Modelling Effect of Circulation Flow Rate on Inclusion Removal in RH Degasser

Based on the similarity principles, a 1 ： 7 scale physical model was established to study the behavior of molten steel flow and inclusion removal in a 145 t Rheinsahl-Heraeus （RH） degasser. On the basis of the quantitative measurements of the circulation flow rate and inclusion removal under various lifting gas flow rates, the effect of circulation flow rate on inclusion removal was investigated in the RH degasser. The inclusion removal rate shows the trend of first increase and then decrease twice with increasing the circulation flow rate when the circulation flow rates are smaller than 104.7 L/min. Whereas, the inclusion removal rate increases again with the further increase in circu- lation flow rate when the circulation flow rate is larger than 104.7 L/min. At lower circulation flow rates, inclusions are mainly removed by Stokes flotation to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow. At higher circulation flow rates, the collision and aggregation of inclusions improves the inclusion removal efficiency. With the further increase in the circulation flow rate, inclusions are mainly removed by following the turbulent fluctuation （turbulent diffusion） to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow.

Effect of gas blowing nozzle angle on multiphase flow and mass transfer during RH refining process

A three-dimensional mathematical model was developed to investigate the effect of gas blowing nozzle angles on multiphase flow,circulation flow rate,and mixing time during Ruhrstahl-Heraeus(RH) refining process.Also,a water model with a geometric scale of 1:4 from an industrial RH furnace of 260 t was built up,and measurements were carried out to validate the mathematical model.The results show that,with a conventional gas blowing nozzle and the total gas flow rate of 40 L·min^(-1),the mixing time predicted by the mathematical model agrees well with the measured values.The deviations between the model predictions and the measured values are in the range of about 1.3%–7.3% at the selected three monitoring locations,where the mixing time was defined as the required time when the dimensionless concentration is within 3% deviation from the bath averaged value.In addition,the circulation flow rate was 9 kg·s^(-1).When the gas blowing nozzle was horizontally rotated by either 30° or 45°,the circulation flow rate was found to be increased by about 15% compared to a conventional nozzle,due to the rotational flow formed in the up-snorkel.Furthermore,the mixing time at the monitoring point 1,2,and 3 was shortened by around 21.3%,28.2%,and 12.3%,respectively.With the nozzle angle of 30° and 45°,the averaged residence time of 128 bubbles in liquid was increased by around 33.3%.

Circulation characteristics of horseshoe vortex in scour region around circular piers

This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter （ADV）. Velocity vector plots and vorticity contours of the flow field on the upstream plane of symmetry （y = 0 cm） and on the planes ：e3 cm away from the plane of symmetry Cv = ~3 cm） are presented. The vorticity and circulation of the horseshoe vortices were determined using the forward difference technique and Stokes theorem, respectively. The results show that the magnitudes of circulations are similar on the planes y = 3 cm and y = -3 cm, which are less than those on the plane y = 0 cm. The circulation decreases with the increase of flow shallowness, and increases with the densimetric Froude number. It also increases with the pier Reynolds number at a constant densimetric Froude number, or at a constant flow shallowness. The relative vortex strength （dimensionless circulation） decreases with the increase of the pier Reynolds number. Some empirical equations are proposed based on the results. The predicted circulation values with these equations match the measured data, which indicates that these equations can be used to estimate the circulation in future studies.

Investigation of earthquake mechanisms and their impact on certain basic concepts in earthquake engineering and seismology

In this paper, mantle circulation flow, continental drift, earthquake origin and other mechanical principles are examined as they apply to earthquake engineering, seismology and dynamics of fluid saturated porous medium. The relationship of mantle flow to earthquakes is examined and clarified, and a new model, different from Haskell’s, is proposed for the earthquake mechanism. The proposed new model is based on the discovery that two pairs of jump stress and jump velocity will start to act from the fault plane. Records obtained directly from recent earthquakes nearby and right on the fault break show a very large velocity impulse, which verify, indirectly, the new mechanism proposed by the author. Further, at least two physical parameters that characterize the seismic intensity must be specified, because according to the discontinuous (jump) wave theory, at the earthquake source, the stress jump and the velocity jump of particle motion should act simultaneously when a sudden break occurs. The third key parameter is shown to be the break (fracture) propagation speed together with the break plane area. This parameter influences the form of the unloading time function at the source. The maximum seismic stress in and displacement of a building are estimated for two unfavorable combinations of the building and its base ground in terms of their relative rigidity. Finally, it is shown that Biot’s theory of wave propagation in fluid saturated porous media is valid only when fluid flow cannot occur.

Numerical Modeling of Sediment Transport and Its Effect on Algal Biomass Distribution in Lake Pontchartrain Due to Flood Release from Bonnet CarréSpillway

In order to protect the city of New Orleans from the Mississippi River flooding, the Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 to divert flood water from the river into Lake Pontchartrain and then into the Gulf of Mexico. During the BCS opening for flood release, large amounts of freshwater, nutrients, sediment, etc. were discharged into Lake Pontchartrain, and caused a lot of environmental problems. To evaluate the environmental impacts of the flood water on lake ecosystems, a two-dimensional numerical model was developed based on CCHE2D and applied to simulate the flow circulation, sediment transport and algal biomass distribution in Lake Pontchartrain. The effect of sediment concentration on the growth of algae was considered in the model. The numerical model was calibrated using field measured data provided by USGS, and then it was validated by the BCS Opening Event in 1997. The simulated results were generally in good agreement with filed data and satellite imagery. The field observation and numerical model show that during the spillway opening for flood release, the sediment concentration is very high, which greatly restricts the growth of algae, so there is no algal bloom observed in the lake. After the closure of BCS, the sediment concentration in the lake reduces gradually, and the nutrient concentration of the lake is still high. Under these conditions, numerical results and satellite imagery showed that the chlorophyll concentration was high and algal bloom might occur.

PROBLEMS ON COMPUTING SHALLOW WATER CIRCULATION AND SIMULATING THE FLOW PAST ISLANDS IN NEARSHORE WATER

This paper continues discussing the problems of numerically solving the shallow water circulation on the basis of ref. 1, For the numerical method proposed in ref. 1, we applied a storage method with dense matrices, which abandoned usual bandwidth concept and attained the intention of saving interior storage, computing time and amount of preparing work before computing. The circulation considered the effect of small islands was successfully simulated by specially dealing with the bottom friction terms and the boundary conditions. In addition, we discussed the action of bottom friction on the dissipation of tidal energy and its effect on stability of period motion.

3D full-loop simulation and experimental verification of gas-solid flow hydrodynamics in a dense circulating fluidized bed

Because of their advantages of high efficiency and low cost, numerical research methods for large-scale circulating fluidized bed （CFB） apparatus are gaining ever more importance. This article presents a numer- ical study of gas-solid flow dynamics using the Eulerian granular multiphase model with a drag coefficient correction based on the energy-minimization multi-scale （EMMS） model. A three-dimensional, full-loop, time-dependent simulation of the hydrodynamics of a dense CFB apparatus is performed. The process parameters （e.g., operating and initial conditions） are provided in accordance with the real experiment to enhance the accuracy of the simulation. The axial profiles of the averaged solid volume fractions and the solids flux at the outlet of the cyclone are in reasonable agreement with experimental data, thereby verifying the applicability of the mathematical and physical models. As a result, the streamline in the riser and standpipe as well as the solids distribution contours at the cross sections is analyzed. Computational fluid dynamics （CFD） serves as a basis for CFB modeling to help resolve certain issues long in dispute but difficult to address experimentally. The results of this study provide the basis of a general approach to describing dynamic simulations of gas-solid flows.

Experimental investigation on flow asymmetry in solid entrance region of a square circulating fluidized bed

To study the influence of back feeding particles on gas-solid flow in the riser, this paper investigated the flow asymmetry in the solid entrance region of a fluidized bed by particle concentration/velocity measurements in a cold square circulating fluidized beds （CFB）. The pressure drop distribution along the riser and the saturation carrying capacity of gas for Geldart-B type particles were first analyzed. Under the condition of u0 = 4 m/s and Gs = 21 kg/（m^2 s）, the back feeding particles were found to penetrate the lean gas-solid flow near the entrance （rear） wall before reaching the opposite （front） wall, thus leading to a relatively denser region near the front wall in the bottom bed. Higher solid circulation rate （u0 =4 m/s, Gs = 33 kg/（m^2 s）） resulted in a higher particle concentration in the riser. However the back feeding particles with higher momentum increased the asymmetry of the particle concentration/velocity profile in the solid entrance region. Lower air velocity （u0 =3.2 m/s） and Gs =21 kg/（m2 s）, beyond the saturation carrying capacity of gas, induced an S-shaped axial solid distribution with a denser bottom zone. This limited the penetration of the back feeding particles and forced the flnidizing air to flow in the central region, thus leading to a higher solid holdup near the rear wall. Under the conditions of uo = 4 m/s and Gs = 21 kg/（m^2 s）, addition of coarse particles （dp= 1145 μm） into the bed made the radial distribution of solids more symmetrical.

Gas-solid flow in a high-density circulating fluidized bed riser with Geldart group B particles

We carried out experiments to explore and characterize the gas-solid flow dynamics of Geldart group B particles in a dense circulating fluidized bed riser. By reducing the pressure drop across the solid control valve and increasing the solid inventory in the storage tank, a high solid circulation rate and a solid holdup above 0.075 throughout the riser were simultaneously achieved. At a solid-to-gas mass flux ratio of approximately 105, flow transitioned from fast fluidization to a dense suspension upflow. In the axial direction of the riser, solid holdup had an exponential profile, increasing with increasing solid circulation rate and Jot decreasing superficial gas velocity. From the riser＇s center to its wall, the solid holdup increased markedly, exhibiting a steep parabolic profile. Increasing the solid circulation rate increased the radial non-uniformity of the solid concentration, while increasing the superficial gas velocity had the opposite effect, In our dense circulating fluidized bed riser, Geldart group B particles had similar slip characteristics to Geldart group A particles,

Cyclone separation in a supercritical water circulating fluidized bed reactor for coallbiomass gasification： Structural design and numerical analysis

A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyclones with a single circular inlet （SCI） or a double circular inlet （DCI） were designed to adapt to the supercritical conditions. We evaluated the separation performance of the two cyclones using numerical simulations. A three-dimensional Reynolds stress model was used to simulate the turbulent flow of the fluid, and a stochastic Lagrangian model was used to simulate the particle motion. The flow fields of both cyclones were three-dimensionally unsteady and similar to those of traditional gas-solid cyclones. Secondary circulation phenomena were discovered and their influence on particle separation was estimated. Analyzing the distribution of the turbulence kinetic energy revealed that the most intensive turbulence existed in the zone near the vortex finder while the flow in the central part was relatively stable. The particle concentration distribution was non-uniform because of centrifugal forces. The distribution area can be divided into three parts according to the motion of the particles. In addition, the separation efficiency of both cyclones increased with the inlet SCaN velocity. Because of its perturbance flow, the DCI separator had higher separation efficiency than the SCI separator under comparable simulations. However, this was at the expense of a higher pressure drop across the cyclone.

Circulating turbulent fluidization-A new fluidization regime or just a transitional phenomenon

While circulating fluidized bed （CFB） reactor has many advantages over the more conventional turbulent fluidized bed （TFB） reactor, it does at least have one significant shortcoming-the rather dilute solids volume concentration in CFB reactor gives rise to less ideal reaction intensity. On the other hand, while having higher reaction intensity, TFB reactor has one fatal drawback of particle back-mixing, making it not suitable for certain reactions such as catalytic reaction where the catalyst requires frequent regeneration. This paper describes some key issues in the development of a circulating turbulent fluidized bed （CTFB） reactor that combines the advantages of both TFB and CFB, that is, to have the high reaction intensity as in TFB but and also to have a suppressed solids back-mixing as in CFB due to a continuous net upflow of solids flux through the bed. Experimental results show enough evidence to suggest that a new fluidization regime is formed, the characteristics of which appears to be distinct from those observed in a regular TFB and from those in either the bottom or the upper sections of regular CFB and/or high-density CFB （HDCFB）. Fundamentally, the difference is that particle-particle interaction （collision） dominates the motion of particles in CTFB and TFB, while gas-particle interaction （drag force） is the key element that determines the two phase flow in CFB including HDCFB.

Experimental and numerical study of pseudo-2D circulating fluidized beds

We present experimental investigations and numerical simulations of a pseudo-2D riser. Experiments were performed for various airflow rates, particle types/diameters, and particle size distributions. Pres- sure distributions along the wall of the riser were measured, Additional measurements from a smaller pseudo-2D riser （Kallio et al., 2009; Shah et al., 2012） were used to analyze horizontal solids volume fraction profiles. The experimental data were compared with simulation results carried out using an Euler-Euler approach, A mesh sensitivity study was conducted for numerical simulations and effects associated with simplifying real 3D geometry to a 2D model were examined. In addition, the effect of using an algebraic equation to represent the granular temperature versus a full partial differential equation also was examined for numerical simulations. Results showed small but significant near-wall sensitivity of the flow variables to mesh size. Substantial differences in mean pressure, solids distribution, and solid velocities were obtained, when 2D and 3D simulation results were compared. Finally, applying the simplified granular temperature equation for turbulent fluidization and for dilute-phase transport can lead to incorrect predictions in models,

Simulation of mass balance behavior in a large-scale circulating fluidized bed reactor

We determine using a compound model the influence of the mass of granular matter on the behavior of a supercritical circulating fluidized bed （CFB） reactor. Population balance enables a stationary-regime modeling of the mass flow of granular matter inside a CFB unit in a large-scale. The simulation includes some important dynamic processes of gas-particle flows in fluidized bed such as attrition, fragmenta- tion, elutriation, and fuel combustion. Numerical calculations with full boiler loading were performed of operational parameters such as furnace temperature, furnace pressure, feeding materials mass flows, and excess air ratio. Furthermore, three bed inventory masses were adopted as experimental variables in the simulation model of mass balance. This approach enables a sensitivity study of mass flows of granular matter inside a CFB facility. Some computational results from this population balance model obtained for a supercritical CFB reactor are presented that show consistency with the operational data for large-scale CFB units.