SOME ASPECTS OF THEORETICAL COMPARISON OF FISCHER-TROPSCH REACTORS

The reactor systems used for the Fischer-Tropsch synthesis, fixed bed, fluidized bed and slurry bed, are compared on the basis of space time yield (STY) and level of conversion obtainable under the same set of feed and operating conditions. The slurry bed and fluidized bed reactor were compared on the basis of a first order reaction model. The performance of these two reactors was found to be comparable at low values of WHSV, but at higher values of WHSV, the fluidized bed reactor gave higher conversions and STY. A power law kinetic expression was used to compare the performance of the slurry bed and fixed bed reactors. Higher conversions and STY were obtained from the fixed bed with varying WHSV. This may be due to the omission of the intra and inter phase mass transfer resistances in the modelling of the fixed bed reactor.     

Novel Gas-Liquid-Solid Reactors

Multiphase reactors involving gas, liquid, and solid phases have several important applications in the chemical industry, particularly in catalytic processes. Some of the well-known examples are: hydrogenation and oxidation of organic compounds, hydro-processing coal-derived and petroleum oils, Fischer-Tropsch synthesis, and methanation reactions. Due to the presence of three phases, the problem of reactor design is often important to achieve effective mass and heat transfer as well as a mixing pattern favorable to the particular process. The reactors are mainly of two types: (a) solid catalyst is suspended either by mechanical agitation or gas-induced agitation and (b) solid catalyst is in a fixed bed with concurrent or countercurrent feed of gas and liquid re-actants. The reactor types conventionally used in industry are: (a) mechanically agitated or bubble column slurry reactors and (b) trickle-bed or packed-bed bubble reactor. The various design and modeling aspects of these reactors have been reviewed by Satterfield [1], Chaudhari and Ramachandran [2], Shah [3,4], Ramachandran and Chaudhari [5], Shah et al. [6], and Herskowitz and Smith [7]. In several industrial processes these reactor designs are modified to achieve a certain specific objective, such as better heat or mass transfer, higher catalyst efficiency, better reactor performance and selectivity, etc. Similarly, specially designed reactors are often used for laboratory kinetic studies or to understand a certain phenomenon. Thus, novel multiphase reactors are becoming important from both academic and industrial viewpoints. Some of the recently introduced novel gas-liquid-solid reactor types are: (a) loop recycle slurry reactors, (b) basket-type reactors, (c) ebullated-bed reactors, (d) internal or external recycle reactors, (e) multistage slurry or packed-bed reactors, (f) column reactors with sieve trays or multiple agitators, (g) gas-induced agitated reactors, and (h) horizontal-packed-bed reactors. are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed. These novel reactor designs are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed.     

一种蜂窝式企业知识管理体系构建方法

旨在探讨一种新的企业知识管理体系结构及其构建方法.分析现有企业知识管理体系存在的问题,研究个人知识管理体系的结构特点及其优点,并结合蜂窝状组织结构方式,提出一种基于个人知识管理构建企业级知识管理体系的方法,并阐述其原理、特点及其构建方法.与现有企业知识管理体系相比,这种新方法使得知识的更新更加快速,系统维护更方便,具有更简便、灵活、高效的特点.     

3D Simulation Research on Urea-SCR DeNO<em>x Catalyst for Diesel Engine

In order to reduce oxides of nitrogen (NOx) emanated from a diesel eng ine, a comprehensive urea selective catalyst reduction (SCR) DeNOx catalys t was modeled in which numerical simulations were used as a complementary tool f or the experimental investigations to make the design decisions, and hence short en the development process. In this approach, relevant conversion reactions were studied in 1D model, and the parameters obtained in this way were transferred t o 3D simulations. According to the results ...     

Hydrodynamics and mass transfer in a bubble column with an organic liquid

Hydrodynamic and mass transfer data in Soltrol-130 (a mixture of C₉+ iso-paraffins) were measured in a 0.305 m diameter bubble column. The gas holdup structure (i.e., the contributions to holdup from the small and large bubble fractions of the dispersion) for this hydrocarbon liquid in the churn turbulent flow regime was analyzed using the dynamic gas disengagement technique. The validity of the assumption of axially uniform gas holdup structure was checked. Literature correlations were found inadequate to explain the observed gas holdup and the volumetric mass transfer coefficients for Soltrol-130. The volumetric mass transfer coefficient per unit volume of large bubbles is shown to be independent of superficial gas velocity for the fully developed churn turbulent regime. The present hydrodynamic and mass transfer data in the churn turbulent regime should be useful in the design and scale-up of bubble columns used in organic process industries.     

Criteria for axial dispersion effects in adiabatic trickle bed hydroprocessing reactors

This paper first outlines an approximate solution to the governing equations for an adiabatic hydroprocessing trickle bed reactor operating in the presence of axial dispersion. The approximate solution agrees very well with the rigorous numerical solution for Peclet numbers greater than approximately three.Using the approximate solution, criteria for significant axial dispersion effect are obtained. These criteria indicate that at high conversions, an adiabatic operation produces a larger axial dispersion effect than the isothermal operation. At low conversions, opposite results are obtained.The derived criteria are used to evaluate the orders of magnitude of Peclet number required to avoid axial dispersion effect in pilot scale adiabatic reactors for (a) residual hydrodesulfurization (b) hydrocracking of gas oils and (c) denitrogenation of shale oils. The calculations indicate that the axial dispersion effect is of less importance in case (c) than in cases (a) and (b).Finally, the role of heat effects on the axial dispersion in a vapor phase fixed bed adiabatic reactor is evaluated.     

DPV: a taxonomy for utilizing deep learning as a prediction technique for various types of cancers detection

Multimedia Tools and Applications - Deep learning (DL) is a type of machine learning capable of processing large quantities of data to provide analytic results based on a particular...     

Generic Adaptive Sliding Mode Control for a Quadrotor UAV System Subject to Severe Parametric Uncertainties and Fully Unknown External Disturbance

International Journal of Control, Automation and Systems - This paper aims to provide a generic robust controller that is able to manipulate all kinds of quadrotor unmanned aerial vehicle (UAV)...     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.     

A cross-layer approach for partition detection at overlay layer for structured P2P in MANETs

Due to limited radio range and mobility of nodes in mobile ad hoc networks (MANETs), the network partitioning and merging could occur frequently. When structured peer-to-peer (P2P) overlays are running over MANETs, then network partition in the physical network can also cause network partition at the overlay layer. Existing approaches for structured P2P overlay over MANETs do not detect network partition at the overlay layer. This paper proposes a cross-layer approach to detect network partition at the overlay layer for structured P2P overlay over MANETs. Simulation results show that the proposed approach is highly effective and efficient in terms of routing overhead, success ratio and false-negative ratio.