Volume 17, Issue 10 -

The granular behaviors in rotating kilns have been investigated using a three-dimensional CFD model based on Euler-Euler multiphase model and the kinetic theory of granular flow. The model is validated by comparing with published experiment data and existing theory. The continuous feeding progress and inclination angles are both taken into account in this work for thorough discussion. Typical regimes of solid motions and velocity distributions are shown in the simulation results. The results show that the impact caused by feeding process has an obvious influence on the velocity distribution of z axis, especially at the charging end of the kiln. A small inclination angle has a slight influence on the velocity distribution of z axis, and causes the thickness of the active region increasing with the increasing of axil distance. The rotating speed is the biggest influencing factor for the velocity distribution in the transverse plane. The result can help the development of three-dimensional models for rotary kilns and the improvement of kiln design and performance.

Typical Geldart B class particles are often used in a gas-solid fluidized bed for various industrial applications. The quality of fluidization of Geldart B particles depends upon the geometry of the bed containing vessel, properties of fluidization medium and the gas flow rate. The presence of large bubbles/slugs that can happen in beds with intermediate class particles is undesirable. The bubbling and slugging, which decrease the quality of fluidization can be prevented with the phenomenon called packed fluidization. Experiments were carried out on the conventional fluidized bed and packed fluidized bed to investigate some of the hydrodynamic characteristics as a function of bed temperature, small particle size, fluidization medium and fraction of voids of packing filled with small particles. The superficial gas velocity required for packed fluidization reduces significantly than conventional fluidization. The minimum fluidization velocity of particles increases with an increase in density of the fluidization gas and decreases with increase in temperature of the bed. A correlation established from experimental data fairly predicts the minimum fluidization velocity for the packed fluidized bed.

Chemical looping combustion (CLC) is a carbon capture technology which enables CO 2 capture with low net efficiency penalty. Calcium sulfate (CaSO 4 ) is an optional oxygen carrier for commercial use, but its usage is limited due to sulfur dioxide (SO 2 ) emission. This study approaches this issue by adding CaO species into the CaSO 4 oxygen carrier to inhibit the release of SO 2 from CaSO 4 oxygen carrier. In this study, the cyclical tests of a CaSO 4 -based oxygen carrier under alternating reducing and oxidizing conditions were performed at 900 °C and 800 °C respectively in a tubular furnace reactor at atmospheric pressure. The effects of reducing gas concentration and molar ratio of CaO/CaSO 4 on the performance of CaSO 4 -CaO oxygen carrier were studied in terms of CO 2 yields, Environmental factors of SO 2 and COS, molar ratios of gas sulfides to CO 2 generated in fuel reactor, and molar ratios of SO 2 and COS to total carbon inlet. The use of CaO additive increased the yields of CO 2 obviously. The release of COS in the fuel reactor and SO 2 in the air reactor decreased, but while the overall release of SO 2 in the fuel reactor increased. However, for per mole CO 2 generation, less gas sulfides released from the fuel reactor. High concentrations of CO were beneficial for CO 2 production and a low SO 2 environmental factor, and meanwhile, the molar ratios of SO 2 released to inlet CO nSO2{{\text{n}}_{{\text{S}}{{\text{O}}_2}}}/nCO{{\text{n}}_{{\text{CO}}}} decreased. However, it led to a drop in CO 2 yield and an increase in COS environmental factor. As a whole, the use of CaO additive and higher CO concentration both accelerated the parallel CaSO 4 reductions in fuel reactor, especially the selectivity of CaSO 4 reduction to CaS.

Frequently optimizations of chemical processes are presented in terms of the maximization of fractional conversion, but the primary concern when implementing a process is much more likely to be the economic viability. These are distinct optima that tend to occur at very different points. It was the purpose of this paper to integrate leaching experimental data with cost analysis to arrive upon economically optimized leaching conditions for the recovery of rare earth elements from phosphogypsum, a water phosphate byproduct. The variables under consideration were the number of leaching reactors and the residence time of each reactor. The modeling results indicated that the optimum residence time was 270 minutes and that the optimum number of stages was one.

The present paper studies through numerical methods, the thermodynamic heat transfer characteristics of free convection flow of supercritical nitrogen over a vertical cylinder. In the present analysis, the values of volumetric thermal expansion coefficient ($\beta$β) are evaluated based on Redlich-Kwong equation of state (RK-EOS) and Van der Waals equation of state (VW-EOS). The calculated analytical thermal expansion coefficient values using RK-EOS are very close to NIST data values in comparison with VW-EOS. A set of coupled nonlinear partial differential equations (PDEs) governing the supercritical fluid (SCF) flow are derived, converted into non-dimensional form with the help of suitable dimensionless quantities and solved using Crank-Nicolson implicit finite difference method. The simulations are carried out for nitrogen in the supercritical region. The obtained numerical data is expressed in terms of graphs and tables for various values of physical parameters. The increasing value of reduced temperature decreases the average Nusselt number and skin-friction coefficient, whereas amplifying value of reduced pressure enhance the heat transfer rate and wall shear stress in the SCF region. Present results are compared with the previous results and the two are found to be in good agreement, i. e. the numerically generated results found to be in agreement with existing results.

In this paper, a Chattering Free Sliding Mode Control (CFSMC) with observer based adaptive Radial Basis Function Neural Network (RBFNN) has been designed for first-order transfer function model of temperature trajectory in a fixed bed reactor. The steady-state behavior and effect of different operating parameters such as feed velocity and temperature on the operation of the fixed bed reactor have been discussed. Due to RBFNN’s capability to map the nonlinear dynamics online through self-learning ability, it is combined with CFSMC to reduce the chattering behavior. The adaptive RBFNN has been used to approximate the nonlinear dynamic behavior of the fixed bed reactor. To predict the states of the system, high gain observer based on adaptive RBFNN has been used. Design parameter of the observer has been estimated using Hurwitz polynomial. The effect of neuron number on the mapping error and the effect of space discretization step on modeling error have also been discussed. To decrease the chattering generated by the Sliding Mode Controller (SMC) in the temperature trajectory tracking, an equivalent control term is neglected from the final controller. It has two main advantages: one is the reduction in chattering behavior which is the main drawback of SMC and the second is the reduction of the high gain requirement. The SMC is used to overcome against external disturbance, load variation, variation in key parameters and model mismatch. To make the simulation realistic, constraints have been applied to control input and input rate. For guaranteeing the system stability, Lyapunov theorem has been applied. To show the suitability of the hybrid controller, a comparison has been carried out between the hybrid and PID controller. To quantify the performance, Integral Time Weighted Absolute Error (ITAE) has been estimated. Under the condition of existing model errors and external disturbances, simulation study of the control of the fixed bed reactor shows that the hybrid control algorithm consisting of sliding mode control and observer-based adaptive RBFNN performs well both for tracking the temperature trajectory and reducing the chattering.

The graphene nanosheets (GNS) have been considered as a support for the synthesis of catalysts applied in various catalytic reactions. In this research, the hydrocracking (HCK) of n-hexadecane as a model component of the long chain paraffin was carried out using synthesized Ni-Mo/GNS and commercial Ni-Mo/Al 2 O 3 -SiO 2 catalysts in a fixed-bed reactor. The physico-chemical properties of catalysts were determined using XRF, TEM, XRD, TGA and NH 3 -TPD analysis. The effect of support on the conversion and product distribution in HCK of n-hexadecane was investigated. The stability of the catalysts in the presence of water and coke deposition was examined for the HCK of nonconventional feeds. The obtained results revealed that the active metals were anchored on the functionalized GNS and the stability of Ni-Mo/GNS was significantly increased compared to commercial catalyst. The obtained results indicated that the GNS-supported catalysts have a higher potential for HCK of n-hexadecane in comparison to commercial Ni-Mo/ Al 2 O 3 -SiO 2 catalysts.

Leaching of indium from an indium-and iron-bearing sphalerite concentrate in sulfuric acid– ferric sulfate solution was examined. The effects of various parameters were studied. Increases in the stirring speed, temperature, ferric ion and sulfuric acid concentrations, and decreases in the particle size, enhanced the indium leaching rate. Scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray diffraction analyses of the unreacted and reacted sphalerite concentrate particles showed that elemental sulfur was formed and precipitated at the particle surfaces. The results show that dissolution was controlled by a mixed-control process. In the initial stage, the dissolution kinetics was chemically controlled. When more elemental sulfur was present on the particle surfaces, the dissolution kinetics was controlled by mass transfer though the sulfur layer. The activation energy of the chemically controlled step was 33.9 kJ/mol. The reaction orders with respect to the initial sulfuric acid and ferric ion concentrations were approximately 0.74 and 0.60, respectively.

The reduction and dissolution mechanism of Fe 3 O 4 in NaCl-CaCl 2 melts system are analyzed by thermodynamics. The electrochemical methods of Fe 3 O 4 in NaCl-CaCl 2 melts are studied by cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry. The effects of temperature on reduction potential and peak current are investigated. The diffusion coefficients of Fe 3+ and Fe 2+ at different temperatures are calculated, and the activation energy E is obtained. Electrolytic products are obtained after 10 min of potentiostatic electrolysis in the melts of NaCl-CaCl 2 -Fe 3 O 4 at 1073 K and 1.9 V. The results of XRD show that no other compounds are formed in the melts, indicating that Fe 3 O 4 do not react chemically in the NaCl-CaCl 2 melts system at 973 K, which is consistent with the theoretical analysis. Fe 3 O 4 is reduced by two-step quasi-reversible reaction in the melts of NaCl-CaCl 2 at 973 K to obtain iron: Fe 3+ → Fe 2+ → Fe. The two-step reaction is controlled by diffusion. The diffusion coefficients are 4.53 × 10 –6 cm 2 ·s –1 and 1.17 × 10 –6 cm 2 ·s –1 , respectively. Fe 3 O 4 is reduced in two steps. The potential shifts with temperature and decreases with the increase of the proportion of Fe 3 O 4 . The activation energies of the two-step reaction are 62.38 kJ·mol –1 and 77.52 kJ·mol –1 . A deposited layer of uniform distribution, high coverage and dense iron is prepared.

In the present work, the influence of Al 3+ , Fe 3+ , SO 4 2– , F – , Mg 2+ on the crystallization of urea phosphate during the synthesis process of urea phosphate with phosphoric acid and urea was investigated. The crystallization time, the yield of urea phosphate, the purity of urea phosphate, crystal morphology, and the characterization of urea phosphate by Fourier transform infrared spectroscopy were studied. The experimental results show that the crystallization time of urea phosphate prolonged with the addition of impurities, the yield of urea phosphate all decreased with the increasing concentrations of Al 3+ , Mg 2+ , Fe 3+ and SO 4 2– , except F – . The impurities have no effect on the content of nitrogen and phosphorus in urea phosphate products. The Al 3+ , Fe 3+ , F – cause the irregular crystal morphology, while the crystal with the Mg 2+ , SO 4 2– has a better dispersion, regular shape and high transparency. This study provides reliable and effective theoretical guidance for the synthesis process of urea phosphate by the wet process phosphoric acid.