Furnace Tapping 2022

Controlled Tapping is a research project funded by the Norwegian Research Council and the Norwegian silicon and ferroalloy industry. The overall goal of the industry is to minimize the amount of uneven tappings and thus to reduce the energy consumption and the risk of hazardous events. In addition, the gassing, in the silicon industry, and the slag/metal separation in the ferroalloy industry, is a concern. The project Controlled Tapping will give fundamental and industrial knowledge to the industry, so these concerns can be addressed. The project focus is how the furnace interior, that is the furnace operation, is affecting the tapping. Tapping is an experience based sub-process that is developed over time at the various plants. To expand the knowledge into the scientific world, numerical modelling is a valuable tool and is the basis in the project. This has been done in SINTEF, NTNU in cooperation with Mintek. A variety of models have been developed calculating the tapping rate. Models describing the whole furnace with accumulated materials, e.g. TiC banks in the SiMn furnace, models that describes the slag metal separation in cascade tapping with various ladle positions, and models describing the tapping where the slag and metal properties are changed, has been developed. For a models to give the true picture, realistic input data is needed, and one of the Ph.D. projects has been to measure the interfacial tension between slag and metal in Mn-ferroalloy production. We also need to know the mechanisms affecting the tapping of industrial furnaces and on the consequences if furnaces accumulate metal and slag. Both industrial campaigns and investigations on mechanisms and material at the lab has been conducted. The industrial campaigns have been to excavate both Mn-ferroalloy and Si furnaces, to find that the tapped silicon is above 1800 °C when all literature says 1600 °C, to see the variances of the metal and slag during a tapping-cycle and over a year and investigating the energy in the gassing. In lab scale, the formation of TiC banks in the SiMn furnaces, the formation of slag, and the formation of SiO gas in Si furnaces and the pressure build up in charges by fines, have been investigated.

The tapping operation of a metal, matte, or slag at a non-ferrous smelting furnace has a number of common aspects from one facility to another. In simple terms, the tap-hole initially requires the safe opening, the molten phase is allowed to flow through the tap-hole, and then the tap-hole needs to be safely closed. Until now, tapping in non-ferrous smelting operations is largely performed by an operator. Safe operations around the tap-hole require proper process control of the smelting furnaces, the proper tap-hole design for the required duty, and high-quality, robust tapping equipment. The present paper describes the successful development of a robotic system for automating the slag tapping operation at a full commercial scale on a large copper flash furnace. The development of this robotic tapping machine is described, and the operating features and performance are discussed.

Drill bits and thermal lances are both perforation tools used in a variety of situations. For drill bit solutions, there exists a lot of theory regarding the proper drill bit selection for each application. However, for thermal lances, despite being a century-old tool, there is no technical information nor a theoretical framework that allows to understand its underlying science, required to properly select a thermal lance for a specific application. This article presents a theoretical framework, developing the concepts and variables that rule the thermal lances behaviour and performance. The proposed framework fits well with experimental results, therefore could be used as a guide to select the proper thermal lance for each tapping process, potentially allowing time savings leading to an increase in the profitability of furnaces operation.

“Carry-over slag” refers to steelmaking slag that is transferred to the steel ladle when tapping a steelmaking vessel (electric arc furnace or oxygen converter). Carry-over slag is oxidizing, causing consumption of deoxidizer (such as aluminum) during ladle processing, and leading to phosphorus reversion to the steel. In principle, mass balances based on the concentrations of several elements—phosphorus, manganese, and aluminum—could be used to assess the amount of carry-over slag. In this work, steel and slag compositions and the amounts of additions during tap were used to estimate the carry-over slag mass, using data from a large number of heats. It is concluded that—for aluminum-killed steel—an aluminum mass balance gives the only reliable estimate.

Assmang Manganese Cato Ridge is an integrated manganese smelter in South Africa producing High Carbon Ferromanganese and Refined Alloys. It was constructed in 1956 and is jointly owned by African Rainbow Minerals and Assore Limited. This paper seeks to share critical considerations to ensure effective, efficient, and sustainable tapping operations. These considerations include tap-hole design, launder design, maintenance practices and procedures, daily operations, critical equipment required, and tapping employees’ skills. The paper will also discuss the benefits of being an inclusive employer whereby more than 50 percent of employees who are tappers are females ranging from the age of 26 to over 50 years. The following are the outcomes of the well-managed tapping process: reduced health and safety risks, metal/slag separation, improved tap block life cycle, no production losses due to unplanned tap-hole blocks maintenance, no V-Shape repairs, and no runaway taps.

This paper presents a review of tapping and melt handling technology of aluminium for those more familiar with steel and iron. The practice for light metals is substantially different to that used for iron and steel. For primary production using the Hall-Heroult technology, a variety of methods are used at the various stages of cell tapping, crucible transfer to the cast house, ladle treatment, liquid transfer to furnaces, furnace tapping and flow control during casting. Level sensor technology is examined including mechanical systems, lasers and capacitors. Refractory types and melt interactions are also covered. Trough design is covered. Future developments such as automated furnace skimming are mentioned.

The Furnace Tapping Conference series is an example of problem-based conferencing. It focusses on tasks all smelters have in common, namely the tapping of liquid slag and alloy or matte from the reactor. The series draws on perspectives from across commodities and across disciplines in Science, Engineering, and Technology. It is a platform where ideas are exchanged between operators, engineering and support, and researchers on how to optimally manage the processes involved. The paper presented here is aimed at new-comers to the field, hence the title Furnace Tapping 101, and is written in two parts. In Part 1, Natural Language Processing (NLP), a branch of Artificial Intelligence (AI), is applied in the review of papers included in the Proceedings of Furnace Tapping 2014 and Furnace Tapping 2018 which took place in South Africa. In Part 2, terminology which newcomers to the field might be unfamiliar with, is explained in the form of a dialogue between a Mathematician and a Pyrometallurgist.

Silicon is mostly produced in rotating submerged arc furnaces with continuous tapping of metal. The burden is often dense due to condensates. Thus, furnace gas does not escape easily to the top of the burden and some gas escapes through the tap-hole. This can cause a hazardous flame jet out of the tap-hole which poses an HES threat to operators. A mathematical CFD model has been developed to study the flow of gas and metal in the furnace through the tap-hole. A modelling challenge is to account for the continuous tapping and the rotating furnace. These aspects differ from earlier CFD studies applied to furnace tapping. Results indicate the difference in tapping behaviour as the burden permeability varies and as the position of the tap-hole varies due to the rotation.

With the advent of the fourth industrial revolution, advanced methods for control and automation of pyrometallurgical furnace plants are beginning to receive considerable attention. One aspect of such work is the development of predictive tools based on fundamental process modelling—such models are able to extrapolate furnace behaviour beyond what is available in historical data. In the present paper, a reduced-order model of tapping from a submerged arc furnace is developed for the case of silicomanganese production. The utility of the resulting model is assessed by comparison to tapping measurements obtained from an industrial furnace plant. Strengths and weaknesses of the model are subsequently identified and discussed in the context of the potential for such models to act as operator guidance and digital twinning tools.

The accounting mass balance on pyrometallurgical plants, to which the tapped masses of alloy and slag are essential inputs, forms an integral part of the process control and planning of any smelter. Thus, it is desirable to be able to predict tapped mass ahead of time. This paper examines three data-driven models that aim to predict tapped alloy mass for a submerged arc furnace producing silicomanganese. All the models are linear and based on lagged data and, thus, can be described as autoregressive models with exogenous inputs (ARX). They differ in the selection of the predictors. Ordinary least squares (OLS) model uses all of the available predictors, whereas least absolute shrinkage and selection operator (LASSO) model selects most important predictors and partial least squares (PLS) model finds best predictors in the latent space. Feature selection analysis is performed on the model results. It is shown that the model based on OLS with a reduced number of the predictors slightly outperforms other models. It is shown that power input is the strongest predictor of the tapped alloy mass, confirming current industry practice. Tap duration, energy input corresponding to the previous tap, and the previously tapped alloy mass are shown to be weak but statistically significant predictors. Using mutual information, it was shown that it was not possible to improve tapped mass prediction accuracy using tapping and recipe data alone.

Slag reduction and viscosity are closely related in the practical operation of a submerged arc furnace for ferromanganese (FeMn) production. The viscosity of slag is dependent on temperature and its composition, and influences different aspects in the FeMn production process, namely reduction kinetics and final MnO content of slag, slag–metal separation, slag flow in the furnace, and ultimately furnace tapping. As such, it is paramount to establish knowledge about the relationship between slag reduction and viscosities. The kinetics of MnO reduction in FeMn slags based on Nchwaning, Comilog, and UMK ores were investigated between 1400 and 1550 \(^\circ{\rm C} \). The extent of reduction was determined by thermogravimetry, slag morphology, and change during reduction was examined by electron probe micro-analyzer and slag viscosities calculated using FACTSage 8.1 thermochemical software. Results show that viscosity of primary FeMn slag is higher and decreases with increasing dissolution of solid phase into liquid as temperature increases.

Optimal tapping of metallurgical furnaces is required for efficient furnace operation. Improper tapping can lead to metal and slag accumulation in the furnace thereby reducing the process efficiency. The mass flow rate of metal and slag during tapping in metallurgical furnaces is driven by the hydrostatic pressure head, i.e., the liquid level, and hindered by the porous particle bed formed by the raw materials in the furnace. To understand the effect of the particle bed, experiments were performed on a lab-scale tank fitted with a tap-hole using water and a mineral oil as fluids emulating the real furnace. The tank was filled with only water and both water and oil and their drainage rates were measured as they were emptied by gravity. The tank was then filled with glass beads to include the effect of the particle bed, adding an extra pressure drop due to the resistance offered by the glass beads and reducing the mass flow rate of the fluids. A significant effect of the particle bed was observed on the tapping flow rates. The presence of air bubbles in the oil and the water phase reduced the tapping flow rates of the phases even in the absence of the particle bed.

Renewable reducing agents are intended to replace significant amounts of fossil-fuel-based reductants in submerged arc furnaces in the upcoming decades. In this study, the interaction of a manganese slag to a charcoal, a semi-coke, and a metallurgical coke was investigated. In a first series, the wettability of the slag was measured, while the electrical resistivity of carbon particles was measured by a four-point measuring technique. It was shown that the contact resistant between the carbon materials significantly decreased by void and pore filling. The results were validated by measuring the bulk resistivity of carbon-slag blended bed. While the slag is nonconductive below melting temperature, electrical current is highly conducted in the molten phase. The higher electrical resistivity of charcoal compared to the fossil-fuel-based reductants improves the local heat generation in the carbon bed, concomitant reducing the viscosity of the slag, which may be beneficial for tapping of the furnace. While the work described here is not specifically on furnace tapping, the work is linked to good furnace operation, hence indirectly relevant.

Optimal current paths through the silicon furnace depend on the electrical properties of the charge materials. It is essential for good tapping conditions that sufficient current is supplied to the arc and lower part of the furnace. As such, the electrical resistivity of the charge mix as it is transformed in the furnace is investigated. Various carbon materials (coal, charcoal, and char) are partially transformed at high temperatures to silicon carbide (SiC) through reactions with silicon monoxide (SiO) gas. The temperature gradient in the crucible creates layers of varying degrees of conversion. These layers are separated and characterized based on SiC, carbon, and Si content. The electrical resistivity of each layer is then measured from 25–1600 °C. When the majority of the material is transformed to SiC, it will raise the resistivity compared to the carbon material, until silicon forms, when it will decrease again. The original structure appears to be more important to the resistivity than the transformation to SiC.

An industry survey of PGM-Ni matte tapping practices was published in 2014 with the aim of providing high-level information on matte tap-hole design, operation, and maintenance practices at different smelting operations. Since then, various innovation trends have been developing within the industry, with regards to safety and automation, environmental considerations, and design and monitoring technological advances aiming at enhancing tap-hole campaign life, minimizing tapping risks, and generally bringing the industry towards safer tapping. Hatch has conducted an updated industry survey, this time including PGM, Nickel, and Copper producers, with an extended view into those industry developments with specific objectives to encourage cross-pollination across industries and organizations and provide a useful reference documenting best practices in matte and metal tapping operations in the base metals and PGM industry.

In 2019, the construction and commissioning of what was to be the world’s first commercially operated ISACONVERT™ furnace was completed at the Kansanshi Copper Smelter. Between 2019 and 2021, the ISACONVERT™ furnace was operated in four campaigns in which the matte treated steadily increased from an average of 35 tonnes per day to an average of 245 tonnes per day. Manual blister and slag tapping were among the areas that had challenges and initially had a significant impact on the plant availability. Frequent failures to close the tap-holes occurred and hot metal spills were experienced as a result, giving rise to safety concerns. Several changes were implemented that resulted in a significant improvement in safety for the tappers, as well as a reduction in plant down time. This paper describes the design and operation of the ISACONVERT™ blister and slag tapping systems, and the improvements that led to successful operation of the furnace.

The first application of the ISASMELT™ furnace in the mid-1980s targeted the treatment of MIM lead-based feeds in a two-furnace oxidation–reduction combination. The first furnace originally transferred molten slag to the second furnace via a water-cooled copper block tap-hole. The next installation of the primary lead ISASMELT™ furnace technology occurred in the 2000s, this time feeding molten slag to a casting machine for solidification. This design had a number of learnings that were incorporated into a recent primary lead ISASMELT™ furnace, built and commissioned in 2012 at the Kazzinc Ltd Metallurgical Complex in Ust-Kamenogorsk, Kazakhstan. This paper presents the patented tapping system developed by Glencore Technology as applied to the lead ISASMELT™ furnace at Kazzinc. It focuses on the development process of this simple and effective tapping system, the current application, and how it has been optimised during the past 10 years of operational experience.

For efficient operation of an electric arc furnace, the tap-hole region is one of the most important parts. It experiences thermal stresses, creep, and erosion. To consider these effects in a virtual design process, it is necessary to use sophisticated thermo-mechanical and fluid dynamics models. We demonstrate application of finite element analysis, computational fluid dynamics, and optimisation methods to obtain tailored refractory tap-hole design. We use linear-elastic and creep models to perform structural mechanics numerical analyses of a geometrically simplified tap-hole area. An experiment-based methodology to obtain Norton-Bailey creep parameters is presented. The significance of considering creep during the design process is demonstrated. Using computational fluid dynamics (CFD) and optimisation methods, we perform a shape optimization of a tap-hole channel. A multi-objective optimisation of mass flow rate and area-averaged wall shear stress with respect to the funnel angle at the beginning of the tapping channel is performed.

Post-mortem investigations of used refractories have proven to be a crucial tool for evaluating process conditions and their effect on the lining. Despite these experiences, refractory samples from tap-holes are often neglected and do not get too much attention—there is a general opinion: “tap-hole refractory wear is due to tapping operations and there is no room for optimization”. However, closer investigations of tap-hole samples provide some valuable insights into wear phenomena and optimization potential (e.g., slag corrosion, non-oxide infiltration, and microstructural changes due to high-temperature load). Even though the possible changes to the actual tapping operations might be limited, it is worth considering, e.g., refractory upgrades. Additional possibilities for optimized tap-hole refractory performance and general tapping procedures are various additional technologies, e.g., sensor technologies.

Decision-making to tap is often based on experience and mass balance calculations. However, better methods are available to optimize the tapping efficiency, making sure tapping occurs at the best moment with minimum losses. Metal tapping should occur at a precise moment when the correct amount is available in the furnace and before overfilling. This moment can be difficult to determine without proper level monitoring. Even for slag tapping, the right timing is difficult to assess and even worse, it often leads to metal value losses and represents a safety hazard. RHI Magnesita offers sensor technologies to help you control levels and detect metal losses. These are used for fact-based decision-making ensuring optimized tapping procedures. The paper will describe and discuss the technologies as well as how to implement them in the furnace operation and what benefits can be achieved.

In ferrochrome (FeCr) production, the tap-hole refractory represents the highest wear area. Preliminary desktop FactSage modelling work conducted by Steenkamp (J South Afr Inst Min Metall 119(8):537–544, 2019) indicated that both alloy and slag had the potential to chemically wear the carbon-based tap-hole refractory material. The current study sought to build on the modelling work, by performing laboratory-scale experiments aimed at validating the modelling outcomes. Experimental work was conducted using a cup test approach, in an induction furnace, at 1450–1650 °C for the alloy-refractory, and 1550–1700 °C for the slag-refractory. Experimental results confirmed the potential for both FeCr alloy and slag to chemically wear the refractory. Tapping temperature was also found to have a marked effect on the extent of the wear.

Viscosity and melting behavior are two of the most important properties of industrial slags as they directly impact the yield of metallurgical processes. Too high fluidity may cause losses during tapping or infiltration of refractory while too viscous liquids can lead to problems regarding the smelting of charged material or metal inclusions. This paper comprises the determination of melting behavior and viscosity of slags as functions of their composition. Therefore, 19 mixtures of different oxides have been prepared and melted by means of an induction furnace. An analysis of the resulting slags in a hot stage microscope and the computation of the corresponding viscosities allow an evaluation of the most important parameters. Significant variations of viscosity and characteristic temperatures can be measured as functions of the content of manganese oxide and the ratio between calcium oxide and silicon dioxide, respectively, besides a strong temperature dependency and a major influence of network-forming oxides.

A submerged arc furnace (SAF) is generally used in the production of ferroalloys (referred to as metal in this study). Viable production of ferroalloys requires a consistent tapping process where metal and slag are extracted from the furnace. The tapping flow rates depend on various in-furnace conditions such as the height of the metal and slag column, presence of a porous coke bed (particle bed), crater pressure, and the physical properties of the fluids. In order to understand the difference in drainage of metals and slags produced in different zones of the furnace, a computational fluid dynamics (CFD) study is performed. Variations in the tapping of metal and slag from the different zones would lead to accumulation in the furnace, thus reducing its efficiency. A comparison between the tapping rates for the metal produced in the front or the back zone of the furnace is performed for a uniformly distributed coke bed and a coke-free bottom region. The tapping rates of slag produced in different zones of the furnace for a uniformly distributed particle bed are also compared. The results showed that the furnace reached a quasi-steady state quicker for the coke-free bottom region compared to the uniformly distributed particle bed, whereas the tapped metal comes equally from all zones of the furnace. It took longer for the simulation to reach a quasi-steady state for extraction of slag produced in different zones due to higher initial volume of slag. At the quasi-steady state, the slag was tapped equally from all zones of the furnace.

Monitoring the refractory wear in the tapblock is key to achieving extended tap-hole and furnace hearth life by informing operation and maintenance plans. The utility of a tapblock condition assessment system can be maximized by enhancing thermal monitoring, using an online monitoring system, data processing, and first-principles process modeling to develop a robust model of the tapblock condition. Another key factor impacting furnace campaign life is the refractory design, which requires balancing of competing priorities such as cost, performance, and constructability. Structural assessment of a hearth system can be used to quantify and optimize these features while identifying potential fatal flaws in a design, avoiding short campaign life. This assessment can be used to determine the impact of design changes, providing confidence in refractory design decisions. This paper will present examples of wear monitoring in the tap-hole region of a flash converting furnace and refractory design optimization for electric arc furnaces.

With environmental, energy-saving, and legislation considerations becoming increasingly important, there is a need for a major improvement in slag handling. The metallurgical industry is directing its efforts into minimizing and processing the slags to achieve sustainable development and a circular economy. An important pillar for the advanced slag treatment is an automated and smooth tapping operation. A well-functioning tap-hole is an essential requirement for stable melting/refining processes as well as for reliable smelter operation. Slag should be tapped from the furnace balancing between production rate, capacity of the downstream vessels, and safety of the operators. In stationary vessels, tapping flow rate and slag flow behavior are dependent on conditions in the furnace (e.g. pressure, bath level, and liquid properties) as well as on tap-hole geometry and its wear level. In conventional slag tapping there can be challenges in maintaining a steady flow. The S-TAP Slag Slide Gate Technology is a solution that enables an accurate regulation of the slag tapping flow rate and quick reaction by tap-hole closing. This implies controlled and steady slag flow, minimized splashing around the tap-hole surroundings, improved safety due to an immediate tap-hole closing in case of an emergency, and brings a higher degree of automation in a metallurgical plant. A vision towards fully automated tapping is also presented in the paper.

Tap-hole clay is a very important material to seal tap-holes in ferroalloy reduction furnaces. Different types of this refractory are available for the ferroalloy industry and to decide which would be the most appropriate material may be a difficult task. This paper shows a comparison between the properties of four different types of tap-hole clays that were designed for ferroalloy furnaces, focusing on the application in metal tap-holes. The goals are to improve the knowledge regarding these materials and guide ferroalloy producers when deciding what type of tap-hole clay should be used. The analyzed mixes differ from each other mainly in terms of the type of aggregate (basic or non-basic) and type of binder (tar, resin, or synthetic oil).

A well-functioning tap-hole is critical for most furnaces and it is important to have a plugging repair paste that contributes to maintain this. Plugging materials mainly containing carbon and oxides have been studied. The best working pastes in this system often contain Coal Tar Pitch high temperature (CTPht) which has been defined as a substance of very high concern under the European Chemicals Legislation (European Chemicals Agency in Annex XIV (authorization list), 2017). Tap-hole pastes that are without CTPht or large amounts of polycyclic aromatic hydrocarbons (PAH) have been developed in this work. An important part has been to develop test and measurement techniques to compare properties of new tap-hole materials with old well-working pastes. Three of these have been, plate viscometry, rapid heat up of samples with or without pressure in simulated tap-holes keeping temperatures up to 1200 °C. From these, properties of the paste and it’s repairing effect on surrounding materials could be measured.