Solid biomass oxy-fuel combustion with external recirculation was demonstrated in a 100-kW atmospheric, down-fired combustor operated close to stoichiometry. The external recirculation setup comprised a particulate filter, a condenser, a fan and O2 addition before the burner inlet. A theoretical description of the recirculation process is presented and validated. Two fuels, softwood (SW) and forest residues (FR), with similar residence times, were compared. Gaseous species, including potassium (K) compounds (atomic K, KOH, and KCl), and gas temperature were quantified in real-time by tunable diode laser absorption spectroscopy (TDLAS) and photofragmentation TDLAS at two locations in the reactor core. Major species (CO2, H2O, O2, and N2) were also measured at the exhaust. Flue gas particles collected with a low-pressure impactor at the exhaust were analyzed by X-ray powder diffraction and scanning electron microscopy. The average CO2 purity (dry) was 90 % for SW and 86 % for FR. The NO concentration was higher for FR due to the larger nitrogen content in the fuel. The gaseous K species concentrations were higher for FR than for SW (factor 2–3), but not as high as expected from the difference in fuel K content (factor 7), likely due to the high content of Si and Al in FR. Gas-phase K was significantly lower than predicted by thermodynamic equilibrium calculations (TEC), probably due to K adsorption by soot particles. The fine and coarse particle concentrations were significantly higher for FR than for SW due to the higher ash content of FR. The FR fine mode particles consisted mainly of K2SO4 and KCl, in good quantitative agreement with TEC of gas phase condensation. Apatite, Ca5(PO4)3OH, likely formed from vaporized Ca and P, was found in the fine mode in all recirculation cases

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

The current manufacturing of carbon black (CB) has a high climate impact and must transition to a carbon-neutral process to meet sustainability goals. In this work, fast pyrolysis bio-oil (FPBO) from biomass and four different upgraded bio-oils (represented by synthetic mixtures made from model compounds) were used to produce renewable CB in an entrained flow reactor (EFR) at different temperatures (1100–1700 °C). The aim of this work was to investigate how the composition of bio-oils produced via the following upgrading technologies, catalytic fast pyrolysis (CFP), catalytic hydropyrolysis (CHP), slurry hydroprocessing (SHP), and slurry hydroprocessing followed by fixed bed hydroprocessing (SHP + FBHP) affects the yield and structural properties of CB. The experimental results demonstrated that CB yield from FPBO were 34–45 wt% on a carbon basis, whereas substantially higher yields (67–93 wt%) were obtained from the upgraded bio-oils depending on the specific upgrading technology and temperature of the EFR. Furthermore, the nanostructure of the CB produced at 1300–1500 °C showed similarities to that of conventional rubber-grade CB, whereas the CB produced at 1700 °C exhibited a higher degree of graphitization, with features more similar to those of conductive-grade CB. Considering the entire conversion pathway from raw biomass to CB, upgrading the FPBO prior to its use as feedstock in the CB reactor was found to increase the overall yield from ∼27 wt% for FPBO to ∼40 wt%. The highest CB yield of ∼44% was obtained for the combination of SHP + FBHP as upgrading technology and a process temperature of 1700 °C in the EFR. The results demonstrate that bio-oil upgrading could be a key strategy for maximizing biomass carbon utilization in renewable CB production

Calcination, where CaCO3 is thermally decomposed to CaO and CO2, is one of the most important chemical reactions. In this work, a CFD model is developed to investigate the flash calcination behavior of lime mud under various temperatures and gas atmospheres. Simulation results are compared with experimental data obtained from a pilot-scale flash calcination experimental campaign conducted in a drop tube furnace at the RISE site in Piteå. The simulated flash calcination temperature ranges from 700 to 1350 °C, with 50 °C increments, under different atmospheric conditions: 100% N2, CO2, and H2O vapor, as well as a 50/50 mixture of CO2 and H2O vapor. The comparison shows overall good agreement between simulations and experiments, with most flash calcination thresholds accurately captured, particularly in cases involving CO2-containing atmospheres. The particle residence time, temperature, and the presence of CO2 and H2O vapor were identified as the most influential parameters affecting flash calcination conversion and the evolution of the specific surface area

A mid-IR TDLAS sensor for NO measurements in high-temperature environments is presented. The diagnostic targets the strong NO transition at 1977.27 cm−1, which provides low spectral interference and weak temperature sensitivity, thus reducing the effect of temperature inhomogeneity along the optical path on the retrieved path-averaged NO concentration. The diagnostic was validated in plasma-heated gases with H2O vapor and in pilot-scale biomass/hydrogen combustion at temperatures up to 1450 K and H2O mole fractions up to 30%. NO concentration obtained by fitting HITEMP-based spectra agreed with FTIR measurements within 15%, with estimated uncertainties of 20%. The sensor achieved a detection limit of about 50 ppm·m. Neighboring H2O transitions were negligible at lab-scale but required in pilot-scale fitting

Methane pyrolysis (MP), where CH4 is thermally decomposed to H2 and solid carbon is a CO2 free H2 production technique. By performing non-catalytic MP experiments in the temperature range of 1100°C-1700 °C we showed that the produced carbon nanoparticles (CNP) have a similar elemental composition (C, H, O, and N) and turbostratic nanostructure compared to rubber grade carbon black (CB) if the reactor temperature is ∼1400 °C with 100% conversion of the CH4 to CNP, C2H2, and H2 with product yields of ∼0.53 g/gfuel, ∼0.23 g/gfuel, and ∼0.24 g/gfuel, respectively. By increasing the reactor temperature above 1400 °C, further decomposition of the C2H2 to CNP and H2 occurs, and the theoretical yield of 0.75 g/gfuel of CNP and 0.25 g/gfuel H2 could be reached. However, the turbostratic nanostructure of the CNP at higher temperatures was too graphitized compared to rubber grade CB and instead more like electro conductive CB

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 N<inf>2</inf> 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 (N<inf>2</inf>+) 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

To effectively mitigate NOX emissions in pulverized coal combustion, Computational Fluid Dynamics (CFD) is frequently employed as a predictive tool. Because fuel-bound nitrogen is the primary source of NOX in these applications, modelling largely relies on coal characterization—data that are often uncertain even with costly experimental measurements. This study introduces a systematic framework for estimating missing fuel‑nitrogen characteristics from standard proximate and ultimate analyses based on correlations from rapid coal devolatilization experiments. Utilizing a conventional CFD approach, we simulated coal combustion in a 150-kW facility, which mimics rotary kiln conditions. A sensitivity analysis evaluates the impact of uncertainties in volatile nitrogen yields, precursor compositions (HCN/NH3), and char surface reactivity on NOX predictions. Results indicate that input uncertainties may account for up to 25% of the total predicted NOX. The ratio of nitrogen released as volatiles versus char-bound nitrogen and the initial char surface area of the coal particles are both critical parameters, while variations in volatile precursor ratios had a negligible effect (<1%). The model was validated against measured NOX emissions from the 150-kW facility, demonstrating that while the framework provides a robust estimation tool, high-fidelity characterization of char properties remains vital for precise emission modelling

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. 

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.