Biomass gasification: Improving yield and quality of ... Gasification-Dr. Kumar...Biomass...

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Biomass gasification: Improving yield and quality of producer gas Ajay Kumar Assistant Professor Biosystems and Agricultural Engineering Department Biobased Products and Energy Center (BioPEC) Oklahoma State University Sep 15, 2010 1

Transcript of Biomass gasification: Improving yield and quality of ... Gasification-Dr. Kumar...Biomass...

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Biomass gasification: Improving yield and quality of producer gas

Ajay KumarAssistant Professor

Biosystems and Agricultural Engineering DepartmentBiobased Products and Energy Center (BioPEC)

Oklahoma State University

Sep 15, 20101

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Thermochemical conversion

Energy conversion pathways

Source Conversion techniques

Products orintermediate

products

agricultural residues,perennial crops,forestry residue,animal waste,municipal wastes, etc.

Biochemical conversion Ethanol

Synthesis gas (syngas)/ producer gas

(38-50% cellulose, 25-32% hemicellulose,

15-25% lignin)

lignin & hemicellulose

Biomass

2

Bio-oil

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Thermochemical Conversions

Pyrolysis

Gasification Gas

Char

Ash

Bio-oilBiomass

Air

Steam

Combustion Heat

Tar

Byproduct 3

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Gasification process

• Required: high temperature & oxidizing agent

• biomass + air + H2O C (char)+ CH4+ CO + H2 + + CO2 + N2 + H2O (unreacted steam) + ash + tar

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Biomass

Air

Gas

Char

Ash

Tar

Steam

Sorghum Switchgrass

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Gasification process - factorsHeating,

Chemical reactions,

catalysis

•Particle size•Bulk density•Proximate analysis•Elemental analysis•Energy content•Cellulose, hemicelluloses &Lignin contents

•Syngas composition•Syngas energy•Carbon conversion efficiency•Energy conversion efficiency•Overall energy efficiency•Amount of tar•Amount of char

•Biomass flow rate•Temperature profile•Flow rates of oxidizing agents (equivalence ratio (ER), steam to biomass ratio, (SBR))•Amount and type of catalyst

Gasification

Biomass properties

Operating conditions

Product properties

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Gasification: technical challenges

• Experimental challenge– Understand and predict the effects of gasification conditions and biomass

properties on yield and composition of product

– Reduce amounts of tar and impurities in the producer gas• Optimize gasification operating conditions & gasifier design

• Improve cold gas cleaning technique

• Improve hot gas cleaning technique

– Increase percentage compositions of CO and H2

– Increase net energy efficiency

– Obtain data for developing gasification reaction kinetics for a wide variety of feedstock

• Computational challenge– Develop gasification reaction kinetics

– Incorporate reaction kinetics into gasification model to reliably predict gas yield and composition 6

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Ongoing projects

1. Design, development and performance evaluation of lab-scale fluidized-bed gasifier (FBG)

2. Evaluate effectiveness of commercial reforming catalysts to crack tar

3. Investigate gasification reaction kinetics using TG-FTIR

4. Gasification of a wide variety of biomass in a downdraft gasifier

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1. Design, development and performance evaluation of lab-scale fluidized-bed gasifier (FBG)

•Biomass feedrate : 3-6 kg/h

Objectives

• Design a new lab-scale FBG with instruments to control and monitor process conditions

• Evaluate performance of the gasifier

• Improve the system components so that it can run continuously for longer duration8

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Gasifier components

Factor considered while designing

Biomass feed rate Physical characteristics of biomass Test duration Equivalence ratio Superficial velocity

Biomass hopper Screw feederGasifier

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Fluidized bed

reactor

HopperCyclone

Separators

Orificeplate

Fig. Fluidized bed gasifier set up 10

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Gasifier temperature profile with time

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Effect of equivalence ratio (ER) on gasifier temperature

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775

800

825

850

875

900

925

0.15 0.25 0.35 0.45 0.55

Tem

pera

ture

(C

)

Equivalence ratio ( Ø )

Avg. reactor bed temperature

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4.0

4.5

5.0

5.5

6.0

6.5

0.00

1.00

2.00

3.00

4.00

0.15 0.25 0.35 0.45 0.55

HH

V (

MJ/

Nm

3 )

Dry

gas

yie

ld

(Nm

3 /Kg

of b

iom

ass)

Equivalence ratio (Ø)

Dry gas yield

HHV of dry gas

Effect of ER on yield and higher heating value (HHV) of producer gas

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0

10

20

30

40

50

60

0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

% v

/v

Equivalence ratio (Ø)

CO

H2

CH4

CO2

N2

C2H2

C2H4

C2H6

Effect of ER on producer gas composition

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Effect of ER on gasifier efficiencies

30

40

50

60

70

80

90

100

0.15 0.25 0.35 0.45 0.55

Effi

cien

cies

(%)

Equivalence ratio (Ø)

Carbon conversion efficiency

Hot gas efficiency

Cold gas efficiency

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Conclusions:

A lab-scale fluidized bed gasifier was designed and developed. The gasifier performance was evaluated for switchgrass as a feedstock

by varying equivalence ratio (Ø) from 0.18 to 0.51 At equivalence ratio of 0.32,

The highest gas heating value was 6.17 MJ/Nm3 (db) , The maximum cold gas efficiency was 80% and The maximum hot gas efficiency was 84%.

The maximum carbon conversion efficiency of 95.95% was observed at Ø value of 0.51.

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Near pilot-scale FBG

•Biomass feedrate: 15-30 kg/h

•Fluidized-bed Gasifier (FBG)

•Gas scrubbing system

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2. Evaluate effectiveness of commercial reforming catalysts to crack tar

• Two stage evaluation– 1st stage: Test catalysts using toluene as a model

tar

– 2nd Stage: Test catalysts using real producer gas with tar

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1st Stage: Evaluation of catalysts to crack toluene as a model tar

Objectives• Evaluate selected commercially available catalysts (Cerium-Zirconium-Platinum, Hifuel R110

and Reformax 250) for their effectiveness in cracking toluene as a model tar• Study effects of reaction conditions such as temperature, catalyst particle size, and steam to

carbon ratio on tar degradation

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Effect of space time (catalyst weight)

Figure Captions :a) Cerium Zirconium Platinum

catalyst powder.

b) Hifuel R110 catalyst powder.

c) Reformax 250 catalyst powder.

50

60

70

80

90

100

110

0 100 200 300

% T

olue

ne C

onve

rsio

n

Time on stream (minutes) 0.25g 0.15g

a)

50

60

70

80

90

100

110

0 50 100 150 200 250 300

% T

olue

ne C

onve

rsio

n

Time on stream (minutes) 0.25g 0.15g

b)

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60

70

80

90

100

110

0 50 100 150 200 250 300

% T

olue

ne C

onve

rsio

n

Time on stream (minutes) 0.25g 0.15g

c)

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Effect of temperature on Cerium-Zirconium-Platinum catalyst

Weight of catalyst tested-0.15g, Steam to Carbon ratio-2.

0

20

40

60

80

100

120

0 50 100 150 200 250 300

% T

olue

ne C

onve

rsio

n

Time on stream (minutes)

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Other Gas Compositions

(Experimental conditions :T=700°C, S/C ratio=2, weight of catalyst =0.25g.)

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 50 100 150 200 250 300Time on stream (minutes)

H2

Conc

entr

atio

n (g

L-1

)

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250 300

CO2

Conc

entr

atio

n (g

L-1

)

Time on stream (minutes)

0

0.02

0.04

0.06

0.08

0.1

0.12

0 50 100 150 200 250 300

CO C

once

ntra

tion

(g L

-1)

Time on stream (minutes)

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Other Gas Compositions (Contd.)

(Experimental conditions :T=700°C, S/C ratio=2,Weight of catalyst =0.25g.)

0

0.005

0.01

0.015

0.02

0.025

0 50 100 150 200 250 300

CH4

Conc

entr

atio

n (g

L-1

)

Time on stream (minutes)

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Conclusions from Bench Scale System

• Cerium Zirconium Platinum , Hifuel R110 and Reformax 250- successfully reduced amount of toluene

• Higher catalyst weight (Space time)- Higher toluene conversion.

• Higher catalyst bed temperature - Higher the conversion .

• Gas Compositions:

For all three catalysts increase in H2, CO2, and decrease in CO and CH4 concentration.

• Overall reaction:

C7H8+H20+H2+CO2+CO+CH4+N2= C7H8+ H20+ H2+ CO2+ CO+ CH4+N2 + C2-C6 HC

• Catalyst Deactivation

Cerium Zirconium Platinum > Hifuel R110 > Reformax 250. Powder > Pellets.

For Cerium Zirconium Platinum catalyst - 600 > 800°C.

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2nd Stage: New catalytic reactor for hot gas cleaning

Objectives

• Design a catalytic reactor to evaluate catalysts in cracking real tar

• Study effects of operating condition of catalytic cracker (air and steam flowrate, temperature, residence time) and various steam reforming catalysts on tar level and gas composition

To FlareAir

H2O (HPLC)

Syngas w/ tar

Gas sampling GuardBed

Tar sampling

Catalytic Bed

Heated gas line

Stop valve

Mass flow controller

To Flare

Gas sampling

Tar sampling

DPI

TITI

TI

TI

TI

D

TI

TI

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3. Investigate gasification reaction kinetics using TG-FTIR

Objectives• Investigate the effects of oxidizing atmosphere, temperature and heating rate on

rate of weight loss, gas and tar composition• Derive volatization kinetics of various feedstocks• Incorporate the kinetic parameter into gasification model to predict producer gas

yield and composition

TGA

GC

FTIR

GC-MS

BiomassEvolved gas

Ash and partial char

Nitrogen or air

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800 900

Temperature (°C)

Res

idua

l wei

ght (

%)

(TG

A)

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

DTG

(%/°

C)TGA (%) DTG (%/°C)

ash +

fixed carbon

Stage IDehydration

volatiles

Stage IIActive pyrolysis

Stage IIIPassive pyrolysis

Kumar et al., 2008. Biomass and Bioenergy.

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Equipment

Coupled TGA-FTIR set-up•Studying reaction kinetics of gasification•Identifying compounds at various reaction conditions Mass Spec with precision sampling system

•Online measurement of gas composition

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TGA profiles of switchgrass for different heating rates in nitrogen atmosphere

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Time (minutes)Time (minutes)

20.020.015.015.0

10.010.05.05.0

Absorbance (Abs)Absorbance (Abs)

0.300.30

0.200.20

0.100.10

-0.00-0.00

Wavenumbers (cm-1)Wavenumbers (cm-1)40004000

30003000

2000200010001000

Online FTIR spectra with varying time (and temperature)

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Results and discussion

Figure. TGA profiles of switchgrass at different heating rates in air atmosphere 30

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Results and discussion

Figure. DTG profiles of switchgrass at different heating rates in nitrogen atmosphere 31

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Results and discussion

Heating rate

(oc/min)

ActivationEnergy (E) in

KJ.mol-1

Frequency factor

(A)

Order of the

reaction (n)

R2

10 99.15 1.91×108 0.39 0.99

30 92.90 1.11×108 0.38 0.99

50 87.85 0.5×108 0.49 0.99

Heating rate

(oc/min)

Activation energy (E )in

KJ.mol-1

Frequency factor

(A)

Order of the

reaction (n)

R2

10 73.12 3.1×105 0.67 0.96

30 68.516 3.09×105 0.74 0.96

50 66.015 2.6×105 0.77 0.96

Table 1. Kinetic parameters during second stage decomposition in air atmosphere

Table 2. Kinetic parameters during second stage decomposition in nitrogen atmosphere

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Results and discussion

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Figure. TGA plot of switchgrass pyrolysis in nitrogen atmosphere

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Weight loss with temperature

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Rate of weight loss with temperature

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Products with increase in temperature (detected by FTIR)

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0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

150 250 350 450 550 650 750 850 950

Inte

nsity

Temperature ( C)

CO2 variationCO variationwater variationC=O variationCH4 variation

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Observations

• Switchgrass decomposition takes place in three stages

• The significant weight loss was observed corresponding to hemicellulose and cellulose decompositions

• Lignin decomposes slowly over a wide range of temperature

• CO2,CO, water, formaldehyde, methane were observed by FTIR as major products during switchgrass pyrolysis

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4. Gasification of a wide variety of biomass in a downdraft gasifier

Air lock

Biomass hopper

Burner

PropaneAir

Ash

To gas cleanup system

Biomass

Tar & particulate measurement system

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Temperature profilefor switchgrass gasification

0

200

400

600

800

1000

1200

0 50 100 150 200

Time from start, minutes

Tem

pera

ture

, C

Tar Cracking,CG1

Below Grate

Flame

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Gas compositionSwitchgrass gasification

0

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20

30

40

50

60

0 50 100 150 200 250 300 350

Time from start, min

% V

olum

e

COH2CH4CO2N2C2H2C2H4C2H6

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Energy efficiencies

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10

20

30

40

50

60

70

80

90

450 500 550 600 650 700

Specific air input rate. kg/h-sq. m

Hot

gas

eff

icie

ncy,

%Wood Pellets

Switchgrass

Sweet Sorghum

Forage Sorghum W2

Wood Shavings

Corn fermentation waste

0

10

20

30

40

50

60

70

80

450 500 550 600 650 700

Specific air input rate. kg/h-sq. m

Cold

gas

eff

icie

ncy,

%

Wood Pellets

Switchgrass

Sweet Sorghum

Forage Sorghum W2

Wood Shavings

Corn fermentation waste

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Personnel and Financial SupportPIs:• Ajay Kumar• Krushna Patil• Danielle Bellmer• Raymond HuhnkeGraduate students/Research engineer:

– Ashokkumar Sharma – Design and study of lab-scale FBG– Prakash Bhoi – Study of downdraft gasification– Vamsee Pasangulapati – Thermochemical characterization of biomass– Akshata Modinoor & Pushpak Bhandari– Design and study of a new catalytic tar cracker– Luz Martin & Akshata Modinoor– Characterization and evaluation of selected catalysts for tar

cracking• Financial Support provided by:

– Oklahoma State Regents for Higher Education– NSF OK-EPSCoR– Oklahoma Bioenergy Center– USDA Special Grant– Director of the Oklahoma Agricultural Experiment Station

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Thank you

Questions?

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