Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Anhui University of Science & Technology
Hanxu Li, Jin Duan, Mingji Ji, Jinyu Xiong, Huadong Hao
Characteristics of Unnormal Slag in Shell Coal Gasification
E-mail [email protected]
Department of Chemical Engineering
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Among various entrained-flow gasification technologies, Shell gasification become one of the most important technologies.phigh carbon conversionplow oxygen consumptionphigh gasification temperaturephigh efficiency pfriendly environment
1. Introduction
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
p Formation of Slag lumpsp Discharge and processing of Slag finesp Blockage of SGCp Processing of Slag Bath water
Problems for syngas productionDEMKOLEC GASIFICATION “FAILURES”
FAILURE FREQUENCY/(per year) LOSS IN POWER
ONE MILL NOT AVAILABLE 12 0
COAL SLUICE PROBLEMS(REDUCED CAPACITY) 52 20
COAL SLUICE PROBLEMS(@ BURNERS OUT) 10 60
SLAG LUMPS 6 100
SLAG FINES 6 30
HEAT SKIRT 1 100
ECONOMISER LEAK 0.5 100
SGC BLOCKAGE 0.3 100
START-UP DELAY 1 100
HPHT FILTER FAILURE 0.2 100
MAJOR INCIDENT 0.1 100
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Slag related problems
Experimental study
Coal qualitiesAsh melting point
Slag viscocityMineral transformation
Main factors
Ash compostionmineral compostion
Melt structure
residual carbon?
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
•Minimizing the potential for these ash-related problems is a fundamental objective in designing and operating gasifiers and advanced combustion systems.
•The objective of this work is to characterize the residual carbon in unnormal slag with high carbon content from Shell gasifiers and to establish a better knowledge of carbon effectiveness in slag for coal gasification units.
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
2.1 Slag samples
(a)U2
(b)U3
(c)U4
(d)U7
Figure 1. Process schematic of Shell coal gasification
Four slag samples were
obtained from Shell
coal gasification in
China in different
unnormal operating
conditions of slag
blockage.
2 Experimental study of residual carbon in slag
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
XPS and XRD analysis
TG-DTG analysis
SEM-EDX
surface morphology of different carbon states
crystal compositions and the graphitic degree of carbon
the carbon content
unnormalslag
samples
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Table 1 Ash composition analysis of slag samples(wt%)
samples SiO2 Al2O3 Fe2O3 MgO CaO Na2O P2O5 TiO2 SO3
U2 40.20 23.27 17.22 0.66 14.99 0.32 0.14 0.25 2.35
U3 43.52 27.56 4.88 0.80 18.81 0.37 0.02 2.39 1.04
U4 44.81 24.63 13.44 0.62 11.33 0.61 0.31 2.33 0.77
U7 40.82 24.81 18.71 0.56 9.99 0.53 0.26 2.36 0.82
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
200 400 600 800 10001200140020
30
40
50
60
70
80
90
100
200 400 600 800 1000 1200 1400
-6
-5
-4
-3
-2
-1
0
59.26%
72.42%
U7
U4
Wei
ght l
oss/
%
T/℃
U2
TG
34.41%
-3.65
-5.00
-5.78
DTG
DT
G/(%
/min
)
Figure 2. TG-DTG curves of unnormal slag samples
(a) U3 (b) U2/U4/U7
3.1 TG-DTG analysis3 Results and discussion
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
1400 1200 1000 800 600 400 200 0
0
50000
100000
150000
200000
250000
300000
Al 2p
Si 2p
S 2p
Fe 2pCa 2p
Inte
nsity
(cps
)
Binding Energy(e.V)
U2 U3 U4 U7
C 1sO 1s (a)
3.2 XPS spectrum of unnormal slag samples
Figure 3. XPS spectrum for unnormal slag samples. (a) broad scan; (b) narrow scan of C 1s
(a) (b)
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Figure 4. fitting bands for C 1s in unnormal slag samples
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Table 2 Carbon microstructure parameters of unnormal slag samples
sample position (eV) FWHM Area
U2 284.46 0.77 19276.73U3 284.89 1.92 10967.46U4 284.87 0.75 20313.56U7 284.91 0.66 33428.70
The results of FWHM suggest the graphitic degree of carbon in these
unnormal gasification slag samples are ordered as U3<U2<U4<U7.
The carbon content in these four unnormal gasification slag samples is also
ordered as U3<U2<U4<U7.
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
3.3 XRD spectrum of unnormal slag samples
A- Ca2Al2SiO8, L- FeOOH, C- carbon, T- FeSFigure 5. XRD patterns of the unnormal slag samples
25.6 25.8 26.0 26.2 26.4 26.6 26.8 27.0
0
2000
4000
6000
8000
10000
12000
Inte
nsity
/cps
2 theta/°
U2 U3 U4 U7carbon
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Table 3. EDX Analysis of U7 Slag SampleFigure 6. SEM image of cloudy or fibrous state in U7 slag
3.4 Surface characteristics of unnormal slag samples
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Spectrum C O Al Si Ca
3 87.27 10.84 0.84 1.05 --
4 25.34 46.30 17.99 9.27 1.10
Table 4. EDX Analysis of U3 Slag Sample
Figure 7. SEM image of cloudy or fibrous state in U3 slag
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Spectrum C O Fe Si Al K Ca Ti
1 86.32 12.02 1.62 -- -- -- -- --
2 39.57 23.77 -- 17.59 8.90 2.48 6.23 1.47
Figure 8. SEM image of cloudy or fibrous state in U2 slagTable 5. EDX Analysis of U2 Slag Sample
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
3.5 The formation mechanism of residual carbon in unnormal slag pIn the process of gasification, unreacted coal chars have experienced oxidization and then graphitization in Shell gasifiers, resulting in different degree of graphitization of residual carbon.pThe fibrous and cloudy carbon are wrapped by molten ash, which causes the precipitation of crystal minerals in melt and even leads to slag blockage.
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
l Carbon content in unnormal slags is quite uniform.l The carbon crystalline structure in unnormal gasification slags is greatly different, which
implies that the carbon in unnormal gasification slags is ordered and graphitic. The results of XRD are consistent with XPS.
l The residual carbon in slag are shaped in two carbon states, the carbon content of fibrous state is higher than cloudy state. The fibrous and cloudy carbon are wrapped by molten ash, which causes the precipitation of crystal minerals in melt and even leads to slag blockage.
4. Conclusion
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST
Ackownledgements
This work was sponsored by the Project of China Petroleum & Chemical Corporation
This work was supported by Natural Science Foundation of China (No.21176003, No.21376006) .
The members of Laboratory of Ash Chemistry, Anhui University of Science and Technology
Laboratory of Ash Chemistry, Department of Chemical Engineering, AUST