Showing papers in "Chemical Engineering Research & Design in 2007"

Design and Development of Three-Dimensional Scaffolds for Tissue Engineering

Abstract: Tissue engineering is a concept whereby cells are taken from a patient, their number expanded and seeded on a scaffold. The appropriate stimuli (chemical, biological, mechanical and electrical) are applied and over a relatively short time new tissue is formed. This new tissue is implanted to help restore function in the patient. The scaffold is a three- dimensional substrate and it serves as a template for tissue regeneration. The ideal scaffolds should have an appropriate surface chemistry and microstructures to facilitate cellular attach- ment, proliferation and differentiation. In addition, the scaffolds should possess adequate mechanical strength and biodegradation rate without any undesirable by-products. Research in this area has been intense over the past 10 years or so on biopolymer formulation and on scaffold fabrication. This paper summarized some important issues related to scaffold design and development from biodegradable polymers. The mechanical properties and bio- compatibility of commonly used biopolymers are reviewed. The scaffold design and fabrication techniques are overviewed, their advantages and manufacturing feasibility are compared. The scaffold architecture, including pore size and size distributions, and its effects on the cells' growth are discussed. The scaffold should offer a hierarchical structure that varies over length scales of 0.1 1 mm. Conventional processing techniques can not yet fabricate a scaf- fold with control over both architecture and surface chemistry. There is, however, an emerging scaffold fabricating technique using solid free form fabrication (SFF). It has shown to be highly effective in integrating structural architecture with changes in surface chemistry of the scaffolds, and integration of growth factors.

Solvent properties of functionalized ionic liquids for CO2 absorption

Abstract: Ionic liquids can be used as solvents for gas absorption operations in order to improve the process economy and general efficiency of gas separations. This work investigates solvent properties of ionic liquids and compares them to amine solutions used for absorption of carbon dioxide (CO2). The CO2 solubility into six different room temperature ionic liquids (RTILs) was measured at temperatures between 298 K and 343 K and pressures up to about 1 MPa. The RTILs used were: [bmim]+[BF4]−, [bmim]+[DCA]−, and four imidazolium-based ionic liquids paired with [DCA] and [BF4], in which the cation was functionalized with either a primary, tertiary amine or a hydroxyl group. The density, viscosity and surface tension of the studied RTILs were measured at temperatures ranging from 293 K up to 363 K. The results showed that CO2 absorption behaviour was influenced by the functionalized chains appended to the RTILs cation. A chemical enhancement of the CO2 absorption was observed when functionalized RTILs were used as absorption solvents. It was possible to increase the ionic liquid volumetric gas load almost threefold by attaching functional groups to the ionic liquid, whereas for the traditional amine solutions the maximum gas load is stoichiometrically limited.

Longitudinal and Transverse Dispersion in Porous Media

Abstract: In the present work, we have analysed the experimental data presented in literature to characterize dispersion in porous media, at different dispersion regimes. The vast amount of data obtained by our group, together with the extensive data available from other sources, mostly for air and water at room temperature, provide a very detailed representation of the functions PeT ¼ f1 (Pem, Sc) and PeL ¼ f2 (Pem, Sc). Empirical correlations are presented for the predic- tion of the dispersion coefficients (DT and DL) over the entire range of practical values of Schmidt number and Peclet number. The simple mathematical expressions represent the data available, in literature, with good accuracy and they are shown to be a significant improvement over previous correlations.

Recent Advances in Crystallization control: An Industrial Perspective

Abstract: Crystallization is the most important unit operation for the separation and purification of chemicals in the pharmaceutical and fine chemical industries. Crystallization processes in pharmaceutical active ingredient manufacturing have been traditionally a recipe-based operations, offering little scope for dynamic process control and improvement. With the change in regulatory climate from quality-by-testing (QbT) to quality-by-design (QbD) and with the advent of the process analytical technology (PAT) initiative, it is timely to examine the impact of such quality-based emphasis on crystallization control. In this paper, we review the important recent developments in the control of crystallization process, and discuss their feasibility and scope for implementation in industrial processes. The control methods to achieve different aspects of crystal product quality, including particle size distribution (PSD), crystal habit and polymorphic form, are discussed separately.

In situ raman spectroscopy for in-line control of pharmaceutical crystallization and solids elaboration processes: A review

Abstract: As Raman spectroscopy enables complex, in situ, non-destructive and fast quantitative measurements of the solid state of pharmaceutical compounds, this technique is expected to allow the development of innovative future industrial applications for monitoring and controlling solids elaboration processes. This review presents important features of Raman spectroscopy, keeping industrial applications in view. The main potential applications of the technique, its advantages and drawbacks, and studies reporting on the real-time use of Raman spectroscopy for monitoring solid pharmaceutical elaboration processes are presented. A particular attention is focused on the in-line monitoring of crystallization processes. As far as routine exploitation of the Raman technology is concerned, it is shown that many problems remain unsolved, which were not fully addressed in published studies.

The Effect of Mixing on the Metastable Zone Width and Nucleation Kinetics in the Anti-Solvent Crystallization of Benzoic Acid

Abstract: The effects of anti-solvent addition rate and location, and agitation speed on the meta-stable zone width of an anti-solvent system were investigated using focused beam reflectance measurement (FBRM) and attenuated total reflectance-Fourier transform infra-red spectroscopy. Benzoic acid in ethanol-water mixtures, with water acting as anti-solvent, was chosen as the model system and was studied at a 500 mL scale. FBRM proved to be the more sensitive method for the detection of nucleation onset. In general, the metastable zone widened with increasing addition rate, with the effect most pronounced when the anti-solvent was added close to the impeller. At this location, an increase in agitation intensity resulted in a narrower metastable zone for all addition rates. For an addition location close to the vessel wall, the metastable zone was narrower and the impact of addition rate and agitation were less pronounced. Substantial variation in the measured metastable zone width was also observed, with nucleation occasionally occurring at bulk concentrations less than the saturation level. It is proposed that the metastable zone width is influenced by the differing degrees of anti-solvent incorporation at each addition location. Close to the impeller anti-solvent is rapidly incorporated leading to consistent results, but, close to the vessel wall, incorporation is hindered by unfavourable mixing conditions leading to premature nucleation and more variability. Computational Fluid Dynamics simulations support this observation. Using the measured metastable zone widths, nucleation kinetics at two different agitation intensities were estimated. Using this data, an agitation dependent expression for the nucleation rate was generated.

The Dos and Don’ts of Distillation Column Control

Abstract: The paper discusses distillation column control within the general framework of plantwide control. In addition, it aims at providing simple recommendations to assist the engineer in designing control systems for distillation columns. The standard LV-configuration for level control combined with a fast temperature loop is recommended for most columns.

Modelling and Simulation of Gas–Liquid Hydrodynamics in Mechanically Stirred Tanks

Abstract: Computational fuid dynamics (CFD) is an increasingly important tool for carrying out realistic simulations of process equipment. In the case of multiphase systems the development of CFD models is less advanced than for single-phase systems. In the present work CFD simulations of gas–liquid stirred tanks are reported. An Eulerian–Eulerian multi-fluid approach is used in conjunction with the simplest two-phase extension of the k–ɛ turbulence model. All bubbles are assumed to share the same size. The effect of inter-phase forces on simulation results is separately considered. As concerns drag, it is shown that the sole parameter needed to characterize the dispersed phase behaviour is bubble terminal velocity, a consideration that eases the estimation of the relevant term in the momentum equations and helps understanding the system physics. Despite the many simplifications adopted, results are found to be in satisfactory agreement with experiment.

CFD modelling of liquid homogenization in stirred tanks with one and two impellers using large eddy simulation

Abstract: A prediction of liquid homogenization in stirred tanks using a CFD code FLUENT is presented. The study was performed for tanks agitated by one and two impellers on a centrally-located shaft. Two types of impellers were used: a six-blade 45° pitched blade turbine and a standard Rushton turbine. Different methods were employed for simulations of fluid flow in the stirred tanks—the multiple reference frames technique together with the standard k–ɛ turbulence model, the sliding mesh technique with the standard k–ɛ turbulence model, and the sliding mesh technique with the large eddy simulation (LES) model and a non-iterative time-advancement algorithm. The dynamic Smagorinsky–Lilly model using a locally calculated subgrid scale dynamic viscosity constant was used in the LES calculations. Tracer mass fractions in the tanks were recorded during time-dependent species transport simulations. The calculated flow field results—velocity profiles, power and pumping numbers were compared with the experimental results from literature. Time traces of normalized concentrations obtained from the simulations were compared with our experiments and the resulting mixing times were compared to literature correlations. The LES approach was the most time-consuming method; however, it described the real flow in stirred tanks better and we obtained more realistic courses of the liquid homogenization and the best agreement of the computed and experimental homogenization times of all the used models.

A Signed Directed Graph and Qualitative Trend Analysis-Based Framework for Incipient Fault Diagnosis

Abstract: In this article a combined signed directed graph (SDG) and qualitative trend analysis (QTA) framework for incipient fault diagnosis has been proposed. The SDG is the first level in this framework and provides a possible candidate set of faults based on the incipient response of the process. The search for the actual fault is performed based on a QTA (level 2), which uses the temporal evolution of the sensors for further resolution. Thus, this framework combines the completeness property of SDG with the high diagnostic resolution property of QTA. Methods to address the problem of incorrect diagnosis arising due to incorrect measurement of initial response have also been presented. The proposed approach is tested on the Tennessee Eastman (TE) case study. Correct fault diagnosis is performed in all possible single fault scenarios. It is shown that this framework provides fast, reliable and accurate incipient fault diagnosis.

Design and Optimization of Flexible Utility Systems Subject to Variable Conditions: Part 1: Modelling Framework

Abstract: Industrial utility systems offer many degrees of freedom to improve their design and operation to achieve substantial savings in capital and/or operating costs. However, minimizing such expenditure also represents a challenging task due to the complex and highly-combinatorial nature of the optimization problem. While conventional approaches have simplified the problem by addressing operational and design (synthesis) issues in a separate or iterative way, the present work proposes a novel computational tool for both the design and operation of industrial utility systems in which their inherent flexibility is fully exploited through different operating scenarios. In order to consider the design and operational parameters of these systems as (continuous) mathematical variables to be optimised simultaneously, a new generic modelling framework for energy equipment has been developed and validated in which performance depends on both unit size and operational load. The first part of this paper describes the linear models developed to solve this problem for multi-fuel boilers, steam and gas turbines and heat recovery steam generators. These are employed to build a robust (multiperiod) MILP formulation to tackle grassroots design, retrofit or operational problems of the size and complexity commonly found in large industrial systems.

Real-Time Measurement of the Growth Rates of Individual Crystal Facets Using Imaging and Image Analysis: A Feasibility Study on Needle-shaped Crystals of L-Glutamic Acid

Abstract: Given that the fundamental process of crystal growth and its associated kinetic control is surface controlled, the use of a single scalar parameter, particle size, usually defined as a volume equivalent diameter, i.e., based on a spherical assumption of particle shape can be misleading for a number of practical crystallization systems, notably pharmaceutical products. Hence, measurement of the growth rate for each individual crystal surface in real-time and within processing reactors could open the way for the development of more effective process and concomitant product quality control. This paper presents the measurement of the growth rates of needle-shaped crystals in two dimensions using on-line imaging and image analysis techniques through a feasibility study of the batch crystallization of β form L-glutamic acid. The length and width of each needle-shaped crystal were measured every 60 s, ranging from 100 to nearly 180 μm in length and from 30 to 45 μm in width, and the values were used to estimate growth rates on both directions. The growth rate in length was found to be four to six times greater than for the width. The (101) plane was found to be the fastest growing surface of the morphology studied and an attempt has been made to estimate its growth-kinetics parameters from measurements of length, whilst it was harder to estimate kinetics from measurements of width for other crystal facets.

Methyl Acetate Hydrolysis in a Reactive Divided Wall Column

Abstract: The combination of reactive distillation and a divided wall column leads to a reactive divided wall column. The first use of such a reactive divided wall column for the hydrolysis of methyl acetate is presented here. For the development of this system, kinetic data for the involved reactions was determined at the University of Stuttgart, mini plant experiments were performed at BASF and an industrial scale column with an inner diameter of 220 mm was run at Sulzer Chemtech. Results of one mini plant experiment and of one experiment in an industrial scale are shown.

Selection and Pilot Plant Tests of New Absorbents for Post-Combustion Carbon Dioxide Capture

Abstract: Post-combustion capture of carbon dioxide is the only technique that can be rapidly and safely employed for substantially reducing carbon dioxide emissions from existing power plants and may also be the best choice for power plants to be built in the near future. For large scale post-combustion capture, absorption is the method of choice. The key question of the absorption/desorption technique for removal of carbon dioxide from flue gases is not its technical feasibility or conceptual process design but process economics, which again are dominated by the choice of the solvent. In the framework of the integrated project CO 2 -CASTOR (Castor, 2004) a solvent selection procedure was carried out. In this work, a consistent criterion for comparison of thermodynamic equilibrium data has been developed and applied to a list of potential solvents. Furthermore, experimental work for screening of solvent degradation has been performed. After the solvent selection procedure based on lab experiments is completed the operation of the absorption/desorption process has to be tested for the most promising solvents. For that purpose, a gas fired mini plant with a complete absorption/desorption cycle was built at University of Stuttgart.

Experimental Analysis and Computational Modelling of Gas–Liquid Stirred Vessels

Abstract: The aim of this work is to investigate the turbulent hydrodynamics of a gas–liquid stirred tank of standard geometry through experiments and simulations. The 2-D velocity fields are obtained by a two-phase PIV technique, consisting of a pulsed Nd:YAG laser, emitting light at 532 nm, and two cameras, each provided with a filter, that allow to discriminate between the light scattered by the fluorescent liquid seeding particles and that scattered by the bubbles. The experimental results obtained at different gas flow rates are presented, compared with single-phase data and discussed for gaining insight into the gas–liquid flows. They are also adopted for the quantitative evaluation of the results produced by CFD simulations based on a Two Fluid Model approach. The agreement between the experimental and the calculated mean velocity fields indicates that the selected CFD modelling is appropriate for the prediction of the mean hydrodynamic features of gas–liquid dispersions in stirred vessels.

Ultimate Flowrate Targeting with Regeneration Placement

Abstract: Water regeneration has been widely accepted as an effective mean to further reduce flowrate targets in a water network, and is often employed after the opportunity for flowrate reduction via water reuse/recycle have been exhausted. In this work, a new numerical targeting procedure is proposed to locate the minimum regeneration flowrate that achieves the ultimate fresh water and wastewater targets for both fixed flowrate and fixed load problems. Literature examples are solved to illustrate the applicability of the developed technique.

Optimization of Operating Conditions for Mitigating Fouling in Heat Exchanger Networks

Abstract: This paper presents a new approach for mitigating fouling in existing heat exchanger networks. It is based on the recognition that operating variables, such as wall temperature and flow velocity, may have a significant effect on fouling deposition rate. The approach combines the optimization of operating conditions with the optimal management of cleaning actions in a comprehensive mitigation strategy. The application of the method is demonstrated with a case study of a refinery crude oil preheat train. Compared with the existing strategy to mitigate fouling by managing cleaning, the proposed approach leads to higher energy savings, lower operational costs and fewer disturbances to the background process.

A Study of Flow Patterns for Gas/Liquid Flow in Small Diameter Tubes

Abstract: Time resolved void fraction data and flow pattern information have been obtained for two-phase air/water flows in a small diameter (5 mm) vertical pipe using conductance probes. The time averaged void fractions are seen to agree with values measured using a completely different approach. Analysis of high speed videos reveals that the probability density function (PDF) technique is inadequate for accurately delineating the transition between slug and churn flows but performs better for the churn to annular flow transition. Instead a novel approach has been developed for transitions between flow patterns using the velocity of structures. This gives good agreement with the present experiments. Additionally, a modification to the bubble-to-slug flow transition of Taitel et al . (1980) gives improved predictions in narrow passages. A flow pattern specific method for void fraction prediction has been applied and its predictions are in good agreement with the measured mean void fraction. The slug flow model gives better predictions of void fraction in churn flow that the annular flow model. The velocities of disturbance waves on the wall film in annular flow are well predicted using the model of Pearce (1979). However, pipe diameter dependence of one of the constants is required.

CFD Modelling of Nano-Particle Precipitation in Confined Impinging Jet Reactors

Abstract: Predictive design of nano-particle production via precipitation requires that the different steps through which particle formation occurs are deeply understood in order to control the final product properties and quality. In this work nano-particle precipitation in a confined impinging jet reactor (CIJR) is studied from the modelling point of view. The mathematical model, based on computational fluid dynamics (CFD), includes a micro-mixing model, the interchange by exchange with the mean (IEM) model coupled with the direct quadrature method of moments (DQMOM) approach, and solves the population balance equation (PBE) with the quadrature method of moments (QMOM). Eventually CFD predictions are compared with experimental data and good agreement is found.

Experimental investigations and modelling of breakage phenomena in stirred liquid/liquid systems

Abstract: The design of stirred tanks for liquid/liquid dispersions usually requires expensive experimental investigations. Models for properties of the dispersion like drop size distribution or interfacial area as a function of power-input, material and process parameters are rare and poorly accurate. With the present experimental investigations of drop breakage processes it is shown, that the modelling of drop size distributions in stirred tanks is sensitive to daughter drop distributions. For the simulation common coalescence and breakage models as well as special daughter droplet distribution models from literature were applied and tested. An efficient commercial solver for the population balance equation (PBE), the program PARSIVAL ® (Wulkow et al ., 2001) was used.

The Formation of Stable W/O, O/W, W/O/W Cosmetic Emulsions in an Ultrasonic Field

Abstract: This paper presents basic research results for production of W/O, O/W and W/O/W cosmetic emulsions under ultrasonic irradiation. A technology for the continuous and batch treatment of fluid mixtures with ultrasound was characterized using cosmetic emulsions as model systems. If cavitation is the dominant mechanism of droplet disruption, these results have to be taken into account for an optimal design of the emulsification apparatus geometry. The theoretical model supports experimental work. The experimental findings prove that final drop size essentially depends on specific power density. Drop size decreases with increasing residence time in the ultrasonic field until a system specific, minimum drop size is obtained. Ultrasonic irradiation leads to turbulent flow conditions on a macroscopic and a microscopic scale. The model based on the theory of turbulent drop bread-up predicts drop size and can be used to design equipment for ultrasonic emulsification. Emulsion used were stabilized using a combination of hydrophilic and hydrophobic surfactants. The ratio of this surfactants is important in achieving stable cosmetic emulsions. It was shown that emulsifier concentration plays great role in controlling the emulsification processes as well as the structured features of the droplets. The rheological behavior and morphological evolution during the ultrasonic emulsification were characterized systematically. The rheological properties were used to asses emulsion stability.

Pressure swing batch distillation for homogeneous azeotropic separation

Abstract: The separation of the homogeneous azeotropic mixture acetonitrile/water by pressure swing distillation (PSD) is considered. In this work, the PSD is operated as a discontinuous (batch) process and two basic batch modes, regular and inverted, are investigated. The processes are analysed and a rigorous dynamic model for both batch PSD processes is formulated. The model takes a cold and empty column as an initial condition. Because of the lack of experimental data, in particular for the inverted batch distillation new experiments were carried out. The regular and the inverted batch PSD consist of two steps, a low pressure and a high pressure run, and experimental results are shown for each step. The simulations fit the experiments with good accuracy. Using the validated model, a simulation study to discuss different batch processes is carried out and an alternative inverted batch process is proposed.

Modelling of Heat and Mass Transport Phenomena and Chemical Reaction in Underground Coal Gasification

Abstract: A two-dimensional axi-symmetric computational fluid dynamic model of an underground coal gasification cavity partially filled with an ash bed has been developed. The model is used to simulate the combined effects of heat and mass transport and chemical reaction during the gasification process. Simulations have revealed that when bottom injection of the oxidant is applied, the flow in the void space above the ash bed is dominated by a single buoyant force due to temperature gradients established by combustion. Optimum oxygen injection rates can be found which maximise the production of chemical energy in the product gas. When the oxidant is injected into the cavity from the top, most of the valuable gasification products are oxidized leading to a product gas with a high temperature and a low calorific value. The simulations eludicate the important transport and reaction processes occurring in the underground cavity and the results are in qualitative agreement with observations from field trials of underground coal gasification.

CFD analysis of caverns and pseudo-caverns developed during mixing of non-newtonian fluids

Abstract: The formation of caverns around the impeller is a characteristic of the mixing of non-Newtonian fluids which exhibit an apparent yield stress. Viscous non-Newtonian fluids which are not viscoplastic show pseudo-caverns instead, especially in the laminar and transitional flow regimes. The formation of caverns in a yield-stress fluid of the Herschel–Bulkley type, and pseudo-caverns in a shear-thinning power-law fluid, was studied in the laminar and transitional flow regimes using a CFD model. A PLIF technique was used to experimentally visualise and hence measure caverns and the rate of fluid mixing in the yield stress fluid. The MFR configuration was employed in conjunction with the laminar model and the apparent viscosity function of the fluid to solve the flow field using the CFX software. Mixing within caverns as indicated by PLIF was very slow. CFD predictions of cavern size agreed very well with experimental measurements at low Reynolds numbers. A number of theoretical cavern/pseudo-cavern models were compared to CFD, and experiment in the case of caverns, with the toroidal model giving the better agreement in terms of shape and size for both types of fluid.

Water Cascade Analysis for Single and Multiple Impure Fresh Water Feed

Abstract: Material reuse/recycle is gaining much attention in recent years for environmental sustainability reasons and the rising costs of fresh resources as well as waste treatment. The advent of process integration techniques for water network synthesis is among the most active area in the past decade. Via in-plant water reuse/recycle, fresh water and wastewater flowrates are reduced simultaneously. However, most focus to date has been dedicated to single pure fresh water source (without impurity). In this work, problems for single and multiple impure fresh water feed is addressed using the numerical targeting tool of water cascade analysis (WCA) technique. A three-step procedure is proposed on the modified WCA technique, which leads to the minimum pure and impure fresh water sources.

The Integration of the Hydrogen Distribution System with Multiple Impurities

Abstract: This paper addresses the minimization of the utility consumption of hydrogen distribution networks with multiple impurities. The impurity profiles, which are plotted according to the impurity concentration versus flowrate, and the impurity deficit diagram of all impurities are proposed. Two systematic targeting procedures for two different types of systems are developed for screening the minimum utility consumption before modifying the distribution system. In the procedures, all impurities are considered at the same time. Although iterative calculation is necessary, this method can determine the minimum utility consumption of hydrogen easily. It can also be used for minimizing the freshwater consumption in water allocation networks.

Graphically Based Optimization of Single-Contaminant Regeneration Reuse Water Systems

Abstract: In this paper, graphical method is employed to optimize single-contaminant regeneration reuse water systems. On the concentration-mass load diagram, three categories of water-using systems with regeneration reuse are analyzed in terms of the geometric features of limiting composite curve. Total regeneration and partial regeneration are identified first. Then based on sequential optimization and at a specified post-regeneration concentration, the optimal water supply lines for regeneration reuse systems can be constructed. The optimal water supply line corresponds to minimum freshwater consumption, minimum regenerated water flowrate and minimum contaminant regeneration load. Formulas for calculating these targets are summarized and interactions of these parameters are discussed. The concepts of limiting points for regeneration reuse, which are the counterpart of pinch for direct reuse, are proposed to indicate the bottlenecks of a water system with regeneration reuse. Different locations of the limiting points for different systems underlie that the optimal regeneration concentration can be greater than, equal to or smaller than the pinch concentration of the system.

Fluid Flow and Kinetic Modelling in Flotation Related Processes: Columns and Mechanically Agitated Cells—A Review

Abstract: In this paper, fluid flow and kinetic models related to minerals flotation process are presented and the advantages and limitations of using this type of models are discussed. The modelling of such processes was firstly developed assuming perfect mixing for the whole system as a black box. Then, a more realistic approach was developed recognizing the interaction between two zones, the particle–bubble collection zone and the froth transport zone. From a hydrodynamic point of view, experimental data showed that single large mechanical flotation cells can deviate significantly from perfect mixing, while the mixing conditions in a flotation bank of mechanical cells (three to nine cells in series) can be well described as a series of continuous perfectly mixed reactors. From plant experience, it was observed that performance of large industrial pneumatic flotation columns, originally regarded as a counter-current operation, also operate closer to a single perfectly mixed reactor. Advances in the field of modelling and design of flotation cells and columns, have been achieved because the fluid flow regime, the mass transport conditions at the pulp/froth interface and the froth transport mechanisms are better known and understood. Key parameters such as the bubble surface area flux, related to the bubble generation and the rate of particle collection, bubble loading related to the mass transport across the pulp-froth interface and froth recovery, which is mainly related to the gas residence time in the froth, are relevant for a deeper understanding of this type of equipment.

Standardization of Mass Transfer Measurements: A Basis for the Description of Absorption Processes

Abstract: Inaccurate mass transfer measurements may lead to an erroneous design of process equipment, since the accuracy of process modelling strongly depends on the quality of the model parameters. While procedures for measuring model parameters have been standardized for distillation, a standard for absorption has not been established yet. Thus the accuracy to predict the effective interfacial area and the mass transfer coefficients in the gas and liquid phase for several column internals varies significantly and the compatibility of data from different sources is limited. Therefore, a procedure to determine these mass transfer parameters is presented in this paper that includes guidelines for the choice of system, the experimental setup and procedure as well as the processing of experimental data. The procedure has been tested for classic and modern random packing types and results of absorption experiments are shown for a 25 mm Pall-Ring. A comparison of the experimental data with existing data and theoretical calculations from existing mass transfer correlations is presented. This comparison reveals not only discrepancies between the experimental and literature data but also the inconsistency of different sources and thus strongly supports the demand for a standardized procedure to determine mass transfer parameters for absorption systems.

Design and Optimization of Flexible Utility Systems Subject to Variable Conditions: Part 2 Methodology and Applications

Abstract: After having described the development of new models for the energy equipment used in industrial utility systems in the first part of this paper, this second part explains how such a modelling framework has been developed into an integrated methodology for the design and optimization of utility plants that exploits the flexibility of these systems. The different types of problems to be addressed (i.e., grassroots design, retrofit and operational) are identified in terms of their major issues and tradeoffs, giving emphasis to the fact that these tasks require a robust optimization procedure to handle industrial cases. Mechanical driver selection is incorporated in the proposed strategy. Several examples demonstrate the applicability and the potential of the suggested approach to provide significant economic benefits when applied to industrial problems.