(Luận án tiến sĩ) nghiên cứu mô phỏng và tối ưu hóa thiết bị tạo khí nitơ sử dụng chu trình hấp phụ thay đổi áp suất

MINISTRY OF EDUCATION AND TRAINING

MINISTRY OF NATIONAL DEFENCE

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY
------------------

PHAM VAN CHINH

INVESTIGATION OF SIMULATION AND
OPTIMIZATION FOR NITROGEN GAS
GENERATOR USING PRESSURE SWING
ADSORPTION

PhD THESIS IN TECHNIQUE

Hanoi – 2021


MINISTRY OF EDUCATION AND TRAINING

MINISTRY OF NATIONAL DEFENCE

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY
------------------

PHAM VAN CHINH

INVESTIGATION OF SIMULATION AND
OPTIMIZATION FOR NITROGEN GAS
GENERATOR USING PRESSURE SWING

ADSORPTION
Specialization: Chemical Engineering
Code:
9520301

PhD THESIS IN TECHNIQUE

Supervisors:
1. Assoc. Prof .Dr. Vu Dinh Tien
2. Dr. Le Quang Tuan

Hanoi – 2021


i

COMMITMENT

I hereby declare that this is my own research. The research results presented
in the thesis and is completely honest. Scientific conclusions have never been
published in any other work by any authors, reference data are fully cited.
March, 19th , 2021
PhD Candidate

Pham Van Chinh


ii

ACKNOWLEDGEMENTS

First of all, I would like to express my sincere gratitude to my supervisors
Associate Professor.Dr. Vu Dinh Tien and Dr. Le Quang Tuan for their
enthusiastically guidance and helping me to complete this thesis. They sincere
cooperation at every stage of my research work, their valuable advice and assistance
always guided me to conduct my research smoothly.
Secondly, I would like to thank Head of Academy of Military Science and
Technology, Training Department of Academy of Military Science and Technology,
Head of Institute of Chemistry - Materials, Department of Physical Chemistry,
Department of Machinery and Equipment for Chemical Industrial, School of
Chemical Engineering, Hanoi University of Technology, Head of Institute of
Technology/General Department of Defense Industry, Department of Chemical
Technology have always enthusiastically guided and helped me in all aspects of the
thesis implementation process.
Finally, I am in debt of my families, friends and relatives for their love and
encouragement and motivation in the process of implementing the thesis.
PhD Candidate

Pham Van Chinh


iii

TABLE OF CONTENTS
Page
NOMENCLATURE ...................................................................................................vi
LIST OF TABLES .....................................................................................................xi
LIST OF FIGURES...................................................................................................xii
INTRODUCTION....................................................................................................... 1
CHAPTER I - OVERVIEW........................................................................................ 7

1.1 Air composition and separation technichques ......................................................7
1.1.1 Air composition ...........................................................................................7
1.1.2 Air separation techniques ............................................................................8
1.2 Absorbent ............................................................................................................17
1.2.1 Introduction of adsorption and adsorbent ..................................................17
1.2.2 Molecular sieve adsorbent .........................................................................19
1.3 Theoretical background of adsorption, desorption and nitrogen gas generator
using pressure swing adsorption. ........................................................................25
1.3.1 Theoretical background of adsorption and desorption processes. .............25
1.3.2 Structure of adsorption column .................................................................28
1.3.3 Mechanism of adsorption process .............................................................29
1.3.4 Structure and principle of N2 gas generator using pressure swing adsorption. ... 31
1.4 Mathematical model, simulation and optimization for a single fixed bed..........34
1.4.1 Mathematical models to describe a single fixed bed .................................34
1.4.2 Simulation for process and equipment in adsorption ................................38
1.4.3 Optimization of nitrogen gas generator ....................................................39
1.5 The results recently. ............................................................................................42
1.5.1 In the world ................................................................................................42
1.5.2 In Vietnam .................................................................................................45
CHAPTER II - OBJECTS AND METHODOLOGY ............................................... 49
2.1 Object and scope .................................................................................................49
2.2 Materials, chemicals and equipment ...................................................................49


iv

2.2.1 Carbon Molecular Sieve ............................................................................49
2.2.2 Analytical equipment for investigating characteristics of adsorbent ........49
2.2.3 A complete experimental system is N2 gas generator using PSA cycle....50
2.3 Methodology .......................................................................................................50

2.3.1 Introduction ...............................................................................................50
2.3.2 General method..........................................................................................51
2.3.3 Studying method about carbon molecular sieve ........................................51
2.3.4 Methods of a building experimental systems for air separator by PSA ....52
2.3.5 Determining method of diffusion coefficient ............................................54
2.3.6 Determining method of pressure drop through particle layer of a bed .....55
2.3.7 Methods establish a mathematical models to describe a single fixed bed 57
2.3.8 Simulation and optimization of air separator ............................................61
2.3.9 Experimental method.................................................................................63
2.2.10 Method scale-up of industry ....................................................................64
CHAPTER III - RESULTS AND DISCUSSION..................................................... 65
3.1 Specifications of CMS-240 .................................................................................65
3.1.1 Some general specifications of CMS-240 .................................................65
3.1.2 Thermal analysis DSC and TG of CMS-240.............................................66
3.1.3 Composition and structure of CMS-240....................................................67
3.1.4 Specific surface of CMS-240. ...................................................................71
3.2 Manufacturing an experimental system to separate nitrogen gas from air .........74
3.2.1 Calculation characteristics and basic dimensions of a single fixed bed ....74
3.2.2 Maximum adsorption capacity calculation of a single fixed bed ..............75
3.2.3 Manufacturing an experimental system to generate nitrogen gas ............77
3.3 Calculation, measure and analyze pressure drop of particle layer .....................83
3.3.1 Pressurization.............................................................................................84
3.3.2 Adsorption .................................................................................................84
3.3.3 Descrease pressure .....................................................................................85
3.3.4 Desorption .................................................................................................85
3.4 Mathematical models describe a single fixed bed by partial pressure ................89


v

3.5 Determine velocity and diffusion coefficient......................................................90
3.5.1 Velocity of air flow through a single fixed bed, uc (m/s) ..........................91
3.5.2 Molecular diffusion coefficient, DAB (cm2/s) ............................................91
3.5.3 Determination membrane diffusion coefficient (Knudsen), Dk (cm2/s) ....92
3.5.4 Axial diffusion coefficient, DL (cm2/s) ......................................................92
3.6 Summary parameters of nitrogen gas generator ...........................................95
3.7 Simulation and optimization for nitrogen gas generator.....................................97
3.7.1 Simulation and optimization for a single fixed bed...................................97
3.7.2 Investigation of simulation and optimization for N2 gas generator using PSA. 122
3.7.3 Simulation and experimental comparision of a single fixed bed and two beds ... 145
3.8 Scale-up industry for equipment and applications ............................................147
3.8.1 Scale-up industry for equipment with different productivity .................148
3.8.2 Application of N2 gas generators for production of RDX explosive ......152
CONCLUSSIONS................................................................................................... 157
THE SCIENTIFIC PUBLICATIONS .................................................................... 161
REFERENCES ........................................................................................................ 163


vi

NOMENCLATURE
ai,1

Coefficient a1 isothermal bi-Langmuir of component i

[-]

ai,2

Coefficient a2 isothermal bi-Langmuir of component i

[-]

bi,1

Coefficient b1 isothermal bi-Langmuir of component i

[l.g-1]

bi,2

Coefficient b2 isothermal bi-Langmuir of component i

[l.g-1]

DL

Axial diffusion coefficient (adsorption bed)

Dia

Diameter of bed

F

Feed raw materials into bed

IP1

Isothermal constant 1 in Aspen Adsorption

[-]

IP2

Isothermal constant 2 in Aspen Adsorption

[-]

ki

Mass transfer coefficient of component i

[1s-1]

Ki

Equilibrium constant of the component i

[-]

L, H

Height of bed

[m]

Z

Axial distance across bed (from top to bottom of bed)

[m]

ΔP

Pressure drop

[bar]

ΔPi

Partial pressure drop of component i

[bar]

Pe

Standard number Peclet of adsorbent particles

qi

Amount of gas absorbed in adsorbent of component i

[g.g-1]

q*i

Amount of gas absorbed in adsorbent of component i in
equilibrium

[g.g-1]

rp

Particle radius

[µm]

S

Cross-sectional area of bed

[cm2]

Vbed

Volume of bed

[cm3]

U

Theoretical velocity of air flow

[m.s-1]

[cm2.phút-1]
[cm]
Nm3/ph, L/ph

[-]


vii

VDj

Volume of dead zone in bed

XFac

Volume correction factor

[-]

ΔPj

Pressure drop in partial j

[bar]

ΔPmax

Maximum pressure drop through bed

[bar]

VT

Total empty column volume

Vx

Empty volume between particles

Vp

Empty volume inside particles

εi

Intergranular porosity (internal porosity)

[cm3]

 m3void 
 m3 


3
 m void 
 m3 


 m3void 
 m3 


3
 m void 

 m3 


 m3void 
 m3 


 m3void 
 m3 



εp

Porosity inside particles (particle porosity)

εt

Internal and intergranular porosity (total porosity)

µ

Viscosity of liquids, gases

ψ

Coefficient of particle shape

ϕ

Pressure drop coefficient

 bar.min 
 cm 2 

P

Pressure of gas

[mmHg,
kG/cm2]

V

Volume of gas

[m3]

T

Absolute temperature of gas

[K]

Rk

Constant of dry air

Rhn

Constants of water vapor

Ci

Concentration of component i in gas mixture

t

Time

[cP]3
[-]

2,153
[mmHg.m3/k
g.K]
3,461
[mmHg.m3/k
g.K]
[mol/cm3]
[s]


viii

U

Velocity inside bed

[m/s]

ρb

Buld density of adsorbent

[g/cm3]

ρp

Particle density of adsorbent

[g/cm3]

ρs

Solid density of adsorbent

[g/cm3]

KL

Coefficient of thermal conductivity along axis

T

Temperature

[K]

Tw

Temperature of wall

[K]

Tatm

Temperature of ambient

[K]

ρg

Density of gas

[g/cm3]

ρb

Bulk density of adsorbent

[g/cm3]

ρw

Density of wall material

[g/cm3]

Cpg

Specific heat capacity of gas

[J/g.K]

Cps

Specific heat capacity of adsorbent

[J/g.K]

Cpw

Specific heat capacity of wall material

[J/g.K]

[J/cm.s.K]

[J/mol
]

ΔH

Thermal effect of adsorption process

hi

Coefficient of internal heating

[J/cm2.K.s]

ho

Coefficient of external heating

[J/cm2.K.s]

RBi

The inner diameter of bed

[cm]

RBo

Diameter outside of bed

[cm]

Rp

Diameter of particle

[cm]

Aw

Cross-sectional area of wall

[cm2]

B

Parameter equations Langmuir extended

[kPa-1]

qm

Equilibrium parameter for extended Langmuir equation

[mol/kg]


ix

Pi

Pressure of component i

K

Coefficient of Langmuir equation expand

ω

LDF coefficient

De

Diffusion coefficient of component in solids

[cm2/s]

Pr

Pressure drop coefficient according to size.

-

Re

Standard number Reynol

-

AAS

Atomic Absorption Spectrometer

ACF

Actived Cacbon Fiber

BET

Brunauer –Emmet-Teller

CA

Controlled Atmosphere

CMS

Cacbon Molecular Sieves

CO

Certificate Original

CQ

Certificate Quality

DNA

Deoxyribonucleic acid

DSC

Differential Scanning Calorimeter

DTA

Differntial Thermal Analysis

EDX

Energy Dispersive X-ray

GAC

Granular Actived Cacbon

IQF

Individual Quick Freezer

ITM

Ion Transport through Membranes

LDF

Linear Driving Force

MMSCFD

Million standard cubic feet of gas per day

[kPa]
[s-1]


x

MAP

Modified Atmosphere Packaging

MTZ

Mass transfer zone

PSA

Pressure Swing Adsorption

PAC

Powdered Actived Cacbon

PLC

Programphg Logic Controler

RNA

Ribonucleic acid

RDX

Cyclotrimetylenethylene trinitriaphe

SCFD

Standard cubic feet per day (gas)

SMR

Steam methane reforphg

SMB

Simulation Moving Bed

SCADA

Supervisory Control and Data Acquisition

SEM

Scanning Electron Microscope

FE-SEM

Field Emission Scanning Electron Microscopy

TEM

Transmission electron microscope

TG

Thermogravimetry

TSA

Temperature Swing Adsorption

VSA

Vaccum Swing Adsorption

VOC

Volatile Organic Compounds


xi

LIST OF TABLES
Page

Table 1. 1 Applications of adsorbents .......................................................................... 18
Table 1. 2 Characteristics of zeolites [19]................................................................... 21
Table 1. 3 Product quality specification of some CMS. ............................................. 24
Table 1. 4 Principle of N2 gas generator ...................................................................... 32
Table 2. 1 Section dimension of some gases [8] ......................................................... 52
Table 3. 1 Moisture and densities results of CMS-240 ................................................ 65
Table 3. 2 Characteristics summary table of a single fixed bed ................................. 74
Table 3. 3 Results of pressure drop through a single fixed bed using PSA cycle ....... 86
Table 3. 4 Comparative mathematical models describing adsorption and desorption
processes in gas and solid phases, respectively ............................................................ 89
Table 3. 5 Calculation results of axial diffusion coefficient DL ................................... 93
Table 3. 6 Synthesizes parameters of N2 gas generator ............................................... 95
Table 3. 7 Setup parameters to investigate for a single fixed bed .............................. 114
Table 3. 8 Simulation and experimental comparision for a single fixed bed ............. 118
Table 3. 9 Parameters setting for two bed, 4-step ...................................................... 132

Table 3. 10 Investigation for two beds 4-step (Skarstrom) ........................................ 135
Table 3. 11 Evaluation and comparison between a single fixed bed and two beds at
feed pressure 5 bar ...................................................................................................... 136
Table 3. 12 Parameters of 6-step cycles (Berlin) ....................................................... 138
Table 3. 13 Comparing of simulation and experimental, optimize for two beds ....... 140
Table 3. 14 Scale-up industry results for N2 gas generators by calculation and simulation...... 152


xii

LIST OF FIGURES
Page
Figure 1. 1 Diagram compositions of air in the atmosphere ........................................... 7
Figure 1. 2 Diagram P&ID technology of gas separation line by cryogenic air
separation industrial. ....................................................................................................... 9
Figure 1. 3 Diagram P&ID gas separation by membrane. ............................................ 11
Figure 1. 4 Diagram of PSA and TSA cycles principle. ............................................... 12
Figure 1. 5 Diagram P&ID of gas separator by PSA cycle. ......................................... 13
Figure 1. 6 Diagram P&ID of gas separator by TSA technology. ................................ 15
Figure 1. 7 Diagram P&ID of gas separator by VSA technology ................................ 16
Figure 1. 8 Structural evolution from primary block AlO4 or SiO4 to a type of
sodalite (also known as β-cage) secondary structure and finally structures of some
typical types of zeolite such as type A, X and Y. ......................................................... 20
Figure 1. 9 Porous structure of carbon molecular sieve and formation ........................ 22
Figure 1. 10Adsorption equilibrium lines of N2 and O2 on CMS carbon molecular
sieve at 25°C [106] ........................................................................................................ 22
Figure 1. 11 Micropore dimensions of some adsorbents and molecular sizes of
components [98] ............................................................................................................ 23
Figure 1. 12 Diagram of langmuir adsorption mechanism on a plane. ......................... 25
Figure 1. 13 Effect of factors on Langmuir isothermal relation ................................... 27

Figure 1. 14 Description of structure of a single fixed bed of N2 gas generator using
pressure swing adsorption and carbon molecular sieve. ............................................... 28
Figure 1. 15 Adsorption mechanism of O2 molecule to CMS adsorbent particle......... 29
Figure 1. 16 Structure and principle of N2 gas generator using PSA. .......................... 31
Figure 1. 17 Model of adsorption column according to PSA cycle .............................. 35
Figure 1. 18 Experimental system of equipment generating N2 by PSA cycle ............ 46
Figure 1. 19 Diagram of nitrogen gas generator based on Aspen Adsorption............. 47
Figure 2. 1 A elemental of a single fixed bed ............................................................. 57
Figure 3. 1 Analysis results of particle size distribution. .............................................. 66


xiii

Figure 3. 2 Thermal analysis results DSC and TG of CMS-240 sample ...................... 67
Figure 3. 3 SEM image 1x10 times of CMS-240 sample ............................................ 68
Figure 3. 4 SEM photo 1x30.000 times of inside CMS-240 ........................................ 68
Figure 3. 5 SEM photo1x50,000 times of inside CMS-240 ......................................... 68
Figure 3. 6 FE-SEM image 1x200K of inside CMS-240 particle................................. 69
Figure 3. 7 Detecting position of coating layer of material particle ............................. 70
Figure 3. 8 X-ray diffraction spectra of EDS-JED 2300 probe .................................... 70
Figure 3. 9 Location at internal layer of adsorbent particles ........................................ 71
Figure 3. 10 X-ray diffraction spectra of EDS – JED 2300 probe ................................ 71
Figure 3. 11 P&ID diagram of a single fixed bed model .............................................. 78
Figure 3. 12 P&ID diagram of N2 gas generator using PSA cycle ............................... 80
Figure 3. 13 Nitrogen gas generator using PSA............................................................ 81
Figure 3. 14 Parameter setting window ........................................................................ 81
Figure 3. 15 Monitor, control and collect data by SCADA window ........................... 82
Figure 3. 16 Window to observe changing of technology parameters ......................... 82
Figure 3. 17 Window to print and export study data .................................................... 83
Figure 3. 18 Pressure drop through a single fixed bed depends on velocity ................ 88

Figure 3. 19 Relationship between velocity uc and axial diffusion coefficient DL ....... 94
Figure 3. 20 Partial pressure of O2 according to time and height of a bed at feed
pressure of 5 bar and running 460s. .............................................................................. 98
Figure 3. 21 Partial pressure of O2 according to time and height of a single fixed at
feed pressure 5 bar and runtime 40s............................................................................. 99
Figure 3. 22 Partial pressure of O2 according to height of column, at 40 s ................. 99
Figure 3. 23 Partial pressure of O2 according to time, at z = 0.65m ........................... 100
Figure 3. 24 Partial pressure of O2 according to time and height of bed at feed
pressure 5.5 bar, runtime 460s. ................................................................................... 101
Figure 3. 25 Partial pressure of O2 according to time and height of bed at feed
pressure 5.5 bar, runtime 40s. ..................................................................................... 101
Figure 3. 26 Partial pressure of O2 according to height of bed, at 40 s ...................... 102
Figure 3. 27 Partial pressure of O2 according to time, at z = 0.65m. .......................... 102


xiv

Figure 3. 28 Workshop window on Presto software ................................................... 104
Figure 3. 29 Window for entering simulation parameters. ......................................... 104
Figure 3. 30 Partial pressure of N2 at outlet of bed at 600s. ....................................... 105
Figure 3. 31 Partial pressure of O2 at outlet of bed at 600s. ....................................... 105
Figure 3. 32 Total pressure at outlet of bed at 600s. ................................................... 106
Figure 3. 33 Partial pressure of N2 in a single fixed bed at 100s. ............................... 106
Figure 3. 34 Partial pressure of O2 in a single fixed bed at 100s. ............................... 107
Figure 3. 35 Simulation diagram of a single fixed bed of N2 gas generator. .............. 108
Figure 3. 36 Parameters of a single fixed bed. ............................................................ 109
Figure 3. 37 Equations and calculation methods for a single fixed bed. .................... 109
Figure 3. 38 Input parameters of F1 stream. .............................................................. 110
Figure 3. 39 Install cycle organizer for operation program of a single fixed bed....... 110
Figure 3. 40 Changing pressure in a single fixed bed by the time. ............................. 111

Figure 3. 41 Changing concentration of N2 and O2 in a single fixed bed by the time.111
Figure 3. 42 Result table of raw materials stream F1 ................................................. 112
Figure 3. 43 Result table of product stream P1 ........................................................... 112
Figure 3. 44 Pressure distribution according to height of bed and time: .................... 115
Figure 3. 45 Mass flow in/out of a single fixed bed time: .......................................... 115
Figure 3. 46 Concentration of N2 and O2 at outlet of a single fixed bed .................... 116
Figure 3. 47 Adsorbed load depend on feed pressure or velocity of raw material ..... 116
Figure 3. 48 Time of pressurization and adsorption depend on feed pressure ........... 116
Figure 3. 49 Pressure drop depend on feed mass flow................................................ 117
Figure 3. 50 Concentration of N2 gas product at outlet of bed depend on feed pressure ....... 117
Figure 3. 51 The amount of O2 absorbed depend on feed pressure. ........................... 117
Figure 3. 52 Partial pressure of O2 in adsorption process from gas phase.................. 123
Figure 3. 53 Partial pressure of O2 in desorption process from solid phase ............... 123
Figure 3. 54 Partial pressure of O2 during adsorption with height of bed at 40 s,
feed pressure 5 bar ...................................................................................................... 124
Figure 3. 55 Partial pressure of O2 during desorption with height of bed at 40 s, feed
pressure 5 bar .............................................................................................................. 125


xv

Figure 3. 56 Partial pressure of O2 during adsorption time at outlet of bed z = 0.65
m, feed pressure 5 bar ................................................................................................. 125
Figure 3. 57 Partial pressure of O2 during desorption time at outlet of bed at z =
0.65 m, feed pressure 5 bar ......................................................................................... 126
Figure 3. 58 Diagram of N2 gas generator using PSA. ............................................... 127
Figure 3. 59 Adsorption parameters of bed B1, B2 .................................................... 128
Figure 3. 60 Working program of bed B1 and B2 ...................................................... 129
Figure 3. 61 Pressure of B1 and B2 time .................................................................... 129
Figure 3. 62 Concentrations change of N2 and O2 at output of equipment ................. 130

Figure 3. 63 Raw material table .................................................................................. 131
Figure 3. 64 Product table P1 ...................................................................................... 131
Figure 3. 65 Pressure change in bed B1 ...................................................................... 133
Figure 3. 66 Pressure change in bed B2 ...................................................................... 133
Figure 3. 67 Mass flow variation in/out two beds....................................................... 134
Figure 3. 68 Concentration of N2/O2 at outlet of two beds. ........................................ 134
Figure 3. 69 Purity of product depend on pressure of product. .................................. 139
Figure 3. 70 Purity of product depend on recovery rate of product. ........................... 139
Figure 3.71 Pressure of bed, two beds alternating ...................................................... 139
Figure 3.72 Pressure of other bed, two beds alternating. ............................................ 139
Figure 3.73 Mass flow in/out of two beds .................................................................. 140
Figure 3.74 Concentration of N2/O2 at outlet of two beds ......................................... 140
Figure 3.75 Comparing concentration of N2 and O2 at outputs between a single
fixed bed and two bed ................................................................................................. 145
Figure 3.76 Simulation results of pi(z, t) adsorption process for a single fixed bed
capacity 50 liters/min at feed pressure 5.5 bar ............................................................ 148
Figure 3.77 Simulation result of pi(z, 60) according to height of bed at 60s .............. 149
Figure 3.78 Simulation result of pi(0.92, t) time at output of bed z = 0.92 m ............ 149
Figure 3.79 Simulation result of pi(z, t) desorption process for a single fixed bed
capacity 50 liters/min. ................................................................................................. 150
Figure 3.80 Simulation result of pi(z, 60) according to height of bed at 60s. ............. 150


xvi

Figure 3.81 Simulation result of pi(0.92, t) time at z = 0.92 m ................................... 151
Figure 3.82 N2 gas bottles supply for hexamine screw system................................... 153
Figure 3.83 Nitrogen gas generator was installed in addition to nitrogen supply
system for hexamine feeder. ....................................................................................... 154
Figure 3.84 N2 gas generator using PSA capacity 50 liters/min, N2 content ≥ 99.5%

at standard conditions. ................................................................................................. 155


1

INTRODUCTION
1. The necessity
Chemical industry's processes and equipment are researched and deployed
from laboratory to industry which is a very complex scientific issue. It plays a very
important role in chemical engineering. In the past, this job often took a lot of time
and effort in the experimental research to find out the working rules of process and
equipment to optimize and scale-up. Afterwards, scientists have studied and
implemented these studies by statistical, physics, uniformity and mathematical
models for simulation, optimization and scale-up. It’s very difficult to solve these
problems by hands which take a lot of effort, think and time. Today, processes and
equipment in chemical engineering which have been researched and deployed on an
industrial scale-up by simulation and optimization with aid of computer and
professional softwares. Which is solved very quickly and effectively [11]. On basis
of process nature, rules and effects of technological parameters described by the
established mathematical models, researching and selection of suitable algorithms,
programming languages and software are installed on computer. Simulation and
optimization of process and equipment in chemical engineering are performed
quickly and accurately. It’s results are a set of parameters to setup for process and
equipment, this is firm basis for scale-up to industry at different productivities. One
of key processes and equipment in chemical engineering is mass transfer, which is
widely used in chemical industry and petroleum refinery such as distillation,
absorption, and adsorption and drying processes [28], [34]. Especially, adsorption
process [43], [49] which is a previously only applied in environmental treatment
technique to recovery of the toxic solvents or color removal solutions. Nowadays,
process and equipment of adsorption has become a mainly used separation process

very efficiently in oil and gas refinery industry to separate components from its mix.
This technique is based on the special characteristics of molecular sieve adsorbents
such as zeolite and carbon molecular sieve, which is selective adsorption capacity
according to molecular size of adsorbent and desorption method. It’s operation is


2

setup automatically according to steps in one cycle. Parameters such as adsorption
time and feed pressure are tightly controlled and stable.
N2 gas is an inert gas widely used in metallurgy industry, fire protection,
welding techniques, laser cutting…. It is increasingly used in industry and civil
[94]. Especially, demand for N2 gas used for production and storage of rice,
propellants - explosives and weapons such as rockets have recently been applied.
Normally, N2 gas is produced by cryogenic air separation technique and fractional
distillation according to boiling point of each component at low temperature,
product is stored and transported in liquid phase at high pressure. This gas needs to
be produced in place to be proactive and warrant safety for production and storage.
Today, in the world has used membrane and adsorption techniques to separate
components from air. Advantages of molecular sieve adsorption technique are low
cost, low pressure, maneuverability and safety. Nitrogen gas generator using this
technique is a typical separative equipment using molecular sieve materials and
adsorption cycles. This equipment should be researched, simulated and optimized to
transfer scale-up industrial in Vietnam with following scientific urgencies and
practical needs:
- In the world, there are some results of mathematical models and
simulations for nitrogen gas generators using pressure swing adsorption that have
been published recently[9], [37], [66]. Some mathematical models which is
describing operation of this equipment have been established and published:
mathematical models are describing a single fixed bed according to concentration,

density, temperature and studied some factors affecting product purity and
productivity. These results have not focused on the studying of pressure swing rule
in a

bed. Simulation and optimization, scale-up of equipment has not been

systematic, has not simulated and optimized for equipment to equipment scale-up to
industry for specific applications in practice. In Vietnam, this separation technique
is still very new, research and develoyment potential of this technique is still very
great for research and application in the fields of air separation and other substances
such as application in processing petroleum, extraction of pharmaceutical products,


3

alcohol and natural compounds. Simulation is becoming a development trend for
many different fields, not only applicable to process and equipment in chemical
engineering, separating substances using adsorption techniques.
- Nitrogen gas generator has small and medium productivity scale which is
used for production and storage of propellants and explosives, military weapons and
food production and storage foods like rice. The demand for this equipment is
increasing more and more. It is necessary to research and develop air separation
techniques using molecular sieve adsorbents and adsorption cycles for air separation
[34], [60] such as separation techniques using pressure swing adsorption (PSA)
[48], [82]. Because this technique has many advantages and is suitable for a number
of applications. Currently, most of these equipment are being imported from abroad
with quite high prices.
On basis of scientific urgency and practical usage, the author chose topic
"Investigation of simulation and optimization for nitrogen gas generator using
pressure swing adsorption" for the doctoral thesis.

2. The objectives
Studying on the rules of adsorption and desorption of O2 gas on the surface
of carbon molecular sieve adsorbent in a single fixed bed of N2 gas generator using
pressure swing adsorption by establish a math model. The math model describes the
change partial pressure of O2 according to time and height. Contemporaneous,
studying on the rule of changing technological parameters such as pressure, flow,
concentration and affecting factors to productivity and purity of product.
Algorithms and programming languages are used in softwares to simulate the
equipment's working process and influence of technology parameters and optimize
equipment. Based on the simulation and optimization results of adsorption and
desorption process in a single fixed bed of N2 gas generator, optimum technological
parameters of equipment can be determined such as adsorption time, flow, feed
pressure and organization of adsorption cycle. So that the equipment can be
achieved the highest productivity (Fp, max) with stable purity and satisfactory for use.


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The goal of this thesis is to find the largest product flow and maintain a stable N2
content ≥ 99.5%.
Studying on the scale-up of gas generator N2 using the pressure swing
adsorption at different capacities for applications by calculation and simulation
methods. Research and development of separation technique using molecular sieve
adsorption materials and adsorption cycle in Vietnam.
3. The contents:
Studying on characteristic properties of carbon molecular sieve; research,
calculation, design and assemble of a experimental system as N2 gas generator;
calculation, measurement and analysis of pressure drop through particle layer in a
single fixed bed during adsorption and desorption processes.
Establishing a mathematical model to describe the working process of

adsorption and desorption processes in a bed according to partial pressure;
determining velocity and diffusion coefficient; investigating of simulation and
optimization for N2 gas generators using pressure swing adsorption by Matlab,
Presto and Aspen Adsorption softwares; doing an experimental investigation of
factors affecting to productivity, purity of product and optimization for a single
fixed bed and two bed or nitrogen gas generator.
Studying on the scale-up nitrogen gas generator from laboratory to industrial
for a number of applications by simulation method; build a complete simulation and
optimization method for gas separation equipment using pressure swing adsorption.
4. The scope:
The object: The rule of O2 gas adsorption and desorption processes on the
surface of carbon molecular sieve (CMS) in a single fixed bed of N2 gas generator
using pressure swing adsorption (PSA).
The scope: at ambient temperature, pressure from 0 to 8 bar and purity N2 ≥ 99.5%.
5. Methodology
Approaching and information collection: document approaching according to
history and scientific logic: based on the in-depth theory of adsorption, results of
latest published works and related issues to thesis topic to identify the object and


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scope of thesis;the modern analytical methods are used to investigate characteristics
of adsorbent, calculation method, design are used to build a controlled experimental
system that can be controlled and observed its rules; calculation, measurement and
analysis of pressure drop in adsorption and desorption processes; establishing a
mathematical model according to law of conservation of lines, binding initial and
boundary conditions, assumptions can be made; compute dynamic parameters and
collect model parameters; using algorithms, languages and softwares to simulate
and optimize for generator; industrial scale-up by calculation and simulation.

The information resolve method: synthesizing, evaluating and commenting
on the results of analysis, calculation and simulation. Contemporaneous, verify the
calculation and simulation results by experimental survey results; commented on
the compatibility of the model; Results of calculation, simulation and measurement
analysis are information processed by tables, 2D, 3D graphs to observe the rules and
optimize equipment.
6. The scientific and practical significance:
a) The scientific significance: the results of the thesis can lead to a further
research direction on the process and equipment separating substances using the
adsorption techniques in Vietnam by simulation and optimization method.
b) The practical significance: the results of the thesis will make a practical
contribution to the proactively deploying separative processes and equipment using
the adsorption techniques from laboratory to the industrial scale-up for different
applications in Vietnam. Results of the thesis also contribute to training program of
engineers, post graduated students on process and separative equipment using
pressure swing adsorption. Results of the thesis are also significant in terms of
simulation and optimization method for other separation processes to save time and
get high efficiency.
7. The structure
Layout:
- Introduction.
+ Chapter I: Overview, presentation on issues related to the thesis.


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+ Chapter II: Object and method of the thesis, presenting purposes, contents,
subjects, methods, materials and facilities to study.
+ Chapter III: Results and discussion, presenting all the results according to
contents of the thesis.

- Conclusion, presents the novelty and achieved results of the thesis.
- List of published scientific work related to the thesis: 10 articles (an article
with ISI Standard, an article published on CASEAN-6 International Seminar and 08
articles are published in Vietnamese Journals).
References: 114 documents (33 Documents in Vietnamese and 81
Documents in English).


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CHAPTER I - OVERVIEW
1.1 Air composition and separation technichques
1.1.1 Air composition
Compositions of air [13, 20] is mainly nitrogen, oxygen (O2) and a small
amount of argon (Ar), carbon dioxide (CO2), water vapor (H2O) and some other
substances such as toxic gases, sol, dust and some unstable gases. Argon (Ar) is mostly
passive (as well as Neon, Kripton and Xenon), it is absent in the troposphere because it
is a heavy gas. Helium (He) is formed by a radioactive reaction, Figure 1.1.

Figure 1. 1 Diagram compositions of air in the atmosphere
In fact, due to the human activities, the industrial activities and the
transportation activities as well as nature, there are many toxic gases in air [13]:
SO2, NO2, NH3, H2S, CH4 ... greatly affect to health of people and organisms in the
environment general. Therefore, in order to separate the air, it must be cleaned first
before entering the separative equipment systems and production lines.
Nitrogen gas (N2)[20] accounts for 78.08% by volume in air, is chemically
very inert and does not participate in energy absorption and is converted into
compounds in atmosphere. Only in the soil layers are some bacteria that use N2 in
their metabolism to convert into the living organisms and at the same time they
release into the atmosphere a small amount of nitrous oxide (N2O) present in the