大颗粒固定床化学链燃烧器内传热

VIP免费

3.0 赵德峰 2024-11-11 4 4 951.46KB 84 页 15积分

侵权投诉

摘要

化学链燃烧技术(Chemical Looping Combustion, CLC)是一种新型的清洁燃烧

技术，有关化学链燃烧器传热过程的研究是一个重要研究方向，本课题采用实验

方法分析固定床化学链燃烧器内复杂的传热过程，研究的重点是化学链燃烧过程

的非定常特性和大颗粒固定床传热所特有的径向不均匀性。目前有关固定床燃烧

器的研究仍处在初期探索阶段，缺乏准确的实验数据，因此该课题具有很大的研

究价值。本文的主要工作包括两个方面，现有实验装置的改进和固定床化学链燃

烧器内非定常传热现象的实验分析。

对现有实验装置进行改进是本课题化学链燃烧传热研究的基础。已有的实验

装置存在三方面的不足，一是管段最高预热温度低；二是管道保温效果差，径向

热损失大；三是通过加热气体来进行预热的方式效率非常低，因此针对以上所有

问题进行了改进，设计了两套加热装置，一套用来提升预热温度，一套用来增强

管道保温效果，该装置必须具备加热功率高、耐热温度高的特性，并在预热过程

中进行细致调试，最终达到较为理想的预热温度和保温效果。

本文工作的重点是分析化学链燃烧中氧化反应和还原反应中传热过程的规律

性，包括非定常传热特性及温度在轴向和径向上的分布。据相关分析研究可知，

在管径/粒径≤10 情况下，床层内存在明显的流量分布不均匀性及壁面效应，导致

近壁处流量分配比例在40%以上，管内孔道分布的不均匀性严重影响着传热。本

课题采用的负载型大颗粒的管径比为 8.3，因此也会存在明显的流量分配不均匀性

和由此产生的传热不均匀性。本文在改进的实验台上对 Cu/CuO（负载在Al2O3上）

载氧剂固定床燃烧器内的传热过程进行了研究，获得了大量的实验数据，分析了

传热过程的非定常特点及轴向和径向温度分布规律，氧化反应和还原反应都放出

大量的热，但氧化反应放热更加剧烈；化学链燃烧过程中管道轴向存在明显的反

应放热和流动传热的叠加现象，排除实验操作等原因造成的特殊情况，轴向温升

前锋推移速度是逐渐增大的，同时管壁处温升较管内可以忽略不计，热量损失主

要由轴向传热造成；活性段径向呈现明显的温度梯度，由于径向流体分布不均匀

性和气固间化学反应导致径向温度梯度存在较大的变化。此外也分析了不同的进

气流量及不同空隙率对传热过程的影响。增大进气流量明显缩短温升前锋轴向推

移时间，使轴向前端对后端传热的影响更小，同时改变了径向温度梯度；减小床

层空隙率可使床层温升整体提高，减小轴向热损失，但同时增大了径向热损失，

因此进气流量及床层空隙率对传热的影响也具有一定的规律。综合研究结果，大

颗粒固定床化学链燃烧器内存在复杂的传热现象，本文的研究结果对于固定床

CLC 燃烧器研究和开发具有一定的指导意义。

关键词：化学链燃烧固定床燃烧器二维拟均相传热大颗粒负

载型 Cu 基颗粒

ABSTRACT

Chemical looping combustion (CLC) is a new clean combustion technology. Heat

transfer in the chemical-looping combustors is one of the important research directions

in the field. This thesis is aimed to analyze experimentally the complicated heat transfer

process in the packed bed combustor filled with large oxygen carrier particles. The

investigation is focused on the transient heat transfer and the peculiar radial

heterogeneity. The study on fixed bed reactor based CLC is still at the initial stage, and

therefore are research in the field either experimental or theoretical, is very limited. The

present work includes mainly two parts: (1) improving the experimental set-up; (2)

investigating the transient heat transfer process in the combustor.

The improving of the existing experimental set-up is essential to perform

thoroughly the planned study on packed bed chemical-looping combustion. Three

existing aspects of the set-up need to be improved. Firstly, the preheat temperature in

the pipe segment is not sufficient; Secondly, pipe insulation is not good enough; Thirdly,

test section was preheated with inflow gas that takes too long time. Two additional sets

of heating device have been designed and installed, one for increasing the preheat

temperature, and another for better insulation. The new heating devices have the high

heating power and high heat-resistant temperature. With the improvements the above

mentioned shortcomings have been finally avoided.

The present work focuses on experimental investigation on the heat transfer

process of chemical looping combustion, which contains the transient heat transfer and

the temperature distribution at the axial direction and radial direction. The CLC packed

beds are usually with small tube-to-particle ratio. According to the previous work, the

flow distribution appears obviously inhomogeneous and wall effect exists in packed

beds under the circumstance of the tube diameter/particle diameter smaller than 10,

which causes the more than 40% of the flow rate through area near the wall. The

distribution inhomogeneity in the beds has strong effects on heat transfer. In the present

work, the tube-to-particle diameter ratio is 8.3, in which flow and heat transfer

inhomogeneity is certainly expected. Research on the heat transfer of the packed bed

combustor filled with Cu-based oxygen carrier (supported with porous Al2O3 particles)

is conducted based on the improved experimental set-up. The study reveals that a great

amount of heat generates in both the oxidation reaction and reduction reaction, but it is

more intense in the oxidation reaction; Heat superposition phenomenon caused by the

reaction and heat transfer appears in axial direction; The front end of the temperature

rise is large goes forward quickly at the axial line, but temperature rise at the walls is

much smaller than inside; It is also found that very obvious radial temperature gradient

exists. Considering the nearly heat insulated wall, the large temperature gradient should

be caused by the flow distribution inhomogeneity and the relevant non-uniform

gas-solid chemical reaction. In addition, Effects of different inlet flow rates and

different void fraction on the heat transfer process have also been investigated. The

increasing inlet gas flow rate will significantly speed up the reaction front axial

movement and at the same time change the radial temperature gradient. Smaller bed

void fraction is found to determine larger temperature rise and large radial temperature

gradient. In conclusion, heat transfer phenomenon are complicated in the packed bed

chemical looping combustion reactor with large particles, and the present work reveals

some interesting insights about it that can be helpful for research and development of

packed bed CLC combustor.

Key Words: Chemical-Looping Combustion, Packed bed reactor,

Two-dimensional homogeneous, Heat transfer, Large particles,

Supported copper-based particles.

中文摘要

ABSTRACT

第一章前言 ............................................................................................................ 1

第二章文献综述 ...................................................................................................... 3

2.1 引言 ................................................................................................................ 3

2.2 化学链燃烧反应器 ......................................................................................... 3

2.2.1 化学链燃烧技术原理.............................................................................. 3

2.2.2 化学链燃烧器的介绍 ............................................................................. 4

2.2.3 固定床燃烧器的流动与传热研究 .......................................................... 9

2.2.4 固定床化学链燃烧的研究现状 ............................................................ 16

2.3 载氧体的研究............................................................................................... 18

2.3.1 载氧体的制备 ....................................................................................... 18

2.3.2 载氧体的研究现状 ............................................................................... 19

2.4 本课题的研究意义和主要工作 .................................................................... 20

第三章固定床化学链燃烧实验装置的改进与调试 .............................................. 22

3.1 固定床化学链燃烧实验装置 ....................................................................... 22

3.1.1 实验装置介绍 ....................................................................................... 22

3.1.2 实验条件及相关参数 ............................................................................ 25

3.2 外加保温层下管道热损失分析 .................................................................... 26

3.3 加热装置的设计与安装 ............................................................................... 28

3.4 实验操作流程............................................................................................... 29

3.5 管道预热过程的调试 ................................................................................... 32

3.6 本章小结 ...................................................................................................... 33

第四章固定床化学链燃烧器内传热的实验分析 .................................................. 35

4.1 还原过程中固定床层内的非定常传热分析 ................................................ 35

4.1.1 水平管道内侧壁面处的变化过程 ........................................................ 36

4.1.2 床层轴心处各位置轴向的传热分析 .................................................... 36

4.1.3 活性段径向的传热分析 ........................................................................ 40

4.2 氧化过程中固定床层内的非定常传热分析 ................................................ 44

4.2.1 水平管道内侧壁面处的变化过程 ........................................................ 45

4.2.2 床层轴心处各位置轴向的传热分析 .................................................... 45

4.2.3 活性段径向的传热分析 ........................................................................ 49

4.2.4 小结讨论 ............................................................................................... 53

4.3 甲烷进气流量对还原反应非定常传热的影响............................................. 53

4.3.1 活性段轴心处轴向传热分析 ................................................................ 54

4.3.2 甲烷流量对活性段反应前锋和热前锋移动过程的影响 ...................... 55

4.3.3 甲烷流量对径向温升分布的影响 ........................................................ 57

4.4 空气进气流量对氧化反应非定常传热的影响............................................. 58

4.4.1 活性段轴心处轴向传热分析 ................................................................ 59

4.4.2 空气流量对活性段反应前锋和热量前锋移动过程的影响 .................. 60

4.4.3 空气流量对径向温升分布的影响 ........................................................ 62

4.4.4 小结讨论 ............................................................................................... 63

4.5 床层空隙率对固定床 CLC 反应过程中温升的影响 ................................... 63

4.5.1 空隙率对轴心处反应过程中温升的影响 ............................................. 64

4.5.2 空隙率对活性段径向温升的影响 ........................................................ 66

4.5.3 小结讨论 ............................................................................................... 67

4.6 本章总结 ...................................................................................................... 67

第五章结论与展望 ................................................................................................ 69

5.1 结论 .............................................................................................................. 69

5.2 不足与展望 .................................................................................................. 70

符号表........................................................................................................................ 71

参考文献 .................................................................................................................... 73

在读期间公开发表论文和承担科研项目及取得成果 .............................................. 79

致谢........................................................................................................................ 80

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

15 积分 4人已下载

立即下载 VIP免费下载

摘要：

摘要化学链燃烧技术(ChemicalLoopingCombustion,CLC)是一种新型的清洁燃烧技术，有关化学链燃烧器传热过程的研究是一个重要研究方向，本课题采用实验方法分析固定床化学链燃烧器内复杂的传热过程，研究的重点是化学链燃烧过程的非定常特性和大颗粒固定床传热所特有的径向不均匀性。目前有关固定床燃烧器的研究仍处在初期探索阶段，缺乏准确的实验数据，因此该课题具有很大的研究价值。本文的主要工作包括两个方面，现有实验装置的改进和固定床化学链燃烧器内非定常传热现象的实验分析。对现有实验装置进行改进是本课题化学链燃烧传热研究的基础。已有的实验装置存在三方面的不足，一是管段最高预热温度低；二是管...

展开>> 收起<<

大颗粒固定床化学链燃烧器内传热.pdf

共84页,预览9页

还剩页未读，继续阅读

大颗粒固定床化学链燃烧器内传热

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

推荐作者

热门标签

举报选择: