ccsem investigation of ash formation during oxyfuel combustionieaghg.org/docs/general_docs/5oxy...

CCSEM Investigation of Ash Formation during Oxyfuel Combustion

Tai ZHANG , Zhaohui LIU *, Xiaohong HUANG , Qing SUN ,Chao LIU , Chuguang ZHENG

State Key Laboratory of Coal Combustion Huazhong University of Science and Technology

5th. Oxyfuel Combustion Research Network MeetingWuhan Oct. 27-30, 2015

*: Email:[email protected]

http://www.ieaghg.org/

http://www.ieaghg.org/

Background1

Outline

Experimental setup and analysis method2

Results and discussion3

Conclusion4

煤燃烧国家重点实验室State Key Lab Coal Combustion

Background1


Oxy-fuel combustion technology

Background1


Many researchers found that the chemical compositions of fly ash and ash deposits were not significantly different between air condition and oxyfuel condition, but higher deposition rate and deposition propensity in oxyfuel condition.

Yu (2011), Fryda (2012), Li GD (2013) et al.

chemical changes of the flue gas

gas flow rate combustion temperature

Mineral??? Composition and size distribution

CCSEM (computer-controlled scanning electron microscopy) is a useful technology on the basic of the mineral particles that can characterize the minerals of ash particles in term of size, shape, abundance and associations.

Background1


Air and Oxyfuel conditions

Different O2 concentrations

Size distribution

Mineral composition

Elemental distribution

The present work was addressed toward the ash characteristic of a Chinese coal by using computer-controlled scanning electron microscopy (CCSEM),

Background1

Outline



Conclusion4




Summary of Features

Particle feed rate 5-500 g/h

Particle residence time 10-2000 ms

Particle heating rate >104℃/s

Gas supply primary burner O2, CO2, N2

Gas supply secondary burner O2, CO2, N2

Operating pressure 0.1 MPa

Reaction tube inner diameter 0.076m

Reaction tube length 1.4 m

Max. electrical heating temperature

1500 ℃

Probes for(fractionated)

ash particle & deposit sampling

gas temperature & composition

High temperature drop tube furnace (DTF)

Experimental setup and analysis method2 Coal Selection

Ultimate analysis (%)Cdaf Hdaf Odaf Ndaf Sdaf

79.66 4.32 14.67 0.69 0.66

Proximate analysis(%)Mad Vad Aad FCad

ZD coal 5.04 49.39 8.55 37.04

SiO2 Al2O3 Fe2O3 TiO2 CaO MgO K2O Na2O SO344.75 19.33 5.47 1.52 11.24 3.44 1.52 4.79 7.55


Sampling time was about 4 hours in DTF, and all samples were ashed at 550℃ to remove organic carbon.

Experiment condition

Feed Rate Temperature(℃)

Burnout Ratio20%

O2/N2

20% O2/CO2

30% O2/CO2

50% O2/CO2

10g/h 1450 90.47 91.92 90.19 92.87

Particle Size: 38~74μm


Mineral liberation analyzer (MLA, IPE CAS)

Analysis method


Type of test Pretreatment

MLA Curing, Grinding, Polishing, Carbon Coating;

Catch the image(BSE)

Deduct the background

Identify the mineral(Zygrlicke and Steadman, 1990)

Background1

Outline



Conclusion4




King（1982）

Correction method

Size distribution of raw coal and bulk ash particles

1 10 1000

2

4

6

8

10

wt%

Diameter (um)

Air OXY 20 OXY 30 OXY 50

refactory vaporization

particle fragmentation

particle temperature

PM2.5 >PM2.5, <PM10 >PM100

10

20

30

40

50

60

wt%

Diameter (um)

mineral in raw coal Air OXY 20 OXY 30 OXY 50



Composition of raw coal

SiO2 Al2O3 Fe2O3 TiO2 CaO MgO K2O Na2O SO30

10

20

30

40

50

Frac

tion

(%)

XRF CCSEM

Quartz

(%)

Hematit

e (%)

Rutile (

%)

Calcite

(%)

Montm

orillon

ite (%

)

K-Al Silic

ate(%

)

Ca-Al S

ilicate

(%)

Na-Al S

ilicate

(%)

Pyrite (

%)

Gypsum

(%)

Unclas

sify (%

)0

5

10

15

20

25

30

Mas

s fra

ctio

n of

min

eral

(%)

Included mineral Excluded mineral

XRF and CCSEM results only have a little error. 86% of ash is excluded mineral and the rest is included mineral.



Composition of bulk ashes

Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 Fe2O30.0

0.5

1.0

1.5

2.0

m /

m0(i

n as

h of

raw

coa

l) Air OXY 20 OXY 30 OXY 50

Compared with ash composition of raw coal, there are just a little different among the samples from these conditions.



Mineral composition in the bulk ashes

20%O2/N2

20%O2/CO2

30%O2/CO2

50%O2/CO2

0 10 20 30 40 50 60 70 80 90 100

Low Middle(co-melting)

High

Unknown Pyrite Pyrrhotite Carbonate(Ca, Fe, Mg) Albite (Na) Sulphate (Ca, Fe, K) Fe Silicate Ca Aluminate Fe-Ca-Al Silicate K-Al Silicate Fe-Al Silicate Ca-Al Silicate Ca Silicate Rutile Iron oxide Mixed Silicate Quartz

melting points

High O2 concentration enhances the co-melting of mineral;High CO2 concentration inhibits the decomposition of carbonate mineral

1600℃ 1200℃

Results and discussion3 Distribution of ash-deposition- related elements


10

20

30

40

50

60

70

80

90

100

Na %

Unknown Albite(Na) Ca Silicate K-Al Silicate Fe-Al Silicate Ca-Al Silicate Mixed Silicate

O2 ↑ Tparticle ↑More Na form the co-melting mineral with Fe, Ca, K;


1 10 1000

2

4

6

8

10

12

14

16

18

20

Na

(Wt%

)

Size (μm)


PM2.5 >PM2.5, <PM10 >PM100

20

40

60

80

Na

/ wt%

Diameter (um)



CO ↑ More Fe form the co-melting mineral;

O2 ↑ Tparticle ↑More Fe form co-melting mineral and unclassified mineral;


1 10 1000

2

4

6

8

10

12

14

16

18

20

Fe (W

t%)

Size (μm)


PM2.5 >PM2.5, <PM10 >PM100

10

20

30

40

50

60

70

80

Fe (w

t%)

Diameter


Air OXY 20 OXY 30 OXY0

10

20

30

40

50

60

70

80

90

100

Fe %

Unknown Pyrite Fe-Ca-Al Silicate Fe-Al Silicate Ca-Al Silicate Iron oxide


Air OXY 20 OXY 30 OXY0

10

20

30

40

50

60

70

80

90

100

Ca

%

Unknown Carbonate(Ca, Fe, Mg) Albite(Na) Sulphate(Ca,Fe K) Ca Silicate Ca Aluminate Fe-Al Silicate Ca-Al Silicate Rutile Iron oxide Mixed Silicate

O2 ↑ Tparticle ↑More calcite was decomposing and forming the co-melting mineral;


1 10 1000

2

4

6

8

10

12

14

16

18

20

Ca

(Wt%

)

Size (μm)


PM2.5 >PM2.5, <PM10 >PM100

20

40

60

80

Ca (w

t%)

Diameter

20% O2/N2 20% O2/CO2 30% O2/CO2 50% O2/CO2

Background1

Outline



Conclusion4


In this study, The effect of gas phase conditions on the physical and chemical changes of ashes were investigated by CCSEM. The following results are obtained:

• Oxyfuel combustion produced less fine particles (<10μm) and more coarse particles (>10μm) than air combustion at the same O2 concentration, and there are more fine particles (<10μm) and less coarse particles (>10μm) in oxyfuelcombustion with the increasing of O2 concentration.

• High O2 concentration enhances the co-melting of mineral, and high CO2concentration not only affects the transformations of coal minerals, but also shortens the decomposition process and extends the oxidation process slightly.

• The increasing of particle temperature can not only enhance the vaporization of refactory oxide, but also enhance interaction of the finely dispersed combined with inherent mineral particles.

Conclusions


4

The end

Thank you for your attention!

This work was supported by the National Natural Science Foundation of China (51390494), Ministry of Science and Technology (2011CB707301 and 2011BAC05B03), and Shenhua Group (GHFKJJS12-067).

ccsem investigation of ash formation during oxyfuel combustionieaghg.org/docs/general_docs/5oxy...

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