Professor G.J. ‘Gus’ Nathan - The Combustion Institute€¦ · Professor G.J. ‘Gus’ Nathan...

15/12/2018

1

University of Adelaide 1

Professor G.J. ‘Gus’ Nathan

[email protected]

Solid Fuel Combustion and Gasification

Gus Nathan, Woei Saw, Philip van Eyk, Peter Ashman, Peter Ashman


CO2 mitigation needed in process heat, transport & electricity

Transport, 38%

Commercial, 8%

Residential, 11%

Industrial, 43%

of which 70% is supplied from natural gas

Australian End use Energy 2012 – 13Sources:

1. Australian end use source data: Energy in Australia 2014, ABRE

2. Processing temperature data CSIRO Energy centre, Beath

Philibert, “Renewable Energy for Industry” IEA

Report (2017)

Anticipated Trends in Global sources of CO2

15/12/2018

2


Industrial Process Heat – a long-term challenge

Philibert, “Renewable Energy for Industry” IEA Final Report (2017)

Low-Med (<400 C) = 52% boiling & drying

ore concentration & digestion

Food industry

High temp (>400 C) = 48% Reduction: Iron & steel, copper

Calcination: cement and alumina

Petrochemical


Annual Additions to Global Electrical Generating Capacity

2015

Cumulative to 2040

New Energy Outlook 2016, Bloomberg New Energy Finance

15/12/2018

3


Projected future mix in electrical energy systems

Global contributions to CO2 mitigation in electricity to 2050

IEA Solar Thermal Technology Roadmap 2014


Ongoing need for air transportation fuels

Source: BREE (2014)

Source: Aus Energy Update (2015)

15/12/2018

4


Long term critical needs for fuels

• Heavy industry: production of iron/steel, cement, alumina, etc

Fuels provide stored source of high temperature heat

Synergistic with CO2 capture, which may be needed

Cement & lime: CaCO3 + heat CaO + CO2

• Low temperature heat: domestic heating and light industry

Direct use of biomass, feedstock for hydrogen, etc

• Liquid transportation fuels:

Jet fuels: no replacement for kerosene is in sight

Diesel: potential co-product from agriculture

• Stored energy for electrical energy networks

Firm supply, black-starts, etc;


Main sources of solid fuels

• Coal - black, brown, lignite etc:

Fossilised biomass;

Large reserves available at low cost;

CO2 capture: potential to avoid climate change, but has limited social acceptance & significant cost

• Biomass – raw, chipped, torrefied, etc:

Renewable form of storable energy

Net life-cycle CO2 emissions must be calculated

Typically limited to moderate scale

• Waste – sludge, plastics, etc

Many are classified as carbon neutral;

Typically contain pollutants, such as chlorine

Source: ecohome.net

Source: ecohome.net

Source: ecohome.net

Source: wikimedia

15/12/2018

5


Application in Fires

• Mechanisms are similar to energy:

Same stages of volatiles, char and ash

• Building fires are often fuel rich

Pyrolysis stage is critical

• Toxic materials are important Plastics, new materials

Source: ecohome.net

Source: ecohome.net


Biomass supply chain: Here as a co-product of higher value product

15/12/2018

6


Biomass supply chain is typically complex:Here for liquid fuel with solar thermal processing

Syngas (H2 + CO)

Cooler

Torrefied pellets

Agricultural residues

PelletizerDryer TorrefierHammer

Mill

Combustor

Heat

Torgas

Air/Natural gas

Heat exchanger

TransportStorage

Solar Hybridized Dual Fluidized Bed

gasifier

Flue gas

Syngas treatment

Fischer-Tropschsynthesis

Liquid fuels

Source: abc.net.au

Source: conbio.info


Challenges and opportunities for biomass

• Biomass is a distributed resource Energy is required to collect, transport and upgrade the fuel

Life-cycle analysis is necessary to evaluate net gain

• Bio-derived energy is most viable as a co-product:

Utilisation only for energy is unstainable and expensive;

Residues have already been collected and transported;

• Biomass resources are insufficient to be a dominant source Global average expectation is for 7% contribution;

• Biomass and waste: highly valuable in niche applications

Residues from sugar, cotton, pulp and paper, etc;

Potential for circular economy to provide transportation fuels

15/12/2018

7


Properties of solid fuels

Dermibras (2014); Prog. Energy Combust. Sci: 30, 219-230.


Composition of typical biomass feedstock

Dermibras (2014); Prog. Energy Combust. Sci: 30, 219-230.

15/12/2018

8


Stages of Combustion of Solid Fuel Particle

Drying

Devolatilization

Char Combustion

Ash / Smelt Fuel

particle

Temperature

Mass

H2OCxHy

CO, CO2 O2


Characterisation of coal type according to rank

15/12/2018

9


Torrefied wood relative to raw wood and coalVan Krevelin diagram

Bergman, Boersma, Zwart & Kiel, “Torrefaction for biomass co-firing in existing powerstations” ECN-C-05-13, ECN Biomass, Netherlands, 2005.

TW(250) Torrefied woodat 250C


Combustion, Pyrolysis, Gasification, Torrefation

Q > 0

T < 100C

Steam Gasification

Pyrolysis Combustion GasificationDrying

Q > 0

300 <T < 700C

O2 = 0

Q < 0

T Adiabatic Flame

O2 > stoich

Q 0

700 <T < 1400C

O2 < stoich

Q 0

700 <T < 1400C

O2 = 0; H2O

Q > 0

200 <T < 350C

Torrefaction

Removes free

moisture

Bio-coalStable LHV

Tars +Char

CO2 + H2Oash +

pollutants

CO, H2 CO2

char +CxHy

H2 + CO Char +

H2S

CxHyH2O CxHy

O2 H2O

H2 CO

Partial combustion

15/12/2018

10


Source: Lawn and Goodridge (1987)

“Matching the Combustion Equipment to the Boiler”, ed: C.J. Lawn, Principals of Combustion Engineering for

Boilers, Academic Press, pp 1 - 60.

Schematic diagram of a coal-fired boiler


10 MWe Coal Water Mixture Flame

Unit 1, Chatham Boiler, Canada

source: Thambimuthu & Whaley (1987)

Pulverised fuel flames

60 MWth Pulverised coal flame in a pellet kiln (LTV steel)

Gyro-Therm burner

Source: FCT Combustion

15/12/2018

11


Typical dimensions of

large boiler (e.g. 500MWe):

• 40 m high

• 15 m deep

• 30 m wide

Burners

500MWe Oil-fired boiler

Source:

Lawn and Goodridge (1987)

Dimensions of large boiler


Residence time in pulverised fuel flames: Typically much longer than chemical times

Mixing rate controls reactions where kinetics are fast compared tomixing


0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

0 0.05 0.1 0.15 0.2 0.25

Residence Time (s)

[NO

]

(pp

m)

15/12/2018

12


Release of Na from burning coal particle in a flat flame

During Volatile

Combustion

During Char

Combustion

Burning Volatiles

Na plume

Source:van Eyk, Ashman, Alwahabi, Nathan, Proc CI., 32, 2099-

2106 (2009)


Volatile release increases with temperature

15/12/2018

13


Sec Air Exit Velocities: 30 m/s

Pre-heated Combustion air: 200 0C (boiler); 1200 0C (cement)

Burner Diameter: 1m (air port in boiler);

200mm (fuel pipe in cement)

Residence Times: 1 - 4 secs

Particle diameter: 60 μm (poly-diserse: 1 - 300 μm )

Particle heating time dp2 / mp cp

Particle burning time dp3 / diff

Volatile release time 100 ms (100m, PF flame)

Particle burning time 1 s (100m, PF flame)

Key Dimensionless Parameters


Reference case: pulverised fuel flame (coal, pelletised wood, etc)

Dfull-scale = 1m, Uf = 30m/s, dp = 100m, Lf = 20m

Residence Time: res Lf / U

char / res < 1 Incomplete combustion (carbon in ash)

char / res > 1 Additional release of volatile inorganics

Lf

DU

Key Dimensionless Parameters

15/12/2018

14


Reynolds number: Re = U D /

Flow speed to Flame Speed: U / USL

Residence Time: res Lf / U burn / res

Stokes Number: St = p / fluid p U dp2 / 18

Lf

DU

Other Dimensionless Parameters


The role of Stokes number

𝑺𝒌 =𝜏𝑝

𝜏𝑓=

𝜌𝑑𝑝2

18𝜇𝐿Sk <<1: particles exhibit strong response

to streamlines in turbulent eddy

Sk 1: particles exhibit partial response to turbulent eddy

Sk >>1: particles exhibit poor response to turbulent eddy

Image from: Mi, Nobes & Nathan, J. Fluid Mech

(2001), 432, 91-125.-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

r/d

x

d

Vortexstructures

S k S k

15/12/2018

15


Reference case: coal-fired burner

Df = 1m, Uf = 30m/s, dp = 100m, Ll = 20m

Scale model at 1/10 scale, same particle size:

Dm = 100mm, dp = 100m, Ll 2m

duRe

Scaling Method (const. particle size, temp, fluids)

Upilot (m/s)

full

pilot

Re

Re

full

pilot

U

U

full

pilot

full

pilot

St

St

Const Reynolds 300 1 10 0.001 100

Const Velocity 30 0.1 1 0.1 10 Const Residence

time ()

3 0.01 0.1 1 1

j

f

resU

L

18

2

pp duSt

Source: Nathan, et al. (2013) Progress in Energy and Combustion Science, 38 (1), 41-61 .

How key dimensionless parameters change when a burner is scaled down by 1/10 relative to a reference burner


NOx emissions from burners and furnaces of four different scales at four air pre-heat temps firing natural gas Source: Weber, R. et al (1996), Proc. Comb. Inst. 26, 2, 3343-3354.

Strengths and Limitations of Dimensional Analysis

Strengths:

• good insight into controlling mechanisms;

• Good reference for more detailed models

Limitations:

• Only consider one parameter

• Limited accuracy

15/12/2018

16


Importance of swirl in stabilising a flame

The influence of swirl on a 2.5 MW coal flame.

Tsec air = 300 0C, Vsec air = 36 m/s, Vprim air = 20 m/s

top: no swirl, bottom: swirl number = 0.9

Source: Smith, Nathan, Smart and Morgan (1999)

No Swirl

Swirl


Key reactions

Molino, A., Chianese, S.,

Musmarra, D. J. Energy Chemistry, 25, 1-25 (2016)

15/12/2018

17


Combustion Models


Combustion Models

15/12/2018

18


Combustion Models


Combustion Models

15/12/2018

19


Typical Structure of raw coal


Cracking of hypothetical coal molecule

15/12/2018

20


Simplified structure of biomass-derived tars

Molino, A., Chianese, S., Musmarra, D. “Biomass gasification

technology: The state of the art overview”, J. Energy Chemistry,

25, 1-25 (2016)


Combustion of solid fuels

15/12/2018

21





Diffusion = [m3/m2/s] = [m/s]

15/12/2018

22





15/12/2018

23




15/12/2018

24


The reaction processes are complex and variable.All models require significant simplifications

• Volatile release depends on particle size, heating rate & Tmax

These are difficult to predict and measure

• Conversion extent depends on tres, Tmax, mixture fraction :

These are non-linear, depending on turbulent mixing processes

• Fuel properties vary both with time and space Size: poly disperse distribution

Composition: natural variability (wood, leaves, bark)

Source: properties depend on soil and growing conditions

• Material properties change with extent of conversion

Char porosity changes with conversion extent;


Particle transport relative to a turbulent flow depends on Stokes number

Lau & Nathan, 2014, J. Fluid Mech., 757, 432-457.

𝑺𝒌 =𝝉𝒑

𝝉𝒇=

𝝆𝒅𝒑𝟐

𝟏𝟖𝝁𝑳

Where:𝝉𝒑 = particle time scale

𝝉𝒇 = turbulent eddy time scale

𝒅𝒑 = particle diameter

𝒑 = particle density

= fluid viscosity

𝑳 = Flow length scale

= dnozzle for this experiment

15/12/2018

25


Instantaneous distributions differ from mean due to clustering

Instantaneous properties that differ greatly from mean values:

• Mixture fraction

• Velocity (mean & RMS)

• Radiation heat transfer

Lau & Nathan (2017), I. J. Multiphase Flow, 88, 191-204.

Instantaneousconcentration

Meanconcentration

Measured Cluster (Rope)


Solid fuels contain ash, nitrogen and sulphur

15/12/2018

26


Inorganic species are also released during combustion

Drying

Devolatilization

Char Combustion

Ash / Smelt Fuel

particle

Temperature

Mass

H2OCxHy

CO, CO2 O2

Volatile Metals at low concentration



“Matching the Combustion Equipment to the Boiler”, ed: C.J. Lawn, Principals

of Combustion Engineering for Boilers, Academic Press, pp 1 - 60.

Ash: can cause fouling and slagging in boilers but is a useful product in cement

Source: private collection

Ash deposits on superheater tubes -

View inside a coal-fired boiler

Ash from fuel is adsorbed into

cement and is even added as

a supplement to limestone.

15/12/2018

27


Release of Na from burning coal particle in flat flame

During Volatile

Combustion

During Char

Combustion

Burning Volatiles

Na plume

Source:van Eyk, Ashman, Alwahabi, Nathan, Proc CI., 32, 2099-

2106 (2009)


Concentration (ppm or g . g-1

)Element

Average Range

Arsenic As 10 0.5 – 80

Beryllium Be 2 0.1 – 15

Cadmium Cd 0.5 0.1 – 3

Cobalt Co 5 0.5 – 30

Chromium Cr 20 0.5 – 60

Gallium Ga 5 1 – 20

Mercury Hg 0.1 0.02 – 1

Manganese Mn 70 5 – 300

Nickel Ni 20 0.5 – 50

Lead Pb 40 2 – 80

Selenium Se 1 0.2 – 10

Antimony Sb 1 0.05 – 10

Vanadium V 40 2 - 100

Biomass and coal also contain trace elements

Typical concentrations of trace elements in coal. (Dugwell, 2000)

15/12/2018

28


Adverse health effects of trace elementsElement Health Effects

As Anemia, gastric disturbance, renal symptoms, ulceration; carcinogen ic to humans

(lung and skin); suspec ted teratogen (birth defects)

Be Respiratory disease and h armful to lymphatic system, liver, spleen and k idney.

Carcinogen ic to animals and probably to humans;

Cd Emphy sema and fibrosis of the lung, renal injury and cardiovascular effects

suspected. Carcinogen ic to animals and probably to humans. Testicular toxicity to

rats and mice; Tetarogenic in rodents

Hg Neural and renal damage, cardiovascular disease. Methyl mercury is tetarogenic in

humans;

Mn Respiratory and other effects

Ni Dermatitis and intestinal disorders. Nickel and nickel oxide are carcinogen ic to

guinea pigs and rats. Nickel refining is associated causa lly with cancer in humans

Pb Amnesia, cardiovascular, neurological, growth retarding and gastro-intestinal effects.

Some compound s are animal and possible human carcinogens; Foeto-toxic and

probably teratogenic to humans


The fate of Trace Elements in a flame

Source: Linak and Wendt, Fuel Processing Technology, 39, 173-198 (1994)

Volatile metals vaporise in a flame and re-condense onto fine particles to much higher concentrations than in raw ash. These are toxic to humans and animals.

15/12/2018

29


The size distribution of ash particles from a pulverised coal flame

Source: Linak and Wendt, Fuel Processing Technology, 39, 173-198 (1994)


Key points

• Solid fuels are heterogeneous, complex and variable

Complex chemistry: long chain organic and inorganic species

Complex mixing: turbulent, multi-phase, multi-scale

Variable properties: size and composition

• All models of practical systems involve many simplifications Empirical constants: needed for the foreseeable future

Significant uncertainty is inherent in any modelling approach

• Validation is essential to give confidence in model

Comparison of prediction with relevant measured data

• Reliable solutions involve comparing alternative approaches

Scaling and analytical models: reference and guide

CFD: comparing a range of assumptions / models

15/12/2018

30


Combustion, Pyrolysis, Gasification

Q > 0

T < 100C

Steam Gasification

Pyrolysis Combustion GasificationDrying

Q > 0

300 <T < 700C

O2 = 0

Q < 0

T Adiabatic Flame

O2 > stoich

Q > 0

700 <T < 1400C

O2 < stoich

Q > 0

700 <T < 1400C

O2 = 0; H2O

Q > 0

200 <T < 350C

Torrefaction

Removes free

moisture

Bio-coalStable LHV

Tars +Char

CO2 + H2Oash +

pollutants

CO, H2 CO2

char +CxHy

H2 + CO Char +

H2S

CxHyH2O CxHy

O2 H2O

H2 CO

Partial combustion


Role of Solar Energy in gasification and pyrolysis

• Drying

Natural Solar energy: low operating cost, but large land area

Waste heat from a process: typically cost effective

• Pyrolysis and Gasification: Concentrated solar radiation: demonstrated at pilot-scale

• Potential advantages

Increases output of product gases

Lowers net CO2 intensity

• Challenges

Increases capital cost and complexity

Technology is still immature

15/12/2018

31


Gasification: Conventional or via Concentrated Solar Thermal Radiation

Biomass(coal)

Conventional Gasification

O2+

CO2

ProcessingPlant (e.g. FT)

H2O

COH2

Biomass(coal)

Gasification

+ Heat

Synthetic Diesel

Solar Gasification

CO2


Drivers and challenges for solar gasification

Biomass(coal)

Conventional Gasification

O2+

CO2

ProcessingPlant (e.g. FT)

H2O

COH2

Biomass(coal)

Gasification

+ Heat

Synthetic Diesel

Solar Gasification

CO2

Drivers:

• Pure syngas product: Avoids CO2 and N2

• Increased Syngas Production: by 40-100%

• Lower net CO2 : 25-40% solar share

Challenges: • Variable solar resource and continuous FT plant

• Capital cost of solar field

15/12/2018

32


Conventional oxy-gasification

Source: Ramezan, 2004.


Gasification Chemistry

15/12/2018

33


Gasification Phase Diagram

MAF: Moisture and ash freeSource: Ramezan, 2004.


Syngas (CO + H2): Building blocks for many products

Via chemical plant to: • Methanol• Plastics• Other chemicals

Via combustion to: • Electricity• Industrial heat

Via Fischer TroppsSynthesis to: • Kerosene (jet fuel)• Diesel• Gasoline

15/12/2018

34


Source: Ramezan, 2004.

Simplified oxy-gasification plant


Solar hybridised dual bed gasification - Typical configuration

Treceiver 950C; Tgasifier 850C;

15/12/2018

35


Solar Hybridised Dual Bed Gasification: Drivers and Challenges

• Drivers Moderate temperature of 850 C compatible with CST

Steady-state gasification greatly simplifies FTL

Direct heating of inert particles through windowless reactor

Potential to achieve AUD$1:20/L from agricultural residues

• Challenges Particle receivers not yet commercial at 1000C

Transport and storage of particles not demonstrated 1000C

Feed-stock supply chain: constrained and variable

Bed agglomeration augmented by successive oxidation/reduction


Hybridising avoids need to develop transient FT reactor

Adams et al (2009), I.J.H.E. 4, (21), 8877-8891Saw, Guo, van Eyk, Nathan, Solar Energy, in press (2017)

15/12/2018

36


Key elements of transient system modelling

Kueh, Nathan, Saw (2015). Applied Energy

Heliostat model(cosine losses, etc)

Receiver model(capacity, efficiency)

Storage model(capacity, efficiency)

Thermal conversion Unit model

(Aspen-hysis)

Losses(dumping)


Pseudo-dynamic model of HSRC in CSP plant

Main assumptions:

Steady-state at each time-step

mass and energy balanced

Good agreement with experiments

Lim, Nathan, Hu, Dally (2015). Applied Energy

15/12/2018

37


Logic diagram for energy flows at each time step

Lim, Hu, Nathan, (2016).

Applied Energy


Pseudo-dynamic system response over 4 days

Lim, Hu, Nathan, (2016). Applied Energy

15/12/2018

38


Levelised Cost of Fuel: re 2020 data

Saw et al. (2016), Internal report to ARENA.


Levelised Cost of Fuel: re 2020 data

Saw et al. (2016), Internal report to ARENA.

Now targeting agricultural residues

15/12/2018

39


Well-to-wheel emissions for coal-biomass blends

Guo, Saw, van Eyk, Stechel, Ashman, Nathan (2017), Energy Fuels, 31 (2), 2033-2043

APPROACH: Continuous operation by

hybridisation

Pseudo-dynamic model

12 month time series

Farmington, New Mexico

KEY ASSUMPTIONS:

Carbon closure for Biomass = 85%

Conversion = 80%

Char separation – 80%

16 hr thermal storage


Conclusions

• Principals of solid fuel combustion & gasification are well known

Three stages of volatile, char and ash reactions

• The details are highly complex and non-linear:

Properties of the fuel are both complex and variable

Coupled with non-linear, two-phase fluid dynamics

• Absolute and a-priori prediction is unrealistic in foreseeable future

No solution is in sight to manage both complexity and variability

• Reliable prediction is nevertheless possible, noting that:

Significant uncertainty will remain due to variability

All models involve some empiricism

Validation and the use of multiple models is necessary

15/12/2018

40


Centre for Energy Technology

Director: Professor Gus Nathan W: http://www.adelaide.edu.au/cet/T: +61 (0)8 831 31448E: [email protected]

Thankyou!

http://www.adelaide.edu.au/cet/

Professor G.J. ‘Gus’ Nathan - The Combustion Institute€¦ · Professor G.J. ‘Gus’ Nathan...

Documents

Transcript of Professor G.J. ‘Gus’ Nathan - The Combustion Institute€¦ · Professor G.J. ‘Gus’ Nathan...