Furnace Wall Research Articles

Optimising the feeding system for improving pellet distribution levels in gas-based shaft furnace based on the improved analytic hierarchy process

To improve the gas flow distribution inside the gas-based shaft furnace and ensure the chemical reaction, the discrete element method was used to calculate the effects of revolving chute inclination, particle size mass distribution, particle size distribution width, and hopper angle on the pellet distribution indicators (particle segregation, porosity, gas permeability and feeding time). An improved analytic hierarchy process was presented to fully analyse the nine schemes set up as part of the research. The findings demonstrated that the positive segregation of small particles at the furnace's centre and wall occurred with several feeding systems. The largest influences on porosity were differences in particle size mass distribution and particle size distribution width, and an increase in the proportion of small particles resulted in a significant decrease in porosity. The increase of the mass ratio of large particles made the highest permeability, but also caused uneven distribution of the furnace charge along the radial direction. The simulation results and the ranking of benefits and drawbacks produced by the improved analytic hierarchy process approach agree, demonstrating the applicability of the method to optimise the feeding system as well as its value in identifying the major influences on the feeding system.

砥石을 통해 본 한반도 동남부지역의 開始期 철기 제작기술

In relation to the beginning of ancient iron production in the southeastern part of the Korean Peninsula, the issue of wrought iron production has been a major issue, with research focused on furnace wall and tuyre fragments, iron materials, and slag found in association within dwellings. However, whetstones, which functioned as a processing tool throughout humankind’s long history, have yet to be fully examined in relation to wrought iron production. Therefore, this paper presents the results of analysis undertaken on the use traces of the ground whetstones excavated from archaeological sites. It was found that the whet-stones can be largely divided into those with the abrasive section located partially or along the entire surface of the stone. In the areas where the iron tools were used from the initial stage, it was identified that the stone manufacturing technology of the local communities was utilized and evidence of the working of iron products could be observed on the sur-face of the whetstones. In addition, the fact that iron objects have have been unearthed in contexts in which iron production by-products have not been identified shows that the use of whetstones was not limited to iron smithing. In addition, in relation to the initial period of iron use ob-served mainly in the Geumho River basin, the characteristics and distribution of iron pro-duction sites from the same period are not uniform, indicating that the nature of iron use and production in the initial period in the southeastern region was not uniform. The development of the initial iron production technology for the southeastern part of the Korean Peninsula was examined by identifying different aspects in the southeastern part of Kyushu, Western Japan, where the situation of reusing iron fragments was con-firmed over a long period of time and over a wide area.

The diversity of bronze production technologies during the Eastern Zhou dynasty revealed by analysis of slags from the Baidian and Xincun sites in Central China

The Eastern Zhou period of China, characterised by complex interactions among vassal states, witnessed significant advancements in bronze production technology. However, the investigation of interactions based on technological comparison among dominant and dependent states remains limited. Focusing on two newly excavated foundry sites, Baidian in Houma, Shanxi, and Xincun in Hebi, Henan, this study provides crucial insights into the bronze production technologies and material sources used by Jin, a major vassal state in Central China, and Wei, a dependent state of Jin, during the Eastern Zhou period. Elemental analysis and microstructural examinations of slags, fragments of crucible wall and furnace wall, show the diversity of bronze production techniques between these two sites: in the Baidian site, bronzes were predominantly produced by co-melting of metallic copper and tin, and remelting of recycled bronzes, whereas in the Xincun site, bronze were probably made by co-melting of copper and tin ore. Furthermore, lead isotope analysis results suggest that the lead materials used for the bronze production at both the sites were likely from the Xiaoqinling region. Integrated with the historical background of complex interactions among vassal states, these findings not only shed light on the technological advancements and resource networks of the Jin and Wei states but also explain the relationships between technology, resources and social dynamics from various perspective. Hopefully this research would promote archeometallurgical study among regions and be applied to other Bronze Age cultures in the world.

Semi-analytical framework for modelling of surface heating and its impact on nonlinear stability of nanotube reinforced doubly curved porous fiber composite panels

In elevated temperatures, the stiffness of the panel deteriorates and can lead to loss of stability of structures. Hence, the stability analysis of thin-walled structures is a critical investigation in the thermal environment. Finding such criticality, the present semi-analytical study investigated the nonlinear stability behaviour of porous doubly curved thin-walled panels subject to surface heating like dome heating and localised heating. To improve the stiffness of the panel, the matrix is reinforced with carbon nanotubes (CNTs). Improper mixing of such nanoparticles can lead to agglomeration or bundling effect, which may reduce the structure's stiffness. Still, its investigation in surface heating can be an essential aspect that is found to be untouched by researchers for porous shell panels. The effective material properties of the three-phase composite panel are determined using the Eshelby-Mori-Tanaka (E-M-T) approach and the Chamis homogenisation technique. Using the variational principle, governing equations are derived and further simplified to non-linear algebraic equations using the Galerkin technique. Gibson and Ashby foam model is used to model cell structure. It is observed that a complete agglomerated state results in higher post-buckling strength, a continuous deformation path due to biaxial compression and curved geometry, and porosity of cellular structure distribution and cell walls are the important parameters to study the stability of panel in a thermal environment are the major conclusions drawn from the current study. Current investigation can be an important contribution towards modelling aircraft structure in supersonic airflow and furnace walls of thermal power plants subjected to localised heating.

Mechanism of Working Fluid Circulation in the Multisource Organic Solid Waste Incinerator

Garbage incineration power generation is utilized to dispose of multi-source organic solid waste. This work constructed a mathematical model for a 750 t/d garbage incinerator to reveal the coupled response between the boiler and furnace sides. Field experiments validated the model, exploring various operating conditions including different loads, fuel blending ratios, primary air, and internal flue gas recirculation (IGR) air flow rates. Increasing the load by 9.1% raised furnace heat exchange by 4.0% but reduced economizer heat exchange by 19.0%. Introducing waste cloth strips and paper mill waste enhanced furnace water-cooled wall heat transfer but reduced economizer heat exchange. A 10.8% rise in primary air flow increased superheater heat exchange by 7.8%. Similarly, a 21.3% rise in IGR air flow increased economizer heat exchange by 9.0%. The temperature rise and enthalpy rise in the superheater were higher when the low calorific value of the fuel was higher. Increasing primary air velocity enhanced heat transfer, raising the outlet temperature of the medium-temperature superheater, necessitating an increase in secondary water spray to adjust the outlet temperature of the high-temperature superheater. This work provides guidance for the design and practical operation of multi-source solid waste incinerators.

The improvement and verification of fluid dynamics simulation on temperature uniformity during heat treatment of ring pieces

The improvement and verification of fluid dynamics simulation on temperature uniformity during the heat treatment of ring pieces are investigated in this study. The accuracy of the temperature field model is validated by comparing the simulation results with the measured temperatures. The findings reveal that the vortex generated near the furnace wall during heat treatment significantly affects the uniformity of the temperature field. To improve this, adjustments are made to the placement of ring pieces based on an experimentally validated fluid dynamics simulation model, and subsequent calculations are performed on this adjusted model. It is observed that these adjustments greatly enhance temperature uniformity in the heating process, with a 39.06 % improvement in medium-temperature zone (732.32–743.69 k) within the furnace compared to the original model. Additionally, surface temperatures of ring pieces in another medium-temperature zone (668.89–691.11 k) show a 34.54 % improvement in comparison to those predicted by the original model.

Computational Fluid Dynamic (CFD) Simulation Thermal Performance and Hydrodynamic Erosion in Circulation Fluidized Bed (CFB) Boiler at PLTU West Kalimantan

Computational Fluid Dynamics (CFD) has been widely used to study Circulation Fluidized Bed (CFB) combustion processes. Analysis of mixed fuel between coal and biomass from PKS (palm kernel shell) in the combustion process that occurs in the boiler at West Kalimantan power plant is carried out by mixing the addition of PKS fuel by 20%, 40%, 60%, and 80%. The simulation uses model set-up data, material properties, and boundary conditions according to PJB (Pembangkitan Jawa Bali) Ketapang's experimental data. Then an analysis was carried out with a fluid flow velocity of 3.2 kg/s and particle sizes of 150 μm, 300 μm, 400 μm, and 500 μm on the erosion rate that occurs on the furnace walls due to sand particles present in the combustion process material at the Steam Power Plant (PLTU). Based on the simulation results of mixing fuel between coal and PKS variations of 20% - 80%, the temperature decreased from 1180℃ – 920.03℃ due to differences in fuel heat. Whereas the erosion rate in the simulation has increased from 0.000189 kg/s – 0.001886 kg/s due to differences in the size of the sand particles and the velocity of the mass flow rate of the particles.

The use and disappearance of vegetal fibres in clay–sand mixtures in furnace walls in pre-seventeenth-century iron smelting sites in the Chūgoku region (Japan)

This paper investigates the importance of the presence of vegetal fibres within clay–sand mixtures in Japanese furnace walls in iron smelting sites in the Chūgoku region during the antique and medieval periods. This presence is all the more interesting as these fibres disappeared with the advent of tatara, the traditional Japanese iron smelting process, at the beginning of the seventeenth century. Understanding this disappearance is a major challenge in the study of the evolution of iron reduction in Japan. The data from archaeological excavations, despite a few scattered clues, are not yet able to give us a sufficiently clear picture of the presence or absence of these fibres in the clay–sand mixture that makes up the furnace walls. Therefore this study highlights the need for systematic research by the creation of a database combined with further analyses and experiments to understand the role fibres might have had in the iron smelting process and why they disappeared from the tatara process in Japan.

Retrofitting Natural Gas–Fired Boiler for Hydrogen Combustion: Operational Performance and NOx Emissions

Abstract The effects of hydrogen fraction (HF: volumetric fraction of H2 in the fuel mixture of CH4 + H2) from 0% to 100% by volume, on the thermal and environmental performance of a 207-MW industrial water tube boiler, are investigated numerically at a fixed excess air factor, λ = 1.15. This study aims to determine the hardware modifications required for boilers to be retrofitted for pure hydrogen operation and investigates how NOx emissions are affected by hydrogen enrichment. The results showed insignificant increases in maximum combustion temperature with increasing the HF, though the distributions of temperature profiles are distinct. In reference to the basic methane combustion, H2 flames resulted in a positive temperature rise in the vicinity of the burner. Increasing the HF from 0% to 2% resulted in higher average thermal NOx emissions at the boiler exit section from 37 up to 1284 ppm, then it decreased to 1136 ppm at HF = 30%, and later it leveled up to 1474 ppm at HF = 100%. The spots for higher differences in NO formation compared to the reference case are shifted downstream at higher HFs. The effect of hydrogen enrichment on CO2 and H2O as radiation sources, as well as the volumetric absorption radiation of the furnace wall and the heat flux at furnace surfaces, has all been presented in relation to the effect of hydrogen addition on boiler performance.

Получение покрытий с высокой инфракрасной излучательной способностью

Introduction. One of the promising modern methods of coating formation is detonation gas dynamic sputtering. Coatings obtained by this method have high adhesion to the substrate, dense structure and specified functional properties. Development of technology for obtaining functional coatings with high emission coefficient in the infrared range is an urgent need for the development of high-temperature industrial processes and technologies. High-temperature industrial processes consume a large amount of energy, so improving the energy efficiency of industrial equipment is considered as one of the ways to overcome the ever-growing energy crisis. To this end, coatings with high infrared emissivity have been developed for industrial furnaces. These coatings are usually applied to the furnace walls, which significantly improves energy efficiency by increasing heat transfer from the heat-emitting surfaces of the furnace. The purpose of the work is to obtain coatings with high emission indices in the infrared range for further recommendation of its use in baking ovens of Shebekinsky machine-building plant. Methods for studying coating specimens obtained by detonation gas-thermal method: scanning electron microscopy, X-ray phase analysis, energy dispersive analysis, infrared spectroscopy. Results and discussion. The microstructure, phase composition, emissivity and thermal cycling resistance of Fe2O3; Al2O3 + 10 % Fe2O3; Ti + 10% Fe2O3 coatings obtained by detonation gas-dynamic powder spraying are investigated in this work. The results of the study showed that the obtained coatings have a dense structure, increased emissivity and resistance to thermal treatment cycles, as a result of which the structure of the crystal lattice of the coatings does not change.

Determination of the optimal total oxygen concentration and oxygen partitioning ratio based on the heat transfer characteristics of oxy-coal combustion in a swirl burner

Oxy-coal combustion is an attractive option for CO2 capture from coal-fired power plants due to high carbon capture efficiency and favorable economic performance. It is critical for the operation of the power plants to maintain similar heat transfer characteristics by rationalizing the partitioning strategy of the oxidant streams when retrofitting coal-fired power plants with oxy-fuel combustion technology. In the present work, the oxy-coal combustion characteristics under various total oxygen concentrations XO2,total of 21 %–32 % and oxygen partitioning ratio conditions in a 100 kW vertical swirl burner were numerically investigated by using computational fluid dynamics (CFD) models. And the effects of the XO2,total and oxygen partitioning ratio on the heat transfer characteristics of oxy-coal combustion were numerically simulated to quantitatively obtain the optimal oxygen supply partitioning strategy for the retrofitting of coal-fired power plants. Then the flame structure, heat transfer flux, and char burnout rate at different oxygen partitioning ratios between the primary and secondary streams were systematically analyzed to further determine the optimal oxygen partitioning ratio. The results showed that the maximum flue gas temperature Tmax increased by 220 K and the total heat transfer flux on the furnace wall increased by 42 % when the XO2,total was increased from 21 % to 32 %, respectively. Under oxy-coal combustion conditions, the Tmax at the XO2,total of 32.4 % was consistent with that under air combustion condition, while the total heat transfer flux at the XO2,total of 29.4 % matched with that under air combustion condition. Moreover, the total heat transfer flux and the flame length were increased by 17.3 % and 46.3 %, respectively, as the oxygen concentration of the primary stream XO2,Pri was increased from 6.5 % to 45 % at the XO2,total of 29 %. More importantly, the total heat transfer flux at the XO2,Pri of 31.9 % under oxy-coal combustion condition matched with that under air combustion condition. The optimal total oxygen concentration and oxygen partitioning ratio of oxy-coal combustion based on the heat transfer characteristics were quantitatively determined, which gave an important reference for the oxy-coal combustion retrofitting of traditional coal-fired power plants.

Analysis of billet temperature non-uniformity in a regenerative reheating furnace: Considering periodic combustion switching and misalignment contact of walking beams

Improving the billet temperature uniformity is crucial for the quality of rolled products. This paper investigated the heat and mass transfer processes in a regenerative reheating furnace by establishing typical heating unit models. The periodic combustion switching and misaligned water-cooled beams were considered. The effects of furnace temperature oscillation and skid marks on the total heat transfer coefficient distribution and billet temperature uniformity were analyzed. The results indicate that during the heating process of the billet, the periodic variation amplitude of furnace temperature decreases from 86 to 25 °C, and the depth of influence on the billet temperature is about 0.03 m. The total heat transfer coefficient on the billet bottom surface shows a wave distribution affected by beams shielding, but on the top surface, the closer it is to the furnace wall, the smaller the total heat transfer coefficient. The misalignment of water-cooled beams effectively eliminates the original skid mark and reduces the range of new skid mark. However, the cross-sectional temperature difference at the new skid marks remain at about 97 °C. Compared to extending the residence time, increasing the furnace temperature in the soaking zone is the optimal measure to reduce the influence of skid marks.

Evaluation of Energy Utilization Efficiency and Optimal Energy Matching Model of EAF Steelmaking Based on Association Rule Mining

In the iron and steel industry, evaluating the energy utilization efficiency (EUE) and determining the optimal energy matching mode play an important role in addressing increasing energy depletion and environmental problems. Electric Arc Furnace (EAF) steelmaking is a typical short crude steel production route, which is characterized by an energy-intensive fast smelting rhythm and diversified raw charge structure. In this paper, the energy model of the EAF steelmaking process is established to conduct an energy analysis and EUE evaluation. An association rule mining (ARM) strategy for guiding the EAF production process based on data cleaning, feature selection, and an association rule (AR) algorithm was proposed, and the effectiveness of this strategy was verified. The unsupervised algorithm Auto-Encoder (AE) was adopted to detect and eliminate abnormal data, complete data cleaning, and ensure data quality and accuracy. The AE model performs best when the number of nodes in the hidden layer is 18. The feature selection determines 10 factors such as the hot metal (HM) ratio and HM temperature as important data features to simplify the model structure. According to different ratios and temperatures of the HM, combined with k-means clustering and an AR algorithm, the optimal operation process for the EUE in the EAF steelmaking under different smelting modes is proposed. The results indicated that under the conditions of a low HM ratio and low HM temperature, the EUE is best when the power consumption in the second stage ranges between 4853 kWh and 7520 kWh, the oxygen consumption in the second stage ranges between 1816 m3 and 1961 m3, and the natural gas consumption ranges between 156 m3 and 196 m3. Conversely, under the conditions of a high HM ratio and high HM temperature, the EUE tends to decrease, and the EUE is best when the furnace wall oxygen consumption ranges between 4732 m3 and 5670 m3, and the oxygen consumption in the second stage ranges between 1561 m3 and 1871 m3. By comparison, under different smelting modes, the smelting scheme obtained by the ARM has an obvious effect on the improvement of the EUE. With a high EUE, the improvement of the A2B1 smelting mode is the most obvious, from 24.7% to 53%. This study is expected to provide technical ideas for energy conservation and emission reduction in the EAF steelmaking process in the future.

Numerical investigation on the effects of air-staged strategy and ammonia co-firing ratios on NO emission characteristics using the Conjugate heat transfer method

Ammonia co-firing is recognized as a promising approach within the realm of achieving carbon neutrality. This method not only effectively mitigates carbon emissions but also augments the stability of ammonia combustion. However, achieving low NO emissions in ammonia combustors remains a formidable challenge. The present study employed numerical simulations to assess the impact of an air-staged strategy and varying ammonia co-firing ratios on NO emissions within a 10-kW industrial ammonia co-firing furnace. To accurately represent the thermal conditions at the furnace walls, a Conjugate Heat Transfer (CHT) model encompassing both solid materials and reacting flow regions was utilized. Initially, the numerical results were compared with experimentally measured NO emissions, validating the accuracy of the customized solver. Subsequently, the effectiveness of the air-staged strategy under the parallel injection system was verified. This approach created a fuel-rich region near the burner primary nozzle, significantly reducing NO production. Under different ammonia co-firing ratios, with ammonia injection levels increasing from 0% to 100%, NO emissions at the furnace outlet displayed an initial increase, followed by a decrease, peaking at a co-firing ratio of 50%. Further analysis of the Rate of Production (ROP) of NO within the furnace revealed that at higher ammonia co-firing ratios, ammonia serves both as a reducing agent and as a fuel for heat release. These findings provide valuable insights for the development and application of ammonia-based industrial furnaces.

The effect of multiple factors on changes in organic-inorganic fractions of condensable particulate matter during coal combustion

Condensable particulate matter (CPM) from coal combustion is the focus of current pollutant emission studies, and CPM can be divided into inorganic and organic fractions according to the component characteristics. At present, the effects of different factors in the combustion process on the organic and inorganic components of CPM have not been discussed systematically. Here, we conducted combustion experiments collected the generated CPM on a well-controlled drip tube furnace, and investigated the effects of different factors on the generation of organic and inorganic components of CPM by varying the furnace wall insulation temperature, the ratio of gas supply components and the water vapor content in the flue gas. The results showed that the increase in combustion temperature (1300–1500 °C) and oxygen concentration (15–25%) reduced the total CPM generation by 9.8% and 19.98%, respectively, and the intervention of water vapor increased the ability of the whole CPM sampling device to capture ultrafine condensable particles. The generation of CPM organic components decreased with the enhancement of combustion temperature and oxygen content on combustion characteristics, and alkanes shifted to low carbon content. The amount of CPM inorganic components increased with the increase of water vapor content in the flue gas, and this change was dominated by SO42−. The above results provide a feasible idea for the next step of the precise reduction of CPM components.

Comparison of Heated Charateristics of Smelting Experiment Furnace Wall Using Geothermometer and Cluster Analysis Method of XRD Data

In this study, 91 samples were collected by layer, direction, and point from the smelting experiment furnace wall, and XRD analysis was performed. These data were compared with the geothermometer method and the cluster analysis method to determine how to effectively interpret heated characteristics. As a result of comparing the heated characteristics of the 1<sup>st</sup> to 4<sup>th</sup> floors, its showed the same results for both methods because of heated by high temperatures in the 1<sup>st</sup> and 2<sup>nd</sup> floors heated. However, in the data from the 3<sup>rd</sup> and 4<sup>th</sup> floors, it was difficult to interpret the difference in heat temperature depending on the direction using the geothermometer method, but the cluster analysis method was able to effectively confirm the pattern of heat spreading from the center to the outside of the furnace wall. As a result, the cluster analysis method can reduce errors that may appear due to mineral identification in the process of estimating heat temperature using the geothermometer method and there is an advantage in that the temperature distribution within the furnace wall can be further refined.

Industrial scale testing on the combustion and NOx emission characteristics of ammonia cofiring in a 40 MWth coal-fired boiler

This paper reports the first industrial scale testing on ammonia (NH3) cofiring in a 40 MWth coal-fired boiler under high ammonia cofiring ratio (ENH3, percent of thermal input) ranging from 0 % to 25 %. A full-scale cofiring swirl burner is designed to inject NH3 gas with pulverized coal through the primary air pipe of the burner. The effects of ammonia cofiring ratio and key boiler operating parameters on boiler NOx emission and fuel burnout are examined. The results show that the boiler can establish stable ignition and combustion under all ammonia cofiring conditions in this study. The burnout of coal under ammonia cofiring conditions are better than those of coal combustion cases. Overfire air (SOFA) has significant influences on boiler NOx emission and burnout of coal and NH3. It is found that there exists optimal SOFA ratio in the range of 15–20 % within which both boiler NOx emission and NH3 slip can be well controlled. Under 20 % SOFA ratio, boiler NOx emission tends to increase and then decrease with the increase of ENH3 reaching the peak value under ENH3 = 5 %. As a result, the NOx emission can be reduced to the level lower than that of coal combustion case under ENH3 > 20 %. Boiler excess O2 also shows significant influences on boiler NOx emission and NH3 slip. With the decrease of boiler O2, boiler NOx emission decreases significantly while NH3 slip increases rapidly. It is found that there exists optimal boiler O2 in the range of 3.0–3.7 % within which both boiler NOx emission and NH3 slip can be kept at relatively low levels. Injection of NH3 from the side wall of furnace is also tested in this study. The NOx emission shows similar trends with the change of ENH3 in the range of 0–20 %. However, above this range the NOx emission tends to increase with further increase of ENH3. The results of this paper demonstrate the technical feasibility of NH3 cofiring in large-scale coal-fired boilers under high cofiring ratios and provide important guidance to the operation of boilers.

Detection of Multiscale Deterioration from Point-Clouds of Furnace Walls

Deterioration surveys of large structures such as furnaces have been mainly conducted by visual inspection, but it is desirable to automatically detect deterioration using point clouds captured by the terrestrial laser scanner. In this study, we propose flexible methods for detecting various scales of cracks, delamination, and adhesion on furnace walls by using a machine learning technique. Since small cracks have few geometrical features, they are detected from the reflection intensity images generated by projecting a point cloud onto a two-dimensional plane. For detecting cracks on the image, we use the U-Net fine-tuned by crack images denoised with a median filter. For detecting delamination and adhesion, a wall surface is approximated by a smooth B-spline surface, and deterioration is detected as differences between the point cloud and the approximated surface. However, in this method, the resolution of the B-spline surface has to be carefully determined according to the expected deterioration sizes. To robustly detect deterioration at various scales, we introduce multiscale 3D features, and detect deterioration using both multiscale 3D features and 2D features. In actual walls, it is difficult to distinguish between cracks and delamination because delamination grows from cracks. To detect both types of deterioration in a uniform manner, we combine the two detectors and propose an integrated detector for detecting deterioration at various scales. Our experimental results showed that our methods could stably detect various scales of degradation on furnace walls.

Influence of PbCl2 and KCl salt mixture on high temperature corrosion of alloy 625

Aggressive corrosion can occur when firing waste or bio-based fuels, due to the presence of high concentrations of heavy metals, alkali metals, and chlorides. These deleterious compounds deposit on furnace walls and can form mixtures that can rapidly accelerate corrosion. The effect of salts containing lead had not been studied extensively at temperatures lower than 400 °C in nickel-based materials. This study investigates the effect of the individual salts PbCl2 and KCl and their mixture on the high temperature corrosion of alloy 625 at 340 °C and 380 °C. Samples of alloy 625 were covered with individual salts or a salt mixture and exposed to high temperatures in an atmosphere of synthetic air, 20-vol% H2O, and 100 ppm HCl. The results show that the presence of individual salts does not induce observable corrosion attack on alloy 625 after 168 h at any tested temperature. The salt mixture did cause a severe corrosion attack at 380 °C, observed after 24 h of exposure. It is suggested that the salt mixture induces the formation of lead chromates that may prevent or disrupt the formation of a protective chromia scale. It is believed that a key part of the mechanism is the formation of eutectic melts by the interaction of the scale with the salt mixture. Thermodynamic equilibria calculations show that the first melting temperature of PbCl2 and KCl salt mixture after reaction with oxygen can be as low as about 382 °C, and even lower (357 °C) if chromates are present.

Boundary geometry reconstruction for orthotropic heat conduction problems based on HT-FEM

It is usually inconvenient to directly measure the inner boundary geometry shape of thermal pipeline and furnace wall in engineering. A non-iterative algorithm is proposed to reconstruct the geometry shape of these structures for orthotropic heat conduction problems in nondestructive evaluation. First, the temperature of measurement points in the real domain is determined by utilizing the hybrid Trefftz finite element method (HT-FEM). Then, a virtual inner boundary is introduced into forming a virtual domain. The deviation between the measured temperature and the estimated temperature is defined as an objective function. The temperature on the virtual boundary is obtained by calculating the minimum of the objective function. Finally, the virtual boundary temperature is substituted into the direct problem to acquire the temperature distribution in the global domain. And the inner boundary geometry shape is identified by searching the isothermal curve. Several numerical examples are provided to verify the stability and effectiveness of the proposed method. The merit of this algorithm is that the unknown geometry shape can be directly and accurately reconstructed without the complex iterative process.