The classification performance of model coal mill classifiers with different bottom incoming flow inlets was experimentally and numerically studied.The flow field adjacent to two neighboring impeller blades was measur...The classification performance of model coal mill classifiers with different bottom incoming flow inlets was experimentally and numerically studied.The flow field adjacent to two neighboring impeller blades was measured using the particle image velocimetry technique.The results showed that the flow field adjacent to two neighboring blades with the swirling inlet was significantly different from that with the non-swirling inlet.With the swirling inlet,there was a vortex located between two neighboring blades,while with the nonswirling inlet,the vortex was attached to the blade tip.The vorticity of the vortex with the non-swirling inlet was much lower than that with the swirling inlet.The classifier with the non-swirling inlet demonstrated a larger cut size than that with the swirling inlet when the impeller was stationary(~0 r·min-1).As the impeller rotational speed increased,the cut size of the cases with non-swirling and swirling inlets both decreased,and the one with the non-swirling inlet decreased more dramatically.The values of the cut size of the two classifiers were close to each other at a high impeller rotational speed(≥120 r·min-1).The overall separation efficiency of the classifier with the non-swirling inlet was lower than that with the swirling inlet,and monotonically increased as the impeller rotational speed increased.With the swirling inlet,the overall separation efficiency first increased with the impeller rotational speed and then decreased when the rotational speed was above 120 r·min-1,and the variation trend of the separation efficiency was more moderate.As the initial particle concentration increased,the cut sizes of both swirling and non-swirling inlet cases decreased first and then barely changed.At a low initial particle concentration(b 0.04 kg·m-3),the classifier with the swirling inlet had a larger cut size than that with the non-swirling inlet.展开更多
The effects of moisture content on the combustion characteristics and pore structure change of coal slime are studied in this paper.The effect of moisture content on the bed temperature change,combustion efficiency,an...The effects of moisture content on the combustion characteristics and pore structure change of coal slime are studied in this paper.The effect of moisture content on the bed temperature change,combustion efficiency,and NO_(x)and SO_(2)emission were obtained in a bench⁃scale fluidized bed reactor,revealing that the lowest bed temperature decreases with the increase in moisture content,but the effect on the highest bed temperature is not the same.Moreover,with the increase in moisture content,the observed degree of blackening of the flue gas increased,and more CO was produced,which in turn leads to a lower combustion efficiency of the coal slime.However,the presence of moisture plays a positive role in the reduction of NO_(x)and SO_(2).With the increase in moisture content,the amount of NO_(x)and SO_(2)produced tends to decrease.The effect of water on the combustion process of slime is mostly the impact of the severe vaporization process in the early stage to form a large water vapor channel,which is beneficial to the evaporation and loss of water,conducive to the reaction of water and coal combustion products,such as the formation of CO,reduction of NO_(x),SO_(2),etc.The large holes formed by the impact of water vapor decreased with the decrease of moisture content,and the nanoscale pores are mostly caused by the combustion process of volatilization and coke formation after the end of vaporization,and increase with the decrease of moisture content.展开更多
A coupled CFD-DEM method was used to study the hydrodynamics of a Wurster coater.Firstly,the CFD part of the model was validated by the accurate prediction of the pressure drops over a pseudo-2D fluidized bed under va...A coupled CFD-DEM method was used to study the hydrodynamics of a Wurster coater.Firstly,the CFD part of the model was validated by the accurate prediction of the pressure drops over a pseudo-2D fluidized bed under various gas velocities.The effect of gas velocity,gap height,tube length and batch volume of the particles on the cycle time and the residence time of the particles was thoroughly investigated.The central jet gas velocity ui was found to speed up the particle cycle but undermine the coating efficiency.The gas velocity at the horizontal transport zone u2 was able to promote the horizontal transport of the particles but should not be too high,otherwise,it would obstruct the normal falling back of the particles in the downward zone.Big gap heights would decrease the coating efficiency but tube length had little impact on that.The increment of batch volume would commonly abase the cycle time and the working efficiency under a given u1.The de-fluidization problem arose when the batch volume increased to 550 mL.However,this problem could be swept out by the optimization of u1 and u2.In a mixture of different sizes,the coarse particles enjoyed higher coating efficiency and could travel closer to the nozzles.This may shield the fine particles from getting enough coating liquids,and thus coarse particles and fine particles were not recommended to get coated in the same batch.展开更多
Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-t...Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.展开更多
The fluidization state in the circulating fluidized bed(CFB)boiler is crucial to its stable and safe operation.However,up to now,the research field has not reached unanimity on whether the fluidization regime that the...The fluidization state in the circulating fluidized bed(CFB)boiler is crucial to its stable and safe operation.However,up to now,the research field has not reached unanimity on whether the fluidization regime that the upper furnace of the boiler operates in is the fast fluidization or pneumatic transport.To this end,this paper reviewed relevant research on the transition between the fast fluidization and pneumatic transport of Geldart group B particles,including the flow characteristics of the fast fluidization,the transition condition between the fast fluidization and pneumatic transport,the determination methods of the transport velocity utr and saturation carrying capacity G_(s)* and the influencing factors on these two parameters.Previous research findings can provide certain guidelines for the design and optimization of the CFB boiler,and result in plenty of prediction correlations for utr and G_(s)*.Nonetheless,owing to insufficient data available on Geldart group B particles,especially the ones obtained under high temperature or pressure conditions and in large-scale CFB apparatuses,the existing correlations are not well suited for the prediction of u_(tr) and G_(s)* of Geldart group B particles.Thus,further efforts are urgently demanded on the fast fluidization transition of Geldart group B particles.展开更多
The supercritical circulating fluidized bed(CFB)boiler,which combines the advantages of CFB combustion with low cost emission control and supercritical steam cycle with high efficiency of coal energy,is believed to be...The supercritical circulating fluidized bed(CFB)boiler,which combines the advantages of CFB combustion with low cost emission control and supercritical steam cycle with high efficiency of coal energy,is believed to be the future of CFB combustion technology.It is also of greatest importance for low rank coal utilization in China.Different from the supercritical pulverized coal boiler that has been developed more than 50 years,the supercritical CFB boiler is still a new one which requires further investigation.Without any precedentor engineering reference,Chinese researchers have con ducted fundamental research,development,design of the supercritical CFB boilers independently.The design theory and key technology for supercritical CFB boiler were proposed.Key components and novel structures were invented.The first 600 MWe supercritical CFB boiler and its auxiliaries were successfully developed and demonstrated in Baima Power Plant,Shenhua Group as well as the simulator,control technology,installation technology,commissioning technology,system integration and operation technology.Compared with the 460 MWe supercritical CFB in Poland,developed in the same period and the only other supercritical one of commercial running in the word beside Baima,the 600 MWe one in Baima has a better performance.Besides,supercritical CFB boilers of 350 MWe have been developed and widely commercialized in China.In this paper,the updated progress of 660 MWe ultra-supercritical CFB boilers under development is introduced.展开更多
A computational particle fluid dynamics （CPFD） numerical method to model gas-solid flows in a circulating fluidized bed （CFB） riser was used to assess the effects of particle size distribution （PSD） on solids di...A computational particle fluid dynamics （CPFD） numerical method to model gas-solid flows in a circulating fluidized bed （CFB） riser was used to assess the effects of particle size distribution （PSD） on solids distribution and flow. We investigated a binary PSD and a polydisperse PSD case. Our simulations were compared with measured solids concentrations and velocity profiles from experiments, as well as with a published Eulerian-Eulerian simulation. Overall flow patterns were similar for both simulation cases, as confirmed by experimental measurements. However, our fine-mesh CPFD simulations failed to predict a dense bottom region in the riser, as seen in other numerical studies. Above this bottom region, distri- butions of particle volume fraction and particle vertical velocity were consistent with our experiments, and the simulated average particle diameter decreased as a power function with riser height. Interactions between particles and wails also were successfully modeled, with accurate predictions for the lateral profiles of particle vertical velocity. It was easy to implement PSD into the CPFD numerical model, and it required fewer computational resources compared with other models, especially when particles with a polydisperse PSD were present in the heterogeneous flow.展开更多
Circulating fluidized bed(CFB)technology plays an important role in the utilization of low-grade coal in China.This article reviews CFB combustion technology development in China and summarizes recent achievements.Sin...Circulating fluidized bed(CFB)technology plays an important role in the utilization of low-grade coal in China.This article reviews CFB combustion technology development in China and summarizes recent achievements.Since 1990 Chinese engineers and researchers have been undertaking work to improve CFB boiler technology.A completely novel CFB boiler design theory was developed and used in the domestic manufacturing of CFB boilers with various capacities.China is the largest supplier and customer of CFB boilers in the world due to the widespread use of CFB boilers.In 2007,the lower energy consumption CFB technology was successfully developed by re-specifying the fluidization state,which reduced the power consumption of forced fans and solved the potential erosion problems on the water wall.Afterwards,in order to increase the electric power generation efficiency,the supercritical CFB(SCCFB)boiler was developed and the first 600 MW SCCFB boiler was demonstrated and put into commercial operation in 2013.The success of the technology is evident with over 80 SCCFB boilers on order with capacities of 350 MW to 660 MW.Chinese scientists and engineers are also developing technology to lower the emissions of CFB combustion to meet the requirements of China’s strict emission regulations.This emission reduction is through high-efficiency desulfurization by limestone injection into the furnace and low NOx combustion,ultra-low emission of SO2 and NOx in the furnace can be realized by improving the bed quality and increasing the solid circulation rate.There is currently further research and design development being undertaken to develop a 660 MW ultra-supercritical CFB(USCCFB)boiler.The new boiler is expected to be operational before 2020 resulting in higher efficiency and lower energy consumption and emissions.展开更多
In this paper,the combustion process of oil shale semicoke was investigated by modeling,where intraparticle mass transfer resistance was especially considered.The ash formation and attrition characteristics of oil sha...In this paper,the combustion process of oil shale semicoke was investigated by modeling,where intraparticle mass transfer resistance was especially considered.The ash formation and attrition characteristics of oil shale semicoke were also investigated by a laboratory test procedure.The burnout time and residence time of different particle sizes were predicted,and the maximum particle size of which oil shale semicoke could be burned out in a 3 MW circulating fluidized bed boiler was obtained.展开更多
As one of the most important auxiliary systems of a circulating fluidized bed boiler,the limestone pneumatic conveying system is of great significance to its operation.Maldistribution of powder in the different inject...As one of the most important auxiliary systems of a circulating fluidized bed boiler,the limestone pneumatic conveying system is of great significance to its operation.Maldistribution of powder in the different injecting ports seriously limits inner-furnace desulfurization performance owing to inefficient mixing of limestone powder and SO2.The gas-solid flow characteristics of an industrial-scale multiple-branching limestone-conveying pipeline system of a 200 MW circulating fluidized bed boiler were studied using a computational particle fluid dynamics method.The maldistribution intensity was studied under different operating conditions of air velocity and particle mass flow rate.Simulation results indicated that when the air velocity increased,the maldistribution was mitigated,but when the particle mass flow rate increased,the maldistribution strengthened.To solve this problem,two improved schemes were proposed:adding a deflector at different angles and changing the height of pipeline distributor.According to the simulation,the maldistribution could be efficiently mitigated using a distributor height in the range of 100-120 mm and a deflector angle of 10°-30°.展开更多
In this paper,the design and operation of a novel coal-fired circulating fluidized bed(CFB)drum boiler that can generate superheated steam using saline water were introduced.The natural circulation water dynamics with...In this paper,the design and operation of a novel coal-fired circulating fluidized bed(CFB)drum boiler that can generate superheated steam using saline water were introduced.The natural circulation water dynamics with a drum was adopted instead of the traditional once-through steam generator(OTSG)design,so that superheated steam can be generated for the better performance of the steam assisted gravity drainage(SAGD)technology in heavy oil recovery.The optimized staged evaporation method was proposed to further decrease the salinity of water in the clean water section of the boiler.The evaporating pipes of the salted water section were rearranged in the back pass of the boiler,where the heat load is low,to further improve the heat transfer safety.A CFB combustion technology was used for coal firing to achieve a uniform heat transfer condition with low heat flux.Pollutant control technologies were adopted to reduce pollutant emissions.Based on the field test,the recommended water standard for the coal-fired CFB drum boilers was determined.With the present technology,the treated recovery wastewater can be reused in steam-injection boilers to generate superheated steam.The engineering applications show that the boiler efficiency is higher than 90%,the blowdown rate is limited within 5.5%,and the superheat of steam can reach up to 30 K.Besides,the heavy oil recovery efficiency is significantly improved.Moreover,the pollutant emissions of SO2,NOV and dust are controlled within the ranges of 20-90 mg/(N·m^(3)),30-90 mg/(N·m^(3))and 2-10 mg/(N·m^(3))respectively.展开更多
Diffusion of oxygen in the ash layer usually dominated the combustion of oil shale semicoke particles due to the high ash content.Thus,effective diffusivity of oxygen in the ash layer was a crucial parameter worthy of...Diffusion of oxygen in the ash layer usually dominated the combustion of oil shale semicoke particles due to the high ash content.Thus,effective diffusivity of oxygen in the ash layer was a crucial parameter worthy of careful investigation.In this paper,the effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke was measured directly using an improved Wicke-Kallenbach diffusion apparatus.The experimental results showed that higher temperature would lead to a higher effective diffusivity and a thicker ash layer had the negative effect.Especially,the effective diffusivity along the direction perpendicular to bedding planes was much lower than that along the direction parallel to bedding planes.In addition,an effective diffusivity model was developed,which could be used to describe the mass transfer of oxygen in the ash layer of oil shale semicoke.展开更多
基金financial support from the National Key Technologies R&D Program of China(2018YFF0216002)。
文摘The classification performance of model coal mill classifiers with different bottom incoming flow inlets was experimentally and numerically studied.The flow field adjacent to two neighboring impeller blades was measured using the particle image velocimetry technique.The results showed that the flow field adjacent to two neighboring blades with the swirling inlet was significantly different from that with the non-swirling inlet.With the swirling inlet,there was a vortex located between two neighboring blades,while with the nonswirling inlet,the vortex was attached to the blade tip.The vorticity of the vortex with the non-swirling inlet was much lower than that with the swirling inlet.The classifier with the non-swirling inlet demonstrated a larger cut size than that with the swirling inlet when the impeller was stationary(~0 r·min-1).As the impeller rotational speed increased,the cut size of the cases with non-swirling and swirling inlets both decreased,and the one with the non-swirling inlet decreased more dramatically.The values of the cut size of the two classifiers were close to each other at a high impeller rotational speed(≥120 r·min-1).The overall separation efficiency of the classifier with the non-swirling inlet was lower than that with the swirling inlet,and monotonically increased as the impeller rotational speed increased.With the swirling inlet,the overall separation efficiency first increased with the impeller rotational speed and then decreased when the rotational speed was above 120 r·min-1,and the variation trend of the separation efficiency was more moderate.As the initial particle concentration increased,the cut sizes of both swirling and non-swirling inlet cases decreased first and then barely changed.At a low initial particle concentration(b 0.04 kg·m-3),the classifier with the swirling inlet had a larger cut size than that with the non-swirling inlet.
基金Sponsored by the Key Technologies Research and Development Program of China(Grant No.2016YFB0600203).
文摘The effects of moisture content on the combustion characteristics and pore structure change of coal slime are studied in this paper.The effect of moisture content on the bed temperature change,combustion efficiency,and NO_(x)and SO_(2)emission were obtained in a bench⁃scale fluidized bed reactor,revealing that the lowest bed temperature decreases with the increase in moisture content,but the effect on the highest bed temperature is not the same.Moreover,with the increase in moisture content,the observed degree of blackening of the flue gas increased,and more CO was produced,which in turn leads to a lower combustion efficiency of the coal slime.However,the presence of moisture plays a positive role in the reduction of NO_(x)and SO_(2).With the increase in moisture content,the amount of NO_(x)and SO_(2)produced tends to decrease.The effect of water on the combustion process of slime is mostly the impact of the severe vaporization process in the early stage to form a large water vapor channel,which is beneficial to the evaporation and loss of water,conducive to the reaction of water and coal combustion products,such as the formation of CO,reduction of NO_(x),SO_(2),etc.The large holes formed by the impact of water vapor decreased with the decrease of moisture content,and the nanoscale pores are mostly caused by the combustion process of volatilization and coke formation after the end of vaporization,and increase with the decrease of moisture content.
基金supported by the National Natural Science Foundation of China(grant No.52276124)the C9 UniversityScience and Technology Project(grant No.201903D421009).
文摘A coupled CFD-DEM method was used to study the hydrodynamics of a Wurster coater.Firstly,the CFD part of the model was validated by the accurate prediction of the pressure drops over a pseudo-2D fluidized bed under various gas velocities.The effect of gas velocity,gap height,tube length and batch volume of the particles on the cycle time and the residence time of the particles was thoroughly investigated.The central jet gas velocity ui was found to speed up the particle cycle but undermine the coating efficiency.The gas velocity at the horizontal transport zone u2 was able to promote the horizontal transport of the particles but should not be too high,otherwise,it would obstruct the normal falling back of the particles in the downward zone.Big gap heights would decrease the coating efficiency but tube length had little impact on that.The increment of batch volume would commonly abase the cycle time and the working efficiency under a given u1.The de-fluidization problem arose when the batch volume increased to 550 mL.However,this problem could be swept out by the optimization of u1 and u2.In a mixture of different sizes,the coarse particles enjoyed higher coating efficiency and could travel closer to the nozzles.This may shield the fine particles from getting enough coating liquids,and thus coarse particles and fine particles were not recommended to get coated in the same batch.
基金the financial support provided by National Key R&D Project of China(grant No.2020YFB0606303)the technical supports received from Sam Clark in CPFD Software,LLC of USA,and from Hi-Key Technology Incorporated of China.
文摘Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.
基金supported by the National Key Research Plan (2019YFE0102100)the Huaneng Group Science and Technology Research Project (HNKj20-H50)the C9 University Science and Technology Project (201903D421009).
文摘The fluidization state in the circulating fluidized bed(CFB)boiler is crucial to its stable and safe operation.However,up to now,the research field has not reached unanimity on whether the fluidization regime that the upper furnace of the boiler operates in is the fast fluidization or pneumatic transport.To this end,this paper reviewed relevant research on the transition between the fast fluidization and pneumatic transport of Geldart group B particles,including the flow characteristics of the fast fluidization,the transition condition between the fast fluidization and pneumatic transport,the determination methods of the transport velocity utr and saturation carrying capacity G_(s)* and the influencing factors on these two parameters.Previous research findings can provide certain guidelines for the design and optimization of the CFB boiler,and result in plenty of prediction correlations for utr and G_(s)*.Nonetheless,owing to insufficient data available on Geldart group B particles,especially the ones obtained under high temperature or pressure conditions and in large-scale CFB apparatuses,the existing correlations are not well suited for the prediction of u_(tr) and G_(s)* of Geldart group B particles.Thus,further efforts are urgently demanded on the fast fluidization transition of Geldart group B particles.
文摘The supercritical circulating fluidized bed(CFB)boiler,which combines the advantages of CFB combustion with low cost emission control and supercritical steam cycle with high efficiency of coal energy,is believed to be the future of CFB combustion technology.It is also of greatest importance for low rank coal utilization in China.Different from the supercritical pulverized coal boiler that has been developed more than 50 years,the supercritical CFB boiler is still a new one which requires further investigation.Without any precedentor engineering reference,Chinese researchers have con ducted fundamental research,development,design of the supercritical CFB boilers independently.The design theory and key technology for supercritical CFB boiler were proposed.Key components and novel structures were invented.The first 600 MWe supercritical CFB boiler and its auxiliaries were successfully developed and demonstrated in Baima Power Plant,Shenhua Group as well as the simulator,control technology,installation technology,commissioning technology,system integration and operation technology.Compared with the 460 MWe supercritical CFB in Poland,developed in the same period and the only other supercritical one of commercial running in the word beside Baima,the 600 MWe one in Baima has a better performance.Besides,supercritical CFB boilers of 350 MWe have been developed and widely commercialized in China.In this paper,the updated progress of 660 MWe ultra-supercritical CFB boilers under development is introduced.
基金provided by the National Program on Key Basic Research Project(973 Program) of China(No.2012CB214900)the financial support from Tekes,VTT Technical Research Centre of Finland,Etel-Savon Energia Oy,Fortum,Metso Power Oy and Numerola Oythe support from Saarijrven KaukolmpOy.
文摘A computational particle fluid dynamics （CPFD） numerical method to model gas-solid flows in a circulating fluidized bed （CFB） riser was used to assess the effects of particle size distribution （PSD） on solids distribution and flow. We investigated a binary PSD and a polydisperse PSD case. Our simulations were compared with measured solids concentrations and velocity profiles from experiments, as well as with a published Eulerian-Eulerian simulation. Overall flow patterns were similar for both simulation cases, as confirmed by experimental measurements. However, our fine-mesh CPFD simulations failed to predict a dense bottom region in the riser, as seen in other numerical studies. Above this bottom region, distri- butions of particle volume fraction and particle vertical velocity were consistent with our experiments, and the simulated average particle diameter decreased as a power function with riser height. Interactions between particles and wails also were successfully modeled, with accurate predictions for the lateral profiles of particle vertical velocity. It was easy to implement PSD into the CPFD numerical model, and it required fewer computational resources compared with other models, especially when particles with a polydisperse PSD were present in the heterogeneous flow.
基金This work was supported by the National Thirteen-Five Year Research Program of China(2016YFB0600201).
文摘Circulating fluidized bed(CFB)technology plays an important role in the utilization of low-grade coal in China.This article reviews CFB combustion technology development in China and summarizes recent achievements.Since 1990 Chinese engineers and researchers have been undertaking work to improve CFB boiler technology.A completely novel CFB boiler design theory was developed and used in the domestic manufacturing of CFB boilers with various capacities.China is the largest supplier and customer of CFB boilers in the world due to the widespread use of CFB boilers.In 2007,the lower energy consumption CFB technology was successfully developed by re-specifying the fluidization state,which reduced the power consumption of forced fans and solved the potential erosion problems on the water wall.Afterwards,in order to increase the electric power generation efficiency,the supercritical CFB(SCCFB)boiler was developed and the first 600 MW SCCFB boiler was demonstrated and put into commercial operation in 2013.The success of the technology is evident with over 80 SCCFB boilers on order with capacities of 350 MW to 660 MW.Chinese scientists and engineers are also developing technology to lower the emissions of CFB combustion to meet the requirements of China’s strict emission regulations.This emission reduction is through high-efficiency desulfurization by limestone injection into the furnace and low NOx combustion,ultra-low emission of SO2 and NOx in the furnace can be realized by improving the bed quality and increasing the solid circulation rate.There is currently further research and design development being undertaken to develop a 660 MW ultra-supercritical CFB(USCCFB)boiler.The new boiler is expected to be operational before 2020 resulting in higher efficiency and lower energy consumption and emissions.
基金the National Program on Key Basic Research Project(973 Program)of China(No.2014CB744305)is gratefully acknowledged.
文摘In this paper,the combustion process of oil shale semicoke was investigated by modeling,where intraparticle mass transfer resistance was especially considered.The ash formation and attrition characteristics of oil shale semicoke were also investigated by a laboratory test procedure.The burnout time and residence time of different particle sizes were predicted,and the maximum particle size of which oil shale semicoke could be burned out in a 3 MW circulating fluidized bed boiler was obtained.
基金the National Natural Science Foundation of China (U1810126).
文摘As one of the most important auxiliary systems of a circulating fluidized bed boiler,the limestone pneumatic conveying system is of great significance to its operation.Maldistribution of powder in the different injecting ports seriously limits inner-furnace desulfurization performance owing to inefficient mixing of limestone powder and SO2.The gas-solid flow characteristics of an industrial-scale multiple-branching limestone-conveying pipeline system of a 200 MW circulating fluidized bed boiler were studied using a computational particle fluid dynamics method.The maldistribution intensity was studied under different operating conditions of air velocity and particle mass flow rate.Simulation results indicated that when the air velocity increased,the maldistribution was mitigated,but when the particle mass flow rate increased,the maldistribution strengthened.To solve this problem,two improved schemes were proposed:adding a deflector at different angles and changing the height of pipeline distributor.According to the simulation,the maldistribution could be efficiently mitigated using a distributor height in the range of 100-120 mm and a deflector angle of 10°-30°.
基金the National Natural Science Foundation of China(Grant No.51761125011).
文摘In this paper,the design and operation of a novel coal-fired circulating fluidized bed(CFB)drum boiler that can generate superheated steam using saline water were introduced.The natural circulation water dynamics with a drum was adopted instead of the traditional once-through steam generator(OTSG)design,so that superheated steam can be generated for the better performance of the steam assisted gravity drainage(SAGD)technology in heavy oil recovery.The optimized staged evaporation method was proposed to further decrease the salinity of water in the clean water section of the boiler.The evaporating pipes of the salted water section were rearranged in the back pass of the boiler,where the heat load is low,to further improve the heat transfer safety.A CFB combustion technology was used for coal firing to achieve a uniform heat transfer condition with low heat flux.Pollutant control technologies were adopted to reduce pollutant emissions.Based on the field test,the recommended water standard for the coal-fired CFB drum boilers was determined.With the present technology,the treated recovery wastewater can be reused in steam-injection boilers to generate superheated steam.The engineering applications show that the boiler efficiency is higher than 90%,the blowdown rate is limited within 5.5%,and the superheat of steam can reach up to 30 K.Besides,the heavy oil recovery efficiency is significantly improved.Moreover,the pollutant emissions of SO2,NOV and dust are controlled within the ranges of 20-90 mg/(N·m^(3)),30-90 mg/(N·m^(3))and 2-10 mg/(N·m^(3))respectively.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.U1810126).
文摘Diffusion of oxygen in the ash layer usually dominated the combustion of oil shale semicoke particles due to the high ash content.Thus,effective diffusivity of oxygen in the ash layer was a crucial parameter worthy of careful investigation.In this paper,the effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke was measured directly using an improved Wicke-Kallenbach diffusion apparatus.The experimental results showed that higher temperature would lead to a higher effective diffusivity and a thicker ash layer had the negative effect.Especially,the effective diffusivity along the direction perpendicular to bedding planes was much lower than that along the direction parallel to bedding planes.In addition,an effective diffusivity model was developed,which could be used to describe the mass transfer of oxygen in the ash layer of oil shale semicoke.
