Furnace Interior Research Articles

Identification of Aluminothermic Reaction and Molten Aluminum Level through Vision System

During the secondary production of aluminum, upon melting the scrap in a furnace, there is the possibility of developing an aluminothermic reaction, which produces oxides in the molten metal bath. Aluminum oxides must be identified and removed from the bath, as they modify the chemical composition and reduce the purity of the product. Furthermore, accurate measurement of molten aluminum level in a casting furnace is crucial to obtain an optimal liquid metal flow rate which influences the final product quality and process efficiency. This paper proposes methods for the identification of aluminothermic reactions and molten aluminum levels in aluminum furnaces. An RGB Camera was used to acquire video from the furnace interior, and computer vision algorithms were developed to identify the aluminothermic reaction and melt level. The algorithms were developed to process the image frames of video acquired from the furnace. Results showed that the proposed system allowed the online identification of the aluminothermic reaction and the molten aluminum level present inside the furnace at a computation time of 0.7 s and 0.4 s per frame, respectively. The advantages and limitations of the different algorithms are presented and discussed.

Excavation and Analysis of a 31 MW SiMn-furnace at Eramet Kvinesdal

The production of SiMn occurs inside a closed furnace at very high temperatures below several hundred tons of charge. Once a SiMn-furnace reaches its end-of-life an opportunity is given for the investigation of the furnace interior. This paper presents the excavation of a 31 MW SiMn-furnace and the following analysis of collected samples. Samples were analysed using SEM & EDSand XRF. The obtained results show large accumulations of carbides and nitrides in both active and inactive regions of the furnace. Additionally, a substantial amount of alkalis was observed. By using the results from the sample analysis, a sketch of the furnace interior is presented together with a description of the different regions.

A novel method for gas flow and impurity control in directional solidification of multi-crystalline silicon

In this paper the potential of a specially designed argon gas injector for controlling the gas flow and transport of impurities in directional solidification of multi-crystalline silicon is evaluated. The gas injector which consists of a valve allows one to control the flow direction independently in the vertical and horizontal directions. Based on a gas flow model derived from a semi-industrial crystallization furnace the impact of different gas injection combinations on the gas flow pattern and impurity transport is studied. Special focus is given to the SiO evacuation from the melt-free surface, the CO formation at graphite surfaces and the CO evacuation from the furnace interior. It is found that for gas flow pattern formed through horizontal rather than vertical gas injection, SiO and CO are evacuated most effectively from the furnace interior and the formation of CO is inhibited. Such a type of gas injector presents a versatile tool for controlling the flow and impurity transport in the gas phase and possibly improving the material properties of crystalline silicon.

The effect of graphite components and crucible coating on the behaviour of carbon and oxygen in multicrystalline silicon

In the present paper the effect of the furnace interior materials on the carbon and oxygen concentrations in multicrystalline silicon (mc-Si) is studied. Mc-Si ingots were produced in a high-vacuum induction furnace by means of the vertical Bridgman technique. Growth experiments with or without graphite components in the furnace as well as with crucible coatings of different oxygen concentrations were performed.The concentration of carbon monoxide in the growth chamber is found to depend significantly on the setup used. A standard, graphite-containing setup results in pronounced CO formation, which can be completely suppressed by applying graphite-free elements. Oxygen in the crucible coating is shown to influence the concentration of carbon monoxide via the formation of SiO.Growth under a CO enriched atmosphere is associated with the formation of a SiC/SiO2 melt surface layer, which pins the carbon concentration in the melt or crystal near its solubility limit, whereas in graphite- or CO-free growth the dissolved carbon segregates approximately according to Scheil’s law. On the other hand, the effect of carbon monoxide on oxygen concentration in the grown crystals appears to be negligible. Instead, the oxygen concentration is directly related to the oxygen content of the crucible coating.

Measured vorticity distributions in a model of tangentially fired furnace

Simultaneous three-component six-sensor hot-wire probe measurements were made in a model of tangentially fired furnace (TFF) to measure the flow properties of an isothermal flow field. The quantities measured including the spatially resolved isothermal air velocity components and their two higher order moment statistical properties, i.e., the skewness and flatness factors, and the vorticity components and their skewness and flatness factors. Detailed experimental data provided an improved understanding of the behavior of the turbulent transport in the burner zone and in the upper and central regions of the TFF. The measured velocity and vorticity fields showed the swirl characteristics of the fluid flow in the TFF interior as expected and that the flow has attached to the walls in the burner zone and central region which is not desired in an operating TFF. The solid walls in these domains, including the pendants located in the upper region, act as vortex generators. Oscillation of the velocity components, and of the other quantities measured in the experiment, may be derived from the fragmentation of the vortexes and the coherent structures existing in the furnace interior. This work helps clarity the fouling and slagging mechanisms and the flow attachment in the burner zone and central region, the flow deviation and residual swirling downstream the pendants in the upper furnace, by giving insight into the vorticity and the coherent structures in the TFF.

Comparison of iron ore reduction in experimental blast furnace and laboratory scale simulation of blast furnace process

The reduction of iron ore pellets in an experimental blast furnace has been surveyed by dissection of the blast furnace. Results of the dissection, as well as some results of measurements taken in the blast furnace interior during operation, have been compared with those of previously conducted laboratory reduction, softening and melting tests using the same type of pellets. The aim of the work was to compare laboratory testing with results from an experimental blast furnace. The high temperature phenomena occurring when reducing olivine iron ore pellets, with limited softening and a short temperature range of the melting process resulting in a thin cohesive zone, were found to be the same in laboratory tests and in the experimental blast furnace. The reduction process down through the burden of the experimental blast furnace, however, was not identical to that in the reduction, softening and melting experiments. The differences obtained were found to arise from different reducing conditions. Therefore, it was concluded that simulation of the reduction occurring in the blast furnace can be conducteded on a laboratory scale, provided that the experimental conditions are carefully chosen for the specific blast furnace process to be simulated. Information about the internal state of the blast furnace can be obtained from the experimental blast furnace.

Reducing defects in remelting processes for high-performance alloys

Defect reduction is one of the most important goals in continuing research to improve remelting technologies, such as vacuum arc remelting, electroslag remelting, or hearth melting (plasma or electron beam), of specialty alloys. Ingot defects may originate from several sources in these processes, such as foreign materials in the melt stock or electrode, drop-in material from the furnace interior, and solidification defects. Laboratory-and industrial-scale melting experiments are used by Sandia National Laboratories and the Specialty Metals Processing Consortium to determine relationships between melt-processing conditions and defect formation. Examples described here include freckle formation, a solidification defect in large ingots of alloy 625 (electroslag remelting), and alloy 718 (vacuum arc remelting). These examples demonstrate how integrated melting experiments, process modeling, and ingot analysis can guide the control of melting conditions to reduce defects.

TACCOS—A thermography-assisted combustion control system for waste incinerators

A novel type of combustion control system is described for municipal waste incinerators using infrared thermography to obtain information about the temperature distribution in the furnace interior. A scanner camera operating in the mid infrared was installed at the waste-to-energy plant in Coburg, Germany during the experiments. Selection of an appropriate wavelength region allows the direct imaging of the fuel bed through the overlying flame and flue gas atmosphere and the determination of temperature distributions within seconds. The fast response time of the thermography system compared to shielded thermocouples allows the detection of furnace temperature fluctuations on a short time scale of a few minutes. These data can be used for fine tuning of the total underfire air (UFA) flow. Local imbalances in fuel bed temperature are evaluated to redistribute UFA between individual grate zones. The influence of variations in calorific value on the position of the main zone of combustion can easily be measured, thus allowing the sensitive adaptation of UFA distribution to local requirements. Incorporation of the camera system results in an improved overall consistency of the combustion process, as reflected by a reduction of excess air fluctuations and of temperature imbalances across the grate. Measurements in the Coburg plant have shown that flue gas as well as residue burnout quality was improved. Compared with conventional control, emissions of carbon monoxide and unburned hydrocarbons were reduced, and also the fraction of unburned matter in the residue.

A comparison of tga and egd kinetic data using a high temperature open cell furnace

The ability to elucidate solid-state reaction kinetic data employing thermogravimetric analysis (TGA) techniques requires rigid control over the operating parameters, identification of the appropriate rate expression and, when possible, confirmation of the proposed stoichiometry via a second simultaneous method. This task of obtaining kinetic data is further complicated when operating in the 1000°C to 2000°C range and in an open cellular furnace where evolved gas detection (EGD) techniques do not respond directly to sample volatiles because of the gas diffusion throughout the furnace interior. Nevertheless, the most formidable problem to overcome is the occurrence of another weight sensitive reaction concurrent to the desired reaction. This problem of weight sensitive simultaneous reactions necessitated the development of an EGD technique comparable in precision to that of a microbalance for distinguishing a single reaction. The carbothermic reduction of metal oxides model the utility of employing both TGA and EGD thermoanalytical methods and will be shown as viable techniques for derivation of kinetic data.