Self-heating in biofuel pellets

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Self-heating in biofuel pellets

Anders Lönnermark, SP Fire Research Adjunct Prof. at Mälardalen University

Seminar on handling of biofuel pellets at large facilities, Teknologisk Institut, Taastrup, Denmark, 2014-04-08

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SP Technical Research Institute of Sweden

The SP group Fire Research

>1300 employees Approx 90 employees

Fire Research

Certification

Glass Electronics

Energy Technology

Chemistry, Materials and Surfaces

Food and Biotechnology Calibration and

Verifications

Measurement Technology

Wood Technology

Process Development Active Safety

Structural and Solid

Mechanics Machinery

Testing and Inspection

Agriculture and environment Bioeconomy

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Swedish-Norwegian fire cooperation: SP Fire Research

SP Fire Technology SINTEF NBL

≈ 120 employees in total

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SP Fuel Storage Safety

An international Center of

Expertise for fire safety during storage and handling of

gaseous, liquid and solid

fuels and recycling of waste

material involving research,

innovation and knowledge

transfer.

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Fuel storage self-heating problems in focus

Self-heating properties and risk for spontaneous ignition

Fire development and risk for escalation

Difficult to detect

 Often limited access

 Difficult and time consuming extinguishing process

 Silo fires often result in total damage

Improved guidelines

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Self-heating

• Microbiological activity generally not significant (as in e.g. piles of wood chips)

• Heat from oxidation of wood constituents

• Oxidation of unsaturated fatty acids proposed to be major heat source

• Self-heating often seen shortly after production

• Some fuel qualities show higher heating activity and can during unfavorable conditions lead to spontaneous ignition

0 50 100 150 200 250 300 350

Time

Temperature (ºC)

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LUBA

• LUBA – Large scale utilization of Biopellets for energy Applications – WP1 :Import of sustainably produced biomass for energy application – WP2: Development of new sampling techniques for suspended biofuels

– WP3: Quantification of important factors causing self-heating, oxygen depletion and off- gassing

• 3.3 Measurements characterizing the self-heating of wood pellets – Self-heating properties: micro calorimeter

– Self-heating properties: oven-basket tests

– Simulation and extrapolation of data towards full-scale – Thermal properties

– Medium-scale verification tests

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Description of pellets tested in LUBA

Pellet Pellet origin Type of pellet

A Swedish fresh pellets Pine

B Scottish pellets , 3 months storage in Denmark Pine

C Swedish fresh pellets Spruce/pine/energy wood

D Pellets from torrefied material+tar additive Spruce (torrefied)

E Russian pellets from harbour in Denmark Spruce/pine

F Portuguese pellets from harbour in Denmark Pine

G Swedish fresh pellets Spruce/pine/energy wood

H Scottish fresh pellets (10 days) Pine

I Scottish pellets from harbour in Denmark Pine

J Scottish fresh pellets Pine

K Swedish fresh pellets Spruce/pine/energy wood

L Swedish fresh pellets Spruce/pine/energy wood

M Scottish pellets stored in 16 kg plastic bags Pine

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Self-heating properties of various materials in different scales

0.00 0.20 0.40 0.60 0.80 1.00

0 5 10 15 20 25

Heat release rate, mW/g

Time, h 60°C

Pellets L, sample 1 Pellets L, sample 2 Pellets M, sample 1 Pellets M, sample 2

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Micro calorimeter method

• Isothermal calorimetry

• Very accurate (mW-scale) measure of the heat of reaction

• 20 mL ampoule

• 2 g, 4 g, 6 g, 8 g

• 40 °C, 60 °C, 80 °C

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Basket-heating test (Crossing-point)

100 2030 4050 6070 8090 100110 120130 140150 160170 180190 200210 220230 240

0 1 2 3 4 5 6

Temp ( C)

Distance from centre (cm)

5 min 10 min 30 min 60 min 90 min 120 min 150 min 180 min 210 min 240 min 270 min 300 min 330 min

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𝜕𝜕𝜕𝜕� = 𝑙𝑙𝑙𝑙 � 𝑄𝑄𝑄𝑄

𝐶𝐶

_𝑃𝑃

� − 𝐸𝐸

𝑅𝑅𝜕𝜕

_{𝐶𝐶𝑃𝑃}

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Transient plain source (TPS)

8 mm

Sample 1

Sample 2

X Y Z

Approx. 25 mm

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Medium-scale tests (1 m

³

)

Label of pellets

Pellet type Bulk density

(kg/m³)

Pellet diameter (mm)

L Agro Energi, Sweden

Sampled relatively fresh from production

715 8

M Verdoe, Scotland

Transported and stored for 3 months before sampled

719 8

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Medium-scale tests – Test set-up

Y X

Z

400

1100

420

360

3600 2495

1100 Ø 600

95+10

2

Pre-heating inflow

95+10

TC_54

160 Ø V3 100

3000

V2

2500

X Z Fan

Heater

Pellets 160 Ø

250Ø

2500

600 16 10

24 25 40

Outflow

Allductsinsulated

A.

B.

C.

100 Ø

TC 52 V1

600

250

TC 46-48

TC 49-51 TC 53

V2

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Medium-scale tests: Measurements

Rear side

Front side (with hatch)

P1

P2 P8

P9

P3

P7 P6

P4 P5

Z X

1500 1100

1100

550

Thermocouple (0.5 mm type K) Thermocouple + gas sampling

50 100

17.

16.

15.

14.

13.

12.

10.

9.

8.

7.

6.

5.

18.

21.

20.

23.

30.

27.

24.

26.

32.

33.

29.

11. 25. 28.

31. 19. 22.

200 150

4.

P1 P2 P3 P4 P5

200 200 200 150

270

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Results – Micro calorimeter

0.00 0.20 0.40 0.60 0.80 1.00

0 5 10 15 20 25

Heat release rate, mW/g

Time, h 60°C

Pellets L, sample 1 Pellets L, sample 2 Pellets M, sample 1 Pellets M, sample 2

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 5 10 15 20

Heat release rate (mW/g)

Time (h)

60°C _{A, pellets}

A, pellets B, pellets B, pellets C, pellets C, pellets C, powder C, powder

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Effect of temperature

0.00 0.50 1.00 1.50 2.00

0 5 10 15 20 25

Time (h)

80 °C, L Sample 1 80 °C, L Sample 2 60 °C, L Sample 1 60 °C, L Sample 2 40 °C, L Sample 1 40 °C, L Sample 2

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Variation in heat release rate

0 0.2 0.4 0.6 0.8 1 1.2

0 5 10 15 20 25

Pellets id

Fresh pine 4g Fresh S/P/EW 4g Fresh pine 8g Fresh S/P/EW 8g Stored pine 4g Stored spruce/pine 4g Stored S/P/EW 4g Stored pine 8g Other 4g

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Results – Medium-scale tests

0 50 100 150 200 250 300 350 400 450

0 10 20 30 40 50

Temperature (°C)

Time (h)

Test 1 Test 2 Test 3 Test 4

0 20 40 60 80 100 120 140

0 10 20 30 40 50

Temperature (°C)

Time (h)

Test 1 Test 2 Test 3 Test 4

Test Pellet type Air temperature in enclosure (ºC)

1 L 90

2 L 105

3 M 90

4 M 105

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Results – Medium-scale tests (2): Increase in temperature

Test Pellet type

Air

temperature in enclosure (ºC)

Pre- heating + 5h

+ 10h + 20h + 30h + 35h

1 L 90 16.1 18.9 23.4 26.5 27.8

2 L 105 20.8 24.7 34.4 55.4 304.6

3 M 90 4.2 7.2 11.6 12.6 12.3

4 M 105 5.8 10.2 17.1 21.4 23.4

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Modelling: Calculated heat production

0 100 200 300 400 500 600 700 800 900 1000

0 50 100 150 200

Heat production rate J/m3s

Temperature (°C)

Pellet M - CP Pellet L - CP Pellet M - µ-cal Pellet L - µ-cal

0 10 20 30 40 50 60 70 80 90 100

0 20 40 60 80 100 120

Heat production rate J/m3s

Temperature (°C)

Pellet M - CP Pellet L - CP Pellet M - µ-cal Pellet L - µ-cal

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Conclusions from the self-heating studies within LUBA (1)

• Micro calorimeter tests

– In total 21 different samples (13 different batches) were tested

• type of pellets

• physical form (whole pellets or crushed into powder)

• storage time (fresh or stored for several months)

• one sample after being involved in a 1 m3 self-heating test – Significant differences in propensity for self-heating

• difference between different types of pellets

• fresh pellets more active than stored pellets

• Increase in activity with increased temperature – Good repeatability in the micro calorimeter tests

– Micro calorimetry and crossing-point gave approximately the same overall ranking

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Conclusions from the self-heating studies within LUBA (2)

• 1 m³ tests

– Effective in separating the self-heating activity of the two types of pellets investigated

• Type M had a very moderate activity

• Type L showed much higher activity, resulting in spontaneous ignition

• The gas production was also higher for Type L – Possibilities for development of test method

• Modelling

– Small differences in heat production rate and critical ambient temperature (1 m³) between type L and type M based on crossing-point data.

– The calculation based on micro calorimeter data gave lower critical ambient temperature and larger difference between type L and type M.

– big silo > normal silo > flat storage > tower silo

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SafePellets: Characterization of the self-heating of wood pellets

Screening and classification

Determination of reaction kinetics (small scale)

– Isothermal calorimetry – Oven-basket experiments – TGA/DSC

Analysis of thermal and other

relevant physical properties of pellets

Mathematical simulations

Medium-scale tests

Real-scale tests

www.safepellets.eu

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Reports from the LUBA project on self-heating

SP Report 2012:49

SP Report 2012:50 www.sp.se

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Examples of other reports and recommendations of interest

www.ieabioenergy.com

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