Description Of Complex Phenomena Research Articles

Current R&D Challenges for Fluidized Bed Processes in the Refining Industry

Fluidized bed processes are widely used in the refining industry, mostly for conversion applications (e.g. fluid catalytic cracking, fluid coking, residue hydroconversion, Fischer-Tropsch Synthesis, etc.). These are large scale processes operating under severe conditions. Fluidized bed processes involve many complex phenomena that need to be considered in order to ensure proper design, operation and reliability. There have been thousands of publications over many years in the field of fluidization, but some of the fundamentals of fluid-particle flows still remain to be clarified. As a consequence, scale-up and industrialization of new technologies or processes remain a difficult, challenging and risky task.IFP is deeply involved with fluidized bed processes used in the refining industry. Over the last twenty years, industrial developments and PhD studies were conducted to explore new concepts, to develop new technologies, to scale-up hydrodynamics, to understand and quantify key phenomena. This paper discusses R&D practices in the field and current challenges encountered, mostly based on IFP experience. It does not intend, however, to provide an extensive literature review of all topics addressed in this paper.Interactions between particles, multiphase flow and reactor geometries are complex issues in fluidized beds. Therefore, experimentation is required to study new concepts such as downflow systems, complex phenomena such as vaporization of droplets in contact with gas-particle systems. The design of the experiment and the development of appropriate instrumentation are never simple and in the absence of simple similarities, anticipation of the main flow features is unavoidable. Modeling of results is then mandatory in order to translate results to industrial perspectives. Over the last 15 years, CFD has appeared as a promising tool to describe multiphase flow phenomena in complex geometries. Unfortunately, the lack of theoretical models to describe gas particle flow, at least for Group A powders, still leads researchers to conduct experiments to validate simulations or to adjust the gas-particle closure equations to validate results. Furthermore, observation in industrial units, during start-up or under steady conditions, when possible, greatly aids in validating research efforts and methodology.Despite its maturity, our industry is moving forward. There are ongoing developments in the energy and fuels market as well as in environmental fields, but also in the scientific background available to describe multiphase flow. Therefore, evolutionary R&D in the field is still needed to progress in the description of complex phenomena in order to optimize reactors and technologies and to face the changes of our industry.

Demographic models for manpower planning and policy

The purpose of this article is to demonstrate the utility, for planning and policy analysis, of mathematical models of individual mobility within organizational labor markets. Recognizing that, in an idealized sense, internal mobility can be characterized as a function of two very different things - individual attributes or job vacancies - two models of mobility are described. Using real data where possible, we demonstrate the ability of both models to forecast total labor costs and trace the change in costs to changes in the age-seniority distributions, changes in the size of the labor force, and changes in salary schedules. This disaggregation is of significance since any effective attempt to control or change total costs must accommodate for the, sometimes conflicting, contribution of each source. Using the vacancy-based model of mobility, the ramifications of alternative recruiting and Equal Employment Opportunity (EEO) strategies are explored. Relatively large increases in both direct (dollar) and indirect (turnover) costs are shown to result from free entry at all grade levels. As for EEO strategies, we show, inter alia, the ineffectiveness of pure EEO strategies in reaching representative parity within a reasonable time, the relatively weak impact of organizational growth on reaching parity levels, and the surprisingly small costs imposed on the majority population by an effective Affirmative Action (AA) program. These illustrations amply serve to demonstrate the counter-intuitive results of alternative policies applied to inter-related labor systems, and underscore the need for mathematical descriptions of complex phenomena in addressing “What if ...?” questions for policy planning and analysis.