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In recent years, as the frequency of debris flow outbreak in strong earthquake areas has increased and the scale has been expanding, in order to explore the erosion characteristics of debris flow, a lateral erosion flume model experimental device has been designed, and 18 groups of incomplete orthogonal experiments have been carried out, with a unit weight of debris flow of 1.6~2.0 g/cm3, a content of fine particles in the accumulation of 0~28.82%, and a longitudinal slope gradient of the gully of 8°~20° as variables. The results show that the erosion width, erosion depth, and erosion volume decrease with the increase in fluid bulk density and increase with the increase in gully slope. When the longitudinal slope of the gully was 16°, the sediment with 11.40% fine particles had the strongest erosion effect, indicating that more or less fine particles are not conducive to the occurrence of lateral erosion of the gully. Finally, through multi-factor variance analysis, it was found that the order of the three factors on the gully lateral erosion degree from strong to weak is: debris flow unit weight, gully slope, and accumulation grading. The analysis results further showed that the unit weight of debris flow has the greatest impact on the erosion degree of the side slope, which is consistent with the experimental results. The research results have important reference significance for revealing the mechanism of lateral erosion and improving the level of debris flow disaster prevention in strong earthquake areas. [ABSTRACT FROM AUTHOR]

Abstract: Numerical technology has been widely used for the study of the electrostatic precipitators (ESP) and the bag filters. This paper presents a numerical model for a scale hybrid particulate collector (HPC), which combines the ESP technology and the filtration technology together. The collection process of the HPC is unsteady as the pressure drop across the bag filter increases with the deposition of the particles. The physical processes of the model include the corona discharge, the fluid flow, the particle charging and the filtration. The corona discharge field is solved by using a finite volume method. For the fluid field, the unsteady and incompressible Navier–Stokes equations with the RNG κ–ε turbulence equations are solved. The effect of the electric field on the fluid field named electro-hydrodynamic is also considered. For the particle charging, the filed-diffusing combined model of Lawless (1996) is adopted. For the filtration, an unsteady cake formation model is proposed. The pressure drop across the cake is calculated according to the mass density of the cake. The coefficient between the pressure drop and the mass density of the cake comes from the experimental data. Applying the numerical model to the HPC, the influence of the hole diameter of the perforated-plate on the collection efficiency of the electrostatic zone is analyzed. Numerical results show that the collection efficiency of the electrostatic zone of the HPC has no certain relation with the hole diameter of the perforated plate. The effect of the hole diameter of the perforated-plate on the collection efficiency of the electrostatic zone becomes weaker with increasing the applied voltage. [Copyright &y& Elsevier]

Abstract: The size distribution, microstructure, and chemical composition of particulate matter samples from coal-fired power plants in China were measured using a laser particle analyzer, a scanning electron microscope (SEM), and an inductively coupled plasma-atomic emission spectrometer (ICP-AES). The size distribution showed differences between the electrostatic precipitator capture efficiencies for coarse and fine particles. The microstructure measurements showed three typical particulate microstructures, spherical particles, plerospheres, and irregular particles. The surfaces of most spherical particles had microspheres that were often agglomerated together. The chemical composition of the particulate matter changed as the size decreased, while had differences from different feed coal. [Copyright &y& Elsevier]

The ash fouling during coal combustion is initialized by a deposition of ‘sticky’ inner layer composed of fine particulate matter (PM). In this work, we present a quantitative investigation on the built-up of the initial deposit layer and its roles in the capture of coarse fly ash particles. The fly ash and ash deposit are sampled in a 25 kW self-sustained pulverized coal combustor for various lignite samples including Zhundong and Hami lignites. The ash collection efficiency onto the probe is positively correlated to the ultrafine particle formation fraction. The deposition rate of fine particle PM 10 is modeled in a combined Eulerian-Lagrangian scheme, with an input particle concentration measured at the entrance of boundary layer. The predicted results divulge that the thermophoresis enhances the impaction efficiencies of submicron and micron sized particles by 1–2 orders. The deposited particles are more concentrated on the central top region of the probe, and the trend is even more remarkable for larger particles, consistent with experimental observations. For both Zhundong and Hami lignites, the deposits are largely composed of fine PM 10 and condensed matter during the initial stage of one minute, but the weight percentages of fine particle deposits over the total deposit mass decrease significantly in the subsequent 5–10 min. Consequently, the average sticking efficiency of the coarse mode PM 10 + increases asymptotically as the deposited PM 10 grows to ~ 1.5 g/m 2 . Zhundong lignite shows higher saturated sticking efficiency of PM 10 + than Hami lignite, which is possibly attributed to the different surface properties of the bulk ash particles. [ABSTRACT FROM AUTHOR]

Thermophoresis is an important mechanism for submicron particle capture by droplets. The thermophoretic deposition efficiencies under varying Reynolds ( Re ) numbers and temperature differences are obtained from the direct numerical simulation of the submicron particle flowing around the droplet. Comparison of the results calculated under the same conditions through the classical thermophoretic deposition efficiency formula and by numerical simulation shows that the Davenport formula always returns greater values than the numerical simulation, by a relative deviation of 19.8%–63.8%. The relative deviation decreased first and then increased with increasing difference in temperature, and increased gradually with increasing Re . The deviation resulted from the assumption that the particle concentration on the droplet surface is equal to that of the incoming flow in the formula deduction process. The convection of the gas and the thermophoresis of the particles together determined the migration of the particles in the boundary layer, and so determined the particle concentration distribution on the surface of droplets. Thus, the particle concentrations on the surface of droplets are actually lower than those of the incoming flow and are distributed bimodally on the surface. The dimensionless particle concentration on the surface of droplets decreased with increasing Re , and increased first then decreased later with increasing difference in temperature. The dimensionless thermophoretic driving velocity and Re were adopted to correct the formula. The results calculated by the corrected formula were consistent with the numerical simulation employed in this paper, such that the maximum relative deviation was reduced from the original 66.8% to less than 8%. [ABSTRACT FROM AUTHOR]

The impact behavior of airborne particles directly affects their capture by droplets in the atmosphere and industrial pollution control processes. This process was simulated by a dynamic model and analyzed for hydrophobic micron particles. Based on the analysis of energy conversion, the criteria were developed and verified by dynamic simulation to ascertain three impaction modes by the submergence/rebound critical velocity ( U S / R ) and the rebound/oscillation critical velocity ( U R / O ). The criteria indicated that surface tension coefficient, contact angle, and particle diameter are the key parameters to affect the critical velocities, between which exists the rebound velocity range. As the surface tension coefficient and the advancing angle increased, U S / R and U R / O increased, the rebound velocity range widened. As the receding angle increased, U S / R remained unchanged, while U R / O decreased, the rebound velocity range widened. As the particle size increased, U S / R and U R / O decreased, the rebound velocity range narrowed. The values of the above-mentioned key parameters considered in the simulation covered the usual parameter ranges of the wet deposition or wet scrubbing process. The simulation results showed the non-negligible possibility of particle rebound in such processes. The attachment efficiency of airborne particles can be determined by the proposed criteria combined with the incidence velocity distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • The PM 0.5 yield drop then rise with CaCl 2 loading, the bottom at 1.5 wt% Ca. • Soot inhibition and CaCl 2 condensation cause the two-stage trend of PM 0.5 yield. • The release rate of Ca into PM 0.5 increases with temperature and CaCl 2 loading. • CaCl 2 -impregnation reduces the sizes of the soot primary particles and aggregates. • The interaction mechanisms between CaCl 2 and soot are proposed. This study investigated the influence of CaCl 2 on fine particulate matter (PM 0.5) formation during coal pyrolysis. Two acid-washed coals were loaded with different amount of CaCl 2 by physical impregnation. Pyrolysis experiments were conducted in a flat-flame burner at 1400 K, 1600 K, and 1800 K. The PM 0.5 yield was evaluated through the size-segregated sampling with a low pressure impactor (DLPI+). Then, the transformation properties of CaCl 2 was analyzed with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the soot properties were analyzed with transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results show that PM 0.5 yield is affected by coal type, CaCl 2 loading level, and pyrolysis temperature. Loading small amount of CaCl 2 can reduce the PM 0.5 yield through soot inhibition, while high loading of CaCl 2 increases the PM 0.5 yield by forming mineral particles, the lowest PM 0.5 yield occurs at 1.5 % Ca content. The PM 0.5 reduction rate of CaCl 2 increases then decreases with temperature from 1400 K to 1800 K. On all tested conditions, the PM 0.5 yield of low-rank Zhundong subbituminous coal was lower than Shenhua bituminous coal. The release rate of Ca into PM 0.5 is positively related to pyrolysis temperature and CaCl 2 loading level. Ca loading decreases the sizes of soot primary particles and agglomerates, and leads to smaller amorphous cores and more disordered graphitic shells in the soot primary particles. CaCl 2 loading also causes the dealkylation and deoxygenation of soot. The influence of CaCl 2 on soot formation can be summarized as the catalytic effect on soot precursor formation, the enhancement of soot nucleation, and the inhibition of soot coagulation. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) generated from pulverized coal combustion is influenced by a process of vaporization, nucleation and condensation/reaction of semi-volatile minerals. The objective of the work is to identify the controlling mechanism of the enrichment of volatile sodium (Na). Three representative kinds of coal with different rank and mineral content, Zhundong lignite, Hami lignite and high-ash-fusion (HAF) bituminous, were burned in a 25 kW self-sustained pulverized coal combustor. Zhundong lignite, possessing medium rank among the three coal samples, exhibits the highest formation ability of ultrafine PM 0.2 , indicating a prominent effect of mineral content over that of coal rank on PM formation. The size partitioning behavior of sodium is affected by the molar ratio Na 2 O/(SiO 2 +Al 2 O 3 ) instead of the absolute Na content. With this ratio increasing from 0.27 (HAF bituminous) to 20 (Zhundong lignite), the gas-to-particle conversion of Na transits from a surface-reaction controlled process to a nucleation-condensation/coagulation dominated pathway. The Na partitioning behavior of Zhundong lignite is then quantitatively interpreted by a population-balance-based theoretical approach. The model reveals the details on the competing processes of homogeneous nucleation and vapor condensation, resulting in that the simulated final particle mass size distribution exhibits reasonable agreement with the experimental result. The model has also successfully reproduced the d p 0 dependence of Na fraction in the ultrafine size regime from a process of homogeneous nucleation under the decreasing gas temperature from 1420 to 1270 K. [ABSTRACT FROM AUTHOR]

Introducing airflow into the low-intensity dry magnetic separator (LIDMS) is an effective means to improve the separating efficiency of ferromagnetic particles under dry conditions. In this study, a multi-physical coupling model was established to compare the separating performance of LIDMS under four typical air supply modes. The result shows that Mode D can maximize the competing force along the normal direction of the drum due to the vertically outward air supply mode, and its separating performance is the best, especially for the particles with a fine diameter. The mechanism of airflow under different modes which enhances the LIDMS is expounded by analyzing the characteristics of the magnetic field and the flow field and calculating the forces on particles with various properties. We expect that this study could provide a reference for the dry separation of magnetic minerals and the development or optimization of LIDMS under airflow conditions. [Display omitted] • The performance of magnetic separation under different air supply modes is compared. • A multi-physical model is established to simulate the magnetic separation process. • The difference in separation performance is explained by analyzing the flow field and forces on particles. • The airflow in a normal direction can maximize the dry magnetic separation efficiency. [ABSTRACT FROM AUTHOR]

With the increasing use of low-rank coal, the upgraded semi-char produced through low-temperature pyrolysis of lignite is one of promising alternatives towards the clean and high efficient utilization. The co-firing of these pyrolytic semi-chars with parent coals has received more attention. In this paper, a kind of semi-char, produced from Hulunbuir (HB) lignite under a pyrolysis temperature of 504 °C, was burned in a 25 kW self-sustained pulverized coal combustor. Different mass blending ratios of semi-char (0%, 40%, 60% and 100%) were used. The results indicate that the PM 0.1 yield from pure combustion of HB lignite is ∼1.6 times of that from semi-char. The PM 0.1 yields of the coal/char blends are much less than the linear summation of yields of two blending fuels without considering their interactions. As for coarser PM mode, the reductions still exist for both PM 0.1–1 and PM 1–10 particles. The different PM yields of pure combustion cases are attributed to less volatile mineral species and also less fragmentation degree of semi-chars during combustion. A mechanism is postulated for PM reduction during the combustion of coal blends. PM 0.1 amounts are decreased since the volatilized mineral species is considerably scavenged by the previously formed semi-char surfaces, as partly evidenced from a time scale analysis. The scavenged compounds then serve as “glue” to convert ash particles to larger agglomerates, which may result in the reduction of PM 0.1–10 yields. [ABSTRACT FROM AUTHOR]

In this work, the pulverized coal combustion of Zhundong lignite was conducted in an optically-accessible, downward Hencken flat-flame burner to investigate the incipient formation of ultrafine particulate matter (PM). The ultrafine PM were collected in - flame from distinct positions under 1800 K, 1500 K and 1200 K using a self-designed thermophoretic sampler, together with extensive conventional transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS) examinations. A novel in situ low-intensity phase-selective laser-induced breakdown spectroscopy (PS-LIBS) was further introduced to diagnose the dynamic behavior of particle-phase sodium during the pulverized coal combustion. The primary particles in the collected ultrafine PM have mean diameter of 8–15 nm, with Si and Na as main mineral components based on TEM/HRTEM–EDS results. The formation of ultrafine PM is regarded as a process of multi-component flame syntheses of mineral precursors, in which the competition between the devolatilization and the coalescence of particles are of most significance. Finally, based on an approach of time scale analysis, three characteristic times of minimum mean diameter of primary particles, the initial increment point of particle-phase sodium and the maximum devolatilization are found to be highly correlated. [ABSTRACT FROM AUTHOR]

• The addition of ion-exchangeable calcium reduces the soot mass yield during coal pyrolysis. • Ion-exchangeable calcium decreases the sizes of soot primary particles and soot aggregates. • Calcium loading shrinks the disordered cores of soot, promotes the soot graphitization, and leads to more compact aggregates. • The size distributions of inorganic species show that calcium and sodium play different roles in soot formation. This work investigated the effect of ion-exchangeable calcium on the mass yield, size distribution and structural properties of carbonaceous particulate matter from coal pyrolysis. The raw, acid washed and calcium-exchanged coal samples were pyrolyzed in a flat-flame burner at 1600 K. The particulate matter was collected with a three-stage dilution sampler. Then, the particle size distributions were measured by a low pressure impactor (DLPI+) and a scan mobility particle sizer (SMPS). The results show that, with the addition of ion-exchangeable calcium, the soot yield reduces, and the size growth of soot particles is inhibited. Transmission electron microscopy (TEM) analysis shows that ion-exchangeable calcium diminishes the sizes of disordered cores in soot primary particles, accelerates the graphitization of soot and makes the soot aggregates more compact. The chemical structures derived from Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) indicate that the graphitization degree of the soot is first enhanced and then inhibited with increasing calcium loading amount. Additionally, the inorganic species in the size-segregated soot particles were characterized. The fractions of calcium and sodium in soot show opposite trend with particle size. Unlike Na, which nucleates before soot inception, Ca tends to participate in both the soot nucleation and surface growth processes, and is enriched at larger particle size. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, recent advances in the discrete-element method (DEM) for describing motion, deposition, agglomeration or aggregation of a large number of adhesive spherical particles immersed in fluid flows, termed as adhesive particulate flow, are reviewed. The constitutive equations together with the length and time scales of DEM are compared with those of other similar Lagrangian particle methods, e.g., molecular dynamics (MD), Brownian dynamics (BD), dissipative particle dynamics (DPD). The adhesive contact force and torque models in the presence of different adhesive effects are examined, including van der Waals force, ligand-receptor binding, liquid bridging force, interface adhesion, and sintering forces, all of which play an important role in DEM formulations for different types of adhesive particulate flow problems of interest in energy, combustion and environmental fluid mechanics problems. A summary of various kinds of particle-field interactions is presented, including fluid forces, electric field forces, acoustic force, and thermophoretic force. The computational method is illustrated by application to a series of examples involving capture of spherical particles by a fiber in a uniform upstream flow, examining the deposition/aggregation patterns of both mono-size and binary-size particles on the cylinder with and without the presence of electric field effects, which may be due either to charging of the cylinder or polarization of the particles. Particle capture problems of this sort are commonly encountered in filtration problems and ash-removal problems experienced in environmental and combustion applications, respectively. The article concludes with a discussion of remaining modeling challenges in development of discrete-element methods for adhesive particulate flow fields. [Copyright &y& Elsevier]