• Energy Research

Abstract A new conical-cylindrical top-discharge blow tank is designed, by introducing the pulsed gas to facilitate discharging, for stable transportation for kaolin powders. A series of experimental studies on pulsed gas characteristic parameters like pulsed gas flow rate Qpulsed (5 m3/h ≤ Qpulsed ≤ 25 m3/h), pulsed interval tpulsed (1 s ≤ tpulsed ≤ 5 s) and pulsed width τpulsed (50 ms ≤ τpulsed ≤ 250 ms) are conducted with the fluidized gas flow rate of 12 m3/h. The experiments mainly test the powder mass flow rate and solid-gas ratio in the conveying process. The results indicate that the mass flow rate and solid-gas ratio range 12.6–278.04 kg/h and 0.9–19.56 kg/m3, respectively. With the increase of the pulsed gas flow rate, the mass flow rate and solid gas ratio first increase and then decrease. When the ratio of fluidized gas flow rate to pulsed gas flow rate is within 0.8–1.2, its conveying capacity reaches the maximum. Meanwhile, the increase in the pulsed interval leads to the decrease of the mass flow rate and solid-gas ratio. Moreover, the increase in the pulsed width leads to the initial increase and then the stabilization of the mass flow rate and solid gas ratio. When the pulsed width is 50 ms, the improvement of discharge would small. Conversely, increasing the pulsed width can increase the discharge, and stabilize subsequently until over 200 ms. Besides, moisture content is one of the important factors affecting kaolin powders discharge. When the moisture content is 0.83%, the pulsed gas does not improve the discharge significantly. Meanwhile, pressure distribution at different locations in the tank is also measured. The results reveal that the introduction of pulsed gas changes the pressure distribution in the tank. A pressure zone is formed on the upper part of the tank, which promotes the powder discharge.

Abstract Mixing behavior of binary particles with different densities in a wet fluidized bed has been experimentally investigated in this work. Some important hydrodynamic characteristics during mixing, such as the minimum fluidization velocity, flow pattern, and flotsam particle distribution are measured. The differences between dry and wet particles are systematically compared. It is found that the minimum fluidization velocity Umf of wet particles is higher than that of dry particles due to the liquid bridge force between particles. Umf reaches its maximum when the liquid saturation S = 0.1, and then decreases, and does not change much when the liquid saturation in the region of S = 0.2–0.3. Liquid addition can bring two opposite effects on the mixing of a binary mixture of particles with different densities. First, the intensity of bubbling in the wet fluidized bed is lower than that in the dry fluidized bed at the same operation gas velocity Uf, which will weaken the mixing. Secondly, the liquid bridge forces between particles can restrain the density segregation, which is beneficial for mixing. A simple method is developed based on the analysis of forces on flotsam particles to evaluate the effect of liquid bridge force on mixing. A segregation index Se, defined as Se = Flift/Fresis, where Flift contains the drag force Fd and buoyancy force Fb, and Fresis contains the gravitation force Fg and liquid bridge force Flb, is used to indicate the segregation potential. The calculated results show that Se > 1 in the dry fluidized bed and Se

Abstract Non-Newtonian fluid flows through packed beds are common in many industries. Our understanding of this flow system is very limited, and the correlations for describing the fluid-particle interaction are not fully established. To overcome these problems, this paper presents a comprehensive study of this system on a sub-particle scale, with a special reference to the interaction between fluid rheology and bed properties. This is done by conducting about five hundred Lattice Boltzmann simulations under different conditions. The fluid rheology is represented by the power-law model to consider the shear-thinning, shear thickening and Newtonian behaviors of fluids. The simulation condition covers a wide range of bed porosity, particle size distribution and Reynolds number (Re). The results show that the effect of fluid rheology on the fluid behavior is strong. This effect varies significantly with bed porosity which is a function of particle size distribution. The interplay between fluid rheology and bed properties is however not strong in determining the distributions of particle-fluid interaction force. Based on the simulation data, a new drag correlation is established and validated against the experimental data in the literature. This correlation is more accurate and consistent than those reported in the past. It can estimate the mean drag forces on individual particles of different sizes, and is recommended to be used generally in the modeling of particle-fluid flows either for Newtonian fluids or for non-Newtonian fluids obeying the power-law model.

This paper presents an attempt to quantify the relationship between porosity and interparticle forces. In particular, it concerns the packing of wet mono-sized spheres where capillary force is dominant. The interrelationships between capillary force, porosity, and liquid content are first analyzed based on well-established theories and experimental observations. The resultant data are then used to correlate porosity with the force ratio defined as the average capillary force to the gravity of a particle. Application of this correlation is finally demonstrated by examples of porosity prediction. Copyright 2000 Academic Press.

Pneumatic conveying of powders is an engineering process used for conveying dry granulate or powder material where energy consumption is a significant cost factor and contributes to greenhouse gas emissions. In this RD&I project, work was conducted to model pneumatic conveying and bulk characteristics of the particulate product being conveyed. Because pneumatic conveyance is highly empirical, general models are difficult to establish. Due to these limitations, evaluating energy efficiency is usually limited to a specific experimental range of conditions. This work is based on engineering optimization of a workflow with data from an industrial operation commanded by a Programmable Logic Controller (PLC) with a control algorithm, performing logical, sequential, and timed tasks for plant control. The PLC communicates with a Human–Machine Interface and a Supervision and Control System, which are the means of interaction through a graphical environment interface with the process operator. By applying mathematics to introduce a systematic method to select the gas (air) pressure and flow necessary to operate a pneumatic conveying system in dense phase mode, it has been shown, on an industrial scale of 10 t/h, the feasibility of controlling an efficient pneumatic conveying system manipulating only two input parameters. This allows operation at pre-determined conveying rates with lower operational expenditures. The same methodology can be explored for several other systems.

Abstract Effective thermal conductivity (ETC) is an important parameter in packed-bed systems and is affected significantly by packing structure. Heat flow through a packed bed can be divided into three parallel paths: the solid-fluid-solid path, the solid-solid path and the fluid path. The models to evaluate ETC in packed beds for the first two paths were previously developed. In the present work, a comprehensive model to consider the heat transfer through the voids of a randomly-packed bed is further developed using the Delaunay tessellation. The results show that heat conduction through the fluid-filled voids becomes significant when the solid-to-fluid conductivity ratio decreases to a certain level (

Abstract Shape is one of the most important properties of particles, and can affect particle flow behavior significantly in particulate systems. In the past, extensive studies have been conducted on the effect of particle size and density on the mixing quality of particle mixtures in gas-fluidized beds, but little is known regarding the influence of particle shape. In this work, CFD-DEM approach is used to investigate the mixing of binary mixtures composed of ellipsoids and spheres. A modified drag model suitable for multicomponent mixtures of non-spherical particles is proposed first, and its validity is then verified by comparison to experimental data. The simulation results show that for the cases considered, adding a second component of ellipsoids to spheres results in reducing the minimum fluidization velocity of the mixtures; however, oblate particles in decreasing the minimum fluidization velocity is more significant than prolate particles. The mixing index of all binary mixtures generally increases with increasing gas superficial velocity. The results also show that with the added component varying from spheres to oblate or prolate particles, segregation happens in the bed and becomes more severe with aspect ratio. It is found that the effect of particle shape on the drag force is responsible for the occurrence of particle segregation.

Abstract Hopper flow characteristics are significantly affected by particle shape. In this work, ellipsoidal particles which can represent a large number of shapes are used to investigate the shape effect on granular flow in a cylindrical hopper. Numerical experiments are conducted by use of the discrete element method, with its validity verified by comparison with the results from physical experiments. The results indicate that particle shape can make a significant effect on the flow pattern. In particular, the increase of deviation from spheres can decrease the mixed region adjacent to the side wall, and increase the stagnant zone at the bottom corner. It may also lead to decreased wall stress. Furthermore, particle shape has a significant effect on the discharge rate. Spheres of unity aspect ratio have the highest flow rate, and the lower or higher aspect ratio, the smaller the flow rate. Based on the numerical results, the Beverloo equation is modified, where parameters C and k in the equation are respectively formulated as a function of aspect ratio.

Non-uniform blast injection often occurs in blast furnace (BFs) ironmaking process, but the consequences in the inner state remain unclear under industrial operating conditions. This paper presents a numerical study of three-dimensional (3D) flow and thermochemical behaviors inside a 5000-m3 commercial BF under non-uniform blast injection. This is based on a recently developed computational fluid dynamics (CFD) process model. The model has been validated under experimental and industrial conditions. It is used here to study the effects of tuyere closure on the asymmetric distributions of 3D inner state and the overall performance of the BF. The numerical results show that the increase in inactive tuyere number substantially enlarges the deadman size and shifts the highest deadman boundary from the BF center to the periphery, consistent with the lab-scale experimental observations. Also, the tuyere closure causes significantly asymmetric distributions of gas, solid, and liquid velocities and temperature, as well as reactions. The phenomenon occurs mainly in the low part of the BF and is more pronounced at a larger inactive tuyere number. When the inactive tuyere number is large, a "W"-shaped cohesive zone (CZ) is observed over the inactive tuyeres, the same as observed by a low-temperature hot-experimental BF model. Corresponding to this "W"-shaped CZ, a cavity forms in the CZ, beneath which a strong liquid flow develops, causing the substantial non-uniformity in liquid temperature distribution. Additionally, tuyere closure affects carbon consumption and liquid temperature oppositely in the regions over the active and inactive tuyeres. These effects are canceled out by each other, leading to inconsiderable variations of overall performance indicators like top gas utilization factor and liquid temperature.