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Synopsis of the Ph.D. Dissertation
EXPERIMENTAL AND COMPUTATIONAL STUDIES ON FLUIDIZED BEDBIOMASS GASIFIER FOR PRODUCTION OF CLEAN ENERGY
By
Deo Karan Ram
Roll No. 511CH105
Under Guidance of
Prof . Abanti Sahoo & Prof. K. C. Biswal
Department of Chemical Engineering
National Institute of Technology
Rourkela-769008
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There is also concern for the availability of the fossil fuels in the near future for which the price
of fossil fuels is fluctuated. Now a reliable and sustainable energy supply has been a major
concern for the global community. To respond this energy crisis it has become essential not only
to use the existing energy sources efficiently but also to develop alternative or non-conventional
sources of energy. In this context a lot of effort has been made to explore renewable energy
production technologies around the world such as hydroelectric, geothermal, wind, solar and
biomass. Of the various renewable energy sources available, biomass appears to offer a
promising solution to tackle the ever increasing energy demand [1]. A wide variety of biomass
can be converted to energy by using gasification. Biomass can either be produced from wastes
which are discarded having no apparent value or dedicated energy crops can specifically be
grown for the production of bioenergy. Gasification is a process that converts organic or fossil
based carbonaceous material into gaseous fuel through partial oxidation. Of the various
renewable energy sources available, biomass appears to offer a promising solution to tackle the
ever increasing energy demand and biomass energy ensures the sustainability of energy supply in
the long term by reducing the impact on the environment. Consequently, producing hydrogenfrom biomass not only offers a zero net carbon emission but also generates electricity and heat
which is clean. Biomass gasification is considered as one of the potential alternatives for the
production of hydrogen, a clean energy.
CHAPTER - 1: INTRODUCTION
This chapter gives introduction to the subject. Significance of biomass gasification has been
discussed in this chapter. Advantages of biomass gasification from environmental aspect have
been stated. Different types of gasifiers which are widely used have been mentioned with the
focus on fluidized bed gasifier. Advantages of fluidized bed gasifier are also discussed in this
chapter. Importance of computational fluid dynamics for gasification is also stated here. Finallyoverview of the project thesis has been given in this chapter.
CHAPTER - 2: LITERATURE SURVEY
This chapter starts with a very brief introduction to fluidized bed biomass gasifier for energy
production. Gasification process has been explained with emphasis on gasifying medium,
gasifier zones and different reactions taking place within the gasifier. Mechanism of gasification
has also been explained here in this chapter. Research works of different researchers [1-4] are
reviewed and summary of some of these research works which are relevant to the fluidized bed
biomass gasification are also mentioned in this chapter.
In the field of fluidization, in particular, the use of CFD has pushed the frontier of fundamentalunderstanding of fluidsolid interactions and has enabled the correct theoretical prediction of
various macroscopic phenomena encountered in fluidized beds. The EulerianEulerian models
are more appropriate for fluidized beds for which this is selected in the present work. A
computational study for the flow behavior of a lab-scale fluidized bed gasifier is also carried out.
Some experimental studies with CFD simulation reported in literature [6-13] have mostly
focused on the effect of temperature for biomass gasification.
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CHAPTER-3: MATERIALS AND METHODS
Different types of commonly available biomass samples are collected from the local area. These
samples are required to be characterized and pretreated before gasification process to estimate
the amount of energy available in the biomass sample. Proximate and ultimate analysis for the
biomass sample is most important steps to know the percentage of basic elements present in the
samples. Feed materials (Biomass samples viz. Saw dust, Rice husk, Rice straw, Wood chips,
Sugarcane Bagasse, Coconut Coir) and bed material viz. Sand, Dolomite and Red Mud are used
in the fluidized bed gasifier for gasification experiments. The physical properties, ultimate
analysis and proximate analysis of the selected samples are shown in Table 1-3.
Table - 1 Physical Properties of Biomass and bed material
Property Mean particle(mm) Apparent density (kg/m3) Porosity Sphericity
Sand 0.38 2650 0.44 0.77
Dolomite 0.55 2800 0.36 0.79Redmud 0.22 1290 0.42 0.72
Rice husk 0.53 426 0.81 0.37
Rice straw 5.00 153 0.46 0.56
Saw dust 0.81 244 0.70 0.45
Wood chips 5.00 481 0.47 0.10
Coconut coir 10.00 352 0.96 0.04
Sugarcane bagasse 10.00 120 0.62 0.01
Table-2 Ultimate Analysis of selected biomass samples
Biomass Carbon (%) Hydrogen (%) Nitrogen (%) Sulfur (%) Oxygen (%)Rice husk 38.45 4.96 0.82 0.18 55.59
Rice straw 38.60 4.55 0.47 0.21 56.17
Saw dust 45.78 5.32 0.16 0.07 48.65
Wood chips 46.23 5.70 0.22 0.12 45.20
Sugarcane 44.60 6.20 0.20 0.50 46.84
Coconut coir 43.76 5.80 0.40 0.22 47.12
Table - 3 Proximate Analysis of selected biomass samples
Sl. No. Biomass Moisture content Volatile matter Ash content (%) Fixed carbon
1 Rice husk 7.34 56.37 15.83 20.46
2 Rice straw 9.38 69.53 3.04 18.053 Saw dust 8.80 87.57 1.94 16.45
4 Wood chips 8.00 74.34 1.80 16.80
5 Sugarcane 5.00 73.80 1.66 19.54
6 Coconut coir 5.30 76.80 0.90 17.00
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Operating Procedure
Biomass sample is fed continuously by the screw conveyer carefully so that they are uniformly
distributed in the bed. The schematic diagrams of gasification unit is own in Fig.-1. A specified
quantity of hot water is added into steam generator for steam-generation. Afterwards feedstock in
the gasifier is ignited to preheat the gasifier by LPG till the temp reaches up to 550-6000C. When
temperatures at the neck and outer wall of furnace reach 900 0C, gasifying agents are driven into
the gasifier and then the tests start up. The temperatures at 7 different points at different intervals
of test were recorded. Temperature profile is shown in Fig.2. The gas yield is measured by a flow
meter simultaneously. Usually, the steady state is reached after around 15 minutes of startup and
then gas sampling is carried out at an interval of 10 minutes. The gaseous sample collected from
the gasifier is then analyzed by online portable type Biomass Gas Analyzer (ACS MODEL ACE
9000 X CGA GAS ANALYSER). The yields of gasifier are noted down for different operating
conditions.
Fig.-1 : Schematic diagram of the experimental setup
1 Air blower
2 Motor
3 Screw
Feeder4 Fluidized
bed
5 Continuous
cleaning
system
6 Bubble cap
7 Orifice
meter
8 Valve
9 Cyclone
se arator
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Fig.-2 : Temperature profile for different zones existing within the gasifier
CHAPTER-4: EXPERIMENTAL OBSERVATIONS AND RESULTS
The calculation of chemical formula is important to determine the stoichiometric amount of air
required for the combustion of the biomass sample [2] . The chemical formulas for these biomass
samples with and without N, S contents are shown in Table - 4. Effects of temperature on syngas
composition on N and S free basis are shown in Fig.-3.
Table4: Chemical formula of biomass samples
Biomass Samples Chemical formula of Biomass
With N, S Without N, S
Rice husk CH1.55O1.08N0.02 S0.02 CH1.55O1.08Rice Straw CH1.49O1.19N0.011S0.0021 CH1.49O1.19
Saw Dust CH1.392O0.8N0.0037S0.00057 CH1.39O0.8
Wood chips CH1.48O0.74N0.0042S0.001 CH1.48O0.74
Sugarcane bagasse CH1.667O0.787N0.0038S0.0042 CH1.667O0.787
Coconut coir CH1.589O0.808N0.0078S0.0019 CH1.589O0.808
Attempt is made to study the effects of different system parameters by correlating the yield of
hydrogen against different system parameters. The developed correlations (Eq.no. 1-6) are
mentioned below [5]. A sample plot is shown in Fig.4 for sugarcane bagasse. The calculated
values of hydrogen yield obtained through these developed correlations are compared against the
experimental values for the respective samples (Table-5). A sample plot for comparison of
experimental and calculated values of hydrogen yield is shown in Fig.-5 Average flow rates of
product gas for different biomass samples and their net heating values (NHV) are measured by
using flowmeter and gas analyser. These observations are listed in Table-6. Carbon conversion
0.00
200.00
400.00
600.00
800.00
1000.00
0 10 20 30 40 50 60
Temp
eraturein0C
Time in min
Drying Zone
Pyrolysis Zone
Oxidation Zone
Gasification andReduction Zone
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efficiency, thermal conversion efficiency and efficiency of the gasifier [1] are calculated for
different biomass samples and listed in Table7.
(a)
For rice husk (b)
For rice straw
(c ) For saw dust For wood chips
(e) For Sugarcane bagasse (f) For coconut coir
Fig.- 3 : Syn-gas composition against temperature for different biomass samples
0
5
10
15
20
25
30
3540
45
4505005506006507007508008509009501000SynGascomposition(vol%
)
Temperature ( 0C )
H2
CO2
CH4
CO
0
5
10
15
20
25
30
35
40
45
4505005506006507007508008509009501000SynGascomposition(vol%
)
Temperature ( 0C )
H2
CO
2
0
10
20
30
40
50
500 550 600 650 700 750 800Syngascomposition(%)
Temp (deg.C)
H2 (vol %)
CO (vol %)
CH4 (vol %)
CO2 (vol %)
0
10
20
30
40
50
60
0 200 400 600 800 1000Temp. (deg.C)
H2 (vol %)
CO (vol %)
CH4 (vol %)
syngas
0
10
20
30
40
50
60
0 200 400 600 800 1000
H2 (vol %)
CO (vol %)
CH4 (vol %)
syngas
0.00
10.00
20.00
30.00
40.00
50.00
4505005506006507007508008509009501000
SynGascomposition
(vol%)
Temperature ( 0C )
H2
CH4
CO2
CO
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Table- 5: Comparison of calculated values of hydrogen yield against the experimental values
Biomass Sample Standard deviation % Mean deviation %
Rice husk 5.835094 -0.17504
Rice straw 0.167728 0.00845
Saw dust 6.670789 -0.13191
Wood chips 13.70658 -0.82464Sugarcane bagasse 8.980832 -0.38822
Coconut coir 7.702166 0.301014
For sugarcane bagasse
198.039.007.0
42.0
2 ..4906.1 Myield RE
B
STH (1)
(a)For coconut coir
31.015.023.0
3835.0
2 ..9494.2 Myield REB
STH (2)
(b) For rice husk :
1782.009.01153.0
545.0
2 ..3989.1 Myield RE
B
STH (3)
(d) For wood chips
103.0222.0035.0
76.0
2 ..3427.0 Myield REB
S
TH (4)
(e)For rice straw
172.0197.0239.0
108.1
2 ..0359.0 Myield RE
B
STH (5)
(f) For saw dust
1887.02662.0211.0
237.1
2 ..0179.0 Myield REB
S
TH (6)
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Table-6: Heating values and flow rates of product gas
Sl. No. Biomass sample HHV,
MJ/kg
Avg. gas production
rate, m3/kg
NHV, Kcal/m3
1 Rice husk 16.2 1.30 2365
2 Rice straw 16.78 1.28 2340
3 Saw dust 16.2 1.12 25864 Wood chips 15.6 1.15 2462
5 Sugarcane bagasse 20 1.4 2650
6 Coconut coir 19 1.45 2317
Fig.-4: Correlation plot for Hydrogen yield against the system parameters [5]
Fig. - 5: Comparison between experimental and calculated values of Hydrogen yield
y = 1.4906x1.378
25
27
29
31
33
35
37
39
41
43
8 8.5 9 9.5 10 10.5 11 11.5
ExperimentalH2-Yield,%
T0.309 (ER)-0.284 (S/B)0.05(Rhom)-0.144
25
27
29
31
33
35
37
39
41
43
25 30 35 40 45
H2-Yield_
Calculated
H2-Yield_Experimental
Calculated Values
experimental Values
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Table-7: Efficiency of the gasifier with different types of biomass samples
Sl.
No.
Biomass sample Carbon
conversion
efficiency, %
Thermal
conversion
efficiency, %
Gasifier
efficiency, %
Deviation,
%
1 Rice husk 93.36 79.71 79.50 -0.264
2 Rice straw 96.88 74.97 76.51 2.013
3 Saw dust 77.96 75.09 77.96 3.681
4 Wood chips 71.24 76.22 78.02 2.307
5 Sugarcane 86.41 77.91 75.22 -3.576
6 Coconut coir 71.01 74.26 74.66 0.536
The amount of hydrogen produced, carbon conversion efficiency and cold gas efficiency, amount
of flue gas produced and net energy produced by gasification of different biomass samples are
listed in the Table-8.
Table-8: Energy content obtained from different biomass samples through gasification
Biomass sample Hydrogen
produced,
kg/kg of fuel
Carbon
Conversion
efficiency,%
Cold gas
Efficiency,
%
Fluegas produced,
m3/hr for 10kg/hr
feed rate
Net Energy
Produced in
kWhr
Rice husk 0.073874 93.13 82.08 11 5. 37
Rice straw 0.060610 95.00 83.05 10 4.32
Saw dust 0.063914 77.76 88.32 11 5.08
Wood chips 0.058675 70.42 85.80 10 4.25
Sugarcane bagasse 0.056000 89.34 80.65 10 3.96
Coconut coir 0.056682 82.30 75.68 10 4.13
CHAPTER-5: CFD SIMULATION
CFD simulation has been carried out for the selected biomass samples with ANSYS FLUENT -
15 for bed hydrodynamics and bed pressure drop along with the temperature distribution within
the Fluidized Bed Gasifier. Both 2D and 3D simulations are studied. Sample plots are shown for
one sample.
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(a)Hydrodynamics with respect to volume fraction
Fig.6.1- contour plot of volume fraction against time for saw dust at air velocity of 0.9m/s for
initial static bed height of 0.1m.
The above figure shows the contours of volume fractions of saw dust obtained at air velocity of
0.9m/s for initial static bed height 0.1m in 2-D fluidized bed after the quasi steady state is
achieved. The contour for air illustrates that volume fraction of the gas is less in fluidized section
than the solid particles.
Fig.6.2- contour plot of volume fraction against time for saw dust at air velocity of 0.9m/s for
initial static bed height of 0.1m.
Fig.6.3- contour plot of volume fraction against time for Saw dust at air velocity of 0.9m/s for
initial static bed height of 0.1m at 3 D modelling.
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(b) Bed pressure drop
The axial pressure drop in a fluidized bed varies from higher value at the bottom of the bed to
zero value at the top of the column. The bed pressure drop can be determined from the difference
of pressure at the inlet and outlet. Fig.2.2 shows the contours of static gauge pressure. It is
evident from the figure that the pressure is higher in the inlet and gradually decreases and
became zero at the outlet.
Fig.7.1: 2D contour of bed pressure drop against air velocity for the fluidized bed for coconut-
coir.
Fig.7.2: contour of bed pressure drop against air velocity for the fluidized bed for 3D Modelling.
Fig.7.3: Graph of bed pressure drop against position for the fluidized bed for coconut-coir.
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(c) Thermal Flow Behavior
Fig.8.1 2D-Temperature profile at different time intervals inside the fluidized bed at temperature-
1273 K for coconut-coir at air velocity 0.9m/s.
Fig.8.2 -Temperature profile at different time intervals inside the fluidized bed at temperature-
1273 K for air at air velocity 0.9m/s 3D Modelling.
Fig.8.3 Graph of Temperature profile at different position inside the fluidized bed at
temperature- 1273 K for Coconut co
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CHAPTER-6: CONCLUSION
From the calculations it is seen that net energy produced per hour for rice husk and saw dust are
slightly more than other biomass samples. However all these biomass samples can be utilized to
meet the energy demand. In general 20% of stoichiometric air is required for gasification which
gives around 75% gasification of efficiency. The increase in stoichiometric air percentage
increases the percentage of efficiency. Varying the types of wood also affects the percentage of
efficiency. Therefore by varying the percentage of stoichiometric air and wood the performance
of gasifier can be studied and thus the gasification efficiency can be optimized. For rice straw,
wood chips and coconut coir the calculated energy is found to be more than 4kW Biomass
gasification offers the most attractive alternative energy system. Biomass gasification offers the
most attractive alternative energy system. CFD simulations are also found to validate the gasifier
design and experimental data implying that the present gasification unit can be scaled up to the
industrial scale using simulation results only.
NOMENCLATURE
T=Temperature (0 K)
S/B = Steam to Biomass Ratio.
E.R. = Equivalence Ratio.
M = Density of Bed Materials (Kg/m3)
REFERENCES
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Group, New York, Year of Publication (2006).
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(2009).
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gasifier. Biomass; 18, 12751. (1989)
4. Warnecke R., Gasification of Fixed Bed and Fluidized Bed Gasifier, Biomass and Bio
Energy, 18, 489-497, (2000).
5.
SahooA.and D. K. Ram, Gasifier performance and energy analysis for fluidized bedgasification of sugarcane bagasse Energy 90 (2015) 1420-1425.
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7. Fletcher, D. F., Haynes, B. S., Christo, F. C., Joseph, S. D., A CFD based combustion
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Publications
1.
Abanti Sahooand Deo Karan Ram. Gasifier performance and energy analysis for
fluidized bed gasification of sugarcane bagasse Energy 90 (2015) 1420 -1425.
2. Ram, D.K.-The Determination of Minimum Bubbling Velocity, Minimum Fluidization
Velocity and Fluidization Index of Fine Powders (Hematite) using Gas-Solid Tapered
Beds International Journal of Science and Research (IJSR), India Online ISSN: 2319-
7064. Volume 2 Issue 2, February 2013, page -287- 293.
3. Abanti Sahoo and Deo Karan Ram Coconut Coir Gasification in A Fluidized Bed
Gasifier: Energy Analysis. Communicated to Renewable Energy Journal, Ms. Ref.
No.: RENE-D-15-02168, Communicated, Under Review.
http://www.sciencedirect.com/science/article/pii/S0960852402000792http://www.sciencedirect.com/science/article/pii/S0960852402000792http://www.sciencedirect.com/science/article/pii/S0960852402000792http://www.sciencedirect.com/science/article/pii/S0960852402000792http://www.sciencedirect.com/science/article/pii/S0960852402000792http://www.sciencedirect.com/science/article/pii/S0960852402000792