PF-firing of wood

Experience feed back Fuel preparation, combustion and ash handling

2015-06-09

Per Lysedal

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

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

Direct Firing Method – Wood ”add on”

To burners

Suction

fan

Rotary

classifier

Babcock millHammer

mill

Reject

Reject

2015-06-09

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

RX1

QX1

TX1

VX5 GX1

VX

4

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

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

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

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

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)

% P

assin

g

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

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

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

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

45036

139

3613

9

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9

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3613

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3613

9

mg/

MJ

0

1

2

3

4

5

6

7

8

9

% R

ESP.

ppm

NOX E ELFILTER P3 (mg/ MJ) CO PANNA 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

Indirect Firing Method – Observations

O2 peeks corresponding to intermittent valve breaking screw operation

2015-06-09

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

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

Babcock mill – Reject system modification

Reject flap was welded in closed position

Reject shute was seald off with concrete

2015-06-09

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

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

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

Babcock mill – Loesche Rotary Classifier

2015-06-09

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

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

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

Refiner mills

Cheap and compact

High specific Power

consumption

45-55 kWh/ton

Not dust explosion

proof

Under pressure

operation

2015-06-09

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

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

Ash handling - Wet system

Wet handling

Safe

Difficult by simple means to prevent depoitsa where

not expected.

2015-06-09

Ash handling – Dry handling

Dry handling

Heat recovery

Enables ash

recirculation with inert

gas (flue gas)

2015-06-09

Ash utilization

Pure wood ash as fertilizer

Wood industry

Rondeco system for municipal waste

2015-06-09

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