6th Intl. Symp. on Sustainable Carbon and Biocoke and their Industrial Application

Despite all modern technologies and innovative developments, carbon is still of major importance in metallurgy. Not only for iron and steel production, but also for nonferrous metals. In many pyrometallurgical processes, coal and coke are the main reducing agents and important energy sources. However, one product of carbon application is always CO₂, which is known as one major problem in climate change. 

As such, it is indispensable to develop and use new sustainable technologies that reduce or eliminate the CO₂ discharge to the atmosphere. In metal production, carbon is still the most important reducing agent and essential for most modern pyrometallurgical processes, and this will not change in near future. In the short- and mid-term, until entirely new processes that are not carbon-based are introduced, the use of coke out of biomass can help to minimize the CO₂ footprint. However, coke must meet several requirements in terms of reactivity, stability, grain size, etc. to be used in specific processes. Here, the influence on the process caused by the much higher reactivity and different impurities needs to be studied and defined, to optimize existing treatment procedures, if necessary.

For replacing fossil coke, which is in use today, the coke produced out of biomass must be as similar as possible so that in best case, no changes in the processes are necessary.

For an environment-friendlier solution, the origin of the biomass is also critical. Preferably, the material is locally available and not of any other use. Depending on the location, this could be agricultural residues like olive stones and fruit tree cuttings or waste wood for example.

Until now, the use of biocoke in lead production and in the Waelz kiln was in the focus of research at Montanuniversitaet Leoben. While the application in lead metallurgy is less problematic and was tested successfully, the substitution of coke in the Waelz kiln is more difficult and places higher demands on the properties of the carbon carrier, especially in terms of reactivity. For this, the reduction of reactivity is now in focus and will be critical for the future of biocoke in this process. Trials showed that an increase of the grainsize (pellets) and a treatment with additives like bentonite, has a positive impact on the properties of the coke and could lead to an efficient application.

The catalytic decomposition of methane in molten metals represents a promising complementary methodology to water electrolysis for the production of CO₂-free hydrogen. In this process, methane is introduced into a liquid, catalytically active molten metal and cracked, whereby the resulting solid carbon is transported to the surface of the metal bath. In order to be able to investigate fundamental issues surrounding the production of hydrogen in this strategically important research segment, the corresponding infrastructure is created in the form of a technical centre (Hydrogen Research Centre, HRC) at the University of Leoben in Austria. In this paper, the relevant equipment is explained in detail and the influence of the scale-up stages of the methane pyrolysis process up to demonstration scale on the products hydrogen and carbon is described. The demonstration plant planned at the HRC consists of different aggregates, which are necessary for a comprehensive investigation of various process parameters affecting methane pyrolysis in the metal bath. The central metallurgical unit is an induction furnace, which can be operated in a metallurgical vacuum and at pressures of up to 10 bar. A hot gas filter with heat exchanger is planned for the subsequent product flow treatment to separate the solid carbon produced during methane decomposition. By means of a membrane separator, the particle-free gas stream, which mainly consists of hydrogen and unreacted CH₄, can be divided in order to enrich H₂. Furthermore, by using a thermal afterburning system, it is possible to completely neutralise all of the products created in this process.

In the context of the growing interest in hydrogen as an energy carrier and reducing agent, numerous industries, including the iron and steel sector, are contemplating an increased adoption of hydrogen. To meet the escalating demand in energy-intensive industries, it becomes imperative to significantly expand and further develop hydrogen production. However, the present hydrogen production methods heavily rely on fossil fuels, resulting in a substantial environmental burden, with approximately 10 tons of CO₂ emissions per ton of hydrogen generated. [1], [2]

To address this challenge, methane pyrolysis has emerged as a promising approach to produce clean hydrogen with reduced CO₂ emissions. This process involves the dissociation of methane into hydrogen and solid carbon, leading to a substantial reduction in the carbon dioxide footprint associated with hydrogen production. [3], [4]

The Montanuniversitaet Leoben (Austria) is currently actively engaged in research concerning methane pyrolysis and the development of a liquid metal bubble column reactor (LMBCR) specifically dedicated to this purpose. While the resulting H₂-rich product gas from methane pyrolysis may have potential applications in various processes, such as iron ore reduction, the carbon product, on the other hand, has stricter requirements in terms of impurities, depending on its intended field of use. Many applications demand very low threshold values for impurities in the carbon product [5]. Therefore, the main objective of this study is to investigate the chemical properties of carbon produced via methane pyrolysis in an LMBCR concerning impurities and to propose process technological improvements to enhance the overall product quality.

Hydrogen represents a pivotal element in transforming the current energy system as its application as a fuel or reducing agent in critical industrial sectors, including transportation and metallurgy, can enhance energy diversity and availability while offering the opportunity to reduce greenhouse gas emissions [1]. However, producing H₂ using conventional methods is associated with the generation of high volumes of carbon dioxide [2]. Therefore, extensive research activities concentrate on developing alternative processes with decreased CO₂ footprints.

Methane pyrolysis in liquid metallic catalysts is an attractive process that shows excellent potential, as its specific energy demand is comparable to that of steam methane reforming, but no CO₂ is emitted due to the base reaction [3], [4]. Furthermore, generated pyrolysis carbon is a valuable product with many possible applications [5].

This work investigates the influence of different compositions of the utilized metal bath on produced pyrolysis carbon. The focus is on modulating its physical properties, especially with regard to marketability and impact on the overall process economics while sustaining sufficient hydrogen yield.