Effect of temperature on gas bypassing and solids circulation rate in an internally circulating fluidized bed

The effect of bed temperature in the annulus region on gas bypassing from annulus to riser and solids circulation rate has been determined in an internally circulating fluidized bed. The bed voidage in the annulus region increases with increasing temperature. The average fractions of gas bypassing of annulus gas are 59.4% and 87% at room temperature and high temperature (400°C to 800°C), respectively. Solids circulation rate increases with increasing annulus gas velocity, but is nearly independent of riser velocity. Solids circulation rate increases with increasing temperature.     

Kinetic analysis and modelling of thermal degradation of perspex (PMMA) and perspex blend plastic waste

The thermal decomposition of pure perspex and a mixture of 50% perspex and 50% poly(ethylene terephthalate; PET) was carried out between 295 and 325°C using a thermogravimetric analyser (TGA) in air and nitrogen (N₂) atmosphere. The weight losses of decomposition products were measured during these experiments. The thermal degradation process is slower in inert atmosphere than air, where oxidation reaction expedites the decomposition process. Kinetic rate constants (k), pre‐exponential factor (A) and activation energy (E) for both pure prespex and a blend of perspex/PET were calculated for both air and N₂ conditions. The thermal degradation process followed a third‐order reaction in air and second‐order in N₂. A second‐order (n = 2) model for the pyrolytic process based on simultaneous reactions was developed using experimental data for pure and blend. The pyrolytic products are gases, liquids, waxes, aromatics and char, which can be ultimately used as raw material and fuel in various applications. It is important to note that the addition of PET to perspex was found to suppress/inhibit the decomposition of perspex compared with pure perspex. Pre‐exponential factor (A) and activation energy (E) values support such an observation. © 2012 Canadian Society for Chemical Engineering     

Model for biomass char combustion in the riser of a dual fluidized bed gasification unit: Part II — Model validation and parameter variation

The two-phase combustion model for biomass char combustion in a riser of a dual fluidized bed gasification unit that has been presented in part I is validated using the data obtained from the 8 MWth dual fluidized bed reactor at Guessing/Austria. The model is capable of calculating the average temperatures in all zones, the gas phase composition, solid hold up, char feed rates and air ratio. The model predictions for the temperature profile along the riser and for the exiting gas composition are in good agreement with the measured values. The simulation results show that the residual char from the gasifier is only partly converted in the riser for char particles larger than 0.6 mm. Un-combusted char is circulated back into the gasification reactor. Parameter variations show that the exact location where additional liquid fuels are introduced in the middle zone of the riser does not affect the global behaviour of the combustion reactor. Based on the simulation results it is proposed that external supply of char (additional) may be a very effective method for reducing producer gas recycling to the riser, which is currently necessary to obtain the desired gasification temperatures.     

Hydrodynamic characteristics of fine particles in the riser and standpipe of a circulating fluidized bed

The hydrodynamic properties in the riser and standpipe. and the cyclone efficiency have been determined in a circulating fluidized bed (CFB) unit consisting of a riser (0.05 m-IDX3.8 m high), a standpipe (0.068 m-IDX2.5 m high) as a primary cyclone/bubbling fluidized bed, and a secondary cyclone. Silica gel powder (mean diameter = 46 μm) was used as the bed material. The effects of gas velocity in the riser and initial solid loading on the solid circulation rate, and the solid holdups in the riser and standpipe have been determined. The effects of gas velocity in the standpipe on the efficiencies of primary and secondary cyclones have been also determined as functions of solid circulation rate and solid entrainment rate. The solid circulation rate increases with increases in the gas velocity in the riser and in the initial solid loading. The efficiencies of primary and secondary cyclones increase with an increase in the gas velocity in the riser. However, the efficiency of primary cyclone decreases and that of secondary cyclone increases slightly, with an increase in the gas velocity in the standpipe.     

Structure and high‐resolution thermogravimetry of liquid‐crystalline copoly(p‐oxybenzoate‐ethylene terephthalate‐p‐benzamide)

Thermotropic liquid‐crystalline copoly(ester‐amide)s consisting of three units of p‐oxybenzoate (B), ethylene terephthalate (E) and p‐benzamide (A) were studied by proton nuclear magnetic resonance at 200 and 400 MHz, wide‐angle X‐ray diffraction, and high‐resolution thermogravimetry to ascertain their molecular and supermolecular structures, thermostability and kinetics parameters of thermal decomposition in both nitrogen and air. The assignments of all resonance peaks of [¹H]NMR spectra for the copoly(ester‐amide)s are given and the characteristics of X‐ray equatorial and meridional scans are discussed. Overall activation energy data of the first major decomposition have been evaluated through three calculating techniques. The thermal degradation occurs in three steps in nitrogen and air. The degradation temperatures are higher than 447 °C in nitrogen and 440 °C in air and increase with increasing B‐unit content at a fixed A‐unit content of 5 mol%. The temperatures at the first maximum weight‐loss rate are higher than 455 °C in nitrogen and 445 °C in air and also increase with an increase in B‐unit content. The first maximum weight‐loss rates range between 11.1 and 14.5%min⁻¹ in nitrogen and between 11.9 and 13.5%min⁻¹ in air. The char yields at 500 °C in both nitrogen and air range from 45.8 to 54.3 wt% and increase with increasing B‐unit content. But the char yields at 800 °C in nitrogen and air are quite irregular with the variation of copolymer composition and testing atmosphere. The activation energy and Ln (pre‐exponential factor) for the first major decomposition are usually higher in nitrogen than in air and increase slightly with an increase in B‐unit content at a given A‐unit content of 5 mol%. The activation energy, decomposition order, and Ln (pre‐exponential factor) of the thermal degradation for the copoly(ester‐amide)s in two testing atmospheres, are situated in the ranges of 210–292 kJmol⁻¹, 2.0–2.8, 33–46 min⁻¹, respectively. The three kinetic parameters of the thermal degradation for the aromatic copoly(ester‐amide)s obtained by high‐resolution thermogravimetry at a variable heating rate are almost the same as those by traditional thermogravimetry at constant heating rate, suggesting good applicability of kinetic methods developed for constant heating rate to the variable heating‐rate method. These results indicate that the copoly(ester‐amide)s exhibit high thermostability. The isothermal decomposition kinetics of the copoly(ester‐amide)s at 450 and 420 °C are also discussed and compared with the results obtained based on non‐isothermal high‐resolution thermogravimetry. © 1999 Society of Chemical Industry     

Hydrodynamics in airlift loop section of petroleum coke combustor

Based on the combustion characteristics of petroleum coke, a coupled gas-solid fluidized bed combustor is proposed in this work. The overall circulating system of the fluidized bed mainly consists of a dense-phase airlift loop section and a dilute-phase riser section. In different operating conditions, the particle flow behaviors in the airlift loop section were investigated systematically by using optical fiber probe. The experimental results show that the airlift loop section can be divided into four regions, namely, the draft tube, the annulus, the bottom region and the particle diffluence region, in which the average cross-sectional solids fraction and the particle velocity are different. The overall solids fraction difference between the draft tube and the annulus provides a driving force for particle circulation flow in the airlift loop section, and the driving force increases with increasing the superficial gas velocity in the draft tube. The ratio of the particle mass flux in the annulus to that in the riser ranges from 8 to 16. The particle circular velocity in the annulus also increases with increasing the superficial gas velocity in the draft tube. Moreover, a model about the particle circular velocity is established on the basis of energy equilibrium principle.     

The effect of variation in polymer properties on the rate of burning

The sensitivity of the burning rate to variations in physical and chemical properties of synthetic polymers has been examined in order to understand the relative importance of the knowledge of these properties. The sensitivity analysis was performed using a numerical pyrolysis model called ThermaKin, which was employed to compute the rate of burning (expressed in terms of mass loss) of a one‐dimensional material object exposed to steady radiative heat. The results of the calculations indicate that the knowledge of decomposition reaction parameters (including the Arrhenius pre‐exponential factor, activation energy, heat, and char yield) is of key importance for prediction of the peak and average burning rates. Copyright © 2009 John Wiley & Sons, Ltd.     

Coal combustion characteristics in a fluidized bed combustor with a draft tube

The effects of gas velocity to draft tube (3–6 U_m), bed temperature (800–900°C) and excess air ratio (0–30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor.     

循环流化床中C类颗粒的干燥

为将循环流化床(CFB)技术应用于C类颗粒(＜30μm)的干燥,在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为研究对象,考察了不同操作参数对其干燥特性及干湿分离情况的影响.结果表明:循环流化床适用于C类颗粒的干燥;干燥速率随气速及进风温度的增大而增大...     

Solids flow characteristics in loop-seal of a circulating fluidized bed

The hydrodynamics of solids (FCC) recycle in a loop-seal (0.08 m) at the bottom of the downcomer (0.08 m-I.D.x4.0 m-high) in a circulating fluidized bed (0.1 m-I.D.x 5.3 m-high) have been determined. Solid flow rate through the loop-seal increases linearly with increasing aeration rate. At the same aeration rate, the maximum solid flow rate can be obtained at a loop-seal height-to-diameter ratio of 2.5. The effects of solid inventory, solid circulation rate and gas velocity on pressure balance around the CFB have been determined. At a given gas velocity and solid circulation rate, pressure drops across the downcomer and loop-seal increase linearly with increasing solids inventory in the bed. At a constant solid inventory, pressure drops across the riser and the downcomer increase with increasing solid circulation rate but decrease with increasing gas velocity in the riser. The obtained solid flow rate has been correlated with pressure drop across the loop-seal.     

旋流气升式环流反应器的气含率轴向分布

为强化环隙气升式环流反应器(AALR)的流动、混合与传质性能, 提出了旋流气升式环流反应器(HALR)。在8.8L的HALR中, 以空气-水和空气-水-K树脂为实验物系, 在表观气速为0.47～2.31cm/s的范围内, 研究了表观气速、导流筒底边与反应器底面的间隙(简称底部间隙)、上升区轴向高度及固体装载量等因素对气含率的影响规律, 并与 AALR 进行了对比。结果表明:对于空气-水组成的两相物系来说, 在表观气速较小时, 旋流片对上升气泡有聚并作用;在表观气速较大时, 旋流片对气泡主要起破碎作用;气含率随着轴向高度的增加而增加, 增加的幅度随表观气速的增加而增加。对于三相物系, 表观气速较大时, 气含率随着固体装载量的增大而增大, 比两相物系气含率高;表观气速较小时, 两相物系的气含率略高于三相物系的。根据实验结果, 提出并拟合出了上升区局部气含率与轴向高度的预测模型:ε_g=(3.00×10^-4h+0.0276)U_g^0.615, 模型的预测值与实验值吻合较好, 平均相对误差为12%。     

Identification of the combustion behaviour of lignite char between 350 and 900 °C

The combustion behaviour of four different lignite samples pyrolysed at 800 and 1000 °C has been studied. The reaction order and the activation energy of the char combustion reaction can be easily determined from the time to reach 50% conversion. Under 550 °C the reaction order of lignite samples are 0.7 and the activation energies are 27.4–27.9 kcal gmole^?1. Above 550 °C the measurement of the intrinsic reaction rate is limited by the film diffusion resistance. The pyrolysis temperature affects the reactivity significantly. The reactivity of char pyrolysed at 800 °C is 3.5 times that of char pyrolysed at 1000 °C.     

Some Issues on Core‐Annulus and Cluster Models of Circulating Fluidized Bed Reactors

The one‐dimensional cluster model and the core‐annulus model are examined based on existing correlations. The core‐annulus model is found to give reasonable agreement with ozone decomposition data when the effective interphase mass transfer rate constant is equal to about 0.1 1/s, which is one order smaller than the reported values based on gas tracer tests. The prediction from the core‐annulus model that the reactor performance decreases with increasing the riser diameter is found to be inconsistent with limited experimental data The one‐dimensional cluster model predicts that a riser reactor performs very close to the pseudo‐homogeneous plug flow reactor because of the high mass transfer rate between the cluster and the dilute phase. The improvement of model predictions lies in the better characterization of the cluster shape, size and the mass transfer rate between the cluster and the dilute phases.     

Kinetics and mechanism of solid reactions in a micro fluidized bed reactor

A novel gas–solid Micro Fluidized Bed Reaction Analyzer (MFBRA) was developed to deduce reaction rates and kinetic parameters through measuring time‐dependent composition changes of evolved gases from the reactions. Application of the MFBRA to the decomposition of CaCO₃ powder resulted in an apparent activation energy of 142.73 kJ/mol and a pre‐exponential factor of 399,777 s^?1. This apparent activation energy was much lower than the thermogravimetry‐measured value of 184.31 kJ/mol, demonstrating a quicker reaction in the MFBRA. This was further verified by CuO reduction in CO, as accelerated by the fast diffusion and high heating rate in the MFBRA. Measurement of pyrolysis of coal and biomass in MFBRA found that the reaction process was completed in about 10 s, a time much shorter than the literature‐reported values in larger fluidized bed reactors. By monitoring the release of gas species from reactions at different temperatures, the MFBRA also allowed deeper insight into the mechanism of pyrolysis reactions. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Influence of microwave heating on the kinetic of acrylic acid polymerization and crosslinking

Kinetics of isothermal formation of poly (acrylic acid) (PAA) hydrogels through polymerization of acrylic acid and crosslinking of the PAA formed in a conventionally heated reaction system and in a microwave heated reaction system were investigated. It was found that in the microwave heated system the reaction rate constant of PAA hydrogel formation significantly increased (from 32 to 43 times) when compared with the conventionally heated system. The isothermal kinetics of the PAA hydrogel formation during the microwave process could be described by the so‐called first‐order chemical reaction kinetics model. In contrast, the so‐called second‐order chemical reaction rate model could best describe the isothermal kinetics of the PAA hydrogel formation during the conventionally heated process. Also, in the microwave heated system, the reaction kinetics of the PAA hydrogel formation and its kinetic parameters changed, that is, the activation energy (E_a) decreased by about 19% and the pre‐exponential factor (lnA) decreased by 2.2 times. The decrease in activation energy, change in entropy of activation energy, and decrease in the pre‐exponential value of PAA hydrogel formation under microwave heating are caused with increased energy of the reactive species when compared with their energy in thermal activation. Increased energy of the reactive species is a consequence of rapid transfer and absorption of the energy of microwave field to the existing reactive species. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

New fluorescent monomers and polymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state. III. Thermogravimetric stability study of the benzazolylvinylene derivatives

Six fluorescent benzazolylvinylene derivatives were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and related molecular parameters. The thermal stability was determined in terms of the steps of degradation and its fitting parameters, such as maximum degradation rate (R_max), maximum degradation rate temperature (T_Rmax), degradation temperature range, which is related to the half‐width at half‐height values (Γ), and the kinetic parameters: activation energy (E_a), pre‐exponential factor (A), and reaction order (n) obtained by Barrett's method. Different organic substitutes and heteroatoms do not play a fundamental role in the thermal behavior of the studied dyes. The compensation effect between pre‐exponential factor and activation energy was confirmed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 495–500, 2006     

空气中PE-LD与PE-LD-g-HEA的非等温热分解行为研究

采用固相接枝法制备了丙烯酸-2-羟乙酯（HEA）接枝低密度聚乙烯（PE-LD）共聚物（PE-LD-g-HEA）,通过X射线衍射仪、傅里叶红外光谱仪分析了不同温度处理下PE-LD、PE-LD-g-HEA的结构变化,并用热重分析法研究了二者的热分解动力学。结果表明,热处理时PE-LD-g-HEA较PE-LD的结晶度变化小,主链断裂缓慢,热稳定性提高;Kissinger法和Crane法计算了PE-LD表观活化能为88.63 kJ/mol、指前因子1.17×106 s-1、反应级数为0.88,接枝产物的表观活化能为217.35 kJ/mol、指前因子5.92×1015 s-1、反应级数为0.95,Ozawa法计算的表观活化能值与Kissinger法相相近。     

高长径比环流反应器中气、固含率的轴向分布研究

在高长径比(H/D=22.2)内环流反应器中,常温常压下,以空气-水-石英砂为物系,研究了表观气速和固体装载量对平均气含率、下降区气含率、上升区固含率、下降区固含率的影响,以及上升区气含率、固含率随轴向高度的分布规律.结果表明:平均气含率、下降区气含率随着表观气速的增加而增加,随ω(固体)增大而下降,ω(固体)≤2.6...     

Gas and solid behavior in cracking circulating fluidized beds

Gas and solid hydrodynamics have been studied in dilute circulating fluidized beds under conditions occurring in catalytic cracking risers. Gas radial velocity profiles and dispersions were established by a tracer technique in a cold set-up. The gas axial dispersion was determined in an industrial riser. The local concentrations of the solid phase were measured by a tomographic technique. This has allowed an assessment of the core—annulus structure of the bed and an estimate of the solid radial and axial dispersions. The axial solid concentration profiles were determined in pilot and industrial scale beds. These show an important accumulation upstream of the abrupt exit. The overall conclusion is that the gas flow can be considered to be plug flow with a radial velocity profile and a radial dispersion; the solid flow is slightly more dispersed due to the core—annulus structure and a high radial mixing.     

Kinetic study of the nonthermal effect of the esterification of octenyl succinic anhydride modified starch treated by microwave radiation

With cassava starch as a raw material and octenyl succinic anhydride as an esterifying agent, octenyl succinic anhydride modified starch (OSA–starch) was prepared in an aqueous medium and treated by water‐bath heating and microwave radiation at a certain temperature, respectively. The reaction kinetics of esterification were studied. The structural analysis and synthesis mechanism of OSA–starch were investigated by means of scanning electron microscopy and Fourier transform infrared spectroscopy. The differences in the esterification reaction kinetics between starches treated with water‐bath heating and microwave radiation were observed. Under the condition of water‐bath heating, the apparent activation energy of the esterification reaction was 52.22 ± 1.21 kJ/mol, and the pre‐exponential factor was 9018.20/min^?1. Under the condition of microwave radiation, the apparent activation energy of the esterification reaction was 50.13 ± 1.16 kJ/mol, and the pre‐exponential factor was 4510.21/min^?1. We found that microwave radiation could reduce both the activation energy of the reaction and the pre‐exponential factor. The lowering effect of the apparent activation energy was greater than that of the pre‐exponential factor under the condition of microwave radiation, and this resulted in increased reaction rates. The change in the esterification reaction kinetics was a nonthermal effect of microwave radiation on the esterification of cassava starch. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43909.