effect of pressure and heating rates on biomass pyrolysis ... agrawal.pdf · effect of pressure and...

Effect of Pressure and Heating Rates on Biomass

Pyrolysis and Gasification

Pradeep K. Agrawal

School of Chemical and Biomolecular Engineering

Georgia Institute of Technology

June 15, 2012

Auburn University

Workshop on Lignocellulosic Biofuels Using

Thermochemical Conversion

Strategies for production of fuels from lignocellulosic biomass

Cellulosic

Biomass

Gasification

Hydrolysis

Pyrolysis or Liq.

SynGas (CO + H2)

Fischer-Tropsch

Methanol, Water-Gas Shift

Aqueous

sugar

Fermentation, Dehydration

Aqueous-Phase Processing

Lignin Lignin Upgrading

Bio-oils Hydrodeoxygenation

Zeolite Upgrading

Alkanes, Methanol

Liquid Fuels

Hydrogen

Ethanol

Aromatic Hydrocarbons

Liquid Alkanes or Hydrogen

Liquid Fuels

Liquid Fuels

Huber et al., Catal. Today 2006, 111, 119. Characteristics of Gasification

Pyrolysis and Char gasification proceed sequentially

Pyrolysis pressure and temperature affect char reactivity

Char reactivity depends on temperature, gas composition,

porosity, ash contents, and transport effects

Langmuir-Hinshelwood kinetic models suggested in the

literature for biomass/char gasification

High pressure gasification has particular significance

Sutton et al., Fuel Processing Technology, 73

(2001) 155-73

Di Blasi,, Progress in Energy & Combustion

Science 35 (2009) 121-140

Cetin, Gupta, and Moghtaderi, Fuel, 84 (2005)

1328-1334

Impact of Pressure on Gasification

• Carbon gasification rate slow step in conversion of biomass to syngas (CO + H2) C + H2O CO + H2 C + CO2 2 CO • Rate catalyzed by alkali metals • Langmuir-Hinshelwood type kinetics • CO and H2 inhibit gasification

• Devolatilization impacts amount of carbon to be gasified and gas composition, including tar and hydrocarbon formation

4

Alkali Catalyzed Carbon Gasification

* + CO2 <-> *(CO2) *(CO2) <-> *(O) + CO * + H2O <-> *(O) + H2

*(O) + C * + C(O) C(O) CO

COHCO

COOH

Ccpbpap

pkpkr

22

22

121

CO

CO

CO bPaP

P

kr

2

1

OH

H

Pa

P

kr

2

2

'1

'

Need to Obtain Rate Data Including Impacts of All

Relevant Species

Biomass Gasification Background

• Biomass gasification is a combination of two series processes – pyrolysis (devolatilization) and char gasification. Char gasification activity is affected by the pyrolysis conditions (heating rate, temperature, and pressure), ash content and composition, and gasification conditions.

• The challenge is to develop experimental protocols that would allow collecting experimental data at conditions that most likely mimic the heating rate, temperature, pressure, residence time, and transport effects likely to be encountered in a commercial gasifier.

Goals/Objectives

• Quantitative understanding of the gasification and pyrolysis along with an improved understanding of the catalytic effect of inorganics present in biomass

• Role of particle morphology in mass transport effects as well as the char reactivity

• Identifying process conditions where synergistic effects of biomass-coal blending are observed. This will include effect of particle size, residence time and proximity of the two feed types

• Building mathematical models based on science and engineering principles that would predict the biomass gasification rate at a given pressure, temperature and feed composition.

• Quantify the effect of pressure and temperature on the formation of tars and light

hydrocarbons.

Innovation for Our Energy Future

Methods

• Experiments in two complementary reactors: • Pressurized entrained-flow reactor (PEFR) at Georgia Tech • Pressurized thermogravimetric apparatus (PTGA) at NREL

• Differences in heating rate, reaction time • Mass/heat transfer limitations

• Three biomass types:

– Loblolly pine – Switch grass – Corn stover

PEFR Vs. PTGA

REACTOR PEFR PTGA

Pressure Up to 80 bar Up to 100 bar

Temperature Up to 1500 C Up to 1200 C

Mode Co-current flow Semi-Batch

Sample size ~1 g/min 10-100 mg

Heating Rate ~10,000 C/s ~10 C/min

Residence time Up to 10 s Up to hours

Kinetic Control

Limit

>1000°C ~800°C

Gas analysis FTIR, GC MS, FTIR

Elemental Composition of Biomass Feed

Element Loblolly

Pine

Switchgrass Cornstover

C 52.4% 48.3% 43.7%

H 6.3% 6.1% 5.9%

N 0.07% 0.36% 0.59%

O 40.9% 44.7% 45.3%

Ash 0.3% 2.2% 6.1%

Volatile Matter 79.1% 77.6% 74.4%

Fixed Carbon 12.8% 12.4% 12.6%

Elemental Analysis of Feed Biomass (ICP)

Element Loblolly Pine Switchgrass Cornstover

Ca 490 1790 1900

Fe 38 20 437

K 358 4980 8675

Mg 203 1540 1325

Approach

• Investigate high temperature pyrolysis of biomass - effect of pressure and temperature on char morphology and reactivity towards gasification

• Gasification kinetics of chars generated from pyrolysis (individual chars, blend pyrolysis chars, and blending of chars generated individually)

• Catalytic effect of inorganics (ash) on char gasification

• Transport effects and mathematical models

Pressurized Entrained Flow Reactor

Pressurized

Entrained

Flow

Reactor

Pressurized Thermobalance (PTGA)

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350

Time, min

Tem

pe

ratu

re, °

C

0

10

20

30

40

50

60

70

80

90

100

Mas

s, %

Pine, 30 bar, 33% CO2

Effect of Pressure and Heating Rate on Loss of Mass

in PTGA Pyrolysis

-5

0

5

10

0 200 400 600 800

-dm

/dt,

mg

/min

Temperature, °C

Loblolly Pine, 5C/min

5 bar 30 bar

-10

0

10

20

30

40

50

0 200 400 600 800-dm

,dt,

g/m

in

Temperature, °C

Loblolly Pine, 25C/min

5 bar

30 bar

Effect of Pressure on Residual Char

0%

10%

20%

30%

0 10 20 30 40

Ch

ar

Yie

ld

Pressure, bar

Loblolly Pine, Final T 900C

FTIR vs. Mass Spectrometer in PTGA

0.E+00

2.E-10

4.E-10

6.E-10

8.E-10

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200

peak h

eig

ht

ab

so

rba

nc

e

time (mins)

CO2 MS (44) vs. FTIR (2319 cm-1)

0.E+00

2.E-12

4.E-12

6.E-12

8.E-12

1.E-11

1 11 21 31 41 51 61 71 81 91

Effect of Pressure on Gas Species Evolution

0.0E+00

1.0E-09

2.0E-09

3.0E-09

4.0E-09

0 20 40

Pressure, bar

H2 (2)CH4 (16)CO (28)CO2 (44)

0.0E+00

1.0E-10

2.0E-10

0 10 20 30 40Pressure, bar

C2H2 (26)

C2H3 (27)

Benzene (78)

0.0E+00

1.0E-10

2.0E-10

3.0E-10

0 20 40Pressure, bar

C2H5 (29)

C2H6 (30)

0.0E+00

5.0E-12

1.0E-11

1.5E-11

2.0E-11

0 20 40

Pressure, bar

Acetic acid/Formaldehyde(60)

Effect of Pressure on Gas Species Evolution

-1.E-11

0.E+00

1.E-11

2.E-11

3.E-11

4.E-11

5.E-11

0 50 100 150

Time, min

Major Gas Species (5 bar)

CO2 (44)

CO (28)

CH4 (16)

H2 (2)

Pine, 10C/min

-1.E-11

0.E+00

1.E-11

2.E-11

3.E-11

4.E-11

5.E-11

6.E-11

7.E-11

0 50 100 150

Time, min

Major Gas Species (30 bar)

CO2 (44) CO (28)

CH4 (16)

H2 (2)

Pine, 10C/min

-1.E-12

0.E+00

1.E-12

2.E-12

3.E-12

4.E-12

5.E-12

6.E-12

0 50 100 150

Time, min

Light Hydrocarbons (5 bar)

C2H5 (29)

C2H2 (26)

C2H3 (27)

C2H3 (30)

-1.E-12

0.E+00

1.E-12

2.E-12

3.E-12

4.E-12

5.E-12

6.E-12

0 50 100 150

Time, min

Light Hydrocarbons (30 bar)

C2H5 (29)

C2H2 (26)

C2H3 (27) C2H3 (30)

Effect of Pressure on Minor Gaseous Products

-5.0E-13

0.0E+00

5.0E-13

1.0E-12

1.5E-12

2.0E-12

2.5E-12

0 50 100 150 200

Time, min

Benzene, Oxygenated Species at 30 bar

Benzene (78) Acetic acid/ Hydroxyacet- aldehyde(60) Furan (68)

-2.0E-13

-1.0E-15

2.0E-13

4.0E-13

6.0E-13

8.0E-13

1.0E-12

1.2E-12

0 50 100 150

Time, min

Benzene, Oxygenated Species at 5 bar

Benzene (78) Acetic acid/ Hydroxyacetaldehyde2(60)

Furan (68)

-5.00E-13

5.00E-13

1.50E-12

2.50E-12

3.50E-12

4.50E-12

0 50 100 150 200

Time, min

Benzene, Methanol at 5 bar

Benzene (78)

CH3O- (31)

-5.00E-13

5.00E-13

1.50E-12

2.50E-12

3.50E-12

0 50 100 150 200

Time, min

Benzene, Methanol at 30 bar

Benzene (78)

CH3O- (31)

Morphology Studies

Effect of Temperature at Constant pressure

Char generated in LEFR

1000 C 800 C 600 C

Effect on Pressure at constant temperature

600 C

5 bar 1 bar 10 bar

800 C

1 bar 10 bar 5 bar


1000 C

1 bar 5 bar 10 bar 1 bar


Gas-Filled Pockets Formed at High Pressures

Pine Char Formed at 15 bars and 1000 C

Gas Composition during Pyrolysis

Species

Gas Composition (mole%) at 5 bars

600 oC 800 oC 1000 oC

CO 45.2 41.2 61.0

CO2 16.7 16.9 12.1

H2 8.9 24.5 21.9

CH4 21.1 16.6 4.75

C2H6 1.42

C2H4 5.70 0.52 0.10

C2H2 0.09 0.22 0.15

C3H8 0.03

C3H6 0.66

C4H10

C4H8

C4H6 0.14

Gas Composition during Pyrolysis

Species Gas Composition (mole%) at 15 bars

600 oC 800 oC 1000 oC

CO 39.4 37.5 65.3

CO2 17.7 17.7 5.9

H2 17.4 29.0 26.0

CH4 21.7 15.6 2.84

C2H6 0.1

C2H4 3.40

C2H2 0.20 0.16

C3H8

C3H6

C4H10

C4H8

C4H6 0.03

BET Surface Area of Switchgrass Chars generated in PEFR Reference: Switchgrass feed BET area 0.8 m2/gm

600 oC

m2/gm

800 oC

m2/gm

1000 oC

m2/gm

1 bar 1.8 2.9 75

5 bars 3.0 187 321

10 bars 3.3 175 278

15 bars 5.2 108 198

Georgia Institute of Technology Innovation for Our Energy Future

Mass Transfer Limitations in Thermobalances

Mass transfer: - from bulk gas to surface of sample holder - from surface of sample to bottom of sample -from surface of particle to center of particle


Impact of Heating Rate

A PEFR 600C 5 bar

B PEFR 1000C 5 bar C PEFR 600C 15 bar D PTGA 900C 5 bar

Chars prepared in PEFR (high heating rate) and PTGA (low heating rate) gasified in PTGA

0%

20%

40%

60%

80%

100%

130 140 150 160 170 180 190 200

Mas

s

Time (min)

A B

D C

900C, 5 bar, CO2


Testing for Mass Transfer Limitations

0%

20%

40%

60%

80%

100%

125 130 135 140 145 150

Time (min)

Ma

ss

25 mg

51 mg

1000°C

0%

20%

40%

60%

80%

100%

200 220 240 260 280

Time (min)

Ma

ss

29 mg

54 mg

900°C

0%

20%

40%

60%

80%

100%

110 130 150 170 190 210

Time (min)

Ma

ss

25 mg

48 mg

850°C

0%

20%

40%

60%

80%

100%

100 150 200 250 300 350 400

Time (min)

Ma

ss

25 mg

50 mg

800°C


Loblolly Pine Gasification in PEFR

Gasification Conditions: 10% CO2, 2% H2O, 0.3% H2, 1.72% CO, 86% N2

900 oC particle size 180-250 µm

Residence Time Percent carbon remaining in the

char Residue Pressure 5 bars Pressure 15 bars

3 sec 50.4 % 52.9 %

6 sec 40.0 %

10 sec 24.5 % 32.0 %


Cornstover Gasification in PEFR

Gasification Conditions: 10% CO2, 2% H2O, 0.3% H2, 1.72% CO, 86% N2

900 oC particle size 106-180 µm

Residence Time Percent carbon remaining in the

char Residue Pressure 5 bars Pressure 15 bars

3 sec 21.5% 29.7%

6 sec 20.3% 24.0%

10 sec 13.2% 18.6%


Conclusions

Pyrolysis pressure and temperature greatly affect char yield and char morphology. High heating rates in PEFR produce char that mimick commercial gasifier operation. PEFR can provide useful kinetic information on biomass conversion, but it will have limitations due to the need to run integral operation. PTGA operation is similar to a semi-batch reactor, which makes it possible to build the kinetic model. Caution is needed to ensure that results are not masked by the transport effects. Both PTGA and PEFR have limitations if used alone. However, when combined together, the two are complementary and would provide a basis for building a reliable mathematical model.

Future Work

• Characterization of Chars – ICP EA, Nitrogen physisorption, SEM, NMR (?), FTIR , C,H,N,O Analysis – carbon balance

• Effect of pyrolysis conditions on the formation of tars and light hydrocarbons- tar characterization

• Kinetics of char gasification (L-H models)

• Catalytic role of recycled ash and inorganic species in char gasification

• Mathematical modeling (transport effects)

Acknowledgements

• Kristiina Iisa (NREL) • Carsten Sievers • Scott Sinquefield • Steve Lien • Pranjal Kalita • Gautami Newalkar • Paige Case • Taylor Donnell • Kathryn Black

• U.S. Department of Energy (Golden, Co; Morgantown, WVa)

effect of pressure and heating rates on biomass pyrolysis ... agrawal.pdf · effect of pressure and...

Documents