Abstract:The aim of this research is to design and operate a 10 kW hot chemical-looping gasification(CLG)unit using Fe2O3/Al2O3as an oxygen carrier and saw dust as a fuel.The effect of the operation temperature on gas...Abstract:The aim of this research is to design and operate a 10 kW hot chemical-looping gasification(CLG)unit using Fe2O3/Al2O3as an oxygen carrier and saw dust as a fuel.The effect of the operation temperature on gas composition in the air reactor and the fuel reactor,and the carbon conversion of biomass to CO2and CO in the fuel reactor have been experimentally studied.A total60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina.The results show that CO and H2concentrations are increased with increasing temperature in the fuel reactor.It is also found that with increasing fuel reactor temperature,both the amount of residual char in the fuel reactor and CO2concentration of the exit gas from the air reactor are degreased.Carbon conversion rate and gasification efficiency are increased by increasing temperature and H2production at 870℃reaches the highest rate.Scanning electron microscopy(SEM),X-ray diffraction(XRD)and BET-surface area tests have been used to characterize fresh and reacted oxygen carrier particles.The results display that the oxygen carrier activity is not declined and the specific surface area of the oxygen carrier particles is not decreased significantly.展开更多
The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical industr...The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical industry.In this paper,a green and sustainable method for azeotrope separation is proposed based on a chemical-looping concept with the help of reversible-reaction-assisted distillation.The central concept in the chemical-looping separation(CLS)method is the selection of a reactant that can react with the azeotrope components and can also be recycled by the reverse reaction to close the loop and achieve cyclic azeotrope separation.This paper aims to provide an informative perspective on the fundamental theory and applications of the CLS method based on the separation principle,reactant selection,and case analysis,for example,the separation of alkenes,alkane,aromatics,and polyol products.In summary,we provide guidance and references for chemical separation process intensification in product refining and separation from azeotropic systems for the development of a more sustainable chemical industry.展开更多
Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the...Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the use of Ca_(2)MnO_(4)-layered perovskites modified with NaNO_(3) dopants,serving as redox catalysts(also known as oxygen carriers),for the CL-ODH of ethane within a temperature range of 700-780℃.Our findings revealed that the incorporation of NaNO_(3) as a modifier significantly-nhanced the selectivity for-thylene generation from Ca_(2)MnO_(4).At 750℃and a gas hourly space velocity of 1300 h^(-1),we achieved an-thane conversion up to 68.17%,accompanied by a corresponding-thylene yield of 57.39%.X-ray photoelectron spectroscopy analysis unveiled that the doping NaNO_(3) onto Ca_(2)MnO_(4) not only played a role in reducing the oxidation state of Mn ions but also increased the lattice oxygen content of the redox catalyst.Furthermore,formation of NaNO_(3) shell on the surface of Ca_(2)MnO_(4) led to a reduction in the concentration of manganese sites and modulated the oxygen-releasing behavior in a step-wise manner.This modulation contributed significantly to the enhanced selectivity for ethylene of the NaNO_(3)-doped Ca_(2)MnO_(4) catalyst.These findings provide compelling evidence for the potential of Ca_(2)MnO_(4)-layered perovskites as promising redox catalysts in the context of CL-ODH reactions.展开更多
Ni-based, Fe-based and Co-based oxygen carriers with perovskite oxides used as the supports were prepared by citric acid complexation method, The oxygen carriers were characterized by thermal analysis, H2-temperature-...Ni-based, Fe-based and Co-based oxygen carriers with perovskite oxides used as the supports were prepared by citric acid complexation method, The oxygen carriers were characterized by thermal analysis, H2-temperature-programmed reduction and X-ray diffraction methods. Performance tests were evaluated through Chemical-Looping Hydrogen Genera- tion in a fixed-bed reactor operating at atmospheric pressure. The characterization results showed that all samples were composed of metal oxides and perovskite oxides. Performance results indicated that CH4 conversion over the oxygen car- riers decreased in the lbllowing order： NiO/LaNiO3〉Co203/LaCoO3〉Fe203/LaFeO3. The ability of NiO/LaNiO3 and F%O3/ LaFeO3 to decompose water was stronger than that of Co203/LaCoO3 as evidenced by our experiments. H2 amounting to 80 mL upon reacting on methane in every cycle could be completely oxidized by NiO/LaNiO3 at 900℃ in the period from the third cycle to the eighth cycle.展开更多
The cycle life of oxygen carrier（OC） is crucial to the practical applications of chemical looping combustion（CLC）. Cycle performance of Cu/SiO2 prepared with a mechanical mixing method was evaluated based on a CLC...The cycle life of oxygen carrier（OC） is crucial to the practical applications of chemical looping combustion（CLC）. Cycle performance of Cu/SiO2 prepared with a mechanical mixing method was evaluated based on a CLC process characterized with an added methane steam reforming step. The Cu/SiO2 exhibited high redox reactivity in the initial cycles, while the performance degraded with cycle number. Through characterization of the degraded Cu/SiO2, the performance degradation was mainly caused by the secondary particles＇ fragmentation and the fine particles＇ local agglomeration, which worsened the distribution and diffusion of the reactive gases in the packed bed. A regeneration method of the degraded OC based on re-granulation has been proposed, and its mechanism has been illustrated. With this method, the performance of the degraded OC through 420 redox cycles was recovered to a level close to the initial one.展开更多
Fe_(2)O_(3)/Al_(2)O_(3) and Fe_(2)O_(3)/Al_(2)O_(3) modified by low content of Ni(below 2%in weight)oxygen carriers were prepared by mechanical mixing and impregnation method.The synthesized oxygen carriers were chara...Fe_(2)O_(3)/Al_(2)O_(3) and Fe_(2)O_(3)/Al_(2)O_(3) modified by low content of Ni(below 2%in weight)oxygen carriers were prepared by mechanical mixing and impregnation method.The synthesized oxygen carriers were characterized by means of X-ray diffraction(XRD),X-ray fluorescence(XRF),scanning electron microscopy(SEM),BET-surface area and temperature programmed reduction(TPR).Besides,redox cyclic reactivity and the performance of chemical looping reforming of methane of the oxygen carriers were studied in a thermal gravimetrical analysis(TGA)and fixed bed at 850℃.It was observed that the redox reactivity of the oxygen carriers is improved by Ni addition because synergic effect may occur between NiO and Fe_(2)O_(3)/Al_(2)O_(3) to form NiFe_(2)O_(4) and NiAl_(2)O_(4) spinel phases.However,the improvement was not apparent as Ni addition reached 1 wt%or more because more nickel loaded resulted in methane decomposition into H2 and carbon leading to carbon deposition.The SEM and BET analysis showed that NiFe_(2)O_(4) and NiAl_(2)O_(4) particles dispersed into the pores of the Fe_(2)O_(3)/Al_(2)O_(3) particles in the course of preparation.In addition,the resistance to sintering of the modified samples increased with the Ni addition increasing.The results of successive redox cycles showed that the Ni modified Fe_(2)O_(3)/Al_(2)O_(3) oxygen carriers have good regenerability.With integration of reactivity and carbon deposition,the content 1.04 wt%of nickel doping was an optimal amount in the three modified samples.展开更多
Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further applicatio...Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC.In this paper,the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products.The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process.Therefore,the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided.In both stages,the dominant resistances were analyzed.The activation energy and the reaction order in both stages were calculated respectively as well.Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations,it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor.This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.展开更多
Coal-direct chemical-looping combustion(CDCLC)is a promising coal combustion technique that provides CO2 capture with a low energy penalty.In this study,we developed a three-dimensional Eulerian-Eulerian multiphase fu...Coal-direct chemical-looping combustion(CDCLC)is a promising coal combustion technique that provides CO2 capture with a low energy penalty.In this study,we developed a three-dimensional Eulerian-Eulerian multiphase full-loop model for simulating the circulation and separation of binary particle mixtures in a novel high-flux CDCLC system.This model comprised a high-flux circulating fluidized bed as the fuel reactor(FR),a counter-flow moving bed as the air reactor(AR),a high-flux carbon stripper,two downcomers,and two J-valves.This model predicted the main features of complex gas-solid flow behaviors in the system.The simulation results showed that quasi-stable solid circulation in the whole system could be achieved,and the FR,AR,and J-valves operated in a dense suspension upflow regime,a near-plug-flow regime,and a bubbling fluidization regime,respectively.The multiphase flow model of binary particle mixtures was used to predict the mechanisms of directional separation of binary particle mixtures of an oxygen carrier(OC)and coal throughout the system.A decrease in the baffle aspect ratio of the inertial separator improved the coal selective separation efficiency but resulted in a slight decline in the OC selective separation;this is believed to be the result of weakening of particle collisions with the baffle.A higher FR gas velocity had a slightly negative effect on the OC selective separation efficiency,but improved the coal selective separation efficiency;this can be attributed to an increase in the particle-carrying capacity of the gas stream.A decrease in the coal particle size led to better entrainment of the coal particles by the gas stream and this increased the coal selective separation efficiency.In real CDCLC applications,the operating variables for separation of binary particle mixtures should be comprehensively assessed to determine their positive and negative effects on the carbon capture efficiency,OC regeneration efficiency,gas leakage restraint,energy consumption,and fuel conversion.展开更多
Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic condi...Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic conditions when the chemical-looping combus-tion(CLC)process is used.The CLC experiments of multi-component solid waste were conducted on a homemade twin-bed reactor and the characteristics of flue gas were investigated for the effect of the mixing ratio of sewage sludge and polyvinyl chloride(PVC).The results indicated that the combustion efficiency was>99.9%for these CLC processes;the highest carbon-conversion rate was obtained at 96.3%for PVC with 60%sludge.The highest NO and SO_(2)emissions were 26%and 19%,respectively,when the sludge was mixed with 20%PVC.As the proportion of PVC blended into the sludge increased,the time when the concentration of NO in the flue-gas peaks moved backwards,while peak SO_(2)concentration moved forward.The general trend was to increase first and then de-crease.In addition,there were multiple peaks in carbon emissions,corresponding to~10%,30%and~70%of the carbon-conversion rate;nitrogen emissions reached 90%of total emissions before the carbon-conversion rate was 40%;sulphur emissions had a longer cycle and were mainly emitted between 10%and 60%of the carbon-conversion rate.The results are expected to provide a reference for solid-waste source suppressing to inhibit the generation of pollutants.展开更多
Chemical-looping gasification （CLG） is a novel process for syngas generation from solid fuels, sharing the same basic principles as chemical-looping combustion （CLC）. It also uses oxygen carriers （mainly metal ox...Chemical-looping gasification （CLG） is a novel process for syngas generation from solid fuels, sharing the same basic principles as chemical-looping combustion （CLC）. It also uses oxygen carriers （mainly metal oxide and calcium sulfate） to transfer heat and oxygen to the fuel. In this paper, the primary investigation into the CLG process with CaSO4 as oxygen carrier was carried out by thermodynamic analysis and experiments in the tube reactor. Sulfur-contained gas emission was mainly H2S rather than SO2 in the CLG process, showing some different features from the CLC. The mass and heat balance of CLG processes were calculated thermodynamically to determinate the auto-thermal operating conditions with different CaSO4/C and steam/C molar ratios. It was found that the CaSO4/C molar ratio should be higher than 0.2 to reach auto-thermal balance. The effect of temperature on the reactions between oxygen carrier and coal was investigated based on Gibbs free energy minimum method and ex- perimental results. It indicated that high temperature favored the CLG process in the fuel reactor and part of syngas was consumed to compensate for auto-thermal system.展开更多
An atomic-level insight into the H_(2)adsorption and oxidation on the Fe_(2)O_(3)surface during chemicallooping combustion was provided on the basis of density functional theory calculations in this study.The results ...An atomic-level insight into the H_(2)adsorption and oxidation on the Fe_(2)O_(3)surface during chemicallooping combustion was provided on the basis of density functional theory calculations in this study.The results indicated that H_(2)molecule most likely chemisorbs on the Fe_(2)O_(3)surface in a dissociative mode.The decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the surface.In particular,the H_(2)molecule adsorbed on an O top site could directly form H_(2)O precursor on the O_(3)-terminated surface.Further,the newly formed H-O bond was activated,and the H atom could migrate from one O site to another,consequently forming the H_(2)O precursor.In the H_(2)oxidation process,the decomposition of H_(2)molecule was the rate-determining step for the O_(3)-terminated surface with an activation energy of 1.53 eV.However,the formation of H_(2)O was the ratedetermining step for the Fe-terminated surface with an activation energy of 1.64 eV.The Feterminated surface is less energetically favorable for H_(2)oxidation than that the O_(3)-terminated surface owing to the steric hindrance of Fe atom.These results provide a fundamental understanding about the reaction mechanism of Fe_(2)O_(3)with H_(2),which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H_(2).展开更多
Copper（Ⅱ） oxide in varying ratios was combined with either an alumina-based cement（Al300）, or CaO derived from limestone as support material in a mechanical pelletiser. This production method was used to investig...Copper（Ⅱ） oxide in varying ratios was combined with either an alumina-based cement（Al300）, or CaO derived from limestone as support material in a mechanical pelletiser. This production method was used to investigate its influence on possible mechanical and chemical improvements for oxygen carriers in chemical looping processes. These materials were tested in a lab-scale fluidised bed with CO or CH;as a reducing gas at 950 °C. As expected, the oxygen carriers containing a greater ratio of support material exhibited an enhanced crushing strength. Oxygen carriers comprised of a 1:3 ratio of support material to active CuO exhibited increased crushing strength by a minimum of 280% compared to pure CuO pellets.All oxygen carriers exhibited a high CO conversion yield and were fully reducible from CuO to Cu. For the initial redox cycle, Al300-supported oxygen carriers showed the highest fuel and oxygen carrier conversion. The general trend observed was a decline in conversion with an increasing number of redox cycles.In the case of CaO-supported oxygen carriers, all but one of the oxygen carriers suffered agglomeration.The agglomeration was more severe in carriers with higher ratios of CuO. Oxygen carrier Cu25Al75（75 wt% aluminate cement and 25 wt% CuO）, which did not suffer from agglomeration, showed the highest attrition with a loss of approximately 8% of its initial mass over 25 redox cycles. The reducibility of the oxygen carriers was limited with CH;in comparison to CO. CH;conversion were 15%-25% and 50% for Cu25Ca75（25 wt% CuO and 75 wt% CaO） and Cu25Al75, respectively. Cu25Ca75 demonstrated improved conversion, whereas Cu25Al75 exhibited a trending decrease in conversion with increasing redox cycles.展开更多
Chemical-looping combustion (CLC) is a novel combustion technique with inherent CO2 separation.Magnetite (Fe3O4) was selected as the oxygen carrier.Shenhua coal (Inner Mongolia,China),straw coke and natural coke were ...Chemical-looping combustion (CLC) is a novel combustion technique with inherent CO2 separation.Magnetite (Fe3O4) was selected as the oxygen carrier.Shenhua coal (Inner Mongolia,China),straw coke and natural coke were used as fuels for this study.Influences of operation temperatures,coal to Fe3O4 mass ratios,and different kinds of fuels on the reduction characteristics of the oxygen carrier were investigated using an atmosphere thermogravimetric analyzer (TGA).Scanning electron microscopy (SEM) was used to analyse the characteristic of the solid residues.Experimental results shown that the reaction between the coal and the oxygen carrier become strong at a temperature of higher than 800℃.As the operation temperature rises,the reduction conversion rate increases.At the temperatures of 850oС,900℃,and 950℃,the reduction conversion rates were 37.1%,46.5%,and 54.1% respectively.However,SEM images show that at the temperature of higher than 950℃,the iron oxides become melted and sintered.The possible operation temperature should be kept around 900℃.When the mass ratios of coal to Fe3O4 were 5/95,10/90,15/85,and 20/80,the reduction conversion rates were 29.5%,40.8%,46.5%,and 46.6% respectively.With the increase of coal,the conversion rate goes up.But there exist an optimal ratio around 15/85.Comparisons based on different kinds of fuels show that the solid fuel with a higher volatile and a more developed pore structure is conducive to the reduction reactivity of the oxygen carrier.展开更多
The micro-interconnected fluidized bed(MIFB)was designed to improve the evaluation condition of oxygen carrier,which is difficult to perform in a lab-scale interconnected fluidized bed because of the large demand for ...The micro-interconnected fluidized bed(MIFB)was designed to improve the evaluation condition of oxygen carrier,which is difficult to perform in a lab-scale interconnected fluidized bed because of the large demand for bed inventory.The reduction of bed inventory in the MIFB was mainly achieved by the appropriate miniaturization of the reactor size,in which the wall effect and operating flexibility should be taken into consideration.With hematite serving as the oxygen carrier,stable and flexible fluidization could be realized with 342.9 g of bed inventory.Internal perforated plates were arranged in the middle of the reactor to improve gas-solid distribution,which also could restrain the slugging formation and increase the particle residence time by 28.9%.A different fluidization phenomenon was observed in this two-stage reactor in which the particle fluidization was reconstructed in the upper chamber.Throughout 48 h of cold operation,the hematite oxygen carrier attrition rate was evaluated as 0.151 wt.%/h corresponding to 660 h lifetime,where 12.5%of particle attrition was contributed by internal perforated plates.An excellent fitting performance was found between the pressure difference in the risers and the upward particle flow,but the correction factor should be adjusted according to the fluidization flow.展开更多
基金Supported by the National Natural Science Foundation of China(51076154)National Key Technology Research&Development Program of 12 th Five-year of China(2011BAD15B05)
文摘Abstract:The aim of this research is to design and operate a 10 kW hot chemical-looping gasification(CLG)unit using Fe2O3/Al2O3as an oxygen carrier and saw dust as a fuel.The effect of the operation temperature on gas composition in the air reactor and the fuel reactor,and the carbon conversion of biomass to CO2and CO in the fuel reactor have been experimentally studied.A total60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina.The results show that CO and H2concentrations are increased with increasing temperature in the fuel reactor.It is also found that with increasing fuel reactor temperature,both the amount of residual char in the fuel reactor and CO2concentration of the exit gas from the air reactor are degreased.Carbon conversion rate and gasification efficiency are increased by increasing temperature and H2production at 870℃reaches the highest rate.Scanning electron microscopy(SEM),X-ray diffraction(XRD)and BET-surface area tests have been used to characterize fresh and reacted oxygen carrier particles.The results display that the oxygen carrier activity is not declined and the specific surface area of the oxygen carrier particles is not decreased significantly.
基金The authors acknowledge financial support from the National Key Research and Development Program of China(2018YFB0604900)the National Natural Science Foundation of China(21690084 and 21878219).
文摘The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical industry.In this paper,a green and sustainable method for azeotrope separation is proposed based on a chemical-looping concept with the help of reversible-reaction-assisted distillation.The central concept in the chemical-looping separation(CLS)method is the selection of a reactant that can react with the azeotrope components and can also be recycled by the reverse reaction to close the loop and achieve cyclic azeotrope separation.This paper aims to provide an informative perspective on the fundamental theory and applications of the CLS method based on the separation principle,reactant selection,and case analysis,for example,the separation of alkenes,alkane,aromatics,and polyol products.In summary,we provide guidance and references for chemical separation process intensification in product refining and separation from azeotropic systems for the development of a more sustainable chemical industry.
基金support of National Natural Science Foundation of China(22179027)gratefully acknowledged.This work was also supported by the Natural Science Foundation of Guangxi Province(2021GXNSFAA075063,2018GXNSFDA281005)+1 种基金the National Key Research and Development Program of China(2017YFE0105500)Science&Technology Research Project of Guangdong Province(2017A020216009).
文摘Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the use of Ca_(2)MnO_(4)-layered perovskites modified with NaNO_(3) dopants,serving as redox catalysts(also known as oxygen carriers),for the CL-ODH of ethane within a temperature range of 700-780℃.Our findings revealed that the incorporation of NaNO_(3) as a modifier significantly-nhanced the selectivity for-thylene generation from Ca_(2)MnO_(4).At 750℃and a gas hourly space velocity of 1300 h^(-1),we achieved an-thane conversion up to 68.17%,accompanied by a corresponding-thylene yield of 57.39%.X-ray photoelectron spectroscopy analysis unveiled that the doping NaNO_(3) onto Ca_(2)MnO_(4) not only played a role in reducing the oxidation state of Mn ions but also increased the lattice oxygen content of the redox catalyst.Furthermore,formation of NaNO_(3) shell on the surface of Ca_(2)MnO_(4) led to a reduction in the concentration of manganese sites and modulated the oxygen-releasing behavior in a step-wise manner.This modulation contributed significantly to the enhanced selectivity for ethylene of the NaNO_(3)-doped Ca_(2)MnO_(4) catalyst.These findings provide compelling evidence for the potential of Ca_(2)MnO_(4)-layered perovskites as promising redox catalysts in the context of CL-ODH reactions.
基金supported by China Petrochemical Corporation(SINOPEC)(Contact No.106002000284)
文摘Ni-based, Fe-based and Co-based oxygen carriers with perovskite oxides used as the supports were prepared by citric acid complexation method, The oxygen carriers were characterized by thermal analysis, H2-temperature-programmed reduction and X-ray diffraction methods. Performance tests were evaluated through Chemical-Looping Hydrogen Genera- tion in a fixed-bed reactor operating at atmospheric pressure. The characterization results showed that all samples were composed of metal oxides and perovskite oxides. Performance results indicated that CH4 conversion over the oxygen car- riers decreased in the lbllowing order： NiO/LaNiO3〉Co203/LaCoO3〉Fe203/LaFeO3. The ability of NiO/LaNiO3 and F%O3/ LaFeO3 to decompose water was stronger than that of Co203/LaCoO3 as evidenced by our experiments. H2 amounting to 80 mL upon reacting on methane in every cycle could be completely oxidized by NiO/LaNiO3 at 900℃ in the period from the third cycle to the eighth cycle.
基金supported by the Beijing Science and Technology Program(Grant no.Z131100005613045)the National Natural Science Foundation of China(Grant no.51306015)the Fundamental Research Funds for the Central Universities(Grant no.FRF-SD-12-013A)
文摘The cycle life of oxygen carrier（OC） is crucial to the practical applications of chemical looping combustion（CLC）. Cycle performance of Cu/SiO2 prepared with a mechanical mixing method was evaluated based on a CLC process characterized with an added methane steam reforming step. The Cu/SiO2 exhibited high redox reactivity in the initial cycles, while the performance degraded with cycle number. Through characterization of the degraded Cu/SiO2, the performance degradation was mainly caused by the secondary particles＇ fragmentation and the fine particles＇ local agglomeration, which worsened the distribution and diffusion of the reactive gases in the packed bed. A regeneration method of the degraded OC based on re-granulation has been proposed, and its mechanism has been illustrated. With this method, the performance of the degraded OC through 420 redox cycles was recovered to a level close to the initial one.
基金The financial support of the National Natural Science Foundation of China(No.51076154)is gratefully acknowledgedThis work was also supported by the National Key Technology R&D Program of 12^(th) Five-Year Plan of China(No.2011BAD15B05)the Science&Technology Research Project of Guangdong Province(No.2010B010900047).
文摘Fe_(2)O_(3)/Al_(2)O_(3) and Fe_(2)O_(3)/Al_(2)O_(3) modified by low content of Ni(below 2%in weight)oxygen carriers were prepared by mechanical mixing and impregnation method.The synthesized oxygen carriers were characterized by means of X-ray diffraction(XRD),X-ray fluorescence(XRF),scanning electron microscopy(SEM),BET-surface area and temperature programmed reduction(TPR).Besides,redox cyclic reactivity and the performance of chemical looping reforming of methane of the oxygen carriers were studied in a thermal gravimetrical analysis(TGA)and fixed bed at 850℃.It was observed that the redox reactivity of the oxygen carriers is improved by Ni addition because synergic effect may occur between NiO and Fe_(2)O_(3)/Al_(2)O_(3) to form NiFe_(2)O_(4) and NiAl_(2)O_(4) spinel phases.However,the improvement was not apparent as Ni addition reached 1 wt%or more because more nickel loaded resulted in methane decomposition into H2 and carbon leading to carbon deposition.The SEM and BET analysis showed that NiFe_(2)O_(4) and NiAl_(2)O_(4) particles dispersed into the pores of the Fe_(2)O_(3)/Al_(2)O_(3) particles in the course of preparation.In addition,the resistance to sintering of the modified samples increased with the Ni addition increasing.The results of successive redox cycles showed that the Ni modified Fe_(2)O_(3)/Al_(2)O_(3) oxygen carriers have good regenerability.With integration of reactivity and carbon deposition,the content 1.04 wt%of nickel doping was an optimal amount in the three modified samples.
基金the support of the National Key Research and Development Program of China (No. 2016YFB0901401)the Chinese Academy of Sciences Frontier Science Key Research Project (QYZDY-SSW-JSC036)
文摘Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC.In this paper,the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products.The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process.Therefore,the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided.In both stages,the dominant resistances were analyzed.The activation energy and the reaction order in both stages were calculated respectively as well.Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations,it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor.This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.
基金This work was financially supported by the National Natu-ral Science Foundation of China(51806035)the Natural Science Foundation of Jiangsu Province(BK20170669)+1 种基金the Fundamental Research Funds for the Central Universities(2242018K40117)the Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development(Y707s41001).
文摘Coal-direct chemical-looping combustion(CDCLC)is a promising coal combustion technique that provides CO2 capture with a low energy penalty.In this study,we developed a three-dimensional Eulerian-Eulerian multiphase full-loop model for simulating the circulation and separation of binary particle mixtures in a novel high-flux CDCLC system.This model comprised a high-flux circulating fluidized bed as the fuel reactor(FR),a counter-flow moving bed as the air reactor(AR),a high-flux carbon stripper,two downcomers,and two J-valves.This model predicted the main features of complex gas-solid flow behaviors in the system.The simulation results showed that quasi-stable solid circulation in the whole system could be achieved,and the FR,AR,and J-valves operated in a dense suspension upflow regime,a near-plug-flow regime,and a bubbling fluidization regime,respectively.The multiphase flow model of binary particle mixtures was used to predict the mechanisms of directional separation of binary particle mixtures of an oxygen carrier(OC)and coal throughout the system.A decrease in the baffle aspect ratio of the inertial separator improved the coal selective separation efficiency but resulted in a slight decline in the OC selective separation;this is believed to be the result of weakening of particle collisions with the baffle.A higher FR gas velocity had a slightly negative effect on the OC selective separation efficiency,but improved the coal selective separation efficiency;this can be attributed to an increase in the particle-carrying capacity of the gas stream.A decrease in the coal particle size led to better entrainment of the coal particles by the gas stream and this increased the coal selective separation efficiency.In real CDCLC applications,the operating variables for separation of binary particle mixtures should be comprehensively assessed to determine their positive and negative effects on the carbon capture efficiency,OC regeneration efficiency,gas leakage restraint,energy consumption,and fuel conversion.
基金supported by the Natural Science Foundation of Hebei Province(E2020502007)the Central University Fund Project(2020MS103).
文摘Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic conditions when the chemical-looping combus-tion(CLC)process is used.The CLC experiments of multi-component solid waste were conducted on a homemade twin-bed reactor and the characteristics of flue gas were investigated for the effect of the mixing ratio of sewage sludge and polyvinyl chloride(PVC).The results indicated that the combustion efficiency was>99.9%for these CLC processes;the highest carbon-conversion rate was obtained at 96.3%for PVC with 60%sludge.The highest NO and SO_(2)emissions were 26%and 19%,respectively,when the sludge was mixed with 20%PVC.As the proportion of PVC blended into the sludge increased,the time when the concentration of NO in the flue-gas peaks moved backwards,while peak SO_(2)concentration moved forward.The general trend was to increase first and then de-crease.In addition,there were multiple peaks in carbon emissions,corresponding to~10%,30%and~70%of the carbon-conversion rate;nitrogen emissions reached 90%of total emissions before the carbon-conversion rate was 40%;sulphur emissions had a longer cycle and were mainly emitted between 10%and 60%of the carbon-conversion rate.The results are expected to provide a reference for solid-waste source suppressing to inhibit the generation of pollutants.
基金Supported by the National~ Natural Science Foundation of China （20876079）, the Natural Science Funds for Distinguished Young Scholar in Shandong Province （JQ200904）, and Shandong Province Key Technologies Research and Development Program of China （2008GG 10006010, 2009GG 10007001）.
文摘Chemical-looping gasification （CLG） is a novel process for syngas generation from solid fuels, sharing the same basic principles as chemical-looping combustion （CLC）. It also uses oxygen carriers （mainly metal oxide and calcium sulfate） to transfer heat and oxygen to the fuel. In this paper, the primary investigation into the CLG process with CaSO4 as oxygen carrier was carried out by thermodynamic analysis and experiments in the tube reactor. Sulfur-contained gas emission was mainly H2S rather than SO2 in the CLG process, showing some different features from the CLC. The mass and heat balance of CLG processes were calculated thermodynamically to determinate the auto-thermal operating conditions with different CaSO4/C and steam/C molar ratios. It was found that the CaSO4/C molar ratio should be higher than 0.2 to reach auto-thermal balance. The effect of temperature on the reactions between oxygen carrier and coal was investigated based on Gibbs free energy minimum method and ex- perimental results. It indicated that high temperature favored the CLG process in the fuel reactor and part of syngas was consumed to compensate for auto-thermal system.
基金supported by National Natural Science Foundation of China(51976071)Fundamental Research Funds for the Central Universities(2019kfy RCPY021)。
文摘An atomic-level insight into the H_(2)adsorption and oxidation on the Fe_(2)O_(3)surface during chemicallooping combustion was provided on the basis of density functional theory calculations in this study.The results indicated that H_(2)molecule most likely chemisorbs on the Fe_(2)O_(3)surface in a dissociative mode.The decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the surface.In particular,the H_(2)molecule adsorbed on an O top site could directly form H_(2)O precursor on the O_(3)-terminated surface.Further,the newly formed H-O bond was activated,and the H atom could migrate from one O site to another,consequently forming the H_(2)O precursor.In the H_(2)oxidation process,the decomposition of H_(2)molecule was the rate-determining step for the O_(3)-terminated surface with an activation energy of 1.53 eV.However,the formation of H_(2)O was the ratedetermining step for the Fe-terminated surface with an activation energy of 1.64 eV.The Feterminated surface is less energetically favorable for H_(2)oxidation than that the O_(3)-terminated surface owing to the steric hindrance of Fe atom.These results provide a fundamental understanding about the reaction mechanism of Fe_(2)O_(3)with H_(2),which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H_(2).
文摘Copper（Ⅱ） oxide in varying ratios was combined with either an alumina-based cement（Al300）, or CaO derived from limestone as support material in a mechanical pelletiser. This production method was used to investigate its influence on possible mechanical and chemical improvements for oxygen carriers in chemical looping processes. These materials were tested in a lab-scale fluidised bed with CO or CH;as a reducing gas at 950 °C. As expected, the oxygen carriers containing a greater ratio of support material exhibited an enhanced crushing strength. Oxygen carriers comprised of a 1:3 ratio of support material to active CuO exhibited increased crushing strength by a minimum of 280% compared to pure CuO pellets.All oxygen carriers exhibited a high CO conversion yield and were fully reducible from CuO to Cu. For the initial redox cycle, Al300-supported oxygen carriers showed the highest fuel and oxygen carrier conversion. The general trend observed was a decline in conversion with an increasing number of redox cycles.In the case of CaO-supported oxygen carriers, all but one of the oxygen carriers suffered agglomeration.The agglomeration was more severe in carriers with higher ratios of CuO. Oxygen carrier Cu25Al75（75 wt% aluminate cement and 25 wt% CuO）, which did not suffer from agglomeration, showed the highest attrition with a loss of approximately 8% of its initial mass over 25 redox cycles. The reducibility of the oxygen carriers was limited with CH;in comparison to CO. CH;conversion were 15%-25% and 50% for Cu25Ca75（25 wt% CuO and 75 wt% CaO） and Cu25Al75, respectively. Cu25Ca75 demonstrated improved conversion, whereas Cu25Al75 exhibited a trending decrease in conversion with increasing redox cycles.
基金the National Natural Science Foundation of China (50776018)the Special Fund of the National Priority Basic Research of China (2007CB 210101) for the financial support of this project
文摘Chemical-looping combustion (CLC) is a novel combustion technique with inherent CO2 separation.Magnetite (Fe3O4) was selected as the oxygen carrier.Shenhua coal (Inner Mongolia,China),straw coke and natural coke were used as fuels for this study.Influences of operation temperatures,coal to Fe3O4 mass ratios,and different kinds of fuels on the reduction characteristics of the oxygen carrier were investigated using an atmosphere thermogravimetric analyzer (TGA).Scanning electron microscopy (SEM) was used to analyse the characteristic of the solid residues.Experimental results shown that the reaction between the coal and the oxygen carrier become strong at a temperature of higher than 800℃.As the operation temperature rises,the reduction conversion rate increases.At the temperatures of 850oС,900℃,and 950℃,the reduction conversion rates were 37.1%,46.5%,and 54.1% respectively.However,SEM images show that at the temperature of higher than 950℃,the iron oxides become melted and sintered.The possible operation temperature should be kept around 900℃.When the mass ratios of coal to Fe3O4 were 5/95,10/90,15/85,and 20/80,the reduction conversion rates were 29.5%,40.8%,46.5%,and 46.6% respectively.With the increase of coal,the conversion rate goes up.But there exist an optimal ratio around 15/85.Comparisons based on different kinds of fuels show that the solid fuel with a higher volatile and a more developed pore structure is conducive to the reduction reactivity of the oxygen carrier.
基金The authors gratefully acknowledge the support of this research work by National Natural Science Foundation of China(Grants51561125001 and 51476029).
文摘The micro-interconnected fluidized bed(MIFB)was designed to improve the evaluation condition of oxygen carrier,which is difficult to perform in a lab-scale interconnected fluidized bed because of the large demand for bed inventory.The reduction of bed inventory in the MIFB was mainly achieved by the appropriate miniaturization of the reactor size,in which the wall effect and operating flexibility should be taken into consideration.With hematite serving as the oxygen carrier,stable and flexible fluidization could be realized with 342.9 g of bed inventory.Internal perforated plates were arranged in the middle of the reactor to improve gas-solid distribution,which also could restrain the slugging formation and increase the particle residence time by 28.9%.A different fluidization phenomenon was observed in this two-stage reactor in which the particle fluidization was reconstructed in the upper chamber.Throughout 48 h of cold operation,the hematite oxygen carrier attrition rate was evaluated as 0.151 wt.%/h corresponding to 660 h lifetime,where 12.5%of particle attrition was contributed by internal perforated plates.An excellent fitting performance was found between the pressure difference in the risers and the upward particle flow,but the correction factor should be adjusted according to the fluidization flow.
