Co-pyrolysis of Coal and Biomass at Transport

Gasifier Conditions

Nathan Weiland, Nick Means, and Ryan Soncini

NETL 2011 Workshop on Multiphase Flow Science

Pittsburgh, PA, August 16-18, 2011

2

NETL’s FY11 In-house Research:

Advanced Gasification Program

• Mission: “Accelerate the development of advanced,

affordable and efficient gasification-based

technologies that promote coal-based fuel flexibility

and reduce pollutants, trace elements, and the

carbon footprint of existing and future coal fired

applications.”

• Tasks/Projects:

1. Biomass Processing

2. Refractory Development

3. Co-gasification Reactions

and Kinetics

4. Device/System Modeling

3

Objective #2

Objective #1

Advanced Gasification Team Approach

Raw / Treated

BiomassCOAL

Blend

Transport

Gasifiers

Entrained

Flow

Gasifiers

Kinetic

Data

Product

Properties

Task 4

Modeling

Task 2

Gasifier

Materials

Task 1

Prep/Feed

Task 3

4

NETL Modeling Approach

• NETL’s C3M program

– Carbonaceous Chemistry

for Computational Modeling

– Interface between kinetics

databases and high-fidelity

computational models

• Kinetic databases need

to be updated

– Add biomass feedstocks

– Account for coal/biomass

co-feeding non-linearities

– Pyrolysis, gasification, tar

– Transport and entrained

flow conditions

Ash

Volatile Matter

Fixed Carbon

CO2 + H2O +CO

+ CH4 +H2

+Tar

CO2 + H2O

+ CO + CH4 + H2

+ Fixed Carbon

CO2 + H2O

O2

O2

Coal

H2O CO + H2O CO2 + H2

O2CO

CO2

CO

H2O H2 + CO

H2

CH4

5

Project Objectives and Goals

• Program Goal: Successfully simulate the PSDF

transport gasifier on co-fed coal/biomass

• Project Goal: Provide fundamental co-pyrolysis and

co-gasification kinetic data for C3M platform

– Determine root cause of

nonlinear coal/biomass

interactions, if present

• C3M’s co-feed data needs:

– Devolatilization kinetics and

product distributions

– Gasification kinetics under

CO2, H2 , H2O and O2

– Homogeneous & heterogeneous

tar cracking kinetics

6

Transport Integrated Gasification (TRIGTM)

• Non-slagging KBR gasifier at PSDF

• Operating conditions

– 2 ton/hour combustor or gasifier

– Air- or Oxygen-blown

– Pressure: 11 – 17 atm

– Temperature: 815 – 1040 C

• Feedstocks

– Coarse, dry feed

– Works well on low rank, high moisture,

high ash coals

• PRB coal, Mississippi lignite

– Biomass: 20% blend typical, up to 100%

• Basis for 582 MW plant in construction

at Kemper, Mississippi

7

Test Matrix

• 8 test points:

– 600 & 800 °C at 1, 4 and 16 atm, 975 °C at 1 and 4 atm

• 4-5 dried fuel mixtures consistent with PSDF testing:

– Pure PRB coal, lignite & pine wood biomass

– 80% PRB/20% wood mixture

– 80% lignite/20% wood mixture (time permitting)

• 5 reaction environments:

– Inert argon for pyrolysis, CO2, H2 , H2O and O2 for gasification

• 160-200 total data points

• Separate product distribution and kinetics tests

• Will also generate co-gasification model validation data with as-

received feedstocks

– Must test the ability of C3M to capture nonlinear co-gasification

behavior (coal-gas and coal-char interactions)

8

Sample Specifications

• Feedstocks dried,

ground, and sieved

– Powder River

Basin (PRB) Sub-

bituminous Coal

– Mississippi

Lignite (Red Hills)

– Southern Yellow

Pine Pellets

• Products:

– 500 to 850 µm

• Kinetics:

– 100 to 300 µm

PRB Coal Miss. Lignite Wood Pellets

as rec'd dry basis as rec'd dry basis as rec'd dry basis

Proximate Analysis

% Moisture 20.43 -- 19.06 -- 4.00 --

% Ash 7.03 8.83 15.43 19.06 1.36 1.42

% Volatile 32.49 40.83 29.60 36.57 81.78 85.19

% Fixed Carbon 40.06 50.34 35.91 44.37 12.86 13.40

Ultimate Analysis

% Carbon 53.50 67.24 45.62 56.36 51.07 53.20

%Hydrogen 3.37 4.23 3.42 4.23 5.99 6.24

%Nitrogen 1.22 1.53 0.86 1.06 0.12 0.12

%Sulfur 0.30 0.38 0.47 0.58 0.02 0.02

%Oxygen(diff) 14.16 17.79 15.14 18.71 37.44 39.00

Energy Analysis

Btu/lb 9102 11439 7786 9619 8485 8839

MAF BTU/lb 12547 11884 8966

9

Product Distribution Tests

• HPTR Tests at NETL Pittsburgh

– Isothermal pyrolysis of a ~1 gram

sample, dropped onto a heated

quartz frit

– Semi-batch operation (1 test/day)

• Ex-situ tar and water trapping

• Quantitative gas sampling by mass

spec:

– CO2, CO, CH4, C2H4, H2S, H2, H2O

• Tests with mass closures between

95 and 105% retained for product

distribution analysis

3-Zone

Heater

Reactor

Tube

Filter

Copper Coil

Tar Trap

Mass

Spec

PT & TC

Filter

To Vent

Quartz

Frit

Drierite

Filter

Ice Bath

~0oC

Sample

DropSweep

Gas

Inlet

High Pressure Tubular

Reactor (HPTR)

10

Primary Products vs. Biomass Blend

• Linear primary pyrolysis

product distributions with

respect to wt. % biomass

• Distribution nonlinearities

seen in literature at lower

temperature not observed in

these experiments

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

600 C Char

Gas

Water

Tar

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

800 C Char

Gas

Water

Tar

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

975 C Char

Gas

Water

Tar

11

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

100% WB

Char

Gas

Water

Tar

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

100% PRB

Char

Gas

Water

Tar

Primary Products vs. Temperature

• Primary pyrolysis product

distributions slightly

nonlinear wrt temperature, as

expected

• In general, condensable

fractions and char converted

to gas at high temperatures

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

80% PRB/20% WB

Char

Gas

Water

Tar

12

0

0.05

0.1

0.15

0.2

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

600 C

CO2

CO

CH4

H2

C2H4

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

975 C

CO2

CO

CH4

H2

C2H4

Gaseous Products vs. Biomass Blend

• Linear gaseous pyrolysis

product distributions with

respect to biomass wt. %

• Higher CO and lower CO2

release with biomass wt. %

and temperature

– Consistent with literature

0

0.05

0.1

0.15

0.2

0.25

0.3

0 20 40 60 80 100

% W

t. o

f Fe

ed

% Wt. Biomass

800 C

CO2

CO

CH4

H2

C2H4

13

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100

Vo

lum

e %

of

Gas

% Wt. Biomass

975 C

CO2

CO

CH4

H2

C2H4

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100

Vo

lum

e %

of

Gas

% Wt. Biomass

600 C

CO2

CO

CH4

H2

C2H4

Gaseous Products vs. Biomass Blend

• More H2 generated by coal than

biomass on volume basis

– Biomass gas ~2x PRB gas

– Biomass has 50% more H,

released as hydrocarbons

• H2/CO ratio decreases as

biomass wt.% increases

– H2/CO ~ 2 for PRB, 0.1 for WB

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100

Vo

lum

e %

of

Gas

% Wt. Biomass

800 C

CO2

CO

CH4

H2

C2H4

14

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

100% WB

CO2

CO

CH4

H2

C2H4

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

100% PRB

CO2

CO

CH4

H2

C2H4

Gaseous Products vs. Temperature

• Increases in total gas

production with temperature

mostly due to CO and

hydrocarbons

– ~40% of biomass weight

converted to CO at 975 °C

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

600 700 800 900 1000

% W

t. o

f Fe

ed

Temperature (°C)

80% PRB/20% WB

CO2

CO

CH4

H2

C2H4

15

GC-MS Gas Analysis

• Qualitative analysis of gas bag samples taken during pyrolysis

at 800 C

– Trace sulfur species appear in PRB tests

– Acetylene, acetaldehyde, toluene more prevalent with biomass

16

Current HPTR-1 Kinetics

• HPTR gas production data

previously unsuitable for

kinetics

• Procedure modifications yield

more accurate and consistent

kinetic data

Test TypeProduct

DistributionKinetics

Sample

quantity1.0 g 0.1 g

Sample size300-1000

μm100-300 μm

Sweep gas

flow rate2.0 slm Ar 4.5 slm Ar

Reaction

location

9” from

bottom

4” from

bottom

Residence

time4.4 s 0.13 s

17

Reactor Setup for Isothermal Kinetics

-12

-8

-4

0

4

8

12

16

20

24

28

32

36

0 200 400 600 800 1000

Po

siti

on

fro

m T

op

of

Hea

ter

(in

che

s)

Temperature [oC]

Frit Location

18

Drop-Tube (Isothermal) Pyrolysis Kinetics

• Total devolatilization

– Measure CO, CO2, CH4, C2H4, H2 and H2O via QMS

– Total gas evolution: mtotal = ∑(mgas)

– Solid mass loss: msolid(t) = mfeed – mgas(t) – mtar(t)

– Assuming that the rate of mtar(t) is proportional to

mgas(t):

• General Rate Equation:

• Integrate for n = 1:

nXk

dtdX 1

)(

)(

)(

)(

gas

gas

solidfeed

solidfeed

m

tm

mm

tmmX

TREAk A *exp*

ktX )1ln(

19

Preliminary Pyrolysis Kinetics Results

• Mass spec sample rate

– ~0.7 s/sample

• Reaction progress, X,

characterized by

dimensionless gas

release

• Reaction rate, k, fit to

initial slope of ln(1-X)

– Best fit covers first 75-

90% of reaction

• Multiple slopes may

better fit a DAEM model

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10

Rea

ctio

n P

rogr

ess,

X

Time (seconds)

100% PRB

80% PRB/20% WB

100% WB

975 °C

y = -41.957x + 0.441R² = 0.9866

y = -1.5268x - 3.0633R² = 0.9993

-6

-5

-4

-3

-2

-1

0

0 0.4 0.8 1.2 1.6

ln (

1-X

)

Time (min)

PRB @ 975 °CPRB total

Initial

Intermediate

20

Preliminary Pyrolysis Kinetics Results

PRB 20% WB WB

EA (kJ/mol) 30.9 24.2 32.9

A (1/s) 16.3 6.5 24.6

R2 0.934 0.967 0.912

• Fit of reaction rates on

an Arrhenius plot

– Considerable scatter in the

reaction rate data

• Potential coal/biomass

reaction rate synergy

– Lower mixture activation

energy and pre-exponential

– Similar to literature results:

• Seo, M. W., et al, J. Anal. Appl.

Pyrol., 88 (2010) 160-167

• Brown, R. C., et al, Biomass &

Bioenergy, 18 (2000) 499-506

• Requires further study

and refinement

2.6

2.8

3

3.2

3.4

3.6

3.8

4

4.2

0.0007 0.0008 0.0009 0.001 0.0011 0.0012

ln(k

[1

/min

])

1/T [1/K]

PRB

Mix

WB

21

Summary

• Pyrolysis product distributions

– Linear primary and gaseous product distributions with

respect to biomass weight %

– Elemental H in PRB coal more likely to evolve as H2

– Elemental H in wood evolves as hydrocarbons, with

more H2 at high temperature

– Pyrolysis H2/CO ratio decreases significantly with

increasing biomass wt. %

• Preliminary pyrolysis kinetics

– Potential nonlinear kinetic coal/biomass synergy

– Preliminary results suggest 2-stage process

22

Future Work

• Refine pyrolysis kinetic analysis

• Modify reactor to increase testing rate

• Study pressurized pyrolysis product distributions

and kinetics

• Gasification rate data for CO2, H2O, O2 and H2

• Generate C3M model validation data on as-received

feedstocks in simulated syngas

• New lab being constructed for studying tar cracking

kinetics

– High speed TGA (100 °C/s), tube furnace, mass spec

– Study tar generation rate, homogeneous and

heterogeneous tar cracking kinetics

23

Tar Cracking Kinetics

Tar trap

On-line MS

Gas analysis

H2, CO,CO2,

H2O, CH4

Off-line GC-MS

Tar compositionsCoal

/biomass

TGA

Generate fresh vapor tar

Tubular reactor

Tar cracking kinetics:

homogeneous without char

heterogeneous with char

Char Off-line BET

Char surface area

Parameters

Temperature: 600-1200oC

Residence time: 2-6 s

Parameters

Temperature: 300-500oC

200 300 400 500 600 700 800 900

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Temperature (oC)

Po

pla

r vo

latile

ge

ne

ratin

g r

ate

(1

/s)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Lig

nite

co

al vo

latile

ge

ne

ratin

g r

ate

(1

/s)

Coal

Poplar

24

Acknowledgments

NETL-RUA Research Faculty

Dr. Goetz Veser

University of Pittsburgh

U.S. DOE - NETL

Dr. Chris Guenther

Dr. Ron Breault

Dr. Bryan Morreale

Dr. Charles Taylor

NETL Site Support Contractors

Nick Means, URS

Ryan Soncini, URS/Pitt

Kevin Resnik, URS

This technical effort was

performed in support of the

National Energy Technology

Laboratory’s on-going research

in coal and biomass conversion

technologies under URS contract

DE-FE0004000.

25