Modeling and energy efficiency analysis of the steelmaking process in an electric arc furnace

This paper presents a comprehensive model of an industrial electric arc furnace (EAF) that is based upon several rigorous first-principles submodels of the heat exchange in the EAF and practical experience from an industrial melt shop. The model is suited for process simulation, optimization, and control applications. It assumes that the energy demand of the process is satisfied by six sources, the electric arc, the oxy-fuel burners, the oxygen lances, the combustion of coal, and the oxidation of metal in the liquid and in the solid phase. The energy exchange between the liquid and the solid phase due to liquid metal splashing is also considered. The different mechanisms of heat exchange are represented in the model as follows: (a) the radiative heat exchange from the arc to the other phases is computed using the DC circuit analogy, where the view factors are calculated using exact formulae and Monte-Carlo algorithms. (b) The energy input from the oxy-fuel burner is modeled using simplified geometries for which heat transfer relationships are known. (c) The amount of heat released by the oxidation of solid metal is described by the quadratic corrosion formula. (d) The energy exchange from the bath to the solid phase due to splashing is modeled using relationships and experimental data that are available in the literature. The model contains the melting rates and the efficiency of the oxygen lancing as free parameters; their values were computed by a least squares fit to process data of an industrial Ultra-High-Power EAF. In comparison with existing EAF models, the model presented here describes the dynamic behavior of the melting process more realistically. Based on the model, time-dependent energy efficiency curves for the various contributions and for the overall process are computed and discussed

Numerical estimation of the geometry and temperature of an alternating current steelmaking electric arc

A channel arc model (CAM) that predicts the temperature and the geometry of an electric arc from its voltage and impedance set-points is presented. The core of the model is a nonlinear programming (NLP) formulation that minimizes the entropy production of a plasma column, the physical and electrical properties of which satisfy the Elenbaas–Heller equation and Ohm's law. The radiative properties of the plasma are approximated utilizing the net emission coefficient (NEC), and the NLP is solved using a global numerical solver. The effects of the voltage and impedance set-points on the length of the electric arc are studied, and a linear formula that estimates the length of the arc in terms of its electrical set-points is deducted. The length of various electric arcs is measured in a fully operative electric arc furnace (EAF), and the results are used to validate the proposed models. The errors in the predictions of the models are 0.5 and 0.4 cm. In comparison, the existing empirical and Bowman formulae estimate the length of the experimental arcs with errors of 2.1 and 2.6 cm. A simplified formula to estimate the temperature of an electric arc in terms of its electrical set-points is also presented

A model identification approach for the evaluation of plant efficiency

Regulations and the public expectations on improving efficiency, reducing the carbon footprint and lowering the environmental impact drive the process industry towards improved operation and the development of new technologies. The efficiency of an existing production plant depends on a variety of factors like capacity utilisation, raw material quality, ambient temperature or operational performance. Identifying the influence of these factors on the performance of the plant helps to take suitable measures to drive it towards a more efficient operation. One approach to assess the resource efficiency potential of a plant is the comparison of the actual performance with the best possible operation under the given circumstances. This work presents a surrogate modelling approach for the identification of the best possible operation based on historical data. The surrogate model is compared to a more detailed rigorous model and advantages and possible shortcomings of the surrogate approach are discussed based on real production data at INEOS in K¨oln

Differential activation of frontoparietal attention networks by social and symbolic spatial cues

Perception of both gaze-direction and symbolic directional cues (e.g. arrows) orient an observer’s attention toward the indicated location. It is unclear, however, whether these similar behavioral effects are examples of the same attentional phenomenon and, therefore, subserved by the same neural substrate. It has been proposed that gaze, given its evolutionary significance, constitutes a ‘special’ category of spatial cue. As such, it is predicted that the neural systems supporting spatial reorienting will be different for gaze than for non-biological symbols. We tested this prediction using functional magnetic resonance imaging to measure the brain’s response during target localization in which laterally presented targets were preceded by uninformative gaze or arrow cues. Reaction times were faster during valid than invalid trials for both arrow and gaze cues. However, differential patterns of activity were evoked in the brain. Trials including invalid rather than valid arrow cues resulted in a stronger hemodynamic response in the ventral attention network. No such difference was seen during trials including valid and invalid gaze cues. This differential engagement of the ventral reorienting network is consistent with the notion that the facilitation of target detection by gaze cues and arrow cues is subserved by different neural substrates

Distributed representations of dynamic facial expressions in the superior temporal sulcus.

Previous research on the superior temporal sulcus (STS) has shown that it responds more to facial expressions than to neutral faces. Here, we extend our understanding of the STS in two ways. First, using targeted high-resolution fMRI measurements of the lateral cortex and multivoxel pattern analysis, we show that the response to seven categories of dynamic facial expressions can be decoded in both the posterior STS (pSTS) and anterior STS (aSTS). We were also able to decode patterns corresponding to these expressions in the frontal operculum (FO), a structure that has also been shown to respond to facial expressions. Second, we measured the similarity structure of these representations and found that the similarity structure in the pSTS significantly correlated with the perceptual similarity structure of the expressions. This was the case regardless of whether we used pattern classification or more traditional correlation techniques to extract the neural similarity structure. These results suggest that distributed representations in the pSTS could underlie the perception of facial expressions

Distributed representations of dynamic facial expressions in the superior temporal sulcus.

Previous research on the superior temporal sulcus (STS) has shown that it responds more to facial expressions than to neutral faces. Here, we extend our understanding of the STS in two ways. First, using targeted high-resolution fMRI measurements of the lateral cortex and multivoxel pattern analysis, we show that the response to seven categories of dynamic facial expressions can be decoded in both the posterior STS (pSTS) and anterior STS (aSTS). We were also able to decode patterns corresponding to these expressions in the frontal operculum (FO), a structure that has also been shown to respond to facial expressions. Second, we measured the similarity structure of these representations and found that the similarity structure in the pSTS significantly correlated with the perceptual similarity structure of the expressions. This was the case regardless of whether we used pattern classification or more traditional correlation techniques to extract the neural similarity structure. These results suggest that distributed representations in the pSTS could underlie the perception of facial expressions

Differential Activation of Frontoparietal Attention Networks by Social and Symbolic Spatial Cues

Perception of both gaze-direction and symbolic directional cues (e.g. arrows) orient an observer’s attention toward the indicated location. It is unclear, however, whether these similar behavioral effects are examples of the same attentional phenomenon and, therefore, subserved by the same neural substrate. It has been proposed that gaze, given its evolutionary significance, constitutes a ‘special’ category of spatial cue. As such, it is predicted that the neural systems supporting spatial reorienting will be different for gaze than for non-biological symbols. We tested this prediction using functional magnetic resonance imaging to measure the brain’s response during target localization in which laterally presented targets were preceded by uninformative gaze or arrow cues. Reaction times were faster during valid than invalid trials for both arrow and gaze cues. However, differential patterns of activity were evoked in the brain. Trials including invalid rather than valid arrow cues resulted in a stronger hemodynamic response in the ventral attention network. No such difference was seen during trials including valid and invalid gaze cues. This differential engagement of the ventral reorienting network is consistent with the notion that the facilitation of target detection by gaze cues and arrow cues is subserved by different neural substrates

Task-invariant brain responses to the social value of faces

Abstract ■ In two fMRI experiments (n = 44) using tasks with different demands-approach-avoidance versus one-back recognition decisions-we measured the responses to the social value of faces. The face stimuli were produced by a parametric model of face evaluation that reduces multiple social evaluations to two orthogonal dimensions of valence and power [Oosterhof, N. N., & Todorov, A. The functional basis of face evaluation

Relaxation Methods for Mixed-Integer Optimal Control of Partial Differential Equations

We consider integer-restricted optimal control of systems governed by abstract semilinear evolution equations. This includes the problem of optimal control design for certain distributed parameter systems endowed with multiple actuators, where the task is to minimize costs associated with the dynamics of the system by choosing, for each instant in time, one of the actuators together with ordinary controls. We consider relaxation techniques that are already used successfully for mixed-integer optimal control of ordinary differential equations. Our analysis yields sufficient conditions such that the optimal value and the optimal state of the relaxed problem can be approximated with arbitrary precision by a control satisfying the integer restrictions. The results are obtained by semigroup theory methods. The approach is constructive and gives rise to a numerical method. We supplement the analysis with numerical experiments

Gaze cueing elicited by emotional faces is influenced by affective context

When we observe someone shift their gaze to a peripheral event or object, a corresponding shift in our own attention often follows. This social orienting response, joint attention, has been studied in the laboratory using the gaze cueing paradigm. Here, we investigate the combined influence of the emotional content displayed in two critical components of a joint attention episode: The facial expression of the cue face, and the affective nature of the to-be-localized target object. Hence, we presented participants with happy and disgusted faces as cueing stimuli, and neutral (Experiment 1), pleasant and unpleasant (Experiment 2) pictures as target stimuli. The findings demonstrate an effect of ‘emotional context’ confined to participants viewing pleasant pictures. Specifically, gaze cueing was boosted when the emotion of the gazing face (i.e., happy) matched that of the targets (pleasant). Demonstrating modulation by emotional context highlights the vital flexibility that a successful joint attention system requires in order to assist our navigation of the social world