Design and adjusting rule of auto-disturbance rejection controller are proposed for aclass of first order nonlinear plants. Tracking differentiator and nonlinear combination are simpli-fied. According to the analysis ...Design and adjusting rule of auto-disturbance rejection controller are proposed for aclass of first order nonlinear plants. Tracking differentiator and nonlinear combination are simpli-fied. According to the analysis of observing error of a secould order extended state observer, anempirical tuning rule is proposed based on theoretic deduction and simulations. Simulations on amultivariable plant with adjustable zeros demonstrate validity of the tuning rule.展开更多
Radial distribution of vapor local parameters, including local void fraction, interfacial velocity, bubblesize, bubble frequency and interfacial area concentration, are investigated through the measurement in an upwar...Radial distribution of vapor local parameters, including local void fraction, interfacial velocity, bubblesize, bubble frequency and interfacial area concentration, are investigated through the measurement in an upwardboiling tube using dual-sensor optical probe. In addition, a new local parameter -"local bubble number concentra-tion" is developed on the basis of bubble frequency. The analysis shows that this parameter can reflect bubble numberdensity in space, and has clear physical meaning.展开更多
In this study, an advanced Lagrangian vortex- boundary element method is applied to simulate the unsteady impeller-diffuser interactions in a diffuser pump not only for design but also for off-design considerations. I...In this study, an advanced Lagrangian vortex- boundary element method is applied to simulate the unsteady impeller-diffuser interactions in a diffuser pump not only for design but also for off-design considerations. In velocity calculations based on the Biot-Savart law we do not have to grid large portions of the flow field and the calculation points are concentrated in the regions where vorticity is present. Lagrangian representation of the evolving vorticity field is well suited to moving boundaries. An integral pressure equation shows that the pressure distribution can be estimated directly from the instantaneous velocity and vorticity field. The numerical results are compared with the experimental data and the comparisons show that the method used in this study can provide us insight into the complicated unsteady impeller-diffuser interaction phenomena in a diffuser pump.展开更多
The adsorption capacity for vapor-phase elemental mercury(Hg0) of residual carbon separated from fly ash was studied in an attempt for the control of elemental mercury emissions from combustion processes. At low mercu...The adsorption capacity for vapor-phase elemental mercury(Hg0) of residual carbon separated from fly ash was studied in an attempt for the control of elemental mercury emissions from combustion processes. At low mercury concentrations(<200 μg/m3), unburned carbon had higher adsorption capacity than commercial activated carbon. The adsorbality of unburned carbon was also found to be source dependent. Isotherms of FS carbon(separated from fly ash of a power plant of Shishi in Fujian Province) were similar to those classified as typeⅡ. Isotherms of XJ carbon(separated from fly ash of a power plant of Jingcheng in Shanxi Province) were more like those classified as type Ⅲ. Due to the relatively low production costs, these residual carbons would likely be considerably more cost-effective for the full-scale removal of mercury from combustion flue gases than other technology.展开更多
The water wall is an important part of the passive natural circulation residual heat removal system in a high temperature gas-cooled reactor. The maximum temperatures of the pressure shell and the water wall are calcu...The water wall is an important part of the passive natural circulation residual heat removal system in a high temperature gas-cooled reactor. The maximum temperatures of the pressure shell and the water wall are calcu- lated using annular vertical closed cavity model. Fine particles can deposit on the water wall due to the thermophore- sis effect. This deposit can affect heat transfer. The thermophoretic deposit efficiency is calculated by using Batch and Shen’s formula fitted for both laminar flow and turbulent flow. The calculated results indicate that natural convection is turbulent in the closed cavity. The transient thermophoretic deposit efficiency rises with the increase of the pressure shell’s temperature. Its maximum value is 14%.展开更多
Five coal char samples were burnt in thermobalance with ramp heating rate of 30 K/min. The pore structure of these char samples was studied through mercury intrusion method. Combined with the kinetic theory of gases, ...Five coal char samples were burnt in thermobalance with ramp heating rate of 30 K/min. The pore structure of these char samples was studied through mercury intrusion method. Combined with the kinetic theory of gases, the data of surface area was used in fitting the results. As a result, the kinetic triplet was given. The analysis showed that five char samples share almost the same intrinsic activation energy of the overall reaction. The phenomenological implication of the derived combustion rate equation was given.展开更多
In this study, 75% and 96% argon diluent conditions were selected to determine the ig- nition delay time of stoichiometric mixture of C2Ha/O2/Ar within a range of pressures （1.3-：3.0 arm） and temperatures （1092-17...In this study, 75% and 96% argon diluent conditions were selected to determine the ig- nition delay time of stoichiometric mixture of C2Ha/O2/Ar within a range of pressures （1.3-：3.0 arm） and temperatures （1092-1743 K）. Results showed a logarithmic linear rela- tionship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×10^30 s^-1cm^-3 in 75% diluent and 1.53×10^29 s^-1cm^-3 in 96% diluent （about 40 times that in 75% diluent）. According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can展开更多
It is clarified that the important method to improve the blast temperature ofthe small and the middle blast furnaces whose production is about two-thirds of total sum of Chinafrom 1000℃ to 1250-1300℃ is to preheat b...It is clarified that the important method to improve the blast temperature ofthe small and the middle blast furnaces whose production is about two-thirds of total sum of Chinafrom 1000℃ to 1250-1300℃ is to preheat both their combustion-supporting air and coal gas. The airtemperature of blast furnaces can be reached to 1250-1300℃ by burning single blast furnace coal gasif high speed burner is applied to blast furnaces and new-type external combustion swirl-flowinghot stove is used to preheat their combustion-supporting air. The computational results of the flowand heat transfer processions in the hot stove prove that the surface of the bed of the thermalstorage balls there have not eccentric flow and the flow field and temperature field distribution iseven. The computational results of the blast temperature distribution are similar to thosedetermination experiment data. The numerical results also provide references for developing anddesigning the new-type external combustion swirl-flowing hot stoves.展开更多
The performance of the flat jet with an inclination angle was investigated bya water model. A mathematical model for the shrinkage and the trajectory of the flat jet with aninclination angle was derived theoretically ...The performance of the flat jet with an inclination angle was investigated bya water model. A mathematical model for the shrinkage and the trajectory of the flat jet with aninclination angle was derived theoretically and verified by experimental data of the water model.The experimental results indicate that the inclination angle (alpha) has no influence on theshrinkage of the flat jet, the shrinkage of the flat jet along the width direction decreases withthe increasing of the initial velocity at the exit (u_0) and the initial thickness of the flat jet(t_0). Enough bigger initial exit velocity (u_0) and initial thickness can suppress the shrinkage ofthe flat jet along the width direction and keep the flat jet stabilized. In addition, thetrajectory of the flat jet with an inclination angle is parabolic and must be taking intoconsideration when to determine the striking distance.展开更多
The influences of Soret effect and Dufour effect on the natural convectionand heal and mass transfer for a porous enclosure were investigated by means of the penalty finiteelement method. Numerical results indicate th...The influences of Soret effect and Dufour effect on the natural convectionand heal and mass transfer for a porous enclosure were investigated by means of the penalty finiteelement method. Numerical results indicate that the Soret and Dufour effects have significantinfluences on heat and mass transfer in the presence of large temperature gradient and concentrationgradient.展开更多
To study the amount of arsenic emission from the coal power stations (mainly Permo-Carboniferous coal) in China in different combustion conditions, the arsenic con-tent of the coal, the fly ash and the cinder in high-...To study the amount of arsenic emission from the coal power stations (mainly Permo-Carboniferous coal) in China in different combustion conditions, the arsenic con-tent of the coal, the fly ash and the cinder in high- tempera-ture power stations as well as mid-low temperature power stations have been analyzed. This note provides a rough es-timate of the total amount of arsenic emission as well as emission ratio from steam coal combustion in China. The results show that by combustion of 1 t of Permo-Carbonif- erous coal (containing roughly 5 mg/kg arsenic), high-tem- perature power stations emit roughly 0.40 g arsenic into the atmosphere and the arsenic emission rate is about 7.70%; mid-low power stations emit roughly 0.15 g arsenic into the atmosphere and the arsenic emission rate is about 2.97%. A total of 600 million tons coal is burnt annually in China power stations, and the coal comes mainly from Permo- Carboniferous depositing in the North China Plate and northwest China coal mines. Taking the average arsenic con-tent of the coal used at the value of 5 mg/kg, the total annual arsenic emission from steam coal combustion into the at-mosphere is about 195.0 t. Most of the arsenic in coal can be released in the process of coal combustion, and the most of the released arsenic can be seized by the fly ash and then both of them are seized by the dust catcher of power station, so the arsenic emission ratio to the atmosphere is declined; in addition, research on the arsenic emission amount and emis-sion rules from the coal power stations in China should go on the coal power stations with the dry-process dust catchers by the experiments results. In the wet process of dust catcher, 20% of the arsenic in the fly ash is dissolved in the water of sedimentation tank in high-temperature power station; in the mid-low temperature power station there are 70% of the arsenic in the fly ash dissolved in the water of sedimentation tank, this is an important source of arsenic pollution in envi-ronment and should not be overlooked. The arsenic emission rate in the process of coal cineration in the laboratory is higher than the actual arsenic emission rate of power station.展开更多
This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence an...This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence angles under low Mach number and low Reynolds number conditions.Experimental techniquss include the oil-film visualization on the profile and the endwall surfaces,the laser-sheet visualization of the flow field inside the blade passage,and the measurement by radial-circumferential traveress using a seven-hole probe.The behavior and nature of the three-dimensional flow with severe separations inside the blade passage and at the exit are obtained.The distributions of the total pressure loss,static pressure,velocity and outflow angle are also given. These results are valuable for establishing the physical model of the three-dimensional complex flow in axial compressors and for examining the computational procedures.展开更多
In the research of a more efficient, leSS costly, more environmentally responsible and less technically difficult method for generating electrical power from coal, the Carried-heat Gasilication Combined Cycle (CGCC) i...In the research of a more efficient, leSS costly, more environmentally responsible and less technically difficult method for generating electrical power from coal, the Carried-heat Gasilication Combined Cycle (CGCC) is introduced by Tsinghua University. The high efficiency cycle includes carried-heat partial gasilication, compressed air heating in a fiuidized bed immersed air heater followed by a combustor and the heat recovery of gas turbine exhaust used as the combustion air for the differential-velocity atmospheric circulating fluidized bed (DFBC). Superheat steam is raised in the DFBC boiler. The comparison of results identifies the causes of performance difference between eight cases. Features of the cycle ensure a high coal conversion efficiency within current state of the art.展开更多
Forced and mixed convection heat and mass transfer are studied numerically for water containingmetallic corrosion products in a heated or cooled vertical tube with variable thermophysical propertiesat super-critical p...Forced and mixed convection heat and mass transfer are studied numerically for water containingmetallic corrosion products in a heated or cooled vertical tube with variable thermophysical propertiesat super-critical pressures. The fouling mechanisms and fouling models are presented. The influenceof variable properties at super-critical pressures on forced or mixed convection has been analyzed.The differences between heat and mass transfer under heating and cooling conditions are discussed. Itis found that variable properties, especially buoyancy, greatly influence the fluid flow and heat masstransfer.展开更多
The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was i...The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was investigated both in field tests and laboratory experiments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time and cyclone performance are analyzed seriatim based on large amount of experimental results. A coal index is proposed to describe the coal rank, defined by the ratio of the volatile content to the coal heat value, is a useful parameter to analyze the char burnout. The carbon content in the fly ash depends on the coal rank strongly. CFB boilers burning anthracite, which has low coal index, usually have high carbon content in the fly ash. On the contrary, the CFB boilers burning brown coal, which has high coal index, normally have low carbon content. Poor gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Increasing the velocity and rigidity of the secondary air could extend the penetration depth and induce more oxygen into the furnace center. Better gas solid mixing will decrease the lean oxygen core area and increase char combustion efficiency. The fine char particles could be divided into two groups according to their reactivity. One group is 'fresh' char particles with high reactivity and certain amount of volatile content. The other group of char particles has experienced sufficient combustion time both in the furnace and in the cyclone, with nearly no volatile. These 'old' chars in the fly ash will be deactivated during combustion of large coal particles and have very low carbon reactivity. The generated fine inert char particles by attrition of large coal particles could not easily burn out even with the fly ash recirculation. The fraction of large coal particles in coal feed should be reduced during fuel preparation process. The cyclone efficiency controls the particle residence time in CFB loop, especially for that of the fine particles. So the cyclone efficiency, especially the cut size, will greatly influence the carbon content in the fly ash.展开更多
文摘Design and adjusting rule of auto-disturbance rejection controller are proposed for aclass of first order nonlinear plants. Tracking differentiator and nonlinear combination are simpli-fied. According to the analysis of observing error of a secould order extended state observer, anempirical tuning rule is proposed based on theoretic deduction and simulations. Simulations on amultivariable plant with adjustable zeros demonstrate validity of the tuning rule.
基金Supported by the National Science Foundation of China(No.59995460-1) and Nuclear Industry Science Foundation (No.Y7100E51001)
文摘Radial distribution of vapor local parameters, including local void fraction, interfacial velocity, bubblesize, bubble frequency and interfacial area concentration, are investigated through the measurement in an upwardboiling tube using dual-sensor optical probe. In addition, a new local parameter -"local bubble number concentra-tion" is developed on the basis of bubble frequency. The analysis shows that this parameter can reflect bubble numberdensity in space, and has clear physical meaning.
文摘In this study, an advanced Lagrangian vortex- boundary element method is applied to simulate the unsteady impeller-diffuser interactions in a diffuser pump not only for design but also for off-design considerations. In velocity calculations based on the Biot-Savart law we do not have to grid large portions of the flow field and the calculation points are concentrated in the regions where vorticity is present. Lagrangian representation of the evolving vorticity field is well suited to moving boundaries. An integral pressure equation shows that the pressure distribution can be estimated directly from the instantaneous velocity and vorticity field. The numerical results are compared with the experimental data and the comparisons show that the method used in this study can provide us insight into the complicated unsteady impeller-diffuser interaction phenomena in a diffuser pump.
基金The National Natural Science Foundation of China(No. 50306010) and the National Basic Research Program(973) of China(No. G1999022200)
文摘The adsorption capacity for vapor-phase elemental mercury(Hg0) of residual carbon separated from fly ash was studied in an attempt for the control of elemental mercury emissions from combustion processes. At low mercury concentrations(<200 μg/m3), unburned carbon had higher adsorption capacity than commercial activated carbon. The adsorbality of unburned carbon was also found to be source dependent. Isotherms of FS carbon(separated from fly ash of a power plant of Shishi in Fujian Province) were similar to those classified as typeⅡ. Isotherms of XJ carbon(separated from fly ash of a power plant of Jingcheng in Shanxi Province) were more like those classified as type Ⅲ. Due to the relatively low production costs, these residual carbons would likely be considerably more cost-effective for the full-scale removal of mercury from combustion flue gases than other technology.
基金Supported by the Special Funds for Major State Basic Research Projects of China (No.2002CB211604) and the National Key Projects in the Ninth Five –Year Plan (96-G01-02-05).
文摘The water wall is an important part of the passive natural circulation residual heat removal system in a high temperature gas-cooled reactor. The maximum temperatures of the pressure shell and the water wall are calcu- lated using annular vertical closed cavity model. Fine particles can deposit on the water wall due to the thermophore- sis effect. This deposit can affect heat transfer. The thermophoretic deposit efficiency is calculated by using Batch and Shen’s formula fitted for both laminar flow and turbulent flow. The calculated results indicate that natural convection is turbulent in the closed cavity. The transient thermophoretic deposit efficiency rises with the increase of the pressure shell’s temperature. Its maximum value is 14%.
基金The work was subsidized by the Special Funds for Major State Basic Research Projects(973).project number G1999022205.
文摘Five coal char samples were burnt in thermobalance with ramp heating rate of 30 K/min. The pore structure of these char samples was studied through mercury intrusion method. Combined with the kinetic theory of gases, the data of surface area was used in fitting the results. As a result, the kinetic triplet was given. The analysis showed that five char samples share almost the same intrinsic activation energy of the overall reaction. The phenomenological implication of the derived combustion rate equation was given.
文摘In this study, 75% and 96% argon diluent conditions were selected to determine the ig- nition delay time of stoichiometric mixture of C2Ha/O2/Ar within a range of pressures （1.3-：3.0 arm） and temperatures （1092-1743 K）. Results showed a logarithmic linear rela- tionship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×10^30 s^-1cm^-3 in 75% diluent and 1.53×10^29 s^-1cm^-3 in 96% diluent （about 40 times that in 75% diluent）. According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can
文摘It is clarified that the important method to improve the blast temperature ofthe small and the middle blast furnaces whose production is about two-thirds of total sum of Chinafrom 1000℃ to 1250-1300℃ is to preheat both their combustion-supporting air and coal gas. The airtemperature of blast furnaces can be reached to 1250-1300℃ by burning single blast furnace coal gasif high speed burner is applied to blast furnaces and new-type external combustion swirl-flowinghot stove is used to preheat their combustion-supporting air. The computational results of the flowand heat transfer processions in the hot stove prove that the surface of the bed of the thermalstorage balls there have not eccentric flow and the flow field and temperature field distribution iseven. The computational results of the blast temperature distribution are similar to thosedetermination experiment data. The numerical results also provide references for developing anddesigning the new-type external combustion swirl-flowing hot stoves.
文摘The performance of the flat jet with an inclination angle was investigated bya water model. A mathematical model for the shrinkage and the trajectory of the flat jet with aninclination angle was derived theoretically and verified by experimental data of the water model.The experimental results indicate that the inclination angle (alpha) has no influence on theshrinkage of the flat jet, the shrinkage of the flat jet along the width direction decreases withthe increasing of the initial velocity at the exit (u_0) and the initial thickness of the flat jet(t_0). Enough bigger initial exit velocity (u_0) and initial thickness can suppress the shrinkage ofthe flat jet along the width direction and keep the flat jet stabilized. In addition, thetrajectory of the flat jet with an inclination angle is parabolic and must be taking intoconsideration when to determine the striking distance.
基金This work was supported by the National Natural Science Foundation of China.(Grant No:59806008)
文摘The influences of Soret effect and Dufour effect on the natural convectionand heal and mass transfer for a porous enclosure were investigated by means of the penalty finiteelement method. Numerical results indicate that the Soret and Dufour effects have significantinfluences on heat and mass transfer in the presence of large temperature gradient and concentrationgradient.
文摘To study the amount of arsenic emission from the coal power stations (mainly Permo-Carboniferous coal) in China in different combustion conditions, the arsenic con-tent of the coal, the fly ash and the cinder in high- tempera-ture power stations as well as mid-low temperature power stations have been analyzed. This note provides a rough es-timate of the total amount of arsenic emission as well as emission ratio from steam coal combustion in China. The results show that by combustion of 1 t of Permo-Carbonif- erous coal (containing roughly 5 mg/kg arsenic), high-tem- perature power stations emit roughly 0.40 g arsenic into the atmosphere and the arsenic emission rate is about 7.70%; mid-low power stations emit roughly 0.15 g arsenic into the atmosphere and the arsenic emission rate is about 2.97%. A total of 600 million tons coal is burnt annually in China power stations, and the coal comes mainly from Permo- Carboniferous depositing in the North China Plate and northwest China coal mines. Taking the average arsenic con-tent of the coal used at the value of 5 mg/kg, the total annual arsenic emission from steam coal combustion into the at-mosphere is about 195.0 t. Most of the arsenic in coal can be released in the process of coal combustion, and the most of the released arsenic can be seized by the fly ash and then both of them are seized by the dust catcher of power station, so the arsenic emission ratio to the atmosphere is declined; in addition, research on the arsenic emission amount and emis-sion rules from the coal power stations in China should go on the coal power stations with the dry-process dust catchers by the experiments results. In the wet process of dust catcher, 20% of the arsenic in the fly ash is dissolved in the water of sedimentation tank in high-temperature power station; in the mid-low temperature power station there are 70% of the arsenic in the fly ash dissolved in the water of sedimentation tank, this is an important source of arsenic pollution in envi-ronment and should not be overlooked. The arsenic emission rate in the process of coal cineration in the laboratory is higher than the actual arsenic emission rate of power station.
文摘This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence angles under low Mach number and low Reynolds number conditions.Experimental techniquss include the oil-film visualization on the profile and the endwall surfaces,the laser-sheet visualization of the flow field inside the blade passage,and the measurement by radial-circumferential traveress using a seven-hole probe.The behavior and nature of the three-dimensional flow with severe separations inside the blade passage and at the exit are obtained.The distributions of the total pressure loss,static pressure,velocity and outflow angle are also given. These results are valuable for establishing the physical model of the three-dimensional complex flow in axial compressors and for examining the computational procedures.
文摘In the research of a more efficient, leSS costly, more environmentally responsible and less technically difficult method for generating electrical power from coal, the Carried-heat Gasilication Combined Cycle (CGCC) is introduced by Tsinghua University. The high efficiency cycle includes carried-heat partial gasilication, compressed air heating in a fiuidized bed immersed air heater followed by a combustor and the heat recovery of gas turbine exhaust used as the combustion air for the differential-velocity atmospheric circulating fluidized bed (DFBC). Superheat steam is raised in the DFBC boiler. The comparison of results identifies the causes of performance difference between eight cases. Features of the cycle ensure a high coal conversion efficiency within current state of the art.
文摘Forced and mixed convection heat and mass transfer are studied numerically for water containingmetallic corrosion products in a heated or cooled vertical tube with variable thermophysical propertiesat super-critical pressures. The fouling mechanisms and fouling models are presented. The influenceof variable properties at super-critical pressures on forced or mixed convection has been analyzed.The differences between heat and mass transfer under heating and cooling conditions are discussed. Itis found that variable properties, especially buoyancy, greatly influence the fluid flow and heat masstransfer.
文摘The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was investigated both in field tests and laboratory experiments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time and cyclone performance are analyzed seriatim based on large amount of experimental results. A coal index is proposed to describe the coal rank, defined by the ratio of the volatile content to the coal heat value, is a useful parameter to analyze the char burnout. The carbon content in the fly ash depends on the coal rank strongly. CFB boilers burning anthracite, which has low coal index, usually have high carbon content in the fly ash. On the contrary, the CFB boilers burning brown coal, which has high coal index, normally have low carbon content. Poor gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Increasing the velocity and rigidity of the secondary air could extend the penetration depth and induce more oxygen into the furnace center. Better gas solid mixing will decrease the lean oxygen core area and increase char combustion efficiency. The fine char particles could be divided into two groups according to their reactivity. One group is 'fresh' char particles with high reactivity and certain amount of volatile content. The other group of char particles has experienced sufficient combustion time both in the furnace and in the cyclone, with nearly no volatile. These 'old' chars in the fly ash will be deactivated during combustion of large coal particles and have very low carbon reactivity. The generated fine inert char particles by attrition of large coal particles could not easily burn out even with the fly ash recirculation. The fraction of large coal particles in coal feed should be reduced during fuel preparation process. The cyclone efficiency controls the particle residence time in CFB loop, especially for that of the fine particles. So the cyclone efficiency, especially the cut size, will greatly influence the carbon content in the fly ash.
