双循环流化床返料量冷态试验研究

双循环流化床生物质气化装置的关键是合理的控制循环返料量。搭建了一个双循环流化床冷态试验台,它主要由提升管和鼓泡床组成。在试验台上就鼓泡床风速、静床高、物料平均粒径和溢流口高度几方面因素对循环返料量的影响进行了试验。试验结果表明:双循环流化床的循环返料量随静床高和鼓泡床风速的增加而增加,随物料粒径和溢流口高度的增加而减小,并且静床高越高循环返料量随鼓泡床风速变化的线性趋势越明显。试验结果对控制双循环流化床的循环返料量具有一定意义。     

双流化床物料循环系统的冷态试验研究

合理控制物料循环流率是双流化床反应器系统装置设计开发和运行的关键。在自主搭建的双流化床物流循环冷态试验平台上,针对燃烧炉风速U_c、热解炉风速U_b、静床层高度H_b及颗粒粒径d_p等运行参数对物料循环流率G_s的影响规律进行了试验研究,结果表明:燃烧炉风速、热解炉风速和静床层高度的增大都会使得物料循环流率增大,但热解炉风速增加幅度不大;同时,分析了运行参数对Loop-seal返料性能的影响,结果表明,在试验运行参数范围内,物料循环流率受运行参数影响程度顺序为:H_bU_cd_pU_b。研究结果可为双流化床反应器的设计及运行提供参考。     

中心提升管内循环流化床颗粒循环流率预测研究

中心提升管内循环流化床生物质气化装置的关键是合理控制物料循环量.自行设计并搭建了中心提升管内循环流化床冷态试验台,在小型试验台上就运行参数对颗粒循环流率的影响进行了试验.试验结果表明:颗粒循环流率随着提升管风速或鼓泡床风速的增加而增加,并且当提升管风速或鼓泡床风速分别增加到一定程度时,颗粒循环流率增加趋于缓慢.在试验基...     

化学链气化串行流化床设计及试验研究

在生物质化学链气化反应基础上设计并搭建了一套串行流化床冷态模型。以石英砂为床料、空气为流化介质,在该冷态装置上开展了压力分布及控制规律试验研究。采用PY500型智能压力检测系统及PV-6型激光颗粒速度测量仪着重研究了循环流化床冷态装置的料层阻力特性及固体循环量,考察了空气反应器、燃料反应器、返料管部件的流化风量对循环状态和流化床内压力分布的影响,获得了串行流化床稳定运行的操作条件和控制规律。试验结果表明,最佳操作状态:燃料反应器流化气速为0.23~0.32 m/s,空气反应器气速为0.42~0.47 m/s,返料管气速为0.07~0.1 m/s,两反应器存料量为2.5~4.5 kg,为热态试验装置的设计、运行提供了参考依据。     

带提升管内循环流化床的流动特性研究

运行参数和结构尺寸是内循环流化床物料循环流率的重要因素。设计并搭建了内循环流化冷态试验台,通过实验分析了气化室风速、提升管风速、返料孔高度及大小对物料循环流率的影响。实验表明:物料循环流率随气化室风速、提升管风速的增大而增大,但增加幅度变化不同;随返料孔位置的增高而下降,且下降速度加快;随着返料孔面积的增大,先增大然后减小。     

滑板式灰控阀调节特性实验研究

灰控阀的可靠性是外置换热器(EHE)良好运行的有效保障,提出了一种新型的滑板式灰控阀,用于控制物料向外置换热器的分流,为了验证其可行性,通过CFB(循环流化床)400滑板阀冷态实验台,在不同系统循环量、返料风速和松动风速下,对滑板式灰控阀的物料分流调节特性进行了深入的实验研究。实验结果表明,滑板阀对物料分流具有良好的调节特性,在0%～80%孔口开度下,物料的分流量随着孔口开度的增加呈线性递增趋势;滑板阀对物料分流量随着循环量的增加而增大,而分流份额随着系统循环量的增加呈递减趋势;滑板阀在实验条件下,返料风速与松动风速的变化对物料分流量的影响不明显。     

循环流化床多联供试验台的冷态试验研究

建立了一个循环流化床与移动床结合的多联供冷态试验台,提升管直径为400mm、高度为6 m,移动床直径为476 mm、高度为2 m,在循环床与移动床之间用气动分配循环物料的流率;进行了物料分配试验和大颗粒移动试验,根据试验结果完善了这个循环流化床多联供冷态试验台,试验为热态试验台的设计提供了一些经验.     

循环流化床物料循环冷态试验研究

在尺寸为 (长 60 0mm×宽 40 0mm×高 60 0 0mm)的三维循环流化床冷态实验台上对不同工况下的试验现象和运行参数进行了观察和记录分析。得到 3种流化风速下 ( 3 .5m/s、4.5m/s、5 .5m/s)不同装料量所对应的主床床体压力分布和物料循环量 ,得到物料循环量与压力分布和流化风速在本实验台上的经验公式 ,并通过测量返料器通向外置换热器的机械阀开度和返料量的关系 ,得到旋风分离器中下落物料进入换热器和直接进入主床的比例关系     

三床串联化学链生物质气化实验分析与预测

在自行搭建的三床串联化学链(TBS-CLC)生物质气化系统上研究了各控制参数(空气反应器风速、燃料反应器风速、循环物料质量和气化室床料高度)对循环流率的影响,将实验测得的129组数据作为训练样本和测试样本,利用反向传播(BP)神经网络模型、遗传算法(GA)优化的BP神经网络模型即GA-BP模型和支持向量机(SVM)模型...     

生物质循环流化床气化系统返料研究

通过分析生物质循环流化床气化系统循环回路压力平衡和流动密封阀的正常工作条件显示,在循环回路中,立管负责把固体颗粒由低压区送至高压区,起着重要的压力平衡作用;立管内循环颗粒形成一定高度的料柱和回送风量,使回料阀内物料达到完全流化状态是返料装置正常工作的必要条件。在此基础上进行了返料对主流化床的影响试验。试验结果表明,返料装置的运行使主流化床内密相区温度较为稳定,且沿床高方向温度分布较为均匀;返料后,主流化床内物料的流化性能明显改善。     

Model validation of a CFB biomass gasification model

The developed 1-dimensional biomass gasification mathematical model [1] was validated using the experimental results obtained from a circulating fluidized bed biomass gasifier. The reactor was operated on rice husk at various equivalence ratios (ER), fluidization velocities and biomass feed rates. The model gave reasonable predictions of the axial bed temperature profile, syngas composition and lower heating value (LHV), gas production rate, gasification efficiency and overall carbon conversion. The model was also validated by comparing the simulation results with two other different size circulating fluidized beds biomass gasifiers (CFBBGs) using different biomass feedstock, and it was concluded that the developed model can be applied to other CFBBGs using various biomass fuels and having comparable reactor geometries.     

Bench-scale bubbling fluidized bed systems around the world - Bed agglomeration and collapse: A comprehensive review

Thermochemical conversion by gasification process is one of the most relevant technologies for energy recovery from solid fuel, with an energy conversion efficiency better than other alternatives like combustion and pyrolysis. Nevertheless, the most common technology used in the last decades for thermochemical conversion of solid fuel through gasification process, such as coal, agriculture residues or biomass residues are the fluidized bed or bubbling fluidized bed system. For these gasification technologies, an inert bed material is fed into reactor to improve the homogenization of the particles mixture and increase the heat transfer between solid fuel particles and the bed material. The fluidized bed reactors usually operate at isothermal bed temperatures in the range of 700–1000 °C, providing a suitable contact between solid and gas phases. In this way, chemical reactions with high conversion yield, as well as an intense circulation and mixing of the solid particles are encouraged. Moreover, a high gasification temperature favours carbon conversion efficiency, increasing the syngas production and energy performance of the gasifier. However, the risk of eutectic mixtures formation and its subsequent melting process are increased, and hence the probability of bed agglomeration and the system collapse could be increased, mainly when alkali and alkaline earth metals-rich biomasses are considered. Generally, bed agglomeration occurs when biomass-derived ash reacts with bed material, and the lower melting temperature of ash components promotes the formation of highly viscous layers, which encourages the progressive agglomerates creation, and consequently, the bed collapse and system de-fluidization. Taking into account the relevance of this topic to ensure the normal gasification process operating, this paper provides several aspects about bed agglomeration, mostly for biomass gasification systems. In this way, chemistry and mechanism of bed agglomeration, as well as, some methods for in-situ detection and prediction of the bed agglomeration phenomenon are reviewed and discussed.     

油页岩流化床燃烧N_2O生成特性

在一个直径20mm,高450mm小型热态流化床燃烧试验台上,进行了不同运行参数对油页岩流化床燃烧过程中N2O排放特性影响的试验研究。试验研究表明,提高燃烧温度、降低过量空气系数、提高循环倍率和进行炉内石灰石脱硫等可以降低N2O的生成量,为油页岩循环流化床锅炉的设计与运行提供了基础数据。     

两相流动对流化床燃烧行为的影响

循环床锅炉沿床高的烟气浓度及燃烧份额分布测试结果证明,鼓泡流化床和循环流化床的重要差异表现为密相区燃烧行为的根本不同,由于床料平均粒径较低,循环床密相区的流动不同于鼓泡床,导致气固两相之间的传质阻力增加,从而影响燃烧反应,密相区的燃烧行为表现为欠氧。循环床锅炉沿床高乃至分离器都有燃烧反应发生,建立了考虑气固相间传质阻力的流化床密相区燃烧模型,并与实际循环流化床锅炉的测试数据比较,计算结果与测试值比较吻合。     

生物质燃料循环流化床锅炉的模型化设计

生物质燃料在循环流化床（CFB）中的燃烧正在得到进一步的应用和开发。在燃煤CFB锅炉模型化设计的基础上，针对生物质燃料的特点和现有的CFB研究成果，进行了生物质燃料CFB锅炉的建模、程序设计和锅炉设计，同时对一些新的模型内容进行了介绍。模型的计算结果同已报道的试验结果较为吻合。     

Sensitivity analysis of a biomass gasification model in fixed bed downdraft reactors: Effect of model and process parameters on reaction front

A detailed sensitivity analysis is performed on a one-dimensional fixed bed downdraft biomass gasification model. The aim of this work is to analyze how the heat transfer mechanisms and rates are affected as reaction front progresses along the bed with its main reactive stages (drying, pyrolysis, combustion and reduction) under auto-thermal conditions. To this end, a batch type fixed-bed gasifier was simulated and used to study process propagation velocity of biomass gasification. The previously proposed model was validated with experimental data as a function of particle size. The model was capable of predicting coherently the physicochemical processes of gasification allowing an agreement between experimental and calculated data with an average error of 8%. Model sensitivity to parametric changes in several model and process parameters was evaluated by analyzing their effect on heat transfer mechanisms of reaction front (solid–gas, bed–wall and radiative in the solid phase) and key response variables (temperature field, maximum solid and gas temperatures inside the bed, flame front velocity, biomass consumption and fuel/air ratio). The model coefficients analyzed were the solid–gas heat transfer, radiation absorption, bed–wall heat transfer, pyrolysis kinetic rates and reactor-environment heat transfer. On the other hand, particle size, bed void fraction, air intake temperature, gasifying agent composition and gasifier wall material were analyzed as process parameters. The solid–gas heat transfer coefficient (0.02 < correction factor < 1.0) and particle size (4 < diameter < 30 mm) were the most significant parameters affecting process behavior. They led to variations of 88% and 68% in process velocity, respectively.     

An investigation into heat transfer in circulating fluidized beds

A model was proposed to predict the heat transfer in a circulating fluidized bed. To verify the model, experiments were conducted in a 102 mm diameter 5.5 m high Plexiglas column, in which the heat transfer coefficient was measured for different superficial velocities and solid circulation rates and two particle sizes. Results were compared with the experimental data of Mickley and Trilling, Kiang et al., Fraley et al, and Kobro and Brereton.     

Modeling of fixed bed downdraft biomass gasification: Application on lab‐scale and industrial reactors

This study aimed at presenting a model to simulate downdraft biomass gasification under steady‐state or unsteady‐state conditions. The model takes into account several processes that are relevant to the transformation of solid biomass into fuel gas, such as drying; devolatilization; oxidation; CO₂, H₂O, and H₂ reduction with char, pressure losses, solid and gas temperature, particle diameter, and bed void fraction evolution; and heat transfer by several mechanisms such as solid–gas convection, bed–wall convection, and radiation in the solid phase. Model validation is carried out by performing experiments in two lab‐scale downdraft fixed bed reactors (unsteady‐state conditions) and in a novel industrial pilot plant of 400 kW_th–100 kW_e (steady‐state conditions). The capability of the model to predict the effect of several factors (reactor diameter, air superficial velocity, and particle size and biomass moisture) on key response variables (temperature field, maximum temperature inside the bed, flame front velocity, biomass consumption rate, and composition and calorific value of the producer gas) is evaluated. For most response variables, a good agreement between experimental and estimated values is attained, and the model is able to reproduce the trend of variation of the experimental results. In general terms, the process performance improves with higher reactor diameter and lesser air superficial velocity, particle size, and moisture content of biomass. The steady‐state simulation appears to be a versatile tool for simulating different reactor configurations (preheating systems, variable geometry, and different materials). Copyright © 2013 John Wiley & Sons, Ltd.     

燃煤循环流化床模型与试验研究

利用循环流化床内气－固两相流动等基础方面的研究成果,根据本文床内气固浓－淡流动模型,建立适用不同结构参数的循环流化床燃烧模型,考虑了床内气体、固体颗粒的返混、循环过程,以及煤燃烧、ＮＯ的生成和分解、颗粒磨损等因素。在循环流化床燃烧试验台上进行实验研究,模型仿真结果和实验数据吻合良好,表明气固两相浓－淡流动模型所建立的循环流化床燃烧系统模型可以正确地模拟循环流化床的燃烧过程。     

Modeling of biomass gasification in fluidized bed

Modeling of biomass gasification in bubbling and circulating fluidized bed (FB) gasifiers is reviewed. Approaches applied for reactor modeling, from black-box models to computational fluid-dynamic models, are described. Special attention is paid to comprehensive fluidization models, where semi-empirical correlations are used to simplify the fluid-dynamics. The conversion of single fuel particles, char, and gas is examined in detail. The most relevant phenomena to be considered in modeling of FB biomass gasifiers are outlined, and the need for further investigation is identified. An updated survey of published mathematical reactor models for biomass and waste gasification in FB is presented. The overall conclusion is that most of the FB biomass gasification models fit reasonably well experiments selected for validation, despite the various formulations and input data. However, there are few measurements available for comparison with detailed model results. Also, validation of models with data from full-scale FB biomass gasification units remains to be done.