Refractory Wall Research Articles

Attrition and morphological analysis of CaCO3 corresponding to oxy-fuel circulating fluidized bed conditions

The specific surface area of CaCO3 has always been an essential parameter for various oxy-fuel combustion processes and chemical looping processes. However, the circulating of bed material through the furnace, cyclone and loop-seal in an oxy-fuel circulating fluidized bed (CFB) reactor may trigger the particle size changes as a result of rapid collisions among particles and friction with the inner refractory wall. Rather than considering only the effect of initial particle size, it is significantly important to emphasize on the change in limestone particle size due to in-reactor attrition. In addition, the changes are further enhanced with calcination reaction that occurred under high-temperature conditions. Herein an investigative account of limestone in a lab-scale CFB process was presented by using two types of fluidizing media (Air, CO2) to determine its attrition and morphological changes under simulated operating conditions for riser and loop-seal. A significant difference in attrition index was observed as calcination of limestone occurred at high temperature under air atmosphere which was not observed under CO2 condition. With similar cross-sectional area observed for both the tested (CO2 condition) and re-carbonated limestone, it was concluded that re-carbonation of calcined lime at high CO2 concentration in the loop-seal resulted in a comparable abrasion resistance that further improved desulfurization performance by reducing the amount of ultra-fine particles generated from limestone.

Autologous myocutaneous flap implantation for chronic refractory chest wall sinus with infection: a case report

BackgroundChest wall sinus with infection is a refractory disease caused by a variety of susceptible factors, and the treatment is still challenging. For clinically complex cases, although there are various surgical methods to choose from, it is still very difficult to achieve clinical cure, especially for patients with older age and many underlying diseases. Complete resection of chest wall sinus and application of repair and reconstruction technology may bring hope to refractory cases.Case presentationHerein, we report a case of a 67 year-old woman who had undergone breast cancer surgery and a history of multiple cycles of radiotherapy and chemotherapy. One year ago, she had a fistula in the left chest wall with yellow purulent fluid. After admission to our hospital, chest computed tomography (CT) showed the formation of the left chest wall sinus, accompanied by high-density images of the left clavicle, part of the ribs and part of the sternu. According to the patient's symptoms, signs and imaging examination, we preliminarily diagnosed the patient as chest wall sinus with infection and chronic osteomyelitis. Therefore, in the first-stage operation, the patient underwent left chest wall sinus resection, left partial rib resection, left partial clavicular resection and left partial sternal resection, After surgery, the wound surface was changed with gauze dressing with sensitive antibiotic solution every day until the wound surface was clean and new granulation was formed. In the second-stage operation, the wound surface was appropriately expanded, and the pedicled latissimus dorsi myocutaneous flap was transferred to the chest wall defect. Finally, the skin paddle was sutured without tension to the normal skin around the chest, and two drainage tubes were placed. Anti-infection, anti-spasm, anti-coagulation and other treatments were given after operation, and the survival of myocutaneous flap, wound healing and sinus disappearance were observed.ConclusionThe application of pedicled latissimus dorsi myocutaneous flap in the treatment of intractable chronic chest wall sinus is an effective method. It does not change the shape of the thorax. The clinical effect is satisfactory in the near and medium term, which is worthy of clinical promotion.

Impact of potassium on bio-ash slagging and resultant slag flowing characteristics under mild reducing environment

This study aims to clarify the role of potassium (K) on the flowability of bio-slag in the reducing gas environment at 900-1400 °C. Through the use of an inclined plate method, a number of approaches were attempted to clarify the flow rate of bio-slags as a function of basic-to-acid ratio, as well as the comparison with a reference coal ash and synthetic ashes made by the blending of bio-ash with CaO, Al2O3 and K2O. At the same base-to-acid ratio (B/A) and 1400 °C, coal slag has a flow rate that is nearly four times larger than that of bio-slag. This is due to the co-existence of abundant K2O and Al2O3 in bio-slag that is in favour of the formation of solid KAlSi2O6. In contrast, the co-existence of abundant CaO and Al2O3 in coal slag is in favour of the formation of molten species. In addition, the inherent K in bio-ash underwent considerable mass loss due to both vaporisation and its interaction with the corundum plate. Upon the increase in the inclination angle of the plate, the extent of K penetrating within the corundum plate was mitigated considerably, which in turn minimised the plate corrosion. Simultaneously, the bio-slag formed readily spread out along the plate. The addition of extra K into bio-ash is beneficial in promoting the flow rate. However, even with an increased base-to-acid ratio to 1.2, the flow rate of bio-slag is still less than that of coal slag at the base-to-acid ratio of 0.72, due to the superiority of Ca2+ over K+ in promoting the bio-slag flow. For practical application, the use of CaO as a flux additive is beneficial in discharging the bio-slag out of the furnace. Moreover, the flow rates of bio-slag in the locations with low angles to the ground within the furnace should be monitored to minimise the accumulation of bio-slag as well as its corrosion against the refractory wall.

Coupling of spectral thermal radiation model with a comprehensive system model for co-combustion of biomass in bubbling fluidized bed

A previously developed 1-D comprehensive model for a bubbling fluidized bed combustor (BFBC) co-firing lignite with cotton residue and limestone is coupled with a 3-D spectral and gray radiation models utilizing method of lines (MOL) solution of discrete ordinates method (DOM). The performance of the coupled models is assessed by comparing their predictions of temperature profiles and gaseous emissions (i) with those of original FBC model without coupling and (ii) with the in-situ measurements from Middle East Technical University (METU) 0.3 MWt BFBC. Comparisons between fluidized bed combustion (FBC) system models with and without radiation reveal that the spectral model improves the predictions only slightly. This is considered to be due to the very small temperature difference between the freeboard medium and hot refractory side walls which results in lower rates of heat transfer from the freeboard to the walls. Furthermore, radiative heat transfer in the freeboard is dominated both by combustion gases and particles.

A proposal of ore particle-wall sticking criterion during the flash ironmaking process

ABSTRACT Particle-wall sticking is a common phenomenon in high-temperature ironmaking reactors, such as flash ironmaking furnaces. In this study, a new criterion for the reduced ore particles was proposed to predict the sticking propensity based on the components, morphology, and particle motion. A comprehensive computational fluid dynamics (CFD) model was also established, and a newly proposed sticking criterion was coded into the traditional gas-particle framework. The results show that the adhesion of particles is more likely to occur at the medium height on the hemispherical refractory wall, and there is a bias under the side-blowing gas flow. The study also shows that particle-wall sticking did not occur when the reaction temperature was below 1300°C, while more than half would stick to the molten slag surface at a higher temperature. However, the sticking propensity did not always increase at a higher experimental temperature because the intermediate products, such as FeO, can reduce viscosity.

Thermal analysis to investigate the effects of operating parameters on conventional cupola furnace efficiency

Background: Thermal analysis was performed on a conventional 6.5 m high dome with a 0.65 m diameter at Nigeria Railway Corporation. Energy and thermal analyses were performed on the furnace to improve efficiency and minimize energy losses in the system. Results: The energy efficiency recorded was 55%. The losses in the furnace amount to 45%, the highest value being the heat loss to the combustion gas at 34%. A parametric study was examined to see the effect of some design and operational parameters on furnace efficiency through energy savings and the study found a positive trend. The parameters include the flue gas temperature, the combustion air inlet temperature, the thickness, and the emissivity of the refractory wall. A decrease in the temperature of the flue gases increased the efficiency of the furnace to 73%, an increase in the air inlet temperature increased the efficiency of the furnace to 61%, and an increase in the thickness of the refractory wall increased the efficiency of the furnace. Oven to 56% and a decrease in emissivity of the refractory wall increased the efficiency of the furnace to 56%. Conclusions: The studied parameters were further combined and their net effect showed a possible increase in furnace efficiency from 55% to 78%. The maximum efficiency of 78% was determined with respect to the minimum/maximum estimated values of the parameters studied, as more metals are melted with the combined energy saved from a variation of these parameters. This implies that cupola furnace or similar furnace designers or operators should be guided on the preheating conditions, thickness, and emissivity of the refractory wall to be used with other parametric combinations to be adopted to ensure energy efficiency and improvement in such furnaces.

Coloring zirconium oxide for novel energy saving industrial applications

White conventional zirconium oxide was mixed to black or rust coloring second phase additives to increase the absorptance and thermal emittance with the aim of exploring novel oxide-based ceramics for energy exploitation and saving, like solar absorbers or even industrial refractory kiln walls. The variation of the optical properties of the colored samples was evaluated as a function of the amount, dopant type and co-doping and it was found that notable changes to the optical spectrum occur already upon introduction of 0.05 wt% pigment. The absorptance of ZrO2 passed from 0.1, in the white ceramic, to 0.75, for the rust-colored ones, and up to 0.82, for black colored materials containing Co-oxide as additive. The thermal emittance and solar absorptance of the black/rust-shaded specimens were calculated for temperatures from 400 to 1500 K and compared to commercial white, black and brown reference to identify the most appropriate composition for the two proposed applications and operating temperatures.

Significant energy saving in industrial natural draught furnace: A model-based investigation

• Model based simulation is carried out for industrial scale natural drought cabin furnace. • Aspen Hysys and exchanger design rigorous (EDR) program used for modelling and simulation. • Sensitivity analysis was carried out to predict the impact of several parameters on the furnace efficiency. • The study shows potential of significant savings in energy, operational cost and carbon footprint. In all industrial petrochemical plants and refineries, the furnace is the source of heat resulting from fuel combustion with air. The model-based furnace simulation is considered one of the efficient methods help to reduce the energy loss and maintain fixed refinery revenues, conserving energy, and finally reducing external fuel consumption and total fuel cost. In this paper, a model-based simulation is carried out for a natural air draught industrial scale furnace related to Liquified Petroleum Gas (LPG) production plant in Libya to thoroughly investigate the most responsible factors in lowering the furnace butane exit temperature, which is supposed to be two degrees Fahrenheit higher than inlet temperature. Therefore, to resolve this industrial problem, Aspen Hysys V10, coupling with EDR (exchanger design and rating) is used to carry out rigorous model-based simulation. This is specifically used to assess the impact of heat loss from inside the firebox to the surrounding medium and heat loss from the furnace stack and walls, besides the effect of excess air on the furnace efficiency. Furthermore, this research intends to verify whether the operating conditions, such as furnace tubes inlet flow rate, temperature and pumping pressure, are conforming to the upstream process design specifications or need to be adjusted. The results confirm that increasing furnace outlet temperature two degrees Fahrenheit from off specification 190 °F instead of 184 °F is successfully achieved by decreasing upstream stream flowrate 25% below the operating value and cutback excess air gradually until 20%. Also, the results clarify the necessity of increasing the flue gas temperature by 7% over design condition, to gain a significant reduction of heat loss of 31.6% and reach as low as 35.5 MBtu/hr. This improvement is achieved using optimum operating conditions of an excess air of 20%, and flue gas oxygen content of 3.3% delivered to stack. Accordingly, the furnace efficiency has been increased by 18% to hit 58.9%. Furthermore, the heat loss from the furnace walls can be also reduced by 68% from 5.41 MBtu/hr to 1.7 MBtu/hr by increasing the refractory wall thickness to 6 in., which entails an increase in the furnace efficiency by 3.66% to reach 58.96%. Decreasing the heat loss fraction through the refractory wall, pip doors, expansion windows and refractory hair cracks would also increase the efficiency by 21% to reach a high of 59.7%. Accordingly, a significant reduction in daily fuel consumption is observed, which costs 1.7 M$ per year. The outcomes of this research clearly show the potential of reducing the operation and maintenance costs significantly.

Degradation mechanism of high alumina refractory bricks by reaction with deposits in a rotary kiln for fluxed iron ore pellets production

The formed deposits wear out of refractory wall linings in the rotary kiln and may cause production disturbances. This study describes the chemical composition and mineralogical phase components at the deposit/refractory interface in the rotary kiln for fluxed iron ore pellets production. The main phases of refractory bricks are corundum and mullite, while the deposits mainly contain hematite and silicates. The main phases in the deposit/refractory brick contact zone are hematite, anorthite (CaAl2Si2O8), mullite, corundum, and silicates. Moreover, the hematite phases in the deposit/brick interface averagely contain 6.98 wt% Al and 1.38 wt% Ti. The silicates in the contact zone contain higher aluminium content and lower iron content than the silicates in the deposits. Finally, the thermodynamic analysis indicates that the main phases in the deposits can react with the refractory to form Al2Fe2O6, CaAl2Si2O8, feldspar, and liquid phases lead to the degradation of bricks in the kiln during the iron ore pellets production.

Hydrogen removal in circulating vacuum degasser under conditions of PJSC “NLMK”

For high­quality steel smelting, stage­by­stage production is required, which has a complex of metallurgical units capable for producing products with high performance properties and low content of harmful impurities. One of the harmful impurities is hydrogen, so it is important to limit its content in the metal. To ensure the specifed hydrogen content, the metal in the steel out­of­furnace treatment at Converter Shop No. 2 (CS­2) of PJSC “Novolipetsk Metallurgical Plant” (“NLMK”) is subjected to vacuum treatment in a circulating vacuum degasser. Despite the prevalence of circulating vacuum derassers, theoretically, mechanism of hydrogen removal in these metallurgical units has been insufciently studied. To increase efciency of hydrogen removal, theoretical calculations were performed to remove it from the metal. There are several mechanisms for hydrogen removing: direct transfer of hydrogen from metal to the surrounding space; formation of gas bubbles in metal and their direct ascent; nucleation of hydrogen bubbles at the border of refractory wall and metal; removal of hydrogen by metal blowing with neutral gas (argon). It is shown that the main ways of hydrogen removal in a circulating vacuum degasser are direct transfer of hydrogen from metal to the surrounding space and blowing of melt with transporting gas. In the CS­2 of PJSC “NLMK”, both ways are implemented at a circulating vacuum degasser. Vacuum pumps provide pressure in a vacuum chamber of less than 101.3 Pa (0.001 atm.). It promotes intensive removal of hydrogen from the metal surface. To ensure circulation of metal, transporting gas argon is supplied to the inlet pipe of the RH degasser, which also takes part in removal of dissolved gases by transferring hydrogen to neutral gas bubbles. Additionally, performed calculations have shown that the main way of degassing in conditions of CS­2 of PJSC “NLMK” is removal of hydrogen into the bubbles of carrier gas.

Hydrogen Removal in Circulating Vacuum Degasser under Conditions of PJSC “NLMK”

For high-quality steel smelting, stagebystage production is required, which has a complex of metallurgical units capable for producing products with high performance properties and low content of harmful impurities. One of the harmful impurities is hydrogen, so it is important to limit its content in the metal. To ensure the specified hydrogen content, the metal in the steel outoffurnace treatment at Converter Shop No. 2 (CS2) of PJSC “Novolipetsk Metallurgical Plant” (“NLMK”) is subjected to vacuum treatment in a circulating vacuum degasser. Despite the prevalence of circulating vacuum degassers, theoretically, mechanism of hydrogen removal in these metallurgical units has been insufficiently studied. To increase efficiency of hydrogen removal, theoretical calculations were performed to remove it from the metal. There are several mechanisms for hydrogen removing: direct transfer of hydrogen from metal to the surrounding space; formation of gas bubbles in metal and their direct ascent; nucleation of hydrogen bubbles at the border of refractory wall and metal; and removal of hydrogen by metal blowing with neutral gas (argon). It is shown that the main ways of hydrogen removal in a circulating vacuum degasser are direct transfer of hydrogen from metal to the surrounding space and blowing of melt with transporting gas. In the CS2 of PJSC “NLMK”, both ways are implemented at a circulating vacuum degasser. Vacuum pumps provide pressure in a vacuum chamber of less than 101.3 Pa (0.001 atm). It promotes intensive removal of hydrogen from the metal surface. To ensure circulation of metal, transporting gas argon is supplied to the inlet pipe of the RH degasser, which also takes part in removal of dissolved gases by transferring hydrogen to neutral gas bubbles. Additionally, performed calculations have shown that the main way of degassing in conditions of CS2 of PJSC “NLMK” is removal of hydrogen into the bubbles of carrier gas.

Effect of submerged entry nozzle wall surface morphologies on boundary layer structure and alumina inclusions transport

During the Al-killed steel continuous casting process, the molten steel corrosion and the accumulation of alumina inclusion deposits affect the submerged entry nozzle (SEN) wall surface, including the surface morphologies of the smooth wall, porous refractory wall, and clogged wall. The SEN wall surface morphology affects the boundary layer structure and alumina inclusions transport. In this study, a physical modeling method was adopted, and the surface morphologies simulation was realized by filling up the natural porous refractory material and inserting the real clog material in the polymethyl methacrylate SEN model. The velocity in the boundary layer was measured using the particle image velocimetry (PIV) technology, and the alumina inclusions transport path in the boundary layer was calculated by MATLAB software. The MATLAB codes combined the velocity data from the PIV measurement results and the inclusion transport equation. The four-quadrant analysis showed that sweep and ejection events existed in the boundary layer. The fluctuations of the velocity and the turbulent kinetic energy in the normal direction were increased in the porous refractory and the clogged wall boundary layer when the sweep and ejection events existed. The transport of the alumina inclusions with a diameter of 1–15 μm was affected by the ejection and the sweep events. The alumina inclusions moved toward the boundary in the sweep event. During the sweep event, the transport path of alumina inclusions with 1 μm diameter was close to the boundary; the alumina inclusions were more easily attached to the boundary. The alumina inclusions escaped from the boundary in the ejection event. In the porous refractory and the clogged walls, the alumina inclusion transport path in the normal direction was increased. When the SEN wall’s morphologies changed from smooth wall to porous refractory wall and clogged wall, the sweep event area proportion increased from 10.17% to 39.77%, and the ejection event area proportion decreased from 32.96% to 9.24%. Moreover, the sweep event’s probability increased from 25.83% to 28.24% when the morphologies of the SEN wall changed from smooth wall to porous refractory wall and clogged wall, which will increase the alumina inclusion deposition rate in the porous refractory wall and the clogged wall boundary.

Recovery of sulfur from sulfur-rich filter cakes in a rotary kiln: Process optimization

In this work, sulfur recovery from sulfur-rich wastes deriving from sulfur filtration was investigated through laboratory experiments and full-scale tests in an industrial combustion rotary kiln, where elemental sulfur is converted to SO2 in a sulfuric acid production plant. Phase equilibria experiments carried out in the temperature range 1100–1400 °C and industrial scale tests demonstrated that temperature is the most important operating parameter in determining the recovery efficiency and the plant operability. The full-scale tests performed on the rotary kiln showed that, at operating temperatures around 1200 °C, a continuous sulfur recovery from the filter cakes was obtained with an average efficiency of 87% and a consequent reduction of about 70% of the solid waste material to be disposed as inert in landfills or used in cement/glass industries. The efficiency of sulfur recovery increases with the increasing operating temperature but, above 1300 °C, the melting of the residual Ca-Fe-Al-silicate phase and the eventual recrystallization at the kiln refractory walls occurred, causing a forced plant shutdown.The chemical-physical interaction between the sulfur-rich filter cake and different refractory materials was further investigated in the temperature range 1100–1300 °C. At the recommended operation temperatures of 1100–1200 °C, the interaction between the refractory material and the combustion ashes is negligible for all tested materials. Nonetheless, the use of Fe- and Cr-free refractory materials for the internal lining of the kiln must be preferred to minimize the deposition/adhesion of Ca-Fe-Al-silicates derived from combustion over long-term operation.

Effect of Thermal Buoyancy on Fluid Flow and Residence-Time Distribution in a Single-Strand Tundish.

Natural convection of molten steel flow in a tundish occurs due to the temperature variation of the inlet stream and heat losses through top surface and refractory walls. A computational fluid dynamics (CFD) model was applied to study the effect of thermal buoyancy on fluid flow and residence-time distribution in a single-strand tundish. The CFD model was first validated with the experimental data from a non-isothermal water model and then applied to both scale-down model and prototype. The effects of flow control devices, including weir, dam and turbulence inhibitor, were compared and analyzed. Parameter studies of different heat losses through the top surface were performed. The results show that thermal buoyancy has a significant impact on the flow pattern and temperature distributions of molten steel in the tundish. The increase of heat loss through the top surface shortens the mean residence time of molten steel in the tundish, leading to an increase in dead volume fraction and a decrease in plug flow volume fraction.

Angular distribution measurement of atoms evaporated from a resistive oven applied to ion beam production

A low temperature oven has been developed to produce calcium beam with Electron Cyclotron Resonance Ion Source (ECRIS). The atom flux from the oven has been studied experimentally as a function of the temperature and the angle of emission by means of a quartz microbalance. The absolute flux measurement permitted to derive Antoine's coefficient for the calcium sample used: A=8.98± 0.07 and B=7787± 110 in standard unit. The angular FWHM of the atom flux distribution is found to be 53.7±7.3∘ at 848 K, temperature at which the gas behaviour is non collisional. The atom flux hysteresis observed experimentally in several laboratories is explained as follows: at first calcium heating, the evaporation comes from the sample only, resulting in a small evaporation rate. Once a full calcium layer has formed on the crucible refractory wall, the calcium evaporation surface includes the crucible's enhancing dramatically the evaporation rate for a given temperature. A Monte-Carlo code, developed to reproduce and investigate the oven behaviour as a function of temperature is presented. A discussion on the gas regime in the oven is proposed as a function of its temperature. A fair agreement between experiment and simulation is found.

A227 UMBILICAL HERNIA INCARCERATION IN LIVER CIRRHOSIS: A RARE COMPLICATION OF PARACENTESIS

Abstract Background Patients with decompensated liver cirrhosis with ascites frequently have umbilical hernias with a prevalence of 20% and are managed with large volume paracentesis (LVP). Common complications of LVP include hemorrhage, infection, and bowel perforation that occur infrequently with a frequency of less than 1%. However, incarceration of umbilical hernias has been reported as a rare complication of LVP and is speculated to be from ascitic fluid decompression that reduces the umbilical hernia ring diameter resulting in entrapment of the hernia sac. It is unclear whether the quantity or the fluid removal rate increases the herniation risk. Based on case series, this rare complication occurs within 48 hours of the LVP and requires emergent surgical repair and involves a high risk of morbidity and mortality due to potential infection, bleeding, and poor wound healing. Aims We describe a case report of an incarcerated umbilical hernia following a bedside large-volume paracentesis. Methods Case report Results A 59-year-old Caucasian male presented to the emergency department with a 24-hour history of acute abdominal pain following his outpatient LVP. His medical history included Child-Pugh class C alcoholic liver cirrhosis with refractory ascites managed with biweekly outpatient LVP and a reducible umbilical hernia. He reported the onset of his abdominal pain 2-hours after his LVP with an inability to reduce his umbilical hernia. Seven liters of clear, straw-coloured asitic fluid was drained. Laboratory values at presentation revealed a hemoglobin of 139 g/L, leukocyte count of 4.9 x109 /L, platelet count of 110 xo 109 /L, and a lactate of 2.7 mmol/L His physical exam demonstrated an irreducible 4 cm umbilical hernia and bulging flanks with a positive fluid wave test. Abdominal computed tomography showed a small bowel obstruction due to herniation of a proximal ileal loop into the anterior abdominal wall hernia, with afferent loop dilation measuring up to 3.4 cm. He was evaluated by the General Surgery consultation service and underwent an emergent laparoscopic hernia repair. There was 5 cm of small bowel noted to be ecchymotic but viable, with no devitalized tissue. He tolerated the surgical intervention with no post-operative complications and was discharged home. Conclusions Ultrasound-guided bedside paracentesis is a common procedure used in the management of refractory ascites and abdominal wall hernia incarceration should be recognized as a potential rare complication. To prevent hernia incarceration, patients with liver cirrhosis should be examined closely for hernias and an attempt should be made for external reduction prior to LVP. A high index of suspicion for this potential life-threatening condition should be had in patients who present with symptoms of bowel obstruction following a LVP. Funding Agencies None

Continuous Erector Spinae Plane Block for Refractory Chest Wall Pain in a Patient With Metastatic Breast Cancer: A Case Report

In this case report, we described the use of the continuous erector spinae plane (ESP) block in a patient presenting with severe chest wall pain due to terminal metastatic breast cancer. Her pain was refractory to most treatment modalities despite being on huge doses of parenteral opioids for 6 months. A single shot ESP block was initially trialed, which provided her complete pain relief. This was followed by an ESP catheter insertion and continuous infusion of local anesthetic, which helped her wean off the parenteral opioids over the next 4 days. She was discharged home with the catheter in situ, attached to a delivery pump.

The Effect of Refractory Wall Emissivity on the Energy Efficiency of a Gas-Fired Steam Cracking Pilot Unit.

The effect of high emissivity coatings on the radiative heat transfer in steam cracking furnaces is far from understood. To start, there is a lack of experimental data describing the emissive properties of the materials encountered in steam cracking furnaces. Therefore, spectral normal emissivity measurements are carried out, evaluating the emissive properties of refractory firebricks before and after applying a high emissivity coating at elevated temperatures. The emissive properties are enhanced significantly after applying a high emissivity coating. Pilot unit steam cracking experiments show a 5% reduction in fuel gas firing rate after applying a high emissivity coating on the refractory of the cracking cells. A parametric study, showing the effect of reactor coil and furnace wall emissive properties on the radiative heat transfer inside a tube-in-box geometry, confirms that a non-gray gas model is required to accurately model the behavior of high emissivity coatings. Even though a gray gas model suffices to capture the heat sink behavior of a reactor coil, a non-gray gas model that is able to account for the absorption and re-emission in specific bands is necessary to accurately model the benefits of applying a high emissivity coating on the furnace wall.

Modeling Air Aspiration in Steel Continuous Casting Slide-Gate Nozzles

Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to occur when the flow control system (slide-gate or stopper rod) causes the pressure inside the nozzle to drop below atmospheric pressure, drawing gas into the system through possible cracks or gaps in the refractory walls. In this work, a 1-D pressure-energy model of the complete metal delivery system from the tundish to the mold is developed to predict the pressure distribution and throughput under dynamic operating conditions and varying clogging conditions. The energy balance approach includes pressure losses in the slide-gate, wall friction, and nozzle geometry variations, including the effects of multiphase flow due to argon gas injection. The model also predicts air aspiration, oxide inclusion formation, and the time for clogging shutdown. The predicted pressure distribution is verified with a three-dimensional numerical simulation of multiphase turbulent flow, and is validated with plant measurements. Parametric studies with different submerged entry nozzle (SEN) designs revealed that a smaller SEN diameter may lessen negative pressure by redistributing the pressure loss from the slide-gate to the entire nozzle through increased friction losses. Under negative pressure, a submillimeter-thin gap was shown to cause considerable air aspiration. Clogging shutdown times were evaluated for several scenarios under static and dynamic operating conditions.

Computational homogenization of elastic-viscoplastic refractory masonry with dry joints

Refractory masonry with dry joints is widely used in the steel-making industry for the linings of several high-temperature components (>1500 ∘C) including steel ladles and furnaces. To properly optimize the design and performance of these linings, thorough numerical models that consider the presence of joints, joints closure and reopening and the nonlinear elastic-viscoplastic behaviour (creep and stress relaxation) of refractories at high temperature are required. The present study reports on the formulation, numerical implementation, and application of a homogenized multi-scale elastic-viscoplastic model for the simulation of refractory masonry linings with dry joints. Refractory bricks are considered to exhibit linear elasticity as well as rate-dependent plasticity. Four joint patterns are predefined based on the state of bed and head joints. The homogenized elastic-viscoplastic behaviour of each joint pattern is determined using finite element based nonlinear homogenization approach. The transition criteria between the four patterns are defined in terms of macroscopic stresses and strains. Verification of the developed homogenized constitutive laws is carried out by comparing the numerical results of the detailed micro models (brick and joints are considered) with the homogeneous equivalent material models. Furthermore, comparisons with experimental results of refractory masonry walls subjected to biaxial compression load at room and high temperature are carried out. Good agreements between the experimental and numerical results are obtained. Then, the validated models are employed to predict the mechanical behavior of refractory masonry structures subjected to different loading conditions. The present numerical model is able to simulate the orthotropic, compressible, rate-dependent homogenized behaviour of mortarless refractory masonry structures, and accounts for joints closure and reopening due to loading and unloading.