Influence of ring-type internals on the solids residence time distribution in the fuel reactor of a dual circulating fluidized bed system for chemical looping combustion

The intensification of gas-solids contact in the fuel reactor of a chemical looping combustion system is enhanced with the installation of ring-type internals. This can be a key issue for achieving the necessary fuel conversion rates. Wedged rings, previously designed and tested, were found to increase the particle concentration in the counter current section of the fuel reactor and hence, to achieve a more homogeneous particles concentration along this zone. The present work investigates the effect of the mentioned internals on the residence time distribution of particles in the fuel reactor of a dual circulating fluidized bed system for chemical looping. The study was carried out in a cold flow model especially designed for the fluid-dynamic analysis of the system equipped with a recently developed residence time measurement device based on the detection of ferromagnetic tracer particles through inductance measurement. Ring internals proved the positive effect on the particles residence time, the residence time distribution is more symmetric and shows lower dispersion, the flow pattern is more plug-flow-like, these effects are intensified with the reduction of the aperture ratio of the rings. On the other hand, the upward particle transport in the counter-current zone of the fuel reactor also increases with the installation of the rings, increasing the bypass flow of solids through the fuel reactor's return loop (internal circulation). For high internal circulation rates the solids residence time distribution of the fuel reactor is dominated by the bypass effect. The findings may be used for focused design improvement of the investigated fluidized bed system.     

CFD simulation of fluidized bed reactors for polyolefin production – A review

This literature survey focuses on the application of computational fluid dynamics (CFD) in various aspects of the fluidized bed reactor. Although fluidized bed reactors are used in various industrial applications, this first-of-its-kind review highlights the use of CFD on polyolefin production. It is shown that CFD has been utilized for the following mechanisms of polymerization: governing of bubble formation, electrostatic charge effect, gas–solid flow behavior, particle distribution, solid–gas circulation pattern, bed expansion consequence, mixing and segregation, agglomeration and shear forces. Heat and mass transfer in the reactor modeling using CFD principles has also been taken under consideration. A number of softwares are available to interpret the data of the CFD simulation but only few softwares possess the analytical capability to interpret the complex flow behavior of fluidization. In this review, the popular softwares with their framework and application have been discussed. The advantages and feasibility of applying CFD to olefin polymerization in fluidized beds were deliberated and the prospect of future CFD applications was also discussed.     

Lower limit law of welding windows for explosive welding of dissimilar metals

The influence of explosive charge thickness on the quality of explosive welding of dissimilar metals was in-vestigated.The lower limit law should be followed in the course of explosive welding.Three welding ex-periments of stainless steel (410S) and steel (Q345R) were carried out in three different kinds of explo-sive charge thicknesses, namely 15, 25 and 35 mm.Interfaces of morphology and mechanical properties of three samples were observed and tested.It was found that micro and small wavy bonding is mainly formed for charge thickness of 15 mm whose strength is the highest with minor deformation and few defects in the interface; small and middle wavy bonding are mainly formed for charge thickness of 25 mm whose strength is comparatively mediocre; big wavy bonding is mainly formed for charge thickness of 35 mm whose strength is the lowest.The cause of high bonding strength of the micro and small wavy interface was analyzed and verified on the basis of the results of Electron Probe Micro-Analyzer (EPMA) tests of three selected samples.     

热轧钢板头尾横裂纹成因分析及改进措施

针对热轧钢板头尾部出现横裂纹现象,取样进行了金相检验,发现裂纹根部无扩展,裂纹两侧组织存在差异,结合现场生产实际情况,确定头尾横裂纹的产生与中间坯局部过冷有关。通过采取提高板坯出炉温度、严格控制中间坯端部翘头和优化除鳞制度的措施,基本杜绝了热轧钢板头尾横裂纹现象。     

Manufacture of Slow-Release Matrix Granules by Wet Granulation with an Aqueous Dispersion of Quaternary Poly(meth)acrylates in the Fluidized Bed

ABSTRACT

Slow-release matrix granules were manufactured in the fluidized bed using an aqueous dispersion of quaternary poly(meth)acrylates (Eudragit® RS 30 D) as binder for granulation. A factorial design was carried out to investigate the influence of the following parameters, spraying rate, applied polymer amount, and inlet air temperature, on various granule properties. Prerequisites for a slow release of the model drug theophylline are high spraying rate, high amount of polymer, and low inlet air temperature. No considerable decrease of the drug release rate can be achieved without a subsequent curing of the dry granules. A clear correlation exists between the moisture content of the fluidized bed, indicated by the terminal moisture content (TMC), and the mean dissolution time for 80% of the drug (MDT₈₀).     

巷道混凝土地坪和水沟连体浇筑技术

斜沟煤矿+700m水平8号煤南翼辅助运输大巷,为矿井的主要运输线路,计划建设成矿井的1条精品和示范性运输线路,对混凝土地坪施工质量要求较高,并要求实现巷道混凝土地坪和水沟连体浇筑一次成型;现场工程技术人员参考地面铺路工艺,并结合煤矿井下施工特点,经过多次试验修改,制定了一套完整的混凝土地坪和水沟连体浇筑工艺,并配套设计制作了插件式整体水沟模板,克服了施工距离长、工程量大、工期紧、质量标准高等难题,达到了矿方要求目标,实现了单点作业日铺80m的速度,有力的支持了施工生产,获得了较好的经济效益。     

Mathematical Modeling and Genetic Algorithm Optimization of Reactive Absorption of H2S

A rate‐based mathematical model was developed for the reactive absorption of H₂S in NaOH, with NaOCl or H₂O₂ as the chemical oxidant solutions in a packed column. A modified mass transfer coefficient in the gas phase was obtained by genetic algorithm and implemented in the model to correct the assumption of instantaneous reactions. The effects of different operating variables including the inlet H₂S concentration, inlet gas mass flux, initial NaOH, concentrations of the chemical oxidants in the scrubbing solutions, and liquid‐to‐gas ratio on the H₂S removal efficiency were studied. A genetic algorithm was employed to optimize the operating variables in order to obtain maximum removal efficiency of H₂S. The model results were in good agreement with the experimental data.     

Thermo-mechanical test rig for experimental evaluation of thermal conductivity of ceramic pebble beds

The experimental determination of mechanical and thermal properties of ceramic pebble beds, such as the lithium orthosilicate or lithium metatitanate, is a key issue in the framework of fusion power technology, for the reason that they are possible candidates in the design of breeder blankets.The paper deals with an experimental method for the evaluation of the thermal conductivity of ceramic pebble beds versus the temperature and compressive strain, based on a steady state heat flux through a material (alumina) of known conductivity. The alumina thermal conductivity is determined by means of the hot wire method. To assess the experimental method, a thermo-mechanical characterization of alumina pebble beds (a material largely available), having different diameters, considering a wide range of temperatures and compression forces has been carried out.Moreover preliminary tests have been performed on lithium orthosilicate and lithium metatitanate pebble beds.     

Crack propagation prediction of CFRP retrofitted steel plates with different degrees of damage using BEM

Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values.