Microsoft Word - Thesis title page.docxAUGUST 2015
DEVELOPMENT OF DOWNDRAFT GASIFIER COOKSTOVES FOR DOMESTIC
APPLICATION
by
DOCTOR OF PHILOSOPHY
AUGUST 2015
Dedicated to
i
Certificate
The thesis entitled Development of Downdraft Gasifier Cookstoves for Domestic
Application being submitted by Mr. Kailasnath Bhimrao Sutar to the Indian Institute of
Technology Delhi for award of the degree of Doctor of Philosophy is a record of original
bonafide research work carried out by him. He has worked under our guidance and
supervision, and has fulfilled the requirements for the submission of this thesis, which has
attained the standard required for a Ph.D. degree of this Institute.
The results represented in this thesis have not been submitted elsewhere for the award of any
degree or diploma.
Professor, Professor,
Indian Institute of Technology Delhi Indian Institute of Technology Delhi
Date:
Gurur Brahma, gurur Vishnu, gurur devo Maheshwara, guru sakshat Parabrahma, tasmai
Shree guruwenmha.
Meaning: Teacher is the God Brahma, teacher is the God Vishnu, teacher is the God Mahesh,
teacher is Parabrahma, I worship the great teacher.
Above shloka (spiritual poem) is exactly suitable for my Ph. D. supervisors Prof. M. R. Ravi
and Prof. Sangeeta Kohli. Prof. Ravi is a very sincere and knowledgeable personality. After
admission to Ph.D., when I first met Prof. Ravi, the way he interacted with me, I decided to
work under him. One of the most important qualities of Prof. Ravi is his quick response to
any query. Due to his experience and intuition, I was able to transcend innumerable
difficulties during the experimental work.
Prof. Sangeeta Kohli is a kind, soft speaking, and studious personality. Prof. Kohli taught me
hundreds of concepts like uncertainty analysis, molar conversions, programming, primary
entrainment, fuel characterization etc. She always says ‘if you are not knowing the things,
don’t worry, Ph. D. is a training process, we will teach you’.
Both the supervisors are dedicated teachers and fine human beings. The long journey of Ph.
D. studies was enjoyable due to the positive attitude of the supervisors. I will never forget the
weekly meetings about which the supervisors were very serious. They never missed the
timings of the meetings. One of the most important qualities of a good teacher is that they
listen to the student carefully during the meeting. They give suggestion for any changes in the
work done or for further work. I used to ask same things several times but they never got
angry at me and every time they tried to explain as if they were explaining for the first time. I
appreciate their patience in dealing with a student like me.
Both the supervisors have helped me a lot personally along with the professional training.
They treated me like a family member. In their extremely busy schedule, they have given
tremendous amount of time for my research work. I have even contacted them on holidays for
my research work. I salute the kind of human values they follow through their day to day
activities.
It is my great pleasure to express my sincere gratitude towards Prof. T. C. Kandpal, my
external examiner from Center for Energy Studies. His valuable suggestions during the SRC
iii
meetings were very helpful in refining and enriching the research work. He helped me a lot in
making of the review article on cookstoves.
I am grateful to Prof. A. Ray, departmental expert in my SRC and my first teacher in IITD,
who taught the subject Convective Heat and Mass Transfer. He is a very effective teacher
who explains the physical significance of the complicated mathematical expressions in a very
simple language. He was my TA supervisor also. He is a very gentle person, who was always
kind to me and enthusiastic about my progress.
I take this opportunity to acknowledge Prof. P.M.V. Subbarao, Chairman of my SRC and
another teacher in IITD, who taught the subject Experimental Methods in Thermal
Engineering. He is an experimentalist and a dedicated teacher. His critical comments during
the SRC meetings helped me in doing the research work. His valuable suggestions helped me
a lot whenever I met him personally.
My special thanks to Dr. Gazala Habib for guiding me in emission measurements and
providing PM emissions measurement set-up for my experimental work. I am grateful to Dr.
M. S. Kulkarni for providing help for explaining the concepts in design of experiments and
during analysis of experimental results. My sincere thanks to Prof. Naresh Bhatnagar and his
team at Central Workshop for providing help in fabrication of Emission Collection Hood. I
am grateful to thank Prof. S. N. Naik from Center for Rural Development Technology
(CRDT) and Prof. Pant from Chemical Engineering Department for guiding me in conducting
the lignocellulosic analysis of biomass species. I am grateful to Prof. S. R. Kale, Head of the
Department, Prof. S. K. Saha, Chairman DRC and Dr. Amit Gupta, Dr. B. Premchandan, Dr.
S. Datta, Dr. P. Talukdar, Dr. A. K. Darpe, Dr. Harish Hirani, for always being kind to me
and for their encouragement during the research work.
It is my great pleasure to acknowledge Mr. Raj S. Amonkar, my colleague in NRCVEE, and
my mentor, who is a man full of positive energy. He was always eager to know my progress
and was always helpful to me and my family. I am grateful to Mr. L. D. Kala and his family
for their co-operation during our stay at IITD campus. My sincere gratitude towards Mr.
Vinod Yadav and his family for their co-operation to me and my family.
My special thanks to Mr. Abdul Rahman Khan, my colleague in Fuel Pollution laboratory
(FPL) and best friend in IITD. He hardly says no to anybody. He was always ready to help
me. My hearty thanks to Mr. Babaso Naik, my colleague, for conducting lignocellulosic
analysis of biomass and for helping me in finalizing the thesis work. My sincere thanks to
iv
Mr. Satyendra Rana, my colleague in FPL who is always ready to help the others. He helped
me a lot while conducting the experimental work. My special thanks to Master Prathyush,
Prof. Ravi’s son for his valuable co-operation during the review article on cookstoves.
Thanks to Miss Zeba Naaz for helping me in arranging references for the review article. I am
grateful to Mr. Dhirendra Mishra, my colleague in Center for Atmospheric Sciences for being
helpful to me.
My sincere thanks to Mr. Deepak Nehate and Mr. Pankaj Zine my colleagues in the
department for always being in contact with me and motivating me in this journey of
research. I am grateful to Mr. Jai Prakash, Miss. Minza and Miss. Annada from the
Department of Civil Engineering and Mr. Amit Ranjan from CRDT, for their co-operation in
conducting the experiments on cookstoves. I am grateful to Mrs. Ankita Singh, Mrs.
Aakanksha Mathur, Mr. Nilesh Pawar, Dr. Dushyant Singh, Mr. Kuldeep, Mr. Vinayak
hemadri, Mr. Amit Arora, Mr. Pranab Daas, Mr. Rashid, Mr. Hitesh, Mr. Bishrat, Mr.
Virendra Kumar and, Mr. Amit Goyel, my colleagues in the department for their co-operation
during this research work.
I will be failing in my duties if I do not acknowledge Mr. Badri Prasad Verma, without whom
it was not possible to conduct the experimental work. I appreciate his punctuality. I am
grateful to Mr. Mangal Sen and Mr. Manoj in Mechanical Engineering departmental office
for their co-operation. I am grateful to Mr. Chopra in accounts section, Mr. Chandar in
Dean’s office and Mr. Devender Kumar in IRD section for their timely help at different
instances. My sincere thanks to Mr. P. S. Negi and Mr. Surender in Thermal Engineering
Laboratory, Mr. Kuldeep in I.C. Engines Laboratory and Mr. Rampal Singh in FPL for their
valuable help in carrying out the experimental work. I am grateful to Mr. Virendra Kumar
and Mr. Lalu Sharma for their co-operation during the experimental work.
My special thanks to Mr. Sheilesh Kamble, my ex student due to whom I came at IITD for
Ph. D. as he first told me about the advertisement for Ph. D. admissions at IITD. He is
constantly in contact with me and encourages me.
Aai maza guru, aai kalptaru, waschalya sindhu aai- Sane Guruji
Meaning: Mother is my teacher, mother is kalpataru (the tree which satisfies our all wishes),
and mother is the ocean of love.
I wish to acknowledge my first teacher, my mother for encouraging and constantly supporting
me for completion of this Ph. D. work. She was the first to support me when I took decision
v
to leave job at Pune and join as full time research scholar at IIT Delhi. She is been always
kind to me and supporting me at a time in her life when I should have taken care of her. I
dedicate this thesis work to my mother. My dearest wife Jayashree and kids Aniruddh and
Aditi joined me in my mission since last five years. My family has made so many sacrifices
during this period. It is due to me, they had to suffer in the extreme climatic conditions at
Delhi. I am grateful to my younger brothers Bhagwat and his wife Pallavi, Bhaskar and his
wife Shubhangi for their constant support and inspiration. I am grateful to all my relatives
and friends who were always caring for me.
I am grateful to all those who directly or indirectly helped me in completion of this research
work.
vi
Abstract
Improving the performance of biomass cookstoves, both in terms of efficiency and emissions,
has been of interest to researchers for a long time. Hundreds of kinds of biomass cookstoves
have been developed by various researchers. Cookstoves that gasify biomass prior to
combustion, referred to as gasifier cookstoves, are cleaner burning alternatives to the
conventional combustion cookstoves. Although several designs of commercial gasifier
cookstoves are available, work on domestic cookstoves using downdraft gasifiers, which are
well-known for their distinct advantages such as high gasification efficiency (∼80%), and low
tar content (<500 mg/m3) in producer gas, is not available in the literature. In the present
work, it is proposed to address this gap, and develop a downdraft gasifier cookstove for
domestic application.
Design methodology is available in literature for large capacity (∼16-220 kWe) downdraft
gasifiers. However, data used in this methodology do not cover smaller gasifiers. The
contribution of the present work is a judicious choice of extrapolation method for these data
for the design of much smaller gasifiers of 4 kWth and 2.5 kWth nominal capacities for
domestic cookstove application. During preliminary trials on the 4 kWth gasifier, it was found
that its overall efficiency was very low, of the order of 15-20% mainly due to inefficient
combustion of the producer gas. Hence a partially aerated producer gas burner was
developed, considering both momentum and buoyancy effects for computing air entrainment
and the burner dimensions. It should be noted that design methodology available in the
literature does not include buoyancy effects to account for gases at temperatures higher than
room temperature, and this is an original contribution of the present work. In order to verify
the burner design, a mathematical model was developed for fluid flow and heat transfer of the
air-producer gas mixture flowing through the burner. It was observed that the use of this
perforated burner improved the overall cookstove efficiency from 15-20% to 35-45%, with
CO and PM emissions within prescribed upper limits recommended by BIS protocol for
biomass cookstoves.
Extensive experimentation has been conducted in the laboratory on these gasifier cookstoves.
An experimental facility for testing of biomass cookstoves was developed for the purpose.
The effect of fuel type, fuel size and gasification air flow rate on the gasifier performance
was studied using this setup. Three kinds of locally available biomass fuels have been used
vii
for parametric studies of the gasifier cookstoves. In the literature on downdraft gasifiers, the
work on study of effect of different sizes of commonly available woody biomass (Leucaena
leucocephala, Syzygium cumini and Azadiratchta indica) is not available. To address this gap,
a detailed characterization of these fuels has been done by conducting proximate and ultimate
analysis, lignocellulosic analysis and thermogravimetric analysis (TGA). The combined
effect of two operating parameters viz., fuel size and gasification air flow rate is studied using
Central Composite Design Methodology (CCD). The performance of gasifier is analyzed in
terms of input power, air-biomass ratio, calorific value of the producer gas, gasification
efficiency and hearth load. The performance of overall cookstove system is analyzed in terms
of overall cookstove efficiency, burner efficiency, producer gas power, CO and PM emission
factors.
Among the three parameters, gasification air flow rate was found to be the most influential
parameter irrespective of fuel type, particle size, gasification air flow rate or even gasifier
size. The air-biomass ratio for all gasifiers was found to remain nearly constant at about 2.
The highest efficiency of 2.5 kWth gasifier cookstove was ~45% with 10-12 mm particles of
Syzygium cumini at producer gas power of ~1.94 kWth. Taylor’s Series Method (TSM) was
used to estimate contributors to uncertainty in various performance indicators of the
cookstove which can be used to reduce the overall uncertainty by controlling these
contributors.
The present work also includes simulation of the processes in the gasifier by adapting an
existing code to the present work. The results showed that the temperature profile matches
well with the experimental results but there is a large discrepancy in producer gas
composition and gasification efficiency. This is likely to be due to the use of equilibrium
reaction model in the oxidation zone.
In the present work, preliminary design of a natural draft gasifier cookstove has been carried
out with fabrication of three different prototypes. The stove is designed for input power of 4
kWth (fuel burning rate of 15 g/min) by balancing the draught due to buoyancy with the
pressure drop. Preliminary experiments on the third prototype showed that it is successful in
generating a good quality producer gas (LCV: 3.9 MJ/Nm3) at fuel burning rate (16-20
g/min) slightly higher than the design value for short periods of time (6-8 minutes), in the
absence of precise control of air supply. More work is needed to get a reliably working
prototype that can provide uninterrupted clean combustion for about one hour.
viii
Contents
2.8 Computational Modelling of Downdraft Gasifiers ...................................................52
2.9 Summary of the Literature ........................................................................................56
2.10 Scope of the Present Work ......................................................................................57
Chapter 3 .....................................................................................................................................58
3.1 Introduction ...............................................................................................................58
3.4 Mathematical Model of the Burner ...........................................................................72
3.5 Burners in Operation .................................................................................................90
4.5 Uncertainty Analysis ...............................................................................................109
5.1 Introduction .............................................................................................................117
5.3 Physics of Working of Downdraft Gasifier Cookstove ..........................................127
5.4 Selection of Parameters for Experimentation .........................................................128
5.5 Transient Performance of Gasifier ..........................................................................131
5.6 Relationship between Performance Parameters ......................................................133
5.7 Effect of Fuel Type .................................................................................................135
5.8 Effect of Fuel Particle Size .....................................................................................141
5.9 Effect of Gasification Air Flow Rate ......................................................................144
5.10 Combined Effect of Fuel Size and Air Flow ........................................................149
5.11 Summary ...............................................................................................................158
Chapter 6 ...................................................................................................................................159
6.1 Introduction .............................................................................................................159
6.4 Variation in Efficiency and CO Emissions with Input Power ................................177
6.5 Combined Effect of Air Flow and Fuel Size ..........................................................178
6.6 Multi-variable Regression for 2.5 kWth Gasifier Cookstove ..................................181
6.7 Summary .................................................................................................................183
Chapter 7 ...................................................................................................................................184
7.1 Introduction .............................................................................................................184
7.3 Adaptation of the Model to the Present Work ........................................................188
7.4 Parametric study......................................................................................................188
7.5 Discussion ...............................................................................................................201
8.1 Introduction .............................................................................................................203
8.4 Prototype II .............................................................................................................207
8.5 Prototype III ............................................................................................................208
9.1 Conclusions .............................................................................................................213
Appendix B ...........................................................................................................................243
B.1 Definition of Parameters for Cookstove Performance Evaluation .........................243
B.2 Details of the 1st stage experiments on 4 kWth gasifier cookstove .........................245
Appendix C ...........................................................................................................................246
Appendix F............................................................................................................................254
Appendix G ...........................................................................................................................257
Appendix H ...........................................................................................................................269
Publications ...........................................................................................................................276
xi
List of Figures
Figure 1.1: Conceptual designs of (a) forced draft and (b) natural draft versions of downdraft
gasifier cookstoves [9]. .............................................................................................................. 3
Figure 2.1: Biomass domestic downdraft gasifier cooking stove [14] ...................................... 8
Figure 2.2: Rice husk downdraft gasifier cookstove cum power generator [17] ...................... 9
Figure 2.3: Crossdraft type Institutional gasifier stove (IGS) [20] ............................................ 9
Figure 2.4:TLUD type natural draft gasifier cookstove [15] ................................................... 10
Figure 2.5:TLUD type forced draft gasifier cookstove [21] .................................................... 10
Figure 2.6: Schematic of energy balance of a biomass cookstove .......................................... 28
Figure 2.7: Coefficients of variation for WBT and EPTP methods [105]. .............................. 30
Figure 2.8: Uncertainty in test duration due to variations in boiling point of water [105]. ..... 31
Figure 2.9: Thermal performance of Sugam II stove [119]. .................................................... 38
Figure 2.10: Thermal performance of five biomass stoves [109]. ........................................... 38
Figure 2.11: Plot of efficiency versus input power for different cookstove fuel combinations
[79]. .......................................................................................................................................... 39
Figure 2.12: Variations in CO and CO2 emissions with fire (input) power for Sugam II stove
[119]. ........................................................................................................................................ 40
Figure 2.13: Variation in CO emissions with (a) Input power and (b) thermal efficiency for
four cookstoves [114]. ............................................................................................................. 40
Figure 2.14: Variation in CO emissions with efficiency for four cookstoves [84]. ................. 41
Figure 2.15: Variation in CO emissions with efficiency for four cookstoves [125]. ............... 41
Figure 2.16: Variation in LCV, H2, CH4 and CO with air flow [135]. .................................... 47
Figure 2.17: Variation in LHV and cold gas efficiency with air ratio [136]. ........................... 48
Figure 2.18: Variation in (a) composition and (b) heating value of producer gas with
equivalence ratio (ER) [137]. ................................................................................................... 49
Figure 2.19: Variation in temperatures in different zones of the gasifier with time [140]. ..... 50
Figure 2.20: Variation in CV and composition of the producer gas with equivalence ratio
[141]. ........................................................................................................................................ 50
Figure 3.1: Important dimensions of a gasifier reactor (hearth). ............................................. 60
xii
Figure 3.2: Plots of a) diameter of nozzle ring (dr) and nozzle opening (dr1) versus hearth
diameter (dh); b) height of nozzle plane above the throat (h) versus hearth diameter (dh) and c)
ratio of total nozzle area to throat area (Am/Ah) versus hearth diameter (dh). .......................... 63
Figure 3.3 The first prototype of 4 kWth gasifier cookstove. ................................................... 65
Figure 3.4 Grate shaking mechanism in the second prototype of 4 kWth gasifier cookstove .. 66
Figure 3.5 Photograph of second prototype of 4 kWth gasifier cookstove .............................. 66
Figure 3.6: Partially aerated burner for producer gas .............................................................. 69
Figure 3.7: Vertical buoyant jet [230]...................................................................................... 69
Figure 3.8: Important dimensions of partially aerated venturi burner ..................................... 71
Figure 3.9: Photograph of a perforated burner top .................................................................. 71
Figure 3.10: Heat transfer through the burner ......................................................................... 73
Figure 3.11: Flow chart of mathematical model for burner design ......................................... 81
Figure 3.12: Experimental set-up for validation of mathematical model for partially aerated
burner ....................................................................................................................................... 82
Figure 3.13: Cold flow validation of model with air flowing through the burner at ambient
temperature .............................................................................................................................. 83
Figure 3.14: Hot flow validation of mathematical model with producer gas-air mixture
flowing through the burner. ..................................................................................................... 84
Figure 3.15: Variation in (a) primary aeration and (b) temperature of air-producer gas mixture
with producer gas flow rate for 4 kW burner ........................................................................... 86
Figure 3.16: Variation in primary aeration with distance between injector top and burner inlet
for 4 kW burner ........................................................................................................................ 88
Figure 3.17: Variation in primary aeration with producer gas flow rate for 2.5 kW burner ... 89
Figure 3.18: Variation in primary aeration with distance between injector top and burner inlet
for 2.5 kW burner ..................................................................................................................... 89
Figure 3.19: (a) 2.5 kW burner with producer gas flow rate of 23 g/min; (b) 4 kW burner for
cookstove application with stand and pot (c) 4 kW burner with producer gas flow rate of 78
g/min and (d) flame with simple tubular burner ...................................................................... 91
Figure 4.1: Schematic diagram of the experimental setup for testing of the gasifier cookstoves
.................................................................................................................................................. 94
Figure 4.3: Photographs of measuring instruments: (a) Moisture meter, (b) Differential
pressure meter, (c) Hot wire anemometer, (d) Mass flow controller, (e) Gas chromatograph,
(f) Flue gas analyzer, (g) Data acquisition system ................................................................... 97
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Figure 4.4: Photograph of three biomass species with three different sizes used for 2nd stage
experiments on 4 kWth gasifier cookstove ............................................................................... 99
Figure 4.5: Central composite design for two factors at α = 2 ........................................... 100
Figure 4.6: Variation in a) input power, b) efficiency and c) CO emissions of Philips forced
draft cookstove while testing according to WBT, BIS and EPTP protocols ......................... 104
Figure 4.7: Effect of fuel feeding rate on variation in CO emissions of Philips forced draft
cookstove during tests according BIS protocol. ..................................................................... 105
Figure 5.1: Pyrolysis of hemicelluloses, cellulose and lignin at the heating rate of 5 K min−1
[241]. ...................................................................................................................................... 120
Figure 5.2: TGA results of three biomass species at different heating rates ......................... 121
Figure 5.3: Plots of ln((dα/dt)/(1-α)) versus 1/T for three biomass fuels at 10°C/min heating
rate.......................................................................................................................................... 125
Figure 5.4: Physics of working of downdraft gasifier cookstove .......................................... 128
Figure 5.5: Variation in gasifier temperatures and combustible gas content with time for 2.5
kWth gasifier cookstove .......................................................................................................... 132
Figure 5.6: Relationships between different performance parameters .................................. 134
Figure 5.7: Effect of fuel type on performance of 4 kWth gasifier at air flow rate of 30 slpm
................................................................................................................................................ 140
Figure 5.8: Effect of fuel particle size on performance of 4 kWth and 2.5 kWth gasifiers ..... 142
Figure 5.9: Effect of fuel particle size on specific surface area and solid fraction ................ 144
Figure 5.10: Effect of gasification air flow rate on performance of 2.5 kWth gasifier with
Syzgium cumini ...................................................................................................................... 145
Figure 5.11: Effect of gasification air flow rate on gasification efficiency and oxidation
temperature for 2.5 kWth gasifier ........................................................................................... 146
Figure 5.12: Effect of gasification air flow rate on a) hearth load and b) producer gas
generation rate. ....................................................................................................................... 148
Figure 5.13: Effect of gasification air flow rate on content of CO, H2 and CH4 for 2.5 kWth
gasifier cookstove using 10-12 mm particles of Syzygium cumini ........................................ 149
Figure 5.14: Effect of volumetric fraction of CO, H2 and CH4 on LCV of producer gas ...... 150
Figure 5.15: Effect of nominal residence time on gasification efficiency ............................. 152
Figure 5.16: Surface plots of a) air-biomass ratio b) input power, c) LCV of producer gas, d)
gasification efficiency, and e) hearth load for 2.5 kWth gasifier cookstove .......................... 157
Figure 6.1: Efficiencies of gasifier cookstove system ........................................................... 160
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Figure 6.2: Effect of LCV of producer gas on burner efficiency ........................................... 161
Figure 6.3: Effect of gasification air flow rate on LCV of producer gas and burner efficiency
for 2.5 kWth gasifier with 10-12 mm diameter particles of Syzygium cumini ...................... 161
Figure 6.4: Effect of LCV of producer gas on cookstove efficiency ..................................... 162
Figure 6.5: Effect of temperature of producer gas on burner efficiency ............................... 163
Figure 6.6: Effect of temperature of producer gas on cookstove efficiency .......................... 164
Figure 6.7: Effect of flow rate of producer gas on burner efficiency .................................... 165
Figure 6.8: Effect of flow rate of producer gas on efficiency of 4 kWth gasifier cookstove . 166
Figure 6.9: Effect of flow rate of producer gas on gasification efficiency ............................ 167
Figure 6.10: Effect of producer gas power on burner efficiency ........................................... 167
Figure 6.11: Effect of producer gas power on cookstove efficiency ..................................... 168
Figure 6.12: The effect of quantity of water on efficiency of 4 kWth gasifier cookstove. .... 169
Figure 6.13: Effect of pot lid on efficiency of 4 kWth gasifier cookstove. ............................ 170
Figure 6.14: Effect of content of CO in producer gas on CO emission factor of the cookstoves
................................................................................................................................................ 171
Figure 6.15: Effect of content of CO in producer gas on PM2.5 emission factor of the
cookstoves .............................................................................................................................. 172
Figure 6.16: Effect of temperature of producer gas on CO emissions of gasifier cookstoves
................................................................................................................................................ 173
Figure 6.17: Effect of temperature of producer gas on PM2.5 emissions of gasifier cookstoves
................................................................................................................................................ 173
Figure 6.18: Effect of flow rate of producer gas on CO emissions of gasifier cookstoves ... 174
Figure 6.19: Effect of producer gas flow rate on PM2.5 emission factor of 2.5 kWth gasifier
cookstove ............................................................................................................................... 175
Figure 6.20: Effect of producer gas flow rate on average CO and PM2.5 emission factors for
2.5 kWth gasifier cookstove ................................................................................................... 176
Figure 6.21: Variation in efficiency of cookstove and CO emissions with input power for 2.5
kWth gasifier cookstove. ........................................................................................................ 177
Figure 6.22: Effect of fuel particle size and gasification air flow rate on CO emissions for 2.5
kWth gasifier cookstove with Syzygium cumini. .................................................................... 179
Figure 6.23: Effect of fuel particle size and gasification air flow rate on CO emissions for 2.5
kWth gasifier cookstove with Syzygium cumini. ................................................................... 180
Figure 6.24: Surface plots of a) cookstove efficiency, b) burner efficiency, c) CO emission
factor and d) PM2.5 emission factor. ....................................................................................... 183
xv
Figure 7.2: Two phase energy model [248] ........................................................................... 187
Figure 7.3: Flowchart showing working of the numerical simulation of the gasifier........... 189
Figure 7.4: Effect of fuel type on variation in temperature along the height of the gasifier 191
Figure 7.5: Effect of fuel type on content of CO, CO2 and CH4........................................... 193
Figure 7.6: Effect of fuel type on cold gas efficiency ........................................................... 194
Figure 7.7: Effect of fuel size on variation in temperature along the height of the gasifier . 195
Figure 7.8: Effect of fuel particle size on content of CO, H2 and CH4. ................................ 197
Figure 7.9: Effect of gasification air flow rate on temperature along the height of the gasifier
................................................................................................................................................ 198
Figure 7.10: Effect of gasification air flow rate on air-biomass ratio ................................... 199
Figure 7.11: Effect of gasification air flow rate on content of CO, H2 and CH4 .................. 200
Figure 7.12: Effect of gasification air flow rate on content of CO, H2 and CH4 .................. 200
Figure 8.1: Natural draft gasifier cookstove Prototype I ...................................................... 205
Figure 8.2: Natural draft gasifier cookstove Prototype II ..................................................... 208
Figure 8.3: Schematic of Natural draft gasifier cookstove Prototype III ............................. 209
Figure 8.4: Photograph of natural draft gasifier cookstove Prototype III ............................. 211
Figure 8.5: Flame at the exit of the burner ............................................................................ 211
Figure 8.6: Variation in temperature at different locations of prototype III cookstove with
time. ....................................................................................................................................... 211
Table 2.1: Summary of some gasifier stove designs available in literature............................. 12
Table 2.2: National ambient air quality standards for USA [85] and India [86]. .................... 20
Table 2.3: Summary of some cook stove testing protocols ..................................................... 24
Table 3.1: Calculation of hearth dimensions for 4 kWth gasifier ............................................. 64
Table 3.2: Calculation of hearth dimensions for 2.5 kWth gasifier .......................................... 64
Table 3.3: Various parameters related to partially aerated producer gas burner ..................... 70
Table 4.1: Instruments used for testing the cookstoves. .......................................................... 96
Table 4.2: Combination of experiments for CCD analysis (Fuel: Syzygium cumini) ............ 101
Table 4.3: Summery of experiments conducted on gasifier cookstoves ................................ 102
Table 4.4: Protocol used vis-à-vis BIS and WBT protocols .................................................. 108
Table 4.5: Systematic and random uncertainties in different quantities for three protocols . 112
Table 4.6: Contributors to uncertainty in input power and efficiency using three protocols 115
Table 5.1: Proximate and ultimate analysis of the biomass fuels .......................................... 118
Table 5.2: Results of lignocellulosic analysis of three biomass fuels.................................... 120
Table 5.3: Summary of TGA results of three biomass fuels.................................................. 122
Table 5.4: Kinetic parameters of three biomass fuels ............................................................ 126
Table 5.5: Variation in composition of producer gas with time ............................................ 132
Table 5.6 Physical characteristics of fuel bed with three biomass fuels of different particle
sizes ........................................................................................................................................ 137
Table 5.7: Regression table for performance parameters of gasifier ..................................... 155
Table 6.1: Regression table for performance parameters of 2.5 kWth gasifier cookstove ..... 182
Table 8.1: Comparison between performances of three prototypes of natural draft gasifier
cookstove. .............................................................................................................................. 210
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Nomenclature
Symbols and Abbreviations b Systematic standard uncertainty Bh Hearth load (Nm3/h/cm2) Cp Specific heat (kJ/kg k) E Energy (kJ) ER Equivalence ratio F Buoyancy flux (kg-m/s3) G Gibbs function (J) h Enthalpy (kJ/kg), Heat transfer coefficient (W/m2K) h Head loss (m) Average heat transfer coefficient (W/m2K) IP Input power (kW) J Radiosity (W/m2) k Thermal conductivity (W/mK) or Reaction rate (s-1) L Length (m) l Thickness (m) LCV Lower calorific value (kJ/kg) m Mass (kg) Mass flow rate (kg/s) M Molecular weight (kg/kmol) MO Momentum flux (kg-m/s2) Molar flow rate (kmol/s) Nu Nusselt number P Pressure (N/m2) Heat flux (W/m2) Re Reynolds number s Random standard uncertainty S Source term (W) t Time (s) T Temperature °C or K TSM Taylor Series Method UMF Uncertainty Magnification Factor v Velocity (m/s) Volume flow rate (m3/s) X Mole fraction Y Mass fraction Z Distance (m)
Subscripts
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annu Annular avg Average b Biomass B Burner bp Biomass particle c Combustion or critical ca Combustion air ch Charcoal ch,d Charcoal dust cl Cellulose cond Conduction
conv Convection CS Cookstove cs Cold start cv Control volume db Dry biomass e Equivalent eqib Equilibrium ex Exit f Fluid fg Vaporization g Gasification ga Gasification air gr Grate h Hole, hearth hc Hemicellulose hs Hot start HT Heat transfer i Injector ins Insulated l Length, Thickness lg Lignin lm Log mean m Maximum mix Mixture n Order of reaction o Operating
Obs Obstruction oxd Oxidation p Port pa Primary air pg Producer gas pyr Pyrolysis r Reactor rad Radiation res Residence s Steam
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sb Stove body sg Solid gas sm Simmering stoic Stoichiometric t Throat th Thermal trans Transmitted tuy Tuyers or Nozzles uins Un-insulated vol Volatiles w Water
Greek symbols
ω Scattering albedo or specific humidity
Φ Scattering phase function ø Diameter (m)
τ Optical thickness (m)
κ Linear absorption coefficient (m-1)
θ Solid angle (sr)
σs Scattering coefficient (m-1)
ƒ Friction factor
KB Sutar(2009MEZ8548)_PhD Thesis.pdf