Cold Model Experiments Research Articles

Agglomeration Detection in Horizontal Stirred Bed Reactor Based on Autoregression Model by Acoustic Emission Signals

Agglomeration occurring in horizontal stirred bed reactors (HSBR) for polyolefin production has negative impacts on the efficiency of the reactor operation and may sometimes lead to unscheduled shutdown of the plant. In this paper, an autoregression (AR) model based on acoustic emission (AE) technique has been proposed to establish the qualitative relationship between AE signals and agglomeration in the HSBR. In this method, the frequency of AE signal varies with particles of different sizes striking the reactor walls. From the cold model experiments, it was found that AR power spectrum became fluctuant after the addition of agglomerations into laboratorial scale HSBR, and meanwhile the low frequency band energy ratio and the variance of AE signals kept rising. Furthermore, this AE-based AR model was also successfully applied to detect the agglomeration in an industrial HSBR unit, showing that the method could monitor agglomerations in an environmentally friendly manner and with fairly good accuracy.

Pressure Drop Models of Seepage Catalytic Packing Internal for Catalytic Distillation Column

A seepage catalytic packing internal (SCPI) consisting of catalyst containers with avert-overflow baffles and corrugated metal sheets was developed for a catalytic distillation column. By changing the width ratio (Rcc/cms) of the catalyst containers (CC) relative to corrugated metal sheets (CMS), the SCPI developed in this work can be suitable to various reaction and separation zones in different catalytic distillation processes. The influence of the Rcc/cms, a significant factor influencing the pressure drop, also was studied. The flooding behaviors and pressure drop were evaluated using cold model experiments in the column (600 mm in diameter × 1500 mm height); the results were compared with that of the catalytic packing typically used in catalytic distillation. A model for predicting the pressure drop of SCPI was developed and compared with experimental results. Results show that the pressure drop was decreased with decreases of Rcc/cms. The results from this work are valuable in the design and scale-up of SCPI in catalytic distillation columns.

Study of Penetration Depth and Droplet Behavior in the Case of a Gas Jet Impinging on the Surface of Molten Metal using Liquid Ga–In–Sn

AbstractTo study the penetration depth in the case of a gas jet impinging on the surface of liquid steel, cold model experiments were carried out using a liquid alloy Ga–In–Sn, which had similar physical properties as liquid steel. A HCl solution was used to simulate the top slag. The top phase was found to have appreciable effect on the penetration depth. Comparison of the experimental data with the predictions of the existing models indicated that most the model predictions deviated from the experimental results at higher lance heights and gas flow rates. New model parameter was suggested based on the present experimental data. The observation of the formation and movement of metal droplets generated by the gas jet was also made. The velocity of the droplet was found to be at a level only about 1% of the terminal velocity. This low velocity suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.

Experimental Design for the Mechanism Study of Lime Dissolution in Liquid Slag

AbstractThe applicability of rotating rod technique in the study of lime dissolution in slag was investigated. Both computational fluid dynamic (CFD) and cold model experiments showed that the mass transfer due to radial velocity introduced by forced convection was zero if the rod was long. The mass transfer by forced convection was also less important in comparison with natural convection and diffusion when the rod was half length of the height of the bath. This finding was in accordance with the criteria put forward by the original work that the method could only be applicable when a thin disk (instead of rod) with big diameter and big liquid bath were used. To study the lime dissolution by forced convection a new experimental technique was developed. A cube was placed in the slag that was eccentrically stirred. The whole system, viz. the sample along with the slag could be quenched. The new technique could study the effect of forced convection on the dissolution. The microscopic study on the quenched slag‐lime samples could reveal the dissolution mechanism successfully.

DEM-CFD Model Considering Softening Behavior of Ore Particles in Cohesive Zone and Gas Flow Analysis at Low Coke Rate in Blast Furnace

Since the cohesive zone has a great influence on the gas flow in the blast furnace, modeling of the cohesive zone is considered to be an important subject. In the cohesive zone, the softening and melting behavior of ore particles is affected by the load from the upper layer and the temperature distribution, and the pressure drop of the ore layer increases remarkably due to shrinkage of the ore particles. In this study, a model of the cohesive zone considering physical properties such as Young’s modulus was developed on the basis of the discrete element method, which can track the individual motions of the numerous particles in a packed bed. To determine the appropriate Young’s modulus of ore particles for the cohesive zone, element model calculations for a softening test under load were carried out, with particular attention to change in the void fraction. The optimized value of Young’s modulus value was then introduced in the discrete element method and computational fluid dynamics (DEM-CFD) model. The changes of gas flow in the vicinity of the cohesive zone were visually expressed by this model. These results were similar to those of cold model experiments and the burden structure observed in the dissected blast furnace. The influence of the coke rate on the gas flow was also analyzed using the above model. The change in the gas flow under a low coke rate condition could be well recognized.

A New Type of Packing Apparatus with High Efficiency and the Experimental Research of its Mass-Transfer Performance

In this paper, a new type of packing apparatus with high efficiency and uniform flow was developed to deal with wall effect and scaling effect of packed column. A desorption experiment was made in a circular cold-model experiment packed column by using air-water-CO2 as working substance, determining the height of mass transfer unit of liquid phase of the cold-model experiment packed column under different gas-liquid loads, with and without the packing apparatus. The experimental results show that under different spray densities, the height of mass transfer unit of liquid phase of the packed column added with the packing apparatus decreased approximately above 19% more than that not added the packing apparatus; the height of mass transfer unit of liquid phase lowers more with the decrease of the spray density, which demonstrated that the mass transfer efficiency of the packed column added with the packing apparatus was much higher than that of the column not added the packing apparatus.

Effect of Gas Injection with Multi-hole Orifices on Bubble Behavior during Metal Refining

Cold model experiments have been conducted to make clear the effect of orifices on bubble behavior based on the comparison of 1-hole and 4-hole configurations. It is found that this effect is closely related to the gas flow rate and the orifice configuration. For 1-hole orifices, bubble behavior is influenced by the hole diameter at low gas flow rate. Nevertheless, in the region of high gas flow rate, this effect becomes less obvious. However, bubble behavior is strongly affected even at high gas flow rate when 4-hole orifices are used. It is also shown there exists an optimal distance between holes for 4-hole orifices. Below this value, the hole distance is too small to adequately avoid bubble coalescence in the radial direction. Above this value, little further contribution to avoidance of bubble coalescence can be made, but weight and cost of the orifices will increase.

Fundamental Study on Interaction between Top Blown Jet and Liquid Bath

AbstractIt is important to understand the physical interaction between top‐blown oxygen jets and liquid steel in basic oxygen steelmaking furnaces (BOF). In the present study, cold model experiments and CFD simulations were carried out with single‐ and multi‐hole nozzles and the velocity profiles of jets were successfully simulated. Water model experiments were also performed to study the cavity formation and the spitting phenomena by the impinging jets. The cavity shapes and the spitting behavior were correlated to the top‐blowing conditions by considering the characteristics of multi‐hole nozzle jets.

Simulation of Flow Field of Oxygen Lance Gas Jet Utilized for 50 t Converter

Based on the operating conditions of oxygen lance utilized for a 50 t converter in Tangsteel, gas jet flow fields of three types of oxygen lances were simulated by FLUENT software. The influence of lance configuration and lance level on penetrating area was studied through cold model experiment. The results showed that the gas flow velocities of four-hole, variable angle four-hole and five-hole oxygen lances declined rapidly with an increase in gas jet length within 1 m, 1 m and 0.8 m, respectively. Besides, the multi gas streams sprayed from these three lances should be syncretized at 1.6 m, 1.7 m and 1.4 m, respectively. At the highest lance level, the effective penetrating area of these three lances could be 0.255 m 2, 0.385 m 2 and 0.0907 m 2, respectively. It was suggested that the effective penetrating area of variable angle four-hole oxygen lance was the biggest, while that of five-hole oxygen lance was the least. The validity of numerical simulation results was proved through cold model experiment. The lance level was suggested to be controlled in the range of 1 – 1.6 m, 1 – 1.7 m and 0.8 – 1.4 m for the four-hole, variable angle four-hole and five-hole oxygen lances, respectively.

Experimental Study of Hydrodynamic Characteristics and CO2 Absorption in Producer Gas Using CaO-sand Mixture in a Bubbling Fluidized Bed Reactor

Producer gas, from biomass gasification process can be used to generate power as an alternative to fossil fuel. Carbon dioxide (CO2) content in the producer gas is acts as a diluent gas resulted in low heating value. We used limestone (which is of rather wide occurrence in Malaysia) that consisted mainly of the mineral calcite (calcium oxide, CaO) as calcium based sorbent to absorb CO2 in the producer gas. Removing the CO2 from the producer gas will improved its heating value. In this paper, the first step was to study the behavior of CaO-sand mixtures in a cold model experiment. The effects of the CaO-sand mixtures, the CaO particle sizes, the volume flow rate and the pressure of air intake were investigated experimentally. Then, the hot model experimental was conducted to investigate CO2 absorption at the optimum condition obtained from the cold model experiment resulted. The CaO percentages of 50 and 40 in sand were found to have a good fluidization at all air pressures (200-600 kNm-2). In addition to that, the 1000 micron particle size of the CaO-sand mixture and the volume flow rate of air between 0.00025- 0.00092 m3s-1 were also found to give a good fluidization. In the hot model experiment, the best CO2 absorption occurred at 50 percent CaO mixture with simulated gas pressure of 300 kNm-2 and the volume flow rate of 0.00075 m3s-1 at 650-750°C in a bubbling fluidized bed reactor (BFBR).

Modeling of Dripping Behavior in Particles Packed Bed Filled with Immiscible Fluid

Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.

Spout Eye Formed at Slag Layer Simulated by Low-Density Particles in a Cylindrical Vessel with Bottom Bubbling

Cold model experiments are carried out to understand the spout eye area in a cylindrical bath agitated by bottom gas injection. Low-density particles are used for slag to investigate the effect of a density ratio of molten slag to molten steel on the spout eye area. The spout eye area increases with a decrease in the density ratio and is governed by the same modified Froude number as that proposed for a silicone oil and mercury system. An empirical equation is proposed for the spout eye area.

Numerical Simulation and Cold Modeling experiments on Centrifugal Casting

In a centrifugal casting process, the fluid flow eventually determines the quality and characteristics of the final product. It is difficult to study the fluid behavior here because of the opaque nature of melt and mold. In the current investigation, numerical simulations of the flow field and visualization experiments on cold models have been carried out for a centrifugal casting system using horizontal molds and fluids of different viscosities to study the effect of different process variables on the flow pattern. The effects of the thickness of the cylindrical fluid annulus formed inside the mold and the effects of fluid viscosity, diameter, and rotational speed of the mold on the hollow fluid cylinder formation process have been investigated. The numerical simulation results are compared with corresponding data obtained from the cold modeling experiments. The influence of rotational speed in a real-life centrifugal casting system has also been studied using an aluminum-silicon alloy. Cylinders of different thicknesses are cast at different rotational speeds, and the flow patterns observed visually in the actual castings are found to be similar to those recorded in the corresponding cold modeling experiments. Reasonable agreement is observed between the results of numerical simulation and the results of cold modeling experiments with different fluids. The visualization study on the hollow cylinders produced in an actual centrifugal casting process also confirm the conclusions arrived at from the cold modeling experiments and numerical simulation in a qualitative sense.

Cold Model Investigations of Melting of Ice in a Gas-Stirred Vessel

The melting of steel scrap in high temperature liquid iron melt is investigated by conducting cold model experiments of the melting of ice sample of different geometries and sizes in an argon-stirred vessel containing water. The melting process of ice samples is observed using a high-speed camera. Design of experiments is based on similarity criteria. The relationships between non-dimensional groups related to heat transfer (Nu, Re, Pr, and Gr) are derived for different experimental conditions. The results are compared with those reported in the literature. The heat transfer coefficient is estimated as a function of mixing power and is found to be in good agreement with the calculated values obtained by using reported relationships in literature.

Effect of Inert Gas Flow Rate on Homogenization and Inclusion Removal in a Gas Stirred Ladle

AbstractIn the present study, the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was investigated. Both industrial trials and cold model experiments were conducted. CFD calculation was also carried out as an auxiliary tool. The mixing times predicted by CFD simulation agreed well with both the model experiments and industrial data. 99% mixing could be achieved in about 2–3 minutes. The increase of flow rate of inert gas would not improve the mixing substantially, while the mixing time decreased somewhat with the increase of gas flow rate. The water model study showed also that the gas flow rate had a negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that a low gas flow rate should be applied in the ladle treatment.

Development of a Co–Ni bimetallic aerogel catalyst for hydrogen production via methane oxidative CO 2 reforming in a magnetic assisted fluidized bed

A novel nano-sized Co–Ni bimetallic aerogel catalyst was synthesized via the sol–gel process followed by the supercritical drying method. The catalyst exhibited at least 28% higher activity and 15% higher H 2 selectivity than those of a monometallic cobalt aerogel catalyst in methane oxidative CO 2 (Oxy-CO 2) reforming. Cold-model experiments revealed that channels were alleviated and the agglomerate size was reduced when the catalyst was applied in a magnetic assisted fluidized bed (MAFB). Owing to the improved fluidization quality of the catalyst in the MAFB reactor, CH 4 conversion was raised by 12% and 7% as compared with those in the fixed bed reactor and the conventional fluidized bed reactor, respectively. Furthermore, the catalytic performance was quite stable during a 50 h reaction. This stable performance can be illustrated both by the superior catalytic property of the Co–Ni bimetallic aerogel catalyst and the intensified gas–solid interaction in the MAFB reactor.

Experimental and Numerical Study of the Flow Field and Temperature Field for a Large-Scale Radiant Syngas Cooler

Experimental and numerical studies on the gas-particle flow field and temperature field in the industrial-scale radiant syngas cooler (RSC) have been carried out. The bench-scale cold model experiment was presented for measuring the gas flow field in the RSC. The accuracy and performance of four turbulent flow models were evaluated according to the comparison of predicted results with experimental results. The ash particle trajectories were predicted by the stochastic Lagrangian model and the interaction between the gas and particle phase was also considered by two-way coupling method. A discrete ordinate model (DOM) was used for solving the radiative heat transfer equation when the radiative properties were calculated by weighted-sum-of-gray-gases model (WSGGM). The Ranz−Marshall correlation for the Nusselt number was used to account for convection heat-transfer between the gas phase and the particle phase. The ash particle radiative heat transfer was also considered. The physical properties of gas mixtu...

Analysis of fluid flow in centrifugal casting

Centrifugal casting process is a fast process with melt, cast and moulds being opaque. It is almost impossible to observe the melt behavior during casting. Cold modeling experiments were conducted using horizontal transparent moulds and transparent fluids of different viscosities to study the effect of different process variables on the flow pattern. Effects of the thickness of fluid cylinder, viscosity of the fluid, diameter of the mould, and rotational speed of the mould on the formation of complete hollow fluid cylinder are investigated. The influence of rotational speed has been studied in aluminum casting. The cylinders are cast at different rotational speed with varying thickness. It is observed that the speed required to form uniform cylinder increases with the increase in thickness of a fluid cylinder. As rotational speed is increased the hardness of the cast cylinder also increases. The flow patterns seen in cold modeling experiments and actual castings agree reasonably well.

Modeling of Dripping Behavior in Particles Packed Bed Filled with Immiscible Fluid

Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.

Explicit Modelling of Slag Infiltration and Shell Formation during Mould Oscillation in Continuous Casting

A mathematical model of the continuous casting process, which explicitly incorporates the presence of slag, molten steel, heat transfer through the mould walls, and shell solidification, is presented. The model is based on the solution of the Navier–Stokes equations for the multiphase slag–steel–air system under transient conditions, including tracking of the interface between these phases. The use of an extremely fine mesh (100 μm) in the meniscus region allows, for the first time, the direct calculation of liquid slag infiltration into the shell-mould gap. Elsewhere, a coarser mesh is used to capture the influence of the metal flow on the overall solution. Predictions are compared with prior, cold model experiments and high temperature mould simulators. Excellent agreement was found for features such as slag film development and heat flux variations during the oscillation cycle. Furthermore, predictions of shell thicknesses and heat fluxes for a variety of simulated casting speeds are also in good agreement with plant measurements. These findings provide an improved fundamental understanding of the basic principles involved in slag infiltration and solidification inside the mould and how these affect key process parameters, such as powder consumption and shell growth. These parameters have a decisive effect on the formation of oscillations marks and transverse cracks, which are a major source of defects in the casting practice.