NOx Chemistry for Biomass and Coal

Larry BaxterBrigham Young University

Provo, UT 84602

17th Annual ACERC ConferenceSalt Lake City, UTFebruary 21, 2003

Initial Fuel Compositions Vary

Pine King Sawdust Alfalfa Switchgrass

C 49 49.7 49 49.8

H 6 6.43 6 6.59

O 44 43.8 42 43.19

N 0.07 0.011 2 0.279

S 0.032 0.101

Cl 0.6

Initial Fuel Compositions Differ

Wood Composition (% daf fuel): Initial FinalC 49 80H 6 2.5N 0.07 0.4O 44 17

• Wood has less nitrogen and no chlorine compared with alfalfa.

• Alfalfa has large fraction of amine nitrogen. Wood has essentially no amine nitrogen.

• C:H ratios and dry ash free heating values are very similar.

• Alfalfa has much more ash than wood, with much more silica in the ash.

Alfalfa Composition (% daf fuel): Initial FinalC 49 80H 6 1N 2 1O 42 18Cl 0.6 0.5

Coal CHNO Release Rates1.0

0.8

0.6

0.4

0.2

0.0

Fra

ctio

na

l L

oss,

[-]

1.00.80.60.40.20.0

Fractional Mass Loss, daf [-]

devolatilization oxidation

carbon nitrogen parity

Biomass (Alfalfa) CHNO and Cl

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

mass loss, daf

Ele

me

nt

Lo

ss

, da

f

C HN OCl

A Reburning Issue

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7 8 9 10

% O2

NO

x w

ith R

ebur

n / N

Ox

Bas

elin

e(e

ach

corr

ecte

d to

3%

O2)

H2

CH4

Particle Effect

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.02 1.12

Reburn Stoichimetry

No

rmal

ized

NO

x (b

oth

dry

at

3%)

No fly ash

Fly ash

No ash, 4/5

Ash, 4/5

Hydrogen vs Solid Fuels

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1

Solid Fuel Fraction

Nor

mal

ized

NO

x (b

oth

dry

at 3

% O

2)

All H2 All Solid Fuel

Wheel/H2

Graphite/H2

Coal/H2

Natural Gas vs Solid Fuels

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1

Solid Fuel Fraction

Nor

mal

ized

NO

x (b

oth

dry

at 3

% O

2)

All CH4 All Solid Fuel

Wheel/CH4

Coal/CH4

Alfalfa/CH4

Alfalfa Generates NH3

0.4

0.3

0.2

0.1

0.0

Sig

nal (

arb

itrary

)

112511201115111011051100

Wavenumber (cm-1

)

Calibration @ 1000 ppm NH3

Alfalfa Calibration @ 250 ppm NH3

Natural Gas

NH3 Reacts with NO

0.4

0.3

0.2

0.1

0.0

Sig

nal (a

rbitra

ry)

112511201115111011051100

Wavenumber (cm-1

)

Conditions Entering Reburn Region NO = 250 ppm NO = 500 ppm

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

No

rma

lize

d N

Ox

(bo

th d

ry a

t 3

% O

2)

900 C, 250 ppm

1200 C, 500 ppm

900 C, 500 ppm

1200 C, 250 ppm

Alfalfa

Coal: Stoichiometry and Temperature Impact Results

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 (b

oth

dry

at 3

% O

2)

900 C, 250 ppm

1200 C, 500 ppm

900 C, 500 ppm

1200 C, 250 ppm

Coal

Ammonia Chemistry (GRI Mech)

0.E+00

1.E-04

2.E-04

3.E-04

4.E-04

5.E-04

6.E-04

7.E-04

8.E-04

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016

time (s)

Mol

e fr

actio

n

1500 K 1600 K

1700 K 1800 K

1900 K 2000 K

2100 K 2200 K

2300 K 2400 K

2500 K

NH3 Chemistry (Kilpenen)

0.E+00

1.E-04

2.E-04

3.E-04

4.E-04

5.E-04

6.E-04

7.E-04

8.E-04

9.E-04

1.E-03

0 0.002 0.004 0.006 0.008 0.01

time (s)

Mo

le fr

act

ion

1500 K 1600 K

1700 K 1800 K

1900 K 2000 K

2100 K 2200 K

2300 K 2400 K

2500 K

HCN Chemistry

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

time (s)

Mol

e fr

actio

n

1500 K 1600 K

1700 K 1800 K

1900 K 2000 K

2100 K 2200 K

2300 K 2400 K

2500 K

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

No

rma

lize

d N

Ox

(bo

th d

ry a

t 3

% O

2)

900 C, 250 ppm

1200 C, 500 ppm

900 C, 500 ppm

1200 C, 250 ppm

Alfalfa