This work investigates the possibility and potential insights gained from in-situ scanning electron microscopy (SEM) experiments focused on the dynamic heating of CaCO3 for calcination processes. MEMS chips were used to facilitate uniform heating, precise control of heating parameters and reproducibility, providing a controlled environment for comprehensive experimentation. This work focuses on the microstructure transformation, with particular emphasis on the meso- and macropores, grain formation, and the sintering behavior of these particles. Influence of heating rates and complex interplay of temperature and microstructural transformations was revealed. The results obtained may be useful for optimization and microstructural-based design of the calcination procedures for complex process engineering in various applications.

Quantitative laser-based diagnostics like Raman spectroscopy are essential for studying high-temperature processes, but their application in intensely luminous and transient environments such as plasma torches is severely limited by overwhelming background emission. This study focuses on the quantitative thermometry of a 7 kW atmospheric air plasma jet, an environment where such measurements are notoriously difficult. To enable these measurements, a Polarization Lock-In Filtering (PLF) Raman technique is used to suppress the intense and fluctuating plasma background. The method successfully yields high-quality N2 ro-vibrational spectra along the jet’s central axis. Model-based fitting of these spectra produces a detailed axial temperature profile, showing a decay from over 3700 K near the nozzle. Furthermore, the high signal quality enabled the detection of singly ionized nitrogen (N2+) in the plasma core, providing direct evidence of its ionized state. These results represent the first application of PLF for thermometry in a plasma torch and provide critical experimental data for validating magnetohydrodynamic simulations. 

In a non-transferred plasma torch, the working gas becomes ionized and forms plasma as it interacts with the electric arc at the cathode tip. However, in certain cathode shapes, particularly flat ones, and under specific conditions, the gas flow can separate at the cathode tip, forming a vortex region. While this flow separation is influenced by geometric factors, it occurs in the critical zone where plasma is generated. Understanding the causes of this separation is essential, as it may significantly impact torch performance. If the separation proves detrimental, it is important to identify ways to mitigate it. This paper presents a computational analysis of a non-transferred plasma torch to investigate the physics behind flow separation. The results highlight the location and causes of the separation, as well as its potential advantages and disadvantages. Finally, the paper explores theoretical approaches to address flow separation in plasma torches, offering practical insights for enhancing their design and efficiency.

The plasma jet produced by a non-transferred plasma torch may initially appear steady and laminar, but it undergoes significant turbulence as it interacts with the surrounding atmosphere. Within the plasma torch, the jet begins as laminar; however, upon exiting, it transitions into a turbulent flow, extending into a long, wavy structure as it develops. This paper explores the complexities of computational modeling for non-transferred plasma torches, focusing on the challenges of simulating the multiphysics and multiphase interactions at the outlet and tracing the evolution of the plasma jet. The computational analysis uses COMSOL Multiphysics software on a 2D axisymmetric geometry, with steady-state simulations incorporating various turbulence models. A comparative assessment of the results from each turbulence model is provided, highlighting their respective strengths and limitations. Although the diffusion of the turbulent jet at the outlet is presented, the turbulence models employed in this study only offer time-averaged values, rather than a detailed breakdown of the complete jet structure. The paper concludes by validating the computationally obtained velocity magnitudes against experimental data, ensuring the accuracy and reliability of the simulation results.

Coal replacement with hydrogen is a strategy for reducing carbon emissions from high-temperature industrial processes. Hydrogen lancing is a direct way for introducing hydrogen to existing coal-fired kilns. This work investigates the effects of hydrogen lancing on nitrogen oxides (NOx) emissions and ignition behaviour in a pilot-scale furnace that employs a 30 % coal replacement with hydrogen lancing. The investigation encompasses the impacts of lancing distance, angling, and velocity. Advanced measurement techniques, including spectrometry and monochromatic digital cameras, characterise the flame and assess emissions.The results indicate that the 30 % coal replacement by hydrogen lancing enhances combustion and reduces the emissions of carbon monoxides (CO). The flame characteristics vary with the location of the hydrogen injection, generally becoming more-intense than during coal combustion. NOx emissions during lancing are similar or up to double the emissions observed for pure coal combustion, depending on the lancing configuration. Increasing the distance between the hydrogen lance and coal burner increases NOx emissions.

In this article, the effects of calcination temperature and calcination atmosphere on the properties of the lime produced during flash calcination of industrial lime mud samples in a pilot-sized drop tube furnace have been studied. Flash calcination was performed at a wide range of temperatures between 800 and 1300 °C and different gas mixtures containing N2, CO2, and H2O in the calcination atmosphere. The effect of the calcination condition on the key conditions of the produced CaO, such as chemical composition, surface area, porosity, and particle morphology, has been shown. The addition of CO2 to the inert atmosphere led to slower calcination rates and a higher onset temperature for the calcination, but no changes to morphology. Furthermore, the addition of H2O to the calcination atmosphere generally led to lower calcination rates at higher temperatures and smoother particles in comparison to CO2 and N2.

Pyrolysis oil (PO) derived from biomass has the potential to serve as a renewable feedstock for future carbon black (CB) production. However, its composition is significantly different from the fossil feedstocks currently used for CB manufacturing, as it contains higher concentrations of oxygen and water that might influence the yield and nanostructure of CB. In this article, we examine how the water content in PO affects the production of CB at high-temperature pyrolysis (1400–1600 °C) in an electrically heated entrained flow reactor. The main objective was to investigate the influence of water content on the yield and quality of the CB produced from upgraded PO with varying inherent water contents (0–20 wt %). The experiments in this work were performed with model compounds to simulate an upgraded PO. The produced CB was characterized by using several analytical techniques, including elemental composition, powder X-ray diffraction, transmission electron microscopy, and nitrogen physisorption. The results show a clear correlation between the water content in the PO feedstock and the output of CB, showing a reduced yield of CB as the water content increases. These results highlight the crucial role of feedstock composition in making PO a viable renewable feedstock for CB production.

Understanding of carbon nanomaterials oxidation is useful in many different applications, e.g., for soot emission abatement, or in defect engineering aiming to improve material properties. In this work, the oxidative behavior of three substantially different qualities of carbon black, multiwall carbon-nanotubes, and few-layer graphene, was studied using a combination of macroscale quantification (using thermogravimetric analysis) and nanoscale imaging of their structural evolution (using environmental transmission electron microscopy, ETEM). The materials were investigated both with and without the addition of a nanoparticulate iron oxide catalyst. Catalyst addition clearly lowered the conversion temperature during oxidation. The ETEM revealed that the catalyst nanoparticles induced primary surface damages in the carbon nanostructure at relatively low temperatures. From there, oxidation could proceed more rapidly at recently exposed edge sites due to their higher propensity for oxidation. Thus, the enhanced oxidation was not solely linked to the interface between catalyst and carbon.

Oxy-fuel biomass combustion can facilitate carbon capture in heat and power plants and enable negative carbon dioxide (CO2) emissions. We demonstrate oxy-fuel combustion (OFC) of softwood powder in a 100-kW atmospheric down-fired pulverized combustor run at a global oxidizer-fuel equivalence ratio of around 1.25. The simulated oxidizer was varied between oxygen (O2)/CO2 mixtures of 23/77, 30/70, 40/60 and 54/46, and artificial air. The concentrations of the main gaseous potassium (K) species: atomic K, potassium hydroxide (KOH) and potassium chloride (KCl), were measured at two positions in the reactor core using photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS). Major species were quantified by TDLAS in the reactor core and with Fourier transform infrared spectroscopy and mass spectrometry at the exhaust. Flue gas particles were collected at the exhaust employing a low-pressure impactor and analyzed by X-ray powder diffraction and scanning electron microscopy. The measured individual K species concentrations in the reactor core agreed with predictions by thermodynamic equilibrium calculations (TEC) within one order of magnitude and the sum of K in the gas phase agreed within a factor of three for all cases. Atomic K was underpredicted, while the dominating KOH and KCl were slightly overpredicted. The ratios of measured to predicted total K were similar in artificial air and OFC, but the distributions of the individual species differed at the upper reactor position. The gaseous K species and fine particle concentrations in the flue gas were directly proportional to the O2 content in the oxidizer. The crystalline phase compositions of the coarse mode particles were rich in K- and calcium-containing species. The fine mode particles, which contained most of the K, consisted mainly of K2SO4 (94%) and K3Na(SO4)2, which is in excellent agreement with TECs of gas phase condensation. As supported by the solid phase analysis, complete sulfation of K species was achieved for all studied cases. A CO2 purity (dry) of up to 94% was achieved for OFC.

This study explores how different electrode shapes affect plasma flow in a non-transferred plasma torch. Various cathode geometries—including conical, tapered, flat, and cylindrical—were examined alongside stepped anode designs. A 2D axisymmetric computational model was employed to assess the impact of these shapes on plasma behavior. The results reveal that different cathode designs require varying current levels to maintain a consistent power output. This paper presents the changes in electric conductivity and electric potential for different input currents across the arc formation path (from the cathode tip to the anode beginning) and relating to Ohm’s law. Significant variations in plasma jet velocity and temperature were observed, especially near the cathode tip. The study concludes by evaluating thermal efficiency across geometry configurations. Flat cathodes demonstrated the highest efficiency, while the anode shape had minimal impact.