Furnace Axis Research Articles

Моделирование трехмерного поля скорости в барабанной вращающейся печи

This paper deals with the problem of laminar axisymmetric incompressible flow in the working area of a rotary drum furnace. A system of second-order partial differential equations is derived and solved numerically using the finite difference method. The obtained solutions are tested for mesh convergence and compared with available analytical solutions for a laminar axisymmetric flow. The numerical results show that furnace rotation significantly affects the gas flow in the working section of the apparatus. Thus, the temperature distribution over the working area and furnace surface can be controlled through the furnace rotation velocity and gas flow rate. The input velocity profile also affects the flow pattern in the furnace. Vortex zones with counterflow occur near the walls, where the axial velocity profile is more elongated than the Poiseuille parabola. On the symmetry axis, the axial velocity is higher than that of the Poiseuille flow. The proposed mathematical model allows one to calculate more accurately the degree of thermal decomposition as a function of temperature and longitudinal coordinate along the furnace axis.

Derivation of the kinetics of devolatilisation and oxidation of pulverized biomass in a drop tube furnace: Sensitivity to volume evolution and drag-coefficient model

Combustion experiments of raw and torrefied pine and demolition wood particles (600–800 µm) are performed at 800 °C in a drop tube furnace. The results provide the oxygen and carbon monoxide profiles along the reactor axis. These data are then used in a numerical model, developed to determine the kinetic parameters of devolatilisation and oxidation of the pulverized biomasses. In order to simulate the gas phase reactions, the model also takes as input the composition of the volatiles of the tested fuels measured during pyrolysis experiments at 800 °C in the drop tube furnace. The model adopts different scenarios of particle volume evolution and different drag coefficient models in order to test their influence on the derived kinetic parameters. One of the volume evolution scenarios is a specific sub-model obtained by optical diagnostics of the combustion of the three biomasses in a previous study. Four other volume sub-models found in literature are also tested. For each of these scenarios, the model estimates close activation energy for devolatilization with a maximum variation of 2 kJ·mol−1 from one scenario to another, while the activation energy of char oxidation is more influenced, varying by 14 kJ·mol−1 with different scenarios. The five scenarios show similar gas concentrations and burnout versus the distance travelled by the particle. Nevertheless, this gives rise to a noticeable difference in the particle temperature along the furnace axis (±100 °C at some positions), in addition to different particle velocity and residence time (~ ±10%). The influence of the drag force is also studied using enhanced non-spherical model versus a spherical model. The non-spherical model leads to 10 to 14 kJ·mol−1 higher devolatilisation activation energies and 10 to 19 kJ·mol−1 higher char oxidation activation energies than the spherical model, along with a better prediction of the CO levels.

Growth of MoS2 nanoflakes near/far from tubular furnace axis and their impact on the efficiency enhancement of the Si solar cells

Molybdenum disulfide (MoS2) nanoflakes were grown on p-type silicon substrates at different locations in a tubular furnace, near and far from the tube axis, by thermal chemical vapor deposition (TCVD). The crystallinity and optical properties of the obtained structures were affected by the location of the substrate near/far from the axis. X-ray diffraction (XRD) patterns confirmed that MoS2 structures in both cases had rhombohedral phase, however the location of the substrate affected the abundant of the MoS2 nanoflakes. Moreover, UV–vis absorption and Raman spectroscopies indicated that the location of the substrate strongly influenced the band gap and the numbers of the obtained MoS2 layers. Moreover, the photovoltaic properties of the Si solar cells assisted by the grown nanoflakes were evaluated based on current-voltage characteristics and external quantum efficiency using a solar simulator.

Fuel Combustion at Blast-Furnace Tuyeres

Abstract—In textbooks on the metallurgy of iron, the chapter regarding the processes in the blast-furnace hearth must be supplemented with information regarding the calculation of the total energy of the composite blast, which determine the size of the combustion zone ahead of the tuyeres; and the total mechanical energy of the hearth gas, which characterizes the penetration depth of the hearth gas with respect to the furnace axis and the temperature at the center of the hearth. Constant monitoring of these total-energy values is required in the blast furnace. Those readings must be compared with the values for the best operating periods.

Influence of the Quality of Iron Ore and Coke on Blast-Furnace Performance

Excellent blast-furnace performance is observed when using screened sinter that is free of fines, with the alternation of tuyeres of normal and enlarged diameter. If the total mechanical energy of the combined blast at the tuyere mouth and the total mechanical energy of the blast-furnace gas increase in these conditions, the combustion zone becomes longer and the blast-furnace gas penetrates further toward the furnace axis. In that case, the benefits of the high-quality raw materials may be maximized.

Влияние качества агломерата и кокса на технико-экономические показатели доменной плавки

Purpose: Compare the results of blast furnace smelting efficiency, when chang-ing the qualitative characteristics of the sinter and coke, and the calculated param-eters of the blowing regime of melting. Methodology: Analysis of technical and economic performance of blast furnaces during periods of work on the agglomerate with different metallurgical characteris-tics and different diameter of the tuyeres. Findings: The experience of blast furnaces with a volume of 2,700 and 2,000 m3 confirmed a known fact of the dependence of furnace efficiency and coke consump-tion not only through the quality of charge materials, but also through the distribu-tion of the gas flow along the furnace section. Originality: The technological analysis of the results of the operation of blast furnaces with the volume of 2700 and 2000 m3 with a change of the quality of the sinter and pellets in combination with the change of the blowing regime parame-ters was performed. On the basis of the performed analysis, it was confirmed the expediency of increasing the gas permeability of the charge by improving the quali-ty of the raw materials while increasing the total mechanical energy of the com-bined gas-blast and hearth-gas, which are responsible for the length of the com-bustion zone and the depth of penetration of the gas flow to the center of the blast furnace. Practical value: Alternation of tuyeres of different diameters along with the im-provement of the quality characteristics of charge materials, additionally contrib-utes to the enhancement of the positive effect due to the expansion of the combus-tion zones in the furnace hearth. And if in this case the total mechanical energy of the mountain gas rises and the depth of penetration of the furnace gas to the fur-nace axis increases, the effect of using high-quality raw materials can be maxim-ized. Keywords: agglomerate, coke, blowing, tuyeres, gas permeability, quality, total energy.

Parametric study of reburning of nitrogen oxide for superfine pulverized coal

An experimental investigation of process parameters design by superfine pulverized coal reburning on NOx reduction is carried out in a one-dimensional bench-scale combustion system. Reburning effectiveness for initial levels ranging from 600 to 650ppm is evaluated. It is found that for Shenhua bituminous coal, NOx reduction performance of superfine pulverized coal owns its unique advantage, 50% higher than conventional particle size. Medium reburning fuel fraction (RF20∼RF25) and low oxygen concentration are recommended to be ensured in this experiment. The yield of HCN and CH4 along the furnace axis does not seem to be decisive on the effect of particle size, but is closely related to the effect of reburning fuel fraction. Both exhaust and in-flame measurements are reported in this paper to provide valuable experimental data for practical engineering applications.

Heat flux and temperature prediction on a volumetric receiver installed in a solar furnace

This paper presents a prediction procedure of the solar irradiance distribution on a plane parallel to the focal one of the Plataforma Solar de Almería’s Solar Furnace, within defined limits, as well as its application to test a sample of a volumetric solar receiver exposed to concentrated solar radiation. From initial heat-flux measurements at different focal planes of the Solar Furnace, this procedure is able to reliably predict the irradiance distribution on any plane and under different operating conditions, such as direct normal irradiance, shutter aperture, and mirror reflectance. As a result, this study allowed predicting the heat flux distribution at different Furnace axis positions selected for testing a sample of a volumetric solar receiver. Furthermore, the temperature reached on the sample surface, which receives the concentrated solar radiation, could be obtained from the flux features previously analysed. It makes possible to preserve the absorber material from overheating areas modifying the operating variables.

Analysis of the state of structure and the basic parameters and indices of the operation of the large EAFs operating in the metallurgical plants in Russia

16 mln t steel were melted in 24 large electric arc furnaces (EAFs) in the metallurgical plants in Russia furnaces in 2011 at an annual capacity of 22 mln t of these furnaces. Among them, 17 EAFs are equipped with eccentric bottom tapping and operate with a “bog.” Three EAFs use the heat of effluent gases for heating of a charged scrap: a shaft heater at the Cherepovets metallurgical works (CherMK) and conveyer heating in the Ashinsk metallurgical plant. The DSP-120 furnace in CherMK has the best indices in Russia for operation with cast iron: electric power consumption of 260 kWh/t and a heat time of 49 min. Nine EAFs operating in metallurgical works use 20–30% liquid iron in a charge, which decreases the electric power consumption by 80–100 kWh/t. The working space and the EAF dimensions are important. A groundless decrease in the electrode failure diameter (1200 mm or smaller) leads to problems in the EAF transformer operation at a transformer power higher than 100 MVA and a secondary voltage higher than 1000 V. The performance of EAFs and the reliability of equipment operation depend on the working space height, the electric holder stroke, the distance between the axes of chair segments, the distance from the furnace axis to the axis of electric holder supports, and so on. Engineers in OOO NTP Akont determined the optimum sizes and relations between them for 120- to 130-t EAFs.

Computational modeling of a utility boiler tangentially-fired furnace retrofitted with swirl burners

The paper presents 3D numerical investigation of OP-380 boiler tangentially-fired furnace utilizing bituminous coal. The boiler was retrofitted by replacing traditional jet burners with RI-JET2 (Rapid Ignition — JET) swirl burners. This kind of solution is unique in power generation systems. The purpose of this work is to show how the flow, combustion performance and heat exchange in the furnace are affected by introducing rapid ignition phenomena in RI-JET2 burners instead of delayed ignition associated with the traditional jet burners. Results were compared to simulations of similarly designed boiler equipped with traditional jet burners. Furnace simulation was preceded with a single RI-JET2 burner simulation at the inlet to a virtual combustion chamber. The results have shown that pulverized coal (PC) concentrator separates the PC into two streams: concentric with fine particles and axial with coarse particles. Stable flame operation was noticed even without secondary and tertiary air swirl. 3D simulations of combustion chamber have shown that in a burner zone a visibly isolated, concentrated flame exists in the furnace axis. This kind of flame shape reduces corrosion risk and furnace walls slagging as a result of RI-JET2 burner's long range.

Prediction of a Turbulent Non-Premixed Natural Gas Flame in a Semi-Industrial Scale Furnace using a Radiative Flamelet Combustion Model

A mixedness-reactedness flamelet combustion model coupled with a comprehensive radiation heat transfer model based on the discrete transfer method of solution of the radiative transport equation is applied for the simulation of a 3 MW non-swirling turbulent non-premixed natural gas flame in the experimental furnace at the International Flame Research Foundation. In the calculation, turbulence is represented by the standard k − e and a differential Reynolds-stress model. Predictions are compared with measurements of mean gas velocity, temperature, major species concentrations and incident radiation wall flux. The radiative mixedness-reactedness flamelet combustion model, irrespective of the model for turbulence, is able to reproduce the basic structure of the experimental flame, which is stabilised downstream of the burner nozzle. In the near burner region, encompassing the non-reacting lift-off zone, good quality predictions are obtained using both the turbulence models, whereas further downstream, within the combusting zone of the jet, the Reynolds-stress turbulence model generates better predictions at and about the furnace axis. The nitric oxide (NO) formation via the thermal- and prompt-NO routes was also calculated and compared with in-flame and flue-gas NO data. The measured NO level at the furnace exit is well reproduced in the calculation, however discrepancies exist near the burner where NO concentrations around the furnace axis are overpredicted.

Study of melt-grown quasicrystalline samples in the Cd-Yb and Al-Cu-Fe systems

The regimes of preparation of bulk samples of the quasicrystalline phase in the Cd-Yb and Al-Cu-Fe systems have been investigated. A thermodynamically stable quasicrystalline phase Cd5.7Yb and its approximant Cd6Yb with a high degree of texture along the cooling axis have been obtained. X-ray diffraction analysis made it possible to reveal changes in the structure and phase composition of bulk samples with variation in the melting temperature and annealing for different methods of sample preparation. It is shown that the presence of a temperature gradient along the furnace axis significantly affects the volume of the quasicrystalline phase. It is established that, with a decrease in the volume of the quasicrystalline phase mixed with the crystalline phase, the character of the temperature dependence of resistivity changes from the semiconductor type to the metallic type and the microhardness decreases according to a linear law.

Characteristics of Co-combustion of Low-Rank Coal with Biomass

The fundamentals of ignition, NOx (NO and N2O) emissions, and ash formation characteristics for biomass and mixtures of coal with biomass are precisely elucidated in this study. In this study, biomass, coal, and a biomass−coal mixture are burned, using an electrically heated drop tube furnace. In the combustion test, the focus is on the ignition behavior, combustion efficiency, NOx emission behavior, and formation characteristics of particulate matter, based on the results of gas compositions along the furnace axis and a collection of particulate matter by a low-pressure impactor. As a result, the addition of biomass into low-rank coal affects combustion behavior, especially for ignition enhancement. The NO and N2O concentrations in co-combustion are almost the same as those in coal combustion, even if the quantity of input fuel nitrogen under the co-combustion condition is half of that under the coal combustion conditions. A kinetic simulation of the NO and N2O behavior results is conducted, using the homogeneous reaction schemes at constant temperature. The simulation result of NO concentration agrees with the experimental result obtained. However, the N2O concentration calculated is less than the experimental result, because the heterogeneous schemes that are related to N2O are not considered in this simulation. Fine particulates with a size of <2 μm during biomass combustion are produced. Burning the biomass with coal shifts the particle size distribution from fine particles to coarse particles, which can be captured by dust collection systems.

CO-COMBUSTION OF PULVERIZED COAL, PINE SHELLS, AND TEXTILE WASTES IN A PROPANE-FIRED FURNACE: MEASUREMENTS AND PREDICTIONS

This paper describes an experimental and numerical investigation on the co-combustion of propane with pulverized coal, pine shells, and textile wastes. Measurements have been performed in a large-scale laboratory furnace fired by an industrial-type swirl burner. Data are reported for in-flame major gas-phase species concentration, including NOx, in-flame gas temperature, and overall char burnout for three flames: a propane/coal flame, a propane/pine shells flame, and a propane/textile wastes flame. For comparison purposes, data are also reported for a pure propane flame. The experimental results show that CO and unburned hydrocarbon emissions from propane cofiring with pine shells and textile wastes can be important due to the relatively large sizes of the solid particles and that NOx emissions data reproduce the impact on them of the fuel nitrogen content via fuel-NO formation for the three solid fuels studied. Also, the cofiring of propane with pine shells and textile wastes yields particle burnout values much higher than that of the propane/coal flame despite the similarities of the three flames revealed by the in-flame data. This is because of the higher volatile matter content of the pine shells and textile wastes, in spite of their much larger particle sizes, compared with coal. The experimental conditions were then simulated numerically. For the numerical predictions, gas-phase calculations were based on the Eulerian approach whereas the particulate phase predictions were based on a stochastic Lagrangian approach. The turbulence model used herein was the standard two-equation eddy viscosity model. The gaseous fuel and volatiles oxidation was assumed to be controlled by both turbulent mixing and chemical kinetics. Radiation was accounted for. The biomass/waste devolatilization was simulated by a single-reaction, first-order decomposition model. Thermal-NO, prompt-NO, and fuel-NO mechanisms were all considered as potential contributors to the NO formation. From the comparisons of the predictions with the experimental data, a good agreement was generally found, except in the near-burner region close to the furnace symmetry axis. The discrepancies are due to the limitations of the k–ϵ turbulence model to simulate high swirling flows. Moreover, the simplified fuel-NO model used herein requires further improvements to yield more accurate results.

Heavy fuel oil combustion in a cylindrical laboratory furnace: measurements and modeling

The finite-volume based commercial CFD-code Fluent was used to simulate the reacting flow in a heavy fuel oil fired laboratory furnace. Both the standard k−ε turbulence model and the Reynolds stress model (RSM) were tested. The combustion model was based on the conserved scalar (mixture fraction) and prescribed probability density function approach. The heavy fuel oil droplet trajectories were predicted by solving the momentum equations for the droplets using the Lagrangian treatment. The soot distribution in the furnace was calculated by solving a transport equation for the soot mass fraction. Simple expressions for the soot formation and oxidation rates were employed. The radiation heat transfer equation was solved using the finite volume method. The formation of thermal NO from molecular nitrogen was modeled according to the extended Zeldovich mechanism. Fuel-based NO was modeled assuming that all the nitrogen in the fuel is released as hydrogen cyanide (HCN), which then further reacts forming nitric oxide NO or molecular nitrogen N 2, depending on the local combustion conditions. The formation of prompt NO was also included in the calculations. The CFD-code was validated against experimental data for a combustor fired by an industry-type swirl burner for which the initial conditions of the spray have been characterized. It was found that the standard k−ε model does not satisfactorily predict the highly swirling flow field in the furnace. The RSM was able to improve the prediction of the flow field. The predicted gas species concentrations were found to be in a reasonable agreement with the measurements, except near the burner and in the vicinity of the furnace axis where discrepancies were found.

Vapour Growth of ZnSxSe1?x Single Crystals

Seeded chemical and physical vapour transport with H 2 and He, respectively, was used to grow twin-free ZnS x Se 1-x (x < 0.15) single crystals with diameter of 50-55 mm and height up to 15 mm. Use of a source with polycrystalline ZnSSe having a composition gradient along the furnace axis, allowed to improve the homogeneity of alloy composition. The change of x per 1 cm along the growth direction in the grown crystals was as small as 1.5%. The etch pit density was (3-5) x 10 4 cm -2 . Specific resistance of ZnSSe wafers was decreased up to 0.06 Ω cm by annealing in liquid Zn:Al.

Chemical Vapor Infiltration of Carbon into Graphite Block with Uniform Bore Capillary Tubes

Chemical Vapor Infiltration of carbon was studied in uniform bore capillary tubes using CH, as deposition gas. The relation between CVI parameters and the resultant deposition profile, rate and microstructure were examined. Higher temperature and pressure produce higher deposition rate and higher degree of prefferred orientation. Lower temperature and pressure yield better deposition uniformity along the capillary. Deposition profile along the furnace axis is determined by temperature profile of the furnace and the amount of deposition species in gas phase. Uniformity of deposition in the capillary depends on location of capillary in the furnace. Longer contact time gives higher rate at mouth of a capillary, and in-pore deposition profile depends on the relative ratioof the rate of diffusion of species and the rate of reaction. On the other hand, shorter residense time shows a better profile, and the profile within the capillary is controlled not only by diffusion/reaction relative ratio but by temperature gradient and by the concentration of deposition species within the capillary. Gas analysis suggests that microstructure along the furnace and within the capillary is affected by the ratio of aromatic species to acetylenic species in the gas phase.

Fundamental study on N2O formation/decomposition characteristics by means of low-temperature pulverized coal combustion

N 2 O formation/decomposition characteristics and its mechanisms in pulverized coal combustion, especially at low temperature, are discussed by using a one-dimensional electrically heated laminar drop furnace for various coal types The behavior of nitrogen compounds along the furnace axis is studied by analyzing both the sampled burning particles and combustion gas and by calculating the mass balance of nitrogen. Additionally, the effects of the combustion efficiency and the ratio of fixed carbon to volatile matter content (fuel ratio) on N 2 O formation/decomposition characteristics are elucidated experimentally. As a result, coals that evolve more HCN than NH 3 produce higher N 2 O concentration. In the down-stream region beyond the point where volatile matter combustion is complete, N 2 O concentration increases but NO concentration decreases gradually. Increase of N 2 O in this region may be caused not only by the reactions between NO and carbon in char (NO+char-C→NCO and NCO+NO→N 2 O+CO) but also by the direct heterogeneous reaction between nitrogen in char and NO (char-N+NO→N 2 O). For the coals with low fuel ratio, N 2 O conversion decreases because of high flame temperature surrounding the coal particles caused by strong volatile matter combustion. The decomposition reaction of N 2 O by H radicals produced by the oxidation reaction of CO by OH radicals also contributes near the particle surface. Thereafter, the combustion atmosphere and temperature surrounding the coal particles affects, N 2 O formation/decomposition characteristics. The exit N 2 O concentration increases with decreasing combustion efficiency and decreasing fuel ratio. Data from testing nine different types of coal show that the exit N 2 O concentration has a good correlation with the combustion efficiency and the fuel ratio.

Modeling flows and solute redistribution resulting from small transverse accelerations in Bridgman growth

An approximate analytical model has been developed to describe the two-dimensional flow field and its effect on solute redistribution during horizontal Bridgman growth at very small Grashof numbers. The purpose of the model is to examine the effects of small residual accelerations in attempts to grow crystals under diffusion limited conditions in a microgravity environment. Also, the model provides insight into the interplay of the various parameters involved and allows scaling laws to be formulated. The model is quite accurate provided the buoyancy-induced flows do not significantly alter the density field. For dilute systems this requires Gr Pr < O(100) or for non-dilute systems, Gr Sc < O(10). The amount of segregation along the growth interface is characterized by a segregation parameter ζ defined as the maximum difference in composition divided by the average composition. This parameter is shown to be directly proportional to the product of Grashof and Schmidt numbers (Gr Sc) and to a complicated expression involving the segregation coefficient, the ratio of the ampoule width to the diffusion length, and the ratio of ampoule width to the characteristic length of the density field. Conditions for maximum coupling are identified for various values of the segregation coefficient. Under these worst case conditions, it is shown that to achieve near diffusion-limited growth conditions (ζ < 0.01), the Gr Sc < 2. This places a severe constraint on the tolerable transverse acceleration, especially for systems with high Sc numbers. Steady or quasi-steady components of the residual acceleration considerably less than 0.1 micro- g in the transverse direction can produce significant solute redistribution, even in systems of modest size ( ∼ 1 cm in diameter). Some relief can be obtained by configuring the system to lessen the coupling between the flow and solute fields as discussed in this paper. Also, transverse accelerations can be minimized by orienting the furnace axis along the residual acceleration vector. If properly oriented, the residual acceleration might also help stabilize the system against the smaller transverse accelerations that can arise due to the small variations in the residual acceleration vector.

In situ measurement of wafer temperatures in a low pressure chemical vapor deposition furnace

Axial and radial temperature profiles within the wafer load of a multiwafer LPCVD furnace were measured in situ using a pair of instrumented wafers. The measurements confirm that the wafer load is not in thermal equilibrium with the furnace tube, as has been widely assumed in many modeling studies. The measurements confirm temperature variations predicted previously from a study of polysilicon film thickness profiles. Temperature variations were small for wafers near the center of the 150-wafer load. However, axial variations of up to 25 degrees C and radial variations of up to 5 degrees C were measured at the extremes of the wafer load. For a representative polysilicon deposition data set, axial and radial thin-film thickness variations were found to correlate closely with measured temperature variations. The temperature profile was found to be insensitive to gas composition and flowrate, establishing radiation as the dominant mode of heat transfer. A pair of polysilicon coated quartz radiation shields was shown to improve polysilicon film thickness uniformity both down the load (along the furnace axis) and across each wafer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>