Showing papers in "Chemical Engineering and Processing in 2005"

Electro-coagulation of reactive textile dyes and textile wastewater

Abstract: Electro-coagulation of a blue reactive dye (Drimarene K2LR CDG Blue) solution has been optimised by experimental design and surface response analysis in terms of colour removal and chemical oxygen demand (COD) decrease. The optimal conditions (pH, current density, reaction time) have then been applied to other reactive dyes solutions as well as synthetic and real textile wastewater samples. The biodegradability before and after electro-coagulation has been assessed by short-term respirometry and is increased by this type of treatment.

Experimental investigation and modeling of gasification of sewage sludge in the circulating fluidized bed

Abstract: Experiments of sewage sludge gasification were performed in a circulating fluidized bed of pilot plant scale (15 m height, 01 m id) For the examination of the influence of the air ratio, gasification temperature, feeding height and fluidization velocity several screening tests were conducted To understand better the results from the screening experiments, axial profiles of the gas composition were measured As the most influencing factor for the heating value of the gasification gas the air ratio was found Additionally, a low feeding height is recommended for good gas quality While feeding into the lower dense zone of a circulating fluidized bed (CFB), mixing of the fuel particles is better With low feeding ports, high velocities are attainable and therefore high fuel throughput can be achieved In a second step a model of the CFB gasifier was developed The fluid dynamics of a CFB were included as well as the complete reaction network of gasification With the measured axial profiles of gas composition during pyrolysis, and gasification with air and a CO2/N2-mixture kinetic rate expressions for sewage sludge gasification under fluidized-bed conditions were determined which may now be used for reactor scale-up calculations

Challenges in biotechnology production—generic processes and process optimization for monoclonal antibodies

Abstract: In manufacturing of biological drugs, product quality is defined by the process (e.g. equipment, sequence of unit operations, operation parameters) because no complete analysis of these complex molecules is possible. Therefore, the process is unavoidably fixed after the first clinical lot production in a pilot plant. There is no further process optimization option parallel to production, which, in the case of small molecule productions, allows further process optimization. Process development times will not increase in future due to increasing pressure on time to market. In addition to that, no change in paradigm seems possible, as complete analysis of complex biomolecules comparable to small synthetic drugs is not seen in near future. As a consequences the challenge is to establish generic processes for different drug classes and to find consistent process development methods, which allow a reliable prediction of large-scale production. Generic in this sense is not understood as a fixed sequence of unit operations with a certain set of generic process parameters. Here, generic means that a typical arrangement of unit operations is set up in an efficient sequence to fulfil the separation task.

Air classification of solid particles: a review

Abstract: An overview is given of modern air classification devices, their operation principles, features and parameters, as cut size, cleanness and recovery. We outline the separation zones common to existing classifiers. In practice, various gravitational and centrifugal classifiers are employed, including those with vertical and horizontal air streams, cascade classifiers, fluidized bed separators, inertial, vortex, rotor classifiers, etc. Choice of the classifier type and designs is dictated by the technological requirements (throughput, cleanness, etc.) and the properties of materials to be classified. Advantages and limitations of the classifiers and basic trends in their development are considered.

Performance evaluation of microporous inorganic membranes in the dehydration of industrial solvents

Abstract: The separation potential of five different commercial tubular inorganic membranes consisting of A-, T- and Y-type zeolites from Mitsui and microporous silica from ECN and Pervatech has been examined in more than 30 dehydration applications. These separations include alcohols, glycols, carboxylic acids, esters, ethers, ketones, amines, nitriles, and halogenated hydrocarbons. The membranes combine excellent permeate flux with very good selectivity up to values of several thousand. Water permeances valuing between 10 and 20 kg/m2 h bar partial pressure difference represent a new dimension in solvent dehydration. The pervaporation separation index (PSI) of standard polymeric membranes is around 100 while for inorganic materials index values of up to 50,000 are achieved. The performance ranking of the membranes in term of selectivity decreases in the sequence zeolite A > zeolite T > Pervatech silica > ECN silica. Regarding the flux the order is reversed with ECN silica > Pervatech silica > zeolite A > zeolite T. The reason for this behavior is founded in the different membrane structure and adsorption characteristics. The separation layer of the zeolite membranes is at least 10 μm thick whereas the thickness of the silica membranes is below 200 nm. On the other hand, zeolite crystals have a strictly defined pore size allowing a sharper separation in comparison to the amorphous silica with a pore size distribution. The water adsorption on zeolites follows a Langmuir isotherm while for silica it is in the Henry region. Thus, concentration polarization effects are more severe for the latter material and viscosity of the systems has a major impact on the transport resistances in the boundary layer. These conclusions were confirmed by a comparison of single component to mixture permeation data. A simple transport model based on normalized permeate flux is used to calculate the influence of operation parameters, such as concentration, temperature and permeate pressure, on the separation characteristic from a single measurement. Water can be separated with high efficiency from complex solvent and reaction mixtures including methanol by A-type zeolite membranes. According to process needs the cut-off can be shifted to the separation of both water and methanol by use of a Y-type zeolite or amorphous silica membrane. The chemical stability of all tested membranes in aprotic solvents is excellent while their acid and base resistance is limited. For the A-type zeolite an acidic environment has to be avoided by all means, whereas the T- and Y-type zeolite can withstand a lower pH to some extent. Standard silica is stable down to a pH value of 3. Durability can be further improved by chemical modifications of the sol. In basic environment, the γ-alumina support is affected at a pH greater than 11. Membranes show no signs of thermal degradation up to 150 °C. In pervaporation, micro-cracks have been detected at high permeation rates above 30 kg/m2 h. A temperature difference is necessary to transfer the heat for the evaporation of the permeating components from feed to permeate side. Hence, thermal stress is a likely cause for the observed destruction of the membrane. Tubular membranes can withstand normal operation pressures of up to 30 bar without any problem. Contact of the membrane with solid particles should be avoided to guarantee mechanical stability. This can be achieved by introducing a feed filter in the range of 10–100 μm into the feed stream.

Microwave-assisted extraction kinetics of terpenes from caraway seeds

Abstract: The process conditions during the extraction of carvone and limonene from caraway seed (Carum carvi L.) with microwave-assisted extraction have been studied with respect to microwave power, radiation dose and extraction time in order to obtain the secondary metabolites selectively. Using classical solid–liquid extraction, limonene, carvone and fatty oils in both the raw material and the residual matrix material were extracted. Yields of limonene, carvone and total oil (C16 ,C 18) were determined by GC and GC/MS analysis for both extracts. The effects of microwaves on cell walls and cells destruction could be seen on SEM micrographs. © 2005 Published by Elsevier B.V.

Food powder handling and processing: Industry problems, knowledge barriers and research opportunities

Abstract: This paper highlights some of the outcomes from a EU Accompanying Measure focussing on food powders. The main goals of the work were to outline the major industrial problems, knowledge barriers, and research challenges and opportunities in relation to food powders, and to promote the creation of a sustainable network of excellence in the area of food powders. Food powders are powders first and foremost, thus many of the research challenges and opportunities are similar to handling and processing of other powders. As a result, much can be learned from other industries that deal with powders. What makes food powders different from many other powders is their composition, which is mainly of biological origin, and that they are eventually consumed by people and animals. Consequently, stability of food ingredient functionality and prevention of contamination are major issues right through from powder production to final application of the powder, which is usually in the form of a wet formulation.

Numerical study of flow field in cyclones of different height

Abstract: This paper presents the results of numerical simulation of flow pattern in cyclones of different height, which have recently been tested for separation efficiency without any information about flow field. Results show that the difference between tangential velocity in the upper cylinder and in the lower cone of a certain cyclone is not significant, suggesting that reduced cross-section in the cone does not lead to tangential velocity acceleration. Tangential velocity in cyclones of different height is quite different. Tangential velocity decreases with increasing cyclone height, and this should be responsible for the lower separation efficiency observed in long cyclones. However, if there exists considerable shortcut flow at the entrance of the gas exit tube, the higher tangential velocity will not give rise to the higher separation efficiency, for example, in the case of the shortest cyclone covered in this study, whose gas exit tube protrudes into the conical part.

A comparison of homogeneous and heterogeneous dynamic models for industrial methanol reactors in the presence of catalyst deactivation

Abstract: Dynamic simulation of a Lurgi type industrial methanol reactor has been studied in the presence of long term catalyst deactivation. The performance of the reactor was investigated using two different dynamic models: (a) a simple homogeneous model, and (b) a heterogeneous model. The models were validated against measured daily process data of a methanol plant recorded for a period of four years. Good agreements were achieved and both models were found to predict almost identical results under industrial operating conditions. The high velocity of the reactant stream was found to be the most important reason for this phenomenon. The simple model represents a useful tool for dynamic simulation, optimization and control of methanol synthesis. Introducing such a simple model reduces the number of typical states to half, and this in itself will significantly reduce the level of computation in the model base estimators.

Control of aggregation in production and handling of nanoparticles

Abstract: In product engineering of particulate systems, the property function relates the dispersity to the product properties, whereas the process function shows how to produce the required dispersity. These principles are applied to the production of nanoparticles. Nanoparticles are controlled by surface forces. Due to their high mobility nanoparticles are unstable and may coagulate rapidly if the particles are not stabilized. Stabilization is achieved by tailoring the particulate surfaces, e.g. through repulsive double layer forces. Macroscopic properties are thus controlled by microscopic control of the interfaces, i.e. we bridge the gap between the molecular level and material properties. These principles are generally valid and are thus applied to precipitation and to nanomilling in stirred ball mills. The mean particle size in precipitation can be controlled by either the mixing intensity or the surface charge density of the particles. In stirred media mills oxide particles as small as 10 nm can be achieved by stabilizing the particles appropriately.

Defluidization modelling of pyrolysis of plastics in a conical spouted bed reactor

Abstract: Thermal pyrolysis for upgrading plastic wastes is one of the better methods for recycling plastics in terms of its perspectives for industrial implementation. The conical spouted bed reactor proposed in this paper may be a solution to the problems arising in fluidized beds handling sticky solids, as particle agglomeration phenomena, which can cause defluidization. In order to avoid defluidization, experiments have been carried out in batch mode in the temperature range of 450–600 °C. A good performance of the reactor is proven under the conditions of maximum particle stickiness.

Separation characteristics of acetic acid–water mixtures by pervaporation using poly(vinyl alcohol) membranes modified with malic acid

Abstract: The pervaporation separation of acetic acid–water mixture was carried out using poly(vinyl alcohol) (PVA) membranes modified using malic acid (MA). The effects of PVA/MA ratio, membrane thickness, operating temperature, feed concentration on the transmembrane permeation rate and separation factor were investigated. Optimum PVA/MA ratio was determined as 85/15 (v/v) for 20 wt.% acetic acid mixtures at 40 °C. The influence of membrane thickness on the separation factor and the permeation rate was studied in the range of 50–100 μm at constant acetic acid concentration. It was observed that separation factor was independent of membrane thickness below a limit value of 70 μm and permeation rate was found to be inversely proportional to the membrane thickness. The prepared membranes were also tested to separate various compositions of acetic acid–water mixtures with 20–90 wt.% acetic acid content at 40 °C. Typically, separation factor of 670 and total permeation rate of 4.8 × 10 −2 kg/m 2 h was obtained for 90 wt.% acetic acid concentration in the feed. Arrhenius-type relation and activation energy of 41 kJ/mol was also found for acetic acid–water mixtures.

Separation of acetic acid–water mixtures through acrylonitrile grafted poly(vinyl alcohol) membranes by pervaporation

Abstract: The pervaporation separation of acetic acid–water mixtures was performed over a range of 10–90 wt.% acetic acid in the feed at temperatures ranging 25–50 °C using acrylonitrile (AN) grafted poly(vinyl alcohol) (PVA) membranes. The permeation and separation characteristics of PVA-g-AN membranes were studied as a function of membrane thickness, feed composition, operating temperature and pressure. When the downstream pressure increased permeation rate increased with decreasing separation factor and at high acetic acid concentrations PVA-g-AN membranes shows grater tendency for the separation of acetic acid–water mixtures. Depending on the membrane thickness, feed composition and temperature PVA-g-AN membranes gave separation factors 2.3–14 and permeation rates 0.18–1.17 kg/m 2 h. It was also determined that PVA-g-AN membranes were found to have lower permeation rate and grater separation factors than PVA membranes.

Rate-based modelling and simulation of reactive separations in gas/vapour–liquid systems

Abstract: In this paper, rigorous modelling of reactive separations is considered. Focus is set to gas/vapour–liquid systems, namely reactive distillation and reactive stripping. The paper describes the modelling framework and the process simulator PROFILER developed within the European research project Intelligent Column Internals for Reactive Separations (INTINT). The application is illustrated by two heterogeneously catalysed esterification processes: the synthesis of ethyl acetate from ethanol and acetic acid via reactive distillation and the synthesis of octyl hexanoate from octanol and hexanoic acid via reactive stripping. For both processes, the simulation results are in satisfactory agreement with the experimental data. A comparison of different model complexities is presented.

Mechanism of mass transfer from bubbles in dispersions: Part II: Mass transfer coefficients in stirred gas–liquid reactor and bubble column

Abstract: Experimental data on the average mass transfer liquid film coefficient ( k L ) in an aerated tank stirred by Rushton turbine and in bubble column are presented. Liquid media were used as 0.8 M sodium sulphite solution, pure or with the addition of Sokrat 44 (copolymer of acrylonitrile and acrylic acid) or short-fiber carboxymethylcellulose (CMC) for the Newtonian and long-fiber CMC for the non-Newtonian viscosity enhancement and ocenol ( cis -9-octadecen-1-ol) or polyethylenglycol (PEG) 1000 for surface tension change. Volumetric mass transfer coefficient ( k L a ) and specific interfacial area ( a ) were measured by the Danckwerts’ plot method. Coefficients k L measured by pure oxygen absorption in pure sulphite solution and Newtonian viscous liquids are well fitted by the “eddy” model in the form of k L = 0.448 ( e v / ρ ) 0.25 ( D / v ) 0.5 with a mean deviation of 20%. Surface-active agents (ocenol and PEG) and non-Newtonian additive (long-fiber CMC) reduced k L value significantly but their effect was not described satisfactorily neither by surface tension nor by surface pressure. It is shown that the decisive quantity to correlate k L in the stirred tank and bubble column is power dissipated in the liquid phase rather than the bubble diameter and the slip velocity. Absorption of air did not yield correct k L data, which did not depend on or slightly decreased with increasing power. This is due to the application of an improper gas phase mixing model for absorption data evaluation.

On-line dynamic optimization and control strategy for improving the performance of batch reactors

Abstract: Since batch reactors are generally applied to produce a wide variety of specialty products, there is a great deal of interest to enhance batch operation to achieve high quality and purity product while minimizing the conversion of undesired by-product. The use of process optimization in the control of batch reactors presents a useful tool for operating batch reactors efficiently and optimally. In this work, we develop an approach, based on an on-line dynamic optimization strategy, to modify optimal temperature set point profile for batch reactors. Two different optimization problems concerning batch operation: maximization of product concentration and minimization of batch time, are formulated and solved using a sequential optimization approach. An Extended Kalman Filter (EKF) is incorporated into the proposed approach in order to update current states from their delayed measurement and to estimate unmeasurable state variables. A nonlinear model-based controller: generic model control algorithm (GMC) is applied to drive the temperature of the batch reactor to follow the desired profile. A batch reactor with complex exothermic reaction scheme is used to demonstrate the effectiveness of the proposed approach. The simulation results indicate that with the proposed strategy, large improvement in batch reactor performance, in term of the amount of a desired product and batch operation time, can be achieved compared to the method where the optimal temperature set point is pre-determined. This paper gathers and integrates efficient well-known methodologies such as EKF, GMC and on-line optimization together, resulting in an applicable, reliable and robust control technique for batch reactors.

Solving large-scale retrofit heat exchanger network synthesis problems with mathematical optimization methods

Abstract: Heat exchanger network optimization is a standard problem in process design. Various mathematical models and heuristics have been developed to help the designer in constructing the network. Different target procedures, like the pinch analysis, are widely used both in academia and industry. Another approach to find cost optimal network structures is to use mathematical programming methods. The advantage with mathematical programming methods is that a rigorous optimization of the structure, sizes of heat exchangers and utility usage can be carried out, whereas the designer makes these decisions if purely pinch-based tools are used. Even if much effort has been put on research within this area, many of the mathematical models consider only grassroot design, whereas most practical cases today seem to be retrofit situations. In addition, these models are likely to be either rigorous but not solvable for bigger (large-scale, real life examples) or deficient and solvable for large-scale problems. This paper takes an attempt to address these problems simultaneously and to develop a rigorous optimization framework based on both a genetic algorithm and a deterministic MINLP-approach and to present an extended model for large-scale retrofit heat exchanger network design problems.

Cooling and seeding effect on supersaturation and final crystal size distribution (CSD) of ammonium sulphate in a batch crystallizer

Abstract: Different cooling policies (natural (NCP), linear (LCP), controlled (CCP), as well as a proposed cooling policy; impulse changes in natural cooling policy (IC-NCP)) and seeding policies (with two different mean seed size and various seed loadings) were employed to investigate the effect of cooling and seeding on the final CSD of ammonium sulphate grown in a batch-cooling crystallizer. The crystallizer was equipped with an on-line density meter for the estimation of supersaturation. By increasing the amount of the seeds, the supersaturation peak was reduced and a uni-modal final CSD was obtained, irrespective of the cooling policy. At high seed loading (Cs), greater than theoretical critical seed loading ( C s , c theo ) predicted by the seed chart, the cooling policy had no significant effect on the final CSD. However, at low Cs, controlled cooling policy was needed in order to ensure uni-modal and narrow final CSD with large mean size. With the help of a simple on-off control, the IC-NCP was applied to overcome the mathematical complexities associated with the controlled cooling policy. All CSD results of the IC-NCP mode were between the linear and controlled cooling policies, and closer to the controlled cooling profile.

Effect of cycling operations on an adsorbed natural gas storage

Abstract: Adsorbed natural gas (ANG) is an interesting opportunity for developing natural gas vehicles technology. In this case, adsorbents such as activated carbons are used to store natural gas at moderate pressure, 3.5 MPa, compared to the high-pressure (20 MPa) required for current compressed natural gas technology. Many studies are devoted to the elaboration of suitable adsorbent materials to optimise the methane storage capacity. Nevertheless, since natural gas (NG) is composed of about 95% of methane mixed with other components, an important deterioration of the storage performance is observed after successive cycles of an ANG system (filling and delivery). It is the result of adsorption of the other components present in NG that are mainly higher molecular-weight hydrocarbons, carbon dioxide and nitrogen. In the present study, the evolution of the storage capacity of a 2 l vessel cycled with NG is experimentally measured. As a function of the cycle number, the gas composition at the outlet of the ANG system is determined using gas chromatography analysis.

Effect of process parameters on bitumen emulsions

Abstract: Bitumen emulsification experiments have been carried out in a continuous pilot scale rotor-stator facility. The effects of the following process parameters, namely the temperature of the aqueous phase and bitumen, the rotor speed, the dispersed phase content, the bitumen grade and the emulsion flow rate were investigated. For each process parameter, the trends obtained for the Sauter diameter ( d 32 ) were compared with those available in the literature on emulsification. A new correlation to predict the droplet size was also proposed. It was shown that the droplet viscosity during emulsification, the rotation speed of the rotor and the dispersed phase content have a significant effect on the droplet size.

Correlation of the surface roughness of some industrial minerals with their wettability parameters

Abstract: This paper reports the relationships found between the surface roughness and wettability of some industrial minerals, namely, calcite, barite, talc and quartz. These minerals were ground in ball, rod and autogenous mills to produce samples for roughness and wettability tests. The surface roughness values of those minerals were determined on the pelleted surfaces of the ground powders by employing HB103-Surtronic 3 + surface roughness measuring instrument. The wettability characteristics ( γ c ) of these minerals ground in these different mills were also determined by flotation technique using the EMDEE MicroFLOT agitator. The experimental results revealed that the degree of hydrophobicity of these minerals increase with decreasing surface roughness and the particles having rougher surfaces lead to higher wettability independently from the mill type employed.

Activated carbon monolith of high thermal conductivity for adsorption processes improvement: Part A: Adsorption step

Abstract: Due to the low thermal conductivity of conventional beds of granular adsorbents (0.15–0.5 W m −1 K −1 ), performances of gas separation as well as gas storage processes are usually strongly inhibited by the induced adsorptive thermal effects. A monolithic composite of intensified overall thermal conductivity (10 W m −1 K −1 ), made of activated carbon (AC) in situ elaborated within a consolidated expanded natural graphite (CENG) matrix has been experimentally tested under both conditions of non-isothermal and non-adiabatic CO 2 adsorption. Heat transfer intensification and process performances improvements for the conventional saturation step is described in terms of induced local temperature increases, adsorbate breakthrough and sorption capacity. Experimental conductive packing achievements are compared to those of a conventional packed bed of commercial TA70 granular activated carbon.

Development of a new method for evaluating cyclone efficiency

Abstract: A new theoretical method for evaluating cyclone efficiency is developed based on the investigation of flow pattern, the critical particle size separation theory and the boundary layer separation theory. The radial particle concentration gradient, instead of the usually assumed uniform radial particle concentration within the cyclone, is considered in this mathematical model. The local particle concentration and the cyclone grade efficiency can be calculated on the base of a time-of-flight model in terms of the particle size distribution of the feed. The availability of the method is verified by comparison of the calculated grade efficiency with experimental data and theoretical counterparts in the literature.

Controlling dust emissions and explosion hazards in powder handling plants

Abstract: This paper presents results from investigations into quantifying and modelling the dust generation and air entrainment mechanisms that occur during free-falling streams of material. Emphasis is placed on the effects of drop height and product temperature. This information is important for the efficient design and operation of dust control systems, as well as minimising the risk and severity of dust explosions.

Simulation and optimisation of extractive distillation with water as solvent

Abstract: Acetone–methanol, methyl acetate–methanol and methanol–chloroform binary extractive single column distillation systems were simulated with the HYSYS software platform, to investigate the effects of solvent feed entry stages, solvent split stream feed and solvent condition on the separation. Water was used in all of the simulations as the solvent. The simulations supported data and findings from experimental column studies of the same systems. A rigorous simulation of the acetone–methanol system including a secondary stripping column and recycle loop was established to simulate an industrially relevant situation. This simulation enabled an economic evaluation of the process to be made. It was found for feed mixtures containing 25, 50 and 75 mol% methanol, the optimum reflux ratios were found to be 3.5, 3.5 and 4.2, respectively. As a consequence one column design could separate binary feed of varying composition between 25 and 75% methanol. The optimum number of ideal stages for the primary column for an equimolar binary feed was determined to be 73. When maintaining a constant solvent flow, the distance between the split feed entry stages had no effect on the economic potential (EP) of the system.

Synthesis of nano-sized particles from metal carbonates by the method of reversed mycelles

Abstract: The nano-sized particles of calcium carbonate and barium carbonate have specific characteristics. They are important materials for the industry. The main object of this investigation is to obtain nanoparticles of calcium carbonate and barium carbonate by chemical reaction carried out in microemulsion of water in oil. The nanoparticles obtained are spherical. Their sizes vary from 20 to 30 nm. The shape and size of particles are determinated by electron microscopy.

Pervaporation separation of ethyl acetate-ethanol binary mixtures using polydimethylsiloxane membranes

Abstract: Pervaporation separation of azeotrope forming ethyl acetate–ethanol mixtures was investigated by using a selfmade polydimethylsiloxane (PDMS) membrane. Sorption, desorption and pervaporation experiments for ethyl acetate–ethanol mixture with different concentrations were conducted at 30, 40 and 50 °C. The effect of process parameters such as feed concentration and temperature on flux and selectivity is discussed. Equilibrium curves are determined by vapor–liquid equilibrium calculations using Wilson equation. Data obtained by pervaporation are compared with the points determined from vapor–liquid equilibrium calculations. Experiments show that PDMS membrane is much more selective to ethyl acetate than ethanol. Increase in temperature yields higher total fluxes and lower selectivities of ethyl acetate. While the ethyl acetate concentrations increase from 20 to 94.5 wt.%, total fluxes and ethyl acetate selectivities change in the ranges of 756–8473 gr/m2h and 5.30–1.18, respectively.

Simulation and analysis of an industrial water desalination plant

Abstract: In this paper, an industrial medium-scale brackish water reverse osmosis plant based on Dow/FilmTec BW30-400 spiral-wound membrane modules was simulated and its performance investigated. Actual operating data is used to validate the computer package. The semi-rigorous model was found to represent the plant with good accuracy; the relative errors in the overall water recovery and salt rejection were 0.37 and 1.33%, respectively. The effects of the arrangement of membrane modules, the operating pressure and the feed flow rate on the performance of the plant were investigated. The single-stage configuration in which all pressure vessels are arranged in parallel was found to yield the best results in terms of the production rate, product quality and overall pressure drop across the feed channel. At low to moderate operating pressures and feed rates, increasing both operating variables will result in higher water production rates and salt rejection. However, high operating pressures lead to a deterioration of the quality of the product whereas high flow feed rates, contrary to one's expectation, result in a reduction in the production rate.

Modelling of the performance of industrial HDS reactors using a hybrid neural network approach

Abstract: A hybrid neural network model is presented for the simulation of the performance of industrial HDS reactors. This model can be used in estimating the catalyst deactivation rate and the impact of feed quality on catalyst activity. A deterministic mathematical code simulating the reactor performance for hydrodesulphurization and hydrogen consumption reactions was used. The deterministic code was coupled with a neural network used to correlate the evaluated kinetic parameters from the industrial data with feed quality and catalyst life time. The neural network is also used to predict the kinetic parameters needed for simulation from the feed quality and the catalyst time on stream. A part of the necessary kinetic parameters were obtained from kinetic experiments performed with the industrial catalyst and with representative feeds in a small scale reactor.

Neural network model-based on-line re-optimisation control of fed-batch processes using a modified iterative dynamic programming algorithm

Abstract: A strategy to overcome the problems of unknown disturbances and model-plant mismatches in fed-batch process optimal control through on-line re-optimisation is presented in this paper. To address the difficulty in developing detailed first-principle models and the time-consuming nature of optimisation based on nonlinear differential equations, neural network-based discrete-time models are used to model fed-batch processes from process operation data. Based on the neural network model, an “optimal” feeding policy is calculated off-line and its first stage is implemented to the batch process. At the end of the first stage, the process output variables are measured and any differences between the measured values and neural network model predicted values reflect the existence of unknown disturbances and model-plant mismatches. Due to the existence of unknown disturbances and model-plant mismatches, the off-line calculated “optimal” feeding policy for the remaining batch period may no longer be optimal and should be re-optimised. Based on the mid-batch process measurements, re-optimisation is carried out for the remaining batch period. A modified iterative dynamic programming algorithm based on discrete-time nonlinear models is developed to solve the on-line re-optimisation problem. The proposed scheme is illustrated on simulations of an ethanol fermentation process.