| 1. |
- Akbarnejad, Shahin, 1978-
(författare)
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Mathematical and Experimental Study on Filtration of Solid Inclusions from Molten Aluminium and Steel
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum and steel have been the most produced metal and alloy, respectively, for many years. Their extensive use in various industries, their fundamental role in our everyday life, and their excellent recycling characteristics are the major driving forces for development of their production towards more sustainable processes. A successful integration and application of molten metal filtration from unwanted inclusions in production processes could result in reducing scrap, rework and would provide a cleaner molten metal which could lead to production of metallic materials with enhanced mechanical properties. Filtration of aluminum melts by ceramic foam filters is an established process in aluminum industry. Ceramic filters are also used in steel foundries to remove inclusions from the melt prior to casting to the mold. However, the use of ceramic filters is either limited to specific types of alloys or casts or to specific filters with large pores and openings. As a result, utilization of ceramic filters in the steel industry has limitations in capturing inclusions, where specifically small size inclusions may not be captured. This research work aims at contributing to the global effort in developing the molten metal production processes to become more sustainable and to increase the quality of the final product. To be specific, it is aimed at shedding more light into filtration applications and the use of ceramic filters for removal of solid non-metallic inclusions from molten aluminum and steel. Thus, permeability characteristics of single 30, 50, and 80 Pore Per Inch (PPI) alumina Ceramic Foam Filter (CFF) grades as well as stacks of three 30, three 50, and three 80 PPI alumina CFF grades were both experimentally and numerically obtained and studied. This provides the information needed to estimate the pressure required to prime and/or push the molten aluminum through the filters. The pressure could either be built up by gravitational or other forces. It has been shown recently that it is possible to prime such filters with electromagnetic forces and filter solid inclusions from molten aluminum. Lastly, physical refining of molten steel from solid alumina inclusions through monolithic extruded square-celled alumina ceramic filter was investigated and studied with a developed mathematical Computational Fluid Dynamics (CFD) model as well as the particle trajectories of inclusions in the size range of 1 to 100 [µm]. The experimentally obtained permeability characteristics as well as the obtained pressure gradient profiles of the single 30, 50, and 80 PPI CFFs were compared to previous research findings from the literature. Overall, a good agreement between the current and previous findings was found. It was also shown that fluid bypassing should be avoided during permeability experiments, otherwise deviations as high as 60% may occur. It was also revealed that similar permeability characteristics for the stacked filters, compared to single filters, could be achieved. However, an about three times higher pressure gradient or pressure needs to be applied when using a stack of three identical PPI filters compared to using single filters. The numerical simulations also validated the experimental findings of the permeability experiments. The CFD simulations and particle trajectories of the solid alumina inclusions in molten steel through the monolithic alumina filter revealed that it was possible to capture all particles larger than 50 [µm]. However, it was not possible to capture all particles smaller than 50 [µm] due to the applied simulation approach as well as current simulation limitations in the software.
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| 2. |
- Al-Saadi, Munir, 1965-
(författare)
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Thermomechanical Processing of Nickel-Base Alloy 825
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alloy 825 material was studied using a Gleeble-3800 thermosimulatorby performing single-hot compression experiments.Optical microscopy and electron backscatter diffraction wereutilized to characterize the microstructure. Dynamicrecrystallization is not considerable in the as-cast alloy anddislocation recovery is deemed to be dominant. Based on thisfinding, the effect of adding trace amounts of alloying additionson the mechanical properties of cast alloy 825 was studied, withemphasis on whether or not dynamic recrystallization occurred.The results show that dynamic recrystallization was moreprevalent under all test conditions in samples containing a traceamount of magnesium, but not for the conventional alloy.However, alloying with trace magnesium did not lead to animprovement of the mechanical properties. Instead, processingmaps for hot forging of conventional Alloy 825 were required toidentify optimal working parameters and to achieve dynamicrecrystallization. The hot deformation behavior of cast Alloy 825was characterized by using dynamic materials modelling of hotcompression data. The results show that the maximum powerdissipation efficiency is over 35%. The highest efficiency isachieved in the temperature range of 1100 ℃ - 1250 ℃ and instrain rates in the range of 0.01 ≤ strain rate / s ≤ 0.1. The optimumprocessing parameters for good strain hardening are obtained inthe temperature range between 950 ℃ and 1100 ℃ with strainrates of 0.3 ≤ strain rate/ s ≤ 10.0. In addition, the influence of thedeformation level on the recrystallization and microstructuralchanges in Alloy 825 during hot forging operations attemperatures between 950 °C and 1200 °C was studied. Themaximum yield strength and ultimate tensile strength wereobtained after forging to achieve a true strain of 0.9 were 413 MPa and 622 MPa , respectively, with a ductility of 40%.However, Alloy 825 is often supplied as annealed bars.Therefore, the effect of the forging strain magnitude andsubsequent annealing on the microstructure, strengtheningmechanisms and room temperature mechanical properties wereinvestigated to assess the suitability of current industrialpractice. The results showed that the majority of strengtheningwas attributed to grain refinement, the dislocation densities thatarise due to the large forging strain, and due to solid solutionstrengthening. The results of calculations are in excellentagreement with experimental data, with less than 1% difference.These results can be used by future researchers and industry topredict the strength of Alloy 825 and similar alloys, especially inmaterial after a completed hot forging operation.
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| 3. |
- Carlsson, Leo, 1992-
(författare)
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Applied Machine Learning in Steel Process Engineering : Using Supervised Machine Learning Models to Predict the Electrical Energy Consumption of Electric Arc Furnaces
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The steel industry is in constant need of improving its production processes. This is partly due to increasing competition and partly due to environmental concerns. One commonly used method for improving these processes is through the act of modeling. Models are representations of the reality that can be used to study and test new processes and strategies without costly interventions. In recent years, Machine Learning (ML) has emerged as a promising modeling approach for the steel industry. This has partly been driven by the Industry 4.0 development, which highlights ML as one of the key technologies for its realization. However, these models are often difficult to interpret, which makes it impractical to validate if the model accurately represents reality. This can lead to a lack of trust in ML models by domain practitioners in the steel industry. Thus, the present work investigates the practical usefulness of ML models in the context steel process engineering. The chosen application to answer this research question is the prediction of the Electrical Energy (EE) consumption of Electric Arc Furnaces (EAF). The EAF process was chosen due to its widespread use in the steel industry and due to the difficulty to accurately model the EE consumption using physical modeling. In the present literature, the use of linear statistical models are commonly used even though the EE consumption is non-linearly dependant on multiple important EAF process variables. In addition, the literature does neither investigate the correlations between input variables nor attempts to find the most optimal model with respect to model complexity, predictive performance, stability, and generalizability. Furthermore, a consistent reporting of predictive performance metrics and interpreting the non-transparent models is lacking. These shortcomings motivated the development of a Model Construction methodology and a Model Evaluation methodology that eliminate these shortcomings by considering both the domain-specific (metallurgical) aspects as well as the challenges imposed by ML modeling. By using the developed methodologies, several important findings originated from the resulting ML models predicting the EE consumption of two disparate EAF. A high model complexity, governed by an elevated number of input variables and model coefficients, is not necessary to achieve a state-of-the-art predictive performance on test data. This was confirmed both by the extensive number of produced models and by the comparison of the selected models with the models reported in the literature. To improve the predictive performance of the models, the main focus should instead be on data quality improvements. Experts in both process metallurgy and the specific process under study must be utilized when developing practically useful ML models. They support both in the selection of input variables and in the evaluation of the contribution of the input variables on the EE consumption prediction in relation to established physico-chemical laws and experiences with the specific EAF under study. In addition, a data cleaning strategy performed by an expert at one of the two EAF resulted in the best performing model. The scrap melting process in the EAF is complex and therefore challenging to accurately model using physico-chemical modeling. Using ML modeling, it was demonstrated that a scrap categorization based on the surface-area-to-volume ratio of scrap produced ML models with the highest predictive performance. This agrees well with the physico-chemical phenomena that governs the melting of scrap; temperature gradients, alloying gradients, stirring velocity, and the freezing effect. Multiple different practical use cases of ML models were exemplified in the present work, since the model evaluation methodology demonstrated the possibility to reveal the true contributions by each input variable on the EE consumption. The most prominent example was the analysis of the contribution by various scrap categories on the EE consumption. Three of these scrap categories were confirmed by the steel plant engineers to be accurately interpreted by the model. However, to be able to draw specific conclusions, a higher model predictive performance is required. This can only be realized after significant data quality improvements. Lastly, the developed methodology is not limited to the case used in the present work. It can be used to develop supervised ML models for other processes in the steel industry. This is valuable for the steel industry moving forward in the Industry 4.0 development.
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| 4. |
- Hessling, Oscar, 1988-
(författare)
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Some aspects of hydrogen reduction of iron ore
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fines of hematite and magnetite were studied in the fluidized bed using a pure hydrogen atmosphere in the temperature range of 768 to 888 K. Hematite pellets were studied based on Thermogravimetric Analysis (TGA) experiments using hydrogen atmospheres containing 0–15 % pH2O, in the temperature range of 873 to 1173 K. Thermocouples in contact with the pellet’s surface and embedded in the pellet’s center recorded the thermal gradient in the pellet during reduction. The fluidized bed and the TGA experiments used an alternative method to start the reaction. The furnace was pre-heated with a reactive atmosphere. After this, the reaction was initiated by introducing the sample to the hot furnace, to eliminate the effect of gas dilution during gas switching. After the experiments, Scanning Electron Microscopy (SEM)analyses were employed to study the reduction microstructures. Both types of fines showed similar reduction rates. Fines and pellets showed high initial reduction rates, which increased with increasing temperatures. The reduction rate in the last reduction stage was low for both fines and pellets. An increasing pH2O content in the atmosphere lowered the reaction rate, and theeffect decreased with increased temperature. A difference between the pellet's surface and center temperatures was observed during reduction. The pellet'smacro-pore structure was seen to be unaltered by changes in temperature or atmosphere. However, at 873 K, the iron product microstructure was found to be highly porous. Furthermore, increasing temperatures caused dense iron to form. In addition, when porous iron or iron oxides were observed, increasing pH2O contentsincreased the pore diameter but decreased the pore amount. Pellet properties with varied pellet compositions were also investigated using Cold Crushing Strength (CCS), reduction in a TGA setup, and melting experiments. The composition was not found to influence the mechanical or reduction properties but significantly affected the phosphorus refining during melting.The results showed that a mixed reaction rate control occurred during the early reduction stage for both the fines and the pellets. The temperature differences observed during this reduction stage resulted from a combined effect of heat transfer and an endothermic chemical reaction. The impact of water in the atmosphere influenced the reaction rate through the backward reaction and mass transfer. At 873 K, the retarding effect is mainly caused by the backwardreaction. The results show the late stage of reduction to be primarily diffusioncontrolled. In addition, it should be possible to alter the pellet composition while maintaining pellet properties to increase the usefulness of the pellet.
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| 5. |
- Huss, Joar, 1993-
(författare)
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A study of the autogenous Hydrogen-DRI slag and its impact on the dephosphorization of fossil-free steel at different oxygen potentials
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present study comprises aspects related to the phosphate capacity, the dephosphorization of fossil-free steel, and the utilization of potential by-products. The focus is mainly given to the functions and impact of the autogenous H-DRI slag in the dephosphorization process and the possibility for future slag valorization.At the outset, the applicability of the phosphate capacity concept on systems containing multivalent species is critically examined. For the examination, the variation in the slag structure depending on the oxygen potential was considered theoretically. To support the theoretical consideration, experiments were conducted to illustrate the dependence and to show the effect on the phosphate capacity. The results demonstrated a significant effect of the oxygen potential on the phosphate capacity. Consequently, the use of the concept for multivalent slags falls under serious question.To better orientate the future steelmaking process, the dephosphorization power of slags related to the autogenous H-DRI slag was investigated experimentally. The CaO-MgO-SiO2-FeO system constituted the fully liquid slags, which were equilibrated with liquid iron at 1873 K. Further, the oxygen potential was fixed by closing the system. The dephosphorization power of the autogenous slag was found to be theoretically sufficient to refine the steel made from H-DRI from phosphorus adequately. Thus, it was concluded that the H-DRI slag could be used as a base for the EAF slag to save energy and material.Due to the industrial novelty of the H-DRI material, little is known about the dephosphorization mechanism. Therefore, to facilitate a more efficient process design, the dephosphorization mechanism for H-DRI with different reduction degrees was studied under two different heat transfer conditions. Firstly, by heating and melting H-DRI in a poor heat transfer situation, i.e., in a gas phase at 1873 K, and secondly, under better conditions where the heat transfer is still insufficient for direct melting, i.e., by heating in a liquid slag at 1923 K. The melting process was found to influence the dephosphorization mechanism significantly. In the poor heat transfer situation, the dissolution of the phosphorus-bearing apatite phase was facilitated by the bulk movement of the autogenous slag, which occurred during the melting of the metal phase. In the better heat transfer situation, the bulk slag penetrated the pore network of the H-DRI, a process that was enhanced by the autogenous slag. Since a greater slag mass was available for dissolution, the steel made from H-DRI was dephosphorized already prior to melting.Lastly, the possibility for vanadium extraction from an especially engineered autogenous H-DRI slag was investigated experimentally at 1873 K. For the production of high-quality ferrovanadium alloy, a feasible vanadium extraction requires the fulfillment of two demands. Phosphorus should be predominantly partitioned to the metal and vanadium to the slag. Thus, the experiments featured an acidic slag of the Al2O3-SiO2-FeOx-VzOy system and liquid iron as the metal phase. Also, to fix the oxygen potential, the system was closed. The dephosphorization power of the acidic slags was very low, within the investigated range, while vanadium was mostly partitioned to the slag. The proposed slag system could, therefore, provide an opportunity to utilize an especially engineered autogenous slag for vanadium extraction.
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| 6. |
- Safavi Nick, Reza, 1977-
(författare)
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Modelling Approaches of Multiphase Phenomena Focusing on an Integrated Steelmaking Route
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improvements in numerical methods and developments of computer hardware brought attention to the modelling of metallurgical processes. This has been a critical step in understanding in-furnace conditions throughout the ironmaking and steelmaking process since it is, if not impossible, extremely difficult to conduct measurements during the process.With the introduction of mathematical models, attention has been on the computational fluid dynamics (CFD) modelling of each process to try to shed light on the furnaces’ interior operations. Moreover, most of these processes fall into the category of a multiphase system where different phases of material interact with each other. For example, in a blast furnace shaft, solid particles descend into the furnace while the blast pushes gas through the packed bed; during the desulphurization process, a powder material is injected into the hot metal by means of inert gas; in the ladle station, the steel cleanness is achieved by means of gas and/or induction stirring.Each of these processes has been the focus of a number of studies where the processes have been modelled using different methods namely, fully Eulerian or Eulerian-Lagrangian methods mostly for solid-fluid systems and Volume-of-Fluid (VOF) or VOF-Lagrangian for liquid-liquid or liquid-gas systems. However, there have been fewer studies where the investigations focused on which of these methods is best fitted for a specific process and why. Thus, the current study has been trying to fill this gap to give an overview of the integrated steelmaking route modelling approaches with a focus on the usability of models in the frame of results and computational efforts for the industry.This study goes through the integrated steelmaking route by looking at solid particles flow in the blast furnace, desulphurization of the hot metal produced by blast furnaces and the ladle refining process where a novel stirring strategy is introduced. Then, the focus turns on one of the most common by-products of the steelmaking process namely, the slag. This is due to the fact that the steelmaking slag contains a substantial amount of energy. However, there has been lesser effort in the utilization of such energy. The recent global greenhouse gas reduction initiative has brought significant attention to different aspects of steelmaking processes with respect to socio-economic development in combination with governmental policies. Hence, the study investigates the utilization of deposited energy within the steelmaking slag by means of a heat exchanger to answer the calls for a greener industry.In the end, the current study recommended to use the Eulerian modelling approach to model solid-fluid interactions in a blast furnace and powder injection into a liquid bath in a sulphur refining station. Furthermore, it is suggested that it can be advantageous to use the Volume-of-Fluid modelling approach to model liquid-gas interactions during the ladle refining process. Finally, it is recommended to use the reduced single-phase model for the conjugate heat transfer mdoelling to predict the static liquid energy dissipation in a slag heat recovery station.
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| 7. |
- Vickerfält, Amanda
(författare)
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A study of an autogenous slag for steel production with consideration of possible vanadium extraction
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis discusses the use of the autogenous slag that forms from the residual oxides present in hydrogen reduced iron (H-DRI) pellets during melting. The studies are motivated by a better understanding of how H-DRI affect the steelmaking operations. A possible optimization of the steelmaking process is to recover the vanadium that is contained in the iron ore raw material. Therefore, understanding the role of vanadium during melting of H-DRI is given an extra focus. Taking advantage of the autogenous slag by utilizing its dephosphorization power to a maximum, or using it to extract vanadium, could make an important contribution to the process economics. To assist the developments in these directions, the phosphorus and vanadium partitions between slag and metal (LP and LV) as well as the phase relationship of the autogenous slag were investigated. The partitions were studied by melting H-DRI with reduction degrees between 91 and 99% in closed systems at 1873 K. The obtained LP and LV were in the ranges 8-26 and 501-1994, respectively. The LV values increased with decreased reduction degrees. The values for LP increased with decreasing reduction degrees until a 97% degree of reduction. Further lowered reduction degrees correlated with decreased LP values. The lowest phosphorus levels encountered in the iron (130 ppm) were obtained after melting of H-DRI with degrees of reduction between 94 and 98%. This indicates that the autogenous slag has a potential to make a significant contribution to the phosphorus refining. To find out about the phase relationship in the autogenous slag at 1873 K, small (5 g) samples of synthetic slag were equilibrated with 1 g iron in closed systems. Composition-wise, these slags corresponded to the autogenous slags from H-DRI with 98.4-99.7% reduction degrees. Preservation of the high temperature phase relationship required fast cooling; therefore, the samples were quenched in oil. This was also the reason for using small samples. Spinel, magnesiowüstite and liquid phase were identified as the stable phases at 1873 K. The spinel and magnesiowüstite phases were high in V, while the liquid contained almost no V. Increased FeO-contents (decreased degrees of reduction) correlated with a decreased amount of spinel, an increased amount of magnesiowüsite, as well as a decreased content of V in both phases. To increase the understanding about the phases in the autogenous slag, a sub-system containing MgO and V2O3 was investigated under conditions relevant to H-DRI melting, namely temperatures between 1661-1873 K and pO2 values between 1.75×10-11 and 1.75×10-10 atm. The phase boundaries for the three stable phases MgO-halite, spinel and V2O3-corundum were established. The oxygen potential and the temperature had limited impacts on the phase boundaries for the spinel and V2O3-corundum phases, while the maximum solubility of V2O3 in MgO-halite was affected to a somewhat larger extent. As earlier research has shown that an acid slag could be suitable for V extraction, the pseudo-ternary phase diagram between Al2O3, SiO2 and V2O3 at 1873 K and pO2=3.4×10-11-3.4×10-9 atm was also investigated. 5 different phases were identified, namely mullite, Al2O3-corundum, V2O3-corundum, cristobalite, and a liquid phase. The most significant effect of the oxygen potential was on the invariant point representing double Al2O3 and V2O3 saturation of the liquid. The multivalent nature of vanadium is suggested as the reason for the slight impact of the oxygen potential on the phase diagrams. To understand how the autogenous slag forms from the residual oxides, individual pellets with 90 and 99% reduction degrees were studied during heating to either 1773 or 1873 K. It was observed that the autogenous slag forms before iron melts. The slag likely forms as FeO melts and dissolves the other remaining oxides. Thereby, vanadium is transferred to the autogenous slag. Before iron melts, the movement of the autogenous slag is restricted to the pellet’s pore network. Thereafter, when iron melts, the slag starts to coalesce as well as to floatate. As the autogenous slag may contain solid phases, the effect of the fraction of solid phase on the slags foamability was finally investigated. This was done by measuring the maximum foaming heights of slags containing Al2O3, CaO, FeO and SiO2, reminiscent in their compositions to the autogenous slag. The slag compositions were chosen so that the fraction of precipitated magnesiowüstite phase was the main variable. It was found that some amount of solid phase (1.6 vol%) increased the foaming height by approximately 7%, while ≥8.7 vol% more than halved the foaming height.
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| 8. |
- Liu, Yu, 1990-
(författare)
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Thermodynamics and Kinetics in Metallurgical Processes - with a Special Focus on Bubble Dynamics
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas stirring is commonly used in the steelmaking processes to reinforce chemical reactions, kinetic transfer, and inclusion removal, etc. This dissertation concentrates on multiphase flows with gas bubbling to study fluid dynamics and thermodynamics in metallurgical processes. A study of bubble behavior has been carried out using a multiscale approach as follows: Prototype scale (macro) → Plume scale → Single bubble scale → Reaction scale (micro).Initially, previous works on physical modeling and mathematical modeling in relation to the gas bubbling in the ladle have been reviewed. From that, several aspects that can be improved were found:For physical modeling, such as mixing and homogenization in ladles, the general empirical rules have not been analyzed sufficiently;The mathematical models focusing on inclusion behaviors at the steel-slag interface need to be improved;The phenomena governing the transfer of elements, vacuum degassing, and the combination of fluid dynamics and thermodynamics, such as in desulfurization, need to be investigated further.The kinetics transfer with regards to temperature and element homogenization is one of the most extensive research fields in steel metallurgy. For the analysis on prototype scale, the optimal plug configuration has been studied for a 50t ladle. For stirring using bottom-blowing, a separation angle between dual plugs of 160 degree is mostly recommended, and the optimal dual-plug radial position is around 0.65R. Moreover, the influence of the tracer’s natural convection on its homogenization pattern cannot be neglected, especially for ‘soft bubbling’ conditions using low gas flow rates.Subsequently, in studies of the statistical behavior of gas bubbling in the plume, mathematical modeling using an Euler-Euler approach and an Euler-Lagrange approach have been compared. With respect to the bubble coalescence and breakup, the Euler-Lagrange approach is more accurate in predicting the flow pattern for gas injection using a porous plug. With regards to the effect of plug design on the statistical behavior of gas bubbling, gas injection using a slot plug promotes kinetic reactions close to the open eye due to the concentrated plume structure, and gas bubbling using a porous plug promotes a good inclusion removal because of the increased amount of bubbles.Focusing on single bubble behavior, under the same flow rate, as the top gauge pressure is reduced, the bubble diameter increases and the bubble generation frequency decreases. During the bubble ascent, a large bubble gradually reaches stable conditions by means of shedding several small bubbles. In a steel-argon system, under a flow rate in the range of 5.0(mL‧min-1)STP to 2000(mL‧min-1)STP, the bubble diameter is in the range of 6.0mm to 20.0mm. Under laminar conditions, the maximum bubble width is 65mm when the surrounding pressure is 0.2bar, and the steady bubble width is around 58mm under a pressure of 2.0bar.Finally, a coupling method, named Multi-zone Reaction Model, has been developed to predict the conditions in the EAF refining process. Using a combined injection of O2 and argon, and the same injected mass of O2, the decarburization rate increases due to an efficient kinetic mass transfer of carbon in the molten steel. Furthermore, using CO2 to replace argon, as the ratio of the CO2 content in the injection increases, the maximum hot spot temperature, the increment rate of average temperature, and the decarburization rate decrease dramatically.The research step from multiphase fluid dynamics to its coupling with high temperature thermodynamics is a large advancement in this study. Moreover, the research process using open source software to replace the commercial software is also an important technical route. This can help the transparent development of future modules for reacting flow in metallurgical processes.
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| 9. |
- Persson, Fredrik, 1971-
(författare)
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A Study of Parameters and Properties Influencing the Size, Morphology and Oxygen Content of Water Atomized Metal Powders
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of metal powders by water atomization is a well-established process, which can be used to produce a wide range of particle sizes for different applications. In general, there is a lack of detailed knowledge about what process parameters that affect the powder properties for water atomized metal powders. More specifically, this thesis focuses on the particle size, morphology and oxygen content of water atomized iron powders. A careful control of the particle size distribution is necessary to atomize powders with a high quality and at a low production cost. Demands on the particle morphologies vary depending on the application for the final product. It is important to control both the melt properties and atomizing parameters, to produce powders with an even particle shape and sintered steel components with tight tolerances. The oxidation of the liquid metal should also be as low as possible during the water atomization, to avoid a large amount of harmful oxide forming in the final powder. Pores are generally considered as defects in metal powders. Therefore, the powder porosity should be as low as possible.The main objective of this thesis is to obtain a more in-depth knowledge of water atomization of metal powders, by investigating some fundamental parts of the process. The study investigates how the median particle size (d50 value) for iron powders is influenced by the water pressure, the melt stream diameter, the jet angle, the water level in the atomizing tank, changed configurations of the water jets, superheat of the melt, and the carbon and sulfur content in the liquid steel. Similarly, the thesis also investigates factors that influence the particle shape, porosity and oxidation of water atomized iron powders.Laboratory and pilot experiments show that the effect on the d50 value was large for the water pressure, medium for the viscosity, surface tension and water to metal ratio, and small for the melt stream diameter. Calculations indicate that the water jet angle has a large effect on the d50 value. In practice, this effect cannot be exploited beyond certain limits caused by instabilities in the atomizing system, which occur if the jet angle is too large.The particle size decreases when the carbon and sulfur contents in the liquid iron are increased. This is attributed to decreased viscosities and surface tensions, respectively. An alternative explanation could be that the superheats at increased carbon contents result in a longer time spent in the molten state before the atomization is completed. This may also lead to a decrease in the particle size. Calculations using a developed d50 model estimate that a decreased viscosity from 6.8 mPa s to 4.3 mPa s leads to a reduction in the d50 value by 33%. Similarly, a decreased surface tension from 1840 mN/m to 900 mN m-1 reduces the d50 value by 27%.The distribution of oxides in pilot water atomized Fe-Mn-C powders was determined by using optical and scanning electron microscopy, combined with energy dispersive X-ray microanalysis. The oxygen in the atomized powders was mainly present as thin surface oxide layers, which increase in thickness from 10 nm to 50 nm as the particle sizes increase from 10 microns to 750 microns. Manganese oxides were observed to be unevenly distributed at the surface of several particles, when the alloy contained 0.3 wt.% manganese. Experimental data indicate that between 10 - 20% of the manganese was present as oxides in the powders. However, equilibrium calculations at 1550 °C estimate that only 4% of the initial manganese content remained in the steel after a completed atomization.The sphericity of the atomized powders decreases as the particle size increases. One feasible explanation is that some larger particles are irregular, since they are formed by collisions of smaller particles. Conversely, smaller particles are formed directly from breakups of the melt and are not the product of collisions between droplets. The sphericity of the size fraction 20-45 microns increases as the carbon content in the iron increases from 0.2 wt.% to 4.2 wt.%. The atomized droplets with larger carbon contents spend a longer time in the molten state, which allows them more time to form a spherical shape during the atomization process. The porosity of iron-carbon powders increases with increasing carbon contents in the melt. Dissociation of steam to hydrogen at the melt surface and precipitation of hydrogen pores in the melt were the most likely mechanisms to cause a pore formation in the powders.Keywords: water atomization; metal powder: particle size; oxygen content; particle shape; porosity; steelmaking
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| 10. |
- Ratnasari, Devy Kartika, 1990-
(författare)
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Enhanced Catalytic Pyrolysis of Biomass for High-Quality Biofuel Production
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid increase in energy demand, the extensive use of fossil fuels, and the urgent need to reduce carbon dioxide emissions have raised concerns in the transportation sector, since transportation has been primarily dependent on fossil fuels. Biofuel from biomass can make significant contributions to overcome the expected depletion of fossil fuels and reduce carbon emissions. The availability and wide diversity of biomass resources have made them an attractive and promising source of fuels. Biomass can be converted into biofuel by thermochemical pyrolysis process. Improvements on the pyrolysis process of biomass fuels are needed to obtain a high-quality of bio-oil. Pre-treatment by acid leaching prior to the pyrolysis process is considered to remove Alkali and Alkaline Earth Metal (AAEM) from the biomass, since AAEM adversely affect the catalytic pyrolysis process. Information about biomass pyrolysis kinetics is also important to evaluate biomass as a feedstock for fuel or chemical production as well as efficient design and control of thermochemical processes. Further, the use of H-ZSM-5 and Al-MCM-41 as a mesoporous and a microporous catalyst has been proved to improve the quality of bio-oil. The influence of a catalyst regeneration on the chemical composition of the upgraded oil is also one of the factors pertaining to the catalytic process.In this study, the catalytic pyrolysis kinetics of lignocellulose biomass with a mixed catalyst of H-ZSM-5 and Al-MCM-41 at different ratios for both, un-leached and leached biomass, is analyzed. The derived activation energies are determined based on the solid-state reaction mechanism. Bench-scale experiments have also been investigated to improve the quality of bio-oil, in terms of Organic Fraction (OF), water content, acidity, favorable fractions, as well as gasoline-range chemicals. The effect of a mixed-catalysts and staged-catalysts consisting of H-ZSM-5 and Al-MCM-41 at different ratios in a lignocellulose biomass pyrolysis has been compared. The ratio of H-ZSM-5 and Al-MCM-41 in the catalyst mixtures for lignocellulose biomass catalytic pyrolysis has also been optimized. Further, the effect of sequential catalyst regenerations of H-ZSM-5 and Al-MCM-41 catalyst mixtures on the obtained catalytic pyrolysis products has been analysed.The bench-scale experiments of lignocellulosic biomass pyrolysis and catalytic pyrolysis were performed using a fixed bed reactor equipped with oil condensers and a gas collection sample bag. The quality of bio-oil produced from the thermal pyrolysis of lignocellulosic biomass, catalytic pyrolysis with single catalyst, catalytic pyrolysis with staged catalyst system, as well as catalytic pyrolysis with mixed catalyst system were studied. Later, the catalyst was regenerated several times and the regenerated catalyst was reloaded in the reactor to proceed with the next run. The composition of the derived upgraded pyrolysis oils in relation to the catalyst regeneration was determined.The results from the acid leaching treatment showed that the optimum leaching process was set to 30 minutes, 30°C and 5 wt.% acetic acid in the leaching liquid. This resulted in 59%, 95%, 99%, and 96% reduction degree of Calcium (Ca), Magnesium (Mg), Potassium or Kalium (K), and Natrium (Na), respectively. The use of the acid leaching process as a treatment prior to catalytic pyrolysis is positive, since it resulted in high devolatilization and reaction rate. For the kinetic studies, the second order (F2) mechanism was able to illustrate the catalytic pyrolysis process, proven by the result that the coefficient of determination (R2) was higher than 0.99, which was high compared to other mechanisms.The bench-scale experiments show that that Al-MCM-41 with H-ZSM-5 in the staged catalyst system enhanced the production of favorable compounds: hydrocarbons, phenols, furans, and alcohols. The favorable compounds yield that boosted 5.25-6.43% of that with single H-ZSM-5 catalyst was produced with H-ZSM-5:Al-MCM-41 mass ratio of 3:1 and 7:1. The pyrolysis and catalysis temperature of 500°C with H-ZSM-5:Al-MCM-41 ratio of 3:1 obtained the optimum quality of bio-oil with 11.08 wt.% of Organic Fraction (OF), 76.20% of favorable fractions, 41.97 wt.% of water content, low TAN of 43.01 mg-KOH/g, high deoxygenation, as well as high gasoline-range production of 97.89%.The catalyst mixture of H-ZSM-5 and Al-MCM-41 with a ratio of 7:1 resulted in a 65.75% deoxygenation degree. An organic-rich bio-oil was obtained with 74.90 wt.% of carbon content, 8 wt.% of hydrogen content, 15 wt.% oxygen content, a 0.39 wt.% water content, and a high heating value of 34.15 MJ/kg. The highest amount of favorable compounds among the studied catalytic experiments was obtained with a value of 95.89%. The significant improvement in the quality of bio-oil with the utilisation of H-ZSM-5 and Al-MCM-41 catalyst mixtures was the rise of favorable compounds in bio-oil.The experiments of sequential catalyst regenerations of H-ZSM-5 and Al-MCM-41 catalyst mixtures show that the catalytic activity decreased as the number of reaction cycles increased, albeit an increase yield of Organic Fraction (OF) and a decrease in water as well as coke yields. The HHV of bio-oils decreased. However, the minimum value of HHV (22.42 MJ/kg) after 6 sequential usage was still higher than the value for the non-catalytic experiment (19.55 MJ/kg). The favorable compounds yield, which includes hydrocarbons, phenols, furans, and alcohol, decreased. The dominant components contributed to the yield of favorable compounds were hydrocarbon aromatics and phenols.
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| 11. |
- Safavi Nick, Arash, 1985-
(författare)
-
Pores, inclusions and electromagnetic stirring : Topics from the continuous casting of steel
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with two topics of relevance to the continuous casting of steel,in view of their importance as regards the quality of the final solidified structure.The first concerns the precipitation of gas pores and inclusions in the interden-dritic region of the solidifying metal. Motivated by experimental results thatindicate the formation of pore-inclusion clusters in the final cast structure, a the-oretical model is developed to describe how thus might occur; the model makesuse of the basic principles of fluid mechanics and heat transfer, with asymptoticmethods then being used in order to obtain solutions. In particular, it is foundthat soluto-thermocapillary drift in a direction perpendicular to the direction ofcasting, as a consequence of the dependence of surface tension at the pore-metalinterface on temperature and sulphur concentration, could explain cluster forma-tion. The second is a theoretical study concerning longitudinal electromagneticstirring (EMS), which is often used in the continuous casting of blooms in order toimprove product quality. Via an analysis of the three-dimensional (3D) Maxwellequations for the components of the magnetic flux density, a flaw is found inthe way that the components of the stirring Lorentz force have previously beencalculated; this is corrected and the new results are confirmed by comparison ofsolutions obtained from asymptotic analysis and time-dependent 3D computa-tions using finite-element methods. The analysis identifies the importance of theproduct of the bloom width and the wave vector of the applied field as a keydimensionless parameter.
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| 12. |
- Sidorova, Elena, 1991-
(författare)
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Non-metallic inclusions in pipeline steels and their effect on the corrosion resistance
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focus on investigations of the influence of non-metallic inclusions on corrosion in steel samples taken at different stages of the steel production when producing pipeline steels. The electrolytic extraction technique was used to extract inclusions from these steel samples and thereafter studying them using scanning electron microscopy in combination with energy dispersive microscopy. This approach enabled three-dimensional evaluations of different non-metallic inclusions present in two metal samples of low-carbon Ca-treated pipeline steels. The modification of the inclusion characteristics was investigated and compared for steel samples taken from various stages of the smelting production process. Thereafter, the corrosion resistance of these steels was discussed depending on the characteristics of non-metallic inclusions present in the steel. In addition, this study also presents a new method of soft chemical extraction for qualitative and quantitative evaluations of the initial corrosion processes of a steel matrix surrounding various non-metallic inclusions. The results showed that the initial dissolution of the steel matrix started in areas surrounding CaS inclusions or inclusion phases containing a CaS phase. Furthermore, the results showed that no dissolution of the metal matrix surrounding CaO·Al2O3 and TiN inclusions could be detected. Key words: pipeline steels, Ca-treatment, non-metallic inclusions, electrolytic extraction, corrosion, chemical extraction.
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| 13. |
- Sjöqvist Persson, Eva, 1962-
(författare)
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On the Origin and Distributions of the Inclusions in Production-scale ESR and PESR Remelted Ingots and Materials from Different Ingot Sizes and Solidification Structures
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The study was carried out with the aim to evaluate the origin, morphology, and distribution of the non-metallic inclusions (NMI) in electro-slag remelted (ESR) steels and in electro-slag remelted steels using a pressured controlled inert atmosphere (PESR). In addition to the NMI studies, the solidification structure in different ingot sizes were studied in order to define the influence of the solidification on the NMI characteristics. The steel grade chosen for the studies was a common martensitic stainless steel. The focus is on the origin and the distribution of oxide inclusions with the assumption that sulfides and nitrides are secondary inclusions in remelted material.In order to get a good statistical basis, a large number of SEM samples from different axial positions were taken from both an electrode and several ESR and PESR remelted ingots as well as processed (rolling/forging) materials. The inclusions were investigated by using both two-dimensional (2-D) and three-dimensional (3-D) methods. Especially for steels with a higher cleanliness, as for example remelted steels, a large analyzed area is important in order to get a true picture of the inclusion morphology. As an attempt to localize the origin of the inclusions, a pilot trial using a La2O3 as a tracer in the ESR process slag was performed. To study the influence of the solidification structure on the inclusions, horizontal slice/slices were cut from different positions from the electrode as well as from ESR and PESR remelted ingots of different sizes. Beside inclusions and chemical composition determinations across the diameter of the slices, also the second dendrite arm spacing (SDAS) and the angles of the dendrites towards the axial plane were measured.The result gave rise to a new classification of the inclusions present in ESR or PESR remelted steels, i) Primary Inclusions. They survive from the electrode because they were trapped inside a steel drop or a fallen steel fragment, without having contact with the ESR/PESR process slag. The size depends on the size of the inclusions in the electrode and the size of the steel droplets. ii) Semi-Secondary Inclusions, primary Al-Mg oxides covered by process slag. Normal size class is ≈ < 30 µm. iii) Secondary Inclusions, precipitated during solidification of the liquid steel as a result of the reactions between alloying elements and the dissolved oxygen. Normal size class is < 10 µm.The structure study showed that the transition from a columnar-dendritic to an equiaxial structure (CET) in the center of the ingot have a strong effect on the number and size of the inclusions. As long as the center of the ingot solidifies in a columnar-dendritic manner, the increase of the inclusion number and size is almost linear with an increasing ingot size. However, after the CET transition in the center, the inclusion number and sizes are much larger. For this steel grade, the transition from a columnar-dendritic to an equiaxial is between the 800 mm in diameter (PESR-800) ingot and the 1050 mm in diameter (PESR-1050) ingot. The primary arms growth rate needed for the CET transition is less than 4 x 10-7m/s. In order to undertake the transition, the temperature gradient must be less than approximately 103 °C/m.On the whole, the results illustrated that the overall cleanliness of the electrode (as well as the composition of the inclusions in the electrode) has an extremely large influence on the cleanliness in ESR and PESR remelted steels. The majority of the failure critical inclusions originates direct or indirect from the inclusions in the electrode. Moreover, the solidification structure (ingot size) also has a direct bearing on the inclusion sizes and contents present in ESR and PESR ingots.
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| 14. |
- Wang, Yong, 1990-
(författare)
-
Characterization of Impurities in Different Ferroalloys and Their Effects on the Inclusion Characteristics of Steels
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ferroalloys have become increasingly important due to their indispensable role in steelmaking. As the performance requirements of steel materials increase, it is necessary to have a better understanding of the impact of impurities in ferroalloys on the steel cleanliness. The quality of the ferroalloy will directly affect the quality of the steel. This is especially important when ferroalloys are added during the late stage of the ladle metallurgy process. The goal of the present work is to gain knowledge about various ferroalloy impurities added in the steel production process and to study the influence of ferroalloy impurities on inclusions in the steel. The research work is divided into four main parts.In the first part, previous works on impurities present in different ferroalloys as well as how these impurities can influence the steel cleanliness have been reviewed. The applications of different ferroalloys and their production trends were discussed. The possible harmful inclusions in different ferroalloys were identified. The results showed that: 1) MnO, MnSand MnO-SiO2-MnS inclusions from FeMn and SiMn alloys have a temporary influence on the steel quality; 2) The effect of trace elements, such as Al, Ca contents, should be considered before the addition of FeSi alloys to steel. Also, Al2O3 inclusions and relatively high Al contents are commonly found in FeTi, FeNb and FeV alloys due to their production process. This information should be paid more attention to when these ferroalloys are added to steel; and 3) specific alloys containing REM oxides, Cr(C,N), Cr-Mn-O, Al2O3, Al-Ti-O, and Ti(C,N) have not been studied enough to enable a judgement on their influence on the steel cleanliness. Moreover, the effect of large size SiO2 inclusions in FeSi and FeMoalloys on the steel cleanliness is not fully understood.In the second part, the impurity assessment of 10 different ferroalloys (FeSi, FeCr, FeMo,FeV, FeTi, FeNb, FeW, FeB, MnN, FeCrN) was carried out by using various characterization techniques. The inclusions obtained in these ferroalloys were mostly silica or alumina, or the oxides of the base elements. Also, the main elemental impurities and inclusions were closely related to their manufacturing route. The advantages and disadvantages of different methods were compared, and the detection technology of ferroalloy inclusions was optimized. The results showed that the traditional two-dimensional method on a polished surface cannot always be applied for the investigation of inclusions in some specific ferroalloys. Moreover, the investigations of inclusions on metal surface after electrolytic extraction showed a big potential to use to detect larger sized inclusions. The results on both the film filter and metal surface should be grouped together to obtain more comprehensive information on the inclusion characteristics. Among these ferroalloys, FeCr and FeNb were found to be relatively less studied ferroalloys. Thus, they were selected for further studies.In the third part, the early melting behaviours of FeNb, HCFeCr and LCFeCr alloys during additions in liquid iron was studied. The experiments were carried out by using the"liquid metal suction" technique. Here, the ferroalloy was contacted with liquid iron for a predetermined time and then quenched. The obtained samples were further studied to determine the microstructure and the formation of inclusions. It was found that the mutual diffusion between solid ferroalloy and liquid iron formed a reaction zone. Also, the initial dissolution mechanism of FeNbs alloy in liquid iron was proposed, and the mechanism was controlled by diffusion. The TiOx inclusions in FeNb alloy will partially or completely be reduced due to a reaction with Nb in the reaction zone. The original stable inclusions, such as Al2O3 in FeNb alloys and MnCr2O4 inclusions in LCFeCr alloys can move in this zone and keep their original forms without experiencing any changes. Under the same conditions, the melting speed of LCFeCr alloy is faster than that of HCFeCr alloy. The addition of FeNband FeCr alloys in steel certainly introduces inclusions to steel.In the fourth part, the influence of the addition of LCFeCr alloys on the inclusions in Ti containing ferritic stainless steel was studied on a laboratory scale. It was found that the theMnCr2O4 inclusions in the LCFeCr alloy would react with TiN and dissolved Ti in the Ti containing steel to form TiOx-Cr2O3 system inclusions. In addition, the removal effect of slag on such inclusions was also studied. The results found that the slag addition can modify their-rich inclusions, but that the Ti content in the steel was significantly reduced. Therefore, a proper amount of TiO2 content should be added into the slag to get a low Ti loss in the steel melt, which should be studied further. Therefore, the composition of the steel directly affects the behaviour of the inclusions from ferroalloys in steel.
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| 15. |
- Zaini, Ilman Nuran, 1990-
(författare)
-
Enhancing the circular economy: Resource recovery through thermochemical conversion processes of landfill waste and biomass
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Currently, the global economy looses a considerable amount of potential secondary raw materials from the disposed waste streams. Furthermore, the existing landfill sites that often do not have proper environmental protection technologies pose a long-lasting risk for the environment, which urge immediate actions for landfill remediations. At the same time, the energy recovery from waste through conventional incinerators has been criticized for its CO2 emissions. Alternatively, pyrolysis and gasification offer the potential to recover secondary resources from waste and biomass streams, which can increase the circularity of the material resources and limit the CO2 emissions.This thesis aims to realize feasible thermochemical processes to enhance the material resources' circularity by treating landfill waste and biomass. Correspondingly, fundamental studies involving experimental works and process developments through lab-scale experiments and process simulations are carried out. The thesis is written based on the results from five different studies that cover the investigation regarding the effect of waste/biomass fuel properties on the performance of the pyrolysis and gasification processes, as well as the process development and improvement of thermochemical conversion processes of waste and biomass.The first study investigates the primary fragmentation behaviour of waste fuel pellets during the pyrolysis stage of thermochemical conversion processes. This study shows that the fragmentation degree of waste pellets correlates well with their volatile matter contents. Meanwhile, there is no clear relation between the fragmentation degree and the pellets’ mechanical strength. Generally, due to the high volatile matter content from plastic, fuel pellets from waste tend to fragment into a high number of smaller particles than typical biomass or coal pellets during thermochemical processes. Hence, for some processes, improving the thermal stability of waste pellets is more relevant than improving their mechanical strength. Subsequently, the second study examines the reactivity and kinetics behaviour of waste-derived char during gasification. In general, it is found that the char reactivity is a function of the ash amount and the ratio of inorganic catalytic elements (K, Ca, Na, Mg, and Fe) to the inhibitor elements (Si, Al, and Cl). More importantly, the char gasification test results demonstrated the significance of the waste sorting processes' operating conditions on the thermal behaviour of the waste fuel, especially during the gasification process.Meanwhile, the third study investigates the syngas and tar formations resulting from different interactions between plastic and paper fractions of solid waste. The results show that the interaction between plastic and paper significantly depends on the hydrocarbon chain structures of the plastic polymer. Specifically, the interactions of aliphatic-structured plastic polymers (represented by PE) and paper cause synergistic effects that reduce the tar and increase the syngas yields. Meanwhile, the synergistic effects tend to be less evident in the case of co-gasification between paper and an aromatic hydrocarbon polymer, represented by PS. Based on the results of the previous studies, a co-gasification process of waste with biomass or biochar is proposed in the fourth study. It is found that adding biochar during the gasification of waste could significantly increase the syngas and H2 production to become higher than that of when adding biomass. Synergistic effects are observed in the form of an extensive syngas yield increment and a tar yield reduction, due to the tar reforming reactions over biochar particles. In general, both biochar and biomass additions result in a higher energy yield ratio, suggesting that it could improve the efficiency of the waste gasification.Finally, the fifth study focuses on process simulations and operational cost assessments of co-production of H2, biochar, and bio-oil from biomass. The process simulation study is carried out to evaluate different scenarios for producing biochar, bio-oil, and H2 based on a biomass pyrolysis process coupled with a steam reforming and a WGS process. Based on the calculations of the total operating cost and the potential revenue, it is found that the production of bio-oil is more economically beneficial than the production of H2. The estimated minimum selling price for biochar and bio-oil based on the operating cost alone is within the price ranges of related commodities in Sweden (i.e., charcoal, coal, coke and oil crude). Nevertheless, capital and operating costs for post-processing of bio-oil should also be considered in the future to obtain a more complete economic judgement.
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| 16. |
- Bölke, Kristofer
(författare)
-
IronArc a New Process for Pig Iron Production : A Numerical and Experimental Investigation Focusing on Mixing
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I den här studien så var syftet att undersöka omrörningen och relaterade fenomen i den nyutvecklade IronArc processen. Processen använder sig av gasinjektion genom plasmageneratorer för att smälta och reducera en slagg bestående av järnoxid. Både penetrationsdjupet hos gasen och omrörningstiden undersöktes under olika förhållanden för att de är viktiga parametrar för processen. Undersökningen har gjorts både genom experiment och Computational Fluid Dynamics (CFD).Först utvecklades en nerskalad modell i akrylplast av IronArc pilot reaktorn i skala 1:3, där både penetrationsdjupet och omrörningstiden bestämdes för ett system med luft och vatten genom fysiska experiment. Sedan så skapades en matematisk modell för att beskriva penetrationen av luft injicerat i vatten. Den validerade modellen användes sedan för att beskriva penetrationsdjupet av den injicerade gasen i slaggen för pilotreaktorn. Vidare så utvecklades en ny metod för att bestämma omrörningstiden i pilotreaktorn med slagg som flytande medium. Slaggen undersöktes också både med hjälp av ljusoptiskt mikroskop (LOM) och även genom beräkningar i Thermo-Calc. Detta gjordes för att undersöka huruvida slaggen är i smält tillstånd då processen körs. Ytterligare en matematisk modell utvecklades sedan för att beskriva omrörningen i den nedskalade modellen av akrylplast med luft och vatten. Samma CFD modell användes för att beskriva omrörningen i pilotreaktorn, där modellen validerades mot de tidigare resultaten från de fysiska experimenten med slagg i pilotreaktorn. Slutligen så utfördes ytterligare försök i pilotreaktorn för att bestämma omrörningstiden, men med vatten istället för slagg. Det bör även nämnas att det enbart var luft som injicerades utan att gasen värmdes upp i plasmageneratorn, då vattnet skulle evaporerat om man värmt gasen.Den genomsnittliga omrörningstiden för den nerskalade modellen där luft injicerades i vatten bestämdes till 7,6 s och 10,2 sekunder för respektive homogeniseringsgrad på 95% och 99%. Detta gjorde då ett inlopp användes med ett gasflöde på 282 NLmin-1 användes. Det visade sig att den genomsnittliga omrörningstiden ökade med 15,8% för 95% homogenisering och 17,6% för 99% homogeniseringsgrad då 3 inlopp användes för samma gasflöde. Penetrationsdjupet visade på ett pulserande beteende med ett maximum och minimum värde för respektive undersökt gasflöde.Penetrationsdjupet för experimentet med gas injicerat i vatten kunde beskrivas korrekt med CFD modellen, där Euler-Euler metoden bestämde penetrationsdjupet av experimentet inom en noggrannhet på 86%. Det visade sig också att denna metod reducerade beräkningstiden jämfört med den andra testade Volume of Fluid (VOF) modellen. Penetrationsdjupet av gas i slagg predikterades till 0.3 m, vilket motsvarar radiens läng i reaktorn.Resultaten visade att möjligt att experimentellt bestämma omrörningstiden i pilotreaktorn genom att addera ett spårämne (MnO2 pulver) till slaggen och ta kontinuerliga prover. Mer specifikt så var tiden för att homogenisera badet under 10 sekunder efter att spårämnet tillsatts. Både LOM (Ljusoptiskt Mikroskop) observationerna och Thermo-Calc beräkningarna indikerade att det var rimligt att anta att slaggen är i smält tillstånd under körning.Den predikterade omrörningstiden för den numeriska modellen för luft-vatten systemet var 7,5 sekunder och överensstämmer med experimentresultaten med 1,3%. omrörningstiden bestämdes till 6.5 sekunder för simuleringen av pilotreaktorn och det stämmer överens med resultaten från experimenten i pilotskalan som visade att omrörningstiden var under 10 sekunder. Även resultaten från experimenten då omörningstiden bestämdes 8,5 och 14 sekunder för 95 % och 99% homogeniseringsgrad, då reaktorn var vattenfylld.Denna undersökning av den nya IronArc-processen har gett värdefull information om omrörningen som kan användas i designbeslut för en framtida storskalig järnframställningsprocess.
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| 17. |
- Compañero, Reinol Josef, 1987-
(författare)
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Recirculation of scrapped resources : The role of material information in enhancing the sustainability of recycling
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industries have responded to the climate change problem by positioning their activities as compatible with concepts such as the Circular Economy. Conveying the idea of maximizing and keeping the resources in a manner that aligns with the principles of sustainable development, the endorsements for implementing circularity measures has arguably become a boon for businesses. Firms that have traditionally consumed both primary and anthropogenic resources in the production of materials used in infrastructure, transportation, and other technological requirements are in a special position. On the one hand, their products are needed for societal development. But on the other hand, their activities emit considerable amounts of greenhouse gases.The steel industry is a classic example where material and energy resource savings are achieved when the End-of-Life (EoL) products are recycled. However, these assumed efficiencies are provisional to scrap being a suitable replacement for ore-based resources. The replacement of primary (i.e. purer) - with secondary (i.e. contaminated) as feedstock for production depends heavily on a recycling system’s capability to deal with the complexity of the ferrous scrap streams that society is generating. More specifically, in reference to recovering the material identity through characterization and sorting that lessens or avoids the current practice of either diluting contaminants or compensating for insufficient alloying through addition of primary resources.This present thesis takes a critical look at the use of scrap with the view that recycling is a technical process that is carried out by enterprises. The impression that recycling consequently replaces the use of primary resources is scrutinized, with consideration of scrap as a characteristically appropriate, but innately challenging feedstock to use. Case studies focusing on the Swedish scrap-based production context revealed that the recycling system actors operate and transact on the basis ofscrap’s quality, which in turn was interpreted as being multidimensional and dependent on each actor’s preferences. The alignment of economic and environmental interests connected with scrap utilization was found to be limited, with companies preferring the use of primary resources when scrap is no longer suitable.The idea of suitability was then ascribed to compositional information regarding scrap and tested at two levels: having access to partial or full information. The former is what is achieved through the current scrap handling in the reverse loop while the latter is an idealized situation where the exact chemistry of the scrap is known. An optimization program was then used to simulate steel recycling where the scenarios tested were designed to focus on the response of the production model to the scrap chemistry of the input materials. The results obtained showed an overall decrease in production costs and an increase in the proportion of scrap used in production. In most cases, this was attributed to the flexibility to allocate scrap based on its composition to the closest matching target products.Finally, additional interviews with industry practitioners further clarified established, company-based protocols for dealing with the lack of information and provided insights with regard to opportunities for increasing scrap utilization. An analysis of the responses suggested that there are contextual differences when it comes to practices by each company, and even attitudes, towards anthropogenic resources. Ultimately, the insights from this thesis lend support to the need of enterprises to address the trade-offs related to scrap utilization and lead to enhanced sustainability in steel recycling.
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| 18. |
- De Colle, Mattia
(författare)
-
Experimental studies to overcome the recycling barriers of stainless-steel and BOF slags
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents several studies aimed at improving the recycling of steel slag. The studies are based on a first evaluation of the state-of-the-artof the recycling applications both with respect to their possibilities and limitations. In addition, an analysis that highlights several properties of allkinds of ferrous slags, such as bulk chemical composition and common mineral phases, is presented to aid the discussion. Specifically, the studiespresented in this thesis cover two main topics: a new recycling application for stainless-steel slags and a theoretical study on the hydration offerropericlase, which is a mineral often present in basic oxygen furnace slags. Most of the studies presented in this thesis focus on the exploration of anew use of stainless-steel slags, aimed at increasing their recycling rate. In fact, this kind of materials are the most problematic slags to recycle, asmost are not viable for most of the state-of-the-art applications. Therefore, the potential to use them as a substitute for lime in the neutralization ofacidic waste waters is investigated. The studies cover a wide range of trials, from test performed at both laboratory and industrial scale with acidicwaste waters collected from stainless-steel plants, to more fundamental studies on the dissolution of slag minerals in acid environment. Overall,the substitution of lime with stainless-steel slags is proved to be successful both in terms of the obtained final pH values as well as in terms ofobtaining an efficient removal of metal ions dissolved in waters. In the last part of the thesis, a theoretical study on the hydration offerropericlase is conducted. This study proposes a possible technical solution to reduce the volumetric expansion of steel slags, which containhigh percentages of periclase. Specifically, it is seen that ferropericlase with high percentages of FeO adsorbs less water. Thus, they expand lesscompared to regular periclase. Therefore, the formation of such a phase during the solidification of slag can provide a higher volumetric stability,which is highly beneficial when the material later is employed in outdoors applications
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| 19. |
- Du, Hongying, 1991-
(författare)
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Evaluations of Non-metallic Inclusionsin Ca-treated Steels and Their Effect on the Machinability
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, a considerable development of steel with respect to the performance of steel has taken place, which also has resulted in large challenges to process these steel grades. Therefore, it is essential to make suitable modifications of non-metallic inclusions (NMI) in the steelmaking process and to have a good control of its characteristics to meet the target mechanical properties and to obtain a good machinability. Based on a case of 316L stainless steel trials with a calcium modification to improve the machinability of steel, the influence and contribution of different NMIs on the machinability were discussed. First, based on the Thermo-Calc calculation results with respect to the appropriate range of Ca additions, steel is produced by an additional Ca treatment at the end of the ladle treatment. In order to evaluate non-metallic inclusions and their influence on machinability tests, steel samples were collected from rolled bars produced by the conventional production route (316R) and an experimental trial with Ca treatment (316Ca). The metal chips generated during the machining test were also collected for the evaluation of chip breakability and NMIs characteristics after machining. In addition, the Electrolytic extraction (EE) technology is used to extract NMIs from steel and chip samples. Then, a three-dimensional (3-D) study is performed on the inclusions collected on a membrane filter using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The morphology, size, number, frequency, and composition of non-metallic inclusions are studied. Four main types of inclusions were found in the 316Ca steel: Type I (elongated MnS), Type II (oxy-sulfides with hard oxide cores), Type III (soft elongated oxides), and Type IV (hard undeformed oxides).The results show that the morphologies of NMIs in stainless steel chips were significantly changed after cutting. Overall, three different main shapes of NMIs were found: i) Group I having similar shapes, ii) Group II stretched inclusions having very thin film-like (Group II-a) and fractured stretched morphologies (Group II-b), and iii) Group III brittlely fractured inclusions. The total areas of MnS and SO inclusions in the secondary deformation zone of the chips were significantly increased (by up to 2-3 times) compared to that of the reference steel sample before the cutting test. It was found that the morphologies of NMIs during machining depend on the location in chips, the workpiece material, as well as the applied cutting speed. This results in different temperatures and metal matrix deformation degrees during machining. In addition, the chip breakability and chip tool contact length of the reference steel and the experimental steel were evaluated and compared with the characteristics of NMIs in the two steels. A new weight-measurement-based method was developed. The results show that the 316Ca steel generally has a better machinability compared to the reference 316R steel. However, the chip-tool contact length results show that the modification of NMIs for machinability improvements is only beneficial in some machining processes. The 316R steel was preferred at low cutting speeds, whereas the 316Ca steel was preferred at high cutting speeds. The different characteristics of NMI in the various cutting conditions and materials lead to different behaviors and functions of NMI during processing. Finally, the possible application of PDA/OES in the steelmaking process was also evaluated. This online survey method developed in the industry during recent years provides a high possibility for implementing a rapid screening of the NMI content and shows the potential of establishing an online control of NMI during the processing of steel.
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| 20. |
- Han, Tong, 1990-
(författare)
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Catalytic pyrolysis of lignin to produce fuels and functional carbon materials
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development of renewable energy carriers and green adsorbents is an essential step in creating a fossil-free and toxin-free future of the world. Lignin is the second highest component of biomass and the only renewable resource of aromatics in nature. Currently, around 70 million tons of lignin are produced annually from the pulp and paper industries word-wide, while only 1-2% of them can be upgraded into value-added products. Pyrolysis is one of the most promising technologies for lignin conversion to produce value-added products. After a lignin pyrolysis process, biooil, biogas, and biochar can be produced. Wherein, after upgrading, biogas and biooil can be used as alternatives to fossil based energy carries to produce fuels or chemicals; biochar can be used as carbon source to produce green adsorbents for pollutants removal. This dissertation provides a systematic research focusing on the catalytic pyrolysis of lignin to produce upgraded biofuels and magnetic activated carbons (MACs). First of all, two specific issues i.e. sulfur and melting unique to lignin pyrolysis process are studied to achieve a thorough understanding of the lignin pyrolysis processes. Investigation of sulfur evolution during the lignin pyrolysis process is the study carried out first. Understanding lignin melting characteristics is the study carried out subsequently. Hereafter, in situ catalytic pyrolysis of lignin over low-cost catalysts is studied to produce upgraded biooils. Low-cost catalysts with different textural and acidic properties screening is the study carried out first. Development of a self-sufficient catalytic pyrolysis of lignin process via using activated carbons (ACs) derived from the same lignin pyrolysis process as catalysts is the study carried out subsequently. At last, pyrolysis and subsequent steam gasification of metal dry impregnated lignin is studied to produce MACs and H2-rich syngas. Development of a streamlined process to produce high-quality MACs for phosphorous adsorption is the study carried out first. Pyrolysis and subsequent steam gasification of metal dry impregnated lignin to co-produce MACs and H2-rich syngas is the study carried out subsequently.The study of sulfur evolution during the lignin pyrolysis process implies that sulfur-containing radicals are more likely to combine with other small radicals during a fast pyrolysis process. As a result, the main detected sulfur-containing compounds are small molecular gases or liquids with low boiling points and the main compounds in liquid phase are sulfur-free. The study of lignin melting characteristics at pre-pyrolysis temperature implies that the degree of cross-linked of the lignin structure determines its melting characteristics. Lignin extracted from pulping process has a less cross-linked structure. Therefore, it melts and softens to a flow state after a glass transition. Lignin extracted from hydrolysis process has a more cross-linked structure. Therefore, it does not melt but rather decompose after a glass transition.The study of low-cost catalysts with different acidic and textural properties screening for in situ catalytic pyrolysis of lignin implies that the use of only commercial AC as a catalyst induces the enhanced yield of monocyclic aromatic hydrocarbons (MAHs) among all low-cost catalysts. Bentonite and red mud catalysts have strong surface acidity but poor porous properties. This determines that produced reactive intermediates are easy to repolymerize to form char or coke without the blocking effect of pore wall. Commercial AC has an abundant porous structure as well as a surface acidity with a certain strength. The produced reactive intermediates could be isolated by pore walls and therefore induce the of MAHs production. A subsequent study of in situ catalytic pyrolysis of lignin over ACs from the same lignin pyrolysis process implies that the use of only AC that has more mesopores than micropores as catalyst could induce a significant decrease of the tarry oil yield and a significant increase of the phenols concentration in aqueous and liquid phase oils. The diffusion efficiency of the reactive intermediates determined by pore size is supposed to be the most crucial parameter that determines the catalytic performance of ACs. The pore sizes of mesopores are much bigger than the sizes of reactive intermediates. Therefore, these pores could allow most of the reactive intermediates to diffuse quickly and to react within their pores.The study of the streamlined MACs production process development implies that iron species can be embedded into a carbon matrix via a lignin melting process. After the pyrolysis/carbonization of lignin and FeSO4 mixture under a nitrogen atmosphere, FeSO4 is decomposed and further reduced to form hagg iron carbide, which is buried into carbon matrix of biochars after a lignin melting. During subsequent steam gasification/activation process, iron species are gradually exposed from the carbon via the pore drilling and widening effect of steam. At the same time, the bare part of iron species are oxidized by steam to form magnetite. The maximum phosphorous adsorption capacity of produced MAC sample calculated using the best-fit Langmuir-Freundlich model is estimated to be 21.18 mg P/g. Further study of pyrolysis and subsequent steam gasification of metal dry impregnated lignin to produce MACs and H2-rich syngas implies that during the pyrolysis of FeSO4 impregnated lignin process, H2 is produced via the catalytic cracking of the volatiles. During the subsequent steam gasification of solid residues, H2 was mainly produced via the steam carbon reactions and the steam gas shift reactions. The maximum overall H2 yield of the integrated process is as high as 42.73 mol/kg-lignin. Also, approximately 70% of phosphorous in real domestic wastewater can be adsorbed by MACs produced from the same process after a treatment for 2 hours.
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| 21. |
- Jagodzińska, Katarzyna, 1990-
(författare)
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Energy and material recovery from high-ash waste through pyrolysis
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Undoubtedly, the past practices of profit maximisation by all means, which fuelled swift industrialisation and urbanisation, left behind a legacy of non-sanitary old landfills polluting the environment. These, together with active landfills supplied with tremendous streams of waste produced annually, are a loose cannon calling for action. Specifically, this action is the transition to resource- and energy-efficient economy model – the so-called circular economy.The circular economy approach includes the closing of material loops by both: i) the recycling of pre- and post-consumer residues and ii) the mining of existing landfills, treated as material stocks. Following this, the possibility of energy and material recovery from two types of high-ash waste was investigated within this thesis. The first type of waste is a fine residue from the shredding of the mixture of industrial and municipal metallic waste with end-of-life vehicles (the so-called 'shredder fines'), which represents the aforementioned pre-and post-consumer residues. The second type of waste is excavated waste from an old landfill, and its recovery falls within the latter way of closing the material loops mentioned above.For the purpose of energy and material recovery, the aforementioned waste was subjected to thermochemical processes, namely pyrolysis and pyrolysis with in-line catalytic decomposition of the produced pyrovapours (volatile pyrolysis products). This thesis consists of four studies on that matter.The research within this thesis started with the characterisation of excavated waste fractions to preliminarily assess their potential further applications. The fractions are characterised by significant contamination with heavy metals (mainly Hg and Pb) and chlorine. Furthermore, they are characterised by highly heterogeneous compositions, reflected in a high complexity of the formed pyrovapours. However, in order to maximise the fractions' utilisation ratio, their collective pyrolysis in the form of refuse-derived fuel (RDF) was proposed for further studies.Following the above, the second study performed within the thesis aimed at the characterisation of the products from excavated RDF pyrolysis. The pyrovapours obtained at 500°C and 600°C showed potential for further catalytic upgrading to higher-quality products. Given the above, a study on the in-line catalytic decomposition of the pyrovapours from excavated RDF pyrolysis was performed. The process was aimed at the production of a H2-rich gas along with carbon nanotubes (CNTs). The study investigated the influence of the catalyst composition, its synthesis method, and catalytic bed temperature on the H2 and CNTs yields. Eventually, the bimetallic Fe-Ni/Al2O3 catalyst prepared using the sol-gel method showed the best performance as it tripled the H2 conversion rate (in comparison to the case without using a catalyst) and yielded 76 mg/gsample_daf CNTs of promising characteristics. Nevertheless, further research on this process is necessary to optimise it and to assess its feasibility subsequently.The final study included in the thesis focused on enhancing metals recovery from shredder fines by subjecting them to torrefaction (low-temperature pyrolysis). The process results in partial decomposition of the so-called 'fluff' (textiles fibres with plastic, wood and rubber particles in which metal particles are entangled), which interferes with the sorting techniques. Therefore, torrefaction seems to be a promising way of liberating metal particles from shredder fines so that metals can be recycled.
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| 22. |
- Jarnerud, Tova, 1976-
(författare)
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Application of Wastes from Pulp and Paper Industries for Steelmaking Processes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the past several years, considerable efforts have been made to develop a more circular economy. The ambition to reuse, remanufacture and recycle materials is of great significance for the establishment of a sustainable society. An extended longevity of materials helps to decrease the amount of wastes in landfills, as well as to reduce the mining of natural assets. Pulp and paper industries and steel industries are two of the largest basic industries and export industrial sectors in Sweden. The pulp and paper industries generate large amounts of organic and inorganic wastes. A significant part of these wastes ends up in landfills. The deposit of wastes in landfills is becoming more costly and more challenging to employ, due to stronger regulations and demands with respect to the environment. During Electric Arc Furnace (EAF) and Argon Oxygen Decarburization (AOD) stainless steelmaking operations, burnt lime (primary lime) is charged together with other slag forming components in the furnace or converter to obtain a specific basicity of the slag and to attain purification from undesired elements by chemical reactions between the steel and slag. In blast furnace (BF) operations, fossil carbon is charged in the form of coke and injected as powder to provide heat to melt the iron ore and to reduce the iron oxides by separating iron from oxygen. The use of this primary lime and fossil carbon does not comply with the closing the loop idea that is being prioritized in modern society. This thesis presents results from preliminary experiments for examining the replacement of primary lime with recovered lime from pulp and paper production waste as slag formers in EAF and AOD converters and as neutralizing agents for acidic wastewaters, as well as hydrochar from organic sludges as a carbon source in BF. The gained results showed a possibility of partly replacing primary lime with recovered lime in the EAF without negative effects on the process. In the AOD process, the use of recovered lime didn´t show any negative effects on the decarburization process nor on the reduction process. Moreover, the desulphurization function was similar when using recovered lime compared to when using the primary lime. However, the P content in the metal increased slightly. Thus, the replacement ratio of the recovered lime will be limited by the acceptable P level in the final steel due to higher P content in the recovered lime materials from pulp and paper mills compared to that in primary lime. Furthermore, the obtained results of laboratory-scale trials using recovered lime materials as neutralizers showed that they can be successfully used instead of primary lime to significantly raise the pH level of the wastewaters as well as to decrease the concentrations of Cr, Fe, Ni, Mo and Zn. Also, the results from the industrial-scale experimental trials using hydrochar derived from mixed organic biosludge and from green waste showed that the production rate of hot metal, amount of dust, fuel rate and amount of injected coal, amount of slag, contents of FeO in slag and %C and %P in the hot metal of the BF process were very similar compared to the reference periods. Thus, it was proven that hydrochar derived from various types of organic residues could be used for metallurgical applications. However, the replacement ratio was very low and longer trial campaigns are needed to obtain more certain results. Moreover, it was revealed during this study that slags from AOD converters can be used as binding agents for briquetting of these recovered lime materials. In summary, these results show that waste materials/by-products from two of the most important Swedish base industries can unite two major industrial sectors in a circular symbiosis towards obtaining a more sustainable future.
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| 23. |
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| 24. |
- Wang, Shule, 1994-
(författare)
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Pyrolysis of Biodegradable Waste for Negative Carbon Emissions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bioenergy with Carbon Capture and Storage represents a crucial technology that enables an energy production with negative carbon emissions, which is needed to achieve global climate goals. Appropriated management of biodegradable waste, including biodegradable lignocellulosic waste, sewage sludge, organic fraction of municipal solid waste, can make this contribution. The implementation of pyrolysis process is able to produce biochar, liquid and gas product from biodegradable waste. Based on the pyrolysis technology, a sustainable management of biodegradable waste for negative carbon emission is proposed in this work. The proposed novel process combines an anaerobic digestion, pyrolysis of the digestate following by catalytic reforming the pyrolytic vapor, then methanation of the reforming gas, separating the stream of CH4 and CO2. The storage of separated CO2 streams and biochar can be considered as negative emissions. Furthermore, the pyrolysis behaviors of the solid residue, which was produced from hydrothermal carbonization pretreatment of biodegradable wastes, are investigated. The pyrolytic liquid was further upgraded to a higher quality product with a less oxygen content, a higher calorific value by using ex-situ and in-situ hydrogen donors. Carbon stability of the pyrolytic biochar, which is one of key parameters to assess the biochar as carbon sink, was evaluated by using the accelerated oxidation method. Finally, energy and mass balance on the proposed process was obtained. The pyrolysis behavior of hydrothermal carbonization-treated sewage sludge digestate, and paper sludges were investigated. Thermogravimetric analysis, Py- Gas chromatography–Mass spectrometry and bench-scale experiments were employed to fulfil this objective. The thermal degradation behavior of these two feedstocks was investigated. Initially, the compounds in the pyrolytic vapor were identified. Thereafter, the pyrolytic product from the bench-scale experiment was characterized. It was found that the pyrolysis reaction of both feedstocks was a two-stage reaction. The organic fraction with a higher heating value around 28.47 to 38.46 MJ/kg was produced from the pyrolysis of hydrothermal carbonization-treated biodegradable waste. More organic fraction can be produced from the pyrolysis of the paper sludge than that from sewage sludge digestate. It was also found that the fixed carbon content in raw materials is difficult to be determined by using the standard method due to the ash oxidation behavior in such materials. Therefore, a method to determine the sample's fixed carbon content without affected by the ash oxidation behavior was developed. Introducing hydrogen donors to upgrade the pyrolytic liquid products for a higher quality product with a lower oxygen content and a higher calorific value is investigated. The H2 was used as an ex-situ hydrogen donor in the lignocellulosic waste pyrolysis in both non-catalytic and catalytic cases. The catalyst used in this study was a commercial HZSM-5, catalyst with a strong selectivity of aromatics. The hydrogen consumption during pyrolysis in the H2 atmosphere was indicated by experiments. The gas and liquid production were promoted while the biochar yield was suppressed in the presence of the H2 atmosphere. However, the presence of an H2 atmosphere was found to increase the acidity of the HZSM-5 and enhance the production of polyaromatics during the pyrolysis process. Further, the study using the sewage sludge digestate as an in-situ hydrogen donor to pyrolysis of lignocellulosic biomass obtained from the salix family was investigated. The sewage sludge digestate was premixed with salix in five blended ratios and pyrolyzed in a bench-scale reactor. The composite of 75% sludge digestate and 25% salix presented the highest mass and energy yields of the organic fraction in the liquid product. The yield of biochar was suppressed in this copyrolysis. The synergistic effect between the sludge digestate and salix was studied with respect to reaction mechanisms, carbon number distribution of the compounds in organic fraction, and biochar stability. The competition reaction between the short-chain carboxylic acid from salix pyrolysis and a long-chain carboxylic acid from digestate pyrolysis was one of the main reasons for the synergistic reaction regarding the composition of the organic fraction. This competition reaction results in a higher amount of long-chain carboxylic acid esters and N-heterocyclic compounds, a lower amount of the long-chain nitriles in the organic fraction produced from copyrolysis compared to it from individual pyrolysis. The stabilities of the biochar products from the copyrolysis of sewage sludge digestate and salix, were determined by using the accelerated oxidation method. It was found that the biochar stabilities are promoted by this copyrolysis. The nitrogen yield in the biochar product was also enhanced by the copyrolysis process. The proposed CO2 negative process was modelled using the process simulation software, and the modelling results were validated by using an experimental data. The pyrolysis temperature and dewatering technology were used for sensitivity analysis. In this process, methane was chosen as the final product. Pyrolytic biochar and compressed CO2 was captured and stored as the negative carbon emission. It was found that for 1000 kg of dry matter digestate, one can obtain 151.4 kg CH4 in a purity of 96 vol%, 304.5kg compressed CO2, and 80.8 kg biochar. The latter two are equal to 355.64 kg negative CO2 emission.
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| 25. |
- Wei, Wenjing, 1987-
(författare)
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Decarbonising the Stainless Steelmaking through Alloy Solutions
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To reach the goal of the Paris Agreement, the reduction of greenhouse gas emissions (GHG)is becoming one of the most pressing issues in the world today. Unlike most other sectors, thestainless steel industry has a significantly higher burden from upstream emissions comparedto operational emissions. The main contributing source of these upstream emissions instainless steelmaking is the use of alloy materials (Mo, Ni, Cr, etc.), accounting forapproximately 70% of the total stainless steel’s CO2 emissions. The thesis provides insights into the decarbonisation of stainless steelmaking through alloy solutions. In order to producea sustainable stainless steel product of high quality, it is necessary to establish decarbonisationstrategies using an interactive optimization framework that considers material, process, andquality factors.First, this is to select low-carbon footprint alloys, which helps to reduce the overall upstreamemissions of the stainless steel production process. In Part I-Material Selection Optimization,the production of FeMo, Ni alloy, and HC FeCr has been assessed through LCA based energyand GHG emissions. The inventory data is calculated by using a static thermodynamic modelbased on mass and energy conservation. The results reveal the following low-carbon alloyoptions: 1) FeMo produced as a co-product from copper mine; 2) nickel metal processed withsulfide ore using a flash smelting process and 3) HC FeCr produced using a closed submergedarc furnace with preheating.The next step is to set up a reliable process model to predict the desired alloy content forprocess optimization. This enables a reduction of the waste, GHG emissions and productioncosts. Nitrogen, as an important alloy element in stainless steel, is normally added by injectingnitrogen gas into the AOD process. In Part II-Process Parameter Optimization, a timedependent thermodynamic model, TimeAOD3TM, was proposed to predict the dissolvednitrogen content in the bath. The model provides good predictions of the nitrogen contentduring the reduction and desulfurization stages. The higher deviation between modelling andmeasurement during the decarburization stage is mostly due to the limitation of the one-cellmodel in which the same total pressure is used for the nitrogen and carbon equilibriumreactions. The improvement of the model requires implementing different gas pressures tocalculate the equilibrium reactions of N and C, as well as considering the kinetic mechanismsof the reactions. To further improve the modelling accuracy of nitrogen, the blown gas mixturein the AOD nozzle was studied by using a kinetic CFD model. The results show that thepressure at the inlet is a crucial parameter for controlling the process, as it impacts theproperties of the gas that is released from the nozzle, including its velocity, density,temperature, flow rate and outlet pressure. With the proposed model, it is possible to capturethe relevant gas properties under a variety of different conditions. Moreover, the predictionof the gas flow’s critical state allows for optimizing the blowing process, which can helpreduce the resources (material, energy) usage and lower the environmental impact.The final step is to ensure that the final steel product meets the requisite quality standards,including the material properties and the environmental impacts. In Part III-Steel QualityOptimization, these quality-related performances are optimized through a statisticalmodelling approach, named a Taguchi based Grey Relational Analysis. This approach wasused to rank multiple performances and to determine the optimal steel design related to alloycontents. The results show that nitrogen plays the most important role in determining thesteel’s combined performance, because it appears in the empirical equations for the pittingcorrosion resistance, proof strength, and tensile strength. Also, the coefficient of nitrogen ismuch higher than the coefficients of other alloy elements, which can significantly influencesteel performance. In addition, the optimum steel designs consist of high contents of nitrogen,chromium, molybdenum, copper and low contents of nickel.The findings of this research provide the fundaments for decarbonisation of the stainlesssteelmaking, highlighting the need for a holistic approach that considers material, process,and product quality in reducing carbon emissions.
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| 26. |
- Wei, Wenjing, et al.
(författare)
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Energy Consumption and Greenhouse Gas Emissions of High-Carbon Ferrochrome Production
- 2023
-
Ingår i: JOM. - : Springer Nature. - 1047-4838 .- 1543-1851. ; 75:4, s. 1206-1220
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- This work presents a process model developed based on mass and energy conservation to assess high carbon ferrochrome production from cradle to gate through four supply routes: (1) a conventional submerged arc furnace (SAF), (2) a closed submerged arc furnace with preheating (CSAF+PH), (3) a closed submerged arc furnace with 60% prereduction (CSAF+PR60%) and (4) a direct-current arc furnace (DCAF). The energy requirements are between 40 and 59 GJ/t FeCr (74–111 GJ/t Cr), and the greenhouse gas (GHG) emissions range between 1.8 and 5.5 tCO2-eq/t FeCr (3.3–10.3 tCO2-eq/t Cr). The upgrading of coal-powered SAF process to a closed furnace CSAF+PH and CSAF+PR60% contributes to an emission reduction of 23% and 18%, respectively. Moreover, the use of hydro-powered electricity leads to a further emission reduction of 68% and 47%, respectively. For CSAF+PR process, the GHG emissions can be reduced by 14% when increasing the pre-reduction ratio from 30% to 80% and decreased by 10% when charging hotter feed from 100 °C to 1000 °C. The proposed process model is feasible in generating site-specific inventory data and allowing for parameter studies as well as supporting companies to improve the transparency of the environmental performance in the FeCr value chain.
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| 27. |
- Wen, Yuming, 1994-
(författare)
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Towards a Sustainable Biomass and Waste Refinery Based on Pyrolysis Combined with a Pretreatment Process
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Some of the naturally accumulated biomass and the massive production of waste by human activities have caused serious environmental problems. The degradation of biomass and waste is one of the main greenhouse gasses (GHG) emission sources. Pyrolysis is a technique that can convert the organic feedstock into char, bio-oil, and gas at 350 - 800 °C and in the absence of oxygen. The diversity of the pyro-products makes pyrolysis one of the most promising techniques for biomass and waste refineries. One of the main challenges of the technique is that the unfavorable physical and/or chemical properties of the feedstock would increase the energy and cost required for the whole refinery process. Combining feedstock pretreatment with a pyro-refinery has the potential to make the entire process more efficient from a cost, energy, and climate perspective. In this thesis, the performance of the peat moss pyrolysis is firstly investigated. It was found that it has a potential to convert peat moss into fuels through pyrolysis. Thereafter, beach-cast seaweed is further considered as a feedstock for the process, which is a high-ash content biomass. Three refinery processes were designed and simulated based on the pyrolysis results. Results showed that it was necessary to have a washing pretreatment for the beach-cast seaweed pyro-refinery. The implementation of washing pretreatment could decrease the direct energy for the whole process from 1485.8 to 1121.0 MJ for treating one ton of dry beach-cast seaweed. The further life cycle assessment (LCA) analysis showed that using the pyro-refinery process with washing pretreatment to treat one ton of dry beach-cast seaweed for the electricity production had the lowest cumulated energy demand (CED). Specifically, it has a value of -3.0 GJ and the lowest global warming potential within a 100-year time frame (GWP100) with a value of -790.9 kg CO2eq compared to the other scenarios of producing liquid biofuel and syngas. Digestate from anaerobic digestion (AD) requires proper treatment. The third work of this thesis compares the pyrolysis behavior of the organic fraction of municipal solid waste (OFMSW) and its digestate. It was found that the AD process could decrease the pyrolytic activation energy of OFMSW. Due to digestate’s higher ash content, the char yield rate of digestate was higher than that of OFMSW. On the other hand, the yield rates of bio-oil and gas of OFMSW pyrolysis were higher than that of its digestate. The moisture content of the digestate is hard to be removed by traditional mechanical dewatering techniques due to digestate’s hydrophilic properties. Thus, the use of a pretreatment combined with hydrothermal carbonization (HTC) and mechanical dewatering has the potential to contribute to the digestate pyro-refinery. In the last work, the effect of HTC on the kinetics and thermodynamics of the agricultural waste digestate (AWD) pyrolysis was investigated. It was revealed that the HTC pretreatment could decrease the pyrolytic activation energy of AWD from 182.9 - 274.4 kJ/mol to 144.6 - 205.2 kJ/mol. Bench-scale pyrolysis experiments, process simulations, and LCA were then conducted based on the kinetic prediction results. In the process simulations and LCA, four scenarios of AWD refinery with different pretreatment combinations with HTC and mechanical dewatering were designed. It was found that the different pretreatment processes could benefit the designed AWD refinery for different targets. The implementation of both HTC and mechanical dewatering pretreatment for refinery based on a 650 °C-pyrolysis presented the lowest CED value of 10.3 GJ for treating one ton of AWD. The least emission of carbon dioxide equivalents (-843.3 kg) was achieved in the case of using a 650 °C-pyrolysis temperature with the pretreatment with only a dewatering process when treating 1-ton dry AWD.
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| 28. |
- Wenjing, Wei, 1987-
(författare)
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Assessment of Raw Materials in Stainless Steelmaking-Their Energy Consumption and Greenhouse Gas Emission
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In stainless steelmaking, around 68% of the total greenhouse gas emissions come from the processing of raw materials. Thus, it is important for steelmakers to make efforts together with their raw material suppliers to implement low-carbon initiatives. To facilitate such initiatives, assessment of raw materials will provide guidance. In this work, the assessment of materials consists of two parts: i) different production scenarios are studied by using a static process model coupled with life cycle assessment approach to investigate the reduction potential of environmental impacts for Mo and Ni alloys; ii) assessment of the effect of trace element content (phosphorus) in stainless steel scrap on steel’s manufacturing cost, resource consumption and environmental impact using an online static process model.The results show that the overall GHG emission of FeMo production varies between 3.16-14.79 t CO2-eq/t FeMo (i.e. 5.3-24.7 tCO2-eq/t Mo). The main variance comes from the mining and beneficiation stages and depends mainly on the ore’s beneficiation degree. However, whether molybdenum is extracted as a co-product from copper mine or not can have an even greater effect on the total GHG emission of molybdenum due to the allocation of the impacts. In the case of nickel alloys, the GHG emissions for producing nickel metal, nickel oxide, ferronickel and nickel pig iron are 14, 30, 6 and 7 tCO2-eq/t alloy (i.e. 14, 40, 18, and 69 tCO2-eq/t Ni), respectively. Extracting sulfide ore through flash smelting process has been shown to have the least energy requirement and greenhouse gas emissions. In comparison to sulfide ore processing, oxide ore processed in an electric furnace is much more energy intensive and less environmental friendly primarily due to high content of gangue. However, by using a sustainable electricity source such as hydro-powered electricity, or applying a thermal heat recovery, it is possible to reduce the impact from electric furnace smelting of laterite. Furthermore, the use of stainless steel scraps with low phosphorous contents reduces slag amount, alloy consumption, production cost and carbon footprint. An estimation equation between phosphorous content and scrap’s value-in-use is obtained in the study to support the development of purchasing strategy.To conclude, the application of static process model based on mass and energy balance provides the possibility to assess raw materials’ environmental impact (energy consumption and GHG emissions) and to identify potentials to realize sustainable stainless steelmaking.
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| 29. |
- Yang, Hanmin, 1992-
(författare)
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Sustainable valorization of Biomass into Syngas/H2 via Biocarbon catalyst
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental issues stemming from the rapid growth in global energy demand and carbon dioxide emissions require urgent resolutions. Biomass represents a viable alternative for displacing fossil fuels, as its energy can be converted into electricity, heat, fuels, and chemical precursors, thus substituting petrochemicals. It is also the only carbon-containing renewable resource with substantial potential to mitigate environmental degradation, attain carbon-negative emissions, and drive sustainable development. Syngas production from biomass pyrolysis and in-line catalytic upgrading has attracted an increased attention, since it is a promising approach for further generating renewable bio-fuels, bio-chemicals, and bio-materials. Hydrogen isolated from bio-syngas is a clean and promising secondary energy source and carrier, capable of advancing a carbon-free energy system across technological, economic, and societal dimensions. This dissertation aims to realize a full valorization of biomass into renewable and affordable hydrogen-rich syngas and carbon-based battery anodes (hard carbons) through pyrolysis and in-line catalytic upgrading using biochar as the core of the catalyst strategy. Biochar, a carbon-enriched solid material with a carbon-neutral nature, emerges as a promising catalyst for promoting volatile upgrading owing to its extensively functionalized surface, porous structure, and resistance to coke deactivation.Optimization of the catalyst strategy using biochar-based catalysts in the catalytic upgrading process to enhance syngas quality is critical for scaling up the proposed process. This dissertation first investigated the effect of Ni-based, biochar, cascaded biochar+Ni-based, and engineered biochar catalysts on the catalytic performance in terms of the syngas yield, hydrogen yield, and gas energy conversion efficiency (GECE). Among them, the cascaded biochar+Ni-based catalyst and the Ni-doped biochar (NiBC) catalyst showed the most excellent catalytic performance. Using NiBC as a reforming catalyst introduced 78.2 wt. % of syngas consisting of an H2+CO proportion of 94.6 vol. % while applying cascaded biochar + NiAlO catalyst strategy resulted in 71 wt. % of syngas with a total H2+CO proportion of 89.5 vol. %. However, after a three-time test repetition, the Ni-doped biochar catalyst showed a slightly decreasing catalytic performance. In contrast, the cascaded biochar+NiAlO catalyst showed a stable promoting performance in terms of syngas and H2 yields after 15 feeding cycles. In addition, plastic waste, being a carbonaceous resource, was also applied in the pyrolysis and in-line catalytic upgrading process for hydrogen and high-value-added carbon production by using biochar as a cracking catalyst. In order to evaluate the techno-economic viability of the proposed process, a novel biorefinery concept was simulated and assessed based on the above results, aiming to produce affordable hydrogen and high-quality hard carbons from biomass and to realize negative carbon emissions. The proposed biorefinery was estimated to produce 75 kg of H2, 169 kg of hard carbon, and 891 kg of captured CO2 (95% purity) per metric ton of biomass while realizing a payback period (PBP) within two years at reference prices of 13.7 €/kg and 5 €/kg for HCs and H2. At the same time, a negative emission of the proposed biorefinery could be achieved with -0.89 kg CO2-eq/kg-biomass based on Sweden’s wind electricity, considering the captured CO2.A pilot-scale system using a continuous pyrolysis reactor was deployed to scale up the capacity of the proposed process. The catalytic performance of biochar was examined in terms of products’ distribution, gas composition and gas properties. Critical parameters, such as the weight hourly space velocity (WHSV), particle size and the morphology of the catalysts, and pressure drop of the catalyst bed, were evaluated. The results showed that a lower WHSV favours a higher syngas yield, a higher H2+CO proportion, and a higher hydrogen yield due to a longer residence time for volatiles-char contacts. Smaller catalyst particle sizes correspond to higher bed pressure drop, which resulted in a higher syngas and hydrogen yield. In addition, biochar particles with larger bulk density and more spherical and rounded shape introduced higher syngas yield, H2 +CO proportion, and H2 yield compared to the particles with elongated and angular shape. The stability of using biochar as a catalyst in a continuous feeding system was also examined and verified in this dissertation, which indicated its great anti-coking performance.
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- Yin, Jun, 1991-
(författare)
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A study of mold flux entrapment and gas entrainment in an ingot casting process
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this work is to study the gas entrainment and mold flux entrapments during the ingot filling process based on physical and numerical modelling.The formation of the free surface was investigated in the uphill teeming method, which illustrates a dynamic change at a quasi-steady state. The influence of several turbulent models on the result was studied. The Reynolds stress turbulence model predictions show a good agreement to the experimental result compared to predictions using k-ԑ based turbulence models. It was found that the Weber number at the free surface is smaller than 12.3, when the inlet velocity is 0.5 m·s-1. This indicates a minor chance for mold flux entrapments, based on previously reported results. In order to reach a calm free surface using an even high inlet velocity, the side teeming process is proposed. A rotational flow field was found to be generated in the side teeming process, due to the horizontal teeming of the molten steel. A vortex cannot be found in the side teeming process because of the weak strength of the swirling flow. However, surface disturbances can be seen close to the wall of the mold, but they are small and vanish at lower teeming velocities.An optimization of the filling angles in the side teeming process was studied to reduce and eliminate the surface disturbances at the edge of the mold. The result showed that the 90 degrees filling angle results in a calm free surface without surface disturbances. Therefore, this design is recommended to use in the ingot casting process.The trumpet was also studied in this work to better understand the gas entrainment phenomenon. Water model experiments were carried out to measure the gas entrainment rate during a quasi-steady. Numerical simulations were performed and the results showed a good agreement to the experimental results. The formation of a big bubble was observed at the bend, which is due to the generation of a low-pressure region. Finally, an angled runner design was constructed to ease the gas entrainment rate. The results showed that the 30-degree angled runner can result in less entrained gas in the horizontal runner and lower hump height compared to the traditional design.
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