Global data set of long-term summertime vertical temperature profiles in 153 lakes

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Measurement(s) : temperature of water, temperature profile Technology Type(s) : digital curation Factor Type(s) : lake location, temporal interval Sample Characteristic - Environment : lake, reservoir Sample Characteristic - Location : global Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.14619009Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Quantifying the CaO and CaF₂ content of industrial ladle furnace slag with optical emissions measured through the casting spout

Abstract CaO and CaF₂ are important slag constituents and additive materials in secondary metallurgy. Optimization of the quantity of these compounds has a key role in adjusting the slag chemistry for optimal refining properties. In this study, the CaO and CaF₂ content of the slag has been analyzed with optical emissions from an industrial ladle furnace measured through the casting spout. Molecular optical emissions from CaO and CaF were observed directly from the molten bath and the arc, whereas atomic emission lines from the slag components were detected in the arc spectra. Optical emissions from CaO, CaF, and atomic calcium lines have been correlated with the CaO and CaF₂ content of the slag. The CaO and CaF₂ content of the slag could be evaluated from the spectra ranging from 10 to 41 min before the X-ray fluorescence (XRF) analysis was finished. The mean differences between the OES and XRF analysis were 0.59 % and 0.61 % for CaF₂, and 2.19 % and 0.67 % for CaO when using the spectra from the molten bath and the arc, respectively. The method has the potential to work as an in situ online measurement system due to real-time data acquisition and fast computation times

Optical emission spectroscopy as a tool for process control of steelmaking burners

Abstract In contemporary steelmaking, burners are widely used for heating slabs in walking beam and annealing furnaces, heat-up of empty ladles, flame cutting of steel, as well as providing additional energy in electric arc furnaces. To facilitate the future of carbon-neutral steelmaking, a transition from natural gas-based burners toward hydrogen-based burners is essential to reduce the CO2 emissions associated with the burners. In addition to this transition, it is important also to optimize the burner practices that are used today, since the transition will take its time. To this end, CO2 reductions could also be realized with process control aiming toward more efficient use of energy and gas resources. This study presents how optical emission spectroscopy could be used for on-line monitoring and process control of the burner flame. A case study of oxy-fuel cutting is presented, where optical emissions from H2O, C2, FeO, Na, and K together with thermal radiation were observed. The flame’s properties, such as temperature and radiative heat transfer, identification of the flame species and impurities, and detection of rapid changes in the flame are analyzed from the OES data

On-line analysis of Cr₂O₃ content of the slag in pilot scale EAF by measuring optical emission spectrum of electric arc

Abstract Control of slag Cr₂O₃ content is essential in stainless steelmaking electric arc furnace (EAF). Excessive Cr₂O₃ content of slag lead to high Cr₂O₃ content after the EAF tapping, since the solid precipitates forming in high Cr₂O₃ contents are not reduced significantly during the tapping procedure. In this work the slag Cr₂O3 content during the EAF process was analysed by measuring the optical emission spectrum of the electric arc. The measurements were conducted in a pilot EAF situated in Aachen, Germany. Cr₂O₃ content of the slag was increased with periodical additions of Cr₂O₃ powder. The line ratios calculated from the optical emission spectra were compared to the results of the X-ray fluorescence (XRF) analysis of the slag samples taken from the furnace. The results indicate that best accuracy in a pilot scale can be obtained by using Ca I, Fe I or Mn I lines as reference for Cr I lines. By combining the most accurate line ratios of these three components, the Cr₂O₃ composition of the slag could be measured with an average absolute error of 0.62%-points and a standard deviation of 0.49%-points. The results suggest that Fe I and Mn I lines are the most promising reference lines for analysing Cr₂O₃ content of industrial EAF slag

Pilot-scale AC electric arc furnace plasma characterization

Abstract Fundamental knowledge of the electric arc properties is important for the development of process control of electric arc furnaces. In this work, a pilot-scale AC electric arc has been studied with optical emission spectroscopy together with filtered camera footage. The properties of the arcs were determined with plasma diagnostics and image analysis in order to obtain both the characteristic plasma parameters and the physical form of the arc. The plasma temperatures, ranging from 4500 to 9000 K, were derived individually for three elements. The electron densities of the plasma were between 10¹⁸ and 10²⁰ cm⁻³ and fulfilled the local thermal equilibrium criterion, but the plasma temperatures derived from atomic emission lines for different elements had high and unpredictable differences. The properties of the electric arcs have been studied with respect to the arc length derived from the image analysis. The slag composition, especially the relative FeO content of over 30%, was observed to have a notable effect on the brightness of the arc on slag and thus also on the radiative heat transfer

Cyanide recombination in electric arc furnace plasma

Abstract Cyanide, among with NOₓ, CO₂, and CO, is one of the adverse compounds that form in the ironmaking and steelmaking industry. High-temperature processes are suitable environments for cyanide formation, and cyanide can form as a result of recombination in electric arc plasma. Even though the cyanides might not survive e.g. the post-combustion process, understanding the formation mechanisms of hazardous materials in the steelmaking industry is important. In this work, the recombination of cyanide in a pilot-scale AC electric arc furnace is studied with optical emissions from the CN molecule. The results show how the optical emissions from the cyanide change in different process steps. Electric input, plasma temperature, and interaction of the arc with solid charge material were observed to have an impact on the CN signal. Additionally, equilibrium composition computation highlights how different sources of carbon change the recombination rate and that the highest recombination occurs at 6821 K

Discerning phase-matrices for individual nitride inclusions within ultra-high-strength steel:experiment driven DFT investigation

Abstract Non-metallic inclusions play a decisive role in the steel’s performance. Therefore, their determination and control over their formation are crucial to engineer ultra-high-strength steel. Currently, bare experimental approaches are limited in the identification of non-metallic inclusions within microstructural phases of complex steel matrices. Herein, we perform a density functional theory study on the characteristics of different nitride inclusions as observed in spectro-microscopy. As per the simulations, TiN inclusions preferentially forms in the austenite matrix while the ferrite matrix generally hosts BN inclusions. Furthermore, although the presence of both BN and TiN inclusions in the Fe3C matrix is possible, their formation is impeded because of strong inclusion-carbon interactions. The observed regularity in the formation of nitride inclusions in different phases of steel is also confirmed by the comparison of simulated and experimental K-edge XAS spectrum of nitride inclusions. Our work shed the light on the formation of nitride inclusions in different steel matrices and facilitates their further experimental identification

Study of synthetic titania slags demonstrating characteristics similar to high titania ilmenite slag

Abstract The upgradation of the ilmenite ore, using a pyrometallurgy method, is performed using a carbothermic reduction of the ilmenite. A high titania slag is obtained which is used as a feedstock for the TiO₂ pigment production. The slag is cooled after tapping in big molds and can take ten days to cool. This cooling method has remained the same since the inception of ilmenite smelting and recently rapid cooling through granulation has been utilized. The work presented in this paper focuses on the microstructural study of the slags that were prepared using different techniques and cooled at different cooling rates. Various analytical techniques, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) were used to exhibit the similarity of these synthetic slags to the properties of high titania ilmenite slag. The slag consisted mostly of pseudo-brookite phase with a M₃O₅ stoichiometry and smaller amounts of silicate and rutile phase. A glassy phase of silica was observed and most of the impurities were found to be present in the silicate phase. These silica phases were observed to be separate from the pseudo-brookite phase and along the phase boundaries. Micro-cracking of the slag surface, which is the characteristic of the M₃O₅ phase formed in the ilmenite slag, were observed under the SEM analysis. The XPS analysis revealed that faster cooling does result in lower amount of oxidation but the difference in the TiO₂ and Ti₂O₃ composition can have larger impact on oxidation than the cooling speed

Industrial ladle furnace slag composition analysis with optical emissions from the arc

Abstract With the strict standards for steel quality and high production rates, the demand for faster and more convenient slag composition analysis for both electric arc and ladle furnaces has become a major issue in industrial steel plants. To overcome the time-delay between slag sampling and results of the slag composition analysis, an on-line slag composition analysis is required. Such a method that can be used in on-line analysis and is also chemically sensitive to the slag composition is optical emission spectroscopy. In this work, the optical emissions from the arc have been measured in an industrial ladle furnace and used for slag composition analysis. This article focuses on CaF₂ and MgO, since the CaF₂ is a common additive material in the ladle treatment and high MgO content means that the ladle refractory lining is dissolving into the slag. The analysis has been carried out by comparing emission line ratios to the XRF analyzed ratios of CaF₂/MgO and MnO/MgO, respectively. The results show that several atomic emissions lines of calcium, magnesium, and manganese can be used to evaluate the CaF₂/MgO and MnO/MgO ratios in the slag. It was found out that the plasma temperature derived from Ca I emission lines has a non-linear relation with the CaF₂ content of the slag. Additionally, the dissociation pathways of molecular slag components were determined and studied in different plasma temperatures with equilibrium composition computation in order to determine the relations between the slag and plasma compositions