In-situ Observation of the Combustion of Air-Dried and Wet ... · • Combustion sequence is similar for dry and wet coal • Cloud ignition takes place via a volatile flame, which

Eleanor Binner, Lian Zhang, Sankar BhattacharyaDepartment of Chemical Engineering, Monash University

Chun-Zhu LiCurtin Centre for Advanced Energy Science and Engineering

Curtin University of Technology

InIn--situ Observation of the Combustion of situ Observation of the Combustion of AirAir--Dried and Wet Brown CoalDried and Wet Brown Coal

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Summary

• Australia’s role as a greenhouse gas emitter• Significance of Victorian brown coal research• Victorian State Government initiative• Dried brown coal combustion project• Preliminary results of dried brown coal project• A taster of the oxy-fuel results

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Greenhouse gas emissions per capita

Source: Commonwealth of Australia October 2008 “Australia's Low Pollution Future: The Economics of Climate Change Mitigation”, Table 3.2

4/20

Power generation mix

Oil7%

Gas21%

Hydro15%

Other10%

Coal30%

Nuclear17%

Oil2%

Gas15%

Hydro6%

Other1%

Black Coal55%

Brown Coal21%

Australia 2005-62European Union 20071

1European Wind Energy Association (2008)2Australian Government department of Resources, Energy and Tourism (2008)

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Power generation mix

Oil2%

Gas15%

Hydro6%

Other1%

Black Coal55%

Brown Coal21%

Australia 2005-62

Brown Coal

•Australia has the largest brown coal reserves in the world, and is the fifth largest producer

•Predominant power source of Victoria

•Cheap, abundant source of energy

•Energy content ~10 GJ/tonne

•Brown coal accounts for ~11% of CO2 emissions in Australia

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Recognising the problem

• Victorian State Government “Energy Technology Innovation Strategy”

• Partnering researchers and industry to tackle the problem• Monash coal science group involvement:

– Dried Brown Coal Combustion– Oxy-Fuel Combustion– Gasification– New projects in chemical looping– Collaboration with Japan/India/Europe

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Victorian brown coal properties

• ASTM classification lignite B• High moisture content (50 – 70 wt%)• Low ash content (<2 wt% dry basis)• Volatile metallic species (Na, Mg, Ca)• High Oxygen (>25 wt% db)• Low carbon (<70 wt% db)• Sulphur generally low (<0.5 wt% db)• Abundant pore structures• Close to the properties of German brown coal, especially

Rhineland• Dissimilar to e.g. Czech and Russian brown coal

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Dried brown coal project

• ~20% of thermal energy generated used to evaporate water and superheat steam

• Efficient drying technologies could significantly decrease CO2 emissions per unit of energy produced

• Drying techniques– Evaporative drying– Non-evaporative drying

• This is an experimental study to determine the potential changes to combustion phenomena

– Ignition– Flame characteristics– Char structure– Char reactivity– AAEM volatilisation

• Complemented by modelling activities at CSIRO

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Dried brown coal project

• Drying will effect– Water content– Physical and chemical structure– Reactivity

• We are first using air-dried coal, and wetting it to obtain the ‘wet’ samples

• Later we will consider using coal dried by more realistic drying processes

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Drop tube furnace

Secondarygas

Coalfeeder

Primarygas

Pyrometer

To gas analyser

High-speedcamera

Water-cooled coal injection probe

2000

mm

300

mm

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Drop tube furnace

Secondarygas

Coalfeeder

Primarygas

Pyrometer

To gas analyser

High-speedcamera

Water-cooled coal injection probe

2000

mm

300

mm

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Drop tube furnace

Secondarygas

Coalfeeder

Primarygas

Pyrometer

To gas analyser

High-speedcamera

Water-cooled coal injection probe

2000

mm

300

mm

13/20

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In-situ studies: high speed camera – 2000 fps, 1000°C

Wet Coal~30% water content

<105 um particle size0.2 m from injector

Dry Coal~10% water content

<105 um particle size0.15 m from injector

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Typical Phenomona Wet Coal Image d (m) Dry Coal Image Typical Phenomena

•Flame usually ignites below this window. 0.20 •Flame usually ignites

at this level or above.

•Constant stream of bright particles observed•Often forming localised fireballs•Clouds of steam evident

0.25

•Approximately 70% of the time, single or clusters of particles burning heterogeneously

•Predominantly individual particles 0.30 •Most of the frames

are blank

In-situ studies: ignition delay

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In-situ studies: particle temperature

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.651000

1020

1040

1060

1080

1100

1120

1140

1160

1180

1200

1220Av

erag

e P

artic

le T

empe

ratu

re (C

)

Distance from Injector (m)

wet dry

total gas flow rate 10 Lmin-1, coal feeding rate ~0.6 gmin-1

error bars represent ± 1 standard deviation

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In-situ studies: Findings

• Combustion sequence is similar for dry and wet coal• Cloud ignition takes place via a volatile flame, which causes

rapid heat-up of the particles and leads to heterogeneous char combustion

• Steam is evolved in the volatile flame in the wet case, decreasing flame stability and suppressing particle heat-up

• Ignition delay ~ 6 - 20 ms for wet coal in this furnace• Combustion is prolonged in wet coal• The maximum particle temperature is ~ 80°C higher in the dry

case

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Dried brown coal – Possible reasons for differences

• Energy used to vaporise water and superheat steam reduces the temperature in the furnace and cause an ignition delay

• Heat transfer in the furnace is expected to be suppressed by the presence of stream

• Other Involvement of water? – Could suppress volatile escape– Physical changes to char– Gasification of the char and/or evolved volatiles

C + H2 O H2 + COCO + H2 O CO2 + H2

– Could affect the role of alkali and alkaline earth metallic species (AAEM), which have a catalytic effect during brown coal combustion

– ?• Extensive analysis of char and ash planned to determine the chemical

effects of moisture content

19/20Furnace temperature 1000Furnace temperature 1000ooC, particle size 105 C, particle size 105 –– 153 um153 um

100 mm 200 mm 300 mm 400 mm

Air

100 mm 200 mm 300 mm 400 mm

21% O2 + 79% CO2

Oxy-fuel Combustion

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Sankar Bhattacharya: [email protected]

Lian Zhang: [email protected]

Ali Akhavan: [email protected]

Eleanor Binner: [email protected]

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References

• ABARE, Energy and Minerals Branch (2008), Energy in Australia, Australian Government Department of Resources, Energy and Technology, p. 40.

• Australian Government (December 2008), Australia’s greenhouse gas emissions fact sheet

• Commonwealth of Australia (October 2008), Australia's Low Pollution Future: The Economics of Climate Change Mitigation, Table 3.2

• Energy Technology Innovation Division D.P.I., (19th December 2008), Energy Technology Innovation Strategy

• Geoscience Australia (2008), Australian atlas of minerals resources, mines and processing centres, E.a.T. Department of Resources

• Li C-Z (2004), Advances in the Science of Victorian Brown Coal, Chapter 1, Elsevier

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Project partners

ResearchFunding

In-kind contributions

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Reactor Capabilities

• Maximum furnace temperature ~ 1,200 °C.• Coal Feeding Rate 50 – 1,500 mg/min (ideally).• Effective furnace length can be changed by varying the coal injector

length.• Gas flow rate 0.5 – 20 L/min.• Residence times 2 – 20 seconds.• Combustion atmospheres of air, oxygen, carbon dioxide, nitrogen,

steam, or any combination, possible.• Transparent quartz reactor with five observation ports.• High speed camera and pyrometer installed to measure coal particle

temperature, velocity and flame properties.• Gas analyser for continuous on-line monitoring of flue gases (O2 , CO2 ,

CO, SO2 and NO)

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Mass f lowcontrollers

Coalfeeder

Primarygas

ONOFF

Temperaturecontrollers

Oscilloscope

Pyrometer

Secondarygas

Thimble filterSilica gel

Air O2 CO2

Air O2 CO2

PC

To gas analyser(O2, CO2, CO, NO, SO2)

High-speedcamera

HPLC pump

H2O

Drop Tube Reactor

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Photos of the Reactor FacilityPhotos of the Reactor Facility

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Burning coal particle observation:

In-situ observed by a state-of the-art high-speed camera (Motion Pro Y3, IDT Co., Ltd, Germany);

Anti-blooming CMOS sensor to avoid brightness saturation;

Shutter speed: 10~ 2000 frames per second (fps) for 2560 ×

2048;

Pre-calibration on its spatial and time resolutions each time;

Mounted with a macro lens having field of view of 2 cm square,and pixel resolution of ~100 µm (particle size~ 20 µm).

InIn--situ Diagnostic situ Diagnostic MethodsMethods (2)(2)

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Coal Samples Used

PROXIMATE• Ash content is 1.9 % (dry basis)• Moisture content 14.5 % (dry) and 31.9 % (wet)• Volatile 51.6% (db)

ULTIMATE• Carbon 65.3% (db)• Hydrogen 4.7% (db)• Nitrogen 0.55 % (db)

SIZE RANGE• <105 µm and 105 – 152 µm available

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(a) (b) (c) (d)

(e) (f) (g) (h)

(i) (j) (k) (l)

Ignition Studies - Phenomena

Combustion phenomena observed at 500 fps and exposure time ~990 ms for wet and dry coal total gas flow rate 10 Lmin-1, coal feeding rate ~0.6 gmin-1

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AAEM volatilisation - Overview

• Alkali and Alkaline Earth Metallic Species (Na, Ca, Mg) are dispersed in the coal on an atomic level, usually weakly bonded to organic compounds

• They can break these bonds and volatilise easily• They can then bind to inorganic anions such as OH-, SO2

-, Cl-, Al-Si etc.

• They can then condense into very small particles causing fouling and health problems

• Therefore, it is important to understand the effect drying the coal will have on the volatilisation of AAEM

• Investigations to be carried out at Chubu University

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AAEM - Chemical Analysis Techniques

• Computer-Controlled Scanning Electron Microscopy (CCSEM) - determine particle size distribution, particle shape and distribution of elements on the particles. Statistical analysis possible. Of a cross section of material.

• X-Ray Diffraction (XRD) – crystalline species measurement and quantification

• X-Ray Fluorescence (XRF) – elemental composition of ash• X-Ray Photoelectron Spectroscopy (XPS) – empirical formula,

chemical state and electronic state of elements of interest

A physical model of inorganic (ash) transformation during combustion

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AAEM - FactSage

• Chemical modelling package to compare with experimental results

• Transformation of refractory minerals and formation of slag

• Transformation of volatile and semi-volatile metals and especially their vaporisation/condensation

• Used to validate and gain a better understanding of the chemical analysis results

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Sample selection

Temperature 800 – 1000 C

Particle Size 106 – 153 µm

AtmosphereAirNitrogen

Gas Residence Time 2 – 4 seconds

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Australia, Kyoto and beyond

• Australian per capita CO2 emissions are 4.5 times the global average

• Australia ratified Kyoto Protocol in December 2007• Target is to increase emissions by 8% from the 1990 level over

the period 2008 – 2012• Projection is that emissions will be increased by 9% over that

period• Stationary energy emissions have increased by nearly 50%

since 1990• National Emissions Trading Scheme to take effect in 2010• Kyoto successor will be more stringent