2. Introduction
Operational experiences and observations from:
Hässelby Power Station
Direct firing wood/oil (70/30) 3*115 MW thermal
Uppsala Power Station
Indirect firing peat or coal 400 MW thermal
Drefviken District heating plant
Indirect firing briquettized wood 82 MW thermal
Jönköping District heating plant
Indirect firing pulverized wood 64 MW thermal
2015-06-09
3. Direct Firing Method
The most simple solution
Will have the best fuel flexibility
(coal-wood)
Will allow drying of the pulverized
wood and sequre early ignition in the
burner.
Will normally sustain a dust
explosion and allow overpressure
operation
If the mills are operated at
overloaded the fuel feed rate will
oscillate and over sized particles will
be sent to combustion
NX1
NX2
RX1VX1 QX1
VX2
VX3
FX1
GX1 Vertical Mill with classifier
TX1 Feed hopper
NX1 Redler Feeder
NX2 Cellular feeder
VX1 Air temeprature mixing valve
VX2&3 PF outlet valves
QX1 Primary air fan
TX1
GX1
2015-06-09
4. Direct Firing Method – Wood ”add on”
To burners
Suction
fan
Rotary
classifier
Babcock mill
Hammer
mill
Reject
Reject
2015-06-09
5. Semi direct Firing Method
RX1 Gravity trap
RX2 PF-Distributor
GX1 Refiner Mill
FX1 Cyclone
TX1 Feed hopper
NX1 Redler Feeder
NX2 Cellular feeder
VX1&2 PF outlet valves
VX4 Recirculation control valve
VX5&6 Hot and cold PA dampers
QX1 PA fan
QX2 Pulverizer aspiration fan
VX6
VX2
QX2
VX1
NX1
NX2
RX1QX1
TX1
VX5 GX1
VX4
FX1 RX2
If the air flow for the best mill
performance exceeds what the
burner are designed for (air to fuel
ratio <2,5/1)
2015-06-09
6. Indirect Firing Method
Mills completely separated from
fuel injection system
Most common solution in case of
conversion from oil firing
In theory ideal air/fuel ratios
In theory ideal fuel distribution to
the burners
Complex design
No heat recovery of grinding
work
2015-06-09
7. Boiler load control – fuel feed
General
Normal fluctuations in Heat value
Combustion preformance vs fuel feed stability
Dosing pelletized or pulverized wood?
Combined grinding and drying
Internal recirculation in the mill loop
2015-06-09
8. Fuel distribution
Comments and Comparisons to coal experiences:
Fuel distribution between the burners
Fuel distribution in the Burner register
Robe flow (Particle density and shape)
Naiver-Stokes falling eq.
2015-06-09
9. Size distribution
PF-firing of Pelletized wood at Hässelby
21,610,710,5
99,9%
99,8%
99,5%
99%
95%
90%
80%
70%
3,15
50%
60%
40%
20%
30%
2,5
Particle size (mm)
%Passing
Feed
PF-proposal New mills
n=58 degrees
0,5% Combustion loss
Estimated Particle
Burnout Rate
Proportional
particle reduction
depth
Product 1,3%
Combustion
loss
Hässelby Power Station 115 MW
The proposed size distribution
and combustion performance
has been verified with in-direct
firing system at full boiler load
With a more stabile fuel feed rate
to the burners, the expected
combustion performance, would
have been achieved with even
less fines in the PF.
There is a clear ”break point” at
1 mm screen size causing
reduced combustion efficiency.
2015-06-09
10. Classification
The use of Rotary classifiers are superior to
classification using screens for the following
reasons:
Aerodynamic classification has a strong physical similarity to succesfull particle
combustion. The probability for an instant particle to pass hole in a screen hasn’t
A Rotary classifier can during operation easily be adjusted with boiler load and normal
variations in fuel feed quality. To adjust a screen requires a mill group shut down.
A Rotary classifier enables one mill to supply PF to more than one burner
2015-06-09
11. Indirect Firing Method – fuel feed stability
Feed rate as a function of rotor speed is linear up
to a certain limited flow.
Feed rate is very sensitive for variations in the
static pressure head over the cellular feeder
2015-06-09
12. Indirect Firing Method
O2 peeks corresponding to intermittent valve breaking screw operation every
90 second
EMISSIONER
0
50
100
150
200
250
300
350
400
450
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
36139
mg/MJ
0
1
2
3
4
5
6
7
8
9
%RESP.ppm
NOXEELFILTER P3 ( mg/ MJ) COPANNA 3 ( mg/ MJ)
O2 I PANNA VÄSTER ( %vg) O2 I PANNA ÖSTER ( %vg)
O2 EFTER ELFILTER P3 ( % O2 ef t er Elf ilt er ( %t g)
O2 medel Öst er 90 s O2 medel Väst er 90 s
2015-06-09
14. Hässelby mill modifications
Babcock 6.3E9-mill
Initial performance and problems:
30-40% boiler load
Severe instability
Frequent fires in the reject system
Modifcations and tests 93-98:
Modification of static classifer
Removal of the entire reject system
Installation of av internal feeder for classifier reject
Installation of rotating throat
Installation of rotating classiifer
Installation of internal ejector
Grooves in the grinding balls
2015-06-09
15. Babcock mill – Static classifier modification
The air velocity was increased in the co-
axial feed funnel to the classifier vanes
The classifier blades was made less high.
Blade angle almost fully open i.e very low
lotation
”Dead zones” were sealed off
2015-06-09
16. Babcock mill – Reject system modification
Reject flap was welded in closed position
Reject shute was seald off with concrete
2015-06-09
17. Babcock mill – Throat modifications
The original throat was reduced to
minimize wood passing it after mill trips
and or at low PA-flow.
A rotating throat was tested but
abandoned after several fire incidents in
the mill wood box.
2015-06-09
18. Babcock mill – Feed system modifications
A pneumatic slide gate was installed
below the original Redler feeder for
security purpose
A cellular feeder was installed to prevent
leakage of hot Primary air
On top of the nut cap an internal feeder
was installed with the objective to force
internal circulation.
2015-06-09
19. Babcock mill – Internal ejector tests
Two different geometries of internal
ejectors were tested. No significant
improvement on capacity was achieved. A
slightly improved stability was reached.
2015-06-09
21. Hässelby mills – Present status
Final performance and problems:
70% boiler load (1,3% combustion loss at 4,5% O2)
Unstablie combustion
Regular grinding of balls required due to non uniform wear
Short running hours of main mill shaft
2015-06-09
22. Vertical mills
Fuel flexibility from coal to
wood
Expensive
Low capacity
50-60% of coal load in MW
Loeche and Alstom grinding
tests
Dust explosion proof
Integrated classifier function
Wood adjustments:
Hight, throat, reject system
classifier vanes & gearbox
2015-06-09
23. Hammer mills
Cheap and compact
Efficient
10.20 kWh/ton
High capacity
25-30 ton/h
Not dust explosion proof
Under pressure operation
Short life time of grinding
elements
2015-06-09
24. Refiner mills
Cheap and compact
High specific Power
consumption
45-55 kWh/ton
Not dust explosion
proof
Under pressure
operation
2015-06-09
25. Boiler load figures
Anläggning Hässelby Drefviken Jönköping Uppsala
Panna P1-P3 ÅP2 KVV
BRÄNSLEDATA
Max bioandel (%) 70% 100% 100% 100%
Bränsle Träpellets/olja Träricketter Träpulver Torv/träbricketter (70/30)
Andel träpulver <1,5 mm 93% 100% 100% 99%
Andel träpulver <1,0 mm 83,0% 98,5% 95,0% 94,9%
Andel träpulver <0,5 mm 43% 51% 65% 87%
Specifikt malaarbete vid full biolast (kWh/ton) 10 65
Installerad malkapacitet (kWh/ton) 16 73
PANNDATA
Typ av panna (Torn, U) Torn U Torn Torn
Max bränsleeffekt vid biopulvereldning (MW) 115 77 75 400
Max bränsleeffekt vid oljeeldning (MW) 115 535
Brännarfabrikat Babcock Petrokraft Burmeister Burmeister
Brännararrangemang (topp,hörn front) Front Topp Sidoväggar 2+2 Front+Bak 9+4
Typ av brännare Axial-Swirl Axial-Jet Axial-Jet Axial-Jet
Antal Brännare 4 4 4
13 olja
10 bio
SNCR P3 Ja
OFA-ROFA P2 OFA
P3 ROFA
OFA ROFA ROFA
Eldstadsvolym (m3) 608 415 435 2116
Strålningsyta i eldstad (m2) 430 320 211 964
Tvärsnittsarea vid brännare (m2) 49 36 34 101
Inbördes avstånd mellan brännare 2,6 H & 3,5 V 2,3 1,53 2,92 H & 3,02 V
NYCKELTAL
Tvärsnittsbelastning (MW/m2) 2,35 2,15 2,23 3,96
Volymbelastning (kW/m3) 189 186 172 189
Gördelbealstning (MW/m2) 1,17 1,70
Medelytbelastning (kW/m2) 267 241 356 415
FÖRBRÄNNING
Luftöverskott i panna (%O2) medelvärde fullast 4,5 4,5 4,4 5
CO (mg/MJ) medelvärde fullast 20 15 60 30
NOx (mg/MJ) medelvärde fullast 60 45 60 60
Förbränningsverkningsgrad (%) 98,70% 99,92% 99,75% 99,90%
2015-06-09
26. Combustion
Ensure fuel feed rate stability and proper fuel
distribution!
Flame root stability is important
Take every possible action to ensure early ignition.
Flame monitoring
Standard coal flame monitoring system can be used.
2015-06-09
27. Ash handling - Wet system
Wet handling
Safe
Difficult by simple means to prevent depoitsa where
not expected.
2015-06-09
28. Ash handling – Dry handling
Dry handling
Heat recovery
Enables ash
recirculation with inert
gas (flue gas)
2015-06-09
29. Ash utilization
Pure wood ash as fertilizer
Wood industry
Rondeco system for municipal waste
2015-06-09
30. Direct Firing Method
The most simple solution
Will have the best fuel flexibility
(coal-wood)
Will allow drying of the pulverized
wood and sequre early ignition in the
burner.
Will normally sustain a dust
explosion and allow overpressure
operation
If the mills are operated at
overloaded the fuel feed rate will
oscillate and over sized particles will
be sent to combustion
NX1
NX2
RX1VX1 QX1
VX2
VX3
FX1
GX1 Vertical Mill with classifier
TX1 Feed hopper
NX1 Redler Feeder
NX2 Cellular feeder
VX1 Air temeprature mixing valve
VX2&3 PF outlet valves
QX1 Primary air fan
TX1
GX1
2015-06-09
