Furnace Configuration Research Articles

Design solutions and characterization of a small scale and very high concentration solar furnace using a Fresnel lens

The use of Fresnel lenses for solar energy concentration technology dates back to the 1950 s. These lenses feature a plano-convex optical design with a series of discontinuous convex grooves. Typically made from materials like polymethyl methacrylate, Fresnel lenses are lightweight, resistant to sunlight, thermally stable, and cost-effective.This study presents a novel Fresnel lens-based solar furnace configuration installed at the Eduardo Torroja Institute for Construction Science in Madrid, Spain. The novelty of this work lies in the exceptional performance and operability of the facility. Experimental characterization revealed a record peak irradiance over 7 MW m−2 for an incident target power exceeding 800 W. Comparison with ray tracing simulations shows good agreement with experimental results. This setup enables high temperature experiments up to 2000 °C with rapid execution times. A fixed receiver, a shutter system and a closed-loop heliostat tracking control system allow for flexible operation up to 5000 suns and straightforward maintenance. The concentrator element costs less than 300 USD (2022) m−2, offering an economical solution to solar-powered high concentration and temperature applications. This innovative design overcomes previous operational challenges, providing a robust and economical method for high-temperature material processing and other industrial applications.

Assessment of narrow-band and full spectrum gas radiation methods in a real industrial glass furnace configuration

This work is dedicated to a comparison of various methods of gaseous flame radiation in a three-dimensional configuration representative of a glass furnace studied at Saint Gobain Research Paris. For this purpose, several narrow band and full spectrum models of flame radiation are assessed against LBL calculations. Among narrow band models, the recently proposed l-distribution method is shown to be more accurate than the k-distribution method. Among global models, the RC-SLW technique provides a high accuracy and can be confidently used for radiative heat transfer calculations in three-dimensional high temperature configurations.

Assessment of engineering gas radiation methods in an industrial glass furnace configuration

This work is dedicated to a comparison of various methods of gaseous flames radiation in a tri-dimensional configuration representative of a glass furnace studied at Saint Gobain Research Paris.

Comparative Study of AC and DC Solvers Based on Current and Power Distributions in a Submerged Arc Furnace

This work discusses 3D models of current distribution in a three-phase submerged arc furnace that contains several components, such as electrodes, central arcs, craters, crater walls, and side arcs that connect electrodes and crater walls. A complete modeling approach requires time-dependent modeling of the AC electromagnetic fields and current distribution, while an approximation using a static DC approach enables a significant reduction in computational time. By comparing results for current and power distributions inside an industrial submerged arc furnace from the AC and DC solvers of the ANSYS Maxwell module, the merits and limitations of using the simpler and faster DC approach are estimated. The conclusion is that although effects such as skin effect and proximity are lost with the DC approach, the difference in the location of energy dissipation is within a 6 pct margin. The given inaccuracies introduced with an assumption about furnace configuration and physical properties are significantly more important for the overall result. Unless inductive effects are of particular interest, DC may often be sufficient.

Experimental and numerical investigations of the Czochralski growth of Li2MoO4 crystals for heat-scintillation cryogenic bolometers

Abstract A new technology for the mass production of lithium molybdate (Li2MoO4) crystals needed for the realization of the cryogenic neutrinoless double-beta decay detectors is under development within the framework of the CLYMENE project. Crystals with 4 and 5 cm in diameter were grown in two different Czochralski configurations. The first configuration, based on inductive heating of a RF coil coupled with a platinum crucible, was used to grow crystals of 4 cm in diameter. Bolometric tests performed with two samples cut from a 230 g crystal have shown less performances of the large sample (158 g), which had a cleavage, as compared to the small non-cracked sample (13.5 g). Numerical modeling was applied to investigate the temperature field in the furnace, the melt convection and thermo-elastic stresses in the crystal. Numerical results reveal 30% higher thermal stress at the bottom part of the ingot in the case of a concave shape of the crystal tail (experimental case) as compared to the case of a convex shaped tail. This could explain why the fracture started at the bottom part of the 230 g crystal boule, and highlights the importance of the crystal shape in the last stage of growth process. The furnace configuration used to grow 5 cm-diameter crystals was numerically optimized in order to reduce the thermal stress in the crystals. The first kg-mass Li2MoO4 ingot grown in the optimized configuration exhibit regular shape and good structural quality.

Fe3+ reduction during melt‐synthesis of LiFePO4

LiFePO4 (LFP) is a safe and low cost cathode material for Li‐ion batteries. Its solid‐state synthesis requires micron‐sized reactants yielding high production costs. Here, we melt‐synthesized up to 5 kg batches of LFP from low‐cost coarse Fe2O3 (509 µm) in an induction furnace. Graphite from the crucible was an effective reducing agent. Adding metallic Fe or CO increased the Fe2+ content and reaction kinetics. Metallic Fe improves the lifetime of the graphite crucible but requires a premixing step for it to be effective, otherwise the Fe powder agglomerates due to the presence of a eutectic in the LiPO3‐Fe‐Fe2O3 system. In a pushout furnace configuration, for an hour‐long holding period, injecting CO into the melt increased the Fe2+ content from 0.301 to 0.315 g/g, which we attributed to melt protection. Likewise, graphite powder floating on top of the melt further improved the Fe2+ content to 0.331 g/g. The Fe2+ content reached 0.325 g/g when using fine Fe3+ (142 µm) and CO as reducing agent at half the holding period at 1150 °C. We attribute the higher reaction rate to the improved contact between the suspended Fe3+ and the CO reducing gas. When the graphite crucible is the unique reducing agent, the reaction rate was proportional to the crucible base surface area. A zero‐order kinetic model characterized the solids disappearance with time. A thermal model developed to compare lab‐scale data against small pilot‐scale demonstrated that the charge lagged the furnace temperature by as much as 22 min at 1000 °C.

Optimization of the controlling recipe in quasi-single crystalline silicon growth using artificial neural network and genetic algorithm

The thermal field in the seeded directional solidification (DS) of quasi-single crystalline (QSC) silicon needs precise control to preserve the seed and maintain a flat solidification interface. Compared with adjusting the furnace configuration and materials properties, optimizing controlling recipe parameters of the DS process is more convenient and efficient in reality for improving the thermal field. However, controlling elements in the furnace interact with each other and the cooperation effect cannot be estimated by qualitatively deducing, which adds difficulties to the design and improvement of controlling recipe. In this study, an optimization system was built to optimize the controlling recipe during crystal growth and an industrial G6 DS furnace was taken as an application example. Flattening the solidification interface, reducing the thermal stress in the growing crystal and shortening the casting time were chosen as three optimization targets. Two independent heaters and a heat gate were the three controlling elements whose recipe parameters were the optimization variables. A 2D heat transfer model along with a thermal stress model was developed and an Artificial Neural Network (ANN) was trained to study the mapping relationship between optimization variables and targets in order to save computing resource and time. Genetic Algorithm (GA) was employed to yield the optimal recipes of the three controlling elements. The results showed that the optimal recipe achieved better crystal quality compared with the original recipe. The effectiveness and efficiency of this optimization system indicates that it can achieve the optimal result that theoretic analysis may hardly access.

The consequences of eliminating the soaking section of a commercial hot-dip galvanising line for HSLA production and a control strategy for improving product consistency

ABSTRACT This paper describes the results of the investigations done to adapt the thermal cycles applied to High Strength Low Alloy (HSLA) steels to the new furnace configuration of a galvanizing line. During the revamping of a hot dip galvanizing line, new radiant tubes were installed in the soaking furnace with the purpose of increasing the line capacity. This modification eliminated the soaking stage and forced to redesign the thermal cycles of the furnace. As the classical cycles proposed for the HSLAs worrisomely increased the percentage of rejections, it was defined a new control parameter based on the strip thickness, time in the furnace and strip temperature to guarantee the mechanical characteristics of these steels.

CFD-based optimization of a transient heating process in a natural gas fired furnace using neural networks and genetic algorithms

In the present study a transient heating process in a natural gas fired test furnace, used for fire resistance tests of construction and building materials, was investigated by computational fluid dynamics (CFD). To ensure the reproducibility of a fire resistance test, the thermal exposure of the tested fire safety material has to be homogeneous and, thus, the temperature distribution is of high importance. For that purpose, a CFD-based optimization of the transient heating process was carried out using different optimization algorithms. Based on the furnace setup, parameters with a potential to improve the temperature distribution were identified and used for the optimization procedure. CFD results were used to create system response surfaces, which represent the temperature distribution in the furnace as a function of the chosen design parameters. The system response was approximated by neural networks and genetic algorithms, and represents the basis for the optimization. Since the duration of the transient process was 35 min, the calculation time of the gas phase combustion and heat transfer is high. Therefore, a novel CFD-based approach was used to investigate and improve the process by converting the transient heating problem to steady-state cases. A comparison of the initial and the optimized furnace configuration showed an improved temperature distribution, where the maximum temperature difference in the furnace at the measurement position was decreased from approx. 200 K to 162 K. This approach showed that the transient simulation can be optimized, and further used for other applications where a transient simulation is computationally too demanding.

Modeling Interface Shape in Czochralski Growth of Sapphire Crystals

AbstractNumerical modeling is applied to investigate the factors affecting the shape of the crystal‐melt interface in Czochralski growth of sapphire crystals having 10 cm in diameter. The modeling is performed for a 2D – axisymmetric furnace configuration, where all the furnace components are included. The shape of the crystal‐melt interface is computed by using the deformable mesh technique. Numerical results show that the conical shape of the interface depends essentially on the internal radiative heat exchanges in the semi‐transparent sapphire crystal, being less influenced by the buoyancy convection. The Marangoni effect enhances the flow near the triple solid‐liquid‐gas point, leading to convex‐concave shape of the growth interface, which is prone to facet formation. Numerically computed shape of the interface is compared to experimental results taken from literature. Applying crystal/crucible rotation has a significant impact on the flow pattern and the shape of the growth interface. Computations performed by applying only crystal rotation at rates higher than a critical value, show a reversed convection at the sample centre, underneath the crystal. This flow affects the shape of the interface, which is less curved and exhibits a convex shape. If the rotation rate is too much increased, the interface shape can be distorted by the intense flow. Application of crucible rotation intensifies the downward flow at the sample centre, leading to increased interface curvature. Rotating both the crystal and crucible in opposite directions generates a complex flow pattern, but has no flattening effect on the interface.

Trends of the Flow-Field Deflection and Asymmetric Combustion in a 600 MWe Supercritical Down-Fired Boiler with Respect to the Furnace Arch’s Burner Span

The asymmetric upper furnace configuration effect (mainly relied on the short upper furnace) and unreasonable burner designs (mainly related to the burner location and burner span on furnace arches) are taken as potential major factors favoring the asymmetric combustion formation in down-fired boilers. To confirm the burner span’s role in this aspect, numerical simulations on coal combustion in a 600 MWe supercritical down-fired boiler that suffered from severe flow-field deflection and asymmetric combustion were carried out at three burner span settings (i.e., CS = 0.387, 0.441, and 0.495), plus full-load industrial-size measurements at the boiler’s design setup CS = 0.441. The boiler’s design setup shows a badly asymmetric combustion performance with poor burnout and high NOx emissions, corresponding to its severely deflected gas/particle flow field. Shortening the burner span to CS = 0.387 greatly improves the flow-field deflection and asymmetric combustion, resulting in a burnout increase and NOx redu...

Effect of burner location on flow-field deflection and asymmetric combustion in a 600 MWe supercritical down-fired boiler

To evaluate the burner location's role on the flow-field deflection and asymmetric combustion that occurring in a 600MWe supercritical down-fired boiler, cold-modeling gas/particle flow experiments and numerical simulations on coal combustion were performed with varying the furnace arch's burner location. Meanwhile, full-load industrial-size measurements at the boiler's design setup were performed to uncover the asymmetric combustion characteristics and verify the simulation validity. The boiler's design setup displayed a severely deflected gas/particle flow field with (i) a large downward gas/particle flow penetration difference appearing in the front- and rear-half sides and (ii) the upward flow fully deflecting towards the front-half side. Accordingly, a badly asymmetric combustion performance (much lower gas temperature levels appearing in the front-half side than in the rear-half side) occurred with poor burnout and high NOx emissions. The calculated coal/air penetration and flow-field deflection extent were found to be shallower than the cold-modeling experimental versions, despite the consistent flow-field deflection pattern respectively gained by the two methods. Positioning burners towards the front/rear wall greatly improved the flow-field deflection in the form of apparently decreasing the aforementioned penetration difference and redirecting the upward gas/particle flow in the furnace’s central part. Consequently, asymmetric combustion sharply weakened to increase burnout and reduce NOx emissions. In contrast, moving burners towards the furnace centerline aggravated the flow-field deflection and asymmetric combustion to worsen the furnace performance in burnout and NOx production. These results suggest that in the absence of coal/air distribution with varying burner location, the local high gas temperatures incurred by asymmetric combustion facilitate the NOx production. Finally, burners are recommended to position towards the front/rear wall as much as possible for weakening the flow-field deflection and asymmetric combustion if a lowered manufacturing cost requires a short upper furnace where the asymmetric upper furnace configuration effect is aggravated.

Increasing the efficiency of the condensing boiler

Analysis of existing designs of boilers with low power consumption showed that the low efficiency of the latter is due to the fact that they work in most cases when the heating period in the power range is significantly less than the nominal power. At the same time, condensing boilers do not work in the most optimal mode (in condensing mode) in the central part of Russia, a significant part of their total operating time during the heating season. This is due to existing methods of equipment selection and joint operation with heating systems with quantitative control of the coolant. It was also revealed that for the efficient operation of the heating system, it is necessary to reduce the inertia of the heat generating equipment. Theoretical patterns of thermal processes in the furnace during combustion gas at different radiating surfaces location schemes considering the influence of the very furnace configuration, characterized in that to reduce the work condensing boiler in conventional gas boiler operation is necessary to maintain a higher temperature in the furnace (in the part where spiral heat exchangers are disposed), which is possible when redistributing heat flow - increase the proportion of radiant heat from the secondary burner emitter allow Perey For the operation of the condensing boiler in the design (condensation) mode practically the entire heating period.

Increasing the efficiency of the condensing boiler

Analysis of existing designs of boilers with low power consumption showed that the low efficiency of the latter is due to the fact that they work in most cases when the heating period in the power range is significantly less than the nominal power. At the same time, condensing boilers do not work in the most optimal mode (in condensing mode) in the central part of Russia, a significant part of their total operating time during the heating season. This is due to existing methods of equipment selection and joint operation with heating systems with quantitative control of the coolant. It was also revealed that for the efficient operation of the heating system, it is necessary to reduce the inertia of the heat generating equipment. Theoretical patterns of thermal processes in the furnace during combustion gas at different radiating surfaces location schemes considering the influence of the very furnace configuration, characterized in that to reduce the work condensing boiler in conventional gas boiler operation is necessary to maintain a higher temperature in the furnace (in the part where spiral heat exchangers are disposed), which is possible when redistributing heat flow - increase the proportion of radiant heat from the secondary burner emitter allow Perey For the operation of the condensing boiler in the design (condensation) mode practically the entire heating period.

A study case of energy efficiency, energy profile, and technological gap of combustion systems in the Colombian lime industry

In this work, the energy audits and evaluation of the kilns used in the calcination stage of the calcium oxide production process of two Colombian factories are shown. The energy intensity and usage distribution were evaluated, as well as the technological state of the presently used heating equipment as compared with the most advanced technology available for the calcination process. For the energy audits, key process data - such as fuel consumption, flue gas temperature and composition, material flows, wall temperature, and furnace configuration - was gathered in-field during visits to production plants. The energy efficiency of the vertical kilns was calculated according to the ISO – 13579 Standard.Substantial heat losses were found especially through the flue gases and kiln walls. The kiln thermal efficiencies calculated were in the range of 54–59%, with combustion efficiencies of 74–78%. The energy performance indicators of the vertical kilns were significantly below those of the most advanced technology available for the calcination stage. Potential energy savings through the introduction of the state-of-the-art kiln technology in the Colombian lime industry is discussed.

Contamination-free graphene by chemical vapor deposition in quartz furnaces

Although the growth of graphene by chemical vapor deposition is a production technique that guarantees high crystallinity and superior electronic properties on large areas, it is still a challenge for manufacturers to efficiently scale up the production to the industrial scale. In this context, issues related to the purity and reproducibility of the graphene batches exist and need to be tackled. When graphene is grown in quartz furnaces, in particular, it is common to end up with samples contaminated by heterogeneous particles, which alter the growth mechanism and affect graphene’s properties. In this paper, we fully unveil the source of such contaminations and explain how they create during the growth process. We further propose a modification of the widely used quartz furnace configuration to fully suppress the sample contamination and obtain identical and clean graphene batches on large areas.

The fate of shrinking boiler nose to improve the flow-field deflection and asymmetric combustion in a 600 MWe supercritical down-fired boiler

The asymmetric upper furnace configuration effect (mainly relied on the short upper furnace and large boiler nose) and unreasonable burner designs are taken as potential major factors that favoring the asymmetric combustion formation in down-fired boilers. To determine the boiler nose's role in this aspect and weaken the boiler nose's effect, two boiler nose's depth shrunk settings of CL=0.199 and 0 were compared with the large design setup CL=0.298 within a 600MWe supercritical down-fired boiler. Numerical simulations on coal combustion were carried out for all three settings, plus full-load industrial-size measurements at the boiler's design setup. The boiler's design setup shows badly asymmetric combustion with poor burnout and high NOx emissions, corresponding to its reported, severely deflected gas/particle flow field. Shrinking boiler nose attains limited improvements (such as shortening the front/rear downward coal/air penetration difference, redirecting a little the upward gas flow towards the upper furnace central part, and shrinking the gas-flow stagnation zone below boiler nose), but unfortunately, essentially fails to change the flow-field deflection pattern and meanwhile decreases the gas fullness in the upper furnace's top zone to generate a potential threat on steam parameters. The absence of effective improvements in asymmetric combustion and apparently shortened flame penetration finally develop a worsened burnout, decreased O2 at the furnace outlet, and lowered NOx emissions as CL decreased. Findings in this work thus exclude boiler nose as a potential major factor that favoring the formation of flow-field deflection and asymmetric combustion and meanwhile, provide useful information that under the circumstances with a short upper furnace aggravating the asymmetric upper furnace configuration effect, a relatively large boiler nose should be used for maintaining (i) the boiler nose's suppression effect on the upward gas flow and (ii) gas fullness in the upper furnace's top zone.

Alleviating gas/particle flow deflection and asymmetric combustion in a 600 MWe supercritical down-fired boiler by expanding its furnace throat space

Cold-modeling gas/particle flow experiments and numerical simulations on coal combustion were performed for evaluating the furnace throat effect on the flow-field deflection and asymmetric combustion in a 600MWe supercritical down-fired boiler. At the furnace design setting (CW=0.529), a severely deflected gas/particle flow field appears, corresponding to a badly asymmetric combustion pattern with poor burnout and high NOx emissions. Shrinking the furnace throat from CW=0.529 to CW=0.500 apparently aggravates both the experimental and simulated flow-field deflection and meanwhile deteriorates asymmetric combustion. In contrast, expanding the furnace throat space to CW=0.558 improves greatly the above problems and the flow-field symmetries are generally acceptable, accompanied by improved burnout rate and lowered NOx emissions. Findings in this work suggest that new down-fired boiler designs should be equipped with a larger furnace throat space under the circumstances with a short upper furnace aggravating the asymmetric upper furnace configuration effect.

Comparison of airflow, coal combustion, NOx emissions, and slagging characteristics among three large-scale MBEL down-fired boilers manufactured at different times

Boilers manufactured by using the down-fired technology of British Mitsui Babcock Energy Limited Corp. (called as MBEL down-fired boiler) account for an about 20% Chinese down-fired boiler’s market share. The published work showed that MBEL down-fired boilers suffered similarly from problems of asymmetric combustion and high NOx emissions, while combustion status and burnout rate varied greatly among boilers manufactured at different times. To uncover the airflow, coal combustion, NOx emissions, and slagging characteristics with respect to various boiler’s parameters (including furnace configuration, burner layout pattern, and air-distribution model), cold-modeling airflow experiments and full-load industrial-size experiments under design parameters were performed for three typical MBEL down-fired boilers (with a boiler capacity of 350, 300, and 600MWe, respectively). All boilers present flow-field deflection, with the downward airflow in one side penetrating much deeper than that in the other side. Consequently, asymmetric combustion appears in real operations, with large gas temperature gaps existing between the front- and rear-half furnace sides. The 350MWe boiler, which has a leptosome furnace pattern and owns the highest secondary-air velocity and volumetric heat capacity, shows the weakest flow-field deflection and highest furnace gas temperature levels corresponding to the lowest burnout loss, but unfortunately, suffers from particularly high NOx emissions and serious furnace-arch slagging. On the contrary, the 300MWe boiler generates the lowest gas temperature levels and NOx emissions and highest burnout loss, without such a slagging problem that appearing in the 350MWe boiler. Although the 600MWe boiler also presents a poor furnace performance, its combustion status, gas temperatures, and burnout rate are all a little better than those of the 300MWe boiler, with the exception of higher NOx emissions and the deduced furnace-arch slagging problem. Finally, the three boilers’ performance comparison generates an appropriate parameter assemble recommended for new MBEL down-fired boiler designs.

Numerical optimization of thermal field in CdTe crystal growth by travelling heater method

Cadmium telluride (CdTe) and his compounds play a leading role in X‐ray and γ‐ray detector technology. One of the most used methods for growing these crystals is the travelling heater method (THM). The ingots obtained by using this technique show excellent composition uniformity, but the structural quality is affected by the presence of large grains which appear because of large curvatures of the solid‐liquid interface during the solidification process. This numerical work investigate the thermal field and melt convection in CdTe processing by THM in order to elucidate the mechanism of growing these crystals. The influence of the furnace geometry on the interface shape and temperature gradient in liquid is analyzed for samples with small (1 cm) and large (5 cm) diameters. The computations include flow effects on thermal field in the melted zone. The thermal conditions are optimized for THM growth of CdTe crystals at high solidification temperatures. A new multi‐zone furnace configuration for growing crystals of large diameter and flattened interface is proposed in this work.