Atmospheric concentration characteristics and gas/particle partitioning of PCBs from the North Pacific to the Arctic Ocean

Polychlorinated biphenyls （PCBs） were measured in atmospheric samples collected from the North Pacific to the Arctic Ocean between July and September 2012 to study the atmospheric concentration characteris-tics of PCBs and their gas/particle partitioning. The mean concentration of 26 PCBs （vapor plus particulate phase） （∑PCBs） was 19.116 pg/m^3with a standard deviation of 13.833 pg/m^3. Three most abundant conge-ners were CB-28, -52 and -77, accounting for 43.0% to∑PCBs. The predominance of vapor PCBs （79.0% to∑PCBs） in the atmosphere was observed.∑PCBs were negative correlated with the latitudes and inverse of the absolute temperature （1/T）. The significant correlation for most congeners was also observed between the logarithm of gas/particle partition coefficient （logKp） and 1/T. Shallower slopes （from ∑0.15 to ∑0.46, average ∑0.27） were measured from the regression of the logarithm of sub-cooled liquid vapor pressures （logpoL） and logKP for all samples. The difference of the slopes and intercepts among samples was insignifi-cant （p〉0.1）, implying adsorption and/or absorption processes and the aerosol composition did not differ significantly among different samples. By comparing three models, the J-P adsorption model, the octanol/air partition coefficient （KOA） based model and the soot-air model, the gas/particle partitioning of PCBs in the Arctic atmosphere was simulated more precisely by the soot-air model, and the adsorption onto el-emental carbon is more sensitive than the absorption into organic matters of aerosols, especially for low-chlorinated PCB congeners.

Numerical and experimental study on the particle erosion and gas–particle hydrodynamics in an integral multi-jet swirling spout-fluidized bed

In this paper,using the computational fluid dynamics based on Euler Lagrange and the commercial software Barracuda VR,the gas-particle hydrodynamics and the erosion of particles on the inner wall and internal components of the spouted bed in the integrated multi-jet swirling spout-fluidized bed(IMSSFB)are studied.Erosion experiments have obtained the characterization of particle erosion on internal components and verified the relevant numerical models.The results show that:the particle distribution within the IMSSFB is uneven due to the cyclonic effect of the axial swirl vane(ASV),resulting in particle erosion for the ASV being concentrated on one side;when the gas reaches the top,too high an erosion gas velocity leads to gas backflow.As the filling height increases,there is a tendency for the erosion position of the particles on the ASV to expand upwards.However,the effect of increasing gas velocity on the erosion position is insignificant.

RESEARCH ON THE PARTICLE DISPERSION IN THE PARTICULATE TWO-PHASE ROUND JET

In this paper, the three_dimensional vo rtex filament method was used to simulate the evolution of vortex structures in the axisymmetric round jet. The results agree well with the ones given by Chung and Troutt. Then one_coupling model was employed to calculate the particle motio n based on the computed flows. The results show that the particle motion is affe cted by flows obviously at the case of particle number St1 and negligibly at St1 ,particles distribute around the vortex structures uniformly at St ～1 . When perturbations with wavenumber 5 are introduced to vortex rings, part icles disperse wider along radial direction, which conforms to the experimental results. The degree of particle dispersion is in the direct ratio to the amplitu de of perturbation. The conclusions given in the paper are useful to the practic e usage.

Experimental Study of a Minitype Atmospheric Non-equilibrium Plasma Source

A mini-type of plasma source was studied experimentally. The results showed that the plasma density, which was generated by an atmospheric non-equilibrium plasma source, rises with the increase in driving electric-field and the momentum of gas particles. For a driving electricfield of 56 kV/cm and a gas particles＇ momentum of 10^9 × 10^-22 g·m/s, the ion density can exceed 10^10/cm^3 while the effective volume of the plasma source is only 2.5 cm^2. This study may help develop a method to generate a minitype plasma source with low energy consumption but high ion concentration. This source can be used in chemical industry, environmental engineering and military applications.

Pollution characteristics of 15 gas- and particle-phase phthalates in indoor and outdoor air in Hangzhou

Phthalate esters(PAEs),typical pollutants widely used as plasticizers,are ubiquitous in various indoor and outdoor environments.PAEs exist in both gas and particle phases,posing risks to human health.In the present study,we chose four typical kinds of indoor and outdoor environments with the longest average human residence times to assess the human exposure in Hangzhou,including newly decorated residences,ordinary residences,offices and outdoor air.In order to analyze the pollution levels and characteristics of 15 gasand particle-phase PAEs in indoor and outdoor environments,air and particulate samples were collected simultaneously.The total PAEs concentrations in the four types of environments were 25,396,25,466.8,15,388.8 and 3616.2 ng/m^3,respectively.DEHP and DEP were the most abundant,and DMPP was at the lowest level.Distinct variations in the distributions of indoor/outdoor,gas/particle-phase and different molecular weights of PAEs were observed,showing that indoor environments were the main sources of PAEs pollution.While most PAEs tended to exsit in indoor sites and gas-phase,the high-molecular-weight chemicals tended to exist in the particle-phase and were mainly found in PM2.5.PAEs were more likely adsorbed by small particles,especially for the indoor environments.There existed a good correlation between the particle matter concentrations and the PAEs levels.In addition,neither temperature nor humidity had obvious effects on the distributions of the PAEs concentrations.

Advances in Supercritical Fluid Crystallization

The supercritical fluid crystallization technique is a novel technology for preparing ultrafine particles. This paper introduced the concept and features of the technique with an emphasis on three kinds of supercritical fluid crystallization techniques, i.e. rapid expansion of supercritical solutions, supercritical fluid anti-solvent and particles from gas saturated solutions Some questions and the prospect of this technique were also discussed.

Investigation on the relationship between the fine particle emission and crystallization characteristics of gypsum during wet flue gas desulfurization process

The relationship between the fine particles emitted after desulfurization and gypsum crystals in the desulfurization slurry was investigated,and the crystallization characteristics varying with the operation parameters and compositions of the desulfurization slurry were discussed.The results showed that the fine particles generated during the desulfurization process were closely related to the crystal characteristics in the desulfurization slurry by comparison of their morphology and elements. With the higher proportion of fine crystals in the desulfurization slurry,the number concentration of fine particles after desulfurization was increased and their particle sizes were smaller,indicating that the optimization of gypsum crystallization was beneficial for the reduction of the fine particle emission. The lower p H value and an optimal temperature of the desulfurization slurry were beneficial to restrain the generation of fine crystals in the desulfurization slurry. In addition,the higher concentrations of the Fe3＋ions and the F- ions in the desulfurization slurry both promoted the generation of fine crystals with corresponding change of the morphology and the effect of the Fe3＋ ions was more obvious.With the application of the desulfurization synergist additive,it was beneficial for the inhibition of fine crystals while the thinner crystals were generated.

Numerical Simulation of Gas-particle Flows with Different Swirl Numbers in a Swirl Burner

Swirl burner design was optimized by simulating swirl gas\|particle flows with different swirl numbers at the exit of a small\|scale swirl burner for pulverized\|coal furnaces using the k\|ε\|k p model. The predicted two\|phase time\|averaged velocities and particle concentration distributions for several different cases were compared to improve the design. The effect of the swirl number on the two\|phase velocities and particle concentration was investigated. The results give the two\|phase axial and tangential time\|averaged and fluctuation velocities and particle concentrations, showing that large recirculation zones of gas and particles forms in the near\|axis region of the burner exit, but the particle concentration in the recirculating zone is very low.

New Statistical Theory and a k-ε-PDF Model for Simulating Gas-particle Flows

A k ε PDF (probability density function) model based on a statistical theory for turbulent gas particle flows is proposed, and a numerical procedure combining the finite difference and finite fluctuating velocity group methods is used. The obtained statistically averaged equations have the same form as that of the equations obtained by the Reynolds averaging. Using the k ε PDF model (PDF particle turbulence model combined with k ε gas turbulence model), many terms, such as the diffusion term in particle Reynolds stress equations, can be exactly calculated for verifying the second order moment model. The k ε PDF model is used to simulate gas particle flows behind a backward facing step. Comparison of the predictions using both k ε PDF and the k ε k p models with experimental results shows that the k ε PDF model gives more reasonable nonisotropic features of particle turbulence.

Cold Gas-particle Flows in a New Swirl Pulverized-coal Burner by PDPA Measurement

A new type of swirl burner has been developed to stabilize pulverized\|coal combustion by burning different types of coal at different loads and to reduce NO x formation during combustion. The burner uses a device to concentrate the coal powder in the primary\|air tube that divides the primary coal\|air into two streams with different pulverized\|coal concentrations. This paper reports the measurement of gas\|particle flows at the exit of the different swirl burners using a 3\|D Phase Doppler Particle Anemometer (PDPA). The effect of different geometrical configurations on the two\|phase flow field is studied. The results that give the two\|phase flow fields and particle concentrations show the superiority of the new swirl burner.

INTERACTION BETWEEN SO_2 FROM FLUE GAS AND SORBENT PARTICLES IN DRY FGD PROCESSES

Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal efficiency to meet both technical and economic requirements, and for making the best quality byproduct gypsum as a useful additive for improving alkali soil. Among the possible modifications two major factors have been selected for study: (1) favorable chemical reaction kinetics at elevated temperatures and the sorbent characteristics; (2) enhanced diffusion of SO2 to the surface and within the pores of sorbent particles that are closely related to gas-solid two-phase flow patterns caused by flue gas and sorbent particles in the reactor. To achieve an ideal pore structure, a sorbent was prepared through hydration reaction by mixing lime and fly ash collected from bag house of power plants to form a slurry, which was first dewatered and then dried. The dry sorbent was found capable of rapid conversion of 70% of its calcium content at 700℃, reaching a desulphurization efficiency of over 90% at a Ca/S ratio of 1.3. Experiments confirmed that the diffusion effect of SO2 is an important factor and that gas-solid two-phase flow plays a key role to mixing and contact between SO2 and sorbent particles. For designing the FDG reactor, a new theoretical drag model was developed by combination of CFD with the Energy Minimization Multi-Scale (EMMS) theory for dense fluidi-zation systems. This new drag model was first verified by comparing calculated and measured drag values, and was then implemented in simulation of gas-solid two-phase flow in two circulating fluidized beds with different sizes and flow parameters. One riser has diameter and height of 0.15 m×3m and another one 0.2m×14.2m. Their superficial gas velocities are 4 and 5.2 m·s-1, respectively, and the circulating rate 53 and 489 kg·(m-2·s-1). FCC particles were used in both cases. The results show that not only the static pressure drop along the riser height, but also radial distributions of particle volume fraction have been very well predicted in comparison with experiments. The new drag model is expected to shed more light on the further improvement of SO2 diffusion to solid sorbent and optimization of reactor structure.

Organic aerosol molecular composition and gas–particle partitioning coefficients at a Mediterranean site(Corsica)

Molecular speciation of atmospheric organic matter was investigated during a short summer field campaign performed in a citrus fruit field in northern Corsica（June 2011）. Aimedat assessing the performance on the field of newly developed analytical protocols, this work focuses on the molecular composition of both gas and particulate phases and provides an insight into partitioning behavior of the semi-volatile oxygenated fraction. Limonene ozonolysis tracers were specifically searched for, according to gas chromatography–mass spectrometry（GC–MS） data previously recorded for smog chamber experiments. A screening of other oxygenated species present in the field atmosphere was also performed. About sixty polar molecules were positively or tentatively identified in gas and/or particle phases. These molecules comprise a wide range of branched and linear, mono and di-carbonyls（C_3–C7）,mono and di-carboxylic acids（C_3–C_18）, and compounds bearing up to three functionalities.Among these compounds, some can be specifically attributed to limonene oxidation and others can be related to α- or β-pinene oxidation. This provides an original snapshot of the organic matter composition at a Mediterranean site in summer. Furthermore, for compounds identified and quantified in both gaseous and particulate phases, an experimental gas/particle partitioning coefficient was determined. Several volatile products, which are not expected in the particulate phase assuming thermodynamic equilibrium, were nonetheless present in significant concentrations. Hypotheses are proposed to explain these observations, such as the possible aerosol viscosity that could hinder the theoretical equilibrium to be rapidly reached.

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.

Passive scalar characteristics along inertial particle trajectory in turbulent non-isothermal flows

The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are based on Eulerian framework,which is not enough for developing the probability density function(PDF) model.In this paper,the instantous behavior and multi-particle statistics of passive scalar along inertial particle trajectory,in homogenous isotropic turbulence with a mean scalar gradient,are investigated by using the direct numerical simulation(DNS).The results show that St^1.0 particles are easy to aggregate in high strain and low vorticity regions in the fluid field,where the scalar dissipation is usually much higher than the mean value,and that every time they move across the cliff structures,the scalar change is much more intensive.Anyway,the self-correlation of scalar along particle trajectory is significantly different from the velocities observed by particle,for which the prefer-concentration effect is evident.The mechanical-to-thermal time scale ratio averaged along the particles,<r> p,is approximately two times smaller than that computed in the Eulerian frame r,and stays at nearly 1.77 with a weak dependence on particle inertia.

Size distribution of particulate polycyclic aromatic hydrocarbons in fresh combustion smoke and ambient air: A review

Polycyclic aromatic hydrocarbons(PAHs) are ubiquitous in the atmosphere and they mostly stem from the imperfect combustion of fossil fuels and biofuels.PAHs are inherently associated with homogenous fine particles or distributed to different-sized particles during the aging of air masses.PAHs carried by fine particles undergo a long-range transport to remote areas while those adsorbed on coarse particles have a shorter lifetime in ambient air.More importantly, PAHs with higher molecular weights tend to be bound with finer particles and can deeply enter the lungs, posing severe health risks to humans.Thus, the environmental fate and health effects of particulate PAHs are strongly size-dependent.This review summarizes the size distributions of particulate PAHs freshly emitted from combustion sources as well as the distribution patterns of PAHs in ambient particles.It was found that PAHs from stationary sources are primarily bound to fine particles, which are slightly larger than particles to which PAHs from mobile sources are bound.In ambient air, particulate PAHs are distributed in larger size modes than those in the combustion fume, and the particle size decreases with PAH molecular weight increasing.The relevant mechanisms and influencing factors of particle size distribution changes are illustrated in this article, which are essentially attributed to combustion and ambient temperature as well as the physical and chemical properties of PAHs.Overall, the study on the particle size distribution of PAHs will contribute for a full understanding of the origin, atmospheric behaviors and health effects of particulate PAHs.

Heat and mass transfer study in fluidized bed granulation-Prediction of entry length

Fluidized bed granulation is a process by which granules or coated particles are produced in a single piece of equipment by spraying a hinder as solution, suspension, or melt on the fluidized powder bed. Heat and mass transfer correlation useful for designing a granulator has been derived based on the equivalence of evaporation rate of the liquid to the heat transferred from hot gas to particles： （m/A）Dp^2λ/Lmf（1-εmf）（Tg-Tl）Kg=hDp/Kg.This equation is applied to data on granulation experiments by different workers to calculate Reynolds number and Nusselt number to obtain a relation between heat and mass transfer from gas to particles during granulation on a logarithmic scale from which the following empirical relation is obtained： Nu=0.0205Re^1.3876 which is comparable to Kothari＇s correlation Nu=0.03Re^1.3.By using the heat and mass transfer correlation obtained, the entry length, that is the length of granulator up to which effective heat transfer from gas to bed particles takes place, is estimated, which is also validated with experimental study. The correct estimation of entry length is useful in optimal design of a granulator.

Numerical analysis of reasons for the CO distribution in an opposite-wall-firing furnace

In practical operations,the carbon monoxide(CO)distribution in an opposite-wall-firing furnace(OWFF)is characterized by a high concentration near the side walls and a low concentration in the center,accompanied by a series of combustionrelated issues.To find the reasons for the CO distribution,a numerical study was conducted on a 660 MWe OWFF.The CO concentration profiles,distribution coefficients of coal and air,mixing coefficients,and the aerodynamic characteristics were extracted for analysis.The CO distribution within the furnace greatly depends on the mixing of coal and air.A mismatch between the aerodynamic behaviors of coal and air causes the non-uniform distribution of CO.Taking into consideration that distinctive flow patterns exist within the different regions,the formation mechanisms of the CO distribution can be divided into two components:(1)In the burner region,the collision of opposite flows leads to the migration of gas and particles toward the side wall which,together with the vortexes formed at furnace corners,is responsible for unburned particles concentrated and oxygenized from the furnace center to the side wall.Thus,high CO concentrations appear in these areas.(2)As the over-fire air(OFA)jet is injected into the furnace,it occupies the central region of furnace and pushes the gas from the burner region outward to the side wall,which is disadvantageous for the mixing effect in the side wall region.As a consequence,a U-shaped distribution of CO concentration is formed.Our results contribute to a theoretical basis for facilitating the control of variation in CO concentration within the furnace.