final synopsis report-d. k. ram

7/25/2019 Final Synopsis Report-D. K. Ram

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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


B

STH (3)

(d) For wood chips

103.0222.0035.0

76.0


S

TH (4)

(e)For rice straw

172.0197.0239.0

108.1


B

STH (5)

(f) For saw dust

1887.02662.0211.0

237.1


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

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, 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.

6. 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).


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7. 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).

8. 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)

9. 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)

10.Patra, C, CFD Modelling for Fluidized Bed Biomass Gasification. M.Tech.(Chemical

Engineering) E-Thesis NIT Rourkela 2014

11.S. Gerber et al., An Eulerian modelling approach of wood gasification in a bubbling

fluidized bed, Fuel 89, 29032917, (2010).

12.Wang Y., Yan L., CFD studies on biomass thermo chemical conversion, Int J Mol

Sci, 9, 11081130, (2008).

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

final synopsis report-d. k. ram

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