جستجوی مقالات مرتبط با کلیدواژه « fouling » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Low-density polyethylene is a subset of polyethylene that is mainly used in the plastics industry. These polymers are formed at high pressures and temperatures using a radical reaction. The fouling phenomenon is the result of the thermodynamic phase separation of polymer and ethylene. This phase separation occurs in the wall area (wall close to the cooling flow) of the tubular reactor, which reduces heat transfer to the reactor jacket, reducing production and in critical cases dangerous decomposition of ethylene. The purpose of this study is to simulate the phenomenon of fouling and its effects on the temperature and pressure of the reactor based on the heat transfer problems. The solved mathematical model is formed based on heat transfer equations to solve the computational fluid dynamics equations which are used to calculate the phase equilibrium data for pressure and temperature: The obtained results show that by increasing the thickness of the fouling, the heat transfer rate decreases. The operating model was used based on thelow-density polyethylene with a grade of 2420H. Based on the model, it was found that with increasing the thickness of fouling from 0.1 to 1.2 mm, the outlet temperature of the reactor increases, but does not have a significant effect on the pressure drop inside the reactor: Moreover,10 °C increase in reaction temperature caused the volume percentage of the second phase (fouling) is reduced from 0.1833 to 0.1818 mm.

Fouling in heat exchangers is main causes of energy losses in oil and gas refineries. One way to reduce this energy loss in these refineries is to predict fouling resistance. In this paper, the fouling resistance rate is first estimated using the Buckingham's dimensionless groups. The resistance rate is then validated with the experimental data derived from the literature. The results show the relative error of 26.79% with the experimental data, which is rather low and acceptable as compared by those reported in the literature ranged from 40-59%. In general, by estimating the fouling resistance rate, the fouling threshold curve can be plotted and the position of the exchangers relative to it can be checked. The position of the exchangers would allow to reduce the amount of fouling and to stay in non-fouling area with the proper justifications of the operating conditions. The curve is also used to estimate the deposition resistance in the unstable state with the asymptotic model. This model has also been validated with the experimental data from the Australian light oil and Tehran refinery data. It is worthy to mention that the prediction of fouling instability has been less considered in the literature, although with this estimate it is possible to have a better and more regular cleaning program for exchangers and to reduce the problems caused by deposition in exchangers leading to lower operational costs.

The main purpose of project is adding graphene oxide nanoplates (0.1 up to 0.75 wt. %) to the polyether sulfone membrane in order to increase the hydrophilicity of membrane that increases the permeation flux and reduces fouling properties. To investigate of efficiency of membranes, distilled water and oil in water emulsions were used as feed of process. It was observed that when nanoplates of GO with the amount of  0.5 wt.% added to the polymer solution, the permeation flux enhanced from 96 up to 139 Kg/m2 h  and 96.12 percentage of rejection (COD) was achieved. The difference of first and last fluxes decreased which show the reduction in the membrane fouling. But with adding more than 0.5 wt. % of GO, properties and efficiency of membranes because of higher viscosity decreased. Therefore, membrane embedded 0.5 wt. % GO indicates not only higher and effective performance but also reduced fouling properties.

In this paper, flux and antifouling performance of PVDF (15wt.%) nanocomposite ultrafiltration mambrane with different functionalized carbon nanotubes (-COOH, -OH, -NH2) are considered. Membranes are prepared with phase inversion method using NMP as solvent. This is the first time that hydrophilicity of different nanocomposite membranes are changing gradually as performance of nanocomposite membrane are considered. Gradually, the change of hydrophilicity explaines the behavior and performance of nanocomposite membrane. Analysing surface pore size by SEM showed no significant diffferent in mean pore size (a few tenths of a micron) of nanocomposite memebranes in comparison with pristine memebrans. The cross section morphology showed that all prepared membranes are asymmetric structure with a compact toplayer and a bottom layer with large pore channels. All modified nanocomposite membranes show better hydrophilicity surface in comparison with pristine PVDF membrane (87°). The results of pure water flux are approved by the results of contact angle and porosity which have been measured. Pure water flux of nanocomposite membranes with optimized carbon nanotube amount is increased more than twofold to pristine membrane (146 L/m2.h). AFM also revealed that nanocomposite membranes have smaller roughness in comparison with pristine membrane (Sa=270 nm). This subject is shown that functional carbon nanotubes have not any detrimental effects on mechanical resistance in modified membranes.

Hemodialysis is a process of purifying the blood of a person whose kidneys are not working normally. Polyethersulfone membrane has the most application in blood purification because of its unique features, but its hydrophobic nature results in poor biocompatibility. When PES-based membranes are contacted with blood, proteins tend to adsorb onto the polymer surface, and this protein layer causes any adverse effects such as the coagulation of blood cells and platelet adhesion. The biocompatibility of pristine PES membrane can be improved by different modification methods. The aim of this research is to improve polyethersulfone (PES) membrane hydrophilicity and antifouling properties by adding pluronic F-127, poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, to the dope solution. In this regard, PPO hydrophobic molecules are bound to PES chains due to hydrophobic–hydrophobic interactions, and membrane hydrophilicity would be improved because of hydrophilic PEO segments. To investigate the effect of adding pluronic F-127 on membrane performance, water contact angle, mechanical properties and filtration tests were carried out. Membranes morphology were characterized by SEM microscopy. Results showed that the addition of pluronic F-127 to the polymeric solution caused permeate flux increase up to 554 L/m2h due to membrane pore size growth and contact angle decrease. Moreover, addition of pluronic F-127 caused a decrease in the tensile strength of the PES/Pluronic F-127 membranes. PES/Pluronic F-127 membranes have improved fouling resistance compared to the pristine membrane.

The main objective of this research is to investigate the effect of surface modification of Polyvinylidene fluoride (PVDF) membrane on its filtration performance and fouling reduction. Considering Titanium dioxide (TiO2) nanoparticles properties in fouling reduction of polymeric membranes and in order to obtain ultrafine and stable nanodispersions on the membrane surface which is the main challenge in this field, composite PVDF/TiO2 ultrafiltration membranes were prepared via phase inversion and colloidal precipitation method. Among various prepared membranes, the PVDF/TiO2 composite membrane using 0.05 g/L of TiO2 in the coagulation bath was selected as the optimum membrane. Roughness reduction of about %24.34 and permeation increase of %15 for the optimum membrane were obtained. The result of the fouling analysis of nanocomposite membranes with BSA showed the improved effect of colliudal precipitation method in naoparticle dispersion on the membrane surface and fouling reduction of the prepared membranes. Indeed, the effect of TiO2 nanoparticle addition via colloidal precipitation method on membrane fouling reduction in membrane bioreactors for refinery wastewater treatment was investigated.

Deposit formation in heat exchangers causes increased pressure drop, flow non-uniformity, energy loss and deterioration of efficiency. A novel, efficient, and environmentally friendly approach to mitigate deposition in heat exchangers, is surface treatment. Surface energy and its polar and dispersion components are modified by coating of surfaces to mitigate fouling. In this study surface energy and its polar and dispersion components are calculated by Wu and OWRK approaches. The determination of surface energy and its polar and dispersion components for crystallization fouling showed that formation of precursor on substrates reduces by increased polar component of surface energy. Comparison with experimental data points associated with CaSO4 crystallization fouling confirm this propensity.

Because most contaminants in water create strong interactions with hydrophobic surfaces, there are usually problems such as flux decline and pore blocking in polyethylene (PE) membranes due to irreversible adsorption of foulants on their intrinsic hydrophobic surface. Therefore, in this work, attempts were made to improve the properties of PE membranes in terms of water flux and membrane fouling resistance by dispersion of silica nanoparticles (NPs). First, NPs were synthesized by sol-gel method at two concentrations of ammonia (0.5 and 1 mol/L). The synthesized NPs with smaller size were used to fabricate the mixed matrix PE membranes containing 0, 0.5, 1 and 2 wt% NPs. FE-SEM and EDX analyses were employed to evaluate the morphology and structure of the fabricated membranes and confirmed the presence of NPs in the membranes matrix. The results of pure water flux test revealed that the membrane containing 1 wt% NPs displayed the maximum flux of 30 L/m2.h. Furthermore, the performance and fouling behaviors of membranes during filtration of humic acid solution, one of the most important contaminants of water resources, were studied using a classical fouling model. Fouling mechanism analysis showed that for neat and NPs-embedded membranes containing 0.5 and 2 wt% NPs, the best fit of the data was obtained by cake layer formation as well as the intermediate blocking mechanisms. However, the best fit of the experimental data of NPs-embedded membrane containing 1 wt% occurred with only cake layer formation mechanism. The investigation on membrane fouling resistance showed that 1 wt% NPs-embedded membrane displayed 58% maximum flux recovery and 52% reversibility to total fouling ratio, respectively.

Carry Over Phenomenon is one of the common problems in Sugarcane boilers that has a important effect at any type of failure, output loss, trip, out of ordering and other equipments (before and after boiler) failure. It’s very important to know how this phenomenon is raised and lead to corrosion failure and fouling on steam drum surface, superheater and reheater tubes, steam turbine blades, … during boiler design and operation.In this paper, we describe how carry over occur and identify its effective ingredient at first. After that survey any kind of them and related efficacy. Then suggest a scope for evaluation and sampling carry over during boiler operation. Finally, offer some solution to decrease occurrence possibility or percentage with some modification that should be performed in system operation.

In quench towers and process water treatment section of steam generators, fouling decreases the performance, heat transfer rate, steam generation rate and increases rate of steam make-up for furnaces. In this study, Effective parameters like temperature, water contaminants, dissolved solids (e.g. Si, Fe,), PH, inhibitors and controlling chemical rates and dissolved oxygen which should be monitored for reducing these problems, are surveyed. Installation of dissolved oxygen monitor in dilution steam generator inlet stream is recommended as a result of this study. As this device provides the possibility of oxygen measurement, optimization of oxygen generating chemicals injection rates could be achieved. The recommended analyzer has not been available in olefin plants so far.

Ultrafiltration (UF) is one of the membrane processes has the most applications in dairy industries such as milk dehydration and whey concentration. Fouling of UF membranes in the milk industry is mostly due to precipitation of microorganisms, proteins, fats and minerals on the membrane surfaces. Thus, chemical cleaning of the membranes is essential. Results from investigations on a polysulfone UF membrane fouled by precipitation of milk components are presented. The effect of different cleaning agents on recovery of the fouled membrane was studied. Results showed that a combination of sodium dodecyl sulfate, EDTA and sodium hydroxide could be used as a cleaning material to reach an optimum recovery of the membrane used for milk dehydration. It seems that the results obtained on an experimental scale can be applied to an industrial scale, and the method is able to overcome fouling on any scale.

Oily wastewaters and oil-in-water emulsions are two major environmental pollutants. However, industrial oily wastewaters, though they may be lower in volume, contain much higher concentrations of pollutants. Treatment of the oily and greasy wastewater of Tehran refinery was experimentally studied using an ultrafiltration (UF) system. In the experiments, a UF membrane Polysulfone (PS) 30 kDa and sample from Tehran refineryoutlet wastewater of the API unit were used as feed. Effects of different operating parameters such as transmembrane pressure (TMP), cross flow velocity (CFV), and temperature on permeation flux, fouling resistance and UF rejection were studied. According to the results, permeation flux was found to improve with increasing TMP, CFV and temperature at constant feed concentration. Fouling of the membrane completely follows Hermia’s model (filtration cake mechanism). Analysis of the UF process showed 99.2, 75.4, 63.3, 42.3, 23.1, 100 and 97.9 % decreases in oil and grease content, total organic carbon (TOC), chemical oxygen demand (COD), biological oxygen demand (BOD5), total dissolved solids (TDS), total suspended solids (TSS) and turbidity, respectively. A comparison of the results shows that UF performs better than conventional biologicalmethods. The results showed that refinery wastewater treatment by using UF process is possible. The obtained UF permeates are suitable to discharge into the environment, even in the special regions in accordance with international requirements.