Solid Fuel Combustion in Controlled Atmos pheres – an E … presentations/6c_1... · Solid Fuel...

Solid Fuel Combustion in Controlled Atmospheres –

E i t l C bilitp

an Experimental Capability

Sabuj Halder, Robert Churpita and William Mahoney*

175 East Park Drive, Tonawanda, NY 14150, USA

*Hans-Boeckler-Strasse 1, D-40476 Duesseldorf, Germany

3rd Oxyfuel Combustion Conference9-13 September 2013 – Ponferrada, Spain

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Solid Fuel Combustion

• Reaction steps (Combustion of a single particle)Pyrolysis (Gases, tar, char formation)Volatile Matter Ignition & CombustionChar Ignition & Combustion

HEAT MIXING MIXING

PULVERIZED SOLID FUEL

PYROLYSISIGNITION of IGNITION &

TRANSFERMIXINGWITH O2WITH O2

• Volatile matter combustion is faster than char combustion• Higher heating rates produce larger yields of volatile matter and lower amount of

PARTICLEIGNITION of

VOLATILE MATTERIGNITION &

OXIDATION of CHAR

g g p g ychar

• Oxidation of char controlled by chemical kinetics of C‐O2 reaction at lower temperatures, mass transport of O2 at high temperatures

Where your talent makes an impact2 | Praxair Business Confidential

p , p 2 g pFocus on Char Oxidation in this presentation

Typical Uses of Solid Fuels

• Electricity Generation (Fuel in Steam boilers) Steam boilers Coal gasification Syngas Steam boiler

Source: http://www.worldcoal.org/coal/uses-of-coal/coal-electricity/

• Materials Processing Applications (Fuel & Reducing Agent) Iron Blast Furnaces Rotary kilns (Cement, Coal based sponge iron) Rotary kilns (Cement, Coal based sponge iron)

• Chemicals Production (feed stock to produce synthetic

Courtesy: www.corusgroup.com

fuels and chemicals through liquefaction, gasification) Methanol Ammonia


Synthetic fuels (Gasoline, Diesel, Synthetic Natural Gas)

Metallurgical Applications

Pulverized Coal/Biomass injection in iron blast furnaces Pulverized coal injected for substitution of coke Injection through blast furnace tuyeres with the hot blast Higher injection rates limited by bed permeability Very low residence times available for combustion (~ 8‐12

msec)

Schematic of a Blast Furnace

Courtesy: www.corusgroup.com

Source: http://mccoy.lib.siu.edu/projects/crelling/character/character html

Pulverized coal burners in rotary kilns Combustion air may be preheated or at room

temperature Used in iron‐ore pelletizing, cement clinker production, www.corusgroup.comaracter/character.htmlp g, p ,

sponge iron production

Coal Burner

Coal/Oil BurnerBurner


Courtesy: www.understanding‐cement.comCartoon of a cement kiln Cartoon of a grate‐kiln iron‐ore pelletizing line

Effects of O2 Enriched Combustion*

K)

Mont. LigniteIllinois #6Model Calc.1700 K80

100

t Tim

e. (m

sec)Single Particle Experiments

@ 1700 K

3000

3200Illinois #6Montana Lignite

5500

(K

erat

ure

(F)

5000Model Calc. 20

40

60

Part

icle

Bur

n-ou

t

2600

2800

Part

icle

Tem

pe

4500

4000 14161820

0

20Ptio

n, (m

sec)

2000

2200

2400

Aver

age

P 4000

3500

468

101214

e fo

r Dev

olat

iliza

t

1800

2000

0 20Oxygen, (%)40 60 80 100

3000

024

Model Calc.

0 20 40 60 80 100

Tim

e

Oxygen percent, (%)


* L. D. Timothy, A. F. Sarofim and J.M. Beer, “Characteristics of Single Particle Coal Combustion”, Nineteenth International Symposium on Combustion, Vol.19, No.1. 1982, pp. 1123‐1130)

High Temperature De-volatilization*

(Coal: Pittsburgh 8 HVA Bituminous, Size: 38‐45 microns)

As De‐volatilization Temp Char , Volatiles


* H. Kobayashi, J. B. Howard, A. F. Sarofim , “Coal Devolatilization at High Temperatures”, International Symposium on Combustion, Vol.16, No.1. 1977, pp. 411‐425

Experimental Apparatus

CHAR SAMPLING PROBE


SECY. OXYGENNAT. GAS (AUX. FUEL)

Solid Fuel Combustion Apparatus

CHAR SAMPLING PROBE• Pilot scale simulation of

industrial combustors

Combustion

• Custom designed unit to study interactions of various solid fuel(s) under a controlled h h i l i Chamber

Section(Adjustable Length)

ENRICH. O2

thermo‐chemical environment: Hot air blasts, furnace specific atmospheres etc.Abilit t t l l i t Length)

BLAST AIR

• Ability to control several input experimental variables and measure the subsequent response

Blast (Combustion Air) Preheating

i

Solid Fuel Burning Device

response• Capability tool to study

sensitivity of different process variables on a pilot scale NOT


Sectionvariables on a pilot scale, NOTfor fundamental research

Solid Fuel Combustion ApparatusControllable Parameters

• Air (or other gas) Flow • Air (or other gas) Temperature• P ~ atmospheric • Oxidant O2 Concentration• Velocity (Diameter)• Residence Time (Length)( g )• Solid Fuel Injection Rate• Solid Fuel Burner Design• Solid Fuel Type, Particle Sizeyp ,• Auxiliary Oxygen/Fuel Source• Auxiliary Gas Injection (e.g., H2 or CO2)

AUXILIARY FUEL BURNER

SOLID FUEL INLET COMBUSTION CHAMBER SECTION


INLET

QUENCHED PARTICLE STREAM

COMBUSTION CHAMBER SECTION

Overall View


Sampling


Test Firing Video


Heating Rate & O2 Mass Transport

85

90

ct.)

Relative Effects of Hot Blast Temperature and Auxiliary Heat Source

A

75

80

out (

Mas

s Pc

B

C

21.0 Vol. Pct. O2 (No Auxiliary Fuel Burner)21.0 Vol. Pct. O (With Auxiliary Fuel Burner)

AB

B, C

1.15 m

60

65

70

Particle Size: - 200 mesh

arbo

n B

urno

Hot Blast ~ 1000 Nm3/hr• Local oxy‐fuel flames act as point heat sources and aid in particle

21.0 Vol. Pct. O2 (With Auxiliary Fuel Burner) 30.0 Vol. Pct. O2 (With Auxiliary Fuel Burner)

BC

50

55

Fixe

d C

a Hot Blast ~ 1000 Nm /hrCharcoal Inject. ~ 27.6 kg/hrAux. Burner NG ~ 4.3 Nm3/hrAux. Burner O2 ~ 8.6 Nm3/hr

heat sources and aid in particle heat‐up and ignition

• Particle heating rate & O2concentration are two handles

A

1600 1700 1800 1900 2000 2100 2200 2300 240045

(oF)

Reference Blast Temperature

2

925870 980 1035 1090 1150 1205 1260 1315 (oC)

• As particle temperature rises, sensitivity towards blast temperature decreases.

Mass transport of O attains significance at high particle


Mass transport of O2 attains significance at high particletemperatures; consistent with fundamental kinetic studies

Particle Size

85

90

ct.)

Effect of Particle Size

Blast Flow Rate ~ 1000 Nm3/hrBlast O Content ~ 21 vol pct

• Char oxidation limited by heat & O mass transfer inside the

75

80

85Charcoal Injection Rate ~ 27.6 kg/hr

t (M

ass

Pc

Blast O2 Content 21 vol. pct & O2 mass transfer inside the particle (for granular charcoal)

• Char oxidation gets quenched for granular charcoal once

No Auxiliary Heat Source

60

65

70

on B

urno

ut partially reacted char is ejected into cold ambient air.

• Particle size control critical for short residence time

Pulverized Charcoal (95% < 75μm)

50

55

60

xed

Car

bo

No Auxiliary Heat Source, -200 mesh No Auxiliary Heat Source, -36 +80 mesh

short residence time combustion applications

1600 1700 1800 1900 2000 2100 2200 230040

45Fix

870 925 980 1035 1090 1150 1205 1260(oF)(oC)

Granular Charcoal (100% > 150 μm)


Reference Blast Temperature870 925 980 1035 1090 1150 1205 1260 ( C)

Solid Fuel Injection Rate

90H t Bl t R t 1000 N 3/h

Effect of Solid Fuel Injection Rate, No Aux. Fuel •No auxiliary fuel injection (secondary burner inactive)

70

7580

85 Hot Blast Rate ~ 1000 Nm3/hrParticle Size: - 200 mesh

Mas

s Pc

t.)

(secondary burner inactive)• Consistent sigmoidal trends in burnout measurements;

• Excess oxygen in relation to b i b ti t

A5560

65

70

Bur

nout

(M carbon in combustion stream for all cases

• Same sensible energy of the hot blast heats up different

B40

45

50

No Auxiliary Fuel Injection

ed C

arbo

n B p

amounts of solid fuel proportionately; radiative heating from combustor walls absent in this case

1600 1700 1800 1900 2000 2100 2200 2300 240025

30

35

(oF)

Fixe 21 Vol. Pct. O2, Charcoal Inj. Rate ~ 27.2 kg/hr

21 Vol. Pct. O2, Charcoal Inj. Rate ~ 54.5 kg/hrA

B

absent in this case.


(oC)131512601205115010901035980925870Reference Blast Temperature

Particle Residence Time

85

90

Effect of Residence Time through Blast Velocity Control

)

70

7580

85

(Mas

s Pc

t.)

C A, B

C

50

5560

65

n B

urno

ut (

No Aux. Fuel, Blast ~ 1000 Nm3/hr No Aux. Fuel, Blast ~ 500 Nm3/hrAux NG 8 7 Nm3/hr Secy Ox 17 2 Nm3/hr Blast 500 Nm3/hr

BABC

C

3540

45

50

Charcoal Inj. Rate ~ 54.4 kg/hrBlast O2 Concentration ~ 21 Vol pct.

xed

Car

bon Aux. NG ~ 8.7 Nm /hr, Secy Ox. ~ 17.2 Nm /hr, Blast ~ 500 Nm /hr

A

C

• Char oxidation rate is stronglydependent on particle temperature, which, depends

d

1600 1700 1800 1900 2000 2100 2200 2300 240025

30 Particle Size: -200 mesh

(oC)(oF)

131512601205115010901035980925870

Fix on residence time.

• Utility of local point heat sources on particle temperature should be

d i li h f i l


Reference Blast Temperature assessed in light of particle residence time

Flame Photographs

Visual Flame Length Estimation Char Sampling from Combustion Stream

Combustion Zone Inside Tube AssemblyCombustion Zone Inside Tube Assembly


(w Auxiliary Pilot Flame)(w/o Auxiliary Pilot Flame)

Thermal Nozzle Technology*

• Applied to (Refractory) Alternative Fuel Combustion• Applied to Partial Oxidations (Gasification)

P h i f f hi h l i / j• Pre‐heating of oxygen to form a high velocity/temperature jet• Temperature and velocity controlled by fuel flow rate• Non water cooled• Non water cooled

O xyg en

H t

O xyg en

H tF u el

H o tO xyg enJet

F u elH o tO xyg enJet


*J. E. Anderson, “Thermal Nozzle Combustion Method”, United States Patent 5266024, Nov. 30, 1993

Hot Oxygen Chemistry

Product Oxygen

T t R t tSonic

V l itTemperature °C

ReactantComposition Percent

Velocitym/s

1350 Oxygen

Natural Gas

100 m³

6.4 m³

Oxygen Carbon Dioxide

Water Vapor

81.9 6.0

12.1 745

1650 Oxygen

Natural Gas

100m³

8.2 m³

Oxygen Carbon Dioxide

Water Vapor

77.1 7.6

15.0800

Water Vapor


Thermal Nozzle Technology: Hot Oxygen Jet


Thermal Nozzle: Hot Oxygen Jet


Visual Observations

BASELINE (21% O2) ENRICHED AIR (25% O2)


AMBIENT OXYGEN INJECTION (25% O2) HOT O2 INJECTION (25% O2)

Experimental Results

3.0

s)

Normalized Average Carbon Burnout under Various Injection Conditions

• Similar O /C ratio and blast

2.0

2.5

rnou

t (U

nits • Similar O2/C ratio and blast

temperature for conditions B, C & D

1.5

Car

bon

Bur • Multiple char samples

collected for each condition• Numbers are likely to

0.5

1.0

Nor

mal

ized

ychange from one kind of pulverized solid fuel to other & blast conditions

A B C D0.0

N

Injection ConditionA: Baseline Condition (21 Volume Pct. O2)B: Enriched Hot Blast (25 Volume Pct. O2)C: Ambient (Cold) Oxygen Injection (25 Volume Pct O )25‐35 mass pct. increment in fixed carbon


C: Ambient (Cold) Oxygen Injection (25 Volume Pct. O2)D: Hot Oxygen Injection (25 Volume Pct. O2)

25 35 mass pct. increment in fixed carbon burnout for Hot O2 injection

Summary.• Controlled atmosphere studies useful for understanding the relative impact of the

various variables on the combustion behavior of various solid fuels.

Char oxidation is limited by O carbon chemical kinetics (low T) and mass transport of• Char oxidation is limited by O2-carbon chemical kinetics (low T) and mass transport of O2 from gas phase (high T); current results support these fundamentals

• In particle streams, heat transport to the particles becomes rate controlling during theIn particle streams, heat transport to the particles becomes rate controlling during the initial stages; O2 concentration in gas phase attains importance after char oxidation reaction enters diffusion transport control regime

• Local point heat sources boost particle heating for applications limited by short residence times for a pulverized solid fuel (Hot Oxygen Technology)

• Granular materials require adequate residence time for oxidation reactions to initiate;• Granular materials require adequate residence time for oxidation reactions to initiate; should be carefully evaluated for short residence time applications

• High O2 concentrations promote volatile matter combustion; effect on char oxidation


g 2 p ;pronounced when char particle temperatures are high enough for O2 mass transport to become rate limiting

Acknowledgements

• Christopher Herby• Valmiro Correia• Lawrence Beiter• William Carey


Questions?


Back-up Materials


Particle Size Distributions of Solid Fuel

90

Pulverized Charcoal (-200 mesh, As Received) Particle Size Distribtution

ASTM Mesh Size Microns

325 45

200 75

60

70

80

etai

ned

(%)

A: -325 meshB: -200 +325 meshC: 100 +200 mesh Granular Charcoal (-36 +80 mesh As Received) Particle Size Distribtution

200 75

100 150

50 300

20

30

40

50

ss F

ract

ion

Re C: -100 +200 mesh

D: -50 +100 meshE: +50 mesh

70

80

90

Granular Charcoal ( 36 +80 mesh, As Received) Particle Size Distribtution

d (%

) A: -325 meshB: -200 +325 meshC: 100 +200 mesh

‐200 mesh

A B C D E0

10

20

Mas

Si Si I l40

50

60

ctio

n R

etai

ned C: -100 +200 mesh

D: -50 +100 meshE: +50 mesh

Sieve Size Interval

10

20

30M

ass

Fra

2 different particle size distributions of charcoal t t d

‐36 +80 mesh


A B C D E0

Sieve Size Interval

tested

Charcoal Analysis

Fixed Carbon (Mass %)

Volatile Matter (Mass %)

Ash

(Mass %)

Moisture

(Mass %)(Mass %) (Mass %) (Mass %)

55-65 23-29 8-11 2.3-3.3

Carbon (Mass %)

Hydrogen (Mass %)

Oxygen

(Mass %)

Nitrogen

(Mass %)

Ash

(Mass %)

68-75 2-2.3 12-15 0.35-0.45 8-11


Hot Blast Temperature Distribution

2500Radial Temperature Profiles

2.0

Cross section of combustion chamber

2000

2250 r0.0

1250

1500

1750

atur

e (o F)

X

‐ 2.0 X= Fixed

750

1000

1250

H t Bl t 1000 N 3/h X = 29 cmTe

mpe

ra X~ 115 cm

• Radial temperature gradients exist

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0250

500Hot Blast ~ 1000 Nm3/hrTC6 (Ref.) ~ 2025-2030oF

X = 56 cm X = 89 cm

• Radial temperature gradients exist in the initial portion of combustion chamber; mixing of blast with cold solid fuel carrier gas.

• Temperature gradients weaken in


2.0 1.5 1.0 0.5 0.0 0.5 1.0 1.5 2.0

Radial Coordinate (Inches)• Temperature gradients weaken in later half of combustion chamber

Particle Size (Granular Charcoal)

50.0

Effect of Particle Residence Time & O2 Concentration

47.5

Hot Blast ~ 1000 Nm3/hr

ss P

ct.) No Auxiliary Fuel Injection

21 Vol. Pct. O2 (Hot Blast ~ 1000 Nm3/hr)

GRANULAR CHARCOAL (100% > 150 μm)

42.5

45.0

Bur

nout

(Mas 2 ( )

25 Vol. Pct. O2 (Hot Blast ~ 1000 Nm3/hr) 30 Vol. Pct. O2 (Hot Blast ~ 1000 Nm3/hr)

•Weak dependence of carbon

40.0

d C

arbo

n B •Weak dependence of carbon

burnout on blast temperature as well as O2 concentration in gas phase

1600 1700 1800 1900 2000 2100 2200 2300 240035.0

37.5

Charcoal Inject. Rate ~ 27.2 kg/hrFixe Particle Size: - 36 + 80 mesh • Limited amount of char oxidation

• Rate is limited, most likely, by heat transfer within the char particle


Reference Blast Temperature (oF)

Char Oxidation

Single Char Particle Analysis

l/cm

2 s)

eat Loss

eneration (ca

t Gen

eration/He

Rate of H

eat G

Rate of H

eat

Particle Temperature

Char Oxidation usually controlled by •A coupled relationship exists between particle &

Superposition of heat generation curves and a family of heat loss curves to determine equilibrium state of particle temperature

R Particle Temperature

Particle TemperatureHeat Generation Curve with Particle Temperature

Char Oxidation usually controlled by (a) Chemical kinetics of oxidation reaction (Low particle

temperature; early stage of oxidation)(b) Diffusion transport of O2 (Higher particle

temperature; later stages)

A coupled relationship exists between particle & gas temperatures, heat and mass transport and char‐O2 chemical reaction•Particle temp can increase beyond gas temperature


* M.A. Field, D.W. Gill, B.B. Morgan, P. G. W. Hawksley , “Combustion of Pulverized Coal”, The British Coal Utilisation Research Association , Leatherhead, 1967

temperature; later stages) temperature

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