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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
Department of Chemical Engineering
National Institute of Technology
Rourkela-769008
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There is 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. Finally
overview 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 fundamental
understanding 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: EXPERIMENTAL ASPECTS
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 thebiomass 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 size (mm) Apparent density (kg/m3) Porosity Sphericity
Sand 0.38 2650 0.44 0.77Dolomite 0.55 2800 0.36 0.79
Redmud 0.22 1290 0.42 0.72
Rice husk 0.53 426 0.81 0.37
Rice straw 5.0 153 0.46 0.56
Saw dust 0.81 244 0.7 0.45
Wood chips 5.0 481 0.47 0.1
Coconut coir 10.0 352 0.96 0.04
Sugarcane bagasse 10.0 120 0.62 0.01
Table-2 Ultimate Analysis of selected biomass samples
Biomass samples Carbon (%) Hydrogen (%) Nitrogen (%) Sulfur (%) Oxygen (%)
Rice husk 38.45 4.96 0.82 0.18 55.59
Rice straw 38.6 4.55 0.47 0.21 56.17
Saw dust 45.78 5.32 0.16 0.07 48.65
Wood chips 46.23 5.7 0.22 0.12 45.2
Sugarcane bagasse 44.60 6.2 0.20 0.50 46.84
Coconut coir 43.76 5.8 0.40 0.22 47.12
Table - 3 Proximate Analysis of selected biomass samples
Sl. No. Biomass samples Moisture content (%) Volatile matter (%) Ash content (%) Fixed carbon (%)
1 Rice husk 7.34 56.37 15.83 20.462 Rice straw 9.38 69.53 3.04 18.05
3 Saw dust 8.8 87.57 1.94 16.45
4 Wood chips 8 74.34 1.8 16.8
5 Sugarcane 5 73.8 1.66 19.54
6 Coconut coir 5.3 76.8 0.9 17.0
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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 temperaturesat 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 analysed 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 Motor3 Screw Feeder
4 Fluidized bedgasifier
5 Continuouscleaning system
6 Bubble cap
7 Orifice meter
8 Valve
9 Cyclone
separator
Fig.-2 : Temperature profile for different zones existing within the gasifier
0.00
200.00
400.00
600.00
800.00
1000.00
0 10 20 30 40 50 60
Temperaturein0C
Time in min
Drying Zone
Pyrolysis Zone
Oxidation Zone
Gasification and
Reduction Zone
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CHAPTER-4: RESULTS AND DISCUSSIONS
(Energy Analysis and Gasifier Performance)
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 CH1.55O1.08
Rice Straw CH1.49O1.19N0.011S0.0021 CH1.49O1.19
Saw Dust CH1.392O0.8N0.0037S0.00057 CH1.39O0.8
Wood chipsCH1.48O0.74N0.0042S0.001 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 saw dust sample. 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 ofproduct 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
efficiency, thermal conversion efficiency and efficiency of the gasifier [1] are calculated for
different biomass samples and listed in Table 7. 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- 5 : Comparison of calculated values of hydrogen yield against the experimental values
Biomass Sample Standard deviation % Mean deviation %
Rice husk 5.84 -0.18Rice straw 0.168 0.01
Saw dust 6.67 -0.13
Wood chips 13.71 -0.82
Sugarcane bagasse 8.98 -0.39
Coconut coir 7.70 0.30
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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 RE
B
STH (2)
(b) For rice husk :
1782.009.0
1153.0
545.0
2 ..3989.1
Myield RE
B
STH (3)
(d) For wood chips
103.0222.0035.0
76.0
2 ..3427.0 Myield RE
B
STH (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 RE
B
STH (6)
Table-6: Heating values and flow rates of product gas
Sl. No. Biomass sample HHV, MJ/kg Avg. gas productionrate, m3/kg
NHV, Kcal/m3of product
gas
1 Rice husk 16.2 1.30 2365
2 Rice straw 16.78 1.28 2340
3 Saw dust 16.2 1.12 2586
4 Wood chips 15.6 1.15 2462
5 Sugarcane bagasse 20 1.4 2650
6 Coconut coir 19 1.45 2317
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Rice Straw Rice Husk
Saw Dust Wood Chips
Sugarcane Bagasse Coconut Coir
Fig.- 3 : Effect of temperature on different components of product gas for different biomass
samples
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Fig.-4 : Correlation plot of Hydrogen yield against the system parameters for saw dust
Fig.- 5 : Comparison between experimental and calculated values of Hydrogen yield for saw dust
Table-7: Efficiency of the gasifier with different types of biomass samples
Sl.
No.
Biomass sample Carbon
conversionefficiency, %
Thermal
conversionefficiency, %
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 bagasse 86.41 77.91 75.22 -3.576
6 Coconut coir 71.01 74.26 74.66 0.536
y = 0.0154x1.0887
R = 0.9113
10
100
100 1000 10000
HydrogenYield,%
T1.15(ER)-0.195(S/B)0.25(Rhom)-0.082
15
20
25
30
35
40
45
50
15 20 25 30 35 40 45
CalculatedHydrogen
Yield,%
Experimental Hydrogen yield%
H2-Cal H2-Exp
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Table-8: Energy content obtained from different biomass samples through gasification
Biomass sample Hydrogenproduced,kg/kg of fuel
CarbonConversionefficiency,%
Cold gasEfficiency,%
Fluegas produced,m
3/hr for 10kg/hr
feed rate
Net EnergyProduced inkWhr
Rice husk 0.073874 93.13 82.08 11 5. 37Rice straw 0.06061 95.0 83.05 10 4.328
Saw dust 0.063914 77.76 88.32 11 5.08
Wood chips 0.058675 70.42 85.8 10 4.25
Sugarcane bagasse 0.056 89.34 80.655 10 3.96
Coconut coir 0.056682 82.3 75.686 10 4.126
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.
(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.
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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.
(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 differenceof 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 andbecame zero at the outlet.
Fig.7.1: 2D contour of bed pressure drop against air velocity for the fluidized bed for coconut-coir.
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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.
(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.
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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
CHAPTER-6 : CONCLUSIONS
From the above 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 theperformance 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.
.
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Biomass gasification offers the most attractive alternative energy system[14]. 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
1. Basu P., Combustion and Gasification in Fluidized beds, CRC Press, Taylor & Francis
Group, New York, Year of Publication (2006).2. Kumar A., Kent E., David, D. Jones. And Milford, A. Hanna. , SteamAir Fluidized
Bed Gasification of Distillers Grains: Effects of Steam to Biomass Ratio, Equivalence
Ratio and Gasification Temperature, Bio resource Technology, 100, 20622068,
(2009).
3. Chern S M, Walawander WP, Fan LT. Mass and energy balance analyses of a Downdraft
gasifier. Biomass; 18:12751. (1989)
4. Warnecke R., Gasification of Fixed Bed and Fluidized Bed Gasifier, Biomass and Bio
Energy, Vol. 18, 489-497, (2000).
5. SahooA.and D. K. Ram, Gasifier performance and energy analysis for fluidized bed
gasification of sugarcane bagasse Energy 90 (2015) 1420-1425.
6. ANSYS FLUENT 15.0,Theory Guide, (2014).
7. Dimitrios S., Investigation of Biomass Gasification Conditions for Energy Production
General Secretariat for Research & Technology of Greece, Joint Research &Technology
Programmes; Greece-Slovakia, Final Report, (2001).
8.
Fletcher, D. F., Haynes, B. S., Christo, F. C., Joseph, S. D., A CFD based combustion
model of an entrained flow biomass gasifier, Applied Mathematical Modeling, 24(3),
165- 182, (2000).
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9. J.R Rao, T Viraraghavan Biosorption of phenol from an aqueous solution byAspergillus
nigerbiomass Bioresource Technology, Volume 85, Issue 2, Pages 165-171 ,
November (2002)
10.K. Papadikis and S. GU, CFD modeling of the fast pyrolysis of biomass in fluidized bed
reactors, Part A: Eulerian computation of momentum transport in bubbling fluidized
beds, Chemical Engineering Science, 63, 4218 - 4227, (2008)
11.Patra, C, CFD Modelling for Fluidized Bed Biomass Gasification. M.Tech.(Chemical
Engineering) E-Thesis NIT Rourkela 2014
12.S. Gerber et al., An Eulerian modelling approach of wood gasification in a bubbling
fluidized bed, Fuel 89, 29032917, (2010).
13.Wang Y., Yan L., CFD studies on biomass thermo chemical conversion, Int J Mol
Sci, 9, 11081130, (2008).
14.Cheng, Jay, Biomass to Renewable Energy Processes, CRC Press, Taylor and Francis
Group, New York. ISBN 978-1-4200-9517-3, 2010.
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