查看更多>>摘要：Environmental pollution has been intensifying in many countries because of the consistent misuse of fossil fuels.It's necessary to develop and utilize sources of solar energy.The main method to use solar energy is through the use of a solar collector.This paper aims to enhance and compare the thermal efficiency of solar collector by applying water,Fe3O4 nanofluid and Fe3O4/MWCNT hybrid nanofluid as the working fluids.The energy efficiency,exergy efficiency,exergy destruction and entropy generation were compared in this study.The evacuated tube solar collector shown the maximum efficiency when the Fe3O4/MWCNT hybrid nanofluid with mixing ration of 1/4 was used as the working fluid which was 26.4% higher than cases of the water.In addition,the exergy efficiency of the evacuated tube solar collector using 0.1 wt% Fe3O4/MWCNT hybrid(l:4)nanofluid and 0.1 wt% Fe3O4 nanofluid was improved by 55.2% and 42.1% comparing to the water,the maximum exergy efficiency was observed when Fe3O4/MWCNT(1:4)hybrid nanofluid was used.Water shown the highest entropy generation while Fe3O4/MWCNT hybrid nanofluid(l :4)shown the lowest.The results in this study indicated the thermal efficiency of evacuated tube solar collector was effectively enhanced by using Fe3O4/MWCNT hybrid nanofluids as working fluid comparing to the water and Fe3O4 nanofluid,the best performance of the evacuated tube solar collector was obtained when Fe3O4/MWCNT(1:4)hybrid nanofluid was used.
查看更多>>摘要：CO2 absorption using benign cost-effective absorbents is an essential unit operation not only in the process industry for CO2 separation and recovery from industrial of f-gas streams but also for direct absorption from air to reduce the carbon footprint.Several absorbents are identified,by researchers,with high CO2 capture efficiency due to their favorable chemical and physical properties,interaction mechanism with CO2> and low regeneration energy cost.However,with the current Environmental Protection Agency(EPA)norms,more efficient low-cost benign absorbents need to be developed.Hence,the primary aim of this work is to comprehensively review various factors which are recently being considered in determining all these crucial parameters for best absorbents selection.The merits and demerits for establishing the physical and chemical absorbents have been discussed.Absorbent properties such as structural,transportation,and chemical properties are also discussed,along with various methods used to determine them.The pKa value based absorbent selection methodology seems an ideal way for absorbent selection.Further,the role of contactors for absorption performance is also reviewed,with a significant focus on the mass transfer coefficients,and the anal that a circular microchannel reactor provides a 2-4 order of magnitude higher mass transfer coefficient value than a conventional reactor.The interaction mechanism of reactive absorbents has been discussed,as they show much better absorption kinetics.A comparative assessment of relative heat duties of these reported absorbents revealed that the catalyst doped,and blend amines systems provide lower regeneration heat duties.A relative cost of the absorption processes focusing on the recent ionic liquid solvent synthesis costs is described.Overall,this review provides a systematic insight that will assist researchers and engineers in understanding an absorption solvent's efficacy for CO2 capture comprehensively.
查看更多>>摘要：A continuous flow photochemical pilot plant unit containing a dry photolytic/photooxidation reactor UV_(185)/UV254/O3 and an aqueous photochemical UV254/H2O2 reactor was used to remove VOC from the waste gas stream with a high flow rate.The efficiency of this system was thoroughly studied through the control of reaction conditions,the detection of intermediates,and the analysis of reaction products during the degradation of styrene,xylene,and their mixture.The conversion of the model substances depends on the initial concentration of the pollutant,the flow rate,and the type of pollutant.The highest conversion after passing through the whole pilot plant unit was achieved at an initial pollutant concentration 50 ppmv and a flow rate 100 m~3·h~(-1),which is related to the residence time in the system.The conversion of styrene,xylene and their mixture after passing through the whole unit for the 100 m~3·h~(-1)flow rate was 74%,46% and 52%,respectively.Although the first dry photolytic/photooxidation reactor using UV_(185)/UV_(254)/O3 was more efficient for styrene degradation,the aqueous photochemical UV_(254)/H2O2 part was more suitable for xylene degradation.These experimental results are in the agreement with carbon balance,which confirmed the outlet air contained only unconverted model pollutant(styrene,xylene or their mixture)and CO2.Figures of merit were calculated in order to evaluate the price efficiency of the technology.This study presents an effective AOPs system for the degradation of VOCs from waste gas streams with a high flow rate and provides an insight into their degradation pathways.
Juan CabelloTania L.G6mez-BorrazArmando Gonzalez-Sanchez
15页
查看更多>>摘要：Direct anaerobic sewage treatment is increasingly adopted in several intertropical developing countries.The reduced carbon footprint of such facilities is based on its low electricity requirements and potential energy(biogas)recovery; however,if dissolved CH4 in the effluent is not controlled,this advantage will be drastically reduced.A suitable option to overcome this situation is to adopt CH4 desorption by an air stream,followed by bio-oxidation in compost biofilters.In such systems,the methanotrophic activity will increase the temperature in the bionTter to inhibiting values(above 40 ℃),reducing the active volume of the compost media and its removal efficiency.This work addresses this process limitation,aiming to assess the temperature variations in the filter media and their effects on methane oxidation performance under different operating conditions.A comprehensive mathematical 2-D porous-medium based model was developed and then calibrated and validated with experimental data.The model considers heat,momentum,and mass balances under non-steady-state conditions,including heat exchange at the bionTter container wall influenced by daily ambient temperature fluctuations and solar radiation.Results obtained from 6 model simulations at different operating conditions show that temperatures above 40 ℃ are reached at the center-upper zones of the compost bionTter due to the heat transported from the methanotrophic active zones located at the bottom(inlet)and container wall.At midday(12-14 h),solar radiation on the wall contributes 14% of the total heat gained in a non-covered biofilter.The model highlights the importance of facilitating heat transport from the compost media to the surroundings; some practical recommendations are presented for that purpose.
查看更多>>摘要：In order to ensure that the diesel particulate filter(DPF)is not damaged during the regeneration process,a DPF regeneration model based on fluid-thermal-solid coupling is established.The temperature,stress and strain distribution during the regeneration process of DPF are analyzed,and the influence of stress and strain on the solid area of porous media under different carbon loads is revealed.The results show that there is an obvious local high temperature region in the center of the plug section of the intake channel and exhaust channel,and the tangential temperature of the inlet and exhaust outlet gradually decreases from the center to the surrounding.With the increase of carbon loads,the peak reaction temperature in the process of regeneration also began to rise.The thermal stress is mainly distributed near the side corners of the porous medium,and the maximum thermal stress is concentrated at the exhaust outlet end.The deformation is mainly concentrated in the solid center area of the plugs at both ends,the deformation amount decreases from the inside to the outside,and the deformation amount of the exhaust end is higher than that of the intake end.It can be found that the central area of the porous medium is the weak point of the structure,which is prone to thermal damage and cracks.
Paulo Gabriel SiqueiraMarcio das Chagas MouraHeitor Oliveira Duarte
13页
查看更多>>摘要：Industrial accidents,such as toxic spills,are one of the main causes of catastrophic environmental damage to animals and plants.The high number of vessels,including oil tankers that navigate the globe,increases the risk of potential oil spills affecting oceanic islands.The frequency estimation is a fundamental step in any risk assessment.However,this step presents shortcomings when dealing with rare,extreme accidents,i.e.,low frequency/high consequence events.Classical statistical approaches are ineffective since available data are generally sparse and of ten censored in this context.To address this issue,we propose a Bayesian population variability-based method to estimate the distributions of accident rates.Based on that,it is possible to merge sparse data about accidents from various databases with the judgment of experts such as captains,pilots and chief of ficers.Finally,this method is applied to a real case of oil tankers that navigate nearby the Fernando de Noronha Archipelago,a UNESCO natural world heritage site in Brazil.The results can support risk assessments and provide decision-makers with helpful information to better address measures to prevent accidents or reduce risks.
查看更多>>摘要：Mg alloy waste dust can react with water to produce hydrogen in the production of Mg alloy products,which has the possibility to lead to fires or explosions.Firstly,from the perspective of safety management,this paper systematically studies the impact of the difference of hydrogen evolution amount of magnesium based alloy waste dust particles(Mg-Al/Mg-Zn)on the risk of wet dust collector under different environmental conditions,and a two-stage hydrogen evolution model was constructed.Secondly,from a technical point of view,a method of using environmentally-friendly,cost-effective sodium phosphate to inhibit the hydrogen evolution reaction of Mg alloys is also proposed.The morphologies of Mg alloy dust particles before and after reaction were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),and chemical dynamics modeling before the related reaction mechanisms were identified.The research outcome of the present study could provide effective technical guidance for preventing hydrogen explosion accidents at Mg alloy fabrication facilities.
查看更多>>摘要：Accidents(such as hazardous chemical accidents and fires)have adverse effects on urban safety and sustainable development.Many countries,such as China,are making great efforts to develop better urban safety strategies to prevent and mitigate accidents in urban areas and to keep cities safer.At national level,and from an accident prevention perspective,this study uses an evidence-based safety approach to propose potential strategies for China's urban safety.The contributions include:(1)the identification and discussion of major urban safety problems and challenges in China,and(2)the development of China's urban safety strategies based on available evidence.This study attempts to provide useful evidence and suggestions for future urban safety management,both within China and in other countries.However,because this paper discusses China's urban safety at macro level,more detailed studies on China's urban safety should be carried out for a deeper understanding and a more targeted solution for China's urban safety.
查看更多>>摘要：Despite the major challenges facing fossil fuels,they are now utilized to supply nearly 80% of the world's energy requirements.Of this amount,about 30% relies on coal-based power plants.Such power plants emit large volumes of pollutant gases into the atmosphere,which has led to serious environmental crises.Therefore,the exploitation of green technologies and/or the integration of environmentally friendly systems in existing power plants are essential.The aim of the article is to introduce and conceptual-thermodynamic design of a lignite coal-based plant that is integrated with monoxide-hydrogen fueled solid oxide fuel cell(SOFC),and parabolic trough solar collector(PTSC)based-solar farms.The present paper provides energy,exergy,and thermodynamic analyzes with considering entropy generation and emission rate of the power plant.In addition,a comparison of system performance when using anthracite instead of lignite is also provided.Also,real climatic data(i.e.,Yazd,Iran)have been used to evaluate the behavior of solar fields.The results showed that nearly 93.7 kg/s of gas is raised from the power plant after the combustion process.In addition,proposed power plant has energy and exergy efficiencies of 70.95% and 35.7%,respectively.Moreover,the PTSC2 solar farm in a lignite-fired power plant should have approximately 6.76-fold larger area than that of anthracite.
查看更多>>摘要：As hazardous wastes from metallurgical processes,high zinc dust(HZD)was considered as a potential alternative resource of Zn.The acid leaching of HZD was a principal step and therefore was highly relevant to efficient utilization.Unfortunately,zinc ferrite(ZnFe2O4)in HZD was difficult to be leached by hydrometallurgical methods.Therefore,in this study,to enhance the recovery of zinc,selective reduction roasting was used to decompose ZnFe2O4.The transformation of Zn phases during the reduction process was investigated by thermodynamic calculation,XRD analysis.The results showed that ZnFe2O4 was converted into acid-soluble ZnO in H2 at 600 ℃,while the further reduction of ZnO to Zn(g)and the volatilization of ZnO was avoided.However,the soluble ZnSO4 in HZD was also reduced to acid-insoluble ZnS.Consequently,a novel method of reduction roasting combined with water leaching was proposed to pretreat HZD.In water leaching,the solid-liquid ratio wasl:10(g/mL).When H2SO4 concentration was 80 g/L,the leaching ratio of Zn was 94.24% after pretreatment,higher than that of direct leaching of HZD(87.76%).Therefore,acid leaching of Zn was promoted by water leaching and reduction roasting pretreatment,which will bring considerable benefits to the high zinc dust recycling enterprises.
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