Showing papers in "Chemical Engineering Research & Design in 2010"

Vanillin production from lignin oxidation in a batch reactor

Abstract: Vanillin production from lignin oxidation is a biomass-based process that employs a by-product of the pulp and paper industry and air to obtain a high-added value compound. However, lignin is an organic polymer with a structure that depends strongly on the source and the conditions to obtain vanillin should be adjusted for different samples. The objective of this work is to establish a fast and standard protocol to characterize lignin conversion to vanillin by batch oxidation. The experimental technique is coupled with a mathematical model that allows us to fit the data and determine kinetic rate constants under non-isothermal conditions. Two examples of vanillin oxidation with very different lignin sources are presented. The results revealed vanillin yields with respect to the lignin mass ranging from 3.5% to 7.6% for the high and low-molecular weight lignins, respectively.

Pyrolysis of wheat straw in a thermogravimetric analyzer: Effect of particle size and heating rate on devolatilization and estimation of global kinetics

Abstract: The influence of different parameters such as particle size, initial weight of the sample, and heating rate on the devolatilization of wheat straw particles have been studied using thermogravimetric analysis. In addition, the variations in proximate analysis with different particle sizes of wheat straw have also been investigated. Results show that the curves corresponding to the third stage of pyrolysis differ for variations in particle size, initial weight, and heating rate of the pyrolysis process. A devolatilization model with three parallel nth-order reactions has been considered to determine the global kinetic parameters using thermogravimetric data. The kinetic parameters such as activation energy (kJ/mol), frequency factor (1/min), and order of the reaction for the three stages considered in devolatilization model were E1 = 69, E2 = 78, E3 = 80; k01 = 2.57 × 1012, k02 = 3.97 × 107, k03 = 3.17 × 106; and n1 = 2.3, n2 = 0.65, n3 = 2.7, respectively. It was noted from the order of the reaction that the second stage of the pyrolysis curve corresponds to the degradation of cellulose and hemicellulose, and the third stage to the lignin degradation.

Simulation and cost estimate for biodiesel production using castor oil

Abstract: Brazilian government has established a regulation that imposes the commercialization of diesel blended with 3% of biodiesel by volume. Castor oil has being considered an option to guarantee the supply of biodiesel needed. For this reason, in this work, a continuous biodiesel plant was designed and simulated in HYSYS simulator using castor oil as feedstock. The developed process was capable of producing biodiesel at high purity using an alkali catalyst. Material and energy flows, as well as sized unit operations were used to conduct an economic assessment of the process. Total capital investment, total manufacturing cost and after annual equivalent cost were also calculated. A study of production costs was performed considering the fluctuations of the raw material prices and the glycerin purification step.

Treatment of oily wastewater using low cost ceramic membrane: Comparative assessment of pore blocking and artificial neural network models

Abstract: This work addresses the performance and modeling of the separation of oil-in-water (o/w) emulsions using low cost ceramic membrane that was prepared from inorganic precursors such as kaolin, quartz, feldspar, sodium carbonate, boric acid and sodium metasilicate. Synthetic o/w emulsions constituting 125 and 250 mg/L oil concentrations were subjected to microfiltration (MF) using this membrane in batch mode of operation with varying trans-membrane pressure differentials (ΔP) ranging from 68.95 to 275.8 kPa. The membrane exhibited 98.8% oil rejection efficiency and 5.36 × 10−6 m3/m2 s permeate flux after 60 min of experimental run at 68.95 kPa trans-membrane pressure and 250 mg/L initial oil concentration. These experimental investigations confirmed the applicability of the prepared membrane in the treatment of o/w emulsions to yield permeate streams that can meet stricter environmental legislations (

Kinetic study of high density polyethylene (HDPE) pyrolysis

Abstract: In this study, 15 mg samples of high density polyethylene (HDPE) were pyrolysed in an isothermal thermogravimetric set-up in a micro-thermobalance reactor with pre-set temperatures. The objective was to study the thermal degradation behaviour of the polymer and determine the kinetic rate constants and overall activation energy (E-o). Yielded pyrolysis products under different temperatures were analyzed and lumped into the following categories: rich gases (C-1-C-4), liquids (non-aromatic C-5-C-10), aromatics (single ring structures), waxes ( C-11) and char. It was observed that the gas yield was increasing with the operating temperature. Data obtained enabled us to propose a novel kinetic modelling approach based on the thermal cracking of the polymer by primary and secondary depolymerisation reactions to form the pyrolysis products. The E-o was estimated to be 147.25 kJ mol(-1) for the total conversion of HDPE in isothermal pyrolysis. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

On the evaluation of synthetic and natural ilmenite using syngas as fuel in chemical-looping combustion (CLC)

Abstract: Chemical-looping combustion (CLC) is a combustion technique where the CO2 produced is inherently separated from the rest of the flue gases with a considerably low energy penalty. For this reason, CLC has emerged as one of the more attractive options to capture CO2 from fossil fuel combustion. When applying CLC with solid fuels, the use of a low cost oxygen carrier is highly important, and one such low cost oxygen carrier is the mineral ilmenite. The current work investigates the reactivity of several ilmenites, some which are synthetically produced by freeze granulation and two natural minerals, one Norwegian ilmenite and one South African ilmenite. A laboratory fluidized bed reactor made of quartz was used to simulate a two reactor CLC system by alternating the reduction and oxidation phase. The fuel was syngas containing 50% CO and 50% H2. A mixture of 6 g of ilmenite with 9 g inert quartz of diameter 125–180μm was exposed to a flow of 900mLn/min syngas in the reduction phase. During the oxidation phase, a 900mLn/min flow of 10% O2 diluted in N2 was used. The experimental results showed that all ilmenites give higher conversion of H2 than of CO. Generally, synthetic ilmenites have better CO and H2 conversion than natural ilmenites and synthetic ilmenites prepared with an excess of Fe generally showed higher total conversion of CO than synthetic ilmenites with an excess of Ti. Most synthetic ilmenites and the Norwegian ilmenite showed good fluidization properties during the experiments. However, for two of the synthetically produced materials, and for the South African ilmenite, particle agglomerations were visible at the end of the experiment.

Spray drying formulation of hollow spherical aggregates of silica nanoparticles by experimental design

Abstract: The present work employs an experimental design methodology to optimize the spray-drying production of micron-size hollow aggregates of biocompatible silica nanoparticles that are aimed to serve as drug delivery vehicles in inhaled photodynamic therapy. To effectively deliver the nanoparticles to the lung, the aerodynamic size (dA) of the nano-aggregates, which is a function of the geometric size (dG) and the degree of hollowness, must fall within a narrow range between 2 and 4 μm. The results indicate that (1) the feed concentration, (2) the feed pH, and (3) the ratio of the gas atomizing flow rate to the feed rate are the three most significant parameters governing the nano-aggregate morphology. Spray drying at a low pH (<7) and at a low feed concentration (<1%, w/w) generally results in nano-aggregates having small geometric and aerodynamic sizes (dA = dG ≈ 3 μm) with a relatively monodisperse size distribution. Spray drying at a higher feed concentration produces nano-aggregates having a larger dG but with a multimodal particle size distribution. A trade-off therefore exists between having large dG to improve the aerosolization efficiency and obtaining a uniform particle size distribution to improve the dose uniformity.

Preparation of liposomes entrapping essential oil from Atractylodes macrocephala Koidz by modified RESS technique

Abstract: A modified technique of rapid expansion of supercritical solutions (RESS) was applied to incorporate essential oil extracted from Atractylodes macrocephala Koidz into liposomes. In the modified RESS process, both the liposomal materials and the essential oil were dissolved in the mixture of supercritical carbon dioxide (SC-CO 2 )/ethanol and then the solution was sprayed into an aqueous medium through a coaxial nozzle to form liposomes suspension. The encapsulation performance of liposomes could be controlled by changing expansion processing conditions such as pressure, temperature of SC-CO 2 and the amount of ethanol. The entrapment efficiency, drug loading and average particle size of liposomes were found to be 82.18%, 5.18% and 173 nm, respectively, under the optimum conditions of at a pressure of 30 MPa, a temperature of 338 K and a ethanol mole fraction in SC-CO 2 [( x (CH 3 CH 2 OH)] of 15%. The formed liposomes appeared as double-layered colloidal spheres with a uniform and narrow particle size distribution. The physicochemical properties of liposomes including entrapment efficiency, dissolution rate and stability were complied with the provisions of Chinese pharmacopoeia. All these results indicate that the modified RESS technique is an innovative way for self-assembly of liposomes incorporation of multi-components extracted from Chinese traditional medicines in the SC-CO 2 .

Evaluation of the pyrolytic and kinetic characteristics of Enteromorpha prolifera as a source of renewable bio-fuel from the Yellow Sea of China

Abstract: The pyrolytic and kinetic characteristics of Enteromorpha prolifera from the Yellow Sea were evaluated at heating rates of 10, 20 and 50 degrees C min(-1), respectively. The results indicated that three stages appeared during pyrolysis; dehydration, primary devolatilization and residual decomposition. Differences in the heating rates resulted in considerable differences in the pyrolysis of E. prolifera. Specifically, the increase of heating rates resulted in shifting of the initial temperature, peak temperature and the maximum weight loss to a higher value. The average activation energy of E. prolifera was 228.1 kJ mol(-1), the pre-exponential factors ranged from 49.93 to 63.29 and the reaction orders ranged from 2.2 to 3.7. In addition, there were kinetic compensation effects between the pre-exponential factors and the activation energy. Finally, the minimum activation energy was obtained when a heating rate of 20 degrees C min(-1) was used. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Effect of bubble hydrodynamic and chemical dosage on treatment of oily wastewater by Induced Air Flotation (IAF) process

Abstract: The objective of this work is to study the treatment of oily wastewater containing anionic surfactant at Critical Micelle Concentration (CMC) by the Modified Induced Air Flotation (MIAF) process. MIAF, which is the combined process between the IAF process and the coagulation process, was applied and also compared with the Induced Air Flotation (IAF) and coagulation processes. The study has shown that the removal efficiency, considered in terms of COD, was related to the alum dosage, pH value and gas flow rate. Moreover, the interfacial area (a) obtained experimentally from the bubble hydrodynamic parameters (bubble size, bubble rising velocity, bubble formation frequency) and the velocity gradient (G) have been proven to be the important parameter for controlling the flotation process efficiency and operation cost. The simple proposed correlation, based on the a/G ratio, provides relatively a good coincidence between the experimental and predicted values of treatment efficiencies in this study.

Fault diagnosis based on imbalance modified kernel Fisher discriminant analysis

Abstract: Process data with imbalance class distribution has brought a significant drawback to most existing pattern recognition based fault diagnosis algorithms, which have assumed that the process data have an equal misclassification cost and relatively balanced class distribution. The frequent occurrence of the imbalance problem in real industrial process indicates the need for extra research efforts. In this paper, three novel imbalance modified kernel Fisher discriminant analysis (IM-KFDA) approaches are proposed to handle this problem. Two sample-level approaches, over-sampling KFDA and under-sampling KFDA, are presented along with proper stochastic sampling strategies. One algorithm-level approach, inductive bias KFDA, is also proposed with incorporating a novel regular weighted matrix (RWM) into the minimum Euclid distance based pattern classification rule. To improve the fault diagnosis performance, model updating modes for the sample-level and algorithm-level approaches are described, respectively. A simulation case study of Tennessee Eastman (TE) process is conducted to evaluate the proposed fault diagnosis approaches.

Study of diesel fuel desulfurization by adsorption

Abstract: Removal of sulfur from diesel fuel by adsorption on a commercial activated carbon and 13X type zeolite was studied in a batch adsorber. Kinetic characterization of the adsorption process was performed applying Lagergren's pseudo-first order, pseudo-second order and intraparticle diffusion models using data collected during experiments carried out to determine the sulfur adsorption dependency on time. The experiments investigating adsorption efficiency regarding initial sulfur concentration were also performed and the results were fitted to Langmuir and Freundlich isotherms, respectively. Activated carbon Norit SXRO PLUS was found to have much better adsorption characteristics. The process of sulfur adsorption on the fore mentioned activated carbon was further studied by statistically analyzing data collected during experiments which were carried out according to three-factor two-level factorial design. Statistical analysis involved the calculation of effects of individual parameters and their interactions on sulfur adsorption and the development of statistical models of the process.

DEM simulation of particle mixing in flat-bottom spout-fluid bed

Abstract: The particle mixing mechanism affects the rate of the process and the achievable homogeneity. This paper presents a numerical study of the particle motion and mixing in flat-bottom spout-fluid bed. In the numerical model, the particle motion is modeled by discrete element method (DEM) and the gas motion is modeled by κ–ɛ two-equation turbulent model. Validation with experiments is first carried out by comparing solid flow pattern and bed pressure drop at various gas velocities. Then, particle velocities, obtained from DEM simulations, are presented to reveal the mixing mechanisms. On the basic, the dependence of mixing index on the time and the effect of gas velocity on mixing and dead zone (stagnant solid) are discussed, respectively. The results indicate that the spouting gas is the driving force for the formation of particle circulation roll, resulting in the mixing. The convective mixing caused by the motion of circulation roll, shear mixing induced by the relative move of circulation rolls and diffusive mixing generated by random walk of particle among circulation rolls are three different mixing mechanisms in spout-fluid bed. The increase of spouting gas velocity promotes the convective and shear mixing. While increasing the fluidizing gas velocity improves significantly the convective mixing and but weakens the shear mixing. Both of them yield a reduction in the dead zone.

Gastroretentive floating sterculia–alginate beads for use in antiulcer drug delivery

Abstract: To improve the bioavailability and therapeutic efficacy of the drugs used for the diseases associated with the stomach, the retention of drug delivery systems in the stomach for longer time is requred. Therefore, in the present study, an attempt has been made to synthesize gastro-retentive floating drug delivery system by simultaneously ionotropic gelation of alginate and sterculia gum by using CaCl 2 as crosslinker. The beads thus formed have been characterized by scanning electron micrographs (SEMs), electron dispersion X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) analysis. The swelling of beads has been carried out as a function of various reaction parameters and pH of the swelling media. In addition, in vitro release dynamics of anti-ulcer model drug pantoprazole from drug loaded beads in different release media has been carried out for the evaluation of the drug release mechanism and diffusion coefficients. Release of drug from beads occurred through Fickian type diffusion mechanism.

Acid hydrolysis of olive tree biomass

Abstract: Olive tree cultivation generates a great amount of biomass residues which have no industrial application. Pruning residues are usually grindered or burnt on fields, causing economical costs and environmental concerns. An alternative issue for these renewable sugar-containing feedstocks may be the conversion into fuel ethanol by hydrolysis and fermentation. As a first step in the bioconversion process, the acid hydrolysis of olive tree pruning is studied and a mathematical model predicting both fiber content and sugar release as a function of operation variables is proposed. Sulphuric acid concentration in the range 0–32% (w/w), process temperature between 60 and 90 °C and hydrolysis time from 0 to 240 min were used as hydrolysis conditions. The process was modelled by first-order reaction kinetics. The apparent kinetic constant relating acid concentration to fiber hydrolysis and sugar release shows a potential dependence; on the other hand, an Arrhenius-type equation has enabled the evaluation of activation energy values of 26.4 and 25.9 kJ/mol for fiber hydrolysis and sugar generation, respectively.

Among the trends for a modern chemical engineering, the third paradigm: The time and length multiscale approach as an efficient tool for process intensification and product design and engineering

Abstract: To respond to the changing needs of the chemical and related industries in order both to meet today's economy demands and to remain competitive in global trade, a modern chemical engineering is vital to satisfy both the market requirements for specific nano and microscale end-use properties of products, and the social and environmental constraints of industrial meso and macroscale processes. Thus an integrated system approach of complex multidisciplinary, non-linear, non-equilibrium processes and phenomena occurring on different length and time scales of the supply chain is required. That is, a good understanding of how phenomena at a smaller length-scale relates to properties and behaviour at a longer length-scale is necessary (from the molecular-scale to the production-scales). This has been defined as the triplet “molecular Processes-Product-Process (3PE)” integrated multiscale approach of chemical engineering. Indeed a modern chemical engineering can be summarized by four main objectives: (1) Increase productivity and selectivity through intensification of intelligent operations and a multiscale approach to processes control: nano and micro-tailoring of materials with controlled structure. (2) Design novel equipment based on scientific principles and new production methods: process intensification using multifunctional reactors and micro-engineering for micro structured equipment. (3) Manufacturing end-use properties to synthesize structured products, combining several functions required by the customer with a special emphasis on complex fluids and solid technology, necessating molecular modeling, polymorph prediction and sensor development. (4) Implement multiscale application of computational chemical engineering modeling and simulation to real-life situations from the molecular-scale to the production-scale, e.g., in order to understand how phenomena at a smaller length-scale relate to properties and behaviour at a longer length-scale. The presentation will emphasize the 3PE multiscale approach of chemical engineering for investigations in the previous objectives and on its success due to the today's considerable progress in the use of scientific instrumentation, in modeling, simulation and computer-aided tools, and in the systematic design methods.

MINLP optimization of mechanical draft counter flow wet-cooling towers

Abstract: In this paper, the problem of the optimal design of mechanical draft counter flow cooling towers that meets a set of specified constraints is formulated as a mixed-integer nonlinear programming (MINLP) problem. The Merkel's method is used to specify the characteristic dimensions of cooling towers, together with empirical correlations for the loss and overall mass transfer coefficients in the packing region of the tower. Water-to-air mass ratio, water mass flow rate, water inlet and outlet temperatures, operational temperature approach, type of packing, type of draft, height and area of the tower packing, total pressure drop of air flow, power consumption of the fan, and water consumption provide the set of optimization variables. The MINLP problem is formulated so as to minimize the total annual cost of the cooling tower. The performance of the proposed procedure is shown with the solution of six examples.

Energy requirements and economic analysis of a full-scale microbial flocculation system for microalgal harvesting

Abstract: Certain strains of microalgae have high lipid yields and appear to be good choices for the production of biodiesel, however, one of the major difficulties is the lack of a large-scale cost effective harvesting technique. Microbial flocculation has the potential to provide a solution without the use of contaminating metallic ions such as Al 3+ . However, such flocculation would require the mixing of mega- or even giga-litres of microalgal culture on a daily basis and therefore it is important to estimate the energy required. By incorporating a baffled hydraulic flocculator into a proposed large scale system that was designed on the basis of laboratory data, the mixing energy required for the flocculation is estimated to be equivalent to 0.893 kWh per 10 3 kg of dry mass flocculated, the overall cost of the process is A$ 0.13 m −3 of the culture medium and the net footprint area of the flocculating system is 0.7% of the proposed 1 km 2 high rate algal pond.

CFD modelling of liquid–liquid multiphase microstructured reactor: Slug flow generation

Abstract: Microreactor technology, an important method of process intensification, offers numerous potential benefits for the process industries. Fluid–fluid reactions with mass transfer limitations have already been advantageously carried out in small-scale geometries. In liquid–liquid microstructured reactors (MSR), alternating uniform slugs of the twophase reaction mixture exhibit well-defined interfacial mass transfer areas and flow patterns. The improved control of highly exothermic and hazardous reactions is also of technical relevance for large-scale production reactors. Two basic mass transfer mechanisms arise: convection within the individual liquid slugs and diffusion between adjacent slugs. The slug size in liquid–liquid MSR defines the interfacial area available for mass transfer and thus the performance of the reactor. There are two possibilities in a slug flow MSR depending on the interaction of the liquids with the solid wall material: a dispersed phase flow in the form of an enclosed slug in the continuous phase (with film—complete wetting of the continuous phase) and an alternate flow of two liquids (without film—partial wetting of the continuous phase). In the present work, a computational fluid dynamics (CFD) methodology is developed to simulate the slug flow in the MSR for both types of flow systems. The results were validated with the experimental results of Tice et al. (J.D. Tice, A.D. Lyon and R.F. Ismagilov, Effects of viscosity on droplet formation and mixing in microfluidic channels, Analytica Chimica Acta 507 (1) (2004), pp. 73–77.).

Scale-up and design of a continuous microwave treatment system for the processing of oil-contaminated drill cuttings

Abstract: A continuous microwave treatment system has been developed for the remediation of contaminated drill cuttings at pilot scale. Using the mechanisms of oil removal as a basis, a design was produced using electromagnetic simulations to find the optimum microwave applicator geometry which yielded the most favourable power density distribution. Bulk materials handling and process engineering principles were systematically integrated with the electromagnetic design to produce a system capable of treating 500 kg/h of material. The effects of the key design parameters are simulated, and a number of the simulations are verified with experimental data. It is shown that the environmental discharge threshold of 1% oil can be achieved in continuous operation, and the sensitivity of the system to changing feedstock properties is also highlighted. The parity between the simulations and experimental results in this paper highlights the necessity of electromagnetic modelling in the design and scale-up microwave processing equipment.

Prediction of solute solubility in supercritical carbon dioxide: A novel semi-empirical model

Abstract: Solubility data of solutes in supercritical fluids (SCF) are crucial for designing extraction processes, such as extraction using SCF or micronization of drug powders. A new empirical equation is proposed to correlate solute solubility in supercritical carbon dioxide (SC CO2) with temperature, pressure and density of pure SC CO2. The proposed equation is ln y2 = J0 + J1P2 + J2T2 + J3 ln ρ where y2 is the mole fraction solubility of the solute in the supercritical phase, J0 − J3 are the model constants calculated by least squares method, P (bar) is the applied pressure, T is temperature (K) and ρ is the density of pure SC CO2. The accuracy of the proposed model and three other empirical equations employing P, T and ρ variables was evaluated using 16 published solubility data sets by calculating the average of absolute relative deviation (AARD). The mean AARD for the proposed model is 7.46 (±4.54) %, which is an acceptable error when compared with the experimental uncertainty. The AARD values for other equations were 11.70 (±23.10), 6.895 (± 3.81) and 6.39 (±6.41). The mean AARD of the new equation is significantly lower than that obtained from Chrastil et al. model and has the same accuracy as compared with Bartle et al. and Mendez-Santiago–Teja model. The proposed model presents more accurate correlation for solubility data in SC CO2. It can be employed to speed up the process of SCF applications in industry.

Optimization of crude distillation system using aspen plus: Effect of binary feed selection on grass-root design

Abstract: With an objective to supplement guidelines available as general rules of thumb for the grass-root design of crude distillation unit (CDU) using binary crude mixtures, this work presents the optimization of crude distillation unit using commercial Aspen Plus software. The crude distillation unit constituted a pre-flash tower (PF), an atmospheric distillation unit (ADU) and a vacuum distillation unit (VDU). Optimization model constituted a rigorous simulation model supplemented with suitable objective functions with and without product flow rate constraints. Three different feed stocks namely Bombay crude, Araby crude and Nigeria crude were considered in this work along with various binary combinations of these crudes. The objective function considered was profit function (subjected to maximization) for cases without product flow rate constraints and raw-materials and energy cost (subjected to minimization) for cases with product flow rate constraints. Parametric study pertaining to feed selection and composition has been conducted in this work to further benefit refinery planning and scheduling. Simulation study inferred that the product flow rate constraints sensitively affect atmospheric distillation column diameter and crude feed flow rate calculations. Based on all simulation studies, a generalized inference confirms that it is difficult to judge upon the quality of the solutions obtained as far as their global optimality is concerned.

Multivariate statistical process monitoring using an improved independent component analysis

Abstract: An approach for multivariate statistical monitoring based on kernel independent component analysis (Kernel ICA) is presented. Different from the recently developed KICA which means kernel principal component analysis (KPCA) plus independent component analysis (ICA), Kernel ICA is an improvement of ICA and uses contrast functions based on canonical correlations in a reproducing kernel Hilbert space. The basic idea is to use Kernel ICA to extract independent components and later to provide enhanced monitoring of multivariate processes. I2 (the sum of the squared independent scores) and squared prediction error (SPE) are adopted as statistical quantities. Besides, kernel density estimation (KDE) is described to calculate the confidence limits. The proposed monitoring method is applied to fault detection in the simulation benchmark of the wastewater treatment process and the Tennessee Eastman process, the simulation results clearly show the advantages of Kernel ICA monitoring in comparison to ICA and KICA monitoring.

Design of a Eutectic Freeze Crystallization process for multicomponent waste water stream

Abstract: Complex, hypersaline brines originating from the mining and extractive metallurgical industries have the potential to be treated using Eutectic Freeze Crystallization (EFC). Although EFC has been shown to be effective in separating a single salt and water, it has yet to be applied to the complex hypersaline brines that are typical of reverse osmosis retentates in South Africa. This paper focuses on the application of EFC for the purification of a typical brine containing high levels of sodium, chlorine, sulphate and ammonia that cannot be achieved with other separation techniques. The presence of ammonia prevents the application of membrane technology to treat the brine, leaving only cooling or evaporation as other possible options. Evaporation produces a mixed salt that requires further treatment. Modelling tools were applied to describe the phase behaviour of the complex saline systems under different process conditions and were experimentally validated. The results showed that Eutectic Freeze Crystallization could be used to selectively recover the sodium as a sodium sulphate salt. The simulation tools were especially useful in the design and optimisation of the process.

Artificial neural network-based modeling of pressure drop coefficient for cyclone separators

Abstract: In order to build the complex relationships between cyclone pressure drop coefficient (PDC) and geometrical dimensions, representative artificial neural networks (ANNs), including back propagation neural network (BPNN), radial basic functions neural network (RBFNN) and generalized regression neural network (GRNN), are developed and employed to model PDC for cyclone separators. The optimal parameters for ANNs are configured by a dynamically optimized search technique with cross-validation. According to predicted accuracy of PDC, performance of configured ANN models is compared and evaluated. It is found that, all ANN models can successfully produce the approximate results for training sample. Further, the RBFNN provides the higher generalization performance than the BPNN and GRNN as well as the conventional PDC models, with the mean squared error of 5.84 × 10−4 and CPU time of 120.15 s. The result also demonstrates that ANN can offer an alternative technique to model cyclone pressure drop.

Isolation of hemicelluloses by ultrafiltration of thermomechanical pulp mill process water-Influence of operating conditions

Abstract: Hemicelluloses could be used to replace fossil-based materials in several high-value-added products. Today, vast amounts of hemicelluloses are discharged from pulp mills all over the world as waste, but these could be isolated by membrane filtration, and utilized in various applications. In this study, the hemicellulose galactoglucomannan was isolated from process water from a thermomechanical pulp mill using ultrafiltration. The retention of hemicelluloses and lignin, and the flux and fouling of three ultrafiltration membranes (ETNA01, ETNA10 and UFX5) were studied at various operating conditions. One of the membranes (UFX5) was found to have a high hemicellulose retention (above 90%) independent of flux and pressure. With the ETNA01 membrane it was impossible to combine a high flux with high hemicellulose retention, while with the ETNA10 membrane the hemicellulose retention could be increased above 90% by running at transmembrane pressures above the critical flux. The UFX5 membrane could be used at the temperature of the process water in the pulp mill (75-85 degrees C), while the ETNA10 membrane could only withstand temperatures below 60 degrees C, increasing the cost due to the need to cool the process water. However, the susceptibility of UFX5 to fouling was much greater than for ETNA10, which would increase the cleaning cost of the UFX5 membrane. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. (Less)

Interval based MINLP superstructure synthesis of heat exchanger networks for multi-period operations

Abstract: The interval based MINLP superstructure (IBMS) presented by Isafiade and Fraser (2008) is applied to the design of heat exchanger networks which can handle multiple period of operations. In multi-period operations, parameters such as supply temperature, target temperature and the flowrates of streams can vary over a specified range. In this paper the IBMS is formulated for multi-period operations involving unequal period durations. In order to ensure that each exchanger connecting the same pair of streams in two or more periods is able to transfer heat in such streams for all the periods, the maximum area per period approach of Verheyen and Zhang (2006) is used in the objective function. This method helps to simplify the model. The new method is applied to three examples from the literature.

Supersaturation tracking for the development, optimization and control of crystallization processes

Abstract: Supersaturation is the key driving force in crystallization operations, determining nucleation and growth kinetics, and heavily influencing physical mechanisms such as agglomeration. Therefore, knowledge of the bulk supersaturation during crystallization can greatly enhance process understanding and optimization.In this paper, a method which facilitates the calibration-free use of in situ ATR-FTIR for crystallization development and control is presented. This methodology uses solute-specific ATR-FTIR absorption peak heights to describe solute solubility and dissolved concentration and, in turn, supersaturation, for the optimization of cooling crystallizations of an active pharmaceutical ingredient (API) and benzoic acid. The approach presented facilitates rapid process understanding, design and optimization. Specifically, the potential to significantly reduce cycle time for both systems studies is demonstrated. In addition, the potential of the method to form the basis of a process control strategy for batch crystallization is successfully demonstrated. © 2010 The Institution of Chemical Engineers.

Induction time studies of calcium carbonate in ethylene glycol and water

Abstract: Induction time for precipitation of calcium carbonate precipitated in mono ethylene glycol and water has been studied by conductivity measurements at ethylene glycol concentrations of 0–90 wt% and temperatures from 25 to 80 °C. The supersaturation ratios, S, were in the range of 3–10. The effect of the solvent was separated from the effect of the supersaturation and temperature. Increasing the concentration of ethylene glycol prolongs the induction times for precipitation of CaCO3 considerably although the supersaturation actually increases, especially at lower temperatures. It was shown that this effect cannot be explained by the change in the interfacial tension. Induction time studies in seeded and unseeded experiments were performed in order to separate changes in the nucleation rate from the impact of the growth time in the varying solvent compositions. The results show that crystal growth is retarded, causing the increased induction time in ethylene glycol containing solutions, and hence that the nucleation rate is actually promoted by ethylene glycol. The nucleation rates determined by measured particle numbers and induction times from unseeded experiments were underestimated for the same reason, thereby illustrating the complexity of nucleation rate investigations in mixed solvents.

Numerical simulations of airflow and droplet transport in a wave-plate mist eliminator

Abstract: In this paper, the droplet transport and deposition in the turbulent airflow inside a wave-plate mist eliminator was studied using an Eulerian–Lagrangian computational method The Reynolds Stress Transport Model (RSTM) with standard wall functions and with enhanced wall treatment was used for simulating the airflow field A computer code for solving the Reynolds-averaged Navier–Stokes (RANS) equations in conjunction with the RSTM on two-dimensional collocated unstructured meshes was developed For droplet trajectory analysis, another computer code was developed that accounts for the drag and lift forces action on the droplets The Eddy Interaction Model (EIM) was used to model the droplet dispersion in turbulent airflow The gas flow code was validated by comparing the computational model results for a fully developed asymmetric channel turbulent flow with the experimental data Then the airflow and droplet trajectory analysis were performed for a mist eliminator with smooth walls and the resultant removal efficiency curves were evaluated and compared with the available experimental data The results showed that the enhanced wall treatment improved the predictions of the droplet removal efficiency especially for small droplets in which the removal efficiency was lower than 50% On the other hand, the Reynolds Stress Transport Model (RSTM) with standard wall functions cannot predict the removal efficiency correctly, especially for low gas velocities