Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance.In the process of fluidization,electrostatic interaction between particles will obviously accelerate particle agg...Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance.In the process of fluidization,electrostatic interaction between particles will obviously accelerate particle agglomerate formation,which consequently reduces the fluidization performance.Pulsed gas flow injection is an efficient method to enhance particle mixing,thereby weakening the occurrence of particle agglomerate.In this study,the two-dimensional hybrid pulsed fluidized bed is established.The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects.Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition.Results show that in the presence of static electricity,the bubble generation position is lower,which is conducive to the particle flow.Pulsed gas flow can increase the particle velocity and improve the diffusion ability.The bubble generation time is different at different frequencies,and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics.Different gas flow ratios have significant impacts on the particle movement amplitude.When the pulse gas flow accounts for a large ratio,the particle agglomerate tends to be larger.Therefore,in order to improve the fluidization effect,the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.展开更多
A continuous fluidized bed bioreactor (FBBR) with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 2...A continuous fluidized bed bioreactor (FBBR) with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2-3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of (30 ± 2)°C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached (42 ± 3) μm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%-92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.展开更多
Precipitation of BaSO4 nanoparticles was studied for the first time in a specially designed rotating packed bed (RPB), which allowed sampling at different radial positions to provide better insight of the mechanism ...Precipitation of BaSO4 nanoparticles was studied for the first time in a specially designed rotating packed bed (RPB), which allowed sampling at different radial positions to provide better insight of the mechanism of precipitation in RPB. Particle size and morphology were characterized by TEM, while the quality of synthesized BaSO4 powders was analyzed by XRD and BET, and compared with those prepared in a stirred-tank reactor. The important role of the inlet region of the RPB in the whole precipitation process was experimentally confirmed, as a significant essence for the design of industrial RPB for the precipitation of sparingly soluble materials. The effects of different operating conditions on particle size were also investigated, showing that particle size decreases with increasing rotational speed and liquid flow rate, due to the enhancement of micromixing in the RPB.展开更多
Employing well-established mixing rules for mean properties, appropriate expressions are derived for predicting minimum fluidization velocities of multi-component solid mixtures in terms of mono- component values for ...Employing well-established mixing rules for mean properties, appropriate expressions are derived for predicting minimum fluidization velocities of multi-component solid mixtures in terms of mono- component values for the velocity and the bed voidage at incipient fluidization. Based on flow regime and the mixing level of constituent species, it is found that these relationships differ significantly from each other, whether related to size-different or density-different mixtures. For mixed beds of size-different mixtures, the effect of volume contraction is accounted for by the mean voidage term, which is absent for segregated beds. Incorporating the volume-change of mixing leads to values of the mixture minimum fluidization velocities even lower than corresponding values for segregated bed, thus conforming to the trend reported in the literature. Size-different mixtures exhibit flow regime dependence irrespective of whether the bed is mixed or segregated. On the other hand, the mixing of constituent species does not affect the minimum fiuidization velocity of density-different mixtures, as the difference in the expres- sions for a segregated and a mixed system is rather inconsequential. Comparison with experimental data available in the literature is made to test the efficacy of the minimum fluidization velocity expressions derived here.展开更多
基金The financial support of the National Nature Science Foundation of China(No.51406031)the Science Foundation of the Jilin Province Science and Technology Agency(Grant No.20160520032JH,20170101123JC)are gratefully acknowledged。
文摘Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance.In the process of fluidization,electrostatic interaction between particles will obviously accelerate particle agglomerate formation,which consequently reduces the fluidization performance.Pulsed gas flow injection is an efficient method to enhance particle mixing,thereby weakening the occurrence of particle agglomerate.In this study,the two-dimensional hybrid pulsed fluidized bed is established.The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects.Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition.Results show that in the presence of static electricity,the bubble generation position is lower,which is conducive to the particle flow.Pulsed gas flow can increase the particle velocity and improve the diffusion ability.The bubble generation time is different at different frequencies,and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics.Different gas flow ratios have significant impacts on the particle movement amplitude.When the pulse gas flow accounts for a large ratio,the particle agglomerate tends to be larger.Therefore,in order to improve the fluidization effect,the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.
文摘A continuous fluidized bed bioreactor (FBBR) with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2-3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of (30 ± 2)°C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached (42 ± 3) μm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%-92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.
基金supported by the National Natural Science Foundation of China(Nos.20821004,20990221)the Beijing Municipal Commission of Education(No.JD100100403)the Innovation Team Program of Ministry of Education of China
文摘Precipitation of BaSO4 nanoparticles was studied for the first time in a specially designed rotating packed bed (RPB), which allowed sampling at different radial positions to provide better insight of the mechanism of precipitation in RPB. Particle size and morphology were characterized by TEM, while the quality of synthesized BaSO4 powders was analyzed by XRD and BET, and compared with those prepared in a stirred-tank reactor. The important role of the inlet region of the RPB in the whole precipitation process was experimentally confirmed, as a significant essence for the design of industrial RPB for the precipitation of sparingly soluble materials. The effects of different operating conditions on particle size were also investigated, showing that particle size decreases with increasing rotational speed and liquid flow rate, due to the enhancement of micromixing in the RPB.
基金the Deanship of Scientific Research at King Saud University for funding this work through the Research Group Project Number RGP-VPP-188
文摘Employing well-established mixing rules for mean properties, appropriate expressions are derived for predicting minimum fluidization velocities of multi-component solid mixtures in terms of mono- component values for the velocity and the bed voidage at incipient fluidization. Based on flow regime and the mixing level of constituent species, it is found that these relationships differ significantly from each other, whether related to size-different or density-different mixtures. For mixed beds of size-different mixtures, the effect of volume contraction is accounted for by the mean voidage term, which is absent for segregated beds. Incorporating the volume-change of mixing leads to values of the mixture minimum fluidization velocities even lower than corresponding values for segregated bed, thus conforming to the trend reported in the literature. Size-different mixtures exhibit flow regime dependence irrespective of whether the bed is mixed or segregated. On the other hand, the mixing of constituent species does not affect the minimum fiuidization velocity of density-different mixtures, as the difference in the expres- sions for a segregated and a mixed system is rather inconsequential. Comparison with experimental data available in the literature is made to test the efficacy of the minimum fluidization velocity expressions derived here.