CO2 Mass Fraction Research Articles

Influence Mechanism of (NH4)2SO4 on the Composition and Structure of Fe-Co Alloys

Fe-Co alloys have the advantages of high saturation magnetization and high magnetic elongation. They are used in electromagnet pole heads, earphone vibration films, magnetostriction transducers, and so on. At present, few papers have been published on the co-deposition process of Fe-Co alloys. In the present work, smooth dense Fe-Co films of 10 μm were successfully prepared in an economical, green, sulfate solution system via electrodeposition. The cathodic polarization curves were measured separately under different conditions, and the electrochemical analyses showed that the increase in the main salt concentration is beneficial for obtaining higher deposition rates. An increase in temperature can increase the current density of electrochemical reduction of Fe2+, and 50 °C is a suitable temperature at which to prepare the Fe-deposited layer with a flat surface. The increase in Co2+ concentration can favor the co-electrodeposition process of Fe-Co alloys. Secondly, the EDS results showed that the mass fraction of Co in the films increased linearly with the increase in Co2+ concentration in the solution. The mass fraction of Co in the films gradually increased with the increase in current density. The mass fraction of Co in the films gradually decreased with the increase in (NH4)2SO4 concentration. In addition, the XRD showed that the grain size of the Fe-Co alloy films was closely related to the concentration of (NH4)2SO4 in the electrolyte, and the smallest crystallite size of the Fe-Co alloy film was 17 nm. SEM showed that (NH4)2SO4 can significantly affect the surface morphology of the films, in which the cracks are obviously removed.

Mitigation of breathing contaminants: Exhaust location optimization for indoor space with impinging jet ventilation supply

Densely occupied spaces (e.g., classrooms) are generally over-crowded and pose a high risk of cross-infection during the pandemic of COVID-19. Among various ventilation systems, impinging jet ventilation (IJV) system might be promising for such spaces. However, the exhaust location of the IJV system used for densely occupied classrooms is unclear. This study aims to investigate the effects of exhaust location on the removal of exhaled contaminants in a classroom (15 × 7 × 5 m3) occupied by 50 students. Exhaled contaminants are modeled by a tracer gas released at the top of each manikin. The reference case has three exhausts evenly distributed in the ceiling. The results indicate that: a) a recirculation airflow entraining exhaled contaminants exists above the occupied zone; b) this recirculation air flow entrains contaminants and accumulates them at the upper part of the room near the diffuser; c) locating merely one exhaust on the same side of the supply diffuser leads to the best indoor air quality, i.e., it reduces the mean age of air from 278 s to 243 s, the mass fraction of CO2 from 753 ppm to 726 ppm, and the concentration of tracer gas from 305 ppm to 266 ppm; d) this layout still performs the best when the supply velocity drops to 0.5 m/s. It is worth noting that the proposed layout has fewer exhausts than the reference case but performs better. These results conclude that the exhaust for large spaces is not evenly distributed but depends on the indoor airflow pattern: the key is locating the exhaust near the region with high contaminant concentration. Factors determining the recirculation airflow are suggested to be further studied.

Combustion of Pulverized Coconut Shell in Lab-Scaled Incinerator Rig using CFD

In power generation, particle size distribution (PSD) of pulverized coal used in a power plant was 65%-70% passing 200 mesh or known as 76 microns. Since coal took hundreds of millions of years to form, it is not renewable energy and coal will release harmful gases after-burn. Thus, biomass has become an alternative fuel for reducing the consumption of coal and the emission of harmful gases. Coconut shell has the potential to substitute coal as fuel. In this study, Computational Fluids Dynamics (CFD) is used for simulating the combustion process in the lab-scaled incinerator rig (LSIR). The behaviours of pulverized coconut shells and the effect of excess air during combustion are studied. The results showed that the average carbon monoxide (CO) and carbon dioxide (CO2) mass fraction was calculated at 0.0196 and 0.257 respectively. The combustion efficiency was determined as 92.94%. The percentage of excess air (EA%) was increased by increasing the velocity of inlet air for investigating the responses of combustion efficiency. The EA with 39% was predicted as the most suitable EA for the combustion because the heat generated at 39% EA was the highest and its volume average temperature was recorded as 1198.7K. Besides, the combustion efficiency was increasing when the EA% is increased by calculating from every volume average of mass fraction of CO and CO2.

Carbon dioxide and acetone mixtures as refrigerants for industry heat pumps to supply temperature in the range 150–220 oC

Industry decarbonization is a key a challenge towards the transition to climate neutrality. Indeed, there is a need to satisfy heat at temperatures higher than 150 °C in relevant industrial sectors by upgrading lower temperature heat flows, such as heat from renewable heat sources, ambient heat or industrial waste heat. High temperature heat pumps (HTHP) can upgrade such heat flows enabling great savings in carbon emissions. New refrigerants are needed to develop HTHPs achieving high performances at high temperatures. This paper proposes the use of a new zeotropic mixture composed of carbon dioxide and acetone as the refrigerant of HTHPs working in the temperature range of 150–220 °C. The new fluid is compared with existing pure refrigerants currently used. The thermodynamic characterization of the CO2/acetone mixtures shows temperature glides below 50 K for CO2 mass fractions up to 10%. The best HTHP performance is shown for the mixture 5% CO2/95% acetone in mass fraction. For instance, such a mixture obtains a COP of 5.63 when the target outlet sink temperature is 200 °C and the temperature difference between the outlet heat sink and the inlet heat source is 70 K, showing an improvement of 46% compared to pure acetone.

Numerical Simulation of the HIsmelt Main Reactor for Optimizing Heat Transfer and Combustion at Different Hot Air Oxygen Contents and Daily Iron Production

ABSTRACT The HIsmelt process uses pulverized coal and iron ore as raw materials, eliminating the need for coking and iron ore lumping compared to traditional blast furnace ironmaking processes, and significantly reducing CO2 and other pollutants emissions. However, as a new ironmaking process, the flow field, heat transfer, and combustion influencing factors of the main reactor are not resolved. Therefore, in this study, based on the consideration of fluid mechanics, heat conduction, and combustion reaction, a two-dimensional mathematical model was developed for the upper space of SRV (smelting reduction vessel), the main reactor of the HIsmelt ironmaking process, based on actual production data. The effects of hot air oxygen content and daily iron production on the velocity field, temperature field, and CO2 content field inside the SRV were investigated. The results show that as the oxygen content of hot air increases, the central airflow in the furnace develops downward, the gas temperature rises gradually, and the CO2 mass fraction generally shows a rising trend. When the daily output of iron increases, the velocity of airflow in the furnace decreases significantly, the gyratory zone moves upward; the high-temperature distribution zone in the furnace contracts; and the CO2 mass fraction decreases.

Numerical and Chemical Kinetic Analyses on the Formation of CO and CO2 for C1–C4 Hydrocarbon Alkanes in a Hot Co-Flow under MILD Combustion

In this present study, computational fluid dynamics and chemical kinetic analysis are conducted to explore the formation of CO and CO2 for a fuel jet comprising C1–C4 hydrocarbon alkanes in a hot co-flow burner under a moderate or intense low-oxygen dilution (MILD) combustion environment. The fuel jet comprises three cases of fuel mixture (case 1: CH4 + H2, case 2: C3H8 + H2, and case 3: C4H10 + H2) having constant mixture density and operating under a fixed jet Reynolds number. The combustion and emission characteristics are analyzed in terms of radial profiles of temperature and mass fraction of OH, CH2O, HCO, CO, CO2, and C2H2 in the MILD combustion region. The formations of CO and CO2 are examined with the help of reacting flow analysis using the computational fluid dynamics (CFD) tool. The formation of CO is reported as maximum for case 3 and minimum for case 1. However, the reverse trend is observed in the case of CO2 formation. The reacting flow analysis from the CFD work suggests that the reaction C2H2 + O = CH2 + CO strongly influences CO formation in all three fuel mixtures cases. In the current study, acetylene is found to be the primary species that affects the CO formation in the adopted fuel mixtures and is mainly responsible for the increased CO concentration in case 3. Likewise, the formation of CO2 is majorly influenced by the reaction CO + OH = CO2 + H. The reacting flow analysis is assisted with the help of a zero-dimensional perfectly stirred reactor (PSR) model to elucidate the underlying chemistry and explore the significant reaction pathways influencing the formation of CO and CO2. The ethylene route in the reaction pathway substantially plays a vital role in the CO formation in all three fuel mixtures.

Deterioration and Instability of Heat Transfer to H2O/CO2 Mixtures in Near-Critical Region for Horizontal Flow

Abstract In this work, we experimentally investigated the deterioration and instability of heat transfer to H2O/CO2 mixtures in the near-critical region, following our series of works on their normal and enhanced heat transfer, hydraulic resistance, and thermophysical properties. The experimental pressure is 24 MPa, temperatures are 330–400 °C, CO2 mass fractions are 9.8 and 15.0%, mass fluxes are above 940 kg/m2/s, heat fluxes are below 211 kW/m2, and flow is horizontal. Experiments show that the heat transfer deterioration for the supercritical H2O/CO2 mixture occurs when the fluid temperature is lower than the pseudo-critical temperature (Tpc) and the wall temperature is higher than Tpc, similar to the condition for supercritical pure fluids, but the onset heat flux is much lower. Results also show that the heat transfer instability for the supercritical H2O/CO2 mixture occurs not only moderately near Tpc (similar to supercritical pure fluids) but also more significantly near the critical miscible temperature. All of these distinct phenomena were attributed to the mixture feature.

Emissions Reduction by Combustion Modeling in the Riser of Fluidized Bed Combustor for Thar Coal Pakistan

Pakistan has experienced a protracted electricity shortage for the past few years. However, despite Pakistan’s abundant coal deposits, modern coal combustion technology is still required to reduce emissions. Pakistan is struggling to utilize its energy resources and currently experiencing an electrical shortage of more than 8000 MW. The research study models the combustion performance in a fluidized bed riser using ANSYS FLUENT software to understand the combustion behavior of low-rank Thar coal. A simple circulating fluidized bed (CFB) combustion riser was modeled for computational fluid dynamics (CFD) to study the hydrodynamics of gas-solid flow in a circulating fluidized bed riser to reduce emissions and operating costs. Three different types of risers/combustors geometries were used center flow, counter flow, and parallel flow. The CFD model for the solids segment with a k-e turbulence model and the viscosity of static particles in the gas segment both showed excellent mixing performance. According to the FLUENT data, the riser/combustor maximum temperature is around 1400 K or 1130 o C at the primary burning sector in the bed center. According to velocity contours, the greatest velocity in the center-oriented riser/combustor peaks at 3.3 m/s. The CO and CO2 both mass fraction counters show maximum concentration in the center geometry, whereas lower CO concentration is found in parallel geometry. The lowest level of NOx is established in the parallel geometry at around 15 ppm, whereas the counter contours establish the maximum level of NOx at about 31 ppm. Circulating Fluidized Bed Combustor is found to be the most advantageous and effective technology for producing power from Thar lignite coal and reducing emissions.

The impact of geological heterogeneity on coupled CO2 storage and geothermal extraction in inclined reservoirs

CO2 plume geothermal (CPG) production is an emerging CO2 utilization approach coupled with CO2 geological sequestration. Geological heterogeneity plays an important role in CO2 fluid and heat flow in the formation. Although the impact of heterogeneity has been investigated during CO2 injection for many sequestration projects, few studies have been reported for CO2-circulation and associated heat extraction. This study aims to numerically assess the impact of spatially correlated heterogeneity on both CO2 plume development (CPD) and subsequential CPG operations in inclined and thinly layered geothermal reservoirs. The simulated field is simplified from a typical depleted oil/gas reservoir block located in a potential geothermal area in North Oman, which had undergone horizontal water flooding as the second oil recovery phase. Formation slope and heterogeneity properties, including variance, azimuth, and correlation lengths, are sampled using the Latin-Hypercube approach in a high dimensional parameter space defined by their ranges. A suite of numerical models simulating CPD-CPG operations by a horizontal well doublet is set up using the slope and heterogeneity parameter samples. Performance metrics for CPD-CPG, including CPD time, CPG time, net injected CO2, maximum pressure decline, minimum CO2 mass fraction in produced fluids, total recovered heat energy, and heat extraction rate, are calculated from each of the numerical models. A response surface model mapping the input (slope and heterogeneity parameters) and output (performance metrics) is developed using these model results. Using the response surface, global sensitivity analysis is efficiently conducted to quantitatively evaluate the impact of slope and heterogeneity on the performance of CPD-CPG operations. It is found that steep slopes can enhance CO2 injectivity, facilitate high CO2 fraction in produced fluids and heat extraction rate; However, it causes early cold CO2 breakthrough to the production well and reduce total recovered heat energy. High variance and x-correlation length of heterogeneous fields create prominent high-permeable preferential paths in the major flow direction (x-axis). Low-permeable lenses created by large y-correlation lengths are perpendicular to the x-axis, acting as flow barriers to both CO2 and brine towards the production well. As for z-correlation length, 15 m is found to be the critical value relative to 20 m of the reservoir thickness. Large z-continuity scale facilitates fluid flow owing to the thick preferential paths when it is below 15 m, but low-permeable lenses tend to significantly block flow as they approximate to the reservoir thickness.

Isobaric Heat Capacity and Density of Supercritical H2O/CO2 Mixtures: Measurements in a Multifunction Apparatus

Abstract Studies on the thermophysical properties of H2O/CO2 mixtures for supercritical conditions, typical for a promising power generation system are far fewer than those for typical conditions of CO2 capture and storage (lower temperatures and pressures). In the previous heat transfer studies, we have setup a high-temperature and high-pressure apparatus. Here, we have extended it to a multifunction apparatus to enable the measurements of both the isobaric heat capacity and density that are important for the understanding and prediction of heat transfer behaviors, besides the design of the power generation system. For the experimental conditions, the pressure is 24 MPa, the temperatures range from 300 °C to 410 °C, and the CO2 mass fractions are 10%, 15%, and 18.5%. The isobaric heat capacities have been measured using the flow calorimeter method. The expanded relative uncertainty is 8.2% for temperatures beyond ±4 °C from the pseudocritical point and is 18.2% near the pseudocritical point. The densities were obtained from the measurements of the pressure drops with an expanded relative uncertainty of 4.8%. These two methods were validated by supercritical pure water experiments. The isobaric heat capacity and density data given in this work, as well as our previous heat transfer data, are self-consistent regarding the pseudocritical temperatures of supercritical H2O/CO2 mixtures.

Experimental Investigations and Numerical Modelling of Compression Ignition Engine Fuelled With Diesel and Biodiesel Blend

In this study, diesel fuel and two hundredth by volume of synthesised biodiesel from waste coconut oil (WB20) were used as fuel in unmodified, naturally aspirated, single cylinder compression ignition engine to study their performance and combustion characteristics at full load condition. Numerical studies were carried out with the use of CFD and compiled with the experimental results. FORTE software was used for CFD simulation. Methyl-palmitate (MPA) and Dodecane (C12H26) were used as surrogate fuels for biodiesel and diesel fuel respectively. The variation of special parts for diesel fuel and WB20 with CI engine in-cylinder pressure, in- cylinder temperature and mass fraction of O2, CO and NO emission at 10p and 20p ATDC were analysed. The mass fraction contours of in-cylinder temperature, O2, CO and NO for diesel fuel and WB20 were found to be decreased with increase in crank angle from 10o to 20° ATDC. The maximum BTE, in-cylinder pressure, in-cylinder temperature, O2, CO2 and NO were obtained for WB20 at 10° ATDC.

Numerical Study of Heat Transfer Characteristics of Impinging Syngas Flames From Multi-Slot Burner

Abstract Characteristics of impinging flames from a multi-slot burner fueled by synthetic gas are studied using a comprehensive numerical model. A multi-slot burner with five fuel slots and six air slots arranged in an alternately has been analyzed. The power rating of the burner is kept at 10 kW, and the air flowrate is fixed at 400% of the stoichiometric air required for the net fuel flowrate. The numerical model incorporates a short chemical kinetic mechanism, variable thermophysical properties, full multicomponent diffusion, thermal diffusion and a radiation sub-model. The location of the solid surface from the burner exit, primary air in fuel stream, dimensions of solid surfaces, and their temperatures have been varied to study the heat flux distributions from impinging flames. Results show that the location of the solid surface from the burner ports and partial premixing affect the heat transfer characteristics. The heat fluxes received by the side and top surfaces depend on the characteristics of neighboring flames located around the central flame. The heat flux distribution and the net heat flux received by the surface are found to be uniform and optimum at a height of 90 mm from the burner exit. Increasing the length of the impinging surface has negligible influence on average heat flux and CO production. The mass fraction of CO is affected by heating height and partial premixing. It remains almost constant for varying temperatures of the impinging surfaces. Primary aeration of 20% is found to be optimum for higher net heat flux and lower CO emissions.

Numerical investigation to evaluate the effects of gravity and pressure on flame structure and soot formation of turbulent non-premixed methane-air flame

In this study, a turbulent non-premixed (diffusion) methane-air flame has been investigated computationally to analyze the influences of pressure and gravity on flame structure and sooting characteristics between 1 and 10 atm. The simulation has been conducted in a 2-D axisymmetric computational domain using the finite volume-based computational fluid dynamics (CFD) code. The interaction of turbulence and chemistry is modeled by considering the steady laminar flamelet model (SLFM) and the GRI Mech 3.0 chemical mechanism. The radiative heat transfer calculation is carried out by considering the discrete ordinate (DO) method and the weighted sum grey gas model (WSGGM). The semi-empirical Moss-Brookes model is considered to calculate soot. The impact of gravity on flame and sooting characteristics are evaluated by comparing the normal-gravity flames with the zero-gravity flames. The effect of soot and radiation on flame temperature is also examined. The results show a close agreement with the measurement when both soot and radiation are included in the numerical modeling. The rates of soot formation, surface growth, and oxidation increase with increased operating pressure, regardless of gravity. Zero-gravity flames have a higher soot volume fraction, a wider soot-containing zone, a higher CO mass fraction, and a lower flame temperature than normal-gravity flames while maintaining constant pressure. In normal-gravity flames, the CO mass fraction decreases with pressure, whereas it increases with pressure rise in flames of zero gravity. Flames of zero gravity appear taller and broader compared to the flames of normal-gravity for a fixed pressure. An increase in pressure significantly reduces the flame length and width in normal-gravity flames. However, the pressure elevation has little effect on the shape of a zero-gravity flame. The outcomes of the present study will assist in fully understanding the combustion and sooting characteristics of turbulent diffusion flames that will help design and develop high-efficiency, pollutant-free combustion devices and fire suppression systems for space application.

A novel cryogenic technology for low-cost carbon capture from NGCC power plants for climate change mitigation

To reduce the high cost and water consumption of carbon capture, we present a novel low-cost carbon capture technology (NLCCT). It includes the generation of a cold nitrogen refrigerant (CNR) using minimum energy. The flow rate and temperature (−102 °C to −175 °C) are controlled with a fairly high coefficient of performance, COP. NLCCT uses a novel technique and regenerative cooling and an efficiently structured pre-cooler and a final cooler. This effectively uses the least amount of the CNR to cool the entire flue gas 10 °C to 15 °C below the thermodynamic de-sublimation temperature of CO2. Thus, 99 % of the original CO2 mass fraction in the flue gas de-sublimates and is captured. Detailed thermodynamic modelling shows that NLCCT can capture 99 % of the CO2 from natural gas combined cycle power plants with energy of 631 MJ/tCO2 and water consumption of 574 L/tCO2, and hence with a cost of about $12/tCO2 excluding labor and maintenance. We study the impact of the processing parameters and discuss how to optimise the capture processes to reduce the energy and water consumption further, for the implementation of NLCCT for climate change mitigation at a low cost.

Cycling of CO2 and H2O constrained by experimental investigation of a model ophicarbonate at deep subduction zone conditions

Ophicarbonates are carbonate-bearing serpentinites and therefore have high concentrations of CO2 and H2O. Their high concentrations of CO2 and H2O potentially make them important contributors to recycling of CO2 and H2O between Earth's surface and interior. However, the phase relations of ophicarbonates under deep subduction zone conditions remain poorly constrained, especially under conditions where melting may occur. Here, we present laboratory experiments on a model ophicarbonate at 3-7 GPa and 700-1100°C. We find that chlorite is stable at 3 GPa and ≤ 800°C, and phase A and balangeroite are stable at 7 GPa and ≤ 700°C. At all other conditions there is no stable residual H2O-bearing phase, providing support for the existence on an “anhydrous nose” in ultramafic rocks between 4-6 GPa in relatively warm subduction zones. We find that the solidus decreases with increasing pressure from between 900 and 1000°C at 3 GPa to between 700 and 800°C at 7 GPa. We find that the near-solidus melt is carbonate-rich and this melt coexists with a residual carbonate phase over a small temperature range. Using mass balance calculations, we estimate phase proportions as function of P and T to estimate mass fractions of CO2 remaining in the solid lithology. When compared to P-T paths of subducting slabs our results suggest that significant amounts of CO2 will be released from the slab in hot subduction zones, while significant amounts of CO2 will be retained in the slab in cold subduction zones of the modern Earth. In ancient subduction zones, ophicarbonate may have been more important to deep C fluxes due to the absence of thick carbonate sequences, and like modern Earth can either deliver significant amounts of CO2 to the mantle wedge or to the deep mantle depending on the P-T trajectories of subducting slabs.

Experimental and analytical investigation of CO2/R32 condensation heat transfer in a microchannel

Previous research has shown that CO2 mixtures can improve the thermal performance of CO2 refrigeration systems. Moreover, the use of a microchannel heat exchanger can reduce the refrigerant charge and improve the heat transfer coefficient. Therefore, in this experimental study, we investigated the condensation heat transfer characteristics of CO2/R32 in a porous flat microchannel with a hydraulic diameter of 0.715 mm. According to the results, the convective heat transfer coefficient decreased rapidly then increased slowly with an increase in the CO2 mass fraction. The minimum value was achieved when the CO2 mass fraction was approximately 55%. In addition, the convective heat transfer coefficient decreased with an increase in the condensation temperature. Higher vapour quality and mass flow rate conditions corresponded to higher convective heat transfer coefficients. The prediction correlations applicable to the in-tube condensation heat transfer exhibited low prediction results for CO2/R32, with a heat transfer coefficient prediction error for the newly established prediction model of 16.77%. This study provides theoretical support for analysis of the CO2/R32 condensation heat transfer mechanism in microchannels and the future design of microchannel condensers.

Paleoenvironmental redox evolution of Ediacaran-Cambrian restricted seas in the core of West Gondwana: Insights from trace-metal geochemistry and stratigraphy of the Bambuí Group, east Brazil

The sedimentary evolution of the Bambuí foreland basin system in the interior of West Gondwana is marked by periods of connection and isolation from the global ocean during the late Neoproterozoic and early Paleozoic. To understand the link between these periods and seawater redox conditions, we present an integrated study of trace-metal geochemistry and stratigraphy of the carbonate-siliciclastic rocks from the two lowermost second order transgressive-regressive sequences of the Bambuí Group, east Brazil. The basal 2nd-order sequence trace-metal pattern shows a progressive decrease of mass fractions of Co, Cr, Ni, Cu, Mo, U, V, Zn, and Cd, concomitant with a progressive decrease of Al and Fe contents and Mo/TOC ratios. Among all these elements, only Cd, Mo and U mass fractions seem to be less or not affected by detrital influence, so they can be used as reliable redox proxies for the paleoenvironmental analysis of the studied Bambuí strata. Moreover, normalization to aluminum shows a progressive increase of trace-metal enrichments for Cd and Mo in the order of 0.1–10 times and for U in the order of 1–100 times, accompanied by a progressive increase of organic carbon content upward section. These changes in sedimentary trace-metal patterns provide evidence for the chemical evolution of basinal deep-waters, whose conditions changed progressively from suboxic-anoxic to anoxic-euxinic at the basal transgressive-regressive sequence. We suggest that the paleomarine system represented by the basal Bambuí Group has probably evolved as an intracontinental silled basin recording changes in seawater chemistry associated with redox variations and restricted hydrographic conditions. Sedimentary trace-metal patterns indicate that Bambuí epeiric sea was initially in communication with open ocean followed by the marine restriction during the transgressive and regressive cycles, respectively. This resulted in a long deepwater residence time and chemical evolution of deep watermass as a response to tectonic pulses and consequent sea-level variations during the restricted stage. Under anoxic-euxinic conditions of seawater, trace metals scarcity and micronutrient fixation limitation would have impacted nitrate bioavailability, preventing the evolution of early benthic metazoans in the Bambuí paleomarine system during the late Ediacaran and early Cambrian.

Accumulation of Co, Ni, Cu, Zn and Cd in Aboveground Organs of Chinese Winter Jujube from the Yellow River Delta, China.

In the present study, winter jujube organs including fruit, fruiting leaf and foliage leaf, and associated soils in 14 typical orchards in Binzhou City, Shandong Province, China were collected and determined for the mass fractions of Co, Ni, Cu, Zn, and Cd. The mass fractions of Co, Ni, Cu, Zn, and Cd in plant tissues generally showed an order of Cu > Zn > Ni > Co > Cd as well as those in the soils decreased as Zn > Cu > Ni > Co > Cd. The values of single factor index and Nemerow pollution index suggested the jujube fruits were not polluted by heavy metals. Values of estimated daily intake for all the elements were far below their associated acceptable reference values, indicating no health risks would be caused by a single trace element. The results of targeted hazard quotient (THQ) of the metals in the fruits decreased as Cu > Ni > Zn > Cd accompanying total THQ (TTHQ) lower than 1 showing no hazard would be caused by those metals. Correlation analysis showed soil might not be the main source of heavy metals in winter jujube organs. Bioaccumulation factors (BAFs) for Co, Ni, Zn and Cd in fruits and leaves were far below 1 suggesting their low bioavailablities. The relatively great BAFs of Cu in the leaves might be due to the application of fertilizers and pesticides containing great amounts of Cu through soil and foliar spraying. To sum up, heavy metals tended not to be a major threat to winter jujube cultivation, and winter jujube had great edible safety.

Coarse-grained rCFD-DEM analysis of coke gasification and iron ore reduction in the shaft region of an ironmaking blast furnace

Understanding the fundamentals of iron ore reduction and coke gasification in the shaft region of an ironmaking blast furnace (BF) is the key to improving iron productivity and stability, yet the particle-scale understanding is hindered by the huge computational cost. In this paper, a coarse-grained reacting CFD-DEM (rCFD-DEM) model is implemented to investigate the complex thermochemical behaviours inside a simplified BF shaft. The results show that, in comparison to the CFD-DEM approach, the coarse-grained rCFD-DEM approach can have a similar accuracy but reduces computational cost by ~89.01% in this study. The typical thermochemical behaviours in respective coke and iron ore layers can be captured at particle scale. Then the effect of key operating parameters is studied quantitatively at particle scale. It is indicated that the inlet velocity increasing from 1.7 m/s to 2.3 m/s improves the reduction degree of iron ore by 16%, but the coke consumption is reduced by 5.51%. The operating temperature increasing from 1200 K to 1250 K increases the coke consumption by 44.92%, but the reduction degree of iron ore only increases slightly. When CO mass fraction in the inlet gas increases from 0.25 to 0.30, the coke consumption increases by 12.68% and the reduction degree of iron ore increases by 16.88%. The findings shed light on the fundamentals of coke gasification and iron ore reduction in the BF shafts. • A coarse-grained reacting CFD-DEM model is developed to investigate the blast furnace shaft. • Compared to previous CFD-DEM approach, the approach have a similar accuracy but reduces computational cost by ~89%. • The typical thermochemical behaviours and the effect of key operating parameters are quantified. • The findings shed light on the fundamentals of coke gasification and iron ore reduction in blast furnace shafts.

Heavy Metal Contamination in Sediments from Wetlands Invaded by Spartina alterniflora in the Yellow River Delta.

Heavy metals are major pollutants that pose threats to wetland environments. In the present study, surface sediments from wetlands vegetated by invasive species Spartina alterniflora in the Yellow River Delta were collected and determined for the mass fractions of Co, Ni, As, Cd and Pb. Results showed mass fractions of Co, Ni, As, Cd and Pb in the sediments of the S. alterniflora communities ranged from 8.5 to 16.0, 13.9–27.9, 3.2–13.8, 0.08–0.24, and 17.6–37.5 mg/kg dw, respectively, generally presenting an order of Pb > Ni > Co > As > Cd. The levels of heavy metals in sediments in the S. alterniflora communities were higher than those in the wetland vegetated by the native plant species Suaeda heteroptera. Correlations among metal elements were highly significant, suggesting that they might have the same sources. Clay and TOC were important factors affecting the spatial distribution of metals. The Igeo values of the investigated elements in the sediments were frequently lower than 0, revealing the slight pollution status of these metals. Relatively slight values of Eri and RI suggested that the potential ecological risks caused by the 5 metals were low. Our findings could provide a better understanding of the correlation between metal pollution and bio-invasion in wetland ecosystems.