| 1. |
- Alevanau, Aliaksandr, 1965-, et al.
(författare)
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Mechanically assisted low temperature pyrolysis of hydrocarbons
- 2014
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Ingår i: Proceedings of the XVII International Conference Foundations & Advances in Nonlinear Science, September 29 - October 3, Minsk 2014.
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Konferensbidrag (refereegranskat)abstract
- We report experimental setups and conditions leading to pyrolysis (cracking) of such gaseous hydrocarbons as methane, mixed propane and butane, at the temper-atures of the heater below 200oC. The process was mechanically assisted by putting the substances being decomposed into a dynamic interaction with the tin and bismuth alloy. The alloy had periodically changing phase state thus creating fractal interfaces between its surface and the gases. Interaction of the gases with mechanically produced fractal surfaces of the alloy made possible gas decomposition even at lower temperatures of the heater (150oC). At this temperature the heater couldn't melt the alloy in the heated volume with the gas.
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| 2. |
- Alevanau, Aliaksandr, 1965-
(författare)
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Study of pyrolysis and gasification of biomass from the self-organization perspective
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the analysis of kinetics of i) low-temperature pyrolysis of gaseous hydrocarbons, ii) high-temperature steam gasification of char of wood pellets (>700oC), iii) high temperature pyrolysis of straw pellets in an atmosphere of argon and steam, and iv) high temperature pyrolysis of slices of transversally cut wooden sticks. The results of the kinetic measurements in the high-temperature cases are approximated using a least-square based optimization software, which was specially developed to analyse kinetics prone for deviation from the Arrhenius law.In the thesis a general analysis of the researched materials and kinetics of their pyrolysis and gasification is presented from the self-organization perspective. The energy transfer phenomena in both the pyrolysis and gasification processes of biomass are discussed with an emphasis on an analysis of basic phenomena involving the self-organized dynamics on fractal structures in the chosen biomass samples.
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| 3. |
- Arzpeyma, Niloofar, et al.
(författare)
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Mathematical Modeling of Postcombustion in an Electric Arc Furnace (EAF)
- 2019
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Numerical modeling was used to study the capability of postcombustion in an electric arc furnace (EAF) equipped with virtual lance burners. The CO flow rate at the molten bath surface was estimated using the off-gas data obtained close to the outlet of an EAF. Then, the effect of the secondary oxygen flow rate on postcombustion was studied. The results show a CO flow rate of 0.6 kgs(-1) and 0.8 kgs(-1) for operation modes of burner and burner + lancing. Increase of the secondary oxygen flow rates of 60% and 70% result in 17% and 7% increase in the postcombustion ratio (PCR) for the burner and burner lancing modes, respectively.
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| 4. |
- Arzpeyma, Niloofar, et al.
(författare)
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Mathematical Modeling of Scrap Melting in an EAF Using Electromagnetic Stirring
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:1, s. 48-55
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Tidskriftsartikel (refereegranskat)abstract
- Numerical modeling has been used to investigate the influence of electromagnetic stirring on melting of a single piece of scrap in an eccentric bottom tapping (EBT) electric arc furnace (EAF). The heat transfer and fluid flow in the melt for both conditions with and without electromagnetic stirring were studied. The buoyancy and electromagnetic forces were considered as the source terms for momentum transfer in the studied conditions. The enthalpy-porosity technique was applied to track the phase change of a scrap piece defined in the EBT region of the furnace. Different scrap sizes, preheating temperatures, stirring directions and force magnitudes were considered, and the heat transfer coefficient was estimated from the heat transfer rate at the melt-scrap interface. The results showed that electromagnetic stirring led to a reduced melting time and an increased heat transfer coefficient by a factor of four. The results for Nusselt number versus Grashof number for natural convection and Reynolds number for electromagnetic stirring were compared with those obtained through correlations from previous studies.
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| 5. |
- Arzpeyma, Niloofar, 1985-
(författare)
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Model Developments to Study Some Aspects of Improving Efficiencies in EAF Plants
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to investigate some aspects of improvements with respect to the energy consumption and raw material selection as well as the understanding of the influence of uncertainties on the performance in electric arc furnace (EAF) plants. The effect of electromagnetic stirring on the scrap melting and post combustion capacity are investigated in two EAFs by using computation fluid dynamic (CFD) models. The results showed that electromagnetic stirring can contribute to a better heat transfer rate at the melt – scrap interface. The Grashof and Nusselt numbers for both electromagnetic stirring and natural convection were estimated, as well as compared to the data from previous studies. Also, the results of the post-combustion in the duct system were used to predict the concentration of uncombusted CO at the possible position to install an off – gas analysis equipment. Also, modeling of the post-combustion in the whole furnace showed that the post-combustion can be improved by increasing the flow rate of the secondary oxygen in a virtual lance burner (VLB) under the meltdown and refining periods of the process. In order to investigate the influence of additions of raw materials on energy, melt composition and slag properties, a static mass and energy balance model is developed. The distribution ratios for metallic elements and dust parameters are calibrated by using process data from an EAF. The model is then applied to investigate the effect of hot briquetted iron (HBI) additions in that particular EAF. The results showed that these additions resulted in an increased electricity consumption and slag amount. The model is then applied to predict how it is possible to adjust the amount of slag formers to reach a desired MgO saturation level. In addition, a statistical model is developed which simulate the melt composition by applying uncertainties in scrap composition, scrap weighing and element distribution factors. The model can estimate the mean and standard deviations in the element concentration of scraps. The results of the model application in an EAF showed that the simulated melt chemical composition is in good agreement with the measured one, when the estimated values for scraps are applied as data in the model.
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| 6. |
- Arzpeyma, Niloofar, et al.
(författare)
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Modeling of post combustion inside the off-gas duct system of the Ovako electric arc furnace
- 2014
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Ingår i: CDF 2014.
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Konferensbidrag (refereegranskat)abstract
- In order to study the post combustion (PC) inside the duct system of an electric arc furnace (EAF), a three-dimensional computational fluid-dynamics (CFD) model was developed. The reactions between the off gas species (oxygen and hydrogen) and oxygen which leaked into the duct, through the air gap, was considered. The off-gas composition, the off –gas velocity and the outlet pressure were considered as parameters affecting the PC. The results showed that there was a considerable amount of the uncombusted CO to be captured. The highest CO concentration was found at the central part of the duct. The results also showed that a higher off-gas mass flow rate and a higher power of the outlet fan led to a higher combustion of CO and H2. An off-gas analysis probe was then installed after the air gap, where the tip of the probe was placed according to the predicted high CO concentration area found in the simulations. Thereafter, the measured off-gas composition was used to predict the off-gas composition at the outlet of the EAF.
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| 7. |
- Bai, Haitong, 1986-
(författare)
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A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.
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| 8. |
- Bai, Haitong, et al.
(författare)
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An Experimental and Numerical Study of Swirling Flow Generated by TurboSwirl in an Uphill Teeming Ingot Casting Process
- 2016
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 56:8, s. 1404-1412
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Tidskriftsartikel (refereegranskat)abstract
- A swirling flow has been demonstrated to be beneficial for making the flow pattern even and to reduce turbulence during filling in ingot casting. A new swirling flow generation device, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mold so that a more stable flow could be obtained. A water model was built including the TurboSwirl with different flaring angles of the divergent nozzle, according to a former numerical study indicating that a much more beneficial flow pattern could be obtained by reducing the flaring angle. To validate the mathematical model, the air-core vortex formed in the water model experiment was used, and the length of the vortex was measured and compared to the numerical predictions. Different turbulence models including the standard k-epsilon, realizable k-epsilon and Reynolds stress model were tested. It was found that only the Reynolds stress model could most accurately simulate the high swirling flow including a vortex. In addition, the radial velocity of the water around the vortex was measured by an ultrasonic velocity profiler (UVP). The experimental results revealed a high turbulence of the swirling flow and strong fluctuations of the vortex. The radial velocity of the water around the upper part of the vortex could be predicted well compared to the experimental results by the UVP measurements.
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| 9. |
- Bai, Haitong, 1986-, et al.
(författare)
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Effect of swirling flow tundish submerged entry nozzle outlet design on multiphase flow and heat transfer in mould
- 2019
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Ingår i: Ironmaking & steelmaking. - : TAYLOR & FRANCIS LTD. - 0301-9233 .- 1743-2812.
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Tidskriftsartikel (refereegranskat)abstract
- Effect of a swirling flow SEN (submerged entry nozzle) outlet design on the multiphase flow and heat transfer in a mould was investigated by using numerical simulation. It was found that different SEN outlet designs could form different flow patterns and temperature distributions on the upper of the mould. The enlarged outlet SEN design had an effect to decrease the horizontal velocity of liquid steel flowing out the SEN outlet, reducing the steel flow velocity towards the solidification front. Although a higher velocity was found near the slag/steel interface with the enlarged outlet SEN, but the turbulent kinetic energy was lower. The reason was that less circulation flows were formed in the region of the mould top. The weak horizontal flow towards the solidification front with the enlarged outlet SEN induced lower wall shear stresses, at the same time it also formed a lower temperature distribution near the solidified shell.
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| 10. |
- Bai, Haitong, et al.
(författare)
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Effect of TurboSwirl Structure on an Uphill Teeming Ingot Casting Process
- 2015
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 46:6, s. 2652-2665
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Tidskriftsartikel (refereegranskat)abstract
- To produce high-quality ingot cast steel with a better surface quality, it would be beneficial for the uphill teeming process if a much more stable flow pattern could be achieved in the runners. Several techniques have been utilized in the industry to try to obtain a stable flow of liquid steel, such as a swirling flow. Some research has indicated that a swirl blade inserted in the horizontal and vertical runners, or some other additional devices and physics could generate a swirling flow in order to give a lower hump height, avoid mold flux entrapment, and improve the quality of the ingot products, and a new swirling flow generation component, TurboSwirl, was introduced to improve the flow pattern. It has recently been demonstrated that the TurboSwirl method can effectively reduce the risk of mold flux entrapment, lower the maximum wall shear stress, and decrease velocity fluctuations. The TurboSwirl is built at the elbow of the runners as a connection between the horizontal and vertical runners. It is located near the mold and it generates a tangential flow that can be used with a divergent nozzle in order to decrease the axial velocity of the vertical flow into the mold. This stabilizes flow before the fluid enters the mold. However, high wall shear stresses develop at the walls due to the fierce rotation in the TurboSwirl. In order to achieve a calmer flow and to protect the refractory wall, some structural improvements have been made. It was found that by changing the flaring angle of the divergent nozzle, it was possible to lower the axial velocity and wall shear stress. Moreover, when the vertical runner and the divergent nozzle were not placed at the center of the TurboSwirl, quite different flow patterns could be obtained to meet to different requirements. In addition, the swirl numbers of all the cases mentioned above were calculated to ensure that the swirling flow was strong enough to generate a swirling flow of the liquid steel in the TurboSwirl.
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