Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However,the authors’experiments showed that the ultra-fine powder CaCO 3 could be stably fluidized in a spouted bed...Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However,the authors’experiments showed that the ultra-fine powder CaCO 3 could be stably fluidized in a spouted bed with a draft tube.The effects of geometric and operating parameters on solid circulation rate of ultra-fine powder CaCO 3 were investigated in a 120 mm diameter transparent semicircular spouted bed with a draft tube.Three draft tubes with different sizes were used in this study.It was found that the solids circulation rate was mainly dependent on the drawing rate of the gas jet from the nozzle, then on the gas transport capacity in the draft tube.With increasing gas feed rate, distance between the nozzle and the draft tube inlet and draft tube diameter,the solids circulation rate could be increased.Based on the jet theory,a quantitative correlation was proposed for predicting the solid circulation rate of ultra-fine powders in a spouted bed with a draft tube by taking into account the gas transport capacity in the draft tube.展开更多
Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 m, respectively....Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of liquid velocity, particle size, surface tension of liquid phase and solid circulation rate on the overall heat transfer coefficient were examined. The heat transfer coefficient increased with increasing particle size or solid circulation rate due to the higher potential of particles to contact with the heater surface and promote turbulence near the heater surface. The value of heat transfer coefficient increased gradually with increase in the surface tension of liquid phase, due to the slight increase of solid holdup. The heat transfer coefficient increased with the liquid velocity even in the higher range, due to the solid circulation prevented the decrease in solid holdup, in contrast to that in the conventional liquid-solid fluidized beds. The values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables.展开更多
A comprehensive study on the hydrodynamics in the downcomer of a liquid-solid circulating fluidized bed(LSCFB) is crucial in the control and optimization of the extraction process using an ion exchange LSCFB.A computa...A comprehensive study on the hydrodynamics in the downcomer of a liquid-solid circulating fluidized bed(LSCFB) is crucial in the control and optimization of the extraction process using an ion exchange LSCFB.A computational fluid dynamics model is proposed in this study to simulate the counter-current two-phase flow in the downcomer of the LSCFB.The model is based on the Eulerian-Eulerian approach incorporating the kinetic theory of granular flow.The predicted results agree well with our earlier experimental data.Furthermore,it is shown that the bed expansion of the particles in the downcomer is directly affected by the superficial liquid velocity in downcomer and solids circulation rate.The model also predicts the residence time of solid particles in the downcomer using a pulse technique.It is demonstrated that the increase in the superficial liquid velocity decreases the solids dispersion in the downcomer of the LSCFB.展开更多
Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was car...Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was carried out in the cold-test rig of an annular furnace CFB with six cyclones. The influence of furnace structure and cyclone arrangement on the non-uniformity of gas-solid flow was obtained. On the basis of these findings, the structure of the annular furnace CFB with six cyclones was optimized, and an optimal structure was obtained. The results show that for newly designed annular furnace CFBs, the non-uniformity of gas-solid flow among loops is no greater than that of traditional CFBs. In terms of uniformity, side cyclones rotating inward are superior to those rotating outward. The position of the side cyclones determines the basic solid circulating rate distribution trend and can dramatically improve flow non-uniformity. The middle cyclone positions and the symmetric modes of the cyclones do not determine the solid circulating rate distribution trend and have less effect on DEVGs. Forty-five degree chamfers of outer ring walls can reduce wall erosion and the non-uniformity of gas-solid flow in the circulating fluidized bed. Regarding the operating and structural conditions in this work, the optimal structure of annular furnace CFBs is Type 6: side cyclones rotating inward and b = a/2, d = 0.1c; the center of the middle cyclone inlet located at the centerline of the furnace cross-section; cyclones on the two sides of the furnace in an axisymmetric arrangement; and a furnace corner shape of 45° chamfers. Under the given operating conditions, the DEV_(Gs) for the optimal structure are approximately 4.0%~10.3%.展开更多
The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circu-lar (? 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investig...The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circu-lar (? 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investigated experimentally. The influence of riser structure on the hydrodynamic behaviors of a high-density circulating fluidized bed was investigated. The solid circulation rate was up to 321 kg/(m2s) with the circular cross-section under the operating conditions of the main bed air velocity 12.1 m/s and loosen wind and back-feed wind flow 25.1 m3/h. Different operating conditions on realizing high density circulation was analyzed, while both solids circulation rate and particle holdup depended highly on operating conditions. The circulating gas-solid flow was accompanied by an evidently-dense character in the riser's bottom zone and became fully developed in the middle and upper zones.展开更多
To better understand the hydrodynamic behavior of an internally circulating fluidized bed,solids holdup in the down-comer(ε_(sD)),solids circulation rate(G_s) and gas bypassing fraction(from down-comer to riserγ_(DR...To better understand the hydrodynamic behavior of an internally circulating fluidized bed,solids holdup in the down-comer(ε_(sD)),solids circulation rate(G_s) and gas bypassing fraction(from down-comer to riserγ_(DR),and from riser to down-comer γ_(RD)) were experimentally studied.The effects of gas velocities in the riser and in the down-comer(U_R and U_D),orifice diameter in the draft tube(d_(or)),and draft tube height(H_R) were investigated.Experimental results showed that increase of gas velocities led to increase in G_s and γ_(DR),and slight decrease in γ_(RD)-Larger orifice diameter on the draft tube led to higher ε_(sD),G_s and γ_(DR),but had insignificant influence on γ_(RD).With increasing draft tube height,both G_s and γ_(DR) first increased and then decreased,while γ_(RD) first decreased and then increased.Proposed correlations for predicting the hydrodynamic parameters agreed reasonably well with experimental values.展开更多
Rotational asymmetric distribution of reactant (ozone) concentration and its evolution along with the gas-solid reactive flow were studied in a 76 mm i.d., 10.2 m high circulating fluidized bed (CFB) riser reactor. Th...Rotational asymmetric distribution of reactant (ozone) concentration and its evolution along with the gas-solid reactive flow were studied in a 76 mm i.d., 10.2 m high circulating fluidized bed (CFB) riser reactor. The superficial gas velocity ranged from 3 to 5 m/s and the solids circulation rates were 50 and 100 kg/(m2 s). Experimental results show that the asymmetry of reactant distribution can extend to a height close to the length of flow developing zone of the CFB riser reactor and then disappears. Based on the hydrodynamics of the gas and solid phases in the solids entrance region, this asymmetry can be attributed to the effect of the solids entrance structure.展开更多
文摘Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However,the authors’experiments showed that the ultra-fine powder CaCO 3 could be stably fluidized in a spouted bed with a draft tube.The effects of geometric and operating parameters on solid circulation rate of ultra-fine powder CaCO 3 were investigated in a 120 mm diameter transparent semicircular spouted bed with a draft tube.Three draft tubes with different sizes were used in this study.It was found that the solids circulation rate was mainly dependent on the drawing rate of the gas jet from the nozzle, then on the gas transport capacity in the draft tube.With increasing gas feed rate, distance between the nozzle and the draft tube inlet and draft tube diameter,the solids circulation rate could be increased.Based on the jet theory,a quantitative correlation was proposed for predicting the solid circulation rate of ultra-fine powders in a spouted bed with a draft tube by taking into account the gas transport capacity in the draft tube.
基金Supported by Korea Institute of Energy Technology Evaluation and Planning (KETEP)GTL Technology Development Consortium (Korean National Oil Corp., Korea Gas Corp., Daelim Industrial Co. and Hyundai Engineering Co.) under "Energy Efficiency & Resources Programs" of the Ministry of Knowledge Economy, Republic of Korea
文摘Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of liquid velocity, particle size, surface tension of liquid phase and solid circulation rate on the overall heat transfer coefficient were examined. The heat transfer coefficient increased with increasing particle size or solid circulation rate due to the higher potential of particles to contact with the heater surface and promote turbulence near the heater surface. The value of heat transfer coefficient increased gradually with increase in the surface tension of liquid phase, due to the slight increase of solid holdup. The heat transfer coefficient increased with the liquid velocity even in the higher range, due to the solid circulation prevented the decrease in solid holdup, in contrast to that in the conventional liquid-solid fluidized beds. The values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables.
基金We acknowledge support from the National High Technology Research and Development Program of China （2012AA06A115）, National Natural Science Foundation of China （51476058, 91434120）, and Fundamental Research Funds for the Central Universities （2014MS13）.
基金supported by the Discovery Grant and Engage Grant from the Natural Sciences and Engineering Research Council of Canada(NSERC)
文摘A comprehensive study on the hydrodynamics in the downcomer of a liquid-solid circulating fluidized bed(LSCFB) is crucial in the control and optimization of the extraction process using an ion exchange LSCFB.A computational fluid dynamics model is proposed in this study to simulate the counter-current two-phase flow in the downcomer of the LSCFB.The model is based on the Eulerian-Eulerian approach incorporating the kinetic theory of granular flow.The predicted results agree well with our earlier experimental data.Furthermore,it is shown that the bed expansion of the particles in the downcomer is directly affected by the superficial liquid velocity in downcomer and solids circulation rate.The model also predicts the residence time of solid particles in the downcomer using a pulse technique.It is demonstrated that the increase in the superficial liquid velocity decreases the solids dispersion in the downcomer of the LSCFB.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences,Grant No.XDA07030100
文摘Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was carried out in the cold-test rig of an annular furnace CFB with six cyclones. The influence of furnace structure and cyclone arrangement on the non-uniformity of gas-solid flow was obtained. On the basis of these findings, the structure of the annular furnace CFB with six cyclones was optimized, and an optimal structure was obtained. The results show that for newly designed annular furnace CFBs, the non-uniformity of gas-solid flow among loops is no greater than that of traditional CFBs. In terms of uniformity, side cyclones rotating inward are superior to those rotating outward. The position of the side cyclones determines the basic solid circulating rate distribution trend and can dramatically improve flow non-uniformity. The middle cyclone positions and the symmetric modes of the cyclones do not determine the solid circulating rate distribution trend and have less effect on DEVGs. Forty-five degree chamfers of outer ring walls can reduce wall erosion and the non-uniformity of gas-solid flow in the circulating fluidized bed. Regarding the operating and structural conditions in this work, the optimal structure of annular furnace CFBs is Type 6: side cyclones rotating inward and b = a/2, d = 0.1c; the center of the middle cyclone inlet located at the centerline of the furnace cross-section; cyclones on the two sides of the furnace in an axisymmetric arrangement; and a furnace corner shape of 45° chamfers. Under the given operating conditions, the DEV_(Gs) for the optimal structure are approximately 4.0%~10.3%.
基金supports by the National Natural Science Foundation of China (51006106)the National High Technology Research and Development of China 863 Program (2006AA05A103)
文摘The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circu-lar (? 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investigated experimentally. The influence of riser structure on the hydrodynamic behaviors of a high-density circulating fluidized bed was investigated. The solid circulation rate was up to 321 kg/(m2s) with the circular cross-section under the operating conditions of the main bed air velocity 12.1 m/s and loosen wind and back-feed wind flow 25.1 m3/h. Different operating conditions on realizing high density circulation was analyzed, while both solids circulation rate and particle holdup depended highly on operating conditions. The circulating gas-solid flow was accompanied by an evidently-dense character in the riser's bottom zone and became fully developed in the middle and upper zones.
基金the financial support by the Beijing New Star Project on Science&Technology of China under grant no.2009B35
文摘To better understand the hydrodynamic behavior of an internally circulating fluidized bed,solids holdup in the down-comer(ε_(sD)),solids circulation rate(G_s) and gas bypassing fraction(from down-comer to riserγ_(DR),and from riser to down-comer γ_(RD)) were experimentally studied.The effects of gas velocities in the riser and in the down-comer(U_R and U_D),orifice diameter in the draft tube(d_(or)),and draft tube height(H_R) were investigated.Experimental results showed that increase of gas velocities led to increase in G_s and γ_(DR),and slight decrease in γ_(RD)-Larger orifice diameter on the draft tube led to higher ε_(sD),G_s and γ_(DR),but had insignificant influence on γ_(RD).With increasing draft tube height,both G_s and γ_(DR) first increased and then decreased,while γ_(RD) first decreased and then increased.Proposed correlations for predicting the hydrodynamic parameters agreed reasonably well with experimental values.
文摘Rotational asymmetric distribution of reactant (ozone) concentration and its evolution along with the gas-solid reactive flow were studied in a 76 mm i.d., 10.2 m high circulating fluidized bed (CFB) riser reactor. The superficial gas velocity ranged from 3 to 5 m/s and the solids circulation rates were 50 and 100 kg/(m2 s). Experimental results show that the asymmetry of reactant distribution can extend to a height close to the length of flow developing zone of the CFB riser reactor and then disappears. Based on the hydrodynamics of the gas and solid phases in the solids entrance region, this asymmetry can be attributed to the effect of the solids entrance structure.
