Analysis of Gas Centrifuge Cascade for Separation of Multicomponent Isotopes and Optimal Feed Position

Abstract

Analysis of the concentration distribution in a gas centrifuge cascade for separation of multicomponent isotope mixtures is different from that in a cascade for separation of two-component mixtures. This paper presents the governing equations for a multicomponent isotope separation cascade. Numerically predicted separation factors for the gas centrifuge cascade agree well with the experimental data. A theoretical optimal feed position is derived for a short square cascade for a two-component mixture in a close-separation case. The optimal feed position for a gas centrifuge cascade for separation of multicomponent mixture is discussed.     

Lessons learnt from assembling screening libraries for drug discovery for neglected diseases

To enable the establishment of a drug discovery operation for neglected diseases, out of 2.3 million commercially available compounds 222 552 compounds were selected for an in silico library, 57 438 for a diverse general screening library, and 1 697 compounds for a focused kinase set. Compiling these libraries required a robust strategy for compound selection. Rules for unwanted groups were defined and selection criteria to enrich for lead-like compounds which facilitate straightforward structure-activity relationship exploration were established. Further, a literature and patent review was undertaken to extract key recognition elements of kinase inhibitors ("core fragments") to assemble a focused library for hit discovery for kinases. Computational and experimental characterisation of the general screening library revealed that the selected compounds 1) span a broad range of lead-like space, 2) show a high degree of structural integrity and purity, and 3) demonstrate appropriate solubility for the purposes of biochemical screening. The implications of this study for compound selection, especially in an academic environment with limited resources, are considered.     

FULLY DEVELOPED LAMINAR FLOW IN A HELICALLY COILED TUBE OF FINITE PITCH

Solutions for steady, fully developed, laminar flow of an incompressible Newtonian fluid through a helically coiled tube of finite pitch were obtained by finite difference calculations. Prior theoretical solutions have apparently been limited to toroidal flow (with zero pitch). The computed results are consistent with those for this limiting case and with prior experimental data for finite pitch. The behavior for helical coils is intermediate between that for a straight pipe and a torus, and, for a moderate degree of pitch differs only slightly from that for a torus. A correlating equation was developed for the friction factor for all Reynolds numbers, all ratios of coil radius to lube radius and all ratios of pitch to coil radius for which the flow remains laminar.     

INERTIAL COUPLING IN DISPERSED POTENTIAL FLOW—USE OF THE METHOD OF IMAGES

Net first and second dipole reflections are computed for several finite and infinite arrays of cylinders or spheres held stationary in a uniform potential flow. The polarizability and resistivity, from which the macroscopic properties of a two-phase flow with corresponding microstructure can be derived, are deduced for the infinite arrays. Finite arrays resemble infinite ones apart from edge and end effects, which are small for some geometries. The added mass coefficient for a regular monolayer of spheres is obtained and shown to be very close to Smythe's (1964) solution for a sphere in a circular tube. Similar agreement is obtained between the solutions for a cubical array of spheres and for a row of spheres in a circular tube.     

Integration of a Gas Fired Steam Power Plant with a Total Site Utility Using a New Cogeneration Targeting Procedure

A steam power plant can work as a dual purpose plant for simultaneous production of steam and elec-trical power. In this paper we seek the optimum integration of a steam power plant as a source and a site utility sys-tem as a sink of steam and power. Estimation for the cogeneration potential prior to the design of a central utility system for site utility systems is vital to the targets for site fuel demand as well as heat and power production. In this regard, a new cogeneration targeting procedure is proposed for integration of a steam power plant and a site utility consisting of a process plant. The new methodology seeks the optimal integration based on a new cogenera-tion targeting scheme. In addition, a modified site utility grand composite curve （SUGCC） diagram is proposed and compared to the original SUGCC. A gas fired steam power plant and a process site utility is considered in a case study. The applicability of the developed procedure is tested against other design methods （STAR？ and Thermoflex software） through a case study. The proposed method gives comparable results, and the targeting method is used for optimal integration of steam levels. Identifying optimal conditions of steam levels for integration is important in the design of utility systems, as the selection of steam levels in a steam power plant and site utility for integration greatly influences the potential for cogeneration and energy recovery. The integration of steam levels of the steam power plant and the site utility system in the case study demonstrates the usefulness of the method for reducing the overall energy consumption for the site.     

A structural model for gas solid reactions with a moving boundary—VI: The effect of grain size distribution on the conversion of porous solids

A distributed model is proposed for a first order, irreversible reaction between a porous solid and a gas in which allowance is made for a grain size distribution in the reactant solid matrix. By using approximate algebraic relationships between conversion and time, adopted from the grain model, solutions were generated for various types of grain size distribution. It was found that in general the plots of conversion against time for a grain size distribution differed from those computed for a single mean grain size. Only for closely sized grains or for a log normal grain size distribution was this difference relatively small. Thus the effect of grain size distribution is thought to be of importance in both the interpretation of experimental data in terms of the grain model and in procedures used for deducing kinetic parameters from experimental measurements.     

KNOWLEDGE EXTRACTION IN CHEMICAL PROCESS CONTROL

Direct access to the control knowledge of a skilled process operator is difficult and time-consuming. We present a framework for extracting process knowledge from human process operations records, using automated data reduction techniques for low-level data analysis and presenting reduced data to a human knowledge engineer for interpretation. We illustrate on a simple neutralization in a continuous stirred-tank reactor and employ a neural network for data reduction.     

Optimization issues of the broke management system in papermaking

This paper presents an optimization strategy for the design and operation of a broke management system in a papermaking process. A stochastic model based on a two-state Markov process is presented for the broke system and a multiobjective and bi-level stochastic optimization model is developed featuring (i) a multiobjective operational subproblem for the optimization of the broke dosage and (ii) a multiobjective design problem formulation. An efficient optimization strategy is proposed for the operational subproblem along with a simulation based Pareto optimal solution for the design problem, and illustrated with a detailed case study.     

Revisiting Johnson and Jackson boundary conditions for granular flows

In this article, we revisit Johnson and Jackson boundary conditions for granular flows. The oblique collision between a particle and a flat wall is analyzed by adopting the classic rigid‐body theory and a more realistic semianalytical model. Based on the kinetic granular theory, the input parameter for the partial‐slip boundary conditions, specularity coefficient, which is not measurable in experiments, is then interpreted as a function of the particle‐wall restitution coefficient, the frictional coefficient, and the normalized slip velocity at the wall. An analytical expression for the specularity coefficient is suggested for a flat, frictional surface with a low frictional coefficient. The procedure for determining the specularity coefficient for a more general problem is outlined, and a working approximation is provided. Published 2011 American Institute of Chemical Engineers, 2012     

Effect of Indenter Geometry on Controlled-Surface-Flaw Fracture Toughness

Fracture toughness values obtained using both Knoop and Vickers-indentation-produced controlled surface flaws were compared as a function of indentation load for a well-characterized glass-ceramic material. At the same indentation load, Knoop cracks were larger than Vickers. As-indented K_c values calculated from fracture mechanics expressions for surface flaws were higher for Knoop flaws than Vickers, but both types gave low K_c values due to indentation residual stress effects. Analysis suggested that theoretical formalisms for indentation residual stress effects based on fracture mechanics solutions for a center-loaded penny crack in an infinite medium should apply to both indentation types. K_c values calculated using the residual stress approach were identical for Knoop and Vickers controlled surface flaws when a "calibration" value for a constant term in the expression for K_c was used for both indentation types.     

Torcrete mix of basic composition for converter lining

Results are presented for a laboratory study of the substance composition of a periclase-carbon torcrete mix for restoring a converter lining, comparative methods for testing a torcrete mix under laboratory conditions, and the main production parameters for a torcrete mix under existing production conditions. Industrial tests are performed in the converter section of the OAO MMK oxygen-converter workshop. The life of a torcrete layer is two melts.     

Acetone in the Urban Atmosphere: A Study in Denver,Colorado

We report 4-h average concentration data for acetone, formaldehyde, acetaldehyde, and carbon monoxide measured in downtown Denver, Colorado, USA from January through December 1993. The correlations between these carbonyl compounds and CO measurements suggest that motor vehicles are a significant source for all three carbonyls, particularly during the winter. The diurnal character of the concentrations of formaldehyde and acetaldehyde suggests that there is at least a small net photochemical source for these compounds during the summer. The diurnal character of the acetone concentration suggests that there is a significant net photochemical source for acetone during the summer. An analysis of the initial photochemical production and loss processes for these carbonyls under typical atmospheric conditions suggests that the production and loss processes for formaldehyde nearly balance. This same analysis for the other carbonyls suggests that there should be a large net photochemical source for both acetaldehyde and acetone. Such a large photochemical source is not observed for acetaldehyde. Acetone is relatively unreactive in the atmosphere on a timescale of urban or regional interest. Thus, atmospheric measurements of acetone concentrations may serve as a useful indicator of the photochemical age or degree of photochemical processing of an air mass.     

Flow through a circular tube with a permeable Navier slip boundary

For Newtonian fluid flow in a right circular tube, with a linear Navier slip boundary, we show that a second flow field arises which is different to conventional Poiseuille flow in the sense that the corresponding pressure is quadratic in its dependence on the length along the tube, rather than a linear dependence which applies for conventional Poiseuille flow. However, assuming that the quadratic pressure is determined, say from known experimental data, then the new solution only exists for a precisely prescribed permeability along the boundary. While this cannot occur for conventional pipe flow, for fluid flow through carbon nanotubes embedded in a porous matrix, it may well be an entirely realistic possibility, and could well explain some of the high flow rates which have been reported in the literature. Alternatively, if the radial boundary flow is prescribed, then the new flow field exists only for a given quadratic pressure. Our primary purpose here is to demonstrate the existence of a new pipe flow field for a permeable Navier slip boundary and to present a numerical solution and two approximate analytical solutions. The maximum flow rate possible for the new solution is precisely twice that for the conventional Poiseuille flow, which occurs for constant inward directed flow across the boundary.     

Multi-enzyme cascade reaction in a miniplant two-phase-system: Model validation and mathematical optimization

Biotechnological application of multiple enzymes in different phases for target compounds synthesis poses a significant challenge for industrial process development. At the same time, a growing demand for natural flavors and fragrances opens up possibilities for novel biotechnological processes to replace current chemical synthesis routes, with additional advantages such as avoiding harsh reaction conditions and toxic chemicals, and less by-products in the system. Within complex biotechnological processes, the key for unfolding their industrial application potential in bioprocess engineering lies in their mathematical modeling. In this contribution, a multi-enzyme cascade reaction in a two-phase system implemented in a miniplant-scale reactor setup is mathematically modeled for the example of the flavoring agent cinnamyl cinnamate. Using our validated model and a mathematical optimization tool based on a genetic algorithm, optimization runs are performed to demonstrate the potential of computer-aided process development for complex biotechnological processes.     

A systematic framework for design of process monitoring and control (PAT) systems for crystallization processes

A generic computer-aided framework for systematic design of a process monitoring and control system for crystallization processes has been developed to study various aspects of crystallization operations. The systematic design framework contains a generic crystallizer modelling toolbox, a tool for generation of the supersaturation set-point for supersaturation control, as well as a tool for design of a process monitoring and control system (also called Process Analytical Technology (PAT) system). This systematic design allows one to generate the necessary problem-chemical system specific model, the necessary supersaturation set-point as well as a PAT system design including implementation of monitoring tools and control strategies in order to produce the desired target product properties notably crystal size distribution (CSD) and shape for a wide range of crystallization processes. Application of the framework is highlighted through a case study involving the design of a monitoring and control system for a potassium dihydrogen phosphate (KDP) crystallization process, where also the one-dimensional CSD and two-dimensional CSD modelling features are highlighted.     

A Thermodynamic Approach to the Integrated Design of a Combined Cycle Cogeneration Plant

A thermodynamically oriented approach for the integrated design of a combined cycle cogeneration plant (CCCP) meeting a given sites requirements for process steam and power has been developed. It has been shown that the most efficient plant, for a targeted stack temperature, is achieved when the gas turbine cycle is designed for maximum specific net work and the steam turbine cycle is designed for maximum cycle efficiency. Based on this approach a computer program for rigorous analysis has also been developed.     

A Genetic Algorithm Based Approach to Coalescence Parameters: Estimation in Liquid‐Liquid Extraction Columns

The population balance model is a useful tool for the design and prediction of a range of processes that involve dispersed phases and particulates. The inverse problem method for the droplet population balance model is applied to estimate coalescences parameters for two‐phase liquid‐liquid systems. This is undertaken for two systems, namely toluene/water and n‐butyl acetate/water in a rotating disc contactor (RDC), using a droplet population balance model. In the literature, the estimation procedure applied to this problem is often based on the deterministic optimization approach. These methods generate instabilities near a local minimum, inevitably requiring information about the derivatives at each iteration. To overcome these limitations, a method providing an estimate for the coalescences parameters is proposed. It is based on a simple and adapted structure of the genetic algorithm, for this particular problem. The agreement between the experimental observations and the simulations is encouraging and, in particular, the models used have proven to be suitable for the prediction of hold‐up and Sauter diameter profiles for these systems. Finally, these results demonstrate that the optimization procedure proposed is very convenient for estimating the coalescences parameters for extraction column systems.