• Energy Research

With two-dimensional particle image velocimetry (2D-PIV), planar flows can be well examined when there is no out-of-plane (perpendicular to the lightsheet plane) flow motion. In gas cyclones, the turbulent swirling flows are three-dimensional. When they are investigated by 2D-PIV, contamination is introduced into the experimental results due to the existence of considerable out-of-plane velocity caused by the tangential gas motion. In this paper, an experimental method is introduced to investigate the axial and radial velocities by 2D-PIV, followed by the proposed contamination-removing schemes. The contamination on the axial velocity has been efficiently eliminated whereas that on the radial velocity is difficult to evaluate. The radial velocity distribution is then obtained based on a local mass balance calculation. The flow pattern in the dust hopper is also well examined.

The separation efficiency and the flow field of a dynamic cyclone were studied experimentally and simulated using commercial CFD software (FLUENT 6.0). The experimental results show that the rotational classifier position and the ratio of the classifier opening area to the inlet area have significant impact on the separation efficiency of the dynamic cyclone. The separation efficiency can be significantly improved as the classifier rotates at a speed beyond its natural swirling frequency. The RSM model was used to simulate the 3-D gas flow field, and the simulation predictions were validated by the experimental results measured by a five-hole pressure probe. The tangential velocity distribution in the dynamic cyclone body can be divided into three zones: inlet, separation, and bottom. Each zone has its own tangential velocity distribution curve. The effects of operating conditions and geometric parameters of the classifier on the tangential velocity distribution were also studied.

Abstract Understanding the swirling flow in a gas cyclone is of great importance in improving the cyclone design. Once the three-dimensional strong swirling flow is fully understood, cyclone performance such as pressure drop and separation efficiency can be improved by optimizing the cyclone design. The swirling flow was investigated by the stereoscopic particle image velocimetry (Stereo-PIV) in this work. The instantaneous whole-field tangential, axial, and radial velocities were measured simultaneously in the cylindrical and conical separation zone, and in the dust hopper area of the cyclone with gas inlet velocity of 7.2 – 15.0 m / s . The time-averaged flow pattern in the cylindrical and conical sections of the cyclone showed: a typical Rankine vortex with inner quasi-forced vortex and outer quasi-free vortex which is generated by tangential gas velocity; inner upward flow and outer downward flow of axial gas velocity; and centripetal flow in the region close to the wall due to the presence of radial gas velocity. In the dust hopper, a secondary longitudinal circular flow is formed in the annulus area between the conical body and the cylindrical wall. Experimental results indicate that the separated particles may be re-entrained into the cyclone from the bin to degrade the separation efficiency of the cyclone.

This paper studies a dynamic cyclone with a rotary impeller inside experimentally and numerically. The experiment mainly focuses on the separation efficiency, while the numerical simulation describes the flow field in the dynamic cyclone. The discrete phase model (DPM) is also used to predict the fractional efficiency of the dynamic cyclone, and the predictions are compared with the experimental results. The dynamic cyclone has been demonstrated to be very helpful for increasing the separation efficiency when the impeller rotates at greater speeds. The simulation predictions prove that the tangential velocity distributions are mainly dominated by the rotational speed for the region of impeller and dominated by the inlet velocity for the region outside of the vortex finder. Both the experiment and simulation show that the effects of inlet velocity on the separation efficiency are different for different rotational speeds.

Abstract Liquefaction of biomass with proper solvents and catalysts is a promising process to produce liquid biofuels and valuable chemicals. In this study, pinewood sawdust was liquefied in the presence of various supercritical solvents (carbon dioxide, water, acetone, and ethanol) and catalysts (alkali salts and acidic zeolites). The liquid, gas and solid products were analyzed using GC–MS, FT-IR, elemental analyzer, 1H NMR, 13C NMR. The experimental results showed that both solvent and catalyst can significantly improve the liquefaction process by increasing the yield of liquid oil and suppressing the formation of solid residue. K2CO3 showed the best performance by doubling the yield of bio oil. Meanwhile, the maximum bio-oil yield (30.8 wt%) and the minimum solid residue yield (28.9 wt%) were obtained when ethanol was employed as the solvent. Solvents can also strongly affect the distribution of liquid products. 2,4,5,7-tetramethyl-phenanthrene and bis(2-ethylhexyl) phthalate were the premier compounds in liquid product as supercritical carbon dioxide is used as solvent while 2-methyl-naphthalene became the main composition when water is used as solvent.

AbstractBitumen extracted from oil sands is a highly viscous fluid; thus, its transportation via pipelines in its original form resembles a major challenge. Partial upgrading is a recently proposed approach that aims to reduce bitumen's viscosity to meet the pipeline specifications. To optimize the process and make it more cost‐effective, a novel approach is proposed and researched in this study. Ionic surfactants were for the first time employed to promote thermal cracking reactions and dispersion of asphaltenes in bitumen at elevated upgrading temperatures. Three surfactants representing the cationic, nonionic, and anionic charges were studied at the thermal upgrading conditions (360–400◦C) at their optimal addition ratios to mimic the bitumen partial upgrading conditions. The results demonstrated that the cationic surfactant (dodecyltrimethylammonium bromide, DTAB) surpassed the other two surfactants and that with the addition of only 0.25 wt% of it, it can effectively reduce the viscosity of bitumen by up to 60% more than the upgraded bitumen with no additives under the same upgrading temperature. The Saturates, Aromatics, Resins, and Asphaltene analysis revealed that the contents of saturates and aromatics within the upgraded bitumen were also enhanced when DTAB was added. Moreover, the detailed asphaltene nanostructural analysis using X‐ray diffraction, high‐resolution transmission electron microscope, and thermogravimetric analysis revealed that the addition of the cationic surfactant (DTAB) resulted in an increased asphaltene nanostructural disorder, smaller polycyclic aromatic hydrocarbons size, and increased fringe curvature, as compared with the upgraded bitumen's asphaltene with no surfactants. Hence, the results have suggested that DTAB, a cheap and readily available ionic surfactant, can serve as a potential upgrading additive for designing partial upgrading procedures to produce upgraded bitumen with much less viscosity at lower upgrading temperatures. This upgrading technique will result in an upgraded bitumen that requires significantly reduced volumes of diluent for transportation.

Abstract The critical transition velocity, Ucr, previously defined by Liang et al. [W.-G. Liang, S.-L. Zhang, J.-X. Zhu, Y. Jin, Z.-Q. Yu and Z.-W. Wang, Flow characteristics of the liquid–solid circulating fluidized bed, Powder Technol., 90 (1997) 95–102.] to demarcate the liquid–solid conventional and circulating fluidization regimes, was found to vary with the total solids inventory and the solids feeding system. In this work, an onset velocity for circulating fluidization regime, Ucf, is proposed to give the lowest Ucr value and to provide a convenient demarcation velocity that is independent of system geometry. This liquid velocity is obtained by measuring the time required to empty all particles in a batch operated fluidized bed under different liquid velocities. This method can be used for a wide range of particles and involves less influence of the operating conditions such as the solids inventory and the solids feeding system. Compared to the critical transition velocity, this newly defined onset velocity is a more intrinsic parameter, only dependent on the liquid and particle properties. Based on the experimental results obtained in this work and other published results, the influence of particle properties and equipment setup on the onset velocity is also discussed.

AbstractCH3OH is an energy carrier that can be generated from renewable resources and be used as a fuel in fuel cells and internal combustion engines and a platform chemical for the synthesis of value‐added chemicals or gasoline. Carbon dioxide (CO2) hydrogenation is one of the widely researched methods to generate methanol. The traditional CO2 hydrogenation reaction method (requires high H2 pressure and temperatures) has attracted considerable attention. However, the new emerging field of catalysis referred to as nonthermal plasma (NTP) catalysis has also been developed extensively for methane reforming and CO2 hydrogenation to methane and CO. The plasma‐assisted approach not only presents remarkable advantages, such as room temperature and atmospheric H2 pressure but also has great potential to be powered by renewable electricity in a flexible way since it can be easily switched on/off. In this account, we review the recent articles published on methanol synthesis from CO2 and H2 using NTP. We reviewed and discussed the mechanism of this reaction under NTP, the modification of the reactor configurations, and the rationale behind the catalyst design. In the end, we discussed the advantages and disadvantages of each of these works and the future perspectives of this interesting privileged reaction. We believe this review is of interest to researchers active in sustainable heterogeneous catalysis.