High density gas-solids circulating fluidized bed riser and downer reactors

A systematic and comprehensive study of hydrodynamics and reactor performance was conducted in a 76 mm i.d., 10 m high riser and a 76 mm i.d., 5.8 m high downer reactor under high density/flux operating conditions using fluid catalytic cracking (FCC) catalyst particles. An optical fiber probe was used to obtain a complete mapping of local solids holdup and particle velocity. Catalytic ozone decomposition reaction was employed to study the characteristics of reactor performance in the CFB riser and downer. The superficial gas velocity (Ug) and the solids circulation rate (Gs) were 3-9 m/s and 100-1000 kg/m2·s, respectively. Based on the spatial distributions of catalyst particles and gas reactant in the riser and the downer, hydrodynamics and reactor performance were fully characterized. Solids suspension having a solids holdup of up to 0.2-0.3 could be maintained throughout the entire high flux/density riser. A homogenous axial flow structure was observed at Gs = 1000 kg/m2s. When Gs exceeded about 800 kg/m2s, the axial profile of the particle velocity became more uniform. The axial particle velocity was affected more significantly by high superficial gas velocity especially under high solids flux/density conditions. No net downward flow near the wall was one of the most important advantages of the high flux/density riser over the conventional low flux/density reactor, leading to a reduction of solids backmixing. Radial distributions of the solids holdup were nonuniform with a dilute region and a dense region. When Gs was higher than 700 kg/m2s, the dilute core region shrank to less than 20% of the cross-sectional area. Solids holdups thereafter increased monotonically towards the wall which could be up to 0.59. Moreover, solids holdup remained higher than 0.4 over a wide cross-sectional area (r/R = 0.7-1.0, about 60% of the cross-sectional area) even at the top section of the riser. Radial distribution of solids holdup in the downer was much more uniform than that in the riser. Radial profiles of solids holdup were characterized by a flat value covering a wide region of the cross section and a relatively high value near the wall in the fully developed section. The uniform distribution of solids flow provided a nearly plug flow condition in the downer reactor. As to the ozone reaction in the CFB system, the axial and radial profiles of the ozone concentration were consistent with the corresponding profiles of the solids holdups which indicated that ozone reaction in the CFB reactors was controlled by the gas-solids flow structure. Strong interrelation was observed between the distributions of solids and reactant concentration. Higher solids holdups would give higher ozone conversions. Most conversion occurred in the entrance region, that is, the flow developing zone of the riser and downer reactors. Overall ozone conversions in CFB riser and downer deviated from plug-flow behavior indicating that hydrodynamics affected CFB reactor performance. The extent of the deviation of the conversion could be attributed to the different gas-solids contacting efficiency

Spatio-temporal Joint Modelling on Moderate and Extreme Air Pollution in Spain

Very unhealthy air quality is consistently connected with numerous diseases. Appropriate extreme analysis and accurate predictions are in rising demand for exploring potential linked causes and for providing suggestions for the environmental agency in public policy strategy. This paper aims to model the spatial and temporal pattern of both moderate and extremely poor PM10 concentrations (of daily mean) collected from 342 representative monitors distributed throughout mainland Spain from 2017 to 2021. We firstly propose and compare a series of Bayesian hierarchical generalized extreme models of annual maxima PM10 concentrations, including both the fixed effect of altitude, temperature, precipitation, vapour pressure and population density, as well as the spatio-temporal random effect with the Stochastic Partial Differential Equation (SPDE) approach and a lag-one dynamic auto-regressive component (AR(1)). Under WAIC, DIC and other criteria, the best model is selected with good predictive ability based on the first four-year data (2017--2020) for training and the last-year data (2021) for testing. We bring the structure of the best model to establish the joint Bayesian model of annual mean and annual maxima PM10 concentrations and provide evidence that certain predictors (precipitation, vapour pressure and population density) influence comparably while the other predictors (altitude and temperature) impact reversely in the different scaled PM10 concentrations. The findings are applied to identify the hot-spot regions with poor air quality using excursion functions specified at the grid level. It suggests that the community of Madrid and some sites in northwestern and southern Spain are likely to be exposed to severe air pollution, simultaneously exceeding the warning risk threshold

Experimental study and mass transfer modelling for extractive desulfurization of diesel with ionic liquid in microreactors

Conventional hydrodesulfurization technology was limited to treat aromatic heterocyclic sulfur compounds in ultralow-sulfur diesel. Extractive desulfurization (EDS) using ionic liquid (IL) exhibited good performance to address these issues, except for its long extraction time (15-40 min). To address this, microreactor was adopted to intensify the IL-based EDS, where dibenzothiophene was extracted from model diesel (MD) as the continuous phase to 1-butyl-3-methylimidazolium tetrafluoroborate as the dispersed phase under segmented flow (which appeared preferably at capillary numbers lower than 0.01). The effects of temperature, residence time and flow rate ratio on the desulfurization efficiency were investigated. The extraction equilibration time could be shortened from more than 15 min in conventional batch extractors to 120 s in microreactors. The extraction process was modeled according to the two-film model applied within a unit cell of the segmented flow, where the mass transfer resistance was considered primarily on the film side of the IL droplet. The mechanism for the improved EDS performance at higher temperatures or larger IL to MD flow ratios was investigated and validated, which was related to the significant increase in the diffusion coefficient or the specific interfacial area. These findings may shed important insights into the precise manipulation of IL-based EDS for a better process design and reactor optimization

Graduate education of library science in China: Current status and recommendations for improvement

More than twenty years ago, Wuhan University and Nanjing University offered library science (LS) graduate programs. Since then, LS graduate education has been grow-ing quickly in many aspects. At the same time, however, LS graduate education was also facing enormous challenges stemming from the dynamic development and wide applications of information technologies into the pedagogical arena of teaching and learning at all levels. Social evolution also made it necessary for LS educators to re-examine once again their graduate education model, curricular composition, educational philosophy and educational missions. In analyzing the present situation of LS graduate education in China, this paper focuses on the following issues: 1) Growing size of LS graduate education (quantity and quality); 2) educational objectives, including research direction and placement for graduates; 3) structure of knowledge and curricular construction; 4) conditions of administering a library school of high quality and 5) the management of teaching resources. The keystone of this paper is to pinpoint where current library science curricular de.ciencies are lying. It is hoped that more serious scholarly discussions and perhaps also even concerted efforts among LS scholars and library practioners may be evoked in having the graduate education system of library and information science thoroughly realigned for the informational needs of the 21st century.</p

Inverse design and realization of an optical cavity-based displacement transducer with arbitrary responses

Optical cavity has long been critical for a variety of applications ranging from precise measurement to spectral analysis. A number of theories and methods have been successful in describing the optical response of a stratified optical cavity, while the inverse problem, especially the inverse design of a displacement sensitive cavity, remains a significant challenge due to the cost of computation and comprehensive performance requirements. This paper reports a novel inverse design methodology combining the characteristic matrix method, mixed-discrete variables optimization algorithm, and Monte Carlo method-based tolerance analysis. The material characteristics are indexed to enable the mixed-discrete variables optimization, which yields considerable speed and efficiency improvements. This method allows arbitrary response adjustment with technical feasibility and gives a glimpse into the analytical characterization of the optical response. Two entirely different light-displacement responses, including an asymmetric sawtooth-like response and a highly symmetric response, are dug out and experimentally achieved, which fully confirms the validity of the method. The compact Fabry-Perot cavities have a good balance between performance and feasibility, making them promising candidates for displacement transducers. More importantly, the proposed inverse design paves the way for a universal design of optical cavities, or even nanophotonic devices

Optimizing the Use of Cultivated Land in China&rsquo;s Main Grain-Producing Areas from the Dual Perspective of Ecological Security and Leading-Function Zoning

In order to achieve the coordinated development of ecological protection and cultivated land use, ecological security and cultivated land use functions (CLUFs) in the study area were evaluated by constructing a comprehensive evaluation index system. The leading CLUFs were measured, and it was determined to use the normalized revealed comparative advantage (NRCA) index. The spatial superposition analysis of the ecological security level and the leading CLUFs was carried out to obtain the zoning of the coordinated development of ecological security and cultivated land use, and differentiated utilization strategies were proposed for different zones. The results of this study showed the following: (1) The ecological security level of cultivated land in Yuanyang County can be divided into high, medium, and low security levels, accounting for 30.68%, 43.42%, and 25.9% of the total cultivated land area, respectively. The overall ecological security level is high. (2) The current cultivated land use mainly has a production function, accounting for 38.39% of the total cultivated land area, the leading CLUFs that are 34.16% of the cultivated land are the ecological function, and 27.45% of the cultivated land is the living function. (3) The spatial superposition analysis of the ecological security level and leading CLUFs yielded four zones of cultivated land use enhancement, including a production core zone, and different control strategies were proposed for the different zones. These strategies may help to fully realize the multifunctionality of the cultivated land without compromising ecological protection. Implementing differentiated protection for cultivated land in different use zones can achieve the coordinated development of ecological protection and cultivated land use, thus promoting the sustainable use of cultivated land resources

Flotation of a Pegmatite Type Spodumene Ore in Xinjiang

This is an essay in the field of mineral processing engineering. Li2O grade of a spodumene ore in Xinjiang is 1.04%. The lithium-containing minerals are mainly spodumene, Lithium-Muscovite and montebrasite. The gangue minerals are mainly quartz, albite and potassium feldspar. Under the condition of grinding finness -0.074 mm content 79.4%, using self-developed collector EM-PN51, the concentrate productswith Li2O grade 5.36%, Nb2O5 content 0.071%, Ta2O5 content 0.044% and Li2O recovery rate 87.38%, Nb2O5 recovery rate 87.33%, Ta2O5 recovery rate 88.26% can be obtained bythe closed flotation circuit of one-roughing, one-scavenging, three-cleaning. The comprehensive recovery of several valuable components in spodumene ore is realized

Comparison of Riser-Simplified, Riser-Only, and Full-Loop Simulations for a Circulating Fluidized Bed

With the development of computing power, the simulation of circulating fluidized bed (CFB) has developed from riser-simplified simulation to riser-only simulation, then to full-loop simulation. This paper compared these three methods based on pilot-scale CFB experiment data to find the scope of application of each method. All these simulations, using the Eulerian&#8722;Eulerian two-fluid model with the kinetic theory of granular theory, were conducted to simulate a pilot-scale CFB. The hydrodynamics, such as pressure balance, solids holdup distribution, solids velocity distribution, and instantaneous mass flow rates in the riser or CFB system, were investigated in different simulations. By comparing the results from different methods, it was found that riser-simplified simulation is not sufficient to obtain accurate hydrodynamics, especially in higher solids circulating rates. The riser-only simulation is able to make a reasonable prediction of time-averaged behaviors of gas&#8722;solids in most parts of riser but the entrance region. Further, the full-loop simulation can not only predict precise results, but also obtain comprehensive details and instantaneous information in the CFB system