Biomass Properties and Consequences

Larry BaxterBrigham Young University

Provo, UT 84602

GCEP MeetingStanford University

April 26-27, 2004

Biomass Energy Economics

Typical biomass Cost

(US$ per ton)

Cost of Electricity compared to feedstock prices,

with various conditions, incentives, or subsidies

Typical Cost of Energy from Conventional Co-firing Combustion

Acknowledgement: Graph provided by Antares Group Inc

PTC – proposed production tax credit

Incentive, e.g., Green Pricing Premium

US Commercial Experience• Over 40 commercial demonstrations• Broad combination of fuel (residues, energy crops,

herbaceous, woody), boiler (pc, stoker, cyclone), and amounts (1-20%).

• Good documentation on fuel handling, storage, preparation.

• Modest information on efficiency, emissions, economics.

• Almost no information on fireside behaviors, SCR impacts, etc.

Major Technical Cofiring Issues• Fireside Issues

• Pollutant Formation• Carbon Conversion• Ash Management• Corrosion• SCR and other

downstream impacts

• Balance of Process Issues• Fuel Supply and

Storage• Fuel Preparation• Ash Utilization

Lab and field work indicate there are no irresolvable issues, but there are poor

combinations of fuel, boiler, and operation.

Fuel Properties

2.0

1.5

1.0

0.5

0.0

H:C

Mol

ar R

atio

1.00.80.60.40.20.0

O:C Molar Ratio

SemianthraciteBituminous Coal

Subbituminous CoalLignite

Anthracite

Cellulose

Average BiomassWood

Grass

Lignin

anthracite bituminous coal subbituminous coal semianthracite lignite biomass

average values

Typical Fuel Properties

Coal & Biomass Elemental Compositions Differ

Black Thunder Pittsburgh #8

Imperial Wheat Straw Red Oak Wood Chips

C

H

N

S

Cl

Ash

O (diff)

COAL:

BIOMASS:

Pittsburgh #8

7.8% Ash

Imperial Wheat Straw

15.4% Ash

Red Oak

1.3% Ash

Black Thunder

7.2% Ash

SiO2

Al2O3

TiO2

Fe2O3

CaO

MgO

Na2O

P2O5

K2O

SO3

Cl

COAL:

BIOMASS:

Coal & Biomass Ash Compositions Differ

Commercial Fuel Mix Varies

Woodland Fuel Mix, Spring-Summer 1993

0%

20%

40%

60%

80%

100%

23-A

pr

30-A

pr

7-M

ay

14-M

ay

21-M

ay

28-M

ay

4-Ju

n

11-J

un

18-J

un

25-J

un

2-Ju

l

9-Ju

l

16-J

ul

23-J

ul

30-J

ul

6-A

ug

13-A

ug

20-A

ug

27-A

ug

EucalyptusAlmondCoffeeMich CalPit MixPitsSawdustShellsPruningsPine DustWhite PineWEYCOUWW

Stoichiometry and Temperature Impacts

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.9 1.0 1.1 1.2

Nominal Reburn Zone Equivalence Ratio

Nor

mal

ized

NO

x (bo

th d

ry a

t 3%

O2)

900 C, 250 ppm

1200 C, 500 ppm

900 C, 500 ppm

1200 C, 250 ppm

Alfalfa

Alfalfa Generates NH3

0.4

0.3

0.2

0.1

0.0

Sign

al (a

rbitr

ary)

112511201115111011051100

Wavenumber (cm-1)

Calibration @ 1000 ppm NH3 Alfalfa Calibration @ 250 ppm NH3 Natural Gas

NOx Behavior Complex (No Surprises)

200

150

100

50

0

Axia

l dist

ance

(cm

)

-20 0 20Radial distance (cm)

500

450

450

450 450

450

400

400

400

400

400 400

400

350 350 350

350

350

350

3

50

350

300

300

250 2

00

200

150

150

100 100

50

50

200

150

100

50

0

Axia

l dist

ance

(cm

)

-20 0 20Radial distance (cm)

450 450

450

400 400

400

400

400

400

400 400 400

400

400

350

350

300 250 250 200 200

150 150 100

100 50 50

200

150

100

50

0

-30 -20 -10 0 10 20 30

600

6

00

600 600

550

550 550

550 500

500

450

450

400

400

400 350

350

350

300

300

250 250

200

150

100 100 100 50 50

Straw (φ = 0.6) Coal (φ = 0.9) 70:30 Straw:Coal (φ = 0.9

NO

NH3

Combustion History: Switchgrass

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4

Vol

ume

(mm

3 )

Time (s)

Char Oxidation

Devolatilization

Heat &Dry

Initial nominal diameter = 3 mm

Particle Shape Impacts

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Mas

s Lo

ss, d

af

Residence Time, s

flake-like exp. flake-like model cylinder-like exp. cylinder-like model near-spherical exp. near-spherical model

Reaction Time vs. Yield

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

0

5

10

15

20

0

5

10

15

20

Con

vers

ion

Tim

e, s

Equivalent Diameter, mm

flake-like cylinder-like near-spherical

aspect ratio:flake-like - 4.0 (width/thickness)cylinder-like - 6.0near-spherical-1.65

Field Tests

Wheelabrator, Shasta, 3 Stokers

Thermo Electron, Delano, 2 BFB

Hydra-Co, Imperial, Stoker

•

•

••Sithe, Marysville, CFB

Thermo Electon, Mendota, CFB

Thermo Electron, Woodland, CFB

•

•Elkraft-Midkraft, Slagelse, Haslev (Denmark), Auger, Cigar Burner

•

Cofiring Deposition

Deposition Rates Vary Widely• Cofiring biomass can

lead to either decrease or increase in deposition rates.

• Cofiring decreases deposition relative to neat fuels.

0.01

0.1

1

10

100

Dep

ositi

on R

ate

(gm

dep

osit/

kg fu

el)

Woo

d

Sw

itchg

rass

Str

aw

Whe

at S

traw

Pitt

sbu

rgh

#8

Eas

tern

Ken

tuck

y

Commercial Stoker

Slag Screen

SecondarySuperheater

PrimarySuperheater

BoilerGenerator Bank

Stokers

Overfire Air

Grate

Stoker

Fuel Bin

1

2 3

4

5

Deposits Dissimilar to Fuel

SiO2 Al2O3 TiO2 Fe2O3 CaO MgO Na2O K2O P2O5 SO30

10

20

30

40

50

60

Mas

s Per

cent

[-]

Fuel

Ceiling/Corner Deposit

Composition Maps Support Corrosion Hypothesis

Cl S Fe

100% Imperial Wheat Straw

85% E. Kentucky 15% Wheat Straw

Fuel Properties Predict Corrosion

Increasing Time

Oxygen Isosurfaces

BL mechanisms

BL deposition flux [g/m2/h]Inertial deposition flux [g/m2/h]

Vapor deposition

Vapor deposition flux [g/m2/h]

Required Aerating Agent

0

0.5

1

1.5

2

2.5

oz/1

00 lb

s ce

men

t

Pure Cement

Class C Fly Ash (25%)

Class F Fly Ash (25%)

Co-fired Fly Ash (25%) (10% switchgrass)

Co-fired Fly Ash (25%) (20% switchgrass)

Surface Conditions of Catalyst

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Nor

mal

ized

Con

cent

ratio

n

Fres

h(1)

Fres

h(2)

Exp

osed

(1)

Exp

osed

(2)

Det

ectio

nL

imit

CaOSSO3Na2OV2O3

Basic Compounds Poison Catalysts

Catalyst Activity vs. Na Poison Amount

0.000.100.200.300.400.500.600.700.800.901.00

0 0.5 1 1.5 2 2.5 3

Poison Ratio (Na:V)

Act

ivity

(k/k

0)

BYU wetBYU dryChen et al.

Field Tests Indicate Little Poisoning1.0

0.9

0.8

0.7

0.6

0.5

Frac

tiona

l Con

vers

ion,

X

140001200010000800060004000

Space Velocity (hr-1)

X NO fresh I X NH3 fresh I X NO fresh II X NH3 fresh II X NO exposed front X NH3 exposed front

Conclusions• Major technical issues include fuel handling, storage,

and preparation; NOx formation; deposition; corrosion; carbon conversion; striated flows; effects on ash; impacts on SCR and other downstream processes.

• Importance of these issues depends strongly on fuel, operating conditions, and boiler design.

• Proper choices of fuels (coal and biomass) and operating conditions can minimize or eliminate most impacts for most fuels.

• Ample short-term demonstrations illustrate fuel handling feasibility. Paucity of fireside and long-term data.

Acknowledgements• Financial support provided by the DOE/EE, EPRI,

NREL, BYU, a dozen individual companies.• Work performed by research group including four other

faculty members, two post docs, ten graduate students, 30 undergraduate students.