Modeling of biomass devolatilization in a fluidized bed reactor

A simple model that simulates a single biomass particle devolatilization is described. The model takes into account the main physical and chemical factors influencing the phenomenon at high temperatures (>700 K), where the production of gaseous components far outweighs that of liquids. The predictions of the model are shown to be in good agreement with published data. The model is then applied to the devolatilization of biomass in a fluidized bed, in which attention is focused on heat transfer, particle mixing and elutriation, and gas production. Predictions on the overall devolatilization time for a biomass particle are compared with experimental results obtained in a fluidized bed reactor in which the process was monitored by continuous measurement of the bed pressure. Good correspondence of predicted with calculated values was obtained, supporting the validity of the many approximations made in the derivation of the governing relationships for the pyrolysis process.     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model. __________ Translated from Chemical Engineering (China), 2007, 35(10): 23–26 [译自: 化学工程]     

生物质流化床空气-水蒸气气化模型研究

根据流化床反应器特点,结合生物质气化动力学反应机理,建立了生物质在流化床内气化的等温稳态、一维二相动力学模型。该模型所做的主要假定如下:流化床分为气泡相和乳相,在气泡相和乳相内均存在化学反应,考虑二相内的轴向气体扩散,生物质热解过程瞬时完成,主要考虑焦碳以及CO,CO2,H2,H2O,CH4等在流化床内发生的8个主要化学反应。数学模型属于常微分方程组边值问题,利用数值计算软件M atlab7.0进行编程求解。以木粉为原料,将模型结果与实验结果进行了对比,模拟结果与试验数据符合良好,在一定程度上证明了模型的有效性和可靠性。     

流化床与沸腾床内部微生物群落演变与分析

用流化床反应器和沸腾床反应器处理焦化废水,对两种反应器运行效能及微生物群落变化进行对比研究。结果表明,提高污泥负荷后流化床COD去除率优于沸腾床反应器。提高进水污泥负荷对沸腾床内微生物的冲击更大,致使其种群丰富程度下降明显。研究结果证明,流化床在宏观去除率、维持菌种丰富度方面具有较大优势。     

流化床电化学反应器研究进展

流化床电化学反应器是一种三维颗粒电极反应器,以其比表面积大、传质速率高而备受关注。就流化床电化学反应器在导电机理、数学模型、结构放大以及应用领域的研究现状和进展进行了综述,阐明了该类反应器开发、设计和模型化方面存在的问题,并提出了研究方向。     

Feedback linearizing control of a fluidized bed reactor

The design of an adaptive nonlinear controller for the control of a fluidized bed reactor is derived by using exact linearization techniques. Reset action and parameter adaptation are used to make more robust the precise compensation of nonlinear terms, which is called for in the linearization technique. A nonlinear antiwindup mechanism is introduced to handle reset windup problem and to provide fast response without large overshoot. Simulation results show that the proposed adaptive controller guarantees good setpoint tracking. The developed estimation algorithm allows accurate estimation of the parameters for which the regressor component is not zero.     

Modeling and control of solar‐grade silicon production in a fluidized bed reactor

A multiscale model predicts silicon production yield and powder loss in a fluidized bed reactor for solar silicon production. The reaction module calculates the silicon vapor deposition and powder scavenging rates. A computational fluid dynamics model predicts temperature and bed density. A population balance model calculates the particle‐mass distribution functions on silicon yield. The model results are validated against industrial data. Furthermore, we conduct a sensitivity analysis to investigate the effect of gas flow rate and inlet silane concentration. Finally, a control strategy is proposed to maintain the process at the desired operating point. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1740–1751, 2014     

Development of a three-phase fluidized bed reactor with enhanced oxygen transfer

A three-phase fluidized bed reactor (TFBR) was developed in this study with the objective to achieve high rates of oxygen transfer from the gas to the liquid phase in the presence of fluidized solid particles. With 2.9 m height, 0.605 m diameter, and a short residence time of 8 h, the TFBR is particularly suitable for industrial applications such as aerobic biodegradation of high-strength wastewaters including refractory compounds. Experiments with tap water and air show that the TFBR enables complete fluidization. With the water and air superficial velocities in the respective ranges of 0.005–0.203 and 0.8–2.0 cm/s, the volumetric oxygen transfer coefficient is 2.3 × 10⁻² s⁻¹, which is higher than that obtained in similar experimental studies on oxygen transfer carried out in the past. These results suggest that the developed TFBR could be very effective in industrial applications where short hydraulic time and high gas-to-liquid mass transfer rates are desirable.     

一体式流化床膜反应器合成二甲基二氯硅烷

提出将陶瓷膜与流化床反应器耦合构成一体式流化床膜反应器,用于直接法合成二甲基二氯硅烷。实验考察了催化剂浓度、脉冲反吹对反应效率和膜分离性能的影响,并对反应前后的触体及陶瓷膜进行了表征。结果表明,催化剂浓度小于4%（质量）时,二甲基二氯硅烷的选择性均可维持在85%以上,硅粉转化率随催化剂浓度的增大而增大;催化剂浓度在4%～8%时,二甲基二氯硅烷的选择性随催化剂浓度增加而略有下降,当催化剂浓度大于8%时,二甲基二氯硅烷选择性明显下降。触体失活后粒径减小,硅粉表面积碳随催化剂浓度的增加而升高。陶瓷膜表面形成内外两层滤饼,内层滤饼主要成分为铜,外层滤饼主要成分为碳;不同催化剂浓度下,陶瓷膜对粉尘的截留率均可达100%,反应过程中跨膜压差随时间变化较小,脉冲反吹可增加硅粉转化率。     

A mathematical model for a biological fluidized bed reactor

A physical model is given in the present report for representing a three-phase biological fluidized bed reaction system which consists of microorganism-coated particles, waste water and air. The system is assumed to be well fluidized. The physical model can be represented by two differential equations describing, respectively, the substrate axial dispersion and diffusion/reaction. Numerical values of the physical parameters are selected from the literature or estimated from semi-empirical equations. The governing system equations are solved by an iterative finite-difference scheme. The theoretical predictions are compared with several experimental measurements and the agreement between them found to be very good, validating the physical model reported here.     

Hydrodynamic study of a toroidal fluidized bed reactor

Hydrodynamic behavior of a newly developed toroidal fluidized bed reactor is studied in this work. The reactor has a gas distributor consisting of angled blades in an annular ring at the reactor bottom. The driving force for particles to move over the distributing blades comes from the velocity head of gas jets accelerated upon entering the blade spacing. Relevant hydrodynamic behaviors are measured with various inert materials in a pilot scale 400-mm toroidal fluidized bed reactor. The observed hydrodynamic behavior is found to be essentially predictable at ambient temperature by conventional hydrodynamic models. Fine particle tracking on the reactor wall is clearly observed through oxidation of zinc dross at a bed temperature of around 1120°C, and is simulated on the basis of a simplified mathematical model. Hydrodynamic issues, such as particle flying trajectory and retention time in the reactor, are discussed based on the developed model.     

Experimental study of the inverse fluidized bed biofilm reactor

A new apparatus, the inverse fluidized bed biofilm reactor, is described. Introduction of the so called inverse fluidized bed, in which low density particles covered by a biofilm are fluidized by downflow of the liquid, allows control of the biofilm thickness and provides a high oxygen concentration in the reacting liquid. Characteristics of the reactor were studied by carrying out two important biotechnological processes: aerobic wastewater treatment by a mixed bacterial culture, and ferrous iron oxidation by the bacteria Thiobacillus ferrooxidans. The bioreaction rates per unit volume of the reactor were up to 14 times higher than those in the equivalent airlift bioreactor. The structure of the liquid flow was determined by a tracer method.     

Modeling of an internally circulating fluidized bed reactor for thermal treatment of industrial solid wastes

A predictive mathematical model is developed to describe and characterize the key design variables of a novel Internal Circulating Fluidized Bed Combustor. The model is based on fundamental principles of heat transfer, mass transfer, hydrodynamics and reaction kinetics. Under justifiable assumptions unsteady state mathematical equations are written and solved. The input parameters of the model are gas and solid flowrates, solid circulation flux, as well as physical properties of gas and solids. The model allows to predict and to investigate the temperature, the combustible conversion, the oxygen concentration, the residence time, the voidage and the solid velocity in the riser. Experiments with spent foundry sand are undertaken in order to assess the validity of the model. The predictions for the transition period of heating clean sand and the treatment of waste compare satisfactorily to the experimental data.     

Circulating fluidized bed combustion reactor: Computational Particle Fluid Dynamic model validation and gas feed position optimization

A 3D Computational Particle Fluid Dynamic (CPFD) model is validated against experimental measurements in a lab-scale cold flow model of a Circulating Fluidized Bed (CFB). The model prediction of pressure along the riser, downcomer and siphon as well as bed material circulation rates agree well with experimental measurements. Primary and secondary air feed positions were simulated by varying the positions along the height of the reactor to get optimum bed material circulation rate. The optimal ratio of the height of primary and secondary air feed positions to the total height of the riser are 0.125 and 0.375 respectively. The model is simulated for high-temperature conditions and for reacting flow including combustion reactions. At the high temperature and reaction conditions, the bed material circulation rate is decreased with the corresponding decrease in pressure drop throughout the CFB for the given air feed rate.     

甲醇制汽油固定流化床试验装置的设计

根据甲醇制汽油反应的工艺要求和影响流化床反应器性能的主要特性参数,设计研制了固定流化床反应器,使其作为前期催化剂实验室研发的一个评价装置,并取得了较佳的效果。     

300 kg/a规模流化床制碳纳米管中试研究

采用Ni-Mg-O复合氧化物催化剂进行了流化床甲烷催化裂解法制碳纳米管的中试实验,研究了主要操作变量对甲烷转化率、催化剂产碳率、产品团聚率及催化剂损失率的影响,得到了适宜的操作条件为：甲烷进气流速16~19 cm/s、催化剂粒径150~220 μm、催化剂加入量50~60 g、反应温度650~700 ℃、反应时间120~140 min。多批次重复性实验表明,在选定的操作条件下,甲烷转化率约为30 %,催化剂产碳率约为10 gCNTs/gCAT。对纯化后的产品进行SEM及TEM形貌表征显示,制得的碳纳米管管径均匀,中空结构明显,碳纳米管的外径为10~30 nm,内径为2~5 nm。     

城市污泥流化床中低温空气气化及重金属迁移特性

利用自行搭建的流化床热态实验装置，系统研究了污泥的中低温气化及重金属迁移特性。研究表明，对冷煤气效率和碳转化率影响最大的是气化温度，其次是空气当量比，而一二次风配比和流化数影响较弱。污泥中低温气化的焦油产率较之高温气化明显增加。随着二次风占比和空气当量比的提高，焦油产率单调下降。气化温度由600℃升至850℃，冷煤气效率和碳转化率均呈升高趋势；空气当量比由0.2升至0.4，冷煤气效率呈先升高后下降的趋势，在0.3时达到最大值，而碳转化率则呈单调升高趋势。随着气化温度的升高，污泥中重金属转移至产气、焦油及飞灰的迁移率升高。随着空气当量比的升高，Ni、Cu的迁移率降低，Cr升高，Cd、Zn、As和Pb等其他重金属的迁移率几乎不变。     

流化床中甲烷芳构化过程

在石英流化床反应器中研究了无氧条件下甲烷直接催化转化制备芳烃的过程.发现催化剂的诱导期长短、甲烷的总转化率与温度、甲烷分压及甲烷空速相关.在973 K下,液体产品中苯的选择性与萘的选择性随着催化剂的失活呈现不同的变化趋势.所得主要技术指标（甲烷转化率、苯的收率与选择性等）与固定床微型反应器中的结果相近.还研究了催化剂上的积炭对甲烷转化率、催化剂失活的影响,为将来的进一步研究提供了基础.