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 lhxtyx@163.com

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