速度进口边界条件对鼓泡床流动影响研究

进口边界条件是影响鼓泡流化床流体动力行为的重要因素之一.本文基于欧拉一欧拉双流体气固两相流模型,对具有中心射流进口的鼓泡流化床进行了数值模拟研究.分别采用脉动和定常进口气体速度边界条件,对鼓泡流化床内气泡的形成、长大、分离,气泡的大小进行了分析和研究.模拟结果与Kuipers等的实验结果进行了比较,研究结果表明考虑进口速度的脉动能够更加合理地预测和分析床内流体动力行为.     

旋涡流化床颗粒夹带和扬析的数学模型

本文结合气体湍流运动模型，颗粒运动的轨道模型和密相床层动力学的经验关联式，建立了旋涡流化床颗粒夹带和扬析的数学模型，发展了相应的求解程序。用本文提出的数学模型对普通鼓泡流化床中颗粒夹带的计算结果与前人的经验公式相符；对旋涡流化床和普通的鼓泡流化床颗粒扬析的计算结果与实验数据吻合较好。     

方截面鼓泡床气液两相瞬态数值研究

在双流体模型中引入界面浓度输运方程,利用界面浓度和气泡平均Sauter直径模化各相间作用力。引入一附加 湍动能输运方程模化气泡诱导引起的液相湍流。利用该模型对方截面鼓泡床内气液两相流进行三维瞬态数值模拟。计算结 果表明该模型能较好得模拟方截面鼓泡床内气液两相流时均和瞬态流动特征。     

气固流化床压力脉动信号的频域熵分析

对气固流化床风室内的压力脉动信号进行频域变换,使用三种熵分析方法,研究了一个内径150 mm、高2.5m流化床不同静床高工况下的流动特性和流型特征。实验结果表明:这三个方法得到的特性曲线可以较好地判别固定/鼓泡/湍动床三个流型;在确定从鼓泡床向湍动床转变的转变点上,DFT熵方法优于小波熵和小波包熵方法,物理意义更明确且计算更快捷。     

瞬变流中气泡动力过程研究

微气泡的生成等基础问题制约着鼓泡脱气技术的发展。本文基于对文丘里鼓泡器内流场的研究,对不同雷诺数下的气泡动力特性进行研究,采用大涡模拟和流体体积法相结合的数值模拟方法,对气泡在不同瞬时动态变化流场下的动力特性进行研究,通过分析气泡在不同湍流下的表面积,气泡球度,以及气泡表面所处的湍流应力,计算气泡所受的破坏应力与聚合应力之比,得到气泡的临界韦伯数随气泡在瞬变湍流中的变化过程,分析气泡破碎的临界条件。     

基于CCRs过程的双流化床反应器设计与冷态试验

双流化床反应器是实现钙基吸收剂循环煅烧/碳酸化法(CCRs)分离烟气中CO2的关键技术.本文在对不同双流化床反应器形式分析的基础上,选择双鼓泡床作为CCRs过程的反应器,并设计、搭建双鼓泡床冷态试验装置.该双鼓床反应器可以长时间稳定运行,实现物料在两个反应器中连续稳定的交换.冷态试验结果表明,鼓泡床流化速度对固体循环量没有影响,随着床料高度、固体喷射管直径与喷射管上所开小孔直径的增大,固体循环量增大.     

竖直环形通道内液氮流动沸腾的MUSIG模型分析 第二部分:径向气泡直径和界面面积浓度的预测

由于考虑了气泡的破裂和聚合,同两流体模型相比,MUSIG模型(多尺寸组模型)能更准确地描述流场内气泡直径。采用MUSIG模型详细分析了不同壁面热流量,液体入口速度,过冷度以及不同管道高度时通道内气泡相界面面积、当地气泡直径、空泡系数等参数沿径向的分布。分析结果表明,MUSIG模型可用来预测泡弹状流型转变区的流动参数,也即该模型拓展了两流体模型的使用范围。     

鼓泡流化床埋管磨损量及其分布的数值研究

本文采用离散颗粒单元法对流化床内颗粒运动及其与固定埋管受热面的相互作用进行颗粒直接数值模拟,其中颗粒之间的碰撞采用Tsuji等提出的软球碰撞模型处理,而流场的计算采用大涡模拟,其亚网格应力为Smagorinsky涡黏性模型,流动工况为两维鼓泡流化床.磨损量的估计是基于祝京旭等人的埋管磨损试验研究的结论,并结合本文数值模拟的结果,揭示了流化床埋管磨损量及其分布的若干规律.     

不同管排方式下三维鼓泡床内气固流型及埋管磨损的LES-DEM研究

埋管具有限制气泡大小和改变床内气固流动特性而被广泛用于密相流化床内,但不同管排方式对改善气固流型特性的作用不同。本文基于LES-DEM耦合方法,在颗粒尺度层面研究了不同管排方式下鼓泡床内颗粒流动特性以及埋管磨损分布特性。发现埋管的存在使得在管束的上部和下部区域存在四个明显的局部颗粒循环.另外,错列管排对颗粒的轴向迁移的限定更为明显,使得颗粒浓度在水平方向上分布更为均匀。由于不同的管排方式导致不同的气固流动特性,管束周围磨损特性差异明显.     

双泡耦合声空化动力学过程模拟

为了对双泡耦合的声空化过程进行模拟,本文从流体动力学控制方程和流体体积分数模型出发,在Fluent软件中构建双泡耦合超声空化三维有限元仿真模型,对超声波驱动下流体中双泡耦合声空化动力学过程进行数值模拟,并通过对空化气泡周围声场的变化进行分析研究双泡耦合声空化的非线性动力学特性.结果显示:在超声波驱动下,球形气泡先缓慢扩张,扩张到最大半径后迅速收缩直至溃灭;耦合双气泡间存在相互作用力,使得空化气泡的扩张受到抑制、气泡收缩时间增长;空化气泡在收缩阶段的能量转换能力增强,相比单气泡声空化,耦合双气泡溃灭时气泡内部的压强更大.本文分析结果将为超声空化泡群的动力学过程模拟提供参考.     

非预混燃烧模型模拟流化床生物质气化器中富氢气体的制备

对用流化床生物质气化器合成富氢气体,建立了基于非预混燃烧的模型对气化器中的生物质在空气-水蒸汽环境中的气化反应过程的模型,并采用流体力学软件 FLUENT 6.0对过程进行了模拟.通过模拟结果与实验结果的对比分析发现,水蒸汽与生物质的比、空氧比和生物质颗粒的粒径大小是决定产气中氢气含量的重要参数.同时,对气化器中氢气的分布进行了研究.     

基于MP-PIC模型的流化床煤气化过程三维数值模拟

本文以多相流质点网格模型(MP-PIC)为基础,采用欧拉-拉格朗日方法,建立了流化床煤气化过程的三维可压缩数理模型,该模型同时考虑了稠密气固流动,传热传质和相内、相间的化学反应。通过不同操作参数下模拟计算,获得反应器内的流型、气体组分分布、化学反应速率变化等规律。模型计算所得的出口气体组分与实验结果进行了比较,数值模拟与实验吻合。     

中试规模的第二代增压流化床联合循环发电技术研究与开发

第二代增压流化床联合循环发电技术(2G PFBC-CC)是当前具有应用前景的洁净煤发电技术之一。东南大学热能工程研究所构建了2 MWt加压喷动流化床部分气化炉,对原有1 MWt增压流化床燃烧炉进行了改造,形成了较完整的2G PFBC-CC系统．经过二年多的调试和试验研究,验证了2G PFBC-CC工艺可行性和先进性,部分气化炉产生的煤气热值在4．2 MJ／Nm3以上,满足燃气透平的要求,排出的半焦可在PFB燃烧炉内稳定燃烧,飞灰含碳量在2％以下,系统碳利用效率在99％以上。     

捕获CO2的部分煤气化氢电联产系统

基于煤炭分级转化、成分对口应用、污染物控制一体化等系统集成思路,提出了一种捕获CO₂的部分煤气化氢电联产系统。该系统利用增压流化床完成煤炭部分气化,降低了气化难度与气化炉造价,具有较好经济性;全面揭示了系统的热力和环境特性规律,指出气化炉碳转化率是影响系统热力性能的主要因素;系统具有良好的热力特性与环境特性,当CO₂的分离率为59.7%时,系统（火用）效率为54.3%。本文的研究为煤炭的清洁高效利用提供了可选择的途径。     

Rational design of thermogravimetric experiments to determine intrinsic char gasification kinetics

The Boudouard reaction is an important heterogeneous reaction that takes place inside the gasifier during char gasification. To evaluate the gasification performance of solid fuels, it is important to know the intrinsic rate of the Boudouard reaction of that particular fuel. Incorrect determination of this rate results in error when used for modelling or gasifier scaling purposes. The thermo-gravimetric analyser (TGA) is an instrument that is widely used for gasification studies, particularly to explore the intrinsic gasification kinetics of coal or biomass char in a controlled environment. As in a real gasifier environment, several experimental parameters in TGA experiments can influence the intrinsic reactivity of the sample char; however, this is rarely discussed in the literature. It is essential to carefully differentiate the physical effects from the pure chemical reaction and to consider their interactions to obtain reliable kinetic parameters. No systematic experimental procedures to minimize the effects of the rate-influencing parameters during TGA experiments are available in the literature. This article presents an analysis for this purpose and demonstrates the variation in the gasification rate when the experimental conditions are not properly optimized. A mathematical model is also presented to explain the possible diffusional interactions with chemical kinetics during un-optimized TGA experiments.     

Dynamic interacting bubble simulation (DIBS): an agent-based bubble model for reacting fluidized beds

In this paper we explore the global dynamics of an agent-type model for bubbles in gas-fluidized beds and demonstrate that these features are consistent with experimentally observed behavior. The model accounts for the simultaneous interactions of thousands of individual bubbles and includes mass-transfer and first-order reactions between the gas and solids so that the impact of the dynamics is reflected in reactant conversion. We start with model parameters that have been demonstrated to produce time average behavior consistent with experimental reactor measurements. By observing the temporal variations of spatially averaged bubble properties, we are able to clearly distinguish the onset of global low-dimensional features that appear to be consistent with previous observations. The most prominent of these features is a large-scale oscillation that exhibits intermittency with power-law scaling in the vicinity of a critical gas flow. We show that the oscillation occurs as the result of a globally synchronized horizontal movement of the bubbles toward the center of the reactor. The oscillation appears to be consistent with the occurrence of the so-called "slugging" phenomenon, which is known to have large effects on fluidized bed reactor performance. Although this model can clearly be further improved, its success in replicating several of the key features of slugging indicates that this approach can serve as a useful tool for understanding and possibly controlling fluidized bed dynamics. We also conjecture that this model may be useful for more generally understanding the occurrence of global features in high-dimensional, multi-agent systems.     

Transformation of the Fe-mineral associations in coal during gasification

The mineral matter associated with coal undergoes various transformations during the coal gasification process. Optimisation of the gasification process is necessary in the coal to liquids technology. The principle aim of this investigation was to determine the changes that the Fe-containing minerals and mineral associations undergo during gasification of coal. Due to the complexity of the counter-current coal-gas process used, a gasifier dissection was undertaken on one of the Sasol gasifiers. Detailed characterisation profiles of various properties of the coal were undertaken after a commercial-scale gasifier was shutdown for routine maintenance of which the Mössbauer spectroscopy technique will be described here. Representative samples from the gasifier were extracted after sufficient cooling was done to allow the safe turn-out of the gasifier. In the coal samples that entered the gasifier, pyrite was the abundant Fe-containing mineral, whilst the pyrite changed gradually to form, in conjunction with the SiO₂ and Al₂O₃ present in the coal, a Fe-containing glass and hematite at the bottom, or ash grate of the gasifier.     

A detailed chemical kinetic model of high-temperature ethylene glycol gasification

In recent experimental investigations, ethylene glycol is used as a model substance for biomass-based pyrolysis oil in an entrained flow gasifier. In order to gain a deeper insight into process sequences and to conduct parametric analysis, this study describes the development and validation of a detailed chemical kinetic model of high-temperature ethylene glycol gasification. A detailed reaction mechanism based on elementary reactions has been developed considering 80 species and 1243 reactions for application in CFD software. In addition to mechanism validation based on ignition delay times, laminar flame speeds and concentration profiles, simulation results are compared to experimental data of ethylene glycol gasification under complex turbulent reactive flow conditions.     

循环流化床内颗粒团流动的研究

循环流化床颗粒相流动具有多尺度效应:单颗粒运动的微尺度、颗粒团运动的介尺度和固相运动的宏尺度。颗粒相流动参数受单颗粒运动和颗粒聚团运动的制约,同时影响气相流动。基于气体分子运动论和颗粒动理学,建立相平均稠密气固两相流流动模型。介尺度模型考虑颗粒团与单颗粒之间、颗粒团与气相之间的动量和能量的传递和耗散。模拟计算颗粒容积份额、速度等参数与实测值相吻合。