Finnish-Swedish Flame Days 2013
17th - 18th of April 2013
Jyväskylä, Finland
Challenges in Combustion of Low Grade
Biomasses – Recent Research
Mikko Hupa
Åbo Akademi
Process Chemistry Centre
Turku, Finland
Low Grade Biomasses:
The Devil is in the Chemical Details
Courtesy by Foster Wheeler and Metso
Low Grade Biomasses:
The Devil is in the Chemical Details
•
Is all ash alkali active in flue gases?
•
NOx – the role of char nitrogen?
•
Ash deposits on surfaces – do they change?
•
How do we know if CFD results are right?
Courtesy by Foster Wheeler and Metso
Fuel types
 Miscanthus (AUT)
 Reed (FIN)
 Wheat straw (DEN)
 Suger cane bagasse (THA)
Fuel analysis
Wire Mesh – Grid Heater
2 x 2 mm
 Electrically heated
wire mesh in a
reactor purged with
N2
 Small and welldefined samples
 Close temperature
control
J Werkelin, M Hupa, Retention of ash-forming matter after fast pyrolysis of small biomass
Samples, in “Impacts of Fuel Quality on Power Production & Environment”, Saariselkä, Finland (2010)
Temperature History of the Wire Mesh
Set temperature
Temp
1000
(°C)
800
Current temperature
600
400
200
0
0
1
Heating time
Rate: 1000 K/s
2
3
4 5 6
Time (s)
Holding time
1 - 4 sec.
Residence time
7
8
Cooling time
Initially fast
9 10
Potassium Retention in Mesh Pyrolysis Raw Data
J Werkelin, M Hupa, Retention of ash-forming matter after fast pyrolysis of small biomass
Samples, in “Impacts of Fuel Quality on Power Production & Environment”, Saariselkä, Finland (2010)
Retention of Biomass Potassium in Pyrolysis Wire Mesh Tests (1000 K/s)
Liq.conc.(μg/l)
1200
1000
800
600
Straw
Retention (%)
120%
850 °C
1000 °C
Liq.conc.(μg/l)
600
100%
500
80%
400
60%
300
400
40%
200
200
20%
100
0
0%
0
1
2
3
4
Holding time atTime
end (s)
temperature (sec)
Retention (%)
120%
Bagasse
100%
80%
850 °C
1000 °C
0
60%
40%
20%
0%
0
1
2
3
4
Holding time atTime
end temperature
(sec)
(s)
J Werkelin, M Hupa, in “Impacts of Fuel Quality on Power Production & Environment” (2010)
Retention of Potassium in Pyrolysis - Summary
Primary release in 1000 C
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Straw
Retention of K (%)
Retention of K (%)
Primary release in 850 C
Reed
Miscant.
Bagasse
0
1
2
Holding time (s)
3
4
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Straw
Reed
Miscant.
Bagasse
0
1
2
3
Holding time (s)
J Werkelin, M Hupa, in “Impacts of Fuel Quality on Power Production & Environment” (2010)
4
Fuel analysis
Low Grade Biomasses:
The Devil is in the Chemical Details
•
Is all ash alkali active in flue gases?
•
NOx – the role of char nitrogen?
•
Ash deposits on surfaces – do they change?
•
How do we know if CFD results are right?
Courtesy by Foster Wheeler and Metso
0,25
0,15
0,1
0,05
What happens with the mass
of a 6 mm particle if we
introduce it to 1000 °C
and 21% O2 ?
0
0
200
time (s)
8
mNO (µg/s)
How much NO is coming out
from the particle during char
oxidation?
devolatilization
char oxidation
ash
0,2
mass (g)
vol
char
ash
devolatilization
6
char oxidation
4
2
0
0
100
time (s)
200
NO Formation during Biomass Char Burn-Out
(900ºC, 10 % O2)
Karlström O, Brink A, Hupa M, Biomass char nitrogen oxidation – single particle model, Energy and Fuels (2013)
Char-C + O2 → CO/CO2
Formation of NO
O2
Char
NO partic
le
Char-N + 1/2O2 → NO
CO/CO2
Reduction of NO
O2
NO
NO + Char-C → CO + 1/2N2
NO + CO
→ CO2 + 1/2N2
Biomass Char-NO – Model Approach
Surrounding gas
particle
Concentrations of NO and
O2 inside and outside
particle considered:
 d 2CO 2 2 dCO 2 
 − kO 2CO 2 = 0
+
DO 2 
2
dr
r
dr


 d 2C NO 2 dC NO
+
DNO 
2
dr
r dr


 − k NO C NO n + ξkO 2CO2 = 0

 d 2CO 2 2 dCO 2 
 = 0
DO 2 
+
2
dr
r
dr


 d 2C NO 2 dC NO
DNO 
+
2
dr
r dr


 = 0

Karlström O, Brink A, Hupa M, Biomass char nitrogen oxidation – single particle model, Energy and Fuels (2013)
Detailed Model
As particle decreases in size,
NO diffuses away at a faster
rate
Less NO reduced & more
NO is released
2
Tgas= 800 oC
O2= 10 %
experiments
model
mNO (µg/s)
mNO (µg/s)
Char NO Formation – Model vs. Experiments
1
0
0
200
100
time (s)
300
2
Tgas= 1050 oC
O2= 10 %
experiments
model
1
0
0
100
50
time (s)
150
Karlström O, Brink A, Hupa M, Biomass char nitrogen oxidation – single particle model, Energy and Fuels (2013)
Low Grade Biomasses:
The Devil is in the Chemical Details
•
Is all ash alkali active in flue gases?
•
NOx – the role of char nitrogen?
•
Ash deposits on surfaces – do they change?
•
How do we know if CFD results are right?
Courtesy by Foster Wheeler and Metso
Temperature Gradient across Superheater Tube
Tflow
Tube wall
(5 mm)
Ash deposit (2,3 mm)
Tgas = 1000 °C
750 °C
550 °C
570 °C
Tsteam = 500 °C
Heat flux = 80 kW/m2
Engblom M. et al 2013
Length ∼60 cm
Material sample rings
Thermocouples
Setup
22
Deposit Probe with Temperature Gradient
Tfurnace
28mm
20mm
14mm
8mm
3mm
1mm
Tring
74 mm
54 mm
37 mm
Probe with Temperature Gradient – 72 h Test
850
Furnace environment
800
750
700
650
Channel 1[°C]
Channel 2[°C]
600
550
500
Probe Surface
450
400
30.10.2012 00:00 30.10.2012 12:00 31.10.2012 00:00 31.10.2012 12:00 1.11.2012 00:00
1.11.2012 12:00
2.11.2012 00:00
2.11.2012 12:00
3.11.2012 00:00
24
Tfurnace 980°C Tring 400°C
°C
1000
900
800
700
600
500
400
300
200
100
0
0
5
10
15
20
Distance from ring surface [mm]
25
30
Deposit after 24 h on the Gradient Probe (500/950 C)
(Na2SO4+NaCl)
0.25 mm
1.1 mm
Salt Grain Close to Molten Surface
NaCl
Eutectic
Salt Mix
Na2SO4
Low Grade Biomasses:
The Devil is in the Chemical Details
•
Is all ash alkali active in flue gases?
•
NOx – the role of char nitrogen?
•
Ash deposits on surfaces – do they change?
•
How do we know if CFD results are right?
Courtesy by Foster Wheeler and Metso
In-Furnace Data from Large Furnaces
85 m
Vainio, E., Brink, A., DeMartini, N., Hupa, M., Vesala, H., Tormonen, K., Kajolinna, T., In-furnace measurement of S and N species in a recovery boiler, ”International Chemical Recovery Conference”, TAPPI (2010)
In-Furnace Gas Sampling and Analysis
Vainio, E., Brink, A., DeMartini, N., Hupa, M., Vesala, H., Tormonen, K., Kajolinna, T, ”International Chemical Recovery
Conference”, TAPPI (2010)
Analyzers
 FTIR
 NO, NO2, NH3, HCN, CO2, CO,
COS, HCl, CS2, H2O, CH4
 O2 -analyzer
 GC
 Reduced sulfur species
 H2S, CH3SH, C2H6S...
SO2,
Gas Sampling Probes
Length = 4 m
Weight = 70 kg
Measurement setup
In-Furnace Gas Sampling Points
Analyzers
Vainio, E., Brink, A., DeMartini, N., Hupa, M., Vesala, H., Tormonen, K., Kajolinna, T, ”International Chemical Recovery
Conference”, TAPPI (2010)
Flue gas:
NO 67 ± 4 ppm
NH3
< 1 ppm
NO
NH3
HCN
1m
54
1
3
2m
59
2
2
NO
NH3
HCN
1m
38
6
1
2m
39
16
4
NO
NH3
HCN
200
153
41
NO
NH3
HCN
1m
24
22
0
2m
17
33
0
0.5m
NO
NH3
HCN
1m
5
122
64
2m
15
140
66
NO
NH3
HCN
1m
3
60
6
2m
1
87
3
NO
NH3
HCN
1m
72
94
1
2m
41
177
3
Furnace Camera (IR, 3,9 µm)
PYROINC 380
• Spectral Filter 3.9 µm
• Temp. Range 400-1500°C
• Temp. Resolution ≤ 1 K
• Field of View 67°x50°
• Diameter of Probe 104 mm
• IR -2D Array 384 x 288 Pixel
• Frame Rate 50 fps
IR Camera in Black Liquor Furnace
- Liquor sprays under two conditions
Liquor temp. 141.5 °C
138.5 °C
Brink, A., Lauren, T., Hupa, M., Koschack, R., & Mueller, C., Tappi Journal (2010)
Low Grade Biomasses:
The Devil is in the Chemical Details
•
Is all ash alkali active in flue gases?
•
NOx – the role of char nitrogen?
•
Ash deposits on surfaces – do they change?
•
How do we know if CFD results are right?
Courtesy by Foster Wheeler and Metso
Aknowledgements