Stratified downdraft gasifiers are a promising technology for decentralized biomass-based combined heat and power generation, but their operation is strongly affected by fuel properties and operating conditions. While several measures have previously been proposed to extend the operable range of such systems, their influence on process stability has not yet been systematically compared. In this work, the process stability of a commercial stratified downdraft gasifier was assessed under different operating strategies, namely reactor extension, air preheating, exhaust gas recirculation (EGR), and load modulation. The analysis combines a stability-focused re-evaluation of previously published datasets with newly generated load-modulation experiments. Stability was quantified using the temporal standard deviations of the air mass flow rate, total hydrocarbon content (THC), and summarized bed temperature fluctuations.The results show that the investigated strategies influence process stability through different mechanisms. For wet fuel operation, increasing the fuel bed height by reactor extension proved to be the most effective stabilization strategy, as it reduced fluctuations of air flow from 1.5kgh−1 to 1.2kgh−1, hydrocarbons, and bed temperatures. Air preheating enabled operation with wetter fuels as well, but acted mainly as a compensatory measure and did not improve stability to the same level, as it increased THC fluctuations from 2000ppmvw.b. to up to 4000ppmvw.b.. For very dry fuels, EGR improved the process stability and restored the thermal behavior of the reactor to levels comparable to near-optimal fuel conditions. Load modulation affected the process differently: reduced load decreased short-term fluctuations of the air mass flow rate and hydrocarbon content, indicating a calmer gasification regime.Overall, the results provide a comparative stability assessment of relevant operating strategies for stratified downdraft gasification and show that stable operation over a broad range of fuel properties requires different stabilization approaches.

A major consumer of natural gas, and consequently a major generator of CO2, is the reheating furnace required before rolling steels. The use of alternative fuel mixtures (m & eacute;thane-O2, H2-Air, H2-O2) would reduce, or even eliminate, this CO2 production. The objective of this study is to evaluate the impact of such a change on steel products, particularly with regard to the rate of scale formation. This article aimed at providing quantitative evaluation of the scale quantity, is based on experimental data obtained on samples of 14 steels and attempts to provide a predictive law for the quantity of scale formed, as a function of the conditions of grade, fuel, oxidant, and heating duration.

Same-hardware, stack-scale evidence for PtX syngas routes is scarce. We quantify, on identical solid-oxide hardware, how operating conditions affect stack voltage and specific electricity demand to guide selection between steam electrolysis, paired downstream with RWGS, and direct co-electrolysis. We report new stack-level steam-electrolysis data and benchmark them against our previously published co-electrolysis dataset on the same five-cell electrolyte-supported stack and test rig. Measurements are non-overlapping with aligned operating windows and a single analysis pipeline. A structured design-of-experiments with regression yields sensitivities to current density, fuel-side composition/flow, and temperature. Electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), and in-plane temperature mapping provide mechanistic context for ohmic, charge-transfer, and transport contributions. Within the tested window, co-electrolysis shows stronger voltage sensitivity to current density and the air-outlet setpoint. Differences in specific electricity demand are modest per stack yet material at plant scale. Holding hardware and analysis constant, we deliver a reproducible benchmark that supports route selection and informs thermal and current-density control in commercial PtX plants.

Accurate prediction of high-temperature oxidation in Fe-Cr-Ni alloys is essential for assessing material performance in technical combustion environments. In this work, a fully coupled numerical model was developed that integrated multicomponent diffusion, CALPHAD-based phase equilibria and a moving oxide/alloy interface. Interdiffusion coefficients were calculated from thermodynamic factors and mobility data, enabling a physically consistent description of mass transport inside both the growing oxide scale and the alloy substrate. An adaptive boundary condition for the oxygen influx allowed the model to dynamically transition between surface-reaction and solid-diffusion-controlled kinetics. For the first time, an oxidation model directly incorporates the resulting concentrations of the combustion products O2, H2O, and CO2 at the gas/oxide interface through gas transport and phase-boundary reactions. The simulations were performed for 1.4307 (X2CrNi18-9) stainless steel at 1200 degrees C and 1300 degrees C under air-fuel and oxy-fuel natural gas and hydrogen combustion atmospheres. The predicted specific mass gains, oxide growth rates and concentration profiles exhibited excellent agreement with experimental and literature findings. Its numerically efficient structure facilitates extension to other alloys through parallelization, more complex multi-layer oxide systems, and transient operating scenarios.

To ensure effective sterilization of medical devices during a steam sterilization cycle, all non-condensable gases must be removed from both the chamber and the interior of the devices. This removal is facilitated by defined phases of increasing and decreasing pressure, which cause steam to condense and re-evaporate, resulting in repeated heating and cooling of the devices. To better understand the influence of phase changes on steam penetration, a computationally efficient numerical model was developed, coupling the Eulerian wall film model with the Eulerian-Lagrangian approach. A new wall adhesion model was developed to account for condensate adherence during phase change. The numerical model was first validated by comparing measured and simulated temperature profiles of stainless steel and aluminum cylinders during typical steam sterilization cycles. The validation covered steam environments with mole fractions from 0 to 0.99 and showed excellent agreement during both condensation and re-evaporation phases. In a second step, steam penetration into a simplified medical device was measured using a setup based on 2f/1f wavelength modulation spectroscopy at 1364 nm. The numerical model accurately predicted the water mole fraction over the entire observed period. Based on the results, several recommendations for improving steam penetration were derived: (1) a 100 % steam environment should be established in the chamber as early as possible, as even small amounts of residual air reduce penetration depth; and (2) internal surfaces of medical devices should be well thermally connected to their exteriors to promote heating via conduction. In summary, the proposed model captures all relevant physical processes of steam sterilization and provides a valuable tool for improving sterilization effectiveness and the safe reuse of medical devices.

The application of OH* chemiluminescence diagnostics is becoming increasingly prevalent in the combustion characterization of hydrogen. As the current literature is lacking a systematic study of OH* chemiluminescence in non-premixed turbulent natural gas (NG) and hydrogen (H2) flames, the present work was designed to address this research gap. Therefore, extensive experiments were performed on a semi-industrial burner operating at 50-100 kW in NG/H2-Air/O2 combustion modes, which were complemented by comprehensive numerical simulations, including 1D laminar counterflow diffusion flamelet calculations and full 3D CFD simulations of the semi-industrial furnace setup. In this way, an OH* chemistry model is presented that accurately predicts the global reaction zone characteristics and their difference between CH4 and H2 in air-fired and oxygen-fired flames. The comprehensive numerical approach, in conjunction with the subsequent study of different operating conditions, yielded novel insights into both combustion modeling and the underlying thermochemical phenomena, providing an essential contribution to the transition of the thermal energy sector towards hydrogen as an alternative carbon-free fuel.

Solid oxide electrolysis cells (SOECs) are central to high-efficiency Power-to-X (PtX) pathways, yet quantita tive data on their long-term stability under application-relevant co-electrolysis conditions remain rare. This study provides a systematic evaluation of SOEC degradation under syngas targets representative of methanol synthesis, Fischer-Tropsch synthesis (H2/CO=2), and methanation (H2/CO=3), using industrial-sized, fuel-electrode-supported planar cells (81 cm2). The cells were operated at 800 degrees degrees C and elevated current densities of 750 mA/cm2 for up to 500 h. Performance evolution was monitored by voltage and temperature measure ments, incremental electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), and outlet-gas analysis. Post-mortem SEM/EDX analysis (surface & cross-section) linked electrochemical degrada tion with microstructural changes. The key findings of this work are: The cells exhibited an initial improvement phase, with voltage reductions of up to 3.5%, associated with enhanced oxygen surface exchange at the air elec trode, consistent with Pt migration from the contacting mesh, followed by degradation. In all operating scenarios, the dominant fuel-electrode degradation mechanism is the coarsening of the Ni-YSZ functional layer, which de creases porosity and increases diffusion-related losses. In the H H2 H2/CO=2 case, the use of only half the air-flow rate applied in the H H2 H2/CO=3 case increased the local oxygen partial pressure, which led to more pronounced Sr surface segregation and partial air-electrode degradation. Corresponding voltage degradation rates were 68.7 and 27.3 mV/1000 h, with ASR degradation of 92 and 36 m Omega cm2/1000 h, the latter increasing at extended operating times. These results provide a quantitative analysis of SOEC degradation under PtX-relevant syngas conditions and highlight operating factors influencing stability during industrially relevant co-electrolysis.

Thin and dense, oxygen-conducting electrolyte films are essential for intermediate-temperature reversible solid oxide electrolysis cells (rSOCs). Such films can be reliably fabricated using scalable thin-film deposition techniques, such as ultrasonic spray pyrolysis (USP). This work proposes an environmentally friendly, cost- and time-efficient USP deposition route for gadolinium-doped ceria (CGO) and yttria-stabilized zirconia oxide (YSZ) electrolyte films. The deposition employs water as solvent, water-soluble metal nitrates as precursors, and it is free of organic chelating additives. The absence of organic species from the precursor solution prevents residual carbon contamination, microstructural defects, and secondary phases that can otherwise compromise the films’ implementation in rSOCs. The deposition is systematically investigated using a design-of-experiments approach and subsequently refined to reduce processing time, while optimizing the film growth on scandium-stabilized zirconium oxide substrates. In a next stage, using the optimized deposition parameters, the electrolyte thin films are deposited onto alumina substrates for the characterization of their conductivity. At 700 °C, the 20 mol

The combined application of CFD and FEM within a fluid-structure interaction framework reveals the effects of thermally induced stresses on burner components resulting from the transition from pure natural gas to pure hydrogen operation. The analysis focuses on a commercially available forced-draft gas burner operating at 358 kW and an air excess ratio of 1.2, with particular attention to an operating point located in the lower turndown ratio range. The temperature fields were obtained from detailed reactive flow simulations using the steady diffusion flamelet model in combination with the nitrogen augmented San Diego reaction mechanism. These data were used and applied as thermal loads in the structural analysis. Results from experimental and numerical investigations indicate that low load operation with pure hydrogen causes elevated temperatures in the near burner region. As a consequence of the thermophysical and combustion related properties of hydrogen, the flame root shifts closer to the stabilization region, resulting in locally intensified thermal loads.The present study demonstrates that, despite significant temperature increases during hydrogen operation, the resulting stresses in the most heavily loaded regions of the baffle plate remain comparable in both shape pattern and local maxima. A global increase in stress levels across the entire baffle plate is observed, with particular focus on the localized rises at manufacturing related features such as the bends of the swirl guiding vanes. Furthermore, the study demonstrates that variations in the baffle plate geometry influence NOx emissions, thermal loads and the shape of the stabilizing flame.

The steel industry must undergo significant transformation to align with the Paris Climate Agreement. One potential measure is replacing natural gas with hydrogen as fuel in reheating furnaces. While scale formation during reheating under conventional natural gas/air combustion has been well studied, research on hydrogen/air combustion remains limited. This work investigates the scale formation of fifteen steel grades with varying chemical compositions and applications. The steels were heat-treated in a semi-industrial setup under industry-relevant conditions. As a measure of scale formation, the specific mass gain was determined for three holding times using four samples per condition. For seven steels, the difference in scale formation between the two combustion atmospheres was within 5%, and only two steels exhibited a moderate increase of over 15% (hydrogen/air compared to natural gas/air). These results indicate that the examined steel grades are largely suitable for hydrogen-based reheating processes.

This study investigates the effect of Oxygen-Enriched Combustion on hydrogen-enriched natural gas (H2-NG) fuel mixtures at a semi-industrial scale (up to 60 kW). The analysis focuses on flame structure, temperature distribution in the furnace, NOx emissions, and potential fuel savings. A multi-fuel, multi-oxidizer jet burner was used to compare two oxygen enrichment configurations: premixed with air (PM) and air-pure O2 (AO) independent feed. The O 2-enriched flames remained stable across the entire fuel range. OH* chemiluminescence imaging for the H-NG fuel mixture delivering 50 2 kW revealed that higher O 2 concentration increases the OH* intensity, narrows and elongates the flame, transitions from buoyancy-to momentum-driven shape, and relocates the reaction zone. At 50 % oxygen enrichment level (OEL), flame shape, OH* intensity, and temperature profiles resembled pure O combustion. Up to 29 2 % OEL, furnace temperature profiles were similar to those of air-fuel combustion. The power required to maintain 1300 +/- 25 degrees C at the reference position decreases with O 2 enrichment. Higher OELs resulted in a sharp increase in NOx emissions. The effect of hydrogen enrichment on NOx levels was significantly less pronounced than that of oxygen enrichment. The rise in NOx emissions correlates with increased OH* in tensities. For a 50 % H 2 blend, increasing the O concentration in the oxidizer from 21 % to 50 % 2 resulted in a 27 % reduction in flue gas heat losses. Utilizing O 2 co-produced with H2 could be strategic for reducing fuel consumption, facilitating the adoption of hydrogen-based energy systems.-

Climate change and food security are tightly linked global challenges. Gas fermentation offers a sustainable route to convert CO₂ into microbial single-cell protein (SCP), with hydrogen-oxidizing bacteria (HOB) emerging as efficient biomass producers via the Calvin-Benson-Bassham cycle. While SCP can replace protein-rich feed components, intracellular polyhydroxybutyrate (PHB) accumulation redirects carbon and reducing power away from biomass and protein synthesis, reducing process efficiency. With this aim, a low amount of PHB is needed to focus on protein production rather than PHB accumulation. This study shows that the PHB formation in Cupriavidus necator H16 during autotrophic gas fermentation is low under non-limiting conditions. Three optimized 48-hour fermentations were analyzed using two quantification methods: GC-FID and HPLC-UV. Both approaches yielded comparable results, but HPLC-UV proved superior in speed, safety, and compliance with green chemistry principles. Time-course analysis revealed consistently low PHB levels (∼6 % CDW) under optimized conditions. These findings demonstrate that tailored process control can suppress PHB accumulation in wild-type strains, improving carbon conversion toward SCP. This approach enhances energy efficiency and supports SCP's potential as a climate-resilient protein source for food and feed applications.

Phosphorus is an essential resource for numerous industrial applications. However, its uneven global distribution makes Europe heavily dependent on imports. Recovering phosphorus from waste streams is therefore crucial for improving resource security. The FlashPhos project addresses this challenge by developing a process to recover phosphorus from sewage sludge, in which phosphorus-rich slag is produced in a flash reactor and subsequently reduced in a Submerged Arc Furnace (SAF). In this process, approximately 250 kg/h of sewage sludge is converted into slag, which is further processed in the SAF to recover about 8 kg/h of white phosphorus. This work focuses on the development of a computational model of the SAF, with particular emphasis on slag behaviour. Due to the extreme operating conditions, which severely limit experimental access, a numerically efficient three-dimensional CFD model was developed to investigate the internal flow of the three-phase, AC-powered SAF. The model accounts for multiphase interactions, dynamic bubble generation and energy sinks associated with the reduction reaction, and Joule heating. A temperature control loop adjusts electrode currents to reach and maintain a prescribed target temperature. To further reduce computational cost, a novel simulation approach is introduced, achieving a reduction in simulation time of up to 300%. This approach replaces the solution of the electric potential equation with time-averaged Joule-heating values obtained from a preceding simulation. The system requires transient simulation and reaches a pseudo-steady state after approximately 337 s. The results demonstrate effective slag mixing, with gas bubbles significantly enhancing flow velocities compared to natural convection alone, leading to maximum slag velocities of 0.9-1.0 m/s. The temperature field is largely uniform and closely matches the target temperature within +/- 2 K, indicating efficient mixing and control. A parameter study reveals a strong sensitivity of the flow behaviour to the slag viscosity, while electrode spacing shows no clear influence. Overall, the model provides a robust basis for further development and future coupling with the gas phase.

Via the replacement of individual burners in industrial furnaces with hydrogen ready oxy-fuel burners, energy consumption and CO2 emissions can be significantly reduced at low investment costs. A main issue that often arises by air- and oxy-fuel co-combustion, especially for hydrogen combustion, is an increase in thermal NOX. A prototype oxy-fuel burner designed for industrial application in such a co-combustion environment is experimentally investigated. The investigated burner uses a novel concept with choked flow oxygen lancing, resulting in an underexpanded jet. Therefore, two burners with a combined power input of up to 635 kW are installed onto a test furnace equipped with several measurement instruments. The results from air-fuel combustion are used as a baseline to compare the effects of standard oxy-fuel co-combustion with high impulse oxy-fuel co-combustion in terms of NOX formation. Additionally, the results include temperature profiles and heat flux profiles for staged and non-staged cases for global hydrogen enrichments up to 85 % and global oxygen enrichments up to 60 %. Results showed significant reduction in NOx formation by high impulse oxygen lancing. Compared to the air-fuel combustion case a reduction of up to 72 % was achieved. Furthermore, the choked flow lancing did not show negative consequences in terms of operational safety, flame stability and temperature or heat flux distribution.

Small-scale biomass gasification with a gas engine is a promising alternative to fossil fuels for decentralized heat and power generation. Downdraft gasifiers are attractive for small-scale use because they require no complex gas cleaning prior to engine utilization, but they are highly sensitive to changes of fuel water content. This study investigates the transient response of a stratified downdraft gasifier to abrupt fuel water content changes. Fuel switches from dry (11%) to wet fuel (18%) and back were performed. Without compensatory measures, a dry-to-wet fuel switch caused a rapid decrease in fuel bed temperatures below 900 degrees C within less than 20 min, ultimately leading to reactor shutdown. By contrast, immediate adjustment of the fuel bed height after the fuel switch maintained stable bed temperatures, prevented downward movement of the reaction front, and enabled a rapid transition of the gas composition to the new steady state. During stabilized operation, permanent gas composition and real-time tar concentrations remained within ranges suitable for gas engine utilization. These results demonstrate that fuel bed height adjustment is a simple and effective strategy to enhance fuel flexibility and process stability during transient operation of stratified downdraft gasifiers.

This research develops and validates a quasi-2D solid-oxide cell model for co-electrolysis and addresses critical modeling challenges. The model incorporates gas flow, Butler-Volmer electrochemistry, and the Dusty Gas Model for diffusion calculations. It assumes isothermal operation, confines electrochemistry to H2O splitting, restricts electrochemical reactions to the electrode-electrolyte interfaces, and gas-phase chemistry to the channels. The model is validated against data from a commercial Elcogen ASC-300C cell operated under various fuel compositions at 800 degrees C. Central model parameters governing activation and concentration overpotentials are fitted to the experiments, and the resulting estimates align well with literature values. The study finds that such a simple model provides accurate predictions for fuel mixtures with H2O-to-CO2 ratios above 0.55 at water-gas-shift equilibrium, a range which covers most relevant industrial co-electrolysis applications such as methanation and Fischer-Tropsch synthesis.

Long-term durability and operating-mode flexibility are barriers to commercial solid oxide electrolysis (SOE) for hydrogen production and supplying syngas for synthetic-fuel synthesis. We report a high-resolution degradation benchmark of a commercial 4 & times; 4 cm2 electrolyte-supported cell operated for 2650 h under six modes that cover steam electrolysis, co-electrolysis at Fischer-Tropsch-relevant syngas conditions at 300 and 500 mA cm-2, repeated steam electrolysis, and reversible electrolysis and fuel cell cycling at 800 degrees C and fixed gas flows. Bihourly electrochemical impedance spectroscopy (EIS) is analysed using a Deep-Prior Distribution of Relaxation Times (DP-DRT)-derived neural DRT solver that processes more than 1200 spectra within minutes, enabling time-resolved separation of ohmic and polarisation contributions. Performance loss is dominated by an increase in ohmic resistance Rs, while polarisation resistance shows only modest net changes. Co-electrolysis mainly adds a low-frequency polarisation contribution that is largely reversible when returning to steam electrolysis. In late-life steam electrolysis at high steam fraction, accelerated ohmic ageing emerges after substantial cumulative operation. Post-mortem SEM reveals fuel-side microstructural coarsening and larger voids. The combination of a single-cell, single-sequence multi-mode campaign with bi-hourly EIS and consistent DRTbased batch inversion provides a uniquely time-resolved, internally comparable degradation dataset that goes beyond end-point voltage trends and enables mode-specific attribution of ageing contributions.

This investigation presents a computationally efficient modeling strategy for partial hydrogen oxy–fuel conversion in natural gas-fired furnaces, combining RANS simulations with a Reactor Network Model for detailed chemistry post-processing. The approach was first validated against comprehensive experimental data from a semi-industrial furnace equipped with a staged low-NOx oxy–fuel burner and a natural gas–air burner. Validation included gas temperature distributions, heat-transfer rate and flue gas composition measurements, as well as OH∗ chemiluminescence imaging for main reaction zone characterization. The model demonstrated high accuracy, with gas temperature deviations within ± 22 K, heat-transfer rate predictions to cooling lances within 3.3%, and excellent agreement in major species concentrations. Reduction of the turbulent Schmidt number was found essential to correctly capture near-burner mixing, while neglecting TCI for minor species was adequate for the investigated operating conditions. The validated method was subsequently applied to a 15 MW industrial reheating furnace model to assess partial burner substitution by hydrogen–oxygen combustion under the operational constraints requiring preservation of the original blooms heating profile. Integration of hydrogen burners reduced fuel consumption by up to 3.8% and CO2 emissions by up to 21%, while improving process efficiency from 71.5% to 74.1%. NOx emissions decreased with the number of integrated hydrogen burners by a maximum of 34%. Despite significant reductions in flue gas mass flow, gas temperature fields, bloom heating curves and overall heat transfer remained comparable to the original behavior. The results demonstrate that partial hydrogen oxy–fuel conversion can significantly reduce carbon emissions while maintaining furnace performance, highlighting the potential of the proposed modeling strategy for industrial applications.

Industrial reheating furnaces face increasing demands for higher efficiency and lower emissions, yet the impact of oxygen-enriched and oxy-fuel combustion on furnace performance is still insufficiently understood on an operational scale. Previous studies often applied fixed burner power distributions across oxidizer conditions, which neglected zone-specific heating requirements and led to deviations from the intended thermal heating behavior of the products. To address this gap, a thermodynamic redistribution method was developed to adjust the zonal fuel input to the oxidizers studied while maintaining the original furnace characteristics and heating curves of the products. A numerically inexpensive three-dimensional RANS model was then coupled with a transient bloom model, enabling consistent representation of both furnace flow and bloom heating and confirming the method. The procedure was validated against detailed furnace measurements, including bloom heating curves, furnace temperature, flue gas compositions, NOx emissions, and wall temperatures. Results showed that enrichment to 25 vol% O2 reduced fuel demand and CO2 emissions by 4.8%, but more than doubled NO formation, whereas partial substitution with oxy-fuel in one combustion zone offered comparable savings while keeping NOx emissions low. Radiation remained the dominant heat transfer mechanism, and overall temperature fields were largely unaffected. Comparison with CFD confirmed that the developed thermodynamic approach reproduces global power balances reliably, demonstrating its robustness and applicability to a wide range of oxidizer-fuel configurations in industrial furnaces. To incorporate the different combustion modes consistently, combustion-dependent coefficients were introduced for the gas absorption coefficient calculation, while burner-type-dependent values were applied for the turbulent Schmidt and Prandtl numbers.