Trends and Advances in Blast Furnace Casthouse Technologies with a Focus on Refractory Lining Performance, Operational Safety and Decarbonisation

Bulletin 2023



The blast furnace is the most used route for iron and steel production due to the numerous advantages it provides, such as low cost and high productivity. However, this process is very energy intensive, in addition to emitting large amounts of CO2 and other pollutants into the atmosphere. In this context, the refractory industry plays an important role in the decarbonisation process through the implementation of safe, integrated, and innovative solutions that enable customers to reduce their CO2 footprint without compromising operational performance. This paper aims to present the latest advances in refractory technologies for blast furnace runner maintenance practices in South America and to share some of the superior results achieved using digital integrated solutions, as well as their impact on the performance, safety, and process stability.


In steelmaking, the blast furnace (BF) is the most widespread globally used route to produce hot metal as it offers several advantages, such as high productivity, continuous operation for long periods of time, and fuel consumption optimisation [1]. Nevertheless, with the intense growth of steel production, the level of associated CO2 emissions has increased dramatically, imposing a series of challenges for this sector, including the transformation of its process conditions and the use of hydrogen as a fuel. Figure 1 presents the relationship between the increase in steel production and the emissions produced, with the blast furnace-basic oxygen furnace route leading the ranking. Consequently, a 25% reduction of CO2 emissions is required based on current global projections relative to a 2-degree warming scenario (i.e., 2DS target), which corresponds to limiting temperature growth to avoid significant and potentially catastrophic changes due to global warming [2].

The refractory industry plays an important role in this decarbonisation process by reducing scope 1, 2, and 3 emissions, through incorporating recycled materials into products (i.e., circular economy), and by developing and implementing safe, integrated, and innovative solutions that enable customers to reduce their CO2 footprint without compromising operational performance [3].

This article addresses the latest refractory technologies, maintenance practices, and project improvements recently implemented in South America’s BF casthouse area that contribute to the current demands regarding energy efficiency, CO2 emission reductions, and safety.

Figure 1. Global CO2 emissions in the steel industry and reductions required to achieve the 2DS target: Crude steel production (million tonnes) for basic oxygen furnaces (BOF), open hearth furnaces (OHF), and electric arc furnaces (EAF) plotted with the total modelled emissions (million tonnes CO2) [2].

Materials and Methods

In order to address the most recent trends and advances in the BF casthouse, different refractory technologies were characterised in the laboratory (e.g., physical, mechanical, thermomechanical, and chemical properties) and further validated in the field. The first approach focused on comparing two castables, namely a conventional castable used for major BF runner maintenance (CARSIT) and a monolithic used to produce precast blocks (CARSITAL K31C-19-BR). The BF runner ultra-low cement castable (Al2O3-SiC-C) and the precast block monolithic were wet mixed in a planetary mixer for 5 minutes. Although both refractories have the same formulation, different water contents were used due to the differences in processing. Prismatic specimens of 160 x 40 x 40 mm were cast, air cured for 24 hours, then dried at 110 °C for 24 hours, 350 °C for 12 hours, and fired at 1400 °C for 5 hours prior to characterisation.

The properties and performance of a ramming mix (CARSIT RAM B14C-8-BR), currently used during minor repairs and emergency shutdowns, were also evaluated in comparison to a sol-bonded gunning mix (CARSIT SOL M10G-5-BR). For the latter mix, gunning panels were prepared during a field refractory installation and prismatic specimens (160 x 40 x 40mm) were cut out, dried at 110 °C for 24 hours, and fired at 1400 °C for 5 hours before characterisation. The ramming mix samples were prepared in the laboratory and heat treated using the same conditions as the sol-bonded mix.

Comparison of Refractory Castable Installation and Precast Blocks

The main physical and mechanical property results for CARSIT and CARSITAL K31C-19-BR samples are presented in Table I. Firstly, it is important to note that even though both refractories have the same formulation, there is a difference in water content due to the type of installation and processing requirements. Water is a key ingredient in such processes and plays a major role by wetting the ceramic particle surfaces, generating strong capillarity forces between large and fine particles (i.e., wall effect), and acting as a crucial component of binding systems [4]. Nevertheless, the increase in porosity associated with the higher water content also promotes a reduction in the mechanical properties besides influencing corrosion resistance. In this context, better mechanical strength levels for the precast block grade were observed as a result of its lower porosity, higher density, and optimised water content.
Although a significant amount of water reacts with the cement to form hydraulic bonding phases, a residual unreacted part facilitates proper installation of the refractory castable, generating porosity after firing [5] and a lower hot modulus of rupture.

Table I. Main physical and mechanical properties of CARSIT (castable) and CARSITAL K31C-19-BR (precast block). Abbreviations include bulk density (BD), apparent porosity (AP), cold crushing strength (CCS), modulus of rupture (MoR), hot modulus of rupture (HMoR), permanent linear change (PLC), and ultra-low cement castable (ULCC).

During operation, the refractory applied in BF runners is subjected to extreme temperature conditions (1490–1530 °C) inherent to the steelmaking process. For example, when in contact with hot metal and slag at high temperatures, the lining is exposed to combined wear mechanisms such as corrosion and thermal shock [6]. In order to assess the materials’ corrosion resistance, tests were performed using both an induction and rotary furnace. The results (Figure 2) revealed similar refractory wear for both materials in the induction furnace—a test used to evaluate the wear at the hot metal/slag interface. However, in the rotary test (widely used to evaluate the wear due to slag chemical attack and its erosive effect on the lining), a higher wear was obtained for the castable product. This result is in accordance with the higher apparent porosity observed (i.e., 16.33% at 1400 °C), which would increase the slag penetration rate, and the lower hot strength (0.70 MPa) that could be associated with decreased erosion resistance.

The thermal shock resistance of both refractories was also evaluated by measuring the elastic modulus (E) after successive cycles of thermal shock (i.e., 1400 °C for 30 minutes). The results showed a lower decrease of E for the monolithic block grade in comparison to the refractory castable (Figure 3), which confirms a superior thermal shock resistance of the CARSITAL K31C-19-BR.

In addition to the beneficial material properties of CARSITAL K31C-19-BR, the refractory secondary runner maintenance schedule is significantly shorter when using precast blocks. This is illustrated by the following real case scenario for a South American customer where a typical runner wear lining installation with castables requires a 36-hour mould assembly stage before the application starts. This step is time consuming because the secondary runner borders are irregular, with no anchoring points to install the moulds. Another important stage when installing castables is the curing (10 hours), which needs to be completed before removing the moulds as the hydration process that takes place during this period is responsible for the castable’s green mechanical strength development. In contrast, no mould assembly is required for precast blocks and only ~2 hours are needed to remove assembly parts after installation of the blocks. Moreover, as the refractory block has already been cured and dried (350 °C/12 hours) during its production, these processing steps are not necessary. Nevertheless, a heating up curve is required for both technologies as the refractory needs to reach a minimal temperature to minimise the thermal shock while ensuring suitable flowability of the slag and hot metal. Table II summarises the overall time requirement for each stage, comparing the installation of 8 blocks (~20 tonnes) with applying a castable in the secondary runners.

Regarding performance, independent of the refractory technology used, a typical secondary runner campaign can last up to 12 months with only minor (hot) repairs required during this time. However, when installing precast blocks in secondary runners, the amount of maintenance material used for repairs is ~20% lower when compared with that required for repairing castables. Therefore, due to its superior properties, the precast block technology can optimise the overall refractory maintenance time and increase the secondary runners’ availability.

Figure 2. CARSIT (castable) and CARSITAL K31C-19-BR (precast block) wear after the induction furnace (IF) and rotary furnace (RF) tests.

Figure 3. Thermal shock resistance: The change in elastic modulus (E) was measured after successive cycles of thermal shock (i.e., 1400 °C for 30 minutes) for CARSIT (castable) and CARSITAL K31C-19-BR (precast block).

Table II. Typical stages and time requirement for refractory installation in the secondary runners using CARSIT (castable) and CARSITAL K31C-19-BR (precast block).

Comparison of Ramming and Sol-Bonded Gunning Mixes

The main physical and mechanical property results for the ramming (CARSIT RAM B14C-8-BR) and sol-bonded gunning (CARSIT SOL M10G-5-BR) mixes are presented in Table III.

Both these materials were used in the same region of a secondary slag runner for hot repairs (between major campaigns) under similar conditions. In both situations, the total repair duration at a customer was about 7 days, but the installation time was optimised (almost 50% less time) using the gunning material. Moreover, this new repair method increased the safety standards due to the fact that an employee’s presence was no longer required inside the slag runner. Figure 4 depicts the stages of a gunning application in a secondary runner as well as the thickness profile before and after the refractory hot installation.

The advantages of using a sol-bonded gunning mix have also been observed during emergency shutdowns or campaign extensions. For instance, when there is a requirement for a main runner drainage, gunning can increase the planned hot metal production by over 30000 tonnes without impacting the operation. Another benefit is that the sol-bonded technology, due to its optimised drying behaviour, can be installed in extreme temperature conditions.

Table III. Main physical and mechanical properties of CARSIT RAM B14C-8-BR (ramming) and CARSIT SOL M10G-5-BR (gunning) mixes. Abbreviations include bulk density (BD), apparent porosity (AP), cold crushing strength (CCS), modulus of rupture (MoR), and hot modulus of rupture (HMoR).

Figure 4a. Secondary runner before repair.

Figure 4b. Secondary runner after the sol-bonded gunning mix application.

Figure 4c. Secondary runner thickness profile (black and white lines) for each stage.


Digital Solutions for the Casthouse: Benefits of Using a 3D Laser Scanner and Optical Pyrometer

Although BFs have been the most effective route to produce iron for over 200 years, several issues can affect their efficiency and stability, such as the runners’ lining condition. Among the main digital solutions implemented, 3D laser scanning has proved to be one of the most effective methods to measure the lining thickness throughout the campaigns, providing a large amount of discrete data points in a very short time. To accomplish this, the scanning equipment is positioned next to the runner and a reference measurement of the original refractory lining is taken. Once the runner reaches at least half of the planned production, a new inspection is performed to assess the remaining refractory lining thickness and establish a new production target. Additionally, in steel plants where the slag line determines the campaign, there is no need for full runner drainage.

The result is a mobile-friendly report automatically generated in about 20 minutes, enabling the operator to have all the data on only one platform called Steel Lining Evaluation Scan (LES), which leads to fast decision making [7]. Figure 5 shows an example of measurements taken for the residual refractory lining in the slag line between tapping.

Figure 5. Full runner inspection results (front view) generated by 3D laser scanning [7].

In a real case scenario, the scanner was successfully used to safely extend a main runner’s campaign following hot inspection of the slag line. Through the implementation of this new technology in a BF with two tapholes and a daily hot metal production of 4200 tonnes, it was possible to increase the campaign by 5 days without draining the runner although the refractory thickness had decreased from 150 mm to 80 mm, taking into consideration the reliability of the data acquired. Furthermore, in a situation where the equipment had an average hot metal production of 90000 tonnes, the 3D laser solution enabled refractory maintenance to be postponed until the hot metal production had reached 108732 tonnes (an increase of 20% in comparison to the original planned campaign). Moreover, the refractory specific consumption (kg of refractory/tonne of hot metal) decreased by 10%, leading to increased annual productivity due to better maintenance practices [7].

It is also important to highlight that by decreasing the number of inspection drainages, a reduction in the CO2 emissions during hot metal production is expected. As a reference, for each tonne of hot metal produced, 2 tonnes of CO2 are released [8]. This means that considering a coke BF with four main runners (operating in pairs) and a campaign of 28 days, eliminating drainage for inspection would represent up to a 3120-tonne CO2 reduction of the annual emissions (26 drainages of a main runner with a hot metal capacity of 60 tonnes were considered for the calculation).

Another digital solution implemented in South American BFs is improved thermal control through integrating continuous hot metal temperature measurements. By replacing the conventional thermocouple procedure (i.e., manual measurements are taken by immersing the thermocouple in the molten bath) with the novel optical pyrometer methodology, it was possible to continuously measure the temperature, improve data reliability, eliminate manual measurements that are a high safety hazard, and to have better control of the BF operation by anticipating necessary actions for process stability [7].
Figure 6 shows a pyrometer being used in the BF casthouse during high-temperature hot metal tapping.

By implementing these digital technologies, it is possible to increase productivity and achieve higher operational stability of casthouse processes. Furthermore, the online hot metal monitoring process associated with the precise control of runner refractory wear are part of the key initiatives that will make the construction of reliable prediction models possible and ultimately the creation of a fully integrated systemic analysis of BF runner campaigns.

Figure 6a. Pyrometer measurements in the BF casthouse – monitoring the temperature during tapping.

Figure 6a. Pyrometer measurements in the BF casthouse – positioning for continuous temperature measurement.

Figure 6a. Pyrometer measurements in the BF casthouse – recorded temperature.


The latest trends and advances in BF casthouse technologies have been outlined in this article with a focus on refractory lining performance, operational safety, and environmental considerations.

Replacing in-situ installed castables with preshaped blocks and ramming mixes with sol-bonded gunning mixes, in combination with the use of digital solutions (3D scanning and an optical pyrometer) in a runner’s lining design results in increased performance, higher production, longer campaign life, and superior safety standards. Additionally, a decrease in the specific refractory consumption (10%) has been observed as well as an optimised number of inspection drainages, which result in lower CO2 emission levels during hot metal production. Taking these aspects into consideration, through the use of integrated solutions safer casthouse operations with higher levels of productivity and stability can be expected.

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Aloísio Simões Ribeiro

RHI Magnesita, Belo Horizonte, Brazil

Bruno Filipe Guimarães

RHI Magnesita, Belo Horizonte, Brazil

Lucas de Brito Nascimento

RHI Magnesita, Leoben, Austria

Victor Luiz Cruz Morais

RHI Magnesita, Belo Horizonte, Brazil

Vitor Guarnier Domiciano

RHI Magnesita, Belo Horizonte, Brazil

Corresponding author
Aloísio Simões Ribeiro

RHI Magnesita, Belo Horizonte, Brazil

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