Iranian Journal of Chemical Engineering (IJChE)

Abstract Nowadays, increasing demand for sustainable energy sources has led to a growing interest in using biomass as a renewable feedstock for producing hydrogen and methanol. The main objectives of this study involve simulation and economic analysis and evaluation of synthesis gas, hydrogen, and methanol production processes from various biomass sources using Aspen HYSYS software. Three lignocellulosic sources were waste wood biomass (WWB), thin hardwood chips biomass (THWCB), and almond shells biomass (ASB). In the first part of the simulation, the unrefined synthesis gas was produced through a multi-stage biomass gasification process. The outcomes reveal that the yield and composition of synthesis gas were increased by raising the steam-to-biomass ratio (SBR). Subsequently, an integrated model for hydrogen production from various biomass sources was examined through gasification in the presence of steam and oxygen through a water-gas shift (WGS) reaction and the separation and purification of the produced hydrogen using a pressure swing adsorption (PSA) unit. Finally, the hydrogen produced in the previous step was fed to the methanol synthesis unit. The results of the simulation of the gasification process of various lignocellulosic biomasses showed that the use of WWB, THWCB, and ASB can yield annual hydrogen production of 261,000, 349,344, and 361,656 kg, respectively. Consequently, the economic analyses indicated that hydrogen and methanol production from biomass is associated with significant efficiency and profitability. Furthermore, the comparison of synthesis gases' heating values derived from three biomasses revealed that the highest heating values were generated from ASB, THWCB, and WWB, respectively.

Abstract This research presents the performance of bladeless wind turbines. It also familiarizes readers with the phenomenon of eddy current, which serves as the foundation for bladeless turbines. In this direction, these kinds of bladeless turbines have been designed, modeled, and simulated. Firstly, a two-dimensional vibrational movement of the cylinder with a natural frequency of 2 Hz was modeled at Re = 51000. Additionally, it was noted that the values of the displacement amplitude, and lift coefficient are -0.1-0.1, and -1.5-1.5  respectively. After that, using 2D simulation, the impacts of two different geometries, horizontal and vertical ellipsoids, on displacement amplitude are examined. Investigations were conducted on important factors such as lift coefficients and displacement amplitude, as well as the vortex flow pattern formed behind these shapes. It was discovered that the vertical ellipsoid shape had the maximum values for the height of the displacement amplitude, and lift coefficient. The most important factor influencing the performance of this type of geometry was examined, namely the dimensionless Reynolds number, which ranges from 15000 to 90000. It was determined that the intended geometry exhibited a larger displacement response as the Reynolds number increased.

Abstract Vacuum swing adsorption (VSA) for CO₂ capture has been a focus of significant research efforts aimed at developing innovative CO2 adsorbent materials. In this study, three adsorbents (MAF-66, AC, and CMS) were utilized for capturing CO₂ from flue gas through the VSA process, and their performances were compared. The adsorption equilibrium and kinetics data were gathered from recent literature. A four-step VSA cycle was employed to assess the adsorbents' performance for CO₂ capture, with a molar feed composition of CO₂:N₂ at 15:85%. Simulations of two-colums VSA lab-scales with different adsorbents were conducted. The operating conditions such as total feed flowrate, feed composition, feed pressure, temperature, and vacuum pressure were kept constant, and the impact of the adsorbent mass on recovery and productivity was analyzed. The simulation results indicated that both recovery and productivity decreased with increasing adsorbent mass. Furthermore, the necessary amount of each adsorbent to achieve a purity of 99.5% was determined. The modeling outcomes suggested that the VSA process employing MAF-66, CMS, and AC adsorbents would require 1.25, 3.19, and 8.2 grams of the adsorbent, respectively, to achieve N₂ purity of 99.5%. Taking into account parameters such as recovery, productivity, and energy consumption, MAF-66 emerged as the most effective adsorbent in this study.

Abstract The Ethanol-water separation involves a well-known azeotrope that confines the achievement of the ethanol purity to the values higher than 95 wt% using straightforward distillation. Many attempts have been made to identify how it can be possible to produce ultra-pure ethanol (99.95 wt%) for various valuable applications. In practice, minimizing the total cost of the process is of high importance beside having the finished product with utmost purity. As a consequence, finding the best process conditions imposed to apply the simulation and statistical optimization methods in combination. Numerical optimization provides the best trade-offs to achieve the goals. In this research, the separation of the ethanol/water mixture (87 wt%) was simulated using azeotropic distillation in Aspen plus^© environment. Indeed, cyclohexane was chosen as an effective azeotrope-former. The UNIQUAC equation was used to describe the phase behavior. The two-column arrangement, in which the first column was used to dehydrate ethanol and the second to recover the entrainer, was applied in this simulation. The effect of important process variables, including the number of the trays in columns and the feed-tray position in each tower on the total capital cost were investigated. Finally, the process variables were optimized via the Response Surface Methodology to minimize the total cost of the process. The results uncovered that the total capital cost would be minimized if the number of the trays in the azeotropic (C1) and recovery (C2) columns were set to 34 and 40, whereas, the feed-tray numbers were adjusted to 19 and 9 respectively.

Abstract Ability and compatibility of the membrane processes for gas separation are evaluated by their membranes’ permeability and selectivity where both have been tried to enhance in promising membrane generation of mixed matrix membranes (MMMs). In the current study, two- and three-dimensional models were constructed for MMMs, and the Fick's first law was solved numerically in them by using the Finite Element Method (FEM) and Computational Fluid Dynamic (CFD) tools. The effects of different MMMs structural parameters such as the volume fraction, size and mode of packing, i.e., regular or random, of the filler particles were investigated on the effective permeability of the pure gaseous penetrants through the MMMs. Furthermore, the interfacial equilibrium constant of the penetrants and their diffusivity ratios were also evaluated in view point of their impacts on the MMMs’ separation performance. Some well-known established models including Maxwell, Bruggeman, Lewis - Nielsen, Pal, and Chiew - Glandt were applied in the modeling. Deviation of the simulation results from the experimentally measured ones were low enough, however, at higher loadings of the filler particles the simulation deviation became greater. Simulated results through PSF - MCM-41 MMMs were compared with those of experimentally measured ones and AAREs of 31.0 (The lowest deviation), 42.7, and 41.0 % obtained for CO2, O2, and N2, respectively.

Abstract Methanol is an important industrial chemical, and its synthesis and purification units are among the most widely used processes in the field of energy. The two-column separation unit of methanol has been analyzed from the thermodynamic and energy points of view in the present study. The simulation has been done by Aspen Hysys V11 and the SRK equation has been regarded as the most appropriate equation of state (EOS) for this simulation with the mean relative error (MRE) of 2 %. Then, the design of the heat exchanger network (HEN) has been calculated using the Aspen Energy Analyzer V11. Both distillation towers have been analyzed using pinch technology. As a result, the amount of hot and cold utilities used has been LP=1.482×〖10〗^8, MP=1.57×〖10〗^4, and Air =1.423×〖10〗^8, respectively. Besides, the total heating and cooling target of the process has been 1.482×〖10〗^8 and 1.423×〖10〗^8, accordingly. Then, the 〖∆T〗_min (minimum allowable temperature difference between hot and cold currents) and its effect on the annual cost have been investigated. The optimum value 〖∆T〗_min is determined to have better-operating conditions and to meet the design of the HEN economically. Reducing 〖∆T〗_min increases operating costs and reduces energy costs.

Abstract The optimization of the ammonia synthesis plant to increase the production of ammonia is studied in this line of research. In this paper, the steady-state ammonia synthesis is simulated using the Aspen HysysV.11 software. By comparing the simulation results with the industrial information, a mean relative error of 7.71 % was obtained, which indicated the high accuracy of the simulation. Then, four effective variables were selected from among 11 independent variables by the Plackett-Burman method. The effects of the Hydrogen flow in the feed stream, Recycle stream pressure, Feed stream temperature, and input temperature of the third reactor were investigated, and the response surface design method of the central composite design was performed to plant optimize. It is obtained that the Hydrogen flow in the feed stream is equal to 6255 , the feed stream pressure is equal to 205 bar, the temperature of the excess stream inlet in the first reactor is equal to 663 K, and the temperature of the stream inlet of the second reactor is 677.5 K which increased the ammonia production by 7.5 %.

Abstract In this study, the main purpose has been to investigate the behavior of the nanoparticles with different structures and similar based materials in polymer nanocomposites. To this end, different samples, containing PS as the matrix, and layered graphene oxide (GO) and/or hollow graphene oxide nanoparticles (HGO), were prepared via the melt mixing process and were subjected to heat conduction and tensile tests. To evaluate all features of the interaction between the polymer phase and the nanoparticles, a thermal/mechanical analytical model was proposed and the results were used to simulate the behavior of specific geometrical structures, corresponding to the real samples, under different thermal/mechanical conditions. The results showed good agreement between the obtained experimental data and simulation/analytical model interpretations. In addition, it was found that the HGO nanoparticle had such a good performance in enhancing the thermal and mechanical properties of the nanocomposite, due to its unique structure.

Abstract Micro-reformers used for producing hydrogen with a high surface-to-volume ratio in small-scale fuel cells were investigated. To this end, scrutinizing and exploiting all areas of micro reformers is very important. Parallel micro-channels have shown good performance in eliminating dead volumes. Inlet/outlet configuration has great effect on the velocity distribution through micro-channels. In this study, four configurations (1 inlet/1 outlet on the same and opposite sides; 1 inlet/2 outlets on the same and opposite sides) were studied through simulation and 1 inlet/2 outlets on opposite sides were found to have the lowest velocity difference, hence having the best configuration. Simulations were carried out at 600 °C, 1 atm, with S/C=3 and feed flow rate of 100 mL/min. Three channel patterns (i.e., parallel, splitting-jointing and pin-hole) were compared in terms of Figure of Merit (FoM) and specific conversion. Parallel channel design revealed a high value of specific conversion to be about 5.36   , while splitting-jointing and pin-hole were 5.33  and 4.91 , respectively. Based on FoM, pin-hole design had a high value of 1.34   , while the values of splitting-jointing and parallel designs were 0.037  and 1.28 , respectively.

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 The distillation process remains as the most common method ofseparation in chemical process industries. The energy used from this process accounts for an estimated 3% of the world energy consumption. The Dividing-Wall Column (DWC) for separation of multi-component mixtures has recently become a major concern ofindustries. The design ofDWC is based on Thermally Coupled Distillation System (TCDS) eliminating some of the operational equipment. This paper presents the results of simulation of a DWC by using 3-simple sequence column model based on shortcut method by a commercial chemical Engineering software for purification of1,3 butadiene unit. From the results, it is shown, by using a DWC instead of two conventional sequential column, the heat duties ofboth the condenser and the reboiler are reduced about 28.5% and also desirable purity ofthe key-components for the case ofstudy have been achieved.

Abstract In this study, simulation of cyclic adsorption process for mercaptan removal from natural gas in non-isothermal and non-adiabatic conditions is presented. This process is used in mercaptan removal unit of South Pars Gas Refinery Phase 1. Six adsorption fixed beds used in this plant contain molecular sieve type zeolite 13X. Three beds are in the process for adsorption purposes and the other three beds are being used for regeneration simultaneously. Regeneration cycle involves two steps for heating and one step for cooling. In modeling of this process, linear driving force (LDF) is used for estimation of adsorption rate. For equilibrium relation between solid and gas phases, the extended Langmuir isotherm is used. The energy balance around the gas phase in the bed includes heat transfer to solid as well as axial heat dispersion. The set of partial differential equations is solved using implicit finite difference. Cyclic steady state (CSS) is obtained using cyclic simulation procedure and the variation of concentrations and temperatures along the bed and at different times.
A good agreement was obtained between the simulation results and those obtained from plant operational data. The effect of various operational parameters, such as regeneration steps, temperature and regeneration flow rate on process product was investigated. With increasing the first heating stage temperature, the concentration of water and mercaptan in the bed outlet decreases, but the decrease in mercaptan concentration is more significant. By increasing the second heating stage temperature, the water concentration in the bed outlet decreases significantly.

Abstract Monte Carlo simulation is adopted to study the aggregation of asphaltene phenomenon in crude oil. Simulation is accomplished by applying two different potential functions to allow for asphaltene-asphaltene, asphaltene- resin and resin-resin interactions to take place. Asphaltene molecule is considered as a flat molecule, consisting of seven spheres. Resin molecule is considered to be a single sphere and the other hydrocarbons molecules contained in crude oil are modeled as a continuum media. The effect of media on intermolecular interactions is described by definition of a parameter that is composed of two dielectric and Hamaker constants. The effects of asphaltene concentration, temperature and solvent type on the aggregation of asphaltene molecules are investigated by applying both of the potential functions. The predicted results are compared.

Abstract Solid transport phenomena drastically affect rotary drying process. A change in any solid movement variable such as particle hold up or input flow rate results in a significant variation of heat and mass transfer rates. Therefore, in this research dynamic study of these phenomena was conducted both experimentally and theoretically. Several experiments was performed employing an industrial granule dryer. The dryer length and diameter were 5 and 1 m, respectively. In each experiment one of the solid movement variables was changed and the resulting dynamic change on the process was measured. The data was used to estimate the parameters of a dynamic distributed parameter model of the system using dynamic optimization method. The data were also employed to evaluate the model. The model predictions for solid hold up and outlet flow rate were compared with those of the experimental data. The average model error for solid hold up and outlet flow rate were 5.6% and 5.4 %, respectively.

Abstract This paper reports the result of CFD simulation of catalytic oxidation of benzene on monolithic catalyst. The geometries ofthe catalyst and reactor were designed in Gambit software and simulation of catalytic oxidation was carried out in fluent 6.2. Results of simulation showed excellent agreement with the experimental data. This study confirmed the accuracy of the used model in this simulation (Mars van Krevelen). Furthermore, CFD made it possible to obtain a more accurate view ofheat transfer and fluid flow. This study confirmed CFD is the best tool for study offluid regime and heat transfer and especially, concentration of species, and surface deposition along the reactor in the chemical process.

Abstract Implicit pressure-explicit saturation method (IMPES) is widely used in oil reservoir simulation to study the multiphase flow in porous media. This method has no complexity compared to the fully implicit method, although both of them are based on the finite difference technique. Water coning is one the most important phenomenon that affects the oil production from oil reservoirs having a water drive source. Since the water coning affects final oil recovery, identification of this phenomenon is very important. In order to study this phenomenon, one should determine the critical production rate, the breakthrough time and watercut percentage. The scale of the problem hinders the numerical simulations, IMPES included, for a long running time. A corrected IMPES method is used here to overcome the long running time problem by choosing larger the time step for the coning problem. A water-oil phase flow system in the cylindrical coordinate that is commonly used to simulate water coning phenomenon is solved by the corrected IMPES method. The validity of the model is checked against Aziz and Settari’s model, which is based on a complicated fully implicit method.  The effects of the production rate and the thickness of the oil zone on the breakthrough time have been investigated. The results were found to be in good agreement with the results of previous studies.

Abstract General modeling and optimization of syngas production via noncatalytic autothermal partial oxidation of methane are carried out using our developed scientific software which was based on the minimization of total Gibbs energy. In this work, a novel application of the direct search and Newton-Raphson methods was introduced to apply to optimization of a complex chemical reaction. Sensitivity analysis was done to investigate the effect of several parameters on the quality of syngas and the production yield. The acceptable concentrations of CO2 and H2O injected into the methane feed are optimized in the specified temperature and pressure range, while H2/CO ratio in the product stream is set to remain at 1.5 or 2, methane slip in the syngas is less than 1.5% and the non-endothermic conversion area of reaction prevail, simultaneously. This facilitates monetizing CO2 in the petrochemical and steel industries. The output from this software is comparable both with the experimental results, cited in Ref [1] , and with that from ASPEN PLUS in simulating the experiments mentioned in Ref [2]