With the development of modern industry, more and more valves need to be serviced under severe working conditions. Due to the high-speed flushing of working media, the failure of valve sealing ...surfaces is not uncommon. Based on the ALE (Arbitrary Lagrange-Euler) algorithm, LS-DYNA is used to simulate the erosion of the valve sealing surface material Stellite21 by high-speed water flow, and the damage degree of grid unit is judged by the damage parameter D. At the same time, the parameters of Stellite21 in the Johnson-Cook material model were first calibrated. In this paper, the impact dynamics simulations of different impact angles and different impact velocities were carried out and the material behaviour under different operation parameters of water jet is studied. It is found that with the increase of impact velocity, the erosion rate of materials has a significant increase. As impact angle increases, the erosion damage rate increases first and then decreases, and material has the maximum erosion damage rate at the impact angle of about 40°.
► SO2 and CO2 could be simultaneously removed by membrane gas absorption technology. ► The existence of SO2 has a slight influence on CO2 absorption. ► Partial membrane wetting results in ...deterioration of system absorption performance. ► Performance of wetted membrane contactor could be retrieved to 86% of fresh one.
Membrane gas absorption technology is a promising alternative to conventional technologies for the mitigation of acid gases. In this study, simultaneous removal of SO2 and CO2 from coal-fired flue gas was carried out in a polypropylene hollow fiber membrane contactor using aqueous monoethanolamine as the absorbent. The influences of liquid and gas flow rates on the simultaneous absorption performance of CO2 and SO2 were investigated. The experimental results indicated that the membrane contactor could eliminate these two sour gases simultaneously and effectively. Absorption of SO2 and CO2 was enhanced by the increase in liquid flow rate and decrease in gas flow rate. It was observed that a small amount of SO2 in the flue gas had a slight influence on the absorption of CO2. In addition, the membrane contactor was operated continuously for two weeks to evaluate its duration performance. The results showed that the CO2 mass transfer rate was decreased significantly with the operating time due to partial wetting of membrane pores. After 14days of continuous operation, the CO2 mass transfer rate of the wetted membrane contactor was decreased by 41% but could be retrieved to 86% of the fresh one by increasing the gas phase pressure.
Mixed oxides of TiO₂-MgO obtained by the sol-gel method were used to convert waste cooking oil into biodiesel. Titanium improved the stability of the catalyst because of the defects induced by the ...substitution of Ti ions for Mg ions in the magnesia lattice. The best catalyst was determined to be MT-1-923, which is comprised of an Mg/Ti molar ratio of 1 and calcined at 923K, based on an assessment of the activity and stability of the catalyst. The main reaction parameters, including methanol/oil molar ratio, catalyst amount, and temperature, were investigated. The catalytic activity of MT-1-923 decreased slowly in the reuse process. After regeneration, the activity of MT-1-923 slightly increased compared with that of the fresh catalyst due to an increase in the specific surface area and average pore diameter. The mixed oxides catalyst, TiO₂-MgO, showed good potential in large-scale biodiesel production from waste cooking oil.
•The PV+HSR system which incorporates station and railway PV systems is proposed.•A techno-economic assessment of PV potential of the Beijing-shanghai high-speed railway is performed.•Case study ...shows that the PV+HSR system is promising to cover bullet trains’ most electricity consumption and achieve high-penetration renewable energy operation.
Cities worldwide are stepping up efforts to reshape their infrastructure to ensure a carbon-neutral and sustainable future, leading to the rapid electrification of transportation systems. The electricity demand of this sector, particularly that of high-speed railways, is increasing. Application of the existing infrastructures of railway stations and available land along rail lines for photovoltaic (PV) electricity generation has the potential to power high-speed bullet trains with renewable energy and supply surplus electricity to surrounding users. In this work, a methodology based on a geographic information system was established to evaluate the PV potential along rail lines and on the roofs of train stations. The Beijing-Shanghai high-speed railway (HSR) was used as a case study. Its total PV potential reached 5.65 GW (of which the station potential accounted for 264 MW, approximately 4.68%, of the total potential), with a lifelong generation capacity of 155 TWh, which corresponds to approximately 12% of the total new installed capacity of China in 2020. Although electricity prices and solar resources differed along the railway line, all PV systems were profitable. Moreover, a comparison between the electricity consumption and generation shows that the PV+HSR system can cover most of the electricity demand of the Beijing-Shanghai HSR without a storage system. This concept can be further expanded to other rail lines and stations. Within the context of global carbon peaks and carbon neutrality, the integration of PV and railway systems should be promoted.
▶ The characterization results confirm that the absorbent molecules diffused into PP polymers during the exposure process, resulting in the swelling of the membranes. The absorption-swelling wetting ...mechanism is proposed to explain observations made during the wetting process. ▶ The strong reduction of contact angles indicates that membrane surface hydrophobicity decreased remarkably during immersion due to membrane–absorbent interaction. Membrane surface morphologies and surface roughness suffer from significant and complicated changes after immersing the membrane fibers in the absorbents. ▶ As indicated by the experimental results, improving membrane surface hydrophobicity may be an effective way of overcoming wetting problems.
Membrane wetting by absorbents leads to an increase in mass transfer resistance and a deterioration in CO
2 absorption performance during the membrane gas absorption process. In order to better understand the wetting mechanism of membrane pores during their prolonged contact with adsorbents, polypropylene (PP) hollow fibers were immersed in three different absorbents for up to 90 days. Monoethanolamine, methyldiethanolamine, and deionized water were applied as absorbent solutions. The characterization results of membrane samples confirm that the absorbent molecules diffuse into PP polymers during the exposure process, resulting in the swelling of the membranes. The absorption-swelling wetting mechanism is proposed to explain observations made during the wetting process. The strong reduction of contact angles indicates that the membrane surface hydrophobicity decreases remarkably during immersion due to membrane–absorbent interaction. Membrane surface morphologies and surface roughness suffer from significant and complicated changes after immersing the membrane fibers in the absorbents. Immersion in an absorbent with a high surface tension results in small changes in membrane surface morphology. As indicated by the experimental results, improving membrane surface hydrophobicity may be an effective way of overcoming wetting problems.
This study investigates the use of CaO-CeO2 mixed oxides as solid base catalysts for the transesterification of Pistacia chinensis oil with methanol to produce biodiesel. These CaO-CeO2 mixed-oxide ...catalysts were prepared by an incipient wetness impregnation method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The cerium improved the heterogeneous catalytic stability remarkably due to the defects induced by the substitution of Ca ions for Ce ions on the surface. The best catalyst was determined to be C0.15-973 (with a Ce/Ca molar ratio of 0.15 and having been calcined at 973 K), considering its catalytic and anti-leaching abilities. The effects of reaction parameters such as the methanol/oil molar ratio, the amount of catalyst amount and the reaction temperature were also investigated. For the C0.15-973 regenerated after five reuses, the biodiesel yield was 91%, which is slightly less than that of the fresh sample. The test results revealed that the CaO-CeO2 mixed oxides have good potential for use in the large-scale biodiesel production.
The preparation of a Li-doped MgO for biodiesel synthesis has been investigated by optimizing the catalyst composition and calcination temperatures. The results show that the formation of strong base ...sites is particularly promoted by the addition of Li, thus resulting in an increase of the biodiesel synthesis. The catalyst with the Li/Mg molar ratio of 0.08 and calcination temperature of 823
K exhibits the best performance. The biodiesel conversion decreases with further increasing Li/Mg molar ratio above 0.08, which is most likely attributed to the separated lithium hydroxide formed by excess Li ions and a concomitant decrease of BET values. In addition, the effects of methanol/oil molar ratio, reaction time, catalyst amount, and catalyst stability were also investigated for the optimized Li-doped MgO. The metal leaching from the Li-doped MgO catalysts was detected, indicating more studies are needed to stabilize the catalysts for its application in the large-scale biodiesel production facilities.
The membrane wetting by amine absorbents results in performance deterioration of membrane gas absorption system for CO
2 post-combustion capture. To solve this problem, in this study, the ...polypropylene membrane fiber was modified by depositing a rough layer on the surface to improve its hydrophobicity. Weighing the coating homogeneity, hydrophobicity and modification process efficiency, the mixture of cyclohexanone and MEK system was considered as the best non-solvent. The contact angle increased dramatically from 122° to 158° by the modification, thereby obtaining superhydrophobic membrane surface. The membrane–absorbent interaction results demonstrated that the modification treatment effectively enhanced the stability and maintained the superhydrophobicity of fibers contacting with the absorbent. In addition, continuous CO
2 absorption experiments for up to 20
days were carried out in untreated and modified polypropylene hollow fiber membrane contactors, using 1
mol
L
−1 MEA solution as the absorbent. The long-term system operation results indicated that, even though additional mass transfer resistance was introduced by the surface coating, the modified polypropylene hollow fiber membrane contactor was still technically feasible for CO
2 capture from the power stations.
Zigzag micro-channel reactors have been fabricated and used for continuous alkali-catalyzed biodiesel synthesis. The influences of the main geometric parameters on the performance of the ...micro-channel reactors were experimentally studied. It has been found that the zigzag micro-channel reactor with smaller channel size and more turns produces smaller droplets which result in higher efficiency of biodiesel synthesis. Compared to conventional stirred reactors, the time for high methyl ester conversion can be shortened significantly with the methyl ester yield of 99.5% at the residence time of only 28
s by using the optimized zigzag micro-channel reactor, which also exhibits less energy consumption for the same amount of biodiesel during biodiesel synthesis. The results indicate that zigzag micro-channel reactors can be designed as compact and mini-fuel processing plant for distributive applications.
Highly permeable and mechanically strong porous SiC tubular supports, used for the fabrication of nanoporous SiC membranes, are prepared by the pressureless sintering of β-SiC particles. Their ...transport characteristics are studied via inert gas (He and Ar) permeation tests, while their surface structure is characterized by atomic force microscopy and electron microscopy analysis. In this paper, the effects of the type of starting powders used and their composition, the sintering temperature, and the amount of sintering aids utilized on the transport characteristics and the surface roughness of the sintered SiC porous supports are systematically investigated. These tubular SiC supports exhibit very high fluxes (a He permeance as high as 5.8×10−5molm−2Pa−1s−1) and are mechanically strong to withstand the pressure drops required in their use as membrane supports. They have been used in the preparation of high quality SiC nanoporous membranes.
•Prepared porous SiC supports have very large gas permeance.•Prepared porous SiC supports have excellent mechanical strength.•Membranes with very good permeation properties are prepared using these supports.•Effects of different variables on permeation properties are investigated.
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