Characteristics of Unnormal Slag in Shell Coal Gasification

Transcription

1 Characteristics of Unnormal Slag in Shell Coal Gasification Hanxu Li, Jin Duan, Mingji Ji, Jinyu Xiong, Huadong Hao Department of Chemical Engineering Anhui University of Science & Technology

2 1. Introduction Among various entrained-flow gasification technologies, Shell gasification become one of the most important technologies. phigh carbon conversion plow oxygen consumption phigh gasification temperature phigh efficiency pfriendly environment

3 Problems for syngas production p Formation of Slag lumps p Discharge and processing of Slag fines p Blockage of SGC p Processing of Slag Bath water DEMKOLEC GASIFICATION FAILURES FAILURE FREQUENCY/(per year) LOSS IN POWER ONE MILL NOT AVAILAB LE COAL SLUICE PROBLEMS (REDUCED CAPACITY) COAL SLUICE PROBLEMS (@ BURNERS OUT) SLAG LUMPS SLAG FINES 6 30 HEAT SKIRT ECONOMISER LEAK SGC BLOCKAGE START-UP DELAY HPHT FILTER FAILURE MAJOR INCIDENT

4 Slag related problems Experimental study mineral compostion Ash compostion Coal qualities Ash melting point Slag viscocity Mineral transformation Main factors? residual carbon Melt structure

5 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.

6 2 Experimental study of residual carbon in slag 2.1 Slag samples Four slag samples were obtained from Shell coal gasification in China in different unnormal operating conditions of slag blockage. (a)u2 (b)u3 (c)u4 (d)u7 Figure 1. Process schematic of Shell coal gasification

7 TG-DTG analysis the carbon content unnormal slag samples XPS and XRD analysis crystal compositions and the graphitic degree of carbon SEM-EDX surface morphology of different carbon states

8 Table 1 Ash composition analysis of slag samples(wt%) samples SiO 2 Al 2 O 3 Fe 2 O 3 MgO CaO Na 2 O P 2 O 5 TiO 2 SO 3 U U U U

9 3 Results and discussion 3.1 TG-DTG analysis 100 TG DTG 0 (a) U3 Weight loss/% % 34.41% 59.26% U U U T/ Figure 2. TG-DTG curves of unnormal slag samples (b) U2/U4/U7-1 DTG/(%/min) -2-3

10 3.2 XPS spectrum of unnormal slag samples Intensity(cps) U2 U3 U4 U7 Fe 2p O 1s Ca 2p C 1s (a) Si 2p S 2p Al 2p Binding Energy(e.V) (a) Figure 3. XPS spectrum for unnormal slag samples. (a) broad scan; (b) narrow scan of C 1s (b)

11 Figure 4. fitting bands for C 1s in unnormal slag samples

12 Table 2 Carbon microstructure parameters of unnormal slag samples sample position (ev) FWHM Area U U U U 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.

13 3.3 XRD spectrum of unnormal slag samples Intensity/cps carbon U2 U3 U4 U theta/ A- Ca 2 Al 2 SiO 8, L- FeOOH, C- carbon, T- FeS Figure 5. XRD patterns of the unnormal slag samples

14 3.4 Surface characteristics of unnormal slag samples Figure 6. SEM image of cloudy or fibrous state in U7 slag Table 3. EDX Analysis of U7 Slag Sample

15 Figure 7. SEM image of cloudy or fibrous state in U3 slag Table 4. EDX Analysis of U3 Slag Sample Spectrum C O Al Si Ca

16 Figure 8. SEM image of cloudy or fibrous state in U2 slag Table 5. EDX Analysis of U2 Slag Sample Spectrum C O Fe Si Al K Ca Ti

17 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.

18 4. Conclusion Carbon content in unnormal slags is quite uniform. 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. 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.

19 Ackownledgements This work was sponsored by the Project of China Petroleum & Chemical Corporation This work was supported by Natural Science Foundation of China (No , No ). The members of Laboratory of Ash Chemistry, Anhui University of Science and Technology

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