Mg(OH)2 in a pressurised fluidised bed at ~ 500°C, 20-30 bar CO2 partial pressure. An assessment is reported for operating the CSM process on waste heat from a limekiln (lime production: 210 t/day) in Pargas, Southwest Finland, i.e. without external energy input apart from what is needed for crushing the rock to the required particle size (a few % of the overall CSM process energy requirement) and compressing the flue gas to be treated. Part of the off-gas from the limekiln (CO2 content ~21%-vol) will be processed without a CO2 separation step. The feature of operating without CO2 separation makes CSM an attractive and cost-competitive option when compared to conventional CCS involving underground storage of CO2. An exergy analysis is used to optimise process layout and energy efficiency, and at the same time maximise the amount of CO2 that can be bound to MgCO3 given the amount of waste heat available from the kiln. Also, experimental results are reported for producing Mg(OH)2 (and Fe,Ca(OH)2) from local rock material.
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| 26. |
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| 27. |
- Sandström, Karin, et al.
(författare)
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Ash-Limestone interactions in quicklime production
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Industrially produced quicklime from a coal-fired rotary kiln was analyzed and compared with laboratory-scale studies of ash-quicklime interaction using i) two coal ashes ii) a coal-olive pomace ash mixture iii) olive pomace ash, and iv) a case without any ash representing an electrically heated process. Multicomponent equilibrium calculations were performed in order to predict ash melting behavior.The industrially produced quicklime showed intrusion of mainly Al and Si up to 800 μm into the quicklime in accordance with the expected ash composition of the coal fuel used.Laboratory-scale studies were performed at 1,100°C and 1,350°C followed by SEM-EDX analyses of the ash-quicklime interface to determine changes in quicklime microstructure and depth of ash infiltration.At 1,100°C, coal ashes appeared solid and no distinctive microstructure differences of quicklime was observed underneath the ash-quicklime interface. At 1,350°C, the ashes appeared molten resulting in densification of the quicklime microstructure.Potassium-rich olive pomace ash resulted in a coarsening of the quicklime microstructure, most obvious at 1,350 °C and probably as a result of a carbonate melt intrusion. Coal-olive pomace ash mixture resulted in a less severe quicklime microstructure coarsening. Without ash, the quicklime showed enhanced densification at the higher temperature. The results show that the different elemental compositions in biomass ash and coal ash results in different melting behavior, impurities and quicklime microstructure. This is important knowledge in the transition to a more sustainable quicklime industry.The effect on quicklime microstructure seen in this study is not necessarily translatable to industrial scale and more studies are needed, for example by introducing the complete fuels resulting in a flue gas atmosphere more comparable to industrial conditions.
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| 28. |
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| 29. |
- Sandström, Karin, et al.
(författare)
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Characterization of limestone surface impurities and resulting quicklime quality
- 2024
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 14:6
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Tidskriftsartikel (refereegranskat)abstract
- Quicklime, rich in CaO(s), is generated by calcining limestone at high temperatures. Parallel-flow regenerative lime kilns are the most energy-effective industrial method available today. To prevent major disruptions in such kilns, a high raw material quality is necessary. Under some conditions, impurity-enriched material may adhere to limestone pebbles and enter the kiln. In this study, limestone and corresponding quicklime were analyzed to evaluate the extent and composition of surface impurities and assess the effect on quicklime product quality, here defined as free CaO. This was performed by sampling and analyzing limestone, quarry clay, laboratory-produced quicklime, and industrially produced quicklime with XRF, SEM/EDX, and XRD; interpretations were supported by thermodynamic equilibrium calculations. In the laboratory-produced quicklime, the surface impurities reacted with calcium forming Larnite, Gehlenite, Åkermanite and Merwinite, reducing the quicklime quality. The results showed that the limestone surface layer comprised 1.2 wt.-% of the total mass but possessed 4 wt.-% of the total impurities. The effect on industrially produced quicklime quality was lower; this indicated that the limestone surface impurities were removed while the material moved through the kiln. Multicomponent chemical equilibrium calculations showed that the quarry clay was expected to be fully melted at 1170 °C, possibly leading to operational problems.
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| 30. |
- Sandström, Karin, et al.
(författare)
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Coal ash and limestone interactions in quicklime production
- 2021
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 300
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on results from detailed studies on coal ash and limestone interactions during calcination. Industrially produced quicklime from a coal-fired rotary kiln was analyzed and compared with laboratory-scale studies of surface interactions between two coal ashes and limestone. Exposure tests were performed at 1,100 °C and 1,350 °C, in a high CO2 atmosphere. SEM-EDX analyses of the ash-quicklime interface were performed to detect and quantify changes in microstructure, as well as the depth of ash interaction into quicklime. Stable phases in the ash-quicklime interface were assessed by multi-component chemical equilibrium calculations based on local EDX analysis. The industrially produced quicklime showed intrusion by extraneous elements, mainly Al and Si, up to 800 µm into the quicklime, in accordance with expected ash composition, based on the ash analysis of coal fuel used. In laboratory-scale and 1,100 °C, ashes appeared solid to a large extent, and no distinctive microstructure difference of quicklime was observed underneath the ash-quicklime interface. At 1,350 °C, the ashes appeared molten to a large extent, and the quicklime microstructure was affected compared to at 1,100 °C, resulting in densification. For both temperatures and both coal ashes, the interface reactions reduced the amount of reactive CaO, thereby resulting in a decrease in product quality. The laboratory methodology was shown to be useful to increase mechanistic understanding of the ash-quicklime interactions. The method could be expanded to test other limestone qualities and fuels, e.g. renewable biofuels.
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| 31. |
- Sandström, Karin, 1991-
(författare)
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Effects of impurities on phase equilibrium in quicklime and cement clinker production
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of quicklime and cement clinker are energy-intensive processes resulting in significant CO2 emissions. Fuel switching, electrified heating, and carbon capture have gained attention as means of addressing this. Conventional production processes are direct-fired, meaning that the impurities, which originate from either quarries or fuels, interact with the product, influencing process performance and product quality. The suggested strategies for addressing CO2 emissions will alter the process conditions. For example, introducing electrified heating using plasma would shift the process atmosphere to primarily CO2, possibly affecting volatilisation and recirculation. The overall aim of this thesis was to generate new knowledge on the impact of impurities under process conditions in the context of the shift towards more sustainable quicklime and cement clinker production. Limestone surface impurities and their effects on quicklime product quality were evaluated. Ash-quicklime interactions were studied both on a laboratory scale and using multicomponent chemical equilibrium calculations (MECs). The volatilisation of minor elements in cement clinker production was investigated on a laboratory scale, and using a counter-current MEC-model with both a conventional combustion atmosphere and high-CO2 atmosphere. The detailed analysis of the limestone surface layer showed enrichment of impurities. However, quicklime sampled from a parallel flow generative kiln (PFR) showed low amounts of reactants from surface impurities, which were suggested to contribute to build-ups and increased levels of lime-kiln dust instead. Laboratory-scale studies of coal ash and quicklime interactions and MECs showed that typical cement clinker phases are thermodynamically stable at the coal ash-quicklime interface. Porosity and pore-size distribution were evaluated in pure quicklime samples and quicklime samples exposed to olive pomace, pine bark, and wheat straw ash. Olive pomace ash affected quicklime microstructure severely by increasing porosity and pore size. The laboratory study on the volatilisation of minor and trace elements in cement clinker formation showed higher retention of K, Na, and S in a high CO2 atmosphere, likely explained by low H2O partial pressure and high CO2 partial pressure. Counter-current MECs showed lower enrichment of K, Na, and S in a high CO2 atmosphere.Future work is suggested to investigate the fate of surface impurities entering industrial PFR kilns. Further, the effect of biomass ash on quicklime microstructure should be evaluated in a complete combustion atmosphere, as should the effects of the rolling bed and recirculation of volatile elements in the rotary kiln. The effects of an altered process atmosphere on cement clinker quality and the volatilisation of minor and trace elements are interesting topics for further studies, e.g. in a pilot-scale rotary kiln.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Sandström, Karin, et al.
(författare)
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Solid biofuel combustion or electrification for limestone calcination: Effects on quicklime surface microstructure
- 2022
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 326
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Forskningsöversikt (refereegranskat)abstract
- Net CO2 emissions from the production of quicklime can be reduced by introducing renewable solid fuels or sustainably produced electricity for heating of the process. This paper reports the results of a study examining the effects of new heat sources on quicklime surface reaction products and on quicklime microstructure. Limestone was heated to 1100 °C and 1350 °C in high CO2 atmosphere under three conditions: i) an ash mixture representing conventional coal and a solid biofuel (olive pomace); ii) olive pomace ash, and iii) no ash representing an electrically heated process. The ash-quicklime interfaces of the samples were analyzed for elemental composition and microstructure using SEM-EDX. Multi-component chemical equilibrium calculations were used to assess the stable chemical phases in the interface. Coal-olive pomace ash mixture resulted in coarsening of the quicklime microstructure; this effect was less severe compared to that of pure olive pomace ash. The calculations indicated that the potassium in olive pomace ash was bound to Si- and Al-rich coal ash phases. Exposure to potassium-rich olive pomace ash resulted in severe coarsening of the quicklime microstructure. The difference was most obvious at 1,350 °C, and was probably the result of intrusion of a potassium-rich salt melt. For limestone without ash, the quicklime showed enhanced sintering and reduced porosity at the higher temperature, in agreement with previous studies. Interface reactions and microstructure coarsening, here most apparent for the case with olive pomace, could be problematic in industrial quicklime production since they may contribute to decreased available CaO and reactivity.
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| 36. |
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| 37. |
- Viggh, Erik, et al.
(författare)
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Early formation of belite in cement clinker raw materials with slag
- 2021
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Ingår i: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 33:6, s. 249-256
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Tidskriftsartikel (refereegranskat)abstract
- Analytical methods for characterising cement raw meal during heating in different atmospheres were investigated. The effect of replacing limestone with 10 wt% slag on the formation of incipient belite and precursors of the clinker liquid in the temperature range 600–1050°C was quantified using thermogravimetry, X-ray diffraction and equilibrium calculations. The results showed that when calculating the lime saturation factor, slags were favoured to sand, resulting in lower amounts of quartz and C2S in the samples containing slag than the reference sample. This suggests that silicon dioxide in slag minerals did not react in this temperature range. The multi-component equilibrium results supported the phase formation sequence established. Allowing for the possible kinetic influences the potential solids solutions offered with the software was a valuable asset. The results showed that the effect of using slags to reduce the carbonate and sand content in a raw meal on potential amounts of incipient C2S was negative. At present, more detailed knowledge is needed regarding how blast-furnace slag and basic oxygen furnace slag contribute to the formation of intermediary compounds such as incipient C2S, C3A, C2F and C4AF in the solid phase at temperatures over 1050°C and affect the formation of C3S.
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| 38. |
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