Multi-objective Optimization of Aluminum Anode Baking Process Employing a Response Surface Methodology

© 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 - The 10th International Conference on Applied Energy. In the aluminum anode baking furnace, the operational parameters have a significant influence on the furnace performance and the resulting anode quality. For this furnace, an important parameter is the fire-cycle, which determines the production rate of the baking kiln and the anodes quality. Shorter fire-cycle results in a higher furnace production rate and a higher fuel consumption (same anode temperature should be obtained in a shorter time). For a particular fire-cycle, flue-gas soaking temperature and soaking time are the other two key parameters that affect anode temperature distribution and furnace energy consumption. Limited studies in the literature focused on employing the traditional one-factor-a-time (OFAT) method to investigate the effect of these factors. Based on a simplified multi-physics model, a high-fidelity computational tool named ABKA (anode baking kiln analysis) software is developed to investigate the effects of these key operational parameters on the anode baking furnace heating performance. ABKA is employed to conduct a three-factors, two-level full factorial design, with a center point, to investigate the effects of varying fire-cycle, soaking temperature, and soaking time on furnace production rate, fuel consumption, and anode maximum, minimum and average temperature. The advantage of the present approach compared to the traditional one-factor-a-time (OFAT) method is that it can provide adequate information on interactions of different input variables, to effectively estimate the significance level of each factor, and to identify clear optimal settings of the three variables. Using ANOVA (analysis of variance), the effect and significance level of each factor and their interactions are effectively estimated. It is observed that soaking temperature has the highest impact on the final anode temperature distribution. Considering the furnace fuel consumption as a response, it is perceived that soaking time and soaking temperature jointly are as significant. Finally, employing RSM (response surface methodology), conducting multi-objective optimization, the optimal settings of the soaking time and soaking temperature for different production rates (fire-cycle values) are also estimated

The Impact of Critical Operational Parameters on the Performance of the Aluminum Anode Baking Furnace

©2020 by ASME. Minimizing energy consumption and reducing pollutant emissions during the carbon anode baking process are critically important for the aluminum industry. The present study investigates the effects of oxidizer inlet temperature, inlet oxygen concentration, equivalence ratio, refractory wall thermal conductivity, and refractory wall emissivity on the baking process using unsteady Reynolds-averaged Navier-Stokes (URANS)-based simulations in conjunction with the presumed probability density function method. Numerical results are combined with a response surface methodology (RSM) to optimize the anode baking process. The advantage of the coupled method is that it can adequately provide information on interactions of different input parameters. It is remarked that the significance level of the studied parameters varies drastically for different outputs. It is noted that diluting inlet oxygen concentration (from 23% in atmospheric air to 15%) at an elevated oxidizer temperature leads to enhanced furnace fuel efficiency, more uniform temperature distribution, and lower pollutant emissions. A linear model is detected to be adequate for response surface modeling of the anode baking furnace NOx formation. On the other hand, furnace soot formation is modeled with a higher-order model due to the quadratic behavior of the response

Optimizing Pulse Combustion Parameters in Carbon Anode Baking Furnaces for Aluminum Production

Copyright © 2019 ASME. Pulsating flame jets have been widely used in open-top carbon anode baking furnaces for aluminum electrolysis. Reducing energy consumption and pollutant emissions are still major challenges in baking (heat-treatment) carbon anode blocks. It is also of immense significance to bake all the anodes uniformly irrespective of their position in the furnace. Baking homogeneity can be enhanced noticeably by optimizing anode baking operational, geometrical, and physical parameters. In the present study, CFD simulations are combined with a response surface methodology to investigate and optimize the effects of pulse pressure, pulse frequency, and mainstream inlet oxygen concentration and mainstream inlet temperature. Two-levels half fractional factorial design with a center point is employed. It is perceived that pulse combustion with short pulse time and high momentum results in significant enhancement of the anode baking furnace energy efficiency. The temperature homogeneity is also significantly improved. It is found that the oxygen concentration is statistically the most significant parameter on NOx and soot formations, followed by the fuel flow rate. For NOx formation, air inlet oxygen concentration has a strong interaction with pulse duration. Coupling CFD models with the response surface methodologies demonstrated great potential in multi-objective optimization of the anode baking process with enhanced energy efficiency and baking uniformity

CFD Modelling of NOx and Soot Formation in Aluminum Anode Baking Furnace

Copyright © 2018 ASME. The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately requires 2GJ of energy per ton of carbon anodes. Moreover, pollutant emissions such as NOx and soot formation are of major concern in the aluminum anode baking furnace. The current study aims at developing an accurate numerical platform for predicting the combustion and emissions characteristics of an anode baking furnace. The Brookes and Moss model, and the extended Zeldovich mechanism are employed to estimate soot and NOx concentration, respectively. Considering a fire group of three burner bridges, one after the other in the fire direction, combustion and emissions features of these three firing sections are interrelated in terms of oxidizer’s concentration and temperature. In the present study, considering this interconnection, the effect of diluted oxygen concentration at elevated oxidizer’s temperature (~1200°C), which are the key features of the moderate or intense low oxygen dilution (MILD) combustion are analyzed. It is observed that by circulating some of the exhaust gases through the ABF crossovers, oxygen dilution occurs which results in higher fuel efficiency, lower pollutant emissions, and more homogeneous flow and temperature fields

Effects of Flue Wall Deformation on Aluminum Anode Baking Homogeneity and Temperature Distribution

The quality of anodes used in aluminum industry depends strongly on the baking process. It is essential to achieve a uniform temperature inside the anode during the baking process. Flue wall may deform during the service life of the furnace that may affects the baking process of the anodes and consequently reduce the quality of the anode. During furnace operation, the thermal expansion of flue walls is restrained due to the presence of headwalls that may promotes the deflection of flue walls. This study aims at investigating this phenomenon by developing a 3D model able to take into account a large number of physical phenomena and parameters that play a role in the baking process and affect the flue wall deformation process. This 3D model takes into account the thermo-hydro-mechanical coupling due to coupled fluid flow and transient heat transfer, packing coke load and the thermal expansion, the model is used to analyze the influence of these parameters on the resistance and deflection of the flue walls. This model can be used as a useful tool to study the effect of flue wall deflection on the aging of carbon anode furnaces

Performance Analysis of a Ring Furnace for Aluminum Production

Anode baking is the most expensive and the most important step during carbon anode production. The operational-geometrical parameters have significant influence on the anode baking furnace performance and carbon anode quality. Numerical modelling is an imperative tool to investigate the effect of different parameters on anode baking process. In the present study, a numerical model is developed which simulates heat transfer and flow distributions of the entire anode baking process. Using this numerical model, effect of various factors on anode temperature distribution is studied. Impact of degraded refractory-wall thermal conductivity on baking process is investigated and it is observed that for the aged furnaces this material properties degradation should be addressed accordingly. During the preheating and firing sections the temperature drops drastically from flue-gas to the center of the anode through the width of the pit which indicates a huge loss of energy. Calculating temperature standard deviation for the entire baking process, it is observed that the temperature non-uniformity presents mostly in the refractory wall and packing coke regions, and anode experiences a homogeneous temperature distribution

Effect of biventricular pacing on diastolic dyssynchrony

ObjectivesThis study sought to examine the changes in diastolic dyssynchrony with cardiac resynchronization therapy (CRT).BackgroundLittle is known about the effect of CRT on diastolic dyssynchrony.MethodsConsecutive heart failure patients (n = 266, age 65.7 ± 10.0 years) underwent color-coded tissue Doppler imaging at baseline, 48 h, and 6 months after CRT. Systolic and diastolic dyssynchrony were defined as maximal time delay in peak systolic and early diastolic velocities, respectively, in 4 basal LV segments. CRT responders were defined as those with ≥15% decrease in LV end-systolic volume at 6 months.ResultsBaseline LVEF was 25.2 ± 8.1%; 63.5% patients were CRT responders. Baseline incidence of systolic and diastolic dyssynchrony, and a combination of both was 46.2%, 51.9%, and 28.6%, respectively. Compared to nonresponders, responders had longer baseline systolic (79.2 ± 43.4 ms vs. 45.4 ± 30.4 ms; p < 0.001) and diastolic (78.5 ± 52.0 ms vs. 50.1 ± 38.2 ms; p < 0.001) delays. In follow-up, systolic delays (45.4 ± 31.6 ms at 48 h; 38.9 ± 26.2 ms at 6 months; p < 0.001) and diastolic delays (49.4 ± 36.3 ms at 48 h; 37.7 ± 26.0 ms at 6 months; p < 0.001) improved only in responders.ConclusionsAt baseline: 1) diastolic dyssynchrony was more common than systolic dyssynchrony in HF patients; 2) nonresponders had less baseline diastolic dyssynchrony compared to responders. After CRT: 1) diastolic dyssynchrony improved only in responders. Further insight into the pathophysiology of diastolic dyssynchrony and its changes with CRT may provide incremental information on patient-specific treatments