利用CFD 模擬催化生質能在快速熱裂解中碳沉積對於催化劑去活化反應影響

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姓名

陸梭(Russel Sevilla) 查詢紙本館藏

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能源工程研究所

論文名稱

利用CFD 模擬催化生質能在快速熱裂解中碳沉積對於催化劑去活化反應影響
(A CFD modeling of catalyst deactivation via carbon deposition during catalytic biomass fast pyrolysis)

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摘要(中)

本研究針對生物質在快速熱解期間催化劑的去活反應，以混合雲杉及松樹做為原料，採用COMSOL Multiphysics 5.3 進行模擬。研究中考慮之去活模式是由於碳沉積在催化劑表面上形成空隙堵塞，使反應物無法流經其活性位點，造成活性催化轉換過程的低落，故本研究目標乃探討不同溫度(773、823 及873 k )及流化氣體速度(0.4、0.5 及0.6 m/s)下的去活狀況。由結果可得，去活行為，會因為高溫造成孔隙的減少而快速的發生，而對於流化氣體速度而言，如其他研究人員所提出，氣體速度明顯的影響物質的停留時間，現象亦對去活行為有著巨大的影響。本論文中，沿流化氣體速度0.4、0.5 及0.6 m/s 下催化劑中心線的平均孔隙率為0.49、0.483 及0.498，然而當考慮催化床體整體表面時，則可明顯的發現，較低的氣體速度對去活行為會優於較高的氣體速度，即較高的氣體速度因停留時間較短，造成表面的積碳較少，故催化劑會因為在高溫低流化氣體速度下形成較多的碳沉積物造成其活性降低。

摘要(英)

The present study investigates about the deactivation of catalyst during the fast pyrolysis of biomass. A mixture of spruce and pine was used as the feedstock. The simulations were carried out using COMSOL Multiphysics 5.3. The study aims to determine the behavior of deactivation on various operating parameters or conditions: different temperature (773, 823, and 873 K) and fluidizing gas velocity (0.4, 0.5, and 0.6 m/s). The mode of deactivation considered in this study was due to carbon deposition or fouling, blockage of the pore of the catalyst due to coke deposits on the surface of the catalyst that prevents the reactants to flow through its active sites, thus, decreasing the activity of the catalytic conversion process. The results showed that at high temperature the deactivation occurs rapidly for the porosity decreases the most at the said condition. Gas velocity greatly affects the time on stream of the species which also affects the deactivation of the catalyst as also mentioned by other researchers. The average porosity along the centerline of the catalyst bed at 0.4, 0.5, and 0.6 m/s is about 0.49, 0.483, and 0.498, respectively. Although, when the whole surface of the catalyst bed was considered, it is noticeable that the least gas velocity suffered from deactivation more than that of with high fluidizing gas velocity which means that the catalyst has the least carbon deposits on the catalyst bed. In conclusion, the catalyst gathered carbon deposits more at high temperature and at low fluidizing gas velocity and with that said, catalyst will deactivate further at this condition. Note that the value of the product should also be considered when performing catalytic biomass fast pyrolysis.

關鍵字(中)

★ 熱裂解
★ 催化劑
★ 生質能
★ 去活化
★ 焦炭
★ 沉積

關鍵字(英)

★ catalyst
★ biomass
★ Pyrolysis
★ deactivation
★ coke
★ deposition

論文目次

摘要 …………………………………………………………………………………..i
Abstract ………………………………………………….….…………………………...ii
Acknowledgements…...………………………………………………………………...iii
Table of Contents ………………………………………………………………………iv
List of Figures…………………………………………………………………………. vii
List of Tables ………………………………………………………………….………...ix
Nomenclature……………………………………………………………………………x
CHAPTER 1 …………………………………………………………………………….1
1.1 Introduction ……………………………………………………………………….1
1.1.1 Biomass resources ……………………………………………………….2
1.1.2 Biomass conversion schemes ………………….…………………………3
Biomass pyrolysis ………………………………………………….3
Pyrolysis oil ……………………………………………………….4
1.1.3 Catalysts ………………………………………………………………….4
Role of catalyst in biomass pyrolysis …………………………….5
1.2 The significance of the Study ……………………………………………………….5
1.3 Objective …………………………………………………………………………….5
CHAPTER 2 …………………………………………………………………………….7
2.1 Introduction to Biomass Energy ………………………………………………….7
2.2 Biomass conversion technology ………………………………………………….7
2.3 Recent studies for biomass pyrolysis …………………………………………...10
2.4 Recent studies on catalytic biomass pyrolysis ………………………………...12
2.4.1 Catalyst Deactivation …………………………………...……………14
v
2.5 Computational Fluid Dynamics ………………………………………………...16
CHAPTER 3 …………………………………………………………………………...21
3.1 Computational Fluid Dynamics ………………………………………………...21
3.2 COMSOL Multiphysics …………………………………………………………...21
3.2.1 Simulation Process ……………………………………………………...21
3.3 Model Description ………………………………………………………………...24
3.3.1 Defining geometry ……………………………………………………...25
3.3.2 Generating mesh ……………………………………………………...27
3.4 Assumptions ……………………………………………………………………...29
3.5 Mathematical Model …………………………………………………………...30
3.5.1 Theory for Euler-Euler Multiphase model interface ………….......…30
Mass Balance ……………………………………………………...30
Momentum Balance …………………………………………...31
Dispersed phase viscosity …………………………...………....32
Interphase momentum transfer ………………………………...33
Solid Pressure ……………………………………………………...34
3.5.2 Theory for Heat Transfer in Solids model interface ………………...34
3.5.3 Theory for Heat Transfer in Fluids model interface ………………...34
3.5.4 Theory for Chemistry interface ……………………………………...36
Chemical reactions ………………………………………………...38
3.5.5 Theory for Transport of Diluted Species model interface …………...42
3.5.6 Theory for Domain ODEs and DAEs model interface ………………...43
3.7 Physics interfaces settings …………………….………………………………..43
3.7.1 Euler-Euler Multiphase model ………………………………..…….45
3.7.2 Heat Transfer model …………………………...……………………48
vi
3.7.3 Transport of Diluted Species model ………………………………...49
3.7.4 Chemistry model ……………………………………………………...51
3.7.5 Domain ODEs and DAEs model ……………………………………...52
3.8 Solver settings ……………………………………………………………………...53
3.9 Material properties ………………………………………………………………...54
3.10 Boundary and initial conditions ………………………………………………...55
3.11 Data Gathering ………………………………………………………………...56
CHAPTER 4 …………………………………………………………………………...58
4.1 Hydrodynamics of fluidized bed reactor…………………………………………...58
4.2 Comparison of products at different conditions ………………….……………..61
4.2.1 Comparison of products during catalytic and non-catalytic pyrolysis ...61
4.2.2 Products at a different temperature during catalytic pyrolysis ……...64
4.2.3 Products at different velocity during catalytic pyrolysis …………...65
4.3 Comparison of catalyst porosity at different conditions ……………..…………….65
4.3.1 The porosity of catalyst at different temperatures ………………….…..67
4.3.2 The porosity of catalyst at different velocities ……………………...70
4.3 Mesh Convergence ………………………………………………………………...72
CHAPTER 5 …………………………………………………………………………...76
References …………………………………………………………………………...77

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指導教授

蕭述三

審核日期

2018-7-27

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