SIMULATION OF FLOW, MASS TRANSFER AND BIO-CHEMICAL REACTIONS IN ANAEROBIC ...

193 Pages·2012·3.58 MB·English

SIMULATION OF FLOW, MASS TRANSFER AND BIO-CHEMICAL REACTIONS IN
ANAEROBIC DIGESTION

By
LIANG YU

A dissertation submitted in partial fulfillment of
the requirements for the degree of

DOCTOR OF PHILOSOPHY

WASHINGTON STATE UNIVERSITY
Department of Biological Systems Engineering

DECEMBER 2012
To the Faculty of Washington State University:
The members of the Committee appointed to examine the dissertation of LIANG YU
find it satisfactory and recommend that it be accepted.

_ JJJJjkkkk Shulin Chen, Ph.D., Chair

_ JJJJj Robt Dillon Manuel Garcia-Perez, Ph.D.

_ JJJJj Robt Dillon Dillon Robert, Ph.D.

_ JJJJjkkkk Konstantin Matveev, Ph.D.
D

ii
ACKNOWLEDGEMENTS
I would like to expess my sincere thanks to my advisor, Dr. Shulin Chen, for allowing me to
pursue this study at the Bioprocessing & Bioproducts Enigeering Laboratory (BBEL). I am
extremely thankful for his personal guidance, assistance and supervision over the course of this
study. My commetee members: Dr. Manuel Garcia-Perez, Dr. Dillon Robert and Dr. Konstantin
Matveev are also gratefully acknowledged for their valuable comments and suggestions during
the dissertation process.
I warmly thank Dr. Craig Frear for his valuable advice and friendly help on my dissertation
work. My warm thanks are also due to Jonathan Lomber, Cynthia Alwine for their kind help in
lab data analysis. I appreciate AD group members: Jingwei Ma, Quanbao Zhao, Baisuo Zhao,
and Nicholas Paul Kennedy, the former members and all BBEL members for their help and
cooperation. Thanks go to John Anderson, Patricia Huggins, Pat King, and Joan Hagedorn for
their administrative support. I extend my thanks to all those who have helped me with my work
in the Department of Biological Systems Engineering at Washington State University.
I also want to dedicate this dissertation to my parents, although they can not see it anymore.
Finally, I thank my wife Dongming Zhao for giving up her claim on my time for these past
four years. My gratitude also goes to my brother Jiang Yu for his support on my Professional
Engineer (PE) Exam.

iii
SIMULATION OF FLOW, MASS TRANSFER AND BIO-CHEMICAL REACTIONS IN
ANAEROBIC DIGESTION

ABSTRACT

By LIANG YU, Ph.D.
Washington State University
DECEMBER 2012
Chair: Dr. Shulin Chen
The aims of the dissertation were to understand and simulate flow, mass transfer and
bio-chemical reactions in anaerobic digesters. Computational fluid dynamics (CFD) and
anaerobic digestion model No. 1 (ADM1) were used to assist the development of a new high
solid anaerobic digestion system. The kinetic theory of granular flow (KTGF) was introduced
and a multi-fluid model was developed to describe the phenomena of settling and suspension in
the anaerobic digestor which is critical to increase biomass retention and improve digestion
performance.
To assess flow fields in a HSAD, a mechanical mixing model was constructed to predict
flow characteristics. The model results show impeller A-310 was not suitable for agitating a high
solid digester due to its impaired mixing performance and large shear rate. The helical ribbon
had a better potential to be more suitable for the mixing of high solids digesters than the Impeller
A-30. Its low shear environment is suitable for microbial flocs in anaerobic digestion. Through
iv
optimization, the power of the helical ribbon used in high solids digesters can be reduced
significantly.
A comprehensive model based on ADM1 was developed to describe a new two-stage HSAD
system. The predictions indicate that a high rate HSAD system could be achieved by adjusting
major parameters such as pH, recycled methanogenic bacteria, and UASB section area. Recycled
methanogenic bacteria increased methane concentration and decreased hydrogen concentrations
in the HSAD reactor, while pH increased in the batch mode, but decreased in the continuous
mode with an increase of recycling rate. The UASB height had little impact on the acetic acid
concentration and methane production.
The mechnisim of a high rate digestor was explored by a multi-fluid model with KTGF. The
simulation results suggest that the dairy manure particles tend to have soft and deformable fluid
properties due to the lower contribution of collisional and kinetic components. The evaluation for
biomass retention allowed the determination of the optimum SRT in anaerobic digestion. Aided
with CFD simulation, the scale-up effect of the hydrodynamic nature from the bottle reactor to
the column reactor was reduced.

v
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ........................................................................................................... iii
LIST OF TABLES ....................................................................................................................... viii
LIST OF FIGURES ........................................................................................................................ x
Chapter 1 : Introduction .................................................................................................................. 1
1.1. Introduction .......................................................................................................................... 1
1.2. Anaerobic Digestion Pathways and Reactions ..................................................................... 3
1.3. Bio-chemical kinetics models ............................................................................................ 17
1.4. Anaerobic Digestion Reactors ............................................................................................ 28
1.5. Black Box Models to Simulate Anaerobic Digestors......................................................... 37
1.6. Phenomenological Models for Simulating Anaerobic Digesters ....................................... 42
1.7. Conclusions ........................................................................................................................ 53
1.8. References .......................................................................................................................... 56
Chapter 2 : Numerical Simulation of Mechanical Mixing in High Solid Anaerobic Digester ....... 1
2.1. Abstract .............................................................................................................................. 74
2.2. Introduction ........................................................................................................................ 75
2.3. Methods .............................................................................................................................. 78
2.4. Results and discussion ........................................................................................................ 84
2.5. Conclusions ........................................................................................................................ 95
2.6. References .......................................................................................................................... 96
vi
Chapter 3 : Experimental and Modeling Study of a Two-Stage Pilot Scale High Solid Anaerobic
Digester System .......................................................................................................................... 100
3.1. Abstract ............................................................................................................................ 100
3.2. Introduction ...................................................................................................................... 101
3.3. Methods ............................................................................................................................ 104
3.4. Results and discussion ...................................................................................................... 113
3.5. Conclusions ...................................................................................................................... 132
3.6. References ........................................................................................................................ 134
Chapter 4 : Multiphase Modeling of Settling and Suspension in Anaerobic Digester ............... 139
4.1. Abstract ............................................................................................................................ 139
4.2. Introduction ...................................................................................................................... 140
4.3. Materials and methods ..................................................................................................... 143
4.4. Results and discussion ...................................................................................................... 152
4.5. Conclusions ...................................................................................................................... 171
4.6. References ........................................................................................................................ 173
Chapter 5 : General Conclusions ................................................................................................ 178

vii
LIST OF TABLES
Table 1.1. Typical composition for the common substrates used in anaerobic digestion ............... 2
Table 1.2. Biochemical rate coefficients (v ) and kinetic rate equations (ρ) for soluble
i,j j
components (i=1-12; j=1-19) ........................................................................................................ 15
Table 1.3. Biochemical rate coefficients (v ) and kinetic rate equations (ρ) for particulate
i,j j
components (i=1-12; j=1-19) ........................................................................................................ 16
Table 1.4. Kinetic coefficients of the first order rate of hydrolysis .............................................. 23
Table 2.1. Geometrical details for digesters with impeller A-310 and helical ribbon (Hoffmann et
al., 2008; Karim et al., 2005) ........................................................................................................ 78
Table 2.2. Parameters of the power-law model for shear stress with temperature (T), flow
behavior index n and consistency coefficient K (El-Mashad et al., 2005) ................................... 85
Table 2.3. Rheological properties and densities of liquid manure for T = 35 °C
(Achkari-Begdouri and Goodrich, 1992; Landry et al., 2004; Wu and Chen, 2008) .................... 90
Table 2.4. Specifications and calculated results of ribbon mixers made in Aaron Process
Equipment ..................................................................................................................................... 93
Table 3.1. Conditions for the mathematic model for the high solids anaerobic digester system 106
Table 3.2. Model parameters in the HSAD system (Batstone et al., 2002; Gali et al., 2009; Rosen
and Jeppsson, 2006) .....................................................................................................................112
Table 3.3. Ranking of roots of mean squared sensitivities ......................................................... 121
Table 4.1. Particle size distribution in the bottle reactor ............................................................. 144
viii
Table 4.2. Model parameters in the ADM1 model ...................................................................... 150
Table 4.3. Dairy manure initial concentration ............................................................................ 168
Table 4.4. Operational conditions and experimental results ....................................................... 168

ix
LIST OF FIGURES
Figure 1.1 Main pathways for anaerobic degradation of organic matter used in the model ........... 7
Figure 1.2. Main pathways for ADM1 model ............................................................................... 12
Figure 1.3. Plot shows the fit of the derived model to the experimental data points and the 95%
confidence interval (Karim et al., 2007) ....................................................................................... 19
Figure 1.4. Dependence of the solids removal reciprocal rate upon solids concentration according
to the firstorder (a) and Contois models with actual (b) and optimal design (c) Model parameters:
first-order (k =0.047 day-1, k =0.45 day-1); Contois (X =0.005 g l-1, Y=0.13g g-1, µ =4 day-1;
1 2 0 m
K* =10g g-1) (Vavilin et al., 2001) ................................................................................................ 26
S
Figure 1.5. Batch reactor (Chynoweth and Isaacson, 1987) ......................................................... 30
Figure 1.6. Continuously stirred tank reactor (Chynoweth and Isaacson, 1987) .......................... 32
Figure 1.7. Plug flow reactor (Chynoweth and Isaacson, 1987) ................................................... 33
Figure 1.8. Up-flow anaerobic sludge blanket reactor (Chynoweth and Isaacson, 1987) ............ 35
Figure 1.9. Two-phase digesters (Chynoweth and Isaacson, 1987) .............................................. 37
Figure 1.10. Schematic diagram of (a) adaptive network-based fuzzy inference system (ANFIS)
models with all input variables and (b) input–output mapping structure of ANFIS model with
only on-line input variables (Pai et al., 2009) ............................................................................... 40
Figure 1.11. Prediction results of COD . (a) ANFIS2-1 and (b) ANN2-1 (Pai et al., 2009) ....... 41
eff
Figure 1.12. Block diagram of Bolle et al.’s (A) (Bolle et al., 1986) and Wu and Hicky’s (B) (Wu
and Hickey, 1997) ......................................................................................................................... 45
x