Investigation of coupling dehydrogenation and hydrogenation reactions in a fixed bed catalytic reactor with well-mixed catalyst pattern

AbstractThe enhancement of ethylbenzene conversion by further displacement of the thermodynamic equilibrium via the influence of the dual-functionality of a well-mixed catalyst pattern has been investigated. A rigorous steady state mathematical model based on the dusty gas model is implemented for the simulation. The simulation results reveal that the introduction of the concept of the reaction coupling has significant effect on the displacement of the thermodynamic equilibrium and considerable enhancement of simultaneous production of styrene and cyclohexane. Almost 100% conversion of the ethylbenzene and benzene is achieved through the application of this approach. It is also found that considerable decrease in the reactor length is achieved by employing a reactor catalyst bed with different bed compositions. Effective operating regions with optimal conditions are observed. An effective reactor length criterion is used to evaluate the performance of the reactor under these optimal conditions. The effective reactor length is found to be sensitive and favored by high feed temperature and pressure. The sensitivity analysis shows that the key parameters of feed temperature, pressure, and the bed composition play an important role on the reactor performance. The results also show that almost 100% conversion of ethylbenzene and benzene at low temperature and shorter reactor length can be achieved by maintaining the reactor beds at different temperatures. This temperature switching policy may result in appreciable energy saving. Moreover, operating the reactor at low temperature protect the catalyst from the excessive temperatures which have destructive effects on the catalysts and the mechanical stability of the reactors. Also, the low temperature operation has significant contribution to the reduction of the operating cost

DETERMINATION OF MIXING HEIGHT IN RIYADH, SAUDI ARABIA

Twice-daily mixing heights, one morning and one afternoon were calculated by using the computational program MIXHTS. MIXHTS utilizes the meteorological data collected from the King Khalid International Airport (KKIA) surface and upper air stations in Riyadh city during the year 2002. Climatic data shows that the city of Riyadh has in general, a hot and dry weather in summer and cold and dry in wintertime, whereas strong insolation is dominant all over the year. Monthly average afternoon mixing heights are ranged from 1629 m to 3971 m, whereas the morning mixing heights are ranged from as low as 935 m to 2920 m. Estimation of mixing heights obtained by this work were found in a good agreement with the daily maximum value obtained from the dry adiabatic temperature method

A dimensão comunicativa dos elementos de design gráfico - Como infográficos

The purpose of the current study is to address a research question about the role that visual design elements have in communication. The data were collected based on their technical relevance, which highlights the general description of the field of research that includes graphics, infographics in the field of communication, and elements of visual design Review of the relevant literature and concepts: To begin with, we must consider the communication aspects of the design in order to produce truly successful visual design elements. The communicative dimension of graphic design elements such as infographics are invaluable in conveying information in a clear and engaging way. Two opened the way for the expansion of the use of visual elements in the manufacture of the media message. This study discusses the communicative dimensions of visual design elements, in general, and infographics in particular, as infographic is part of information visualization. This study discusses the communicative dimensions of visual design elements, in general, and infographics in particular, as Infographic is part of information visualization, in addition to that it is a research field related to communication as it focuses on patterns and trends in abstract data sets, and the field of infographic design, and information visualization combines the concepts of computer science, data mining, cognitive sciences and graphic design, this is important in controlling and measuring the quality of communication because the ability to collect, store and manage data, despite the increasing pace of its updating, remains our ability On their understanding relatively constant. The size, shape, and color of visual design elements can also play a role in communication. According to the results obtained, it was determined that the use of graphs as a visual communication tool was effective in evaluation, understanding and continuity.El objetivo del presente estudio es abordar una pregunta de investigación sobre el papel que juegan los elementos de diseño visual en la comunicación. Los datos fueron recolectados en base a su relevancia técnica, en la que se destaca la descripción general del campo de investigación que incluye gráficos, infografías en el campo de la comunicación y elementos de diseño visual Revisión de la literatura y conceptos relevantes: Para empezar, debemos considerar los aspectos de comunicación del diseño para producir elementos de diseño visual verdaderamente exitosos. La dimensión comunicativa de los elementos de diseño gráfico, como las infografías, es invaluable para transmitir información de una manera clara y atractiva. Dos allanaron el camino para expandir el uso de elementos visuales en la fabricación del mensaje mediático. Este estudio discute las dimensiones comunicativas de los elementos de diseño visual, en general, y de la infografía en particular, ya que la infografía es parte de la visualización de información. Este estudio discute las dimensiones comunicativas de los elementos de diseño visual, en general, y de la infografía en particular, ya que la infografía es parte de la visualización de información, además de ser un campo de investigación relacionado con la comunicación, ya que se enfoca en patrones y tendencias en conjuntos de datos abstractos, y el campo del diseño infográfico y la visualización de información combina los conceptos de informática, minería de datos, ciencia cognitiva y diseño gráfico, esto es importante para controlar y medir la calidad de la comunicación porque la capacidad de recopilar, almacenar y administrar datos, a pesar del ritmo cada vez mayor de su actualización, nuestra capacidad para entenderlo se mantiene relativamente constante. El tamaño, la forma y el color de los elementos de diseño visual también pueden desempeñar un papel en la comunicación. De acuerdo a los resultados obtenidos se determinó que el uso de gráficos como herramienta de comunicación visual fue efectivo en la evaluación, comprensión y continuidad.O objetivo do presente estudo, é abordar uma questão de pesquisa sobre o papel que os elementos de design visual têm na comunicação. Os dados foram coletados com base em sua relevância técnica, que destaca a descrição geral do campo de pesquisa que inclui gráficos, infográficos no campo da comunicação e elementos de design visual Revisão da literatura e conceitos relevantes: Para começar, devemos considere os aspectos de comunicação do design para produzir elementos de design visual verdadeiramente bem-sucedidos. A dimensão comunicativa dos elementos de design gráfico, como infográficos, é inestimável para transmitir informações de maneira clara e envolvente. Dois abriram caminho para a ampliação do uso de elementos visuais na fabricação da mensagem midiática. Este estudo discute as dimensões comunicativas dos elementos de design visual, em geral, e dos infográficos em particular, visto que o infográfico faz parte da visualização da informação. Este estudo discute as dimensões comunicativas dos elementos de design visual, em geral, e infográficos em particular, já que o infográfico faz parte da visualização de informações, além de ser um campo de pesquisa relacionado à comunicação, pois enfoca padrões e tendências em conjuntos de dados abstratos, e o campo do design infográfico e visualização de informações combina os conceitos de ciência da computação, mineração de dados, ciências cognitivas e design gráfico, isso é importante para controlar e medir a qualidade da comunicação porque a capacidade de coletar, armazenar e gerenciar dados, apesar o ritmo crescente de sua atualização, permanece nossa capacidade de compreensão relativamente constante. O tamanho, a forma e a cor dos elementos de design visual também podem desempenhar um papel na comunicação. De acordo com os resultados obtidos, foi determinado que o uso de gráficos como ferramenta de comunicação visual foi eficaz na avaliação, compreensão e continuidade

Homoclinicity in the dynamics of forced fluidized bed catalytic reactors

The dynamic behaviour of the non-isothermal oscillating fluidized bed catalytic reactor subjected to high and low frequency forcing is investigated. Resonance horns and period doubling loci inside the horns are constructed, using efficient algorithms, for different positions of the centre of forcing relative to the homoclinical orbit (infinite period orbit) of the autonomous (unforced) system. The analysis shows that the reactor behaviour is very sensitive to the position of the centre of forcing relative to the homoclinical orbit. For high frequency forcing (ω/ω0 = 5/1) with centre of forcing close to the homoclinical orbit, the system shows period doubling to chaos at very small amplitudes. For low frequency forcing (ω/ω0 = 2/1), incomplete period doubling not leading to chaos is observed in some cases and the new period adding bifurcation is also uncovered for other cases. The interactions between different resonance horns are investigated and the resulting bistabilities are elucidated. Quantitative methods proved that the strange attractors encountered are chaotic with one positive Lyapunov exponent and a Lyapunov fractal dimension between 1 and 2

Application of the Green Element Method to Chemical Engineering Problems

The novel Green element method (GEM), which applies the singular boundary integral theory (a Fredholm integral equation of the second kind) on each element at a time, is herein implemented on chemical engineering problems. The method overcomes some of the limitations of classical boundary element approach and uses the finite element methodology to achieve optimum inter nodal connectivity. The global coefficient matrix is banded and numerical difficulties from a densely populated matrix are eliminated. Two numerical examples are used to demonstrate the capabilities of the method. The results are compared with orthogonal collocation method, finite element method and experimental data. It has been shown that the Green element method is very reliable and efficient. Keywords: Finite element method, green element method, orthogonal collocation method, diffusion, reactio

Influence of Hydrodynamic Flow Regimes on the Prediction of Gas Hold-up and Liquid Circulation in Airlift Reactors

The influence of the recently identified hydrodynamic flow regimes on the prediction of gas hold-up and liquid circulation velocity in airlift reactors has been investigated. Some hydrodynamic models based on momentum balance are considered. Experiments were conducted on a pilot plant, external loop airlift reactor using air-water system. The generalised equation of Joshi and Lali for the homogeneous regime predicts the overall gas hold-up in this region with satisfactory accuracy and the difference between the experimental and predicted values is lower than ± 8%. Hsu and Dudukovic model predicts the liquid circulation velocity based on the gas hold-up correlations proposed for the homogenous, transition and heterogeneous flow regimes and two-phase friction factor with satisfactory accuracy (within 4.9 %). The results also show that the friction factor has pronounced effect on the model predictions. It would appear, also that the characterisation of various flow regimes has profound effect on the predictions of these important design parameters. Superposition approach is implemented to develop a correlation for the prediction of the axial gas hold-up in the riser as a function of the height and superficial gas velocity. The proposed correlation gives an average error of 4.7%. Keywords: Airlift reactors, flow regimes, gas hold-up, liquid circulatio

Low temperature catalytic reforming of heptane to hydrogen and syngas

The production of hydrogen and syngas from heptane at a low temperature is studied in a circulating fast fluidized bed membrane reactor (CFFBMR). A thin film of palladium-based membrane is employed to the displacement of the thermodynamic equilibrium for high conversion and yield. A mathematical model is developed to simulate the reformer. A substantial improvement of the CFFBMR is achieved by implementing the thin hydrogen membrane. The results showed that almost complete conversion of heptane and 46.25% increase of exit hydrogen yield over the value without membrane are achieved. Also a wide range of the H2/CO ratio within the recommended industrial range is obtained. The phenomena of high spikes of maximum nature at the beginning of the CFFBMR are observed and explanation offered. The sensitivity analysis results have shown that the increase of the steam to carbon feed ratio can increase the exit hydrogen yield up to 108.29%. It was found that the increase of reaction side pressure at a high steam to carbon feed ratio can increase further the exit hydrogen yield by 49.36% at a shorter reactor length. Moreover, the increase of reaction side pressure has an important impact in a significant decrease of the carbon dioxide and this is a positive sign for clean environment

Parametric sensitivity analysis to investigate heptane reforming in circulating fast fluidized bed membrane reactors

In this paper, we present mathematical modeling and numerical simulation tools in searching the high parameter space of steam reforming of heptane for the key design parameters, which have the potential to give high heptane conversion, high hydrogen yield and hydrogen to carbon monoxide ratio within the industrial limits for the syngas used as a feedstock for the gas to liquid processes (GTL). The system under consideration is the novel circulating fast fluidized bed membrane reactor (CFFBMR). The simulation results show that the hydrogen membrane has a significant role in the displacement of the thermodynamic equilibriums of the reversible reactions and production of ultraclean hydrogen, which can be used as a fuel for the fuel cells. Also the results of the sensitivity analysis show that the best performance of the CFFBMR can be obtained by a proper selection of combination of several parameters of high feed temperatures, high steam to carbon feed ratios, high reaction side pressures coupled with a large permeation area of a composite thin film membrane. These parameters are interacting in a very complex manner to give 100% conversion of heptane and 496.94% increase in hydrogen yield compared to the reformer without hydrogen membrane. It was found that under these selected operating conditions a low H2/CO ratio of 1.15 is achieved satisfying the practical recommended industrial range

Development of exotic geometrical structures in complex dynamics of a forced bioethanol reactor

In this short communication, the impact of the influence of a dynamic membrane on a bioreactor forced by high amplitude oscillations is investigated. The chaotic state of the reactor bifurcates to unprecedented complex dynamics. Very interesting exotic geometrical structures embedded in a high dimensional phase space are developed. Despite the complexity of the dynamics of this system, it can produce an increase of average ethanol yield up to 19.62% compared to unforced system. Keywords: Bioethanol, Chaos, Dynamic membranes, Exotic geometrical topologies, Forced bioreacto