Furnace Chamber Research Articles

Electronics and waste material recycler energy-efficient electric furnace system

Steel and iron manufacturing, nonferrous metal production, glass production, ceramic processing, and the creation of various forms of items all rely on material production. High temperatures are used in furnaces for smelting and recycling. An electric furnace may be suitable as natural gas is not widely available everywhere. Bangladesh's melting and recycling machinery is powered by a traditional gas furnace, which is expensive and inefficient. By recycling and reusing scrap metal, natural ore, and alloys, the suggested model has the potential to revolutionize, reducing the build-up of natural energy alloys, gas, and ores. The proposed electric furnace has an enclosed form and uses electricity to generate heat efficiently. To melt reusable metals, electronic materials, and waste materials, an electric furnace system based on the Arduino Mega as an alternative to the PID controller with Solid State Relay has been developed, which will manage and control the temperature around 1350 °C (1623.15 K or 2462 °F) by collecting data from the furnace thermostat. This model is made of stainless steel, with a steel frame for the outer shape of the furnace body and control box, a ventilation hole for removing hot gas from inside the furnace, an airtight door for opening the furnace chamber, a digital temperature controller with a furnace B-type thermocouple for measuring and controlling temperature, an ELB for safety, and heat insulation materials with a Nichrome80 heating element in the chamber. The model uses an Arduino Mega to regulate power and temperature while reducing heat loss via the furnace body, reducing time delays, and increasing efficiency. The findings demonstrate that the desired temperature is reached fast and with less electricity than the other electric furnaces, indicating that the model is energy efficient. The smelting temperature for aluminum, copper and other similar materials has been effectively covered. This model has better efficiency since there is no heat loss. The melting and recycling processes will help the furnace-related sectors the most. However, this could be especially beneficial for a developing economy like Bangladesh, where gas and fuel are expensive. • This article develops an electric furnace system that may be operated manually (PID) or automatically (Arduino Mega). • The proposed system is capable of producing temperatures of around 1350 °C (1623.15 K or 2462 °F). • Compared to other traditional furnace systems, the suggested furnace system can attain the desired melting temperature in short period. • When the thermocouple circuit reaches the predetermined melting temperature, the control system switches it off automatically. • Reduce melting cost, heat loss, increase efficiency, carries more benefits for the melting/recycling for reusing waste materials.

Investigation of air and rice husk cold flow structures in the suspension furnace chamber through a simulation study

Rice husk combustion in the suspension furnace is not an easy matter. Until now, there are still many obstacles faced in its process as characterized by low combustion conversion. The main cause is the poor air-particle contact as well as the probability of particle elutriation out of the furnace chamber before combustion completely occurs. Thus, in-depth and detailed understanding of air and rice husk cold flow structures in the furnace chamber, as proposed in this study, becomes necessary. The simulation study was conducted using Reynold stress model (RSM) for fluid flow quantification whereas discrete phase model was utilized for particle flow quantification. The simulation results reveal that cylindrical chamber gives a more significant particle residence time rather than rectangular chamber for every similar excess air amount. Besides, providing burner with a tangential air inlet of 90o results in high turbulence, intense swirl phenomenon, and long particle residence time. Moreover, the furnace chamber equipped with a smaller burner diameter and longer burner length together will augment the air-particle contact in the furnace chamber. Despite providing the best condition for the furnace, the design must not forget to consider the economical aspect.

Boilers slagging when burning wood pellets

A promising trend for upgrading wastes from timber cutting, processing and treatment is their granulation. It allows to increase their specific heats of combustion by 2.5– 3.5 times and their portability characteristics by 3–4 times, to reduce transportation costs by 6– 10 times and to improve all the operations stages. The construction and commissioning of boiler facilities operating on refined biofuel made it possible to form a stable domestic market for wood pellets. However, 0.5 – 1.5 MW nominal capacity hot water boilers equipped with furnaces and profiled burners at the bottom, in cold seasons had fast accumulation of focal residues deposits in the burners and on the furnace chambers lining. The process was complicated by these deposits hardening due to their melting and sintering. These circumstances cause a decrease in the energy and environmental performance of heat-generating installations and their reliability, and also leads to the unplanned shutdowns to clean the boiler furnaces. To find out the reasons for these negative phenomena and to develop recommendations for their elimination, a set of research operations was carried out with wood pellets shipped by the manufacturer and supplied to the burners of the boilers under the analyses; with focal residues accumulated in the burners and on the lining of the furnace chambers; as well as an analysis of the heat generating facilities operation modes. The studies carried out made it possible to identify the main factors that caused these negative phenomena and to develop the recommendations for their elimination.

Study on the Morin Transition of α-Fe2O3 Thin Film by Synchrotron Mössbauer Source with the Development of Small Furnace Chamber for It

Study on the Morin Transition of α-Fe₂O₃ Thin Film by Synchrotron Mössbauer Source with the Development of Small Furnace Chamber for It

Ignition and combustion enhancement of composite fuel in conditions of droplets dispersion during conductive heating on steel surfaces with different roughness parameters

The ignition and combustion of single organic coal-water fuel (OCWF) droplets made of coal (30%), waste engine oil (35%), and water (35%) during conductive heating on the surfaces of the machine steel modified with abrasive materials and laser radiation were studied experimentally. The experimental conditions (material and temperature of the heating surfaces) corresponded to the operating conditions of modern furnace chambers of boilers at thermal power plants. It is found that the ignition delay and burnout times during conductive heating of OCWF droplets on steel surfaces can be controlled by changing the surface roughness parameters. On the example of 7-mg OCWF droplets with a radius of about 1.2 mm, it is shown that for processing of heating surfaces, it is necessary to use the abrasive materials with an average grit size of 100 μm to decrease the ignition and burnout times. The abrasive materials with an average grit size of more than 100 μm have an insignificant effect on the ignition delay and burnout times of OCWF droplets. However, such processing significantly increases the deposition of solid combustion products (ash deposits) with an increase in the surface roughness. Laser processing of steel surfaces is of particular interest in the implementation of passive ways of controlling the ignition and combustion characteristics of OCWF droplets. This way of changing the surface texture allows controlling the ignition delay and burnout times in a wide range of the heating source temperatures, as well as reducing the intensity of the solid product deposition on the heating surface during the OCWF combustion. The positive effect from laser processing of heating surfaces to intensify the fuel droplet combustion consists in increasing the velocity of vapor flows from combustible fuel components due to the droplet dispersion. This, in turn, intensifies the formation of a combustible vapour-gas mixture and increases the velocities of flame propagation together with the dispersion products of fuel droplets along the textured surface.

Electroplasma processing of medical and biological waste

The article presents an experimental study of biomedical waste in the form of disposable masks. The study was carried out on a laboratory plasma arc installation with a capacity of 20 kg/h. During the experiments, the most important technological parameters were studied: the composition of the exhaust gases, the dependence of the exhaust gases on the temperature in the chamber of the plasma arc furnace, etc.

Influence of Nitrocarburizing on Increasing the Service Life of Elastic Elements of Direct Flow Valves

The effect of the nitrocarburizing process in pastes with heating in a chamber furnace on the struc-ture and strength characteristics of 09Cr15Ni8Al corrosion-resistant steel was investigated. The tech-nology of chemical-thermal treatment was developed, which included nitrocarburizing in pastes with heating in a chamber furnace at different holding times. The thickness of the diffusion layer and its microhardness were determined after nitrocarburizing. To determine the efficiency and select the modes of chemical-thermal treatment, tests were carried out for the investigated steel's strength characteristics. The main feature of the structure of the diffusion layers of valve steels, obtained by nitrocarburizing in the nitrogen-carbon paste, is the presence of an inhomogeneous layer with clearly distinguished zones.

Ceramic sintering furnace based on combustion of premixed natural gas in porous inert media

Development of new energy-efficient high-temperature sintering furnaces is one of the key factors for cost reduction of refractory ceramic manufacturing. In this paper, a sintering furnace in which the volume of the furnace chamber is completely filled with a packed bed of ceramic spheres, and the energy source is the premixed combustion of natural gas with atmospheric air and oxygen has been experimentally studied. The furnace design allows the use of two combustion modes: (i) filtration combustion, when the narrow reaction front (combustion wave) freely propagates through the packed bed, (ii) jet-stabilized combustion when the reaction front is stabilized near gas inlet nozzles used for supplying the fresh mixture into the packed bed. Experimental analysis of both combustion modes was performed in the ranges of specific fuel flow rate from 7·10–3 to 107·10–3 Nm3·s–1/m2, firing rate from 244 to 3724 kW/m2, fuel-to-oxidizer ratio from 0.40 to 3.30, oxygen content in the oxidizer from 21 to 30 vol%. In these ranges, the temperature of the packed bed can be controlled within 1230–2220 K. Test sintering of samples pressed from powders of MgO and Al2O3 was carried out at 2170 K. It was found that the filtration combustion mode is effective for sintering parts with a characteristic size of up to 10 mm, and the packed bed can be completely formed of samples to be sintered. Jet-stabilized combustion mode is effective for sintering large pieces. In such a case, submerging samples within the packed bed enables double fuel saving compared to the stacking of samples in a furnace chamber of a conventional free-volume design. The new furnace based on the principles of premixed combustion in porous inert media can be in demand for small-scale production of ceramic parts.

Investigation of the influence of the configuration of the fire furnace chamber on the temperature regime during the implementation of tests for fire resistance

The issue related to the conditions for creating the required temperature regime of fire when testing structures for fire resistance has not been studied in detail up to now. That necessitated determining the technical conditions under which it is possible to comply with the standard temperature regime of fire in the fire chamber of the furnace. The influence of the design parameters of the fire furnace chamber on the condition of compliance with the standard fire temperature regime when tested for fire resistance has been established. One of the most effective methods for examining such an impact is computer simulation. A computer model of the fire furnace was built on the basis of a comprehensive analysis and earlier work on the study of such furnaces, taking into consideration technical characteristics, in particular, geometrical parameters, fuel and air supply systems. The obtained research results are a prerequisite for scientific substantiation of the design parameters of fire furnaces and their engineering systems, which is necessary to comply with the standard temperature regime of fire in the furnace fire chamber. This makes it possible to provide the necessary conditions for testing building structures for fire resistance in compliance with the requirements of the relevant standards. The computer model constructed makes it possible to create the necessary temperature regime in the fire chamber of the furnace (in this study, the standard temperature of fire). As a result of the study, the technical parameters of the fuel supply and ventilation system were determined, which ensure compliance with the standard temperature regime in the fire chamber of the furnace. That makes it possible to build an automated complex of the testing process for fire resistance of building structures. In addition, the data obtained can be the basis for the design of such fire furnaces with the ability to comply with different fire temperature regimes without the intervention of the operator.

Influence of Gas Pressure and Blowing Agent Content on the Formation of Aluminum Alloy Foam

Apart from density and alloy composition, the structure of solid metallic foams determines their mechanical performance. Herein, the effect of ambient pressure on the foaming behavior of AlSi6Cu4 precursors is studied. In situ X‐ray radioscopy is applied while foaming in a furnace chamber pressurized up to 40 bar. The content of the blowing agent (TiH2) is varied for each of the pressures chosen. The foam density and morphology are analyzed quantitatively using time‐resolved X‐ray radioscopy sequences and postsolidification X‐ray tomography data. The optimal content of blowing agent as well as the pore sizes and distributions is found to depend strongly on the ambient pressure. At high pressures very small, round, and uniformly distributed pores are formed and crack formation is avoided during the gas nucleation stage, which helps to prevent structural defects. Adjusting the ambient pressure allows for better control of the foam structure and density, which is relevant for commercial production and application.

Two-level comprehensive energy-efficiency quantitative diagnosis scheme for ethylene-cracking furnace with multi-working-condition of fault and exception operation

Because ethylene-cracking furnace accounts for vast majority of energy consumption in ethylene production, energy-efficiency diagnosis of ethylene-cracking furnace is of great significance for improving energy utilization and production operation. In this paper, a two-level comprehensive energy-efficiency diagnosis problem is considered for both furnace level and internal chambers level. Apart from production load and feed composition, fault and exception operation also have influence on energy-efficiency, which leads to a multiple-working-condition energy-efficiency diagnosis problem under fault and exception operation. Therefore, this paper proposes a new energy-efficiency diagnosis scheme for ethylene-cracking furnace. Firstly, a two-level index system is designed to have an overall understanding of energy-efficiency of ethylene-cracking furnace and internal chambers. Secondly, fault and operation diagnosis criteria are established to identify fault samples, exception operation samples, and fault-and-exception-operation samples from inefficient samples after multi-working-condition classification. Thirdly, contributions of operation conditions, outputs, and internal chambers are quantified by step-by-step transformation and total differential methods to locate weak links in energy efficiency. Finally, effectiveness of diagnosis scheme is verified by applying it to a Chinese ethylene plant. Not only are three inefficient types detected, but also contributions of root causes resulting in inefficiency are quantified, which provides energy conservation and efficiency improvement suggestions for decision-makers.

Combustion of petroleum waste in the marine boilers – Waste preparation technologies and exhaust emission. Part 1: Preparation technologies and their influence on waste morphology

Petroleum waste occurring during operation of marine power systems in compliance with Marpol convention [1] needs to be collected on the ship, and the crew is obliged to run the record of their amount in so called oil record book. Collected waste is transported to the land or can be used as a fuel on the ships. Physico-chemical properties of petroleum waste containing different types of petroleum waste mixed in different proportions are difficult to define what makes it more difficult to choose a correct heating temperature in order to obtain required viscosity that would enable correct spraying and obtaining good combustion quality. Moreover, petroleum waste usually contains high amount of water, solid emissions and coagulants originating as a result of reactions between different types of petroleum products that are part of petroleum waste. Petroleum waste before and after homogenization have undergone laboratory tests by processing microscopic images of their samples with the use of specialized computer programme and spectral analysis in order to specify the morphology of the waste. The physico-chemical properties of the waste have also been determined. The results of the studies carried out showed a significant variety of physicochemical properties and composition of petroleum waste taken from the ships. Density in 15 °C changed in the range of 924.9–986.1 kg/m3, kinematic viscosity in 50 °C in the range 12.25–28.74 mm2/s, water content from 9.80 to 28.74 % mass, caloric value from 21.5 to 33.2 MJ/kg, resins in the range 12.1 – 38.2 % mass, and asphaltenes insoluble in n-hexane from 3.2 to 28.3 % mass. The size of asphaltene-resin particles and a number of water droplets of minimal and maximal measured diameter affecting the quality of spraying process and fuel combustion changed in the following range:Asphaltene-resin particlesWater droplets.Particle size: Diameter and number: 0.5 µm: 0.0 – 0.8 % volume 5–15 µm: (1.0 – 11) 103.100 µm: 0.0 – 6.8 % volume50–100 µm: (0.6 – 0.8) 103.This requires proper preparation process of waste before combustion. Taking into consid- eration the fact that the combustion quality control is facilitated, petroleum waste can be used as a fuel in the boilers. The article presents studies’ results of morphology of petroleum waste that undergoes cleaning process and process of preparation for combustion with different methods, their physicochemical properties as well as exhaust emissions in the marine boiler For this reason we designed and made the modernization of fuel system for the ship boiler on the specialized ship for collection and combustion of petroleum waste with use of static and dynamic homogenizer. We have carried out homogenization with use of each of homogenizers at their serial operation. After homogenization petroleum waste samples were subjected to laboratory studies with use of microscope pictures processed with use of computer programme and spectral analysis in order to determine their morphology. Physico-chemical properties of studied petroleum waste have been determined. It has been proventhat the best effects have been achieved when both static and dynamic homogenizer were working in series. The sizes of asphaltene-resin particles and number of water droplets of minimal and maximal measured diameter changed in the following range:Asphaltene-resin particlesWater droplets.Particle size: Diameter and number: 0.5 µm: 0.2 – 3.2 % volume 5–15 µm: (24 – 45) 103.100 µm: 0.0 – 0.1 % volume 50–100 µm: (0.0 – 0.0) 103.In order to obtain the correct spraying quality of petroleum waste and their combustion it is required that asphaltane-resin particles are of size in the range from 5 µm to 30 µm and water roplets of diameter up to 20 µm. The developed technology of preparing for petroleum waste combustion ensures achieving the required diameters. It needs to be highlighted that all particles of size between 50 and 100 µm underwent fragmentation and the number of particles fragmented to the diameter of 0.5 µm and size of 5–15 µm increased.The authors believe that the obtained research results are valuable and worth making available through publication for a wide audience. The research was carried out with the use of 6 types of specific marine petroleum waste collected from ships, which differ significantly in composition, water content and properties. The designed and constructed fuel installation enables to obtain the morphology of waste enabling good quality of its atomization and combustion in the boiler furnace chamber. The technology developed in this way and the wide scope of research carried out with the use of marine petroleum waste are not found in the literature.

Evaluation of nature and intensity of fire concrete spalling by frequency analysis of sound records

The paper presents a new method for identifying the form and intensity of spalling using an analysis of the acoustic signal emitted by concrete. To assess the intensity and monitor the course of concrete spalling during fire exposure, the analysis of the recorded sound from the furnace chamber is used. The spalling intensity was determined based on signal amplitude analysis. Investigation of sound records showed that the character of spalling can be categorized by a well-defined frequency value. Based on the analysis of the Fast Fourier Transform (FFT) spectrum, the authors have distinguished the following phenomena that are the source of the signal by assigning the corresponding frequency of the sound wave vibration: explosive spalling, aggregate spalling and destructive spalling.

Measuring dimensional and morphological heat alterations of dismemberment-related toolmarks with an optical roughness metre.

This experimental study provides a further understanding of the post-burning nature of sharp force trauma. The main objective is to analyse the distortion that fire may inflict on the length, width, roughness, and floor shape morphology of toolmarks induced by four different implements. To this end, four fresh juvenile pig long bones were cut with a bread knife, a serrated knife, a butcher machete, and a saw. A total of 120 toolmarks were induced and the bone samples were thus burnt in a chamber furnace. The lesions were analysed with a 3D optical surface roughness metre before and after the burning process. Afterwards, descriptive statistics and correlation tests (Student's t-test and analysis of variance) were performed. The results show that fire exposure can distort the signatures of sharp force trauma, but they remain recognisable and identifiable. The length decreased in size and the roughness increased in a consistent manner. The width did not vary for the saw, serrated knife, or machete toolmarks, while the bread knife lesions slightly shrunk. The floor shape morphology varied after burning, and this change became more noticeable for the three knives. It was also observed that the metrics of the serrated knife and machete cut marks showed no significant variations. Our results demonstrate that there is a variation in the toolmark characteristics after burning. This distortion is dependent on multiple factors that influence their dimensional and morphological changes, and the preservation of class features is directly reliant upon the weapon employed, the trauma caused, and the burning process conditions.

Influence of the location of billets in chamber furnaces on time of their heating and temperature drop over the section at cold and hot charging

The heating of blooms and cold-charged ingots before metal forming in chamber furnaces, due to the large cross-sections of the billets and their multi-row arrangement in the furnace, contributes to the shielding of the metal and the creation of an uneven temperature field in it, which increases the charge heating time, reduces the furnace productivity and contributes to the at the initial moment of heating the elastic temporary and residual temperature stresses formed in the body of the workpiece after cooling the previous heating. Residual and temporary stresses are added, due to the coincidence of their signs, and can lead to metal buckling and formation of cracks in it. The magnitude of temperature stresses, in addition to the cross-section of the workpiece, is significantly influenced by their location in the furnace. The heating of hot-charged ingots significantly increases the productivity of the furnace units. Knowledge of the temperature field in the heated metal of cold and hot charge, both at the beginning and at the end of heating before metal processing by pressure, is a necessary condition for reducing fuel and electricity consumption, increasing the productivity of the furnace unit and obtaining high-quality deformed metal. In the presented work, a study was made of the influence of the arrangement of blooms in an electric heating well and ingots made of ShKh15 steel in a roller hearth furnace on the time of their heating, the temperature field across the cross section and the furnace productivity. Also, using the literature data on the initial temperature distribution in an ingot made of 02Kh22N5AM3 steel with a mass of 7 t with a liquid core, the temperature field in a hot ingot was calculated after its “undressing”, complete crystallization and further heating for forging. The temperature field in the metal under study and the time of its heating in chamber furnaces were calculated using the Excel tool for solving the differential equation of thermal conductivity in partial derivatives by the finite difference method using an implicit difference scheme under the conditions of the initial uniform and non-uniform temperature distribution over the metal section. The calculations of the heat transfer coefficients by convection and radiation, as well as the thermophysical parameters of the heated metal for the investigated furnaces, billets and their stacking schemes, were carried out using the mathematical package MathConnex (part of MathCadPro).

Features of heat treatment of high-strength lean alloyed cold-resistant steel

Mechanical characteristics of an alloy, used for manufacturing parts of heavy-duty machines, operating under conditions of dynamic and cyclic loads, should meet increased requirements. According to the concept of lean alloying, quality of an alloy and highest possible properties of a chemical composition are determined by the modes of heat treatment. Results of a study of quenching temperature effect on microstructure and properties of a new lean alloyed steel MAGSTRONG 450L having the following chemical composition, %, mass: 0.21 С; 0.23 Si; 0.96 Mn; 0.03 Cr; 0.41 Ni; 0.023 Ti; 0.0021 B presented. Smelting of ingots of a given chemical composition was carried out in a vacuum induction furnace ZG-0.06L. Reduction of ingots was carried out on a hydraulic press П6334 and on a single-stand reversing hot rolling mill 500 duo. The samples were heated in a ПКМ 3.6.2/12,5 chamber furnace. Best mode of the hardening heat treatment of sheet rolled product of steel MAGSTRONG H450L was established, ensuring forming of a mixed structure, comprising 80% of lath martensite and about 20% of high temperature lamellar martensite. Such a structure ensures maximum values of impact toughness KCV–40 = 38 J/сm2 at high strength parameters (tensile strength σв = 1514 МPa, offset yield strength σ0,2 = 1243 МPа, hardness 460 HBW) and satisfactory indices of plasticity (percent elongation δ50 = 16 %) which correspondents to requirements ТС 14-101-1034–2015. Based on results obtained, recommendations were elaborated for heat treatment of the sheet steel MAGSTRONG H450L, thickness 8–20 mm as per OJSC “BELAZ” order. Application of the obtained results of the study will enable to create and perfect the technological modes of heat treatment of alloys with similar composition.

Friction Characterization of Al-Si Coated Ultra-High Strength Steel under Hot Stamping Conditions

Friction characterization of a hot stamped 1,800 MPa Al-Si coated ultra-high-strength steel (UHSS) is considered. Quantification of the coefficient of friction during a hot stamping process is essential for an accurate constitutive finite element model. The current work considers the twist compression test (TCT), in which an annular cup rotates against the surface of a fixed specimen using heated tooling. The measured sliding force and normal force determine the coefficient of friction. The test conditions used in this research simulate thermo-mechanical histories operative during hot stamping. Specimens are austenitized in a chamber furnace at a nominal temperature of 930 °C and a hold time of 5 minutes. They are then transferred to the TCT apparatus in which frictional sliding and die quenching occur simultaneously. The tooling components are uncoated and heated to 80 °C. Contact pressure of up to 30 MPa was considered between the tooling and specimen and a sliding speed of up to 38 mm/s. An increase in contact pressure caused the coefficient of friction to increase during dynamic friction. On the other hand, changes in sliding speed did not have a significant impact on the coefficient of friction. Likewise, repeated tests on the same tooling surface show that the coefficient of friction remains consistent during tool wear. Surface roughness of the tooling only increased after the first test and then remains stable during subsequent tests.

Chemical and Electronic Sensitization Effects Promoted By Noble Metal Nanoparticles on Gas Sensors Based on SnO Nanobelts

IntroductionSemiconducting metal oxides (SMOx) are the most studied materials for gas sensing applications due to their outstanding capacity to detect flammable and toxic gases, and their low-cost processing and ease of handling. [1,2]Many strategies have been developed attempting to achieve materials with improved sensor performance, including surface functionalization. The most common SMOx surface functionalization species are noble metal nanoparticles (NPs) given the possibilities to present both chemical and electronic sensitization effects.[3]This work reports on the gas sensing response of pristine and Pt and Pd decorated stannous oxide nanobelts. The responses of devices to different analytes (H2, CO and NO2) were measured in dry air baseline atmosphere as function of the analyte concentration (1–1000 ppm) and temperature (150-350 °C). Method Stannous oxide nanobelts were synthesized by a carbothermal reduction method using a mixture of SnO2 powder (Sigma-Aldrich, 99.9% purity) and carbon black (Union Carbide, > 99% purity) in the molar ratio of 1.5:1 (SnO2:C) as starting material.[4] The nanoparticles (Pt and Pd) used to functionalize the surface of nanobelts were prepared by the polyol method.Samples were characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study their morphology and crystalline structure.Suspensions of pristine and functionalized materials were deposited onto interdigitated platinum electrode arrays to perform the gas sensor measurements. The devices were placed in a temperature-controlled tubular furnace chamber, where the electric current was monitored under a constant applied voltage. Synthetic dry air was used as baseline and the analytes (NO2, H2 and CO) were introduced into the chamber using mass flow controllers. Gas sensor measurements were performed ranging from 150 °C to 350 °C. Results and Conclusions SEM and TEM results showed that obtained materials were nanobelts in the SnO phase. Moreover, functionalization with noble metal nanoparticles was successful, presenting disperse nanoparticles (< 15 nm) over nanobelts surface.About the gas sensing measurements, pristine devices are both sensitive and selective for nitrogen dioxide (NO2) molecules between 100 and 250 °C. In addition, both Pd- and Pt- functionalized devices present excellent selectivity to H2 at 300 and 350 °C. Moreover, Pt- functionalized device presented good selectivity for high concentrations of CO (>200 ppm) at low temperatures (100 and 150 °C). Then, results showed that noble metal decorated devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap (0.6 eV). Values showed that while Pt0 and Pt2+ promotes a high potential barrier with SnO nanobelts, Pd0 does not have this effect. Based on these findings, we propose an array based on pristine and NPs-functionalized SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Furthermore, electronic sensitization mechanism is elucidated based on the band diagram of materials.Results presented here are important to engineer high performance sensor devices by selecting the better work function of nanoparticles, depending on the Fermi level of semiconductor.

Investigation of factors affecting thermal performance in a coal - fired boiler and determination of thermal losses by energy balance method

In this study, a coal-fired industrial type boiler's performance and emission tests were performed using the energy balance method. During the experiments, the directives in the test standard (ASME PTC - 4) were followed. This tested boiler has a capacity of 75 t/h and is used in the mining industry. This boiler is a steam drum boiler equipped with an atmospheric circulating fluidized bed furnace. The furnace chamber with a rectangular cross-section has its width of 4250 mm and a depth of 4100 mm. In order to minimize the height of the furnace chamber and whole boiler, the middle wing walls are built-in the furnace chamber. As a result of the performance test, the boiler efficiency (indirect method) was found to be 93.07% (base on the lower heating value of fuel). According to the indirect method, the first three significant losses in total boiler losses were, respectively; the conversion of H2 in the fuel to water after combustion by 4.036%, the loss of dry flue gas by 3.231%, and the proportion of unburned carbon in residual products at the end of combustion with 1.653%. Due to the fluidized bed boiler's structural characteristics, it was also shown in the test results that emissions were suppressed in the combustion chamber, which was kept in the temperature range of 850–950 °C.

High-Temperature Oxidation Behaviour of AISI H11 Tool Steel

The high-temperature oxidation of hot-work tool steel AISI H11 was studied. The high-temperature oxidation was investigated in two conditions, the soft annealed condition, and the hardened and tempered condition. First, calculations of the compositions of the oxide layers formed were carried out using the CALPHAD method. The samples were oxidised in a chamber furnace and in a simultaneous thermal analysis instrument, for 100 h in the temperature range between 400 °C and 700 °C. The first samples were used for metallographic (optical microscopy and scanning electron microscopy) and X-ray diffraction analysis of the formed oxide layers, and the second ones for the analysis of the oxidation kinetics by thermogravimetric analysis. Equations describing the high-temperature oxidation kinetics were derived. The kinetics can be described by three mathematical functions, namely: exponential, parabolic, and cubic. However, which function best describes the kinetics depends on the oxidation temperature and the thermal condition of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. The oxide layers consist of three sublayers, the inner one being spinel-like oxide (Fe, Cr)3O4, the middle one a mixture of magnetite and hematite and the outer one of hematite. At 700 °C there is also some wüstite in the inner oxide sublayer of the soft annealed sample.