Estimation of Water of Constitution in Chinese Coals Using...

Estimation of Water of Constitution in Chinese Coals Using Mineral

Liberation AnalysisMartin Gräbner a

Edward Lester b

7th International Freiberg/Inner Mongolia Conferenc e - Coal Conversion and SyngasHuhhot, Inner Mongolia, China | June 7-11 2015

a Air Liquide Forschung & Entwicklung GmbH | Frankfurt Research & Technology Center | Germany b Department of Chemical and Environmental Engineerin g | The University of Nottingham | United Kingdom

Outline

Background and MotivationAir Liquide’s CoAL gasification R&D program

Lurgi FBDBTM Mk PlusTM development

Chinese coals & impact of minerals

Kaolinite in coal

ExperimentalSelection of experimental techniques

Sample selection

Air Liquide, world leader in gases for industry, health and the environmentResearch & Development2

Sample selection

Reference case for verification

Results and Discussion

Results of mineral liberation analysis (MLA)

Calculation of ash from mineral matter

Comparison of MLA vs. XRF ash composition

Analysis of the results

Conclusions

2015

Air Liquide‘s CoAL Gasification R&D Program

Feedstock characterization

� Coal lab with large coal database of 50 years operation experience

� Detailed standard test program

� Proprietary tests tailored to FBDB, coal test development

Support to Lurgi FBDB Mk+ development

� Development of experimental equipment

� Innovation towards reduced environmental footprint

� High-pressure reactivity

� Kinetic gasification model

Co-product analysis and valorization

� Tar, oil, naphtha characterization,

Air Liquide, world leader in gases for industry, health and the environmentResearch & Development3 2015

� Tar, oil, naphtha characterization, prediction and utilization

� Optimization of co-product processing units

� Ash and slag valorization

Beyond the lab…

� World wide network of academic partners

Support to operation

� Coal blending

� Ash and slag behavior

Lurgi FBDBTM Mk PlusTM Gasification

Reactor Temperature Profile

Typical FBDBGas Composition

H 38%

Feedstock� Low value coals (high

ash & moisture) � Direct use of coarse

coal � No drying, milling or

washing required

Decomposition of minerals


source KIT

High Thermal Efficiency � Hot syngas is drying the coal� Hot ash is preheating the blast

Advantages� Energy efficient gasification of:� High ash coals with high AFTs� Coals with high moisture content � High concentration of CH4in the syngas

H2 38%

CO 22%

CO2 28%

CH4 12%

High Value Co-Products � Tar, Oil, Naphtha � Phenol & Ammonia

2015

Chinese coals & impact of minerals

Higher-rank coals can show high contents of clay minerals [1,2]:

North China: Carboniferous-Permian coals with elevated clay content (kaolinite) [3]

� Daqingshan coal from Inner Mongolia


Problems:

� Significant content of water of constitution � devolatilization at 500-600°C

� Large bias in proximate and ultimate analyses (inorganic O+H)

� Correction required: key design figures for Lurgi FBDB coal gasification

2015

� Daqingshan coal from Inner Mongolia

� Taiyan coal of Tongchuan area

� Datong coal area of Shanxi

Kaolinite in coal

Characteristics of coal with high kaolinite in mineral fraction:� 13.95% theoretical mass loss [2]

� Shiny white ash and very high ash fluid temperature


�kaolinite-rich coals are very suitable for fixed-bed dry-bottom coal gasification

e.g. Coal with 20 wt%(d) ash originating from 100% kaolinite can have a bias of 2.9 %-pts in oxygen (by difference) only from kaolinite water

� TASK: Quantify kaolinite content in a coal sample!

Selection of experimental technique

Technique Limitation

Petrographic Analysis

• Resolution limited to several microns [4]• Only well crystallized minerals visible, density assignment

required [5]

XRD • General identification of clay crystals possible• No easy quantification due to maceral matrix, nature of clay

XRF • Ash composition in the oxide state requires ashing• Assignment of Al2O3 and SiO2 to the correct clay mineral


2 3 2

DTA/TGA • Coal pyrolysis products overlap with release of clay water• Alternative: ashing at <370°C required before analysis [6]

SEM with EDX/BSE

• Mineral Liberation Analysis procedure (identification of coal particles in polished cut, detection of elemental composition of each particle, use minerals database and assign density)

XRD: X-ray diffraction, XRF: X-ray fluorescence, DTA: Differential thermal analysis, TGA: thermogravimetric analysis, SEM: scanning electron microscopy, EDX: energy dispersive X-ray spectroscopy , BSE: back-scattered electron detector

Sample selection

Objective: Evaluate applicability of MLA for estimating the maximum bias in elemental and ultimate analysis caused by water of constitution

Sample ID Coal Rank

Ash content

Mean Vitrinite

ReflectanceStdev of mean

reflectance Vitrinite LiptiniteTotal

inertiniteVisible

mineralsASTM wt%(wf) % % area-% area-% area-% area-%

CC1-BLignite and sub-

bituminous A16.3 0.36 0.10 26.8 1.6 64.8 6.8

CC2-U Sub-bituminous B 39.6 0.47 0.04 19.6 7.2 45.6 27.6

CC2-W Sub-bituminous B 17.3 0.47 0.03 25.2 8.6 53.4 12.8


CC3-A Sub-bituminous A 24.9 0.49 0.04 31.8 6.6 44.2 17.4

CC3-B Sub-bituminous A 19.8 0.50 0.03 38.0 8.6 42.8 10.6

Three Chinese Coals (CC):� CC1 = coal blend (B) of lignite and clay-bearing sub-bituminous A coal

� CC2 = sub-bituminous B coal, (U = unwashed, W = washed coal)

� CC3 = sub-bituminous A coal, (A and B = different strata from same deposit)

Reference case for verification

wt%Unwashed CC2-U Washed CC2-W

Raw dataWater

correctionDelta Raw data

Water correction

Delta

Proximate waf dmmf waf dmmfA (wf) 39.45 17.26

Selection of CC2: � Heaviest sinks >95% kaolinite � XRF oxide composition used to estimate water of

constitution � calculation of dry-mineral-matter-free basis (dmmf)

� Organic phase before and after washing should be of equivalent dmmf composition

600

700

800

900

1000

92

94

96

98

100

Te

mp

era

ture

(°C

)

Ma

ss (

%)

Mass

Temperature

14.56% kaolinite

water and


VM 40.0 33.4 -6.6 35.2 32.9 -2.3FC 60.0 66.6 +6.6 64.8 66.1 +2.3

Ultimate waf dmmf waf dmmfC 73.41 80.95 +7.54 78.11 79.86 +1.75H 5.11 4.49 -0.62 4.64 4.50 -0.14O 19.09 11.92 -7.17 14.96 13.29 -1.66N 1.20 1.33 +0.13 1.26 1.29 +0.03S 1.19 1.31 +0.12 1.03 1.06 +0.03

Heaviest sinks from washing for TGA

0

100

200

300

400

500

80

82

84

86

88

90

0 500 1000 1500 2000 2500 3000 3500 4000

Te

mp

era

ture

(

Ma

ss (

%)

Time (s)

water and

organic VM

Pyroclastic kaolinite-tonstein

CC2-U ash: SiO2 47.7 wt%, Al2O3 46.8 wt% CC2-W ash: SiO2 35.0 wt%, Al2O3: 49.9 wt%

MLA Results - Images

CC1-B CC2-U CC3-A


CC1-B CC2-U

CC2-W

CC3-A

CC3-B

MLA Results – Mineral fractions

CC1-B CC2-U CC2-W CC3-A CC3-BSpecies Formula wt% wt% wt% wt% wt%Muscovite K2O3·Al 2O3·6SiO2·2H2O 23.5 0.3 0.1 0.1 0.2Kaolinite Al2O3·2SiO2·2H2O 20.6 95.2 95.9 96.8 85.8Quartz SiO2 10.8 1.7 0.1 0.2 0.2Hematite Fe2O3 28.2 0.0 0.0 0.0 0.1Pyrite FeS2 3.7 2.1 2.1 1.4 5.1Calcite CaCO3 5.1 0.6 1.8 1.4 8.5

Detected mineral fractions on coal-free basis:


3

Siderit FeCO3 1.2 0.0 0.0 0.0 0.1Albite Na2O·Al 2O3·6SiO2 0.7 0.0 0.0 0.0 0.0Orthoclase K2O·Al 2O3·6SiO2 1.2 0.1 0.0 0.0 0.0Dolomite CaCO3·MgCO3 4.4 0.0 0.0 0.0 0.0Ankerite CaCO3·FeCO3 0.7 0.0 0.0 0.0 0.0

CC1-B: divers minerals mainly hematite, muscovite, kaolinite, quartz (blend!)CC2-U/W: high kaolinite content, quartz removed by washingCC3-A/B: kaolinite content is high; pyrite and calcite increased for CC3-B

Calculation of ash from mineral matter

Species Decomposition reaction Mass loss Temperature [1,2]Muscovite K2O3·Al2O3·6SiO2·2H2O � K2O·3Al2O3·6SiO2 + 2 H2O -4.5% 450-700°CKaolinite Al2O3·2SiO2·2H2O � Al2O3·2SiO2 + 2 H2O -14.0% 400-600°CQuartz SiO2 � SiO2 0.0% noneHematite Fe2O3 � Fe2O3 0.0% nonePyrite 2 FeS2 + 7.5 O2 � Fe2O3 + 4 SO3 -33.5%* oxidationCalcite CaCO3 � CaO + CO2 -44.0% 920°C**

Decomposition mechanism of detected minerals:


Siderit 2 FeCO3 + 0.5 O2 � Fe2O3 + 2 CO2 -31.1% 580°C + oxidationAlbite Na2O·Al2O3·6SiO2 � Na2O·Al2O3·6SiO2 0.0% noneOrthoclase K2O·Al2O3·6SiO2 � K2O·Al2O3·6SiO2 0.0% noneDolomite CaCO3·MgCO3 � CaO·MgO + 2 CO2 -47.7% 780 and 920°CAnkerite 2 CaCO3·FeCO3 + 0.5 O2 � 2 CaO + Fe2O3 + 4 CO2 -37.1% 700°C* Without SO3 capture in ash (otherwise +37.1%), **does not apply to proximate analysis conditions

� Conditions according to ultimate analysis (oxidizing atmosphere, >1000°C) [7]

� Sulfur retention in ash balanced according to availability of calcinated lime or dolomite (e.g. CaO + SO3 � CaSO4)

Comparison of MLA vs. XRF ash composition

CC1-B CC2-U CC2-W CC3-A CC3-Bwt% wt% wt% wt% wt%

MLA XRF MLA XRF MLA XRF MLA XRF MLA XRFSiO2 34.0 43.9 53.6 47.7 51.8 35.0 52.4 45.2 45.0 38.8Fe2O3 33.4 7.5 1.7 1.5 1.6 2.2 1.1 1.2 3.9 3.1Al2O3 18.5 15.7 43.8 46.8 43.8 49.9 44.3 47.6 38.0 46.9CaO 4.6 17.1 0.4 1.4 1.2 3.7 0.9 2.1 5.3 4.9MgO 1.0 4.4 0.0 0.14 0.0 0.33 0.0 0.3 0.0 0.4Na O 0.1 0.9 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2


Na2O 0.1 0.9 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2K2O 3.1 1.4 0.1 0.23 0.0 0.19 0.0 0.2 0.0 0.3SO3 5.2 7 0.5 0.82 1.6 2.5 1.3 1.2 7.6 3.4

� MLA systematically over-estimates SiO2 while Al2O3 is lower vs. XRF

� Greater deviations for the CC1 (esp. Fe2O3 and CaCO3) and for CC2-W washed coal mainly for SiO2.

� MLA is less confident due to density assignment

Analysis of the results

CC2-U CC2-W

wafuncorr.

dmmfMLA

dmmfXRF

wafuncorr.

dmmfMLA

dmmfXRF

C 73.41 83.41 80.95 78.11 81.10 79.86

H 5.10 4.53 4.49 4.65 4.45 4.50

O 19.10 10.16 11.92 14.94 12.20 13.29

N 1.20 1.37 1.33 1.26 1.31 1.29S 1.19 0.52 1.31 1.03 0.94 1.06

Since the organic matrix should be equivalent for CC2 and CC3, the quality of the correction can be assessed.

� CC2: Differences in dmmf ultimate analyses are greater for the MLA correction than for the XRF correction.

� For CC3 the corrections are similar.

CC3-A CC3-B

waf uncorr.

dmmfMLA

dmmfXRF

wafuncorr.

dmmfMLA

dmmfXRF

C 77.65 82.28 81.31 78.25 81.52 80.56

H 4.55 4.21 4.24 4.44 4.26 4.25

O 15.54 11.23 12.09 14.69 11.48 12.49

N 1.15 1.22 1.21 1.20 1.25 1.23S 1.11 1.06 1.16 1.43 1.49 1.47


Delta to uncorrected Delta to uncorrected

C -10.0 -7.54 -2.99 -1.75

H +0.57 +0.62 +0.19 +0.14O +8.93 +7.17 +2.75 +1.66

N -0.16 -0.12 -0.05 -0.03

S +0.66 -0.12 +0.10 -0.02

� For CC3 the corrections are similar.

� XRF data more precise due to very homogeneous ash (~95% kaolinite, no other clays)

Delta to uncorrected Delta to uncorrected

C -4.63 -3.65 -3.27 -2.32

H 0.34 0.31 0.18 0.20O 4.31 3.45 3.20 2.20

N -0.07 -0.05 -0.05 -0.04

S 0.05 -0.05 -0.07 -0.04

Conclusion

� MLA data can be used to quantify the water of constitution by theoretical ashing.

� Correction of ultimate analysis ranges between 1.7 and 8.9 wt% for oxygen (using MLA and XRF data)

� The MLA can provide deeper insights into the mineral structure of the coal and can help to estimate the clay content in the minerals fraction


References

References:(1) Gräbner, M.: Industrial Coal Gasification Technologies

Covering Baseline and High-Ash Coal, Wiley-VCH Verlag GmbH, ISBN 978-3-527-33-690-6, 2014

(2) Gumz, W.; Kirsch, H.; Mackowsky, M.T.: Schlackenkunde: Untersuchungen über die Minerale und die Auswirkungen im Kesselbetrieb, Springer, 1958

(3) Shuli, D.; Qinfu, L.; Mingzhen, W.: Study of kaoliniterock in coal bearing stratum, North China, ProcediaEarth and Planetary Science 1, p. 1024-1028, 2009

(4) Stach, Erich: Stach’s Textbook of Coal Petrology, 3rd Edition, 535pp, Lubrecht & Cramer Ltd; 3 Sub edition,


Edition, 535pp, Lubrecht & Cramer Ltd; 3 Sub edition, 1982

(5) Davis, Alan: Petrographic determination of the composition of binary coal blends, International Journal of Coal Geology, Volume 44, Issues 3–4, Pages 325-338, 2000

(6) Australia Standards, Higher rank coal – mineral matter and water of constitution, Australian Standard 1038 Part 22, pp. 20, 2000

(7) ASTM D-388, Standard practice for ultimate analysis of coal and coke, West Conshohocken, PA, 2009

Thank you for your attention!

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