Iranian Journal of Chemical Engineering (IJChE)

Abstract Natural gas (NG) is one of the cleanest and safest sources of energy transmitted in a high pressure that must be reduced before entering City Gas Station (CGS). Identifying the effective parameters in creating the hazardous areas of CGS is essential to crisis and management. This study using PHAST version 7.11(created by DNV Company) conducted a consequence modelling in three scenarios at three CGS stations in Qazvin Province, by actual data including weather conditions, gas pressure and temperature. The main results for the modeling in all three scenarios were jet fire, flash fire, and explosion. Based on the modeling results, most flame length was obtained in Avaj station with 10 meters more than others. Most radiation levels were also in Avaj station in about 150 m downwind distance, which can be caused by the longer flame length in this station.
The results showed that in fire jet modeling, an increase in air temperature can lead to an increase in gas pressure and temperature, which in this study increased the flame length of 2 to 3 meters. However, the flame length and the hazardous area was higher during the day and summer. The use of PHAST modeling software can provide useful information including high-risk operational area, hazard area, high-risk time period (day, night and season) for the management team to respond to emergency situations in process industries. In addition, it is necessary to consider the combination of different operating parameters such as gas pressure and gas temperature with different weather conditions.

Abstract During the regeneration-coupling process, a novel, plantwide control framework for the diethyl oxalate production unit is provided in this article. This study's benefit is that it uses process improvements that do not possess the intricacy and expense of the two prior structures described by Zhu and Luyben. The development of a plantwide control structure for this process was completed in two stages. The efficiency of the process was initially evaluated using a straightforward structure, with the primary goal being to prevent the usage of concentration controllers and complex cascading mechanisms to the greatest extent feasible. Due to the presence of persistent variations in the process effluents in the original structure, it was determined that there were numerous disruptions present that influenced the response during both recycle streams in the process and created variations. During the second phase, using trial and error to implement a functional adjustment in the process, the minimum amount of recycle stream during which the variations were fully removed was separated from the process, and a novel feeding stream was inserted. Following implementing these modifications, it was discovered that the effluent variations of the process are fully removed with just two concentration controllers, and this structure demonstrates instantaneous plantwide control over receiving disturbances.

Abstract In this study, the inactivation performance of units against pathogenic and biotoxin threats in a water treatment plant is studied. The assessment of the units and hazards of the water treatment plant against each of threats is studied by the RAMCAP risk analysis. The experiments showed that the Aflatoxin was eliminated only by disinfection units. The reverse osmosis unit had high efficiency in removing Ricin, while the sand filtration had the lowest efficiency in removing biotoxins. The microbial analysis showed the total coliform bacteria, thermotolerant coliform and HPC index were increased slightly by increasing the incoming water's pH and turbidity, while their count were significantly reduced by increasing the free residual chlorine. Changes in the water temperature also had minor effects on microbial indexes. The RAMCAP analysis is used to reduce the vulnerability of units to conventional threats by determining

Abstract Simulation of a process and analysis of its resulting data in both dynamic and steady-state conditions are fundamental steps in understanding the process in order to design and efficient control of system as well as implementing operational cost reduction scheme. In the present paper, steady and unsteady state simulation of Amir Kabir1, 3 butadiene purification units has been done by using Aspen and Aspen Dynamic software together with the Peng- Robinson equation of state to investigate the system responses to the disturbances.
In the unsteady state simulation mode; the flow rates, pressure, temperature and level (FPTL) were controlled by Proportional-Integral-Derivative (PID) controllers in the unit. Finally, transient responses to changes such as feed temperature, feed flow rates, steam flow rates and the duties of the re-boiler of columns in unit were gained. For reaching to purified 1,3 butadiene, sensitivity of the process to the fluctuations of feed temperature and on the duties of the re-boilers of the columns is noticeable .

Abstract Digital Image Analysis (DIA) has been employed to characterize the time evolution of a bubble injected from a single orifice into a pseudo 2-dimansional gas-solid fluidized bed. The injected bubble diameter increased with the square root of time before detachment. During bubble free flight in the bed, its diameter remains approximately constant. The center of mass of the bubble increases with the second power of the time. The results show that the classical models for bubble injection can predict the time evolution of bubble diameter, and its center of mass. Bubble tends to elongate during injection and after detachment its height to width aspect ratio decreases. Image analyzing results used also for the study of gas leakage from the bubble to emulsion phase, and it has been shown that the dense phase expands up to 1.04 times of the minimum fluidization condition for large bubbles. The expansion ratio of the dense phase increases linearly with bubble diameter.

Abstract "> Sodium montmorillonite (Na-MMT) was organically modified using 11- aminoundecanoic acid (AUA) and methacryloxyethyltrimethylammonium chloride (MAETAC) via cation exchange reaction. The effect of the modifier type and concentration on the structure and surface properties of the organically modified montmorillonites (OMMTs) was investigated. According to the results, the basal spacing of organoclays was enlarged considerably with increasing the AUA concentration, while increasing the MAETAC concentration had no significant influence on OMMT’s gallery height. On the other hand, contact angle measurements revealed that increasing the modifiers concentration would increase the hydrophobicity of pristine montmorillonite. The FTIR spectra showed that the OMMTs interlayer environment changed from liquid-like to solid-like as the modifier concentration increased. A mean-field lattice-based model was applied to various polymer/OMMT systems to predict the affinity between the prepared OMMTs and some polymers with different hydrophobicity. The model results showed that high polar and hydrophilic polymers, such as poly(ethylene oxide), exhibit more negative free energy change and stronger interaction with the OMMTs and, consequently, higher potential for preparation of composites with desirable nanostructure and mechanical properties.

Abstract > Copper-silica aerogel was synthesized by the sol-gel method and was heated at 400, 500 and 600°C for 3 h in the air. The gained materials were named as sample (a), (b) and (c) respectively. Then all samples were characterized by FE-SEM, EDX and FTIR spectroscopy. For resistance measurements the pulverized material was pressed to form a disk-type sensor. The measurements of resistance in the relative humidity range of 11.3-84.3% were performed for all samples. For the following experiments sample (a) was chosen. Then the response time and stability properties were examined. The response time of 7.5 minutes was obtained and the stability graphs showed that in the higher RH the sensor was more stable.

Abstract The growth kinetics of Lactose particles in a top spray, small scale fluidized bed granulator is studied experimentally and the effects of binder flow rate and concentration, nozzle air pressure and the fluidizing air temperature on the growth kinetics of granules are studied. The results have been explained by the aid of sequentially main effects of each parameter in the process. The effect of each operating variable has been discussed in detail, qualitatively.

Abstract The purpose of this study is development of some parametric emission factors for gas flares using pilot-scale flare and investigation of the effect and interaction of important parameters on the emission factors. The considered parameters were flame Reynolds number, superheat steam-air flow rate and wind speed. Every variable was considered in four levels and the experiments were carried out two times. The results of 128 experiments showed that the average emission factors of CO 2, CO and NO x pollutants are 127.183, 0.731 and 0.074 lb/MMBtu (pound per Million British thermal unit), respectively. In addition, variance analysis of variables showed that the CO 2 and CO emission factors are significantly influenced by wind flow and NO x emission factor is influenced by superheat steam-air flow rate.

Abstract Continuous bioreactors are critical unit operations in a wide variety of biotechnological processes. Due to the level of detail built in their mathematical formulation, cell population balance models represent the most accurate way of describing the microbial population heterogeneity in continuous bioreactor. In this work,the equation set of the model was solved numerically using rigorous'space–time conservation element and solution element' CE/SE method.MATLAB/Simulink pre-existing blocks are used for modeling and control of the different moments of cell mass distribution in a continuous bioreactor. For investigating the efficiency of automatic controller, 10% increase in maximum specific growth rate in Ks, was considered. The set point for zeroth, first and second moments of distribution were taken to be; M0,sp =0.6706 , M1,sp =0.1541 , M2,sp =0.0505, which correspond to a dilution rate of 0.953 h -1 and 0.6 h -1 . In the first case the controller response after 10 hours was (0.92 h -1 ± .05), (0.87 h -1 ± 0.4) and (0.92 h -1 ± 0.2). For the second case the controller response was close to set point(0.6 h -1 ± .001) after 20 hours.

Abstract It was reported that the industrial application of Sub-Molten Salt method for production of potassium titanate from ilmenite concentrate is limited by feed particle size. Therefore, the objective of this study was to develop an improved approach for decomposition of ilmenite under industrial conditions. Using an ilmenite concentrate from Kahnooj Titanium Complex, experiments were performed at different conditions designed by the Response Surface Methodology (RSM) method. From the results of the tests, it can be noted that high conversion rate would be achieved even for particle size distribution similar to the industrial conditions. Statistical analysis of the results showed that conversion rate of titanium was significantly affected by process temperature. Optimized decomposition conditions were obtained at temperatures around 220 oC, KOH concentration of 84 wt%, KOH-to-ilmenite mass ratio of 9 and stirring rate of 800 rpm. Under these conditions, more than 96% of titanium can be recovered as potassium titanate. A quadratic model was obtained for the prediction of decomposition. Validity of the model was also experimentally confirmed. Observed effects of the relevant operating variables on conversion rate were consistent with a chemical reaction controlled kinetic model. Apparent activation energy for decomposition of ilmenite was found to be 80.15 kJmol−1.

Abstract The coalescence of water droplets in oils may be enhanced by application of an electric field. This approach is commonly used in the crude oil and petroleum industry to separate water from crude oil extracted from oil well. By application of an electric field two patterns of drop-interface coalescence may occur: complete coalescence and partial coalescence. The former is obviously the desirable pattern for industrial coalescers. However in practice, the process of coalescence could actually produce smaller droplets which become more difficult to remove, and hence undesirable. This is caused by either necking, due to extensive elongation of the droplet, or reaction to a fast and energetic coalescence and is referred to as partial coalescence. The volume of the droplets formed in this way has been analyzed as a function of the initial droplet size, electric field strength and change in interface tension between two phases as a result of surface active agents. There is a considerable growth in secondary droplets volume. Expansion speed of the neck connecting the droplet and interface at the beginning of the pumping process has also been quantified and partial coalescence has been explained as a result of competition between pumping and necking processes. These results are useful in optimizing the electro-coalescence process.

Abstract The separation of immiscible liquids plays an important role in the oil and petrochemical industries. In the outlet stream of a catalytic reactor of dehydrogenation of ethyl benzene to styrene monomer, water is present because it is used as high pressure steam to provide reaction heat. Therefore, aqueous and immiscible organic phases should be separated in a horizontal separator before fractionation. The objective of this work is to study the separation of ethyl benzene, styrene, and water in a horizontal pilot scale separator. Experiments showed that the performance of the separator is affected by feed flow rate and composition. Furthermore, the thickness of mesh installed in the inlet zone of the separator has an effect on the hydrodynamic behavior of the separator and its performance.

Abstract Spray dryer was used to produce potato powder from potato juice. Turning potatoes into powder will increase its substance durability, ease of transportation and the storage. The important factors affecting the powder produced by spray dryer include inlet air temperature, volumetric flow rates of feed and air. Experiments were conducted according to Taguchi’s method by considering 3 levels for each one of the mentioned parameters and 2 levels for atomizer’s nozzle diameter. The objective was to obtain the optimized process conditions for producing potato powder with desirable color. By analyzing the experimental results, the optimized conditions for producing potato powder by spray dryer were determined. It was also revealed that by adding 1 percent maltodextrin (dry mass basis) to the feed, the product’s adhesion will decrease significantly and the amount of product will be increased.

Abstract Differential Evolution algorithm (DE), one of the evolutionary algorithms, is a new optimization technique capable of handling non-differentiable, non-linear and multimodal objective functions. DE needs a large run time for optimizing the complex objective function. Thus, an attempt to speed up DE is necessary. This paper introduces a modification on original DE that enhances the convergence rate by reducing vector dispersal at any iteration. Our Adaptive Differential Evolution algorithm (ADE) utilizes variable scaling parameter (F) against constant scaling parameter in original DE at any iteration. The proposed ADE is applied to optimize three non-linear chemical engineering problems. The obtained results have been compared with those results obtained using DE. The considered comparison criteria are the vectors dispersal,
convergence history (run time and number of iterations that led to reach to global optimum) and error in any iteration. As compared to DE, ADE is found to perform better in locating the global optimal solution, reduces the memory and computational efforts by reducing the number of iterations required to reach the global optimal solution for all the considered problems.

Abstract The shelf life of fish was extended using disinfection properties of ozone. For this purpose, Trout specimens were exposed to ozone in the aqueous media for two hours and their microbial growth and biochemical properties were measured over time. Microbial growth of ozone treated fish was significantly slower than the control sample, resulting in lower counts of bacteria (Acceptable point: less than 5*104/gr or cm 2). According to the biochemical tests; ozone treatment had no negative effects on fat, protein and the humidity of the fish. Peroxide and TVN (Total Volatile Nitrogen) measurements showed that treatment by ozone increased the trout shelf life from 4 days to 6 days. According to the sensory analysis, no changes were observed in the color or flavor of the ozone treated trout.

Abstract In low-temperature processes, heat rejected from separation columns is removed by refrigeration systems to heat sinks (reboilers & pre-heaters), process streams, other refrigeration streams, or external utilities. The need for efficient utilization and recovery of energy in sub-ambient gas separation processes is still challenging. Performance and reliability of Simulated Annealing (SA) for simultaneous design and optimization of such systems has been investigated previously. In this work, the effect of different refrigerants satisfying a set of process cooling duties at different temperatures is addressed. Cost reduction can be realized by encompassing both effective screening of heat-integrated separation columns and selecting the best refrigerants. A 29.7% cost savings has been shown through a case study. Afterwards, a comprehensive thermodynamic analysis has been carried out on achieved solutions to verify the accuracy of existing shortcut models and robustness of optimized structure. It has been shown that exergy analysis using two different approaches (i.e. stream wise and unit operation wise) are the same, which indicate the accuracy of the used models. Moreover, we have indicated that both utility costs and exergy losses can be considered as an objective function when optimizing the designs.

Abstract The aim of the present work was to evaluate the effect of soy protein isolate (SPI)-gum arabic (GA) composite on the stability of beverage emulsion prepared as the orange oil-in-water (O/W) emulsion. Response surface methology (RSM) was used to study the influence of the two independent variables, each at three levels (homogenization speed
as x1 (1500, 15700, and 30000 rpm) and GA:SPI ratio as x2 (1, 0.6, and 0.2) on the two dependent variables namely, size of the emulsion droplet (EPS) as y 1 and emulsifying activity (EA) as y 2 . The results were discussed on the two empirical models obtained. Analysis of variance (ANOVA) showed a high coefficient of determination (R2 ) value of 0.937 and 0.979 for EPS and EA, respectively, ensuring a satisfactory adjustment of the second-order regression model with the experimental data. The negative sign for the regression coefficient of x1, indicated that size of the emulsion droplet increased with the decreased level of factor x1 from 30000 to 1500 rpm, while EA increased with increased levels of factor x1 . Thus, GA: SPI ratio with the lowest amount of GA along with the homogenization speed at high level, gave the smallest size of emulsion droplet (1μm). This size corresponded to the high emulsifying activity and stability. Sodium chloride and freeze-thaw cycling are two environmental factors affecting emulsion stability. Results of freeze-thaw cycling test showed a large decrease in the EA of the sample prepared with a low level of SPI:GA ratio and no dependence of the EA on the NaCl concentrations in the range of the tested levels was observed (50-150 mM). Long-term storage stability test (storing the emulsion samples at 4, 16, and 30ºC each for 8 days) showed the size of the emulsion droplet increased with the storage time. Results of use of SPI as a readily available plant source of protein for preparation of the encapsulant for orange oil-emulsion were encouraging, especially when one considers the dependence of the beverage industry on the unreliable source of supply of GA. RSM was successfully applied for the modeling of the emulsion preparation.

Abstract One of the important aspects of distillation control design is the choice of a good control structure since improper choice of manipulated/controlled variable pairing can lead to poor control performance. In this paper, comparison and selection of structures is mainly based on the plant condition number. Columns with reflux ratios less than unity or greater than five show large condition numbers. For the ratio structures, the results show that double-ratio structures such as the (D/(L+D))(V/B)-structure have smaller values of the relative gain array element (λ11 ) compared with single-ratio structures, such as the (D/(L+D))V-structure. In addition, the relative values of λ11 corresponding to the values of minimized condition number (γmin), instead of condition number (γ), provides a better basis for comparison. It has also been shown that the maximum singular value (σmax) of the relative gain array (RGA) is a good criteria between ratio and non-ratio structures, and also between various ratio structures selection. At a constant reflux ratio, columns with smaller values of σmax show small values of γmin . Finally, a frequency-based analysis is performed for the selection of the appropriate structure. The analyses show that although the DV-structure has a relatively small value of condition number with respect to other structures, the value of λ11 is far from unity. In contrast, ratio structures have λ11 values near unity. Frequency-based behavior of ratio structures show small oscillations at higher frequencies (> 1 rad/min), while the conventional LV-structures show large oscillations for smaller values of λ11 at higher frequencies.

Abstract A satellite with a passive thermal control system mainly uses thermal coatings and paints to maintain temperatures within safe operating limits. Satellite coatings, exposed to harsh space environments such as ultraviolet (UV) radiation and atomic oxygen (AO), undergo physical damage and thermal degradation, which must be considered by the satellite thermal designer for design optimization and cost reduction. In this paper, we have briefly reviewed the effects of space environment effects on degradation of satellite coatings. To study the consequences of paints degradation on the thermal performance of satellites with passive thermal control, a small cubical satellite in Low Earth Orbit (LEO) has been considered. The satellite’s bottom surface faces the Earth, and the top surface faces deep space. The satellite’s lateral sides are covered with solar panels, and the top surface, which acts as the satellite radiator, is covered with white paint. The satellite orbit is sun-synchronous with an inclination angle of 99º. Three radiator coatings (Chemglaze A276 and SG121FD white paints, and AZW-11LA ceramic white coating) have been used in turn, and the satellite has been thermally analyzed for each case. In these analyses, beginning-of-life and end-of-life optical properties have been used to predict the satellite temperatures, before and after degradation of the coatings. The analyses results show the importance of stability of optical properties of the thermal coatings for the long-term thermal control of satellites. On considering the rate of thermal performance degradation, lower production cost, and ease of application on satellite surfaces, SG121FD white paint is recommended as a suitable satellite radiator paint for use in satellite thermal control applications, with the same design requirements, mission life and orbital parameters as the satellite considered in this study.

Abstract Carbon black or soot is a carbon rich material which is widely used as a modifier and filler. Usually carbon black is produced via thermal decomposition of heavy hydrocarbons. This process is too complex to be modelled fundamentally. In this study, the effect of reaction feed composition on the soot production yield was studied experimentally in a lab-scale reactor. The soot production was optimized based on feed Composition and economical aspects. The effects of reaction time and temperature on the product particle size produced using the optimized feed were also investigated experimentally. Then a semi-empirical model was developed to predict soot particle size as a function of reaction time and temperature. The model has been validated upon the experimental data successfully.

Abstract > Secondary growth technique was successfully applied for the synthesis of nanostructure sodalite membranes with vacuum seeding on tubular α-Al2O3 supports. In the seeding process, a thin, uniform and continuous seeding layer was closely attached to the support external surface by the pressure difference between the two sides of the support wall. The final nanostructure sodalite top-layers were synthesized on the seeded support into a stainless steel autoclave with a Teflon holder. The effect of seeding time on the microstructure of the synthesized sodalite top-layers was investigated at four different levels 60, 120, 180 and 240 s. The synthesized membranes were characterized by XRD, SEM and mercury porosimetry. The obtained results showed that sodalite zeolite was synthesized on the membranes top-layers with uniform surfaces. But, the top-layers thickness increases by increasing the seeding time and tends to reach a plateau. Further increasing the seeding time causes dense top-layers to form. Also, the performance of the manufactured sodalite membranes was evaluated by permeations of single gases (H2 and N2) under different pressure differences at a temperature of 283K. It is found that the membrane permeance shows a maximum value at seeding time 180 s with a constant permselectivity (H2/N2) of about 2.5. The permeation results were confirmed by SEM micrographs which showed a thick and low-dense top-layer in the membranes manufactured with the seeding time of 180 s.

Abstract The spreading of a tracer in a bubbly two-phase grid-generated turbulent flow system is studied. In this work both particle image velocimetry (PIV) and planer laser-induced fluorescence (PLIF) are used to study the effect of the dispersed phase flow rate on the mixing characteristics of the tracer. The turbulent intensity of the continuous phase in the bubbly two-phase grid-generated turbulent flow is close to isotropic, and increasing the gas void fraction reduces the degree of non-isotropicity. The self-similarity of mean and RMS values of the cross-stream concentration distribution is observed. A new mathematical model is suggested to describe the self-similarity of the cross-stream profiles of the mean concentration based on two separate Gaussian curves into the central and outer region of the flow. The turbulent diffusivity is calculated using the Taylor hypothesis, which is based on the growth of the variance of the cross-stream profiles of the mean concentration, with a position along the direction of the flow. An increase in the void fraction does not affect the diffusivity of the superimposed distribution of the plume in the central region, however it did increase in the outer region.

Abstract The aim of this study was to investigate the particulate dispersion from Kerman Cement Plant. The upwind – downwind method was used to measure particle concentration and a cascade impactor was applied to determine particle size distribution. An Eulerian model, Gaussian plume model and an artificial neural network have been used to compute and predict concentration of PM₁₀ from Kerman Cement Plant. Eulerian model incorporates source related factors, meteorological factors, surface roughness and particle settling to estimate pollutant concentration from continuous sources. The measured data have been used to create an artificial neural network for predicting suspended particle concentration from Kerman Cement Plant. The data includes particle concentration, distance from source, mixing height, lateral and vertical dispersion parameters and 10 meters wind speed. The performance of these models has been compared with the measured data. The AAPD (Average Absolute Percent Deviation) parameter for the results of the Eulerian model, Gaussian model and ANNs was 25.53%, 15.38% and 5.91% respectively.
 
 
 
 
 

Abstract Distillation control is a challenging undertaking given the inherent nonlinearity of the process, severe coupling present for dual-composition control and the sensitivity of disturbances. Among various distillation operations, management of the high-purity column poses a difficult control situation due to a number of characteristics of these systems, including strong directionality, ill-conditioning and strongly nonlinear behaviour. In this paper, a diagonal PID controller is designed and analysed for a high-purity distillation column by computing the structured singular value μ introduced by Doyle (1982). For this purpose, a structured uncertainty model has been developed which describes the dynamics of the column for the entire operating range. The achievable manageable performance is also defined in terms of the H-norm of the weighted sensitivity function.