The rotary pressure exchanger (RPE), one of the most important pieces of equipment in the recycling of brine pressure energy in the reverse osmosis desalination process, contributes greatly to reducing power consumption and system operation cost. In this work, three-dimensional geometric models of five kinds of RPEs with different sizes and structures were built. The sliding mesh technique and species transport equations were used in the simulation process. FLUENT software was used to analyze the characteristics and factors influencing the concentration distribution at a rotor cross section on the seawater side after the model was enlarged and the number of rotor rings was increased. Moreover, the structure of the endcover was changed from the original two-port to the current four-port. Simulation results revealed that the model size, rotor ring number, and endcover structure affected volumetric mixing. This research will provide theoretical guidance and innovative ideas for the design and structure modification of RPE devices.
Due to the potential structural degradation when the lubricating grease was heated to improve its fluidity and pumpability, fresh NLGI 3 lithium grease was heated to simulate the static thermal ageing by using drying oven. The microstructure and infrared spectra of grease samples were studied by using field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) technique respectively. And by using rotational rheometer, the frequency sweep and controlled-stress tests were carried out to estimate its entanglement and structural strength. At last, the mechanical reversibility was studied by carrying out triple-step-shear stress tests. It is found that the original structure of grease sample could be basically maintained after being aged at 120°C within 24 h, while the irreversible structure hardening and degradation are shown after being aged at 150°C.
A method for estimation of the volumetric mass transfer coefficient of an entire aeration tank for optimization of tank design was investigated. The gas holdup, bubble diameter, and volumetric mass transfer coefficient of an aeration tank were measured by experiments and the experimental results were compared with two estimation method. One method used empirical equations, while the other used CFD simulation. The rate of oxygen transfer into the aeration tank was assumed to be the sum of the rates at the bubble-liquid interface and free surface. The empirical equation method showed good agreement with the measured gas holdup by assuming that the aeration tank was divided two zones. On the other hand, the CFD simulation method provided a good estimation of the gas holdup and bubble diameter. The sum of the estimated volumetric mass transfer at the bubble-liquid interface and free surface showed good agreement with the measured volumetric mass transfer coefficient of the entire aeration tank.
The relationship between the solid circulation rate and the pressure drop in the riser of a pressurized circulating fluidized bed (CFB) was investigated. The pressure drop of the riser was measured based on variations in the pressure, gas velocity, solid flux, and particle diameter using glass beads as the bed material. The pressure drop of the riser was shown to decrease as the pressure increased. Under the gas flow conditions, the momentum per unit mass of the gas used to accelerate the solid particles was shown to be finite. The time required for the gas to accelerate the solid increased linearly with the solid circulation rate under the given gas flow conditions because the gas momentum shared per unit mass of the particles decreased. Therefore, the pressure drop of the riser increased linearly with the solid circulation rate at the given gas velocity. The slope of the linear relationship is related to the ratio of the momentum flux due to gravitational and buoyancy forces on the solid to the gas momentum per unit mass of gas transferred from the gas to the solid. The transferred gas momentum per unit mass of the gas increased as the gas velocity increased or as the particle diameter or pressure decreased. The gas momentum shared per unit mass of the solids decreased as either the particle density or diameter increased. A correlation that represents the relationship between the pressure drop and the solid circulation rate in the riser of the CFB was successfully proposed.
We have developed two techniques for preventing the oxidation of nickel nanoparticles upon their removal from the gas phase reactor into the air atmosphere. In the first method the nickel particles are collected in an organic liquid, where they have no contact with air, by using a trapping apparatus connected to the reactor. In the second approach the nickel particles are coated with an organic solid which prevents their contact with oxygen in the air. We confirmed that the surfaces of nickel nanoparticles coated with stearic acid at a thickness of 23 nm were not oxidized after exposure to air for 77 d.
Liquid membranes of triethylenetetramine mixed with ionic liquids were prepared on a hydrophobic microporous membrane using a novel nanoparticle-supported construction. A flat membrane module with the amine/ionic liquid membrane was used for the recovery of CO2 from room air. CO2 was enriched 3–5 times in the sweep air passing through the membrane module. There was an optimum amine/ionic liquid ratio of 10–25 wt% to effectively concentrate the CO2. These permeation results were analyzed in terms of permeability based on a solution–diffusion mechanism. The present membrane process for CO2 separation has proved to be reasonably durable for a greenhouse application.
Hot compressed water extraction (HCWE) is a promising green alternative to the screw press in the palm oil processing. In this study, the steady-state characteristic of the HCWE was modeled by using an artificial neural network (ANN). The overall oil yield and other outputs; β-carotene, α-tocopherol and α-tocotrienol concentration, were described by the pressure and temperature in the HCWE. The results show that the predicted yield and concentrations agree well with experimental data. These models were used to estimate the optimum conditions of the HCWE process.
Novel hygroscopic carboxymethyl cellulose (CMC) graft copolymer adsorbents (CMC-g-AA and CMC-g-AM) were synthesized by solution polymerization, using CMC as a raw material and acrylic acid (AA) or acrylamide (AM) as a modifying monomer. The influence of synthetic conditions, including the mass ratio of monomer and CMC, degree of neutralization, polymerization temperature, and time on the adsorption performance of the CMC graft copolymer adsorbents were discussed. Based on the optimized conditions, the CMC graft copolymer/silica gel composite adsorbents (CMC-g-AA/B, or CMC-g-AM/B) were obtained by impregnating silica gel type B (B) into copolymer solutions. The compositions, structures, and pore size distributions of the composite adsorbents were characterized using Fourier transform infrared spectroscopy (FTIR) and porosity analysis, while their adsorption/desorption performances, and thermal stabilities were also tested by static and dynamic adsorption, thermogravimetry (TG), and temperature programmed desorption (TPD). Cycle stability was also taken into consideration. The results showed that, the copolymer/silica gel composite adsorbents had excellent adsorption performances compared to silica gel, while their desorption activation energies were slightly increased. This was attributed to the enhanced interaction between the CMC graft copolymers and water molecules. TG analysis and the adsorption/desorption cycles suggested that the composite adsorbents had excellent thermal and cycle stabilities for water vapor adsorption.
We report a highly selective adsorbent for Cu(II) prepared using the metal-imprinted technique. As the base material, we used the natural adsorbent chitosan, which can be obtained from chitin by the deacetylation reaction. Chitosan was modified with ketoglutaric acid to introduce multiple functional carboxyl groups, which interact with metal cations. Cu(II)-imprinted chitosan was prepared by the imprinting technique and its behavior as an adsorbent for various metal ions, including Cu(II), Ni(II), Co(II), Zn(II), and Cd(II), was investigated. Cu(II)-imprinted chitosan exhibited extremely high selectivity for the imprinted Cu(II) ion compared with the other metal ions. This result indicates that the metal imprinting technique is very useful for the development of highly selective adsorbents. However, desorption of Cu(II) from the imprinted adsorbent was not sufficient because of the strong binding between Cu(II) and the imprinted adsorption sites.
The present study investigates the dehydration performance of a carbon hollow fiber membrane prepared from sulfonated poly(phenylene oxide) (SPPO) in the separation of aqueous 2-propanol (isopropanol, IPA) mixtures by vapor permeation. In pure water permeation, the flux increased with increasing feed pressure, which was larger than 15 kg m−2 h−1 at 150°C and 370 kPa. The effects of feed pressure, permeation temperature, and water concentration in the feed solution on the vapor permeation of water/IPA mixtures were studied. The SPPO carbon membrane showed water selectivity against IPA, mainly due to the molecular sieving mechanism in addition to the adsorption effect. The water permeance and ideal selectivity decreased with increasing total feed pressure from 165 to 365 kPa. Increasing the temperature resulted in lower water permeance, and the water permeance gradually increased with increasing water concentration at constant feed pressure. However, the SPPO carbon membrane showed excellent ideal selectivity, greater than 10,000, under various conditions. The carbon membrane also showed long-term stability and its performance was maintained for one month.
The present study focuses on determining the potential applicability of ammonia (NH3) as a carbon-free alternative fuel through numerical simulations. The combustion and emissions characteristics of premixed NH3–air flame at preheating conditions were numerically investigated. The burning velocity and all species mole fraction were determined using the Miller and Bowman and the Reductive Konnov mechanism. The results show that both the equivalence ratio and preheating temperature have important effects on the laminar burning velocity and adiabatic flame temperature of NH3. The reaction rate of production and mole fraction of H, O, and OH radicals, together with nitrogen radicals such as NH2, NH, and N in the reaction zone, increases as the preheating temperature is increased from 298 to 573 K. Although NO concentrations in the exhaust gas increased with increasing preheating temperature under fuel-lean conditions, they could be maintained at a reasonably low level at all preheating temperatures, mainly due to the increased reduction reaction of NO with NH2, NH, N radicals. The main N radical formation in the NH3–air combustion originates from NH3 rather than N2, which indicates that the N2 dilution effect of NH3–air flame is negligible for NO formation. Furthermore, the equivalence ratio has a dominant effect on NO yields, because of the higher reduction reaction and lower flame temperature at higher equivalence ratio conditions, leading to a lower formation of HNO, which indicates a potential in reducing NO emissions in NH3 combustion. Therefore, the preheating temperature and equivalence ratio should be given sufficient consideration in practical operations to minimize NO formation in combustion of NH3 as a clean fuel.
Absorption heat pump systems (AHP) are an attractive technology to upgrade and utilize low temperature exhaust heat for refrigeration or heating-up without emitting global warming gases. This work proposes a method for forming a fine-particle slurry of LiBr crystals and evaluates the particle size distribution and effectiveness of the slurry for advancement of the vapor absorption performance in LiBr/water AHP. It was found that the fine-particle slurry of LiBr crystals is formed stably in solution under super-saturation conditions and the median diameter is correlated linearly with the mass ratio of crystal to zeolite in the slurry when zeolite powder is suspended. This phenomenon can be caused by the crystal growth around the zeolite particles, which function as nuclei. However, the deviation from this correlation becomes significant for ratios greater than 1.4 kg-LiBr/kg-zeolite and remarkable crystal growth is caused, such that size measurement is not possible beyond 2 kg-LiBr/kg-zeolite. The lab-scale vapor absorption examination revealed that the slurry improves the absorption rate by up to twice that of the homogeneous solution with 60% in LiBr concentration due to dissolution of the crystal, even if the solution is diluted by the absorption of water vapor in the absorber.
Ni/MgO–Al2O3 catalysts derived from NiMgAl hydrotalcite presursors with Ni/Mg/Al ratios of (0.2–1.0) : 2 : 1 were prepared and characterized. The effect of Ni ratio on the physico-chemical and the catalytic properties were investigated. The Ni ratio influenced the specific surface area and pore size distribution, surface acidic, basic and reducibility properties, and catalytic behavior in condensation and hydrogenation of acetone. The Ni/Mg/Al ratio of 0.2 : 2 : 1 presented the suitable ratio for catalytic performance, with an acetone conversion of 53.10% with MIBK selectivity of 47.38% and DIBK selectivity of 18.91% reached at a temperature of 160°C, H2/Ac molar ratio of 1.0 and LHSV of 4.8 mL/(g h).
The present study determines the kinetics for decomposition of mannose, its corresponding uronic acid (mannuronic acid (MA)), and sugar alcohol (mannitol) under hydrothermal condition. The experimental work was conducted using a continuous-flow-reactor at temperatures ranging from 170 to 250°C, and with residence time between 3 and 15 s. The operating pressure was fixed at 25 MPa throughout the experiment. The remaining amount of all compounds decreased as the temperature increased. The decomposition reaction followed first order kinetics at shorter residence times. The decomposition rate increased in the order of MA<mannitol<mannose with similar activation energies of 28.3, 29.1 and 44.6 kJ/mol, respectively. However, the pre-exponential factors were 282, 6.19, and 9,600 s−1 for Ma, mannitol, and mannose, respectively, indicating that uronic acid is twice as easily decomposed, while sugar alcohol is less reactive than mannose by two orders of magnitude for the temperature range studied here.
Packed-bed reactors filled with ion-exchange resin catalysts are very effective for the continuous production of various chemicals. However, the resin tends to swell or shrink depending on the composition of the surrounding solution, and this can greatly alter the resin bed height and the volume of the liquid phase above the resin in a fixed-volume reactor. Because this liquid phase does not contribute to the production of chemicals in the reaction, it is important to minimize the liquid-phase volume to increase the productivity. In the present study, an adjustable-volume packed-bed reactor system was developed, and its effectiveness for the continuous production of fatty acid esters and regeneration of the resin were evaluated. The column height was adjusted by controlling the position of a movable plunger to minimize the liquid-phase volume in the upper part of the column. In fatty acid ester production using the adjustable-volume reactor, the residence time of the reactants in the liquid phase was shorter than that in a fixed-volume reactor, and the solution was rapidly eluted from the column, which improved productivity. For resin regeneration, minimization of the liquid-phase volume in the adjustable-volume reactor reduced the effect of dilution on the performance of the regeneration solutions compared to that in the fixed-volume reactor, and less regeneration solution was required. The adjustable-volume reactor could allow for more efficient and environment-friendly production of chemicals than a fixed-volume reactor.
In the chemical industry, the components of the production process are 1) production plant personnel, 2) the production unit, and 3) the production support system (PSS). These elements are the sources of process resilience. Resilience refers to the capability to restrain the disruptive signals that occur inside and outside the production process. The resilience always changes and its deterioration invites various influences that disturb the production activities. Therefore, it is necessary to observe, maintain, and improve the resilience to maintain productivity. However, quantitative estimation of resilience has not been attempted yet, because estimating the resilience can be difficult. The reasons are 1) the sources of resilience are not clear, 2) the scale of estimation is not specific, and 3) the object to be restrained is not apparent. In this paper, a metric, criterion of measurement, and method for quantitative estimation of resilience in a PSS in the production process are proposed. The procedure to estimate the resilience is as follows. First, the skills of the production plant personnel are classified into three categories: operational, memory, and communication skills. Next, the work hours of production plant personnel in the daily routine are measured, and based on these data, the work hours devoted to each skill (WHDS) are estimated to obtain the value of the skills (VOS). The value of the skills is the criterion used to estimate the skill of the production plant personnel, and this value includes the level of the skills and the knowledge of the production plant personnel. As each function of the PSS is implemented instead of the skills of the production plant personnel, it is possible to obtain replaceable work hours devoted to the skills by PSS. Therefore, based on the level of the skills and knowledge replaced by the PSS in the daily routine of the production plant personnel, the resilience produced by the PSS can be estimated.
With the recent rapid development of in situ real-time measurement for crystallization processes such as focused beam reflectance measurement (FBRM) and particle vision measurement (PVM), an increasing amount of process data has become available for developing multivariate statistical process control (MSPC) tools to monitor crystallization processes efficiently. To tackle the transitional phase changes because of process nonlinearity and time-varying characteristics in a semi-batch pH-shift reactive crystallization, an integrated monitoring method based on moving window multi-way principal component analysis (MPCA) combined with batch-wise unfolding of batch data arrays using crystallizer volume as an indicator variable is developed in this study. Simulation results reveal that, compared to the conventional MPCA and multi-way partial least squares (MPLS) methods, the proposed monitoring scheme not only can detect an abnormal batch efficiently, but it also reflects the contributions of the control actions to revert the process to an in-control state.
In order to operate batch process systems stably and safely, it is necessary to analyze the faults occurring in the systems quickly and accurately. The activities concerning fault analysis include fault detection, fault diagnosis and fault avoidance control. To perform these activities in a rational and efficient manner, a dynamical model which is available for analysis of inexperienced faults is essential. This paper presents a method for modeling abnormal behaviors of batch process systems. It also discusses fault avoidance control.
Fault analysis, including accurate fault detection and careful fault avoidance, is very important for the stable and safe operation of a process. It is, however, difficult to rationally analyze faults occurring in a process using a rational process model. Since the behavior of a batch process is characterized by an event-driven state transition mechanism, a batch process is regarded as a discrete event system. The Petri net is a promising modeling tool for studies of discrete event systems. This paper presents a method of detecting faults and constructing fault avoidance controllers for batch processes with uncontrollable events and unobservable statuses based on Petri net analysis techniques and control schemes.