REWAS 2022: Energy Technologies and CO2 Management (Volume II)

This research work falls under the generic theme of modeling high-temperature processes, during energy conversion, flaking, and corrosion phenomenon, for systems converting mainly organic matter into energy. Energy conversion facilities are made of a metal alloy of the type Fe–Cr–Ni–V–Mo–W and are exposed to gaseous species from combustion, or from the flying of ashes. Under certain conditions, highly corrosive molten salts may be formed, causing the protective oxide layer of the steel to be transformed into either chromates, molybdates, tungstates or vanadates, or their mixture. This is called “catastrophic” corrosion. The presence of ash deposits limits the maximum operating temperature and the energy efficiency of the process. Thus, this research aims to develop a thermodynamic model including chromates, molybdates, tungstates, and vanadates that may form in environments containing O–H–S–C–Cl and alkaline salts, to predict the limiting conditions at which ash deposition and corrosion can occur.

The role of Cu-based phases in combustion processes has boldly emerged with the drastic increase in waste combustion, initiating the need to update thermodynamic databases for a better understanding and control of problems arising at high temperature. In the present work, we have reviewed the content and sources of Cu in selected biomass fuels and ashes, and examined the mechanisms through which it affects combustion processes and the environment. Phase equilibria and thermodynamic properties of phases in the CuCl-CuSO₄ system and their effects on the melting behavior of chlorides and sulfates of Na, K, Cu, Pb, Zn, and Fe were investigated. The observed results are presented and discussed.

Lightweight nano-composite materials, nano-coatings, nanocatalysts, and nano-structured materials have demonstrated an ability to reduce emissions and maximize clean energy production. Nanoparticles play an important role in engineering and decarbonization for energy applications, and a wide range of nanoparticle synthesis methods have been developed to include those that enable control over particle morphology. The ability to control nanoparticle morphology allows the tailoring and improvement of material properties that will accelerate efforts towards lowering carbon emissions by developing advanced catalysts for carbon sequestration and will enhance energy-efficient processes and technologies. Synthesis methods aimed towards shape control of nanoparticles have demonstrated an ability to form spheres, rods, flower-like shapes, cubes, plates, shells, and chiral geometries. Processing methods used to form these morphologies include microwave-assisted synthesis, solvothermal, hydrothermal, and a wide range of capping agents. A discussion of a few of these methods is given along with results and applications.

The production of silicon with hydrogen is very challenging, although it is possible to get partway there, as SiO gas can form from SiO₂ and H₂. For some applications, metallurgical grade silicon is only an intermediary to gas-phase silicon species and “not needed” from a value-chain point of view. This work explores the possibility of going directly from SiO gas to useful Si-based gases with gas-phase chemistry. In particular, it looks into reactions between SiO gas and Cl₂ gas to form SiCl₄, which can be turned into raw materials for polysilicon production in the Siemens process. If successfully implemented, this would make CO₂-free polysilicon production possible. The work is theoretical in nature and is based on thermodynamical calculations using FactSage. Assessing the process steps in isolation, calculations show that both SiO formation from H₂ and SiO₂ and the formation of SiCl₄ from SiO are thermodynamically favourable. Combining the two steps in a process is likely to be challenging however, since if H₂/H₂O from the first step is present during the second, this will interfere with the chlorination of SiO, representing a serious bottleneck. Unless SiO can somehow be separated from H₂/H₂O at very high temperatures, success seems to be dependent on rapid quenching while suppressing back-reactions.

Decarbonization of long-haul transportation, i.e., ships and trains is among the toughest challenges toward eliminating greenhouse emissions, but metal-air batteries have extraordinary potential to meet this challenge. More specifically, Mg-air batteries have the potential for 30–40 times the energy of lithium-ion batteries at very high efficiency, and their Mg anode and molten salt materials are abundant in seawater. The two main criteria for these batteries are stability of the cathode material and removal of MgO product from the electrolyte through directional solidification. This talk will present experimental and modeling results for a novel molten salt magnesium-air battery with an MgCl₂–NaCl–KCl electrolyte operating at 420–620 °C. O²⁻ dissolves at the cathodes and Mg²⁺ at anodes. Experimental results show 1.9 V open-circuit voltage, which is the highest to date for an Mg-air battery. Modeling shows up to 1.17 W/cm² at 73% efficiency and 2.89 W/cm² at 36% efficiency. This work illustrates the proof of concept of Mg-air batteries and discusses the requirements for larger-scale cells.

The hydrogen-based direct reduction of iron ore combined with EAF smelting is being widely discussed as a possible replacement for the commonly used BF/BOF route in steelmaking when targeting carbon footprint reduction. One alternative to shaft furnaces is Metso Outotec’s Circored process, which uses fine ore as feed for fluidized bed reactors, eliminating the cost and energy-intensive pelletizing step. As a direct reduction process using 100% hydrogen as the reductant, Circored has already proven its functionality in an industrial-scale demonstration plant. Direct charging of hot DRI to a smelter would further increase the energy efficiency of the process. Metso Outotec’s rectangular six-in-line smelting furnace combines a flash smelter body and the Söderberg electrodes. This DRI smelting solution can replace small/medium-sized BFs and produce hot metal with the desired carbon content in existing steel plants with BOF converters. The large furnace volume enables the processing of low-grade iron ore with high gangue content and thus the use of BF-grade feed for DRI production.

Increased usage of lithium in lithium-ion batteries to power portable electronic devices as well as electric vehicles has resulted in a considerable global increase in demand for the metal. Consequently, the treatment of a Lepidolite ore was investigated for lithium extraction and purification through a combination of sodium carbonate roasting and water leaching. Various parameters such as ore: salt ratio, roasting temperature, and reaction time were studied. Experimental results showed the formation of various compounds as the roasting + water leaching process proceeded, yielding 91.2% lithium extraction efficiency, subsequently beneficiated to produce 99.1% pure Zabuyelite (Li₂CO₃: 83–1454, m.p. 720 °C). The product as characterized could be used as a precursor in lithium-ion batteries.

The main contributor to global warming is carbon dioxide (CO₂), herewith referred to as a greenhouse gas, with a growth of nearly 2.7%, 60% above that recorded around late twentieth century. Globally, the regulation and minimization of CO₂ have consequently become a consensus. In South Africa (SA), most CO₂ releases are from burning coal and future forecasts show that CO₂ releases will increase more and more should there be no counter-progress in the creation of carbon capture technologies (CCT). Additionally, by integrating CCT into the main sources of anthropogenic CO₂ releases, like coal power plants (CPPs), challenges of CO₂ releases will be brought to the barest minimal. Despite the challenge it presents, yet an inherent research opportunity therein, with possibility of developing a novel CCT. Hence, this paper presented a review on the theme “hydrotalcite-derived material from waste metal dust, a solid adsorbent for CO₂ capture: Challenges and opportunities in SA’s CPPs”. This theme was subdivided into the following sub-themes: challenges and opportunities inherent in SA’s CPPs; review of past and current publications on CO₂ capture from CPP. The conclusions reached are that the use of waste metal dust and/or coal fly ash to produce solid adsorbents will go a long way to saving significant cost of managing CO₂ emissions, while the conversion of this waste to product amongst other benefits will strengthen the goal of achieving a circular economy in the mining industry.

The use of “smart” power meters across a distribution network on an industrial facility can generate information for product cost allocation, operational efficiency improvement, reliability metrics (predictive maintenance), and Root Cause Fault Analysis (RCFA) or troubleshooting. To reach all the potential benefits of the network, it needs to be designed with a modern digitalization approach, able to convert electrical power measurement signals into useful business information. This session will explore the different units that a modern power measurement device can register and how they can be extrapolated to become useful business information, for example, power factor and utility bills, demand, curtailment restrictions, Total Harmonic Distortion (THD), and electrical failures. Then, it will discuss the optimal network architecture to optimize the level and amount of information collected the protocols to share that information and the security firewalls to prevent unauthorized access to the devices to close with the implications this may have in your CO₂ footprint.

The concept of a laboratory-scale solar convective furnace system (SCFS) has been proposed in a previous publication (Patidar et al. in JOM 67:2696–2704, 2015). In the present work, hot air generated from concentrated solar radiation heats ingots in an aluminium soaking furnace. The SCFS consists of the following components: an open volumetric air receiver (OVAR) to heat ambient air, thermal energy storage to address the intermittency of solar radiation, and a retrofitted soaking furnace. The TES is charged by hot air from the OVAR. Hot air recovered from the TES heats ingots in the retrofitted furnace. The present paper has three objectives. First, the modes of operation of a SCFS will be explored. Herein, the possible circuits which depict the interconnection between the components of a SCFS for day and night operations will be discussed. Second, the design basis and results of a laboratory-scale SCFS will be shown. Third, a preliminary mathematical model of a SCFS circuit will be presented.

Heat islands are urbanized areas that experience significantly higher day and night time temperatures than the surrounding rural areas on account of the influence of the buildings, roadways, and industries on the local weather. Heat island mitigation strategy depends on the weather patterns at the urban geographical location. Mitigation of heat island effect has been demonstrated by increased use of shade and materials that alter the reflectance and emissivity of the surfaces impacted by solar radiation. Interest in the use of PCM for urban infrastructure for further enhancing the mitigation through heat storage and liberation is more recent. Key physical properties needed for PCM use are the latent heat of fusion, thermal conductivity, density, and specific heat. This paper reviews the physics involved in choosing the right PCM for buildings, placement of PCM in the infrastructure, and modeling methods for optimal energy costs.

Wellbore cement is the primary hydraulic barrier material used in wellbore construction, with properties similar to the formation rock. It serves multiple purposes such as providing mechanical support and zonal isolation, maintaining well performance, and restoring sealing barriers during the wellbore abandonment. However, Portland cement can have a brittle nature making it subject to mechanical failure at downhole conditions. To improve wellbore cement properties that impact it resistance to failure, three materials are explored as additives: (1) olivine to prevent chemical attack from CO₂-rich geofluids, (2) zeolite for its water storage and slow moisture release that can potentially prevent drying shrinkage, thus allowing secondary cement hydration and potentially promoting self-healing capabilities, and (3) graphene to increase strength and/or decrease tendency of the material to brittle fracture. Investigation of the mechanism for how each of these micro-nano aggregates contributes to the enhanced performance of the cement matrix indicates that all can have positive impact on cement properties that enable effective and resilient zonal isolation.

Salt hydrates are a class of phase-change materials (PCMs) capable of storing thermal energy at a high volumetric energy density for a low cost (<$10/kWh_th), making them of interest for improving the energy efficiency of buildings and displacing peak load associated with environmental control systems. However, select salt hydrates are susceptible to irreversible degradation associated with phase segregation, and to undercooling—the occurrence of a metastable liquid below the melting point due to a lack of nucleation sites for the crystalline solid. Here, we present a study of phase-specific epitaxial nucleation agents which mitigate undercooling in eutectic nitrate salt hydrate systems. While eutectics can depress melting temperatures into favorable ranges, metastable eutectics experience undercooling. We demonstrate that the nucleation of multiple phases in systems which are susceptible to undercooling can increase the potential for phase segregation and chemical stratification to occur. Furthermore, we illustrate the utility of multiple nucleation agents in these systems to co-crystallize multiple crystalline phases.

Multiple reports exist on the range of cost of production of hydrogen from about $1.20/kg to about $12.00/kg. Hydrogen exists mainly as part of compounds and the elemental hydrogen has to be produced from these compounds and/or mixtures of compounds by spending energy. A detailed thermodynamic analysis revealed that this spectrum of costs exist primarily from the energy conversion costs and economics of such energy conversions. This analysis leads to the simple low-cost possibilities of hydrogen from hydrocarbons called ‘orange’ hydrogen, which is CO₂-free, along with the ease of making it from the ground using present-day renewable energy as needed.

Africa is rich with an abundance of renewable energy sources that can help in meeting the continent's demand for electricity to promote economic growth and meet global targets for CO₂ reduction. Green hydrogen is considered one of the most promising technologies for energy generation, transportation, and storage. In this paper, the prospects of green hydrogen production potential in different countries in Africa are investigated along with its usage for future implementation. Moreover, an overview of the benefits of shifting to green hydrogen technology is presented. The current African infrastructure and policies are tested against future targets and goals.

Producing silicon with H₂ would be advantageous from an environmental viewpoint because it opens up a potentially CO₂-free process. This study investigated the interplay between atmosphere and the reaction between SiC and SiO₂ pellets. Process gasses containing Ar, H_2, and CO were examined at 1650 and 1750 °C. In pure Ar, the reaction was slow and found to be limited by mass transfer. The reaction was faster in the presence of H₂, and, in this case, it was instead slow reaction kinetics that was rate limiting. However, the effect disappeared when adding CO together with H₂. Both H₂ and CO produced SiC whiskers at 1650 °C, but H₂ to a greater degree than CO. The whiskers reinforced the pellets, which resulted in up to 20 times higher strength for a CO and H₂ containing process gas. Process gasses without of CO resulted in weaker pellets instead.