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Frontiers in Energy

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Front. Energy    2022, Vol. 16 Issue (6) : 1037-1047    https://doi.org/10.1007/s11708-022-0824-x
RESEARCH ARTICLE
Crystallization and viscosity-temperature characteristics during co-gasification of industrial sludge and coal
Linmin ZHANG1, Bin LIU1, Juntao WEI2, Xudong SONG1(), Yonghui BAI1, Jiaofei WANG1, Ying ZHOU3, Huijun YANG3, Guangsuo YU4()
1. State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, China
2. Joint International Research Laboratory of Biomass Energy and Materials, Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China
3. Institute of Coal Chemical Industry Technology, Ningxia Coal Industry Co., Ltd., Yinchuan 750000, China
4. State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, China; Institute of Clean Coal Technology, East China University of Science and Technology, Shanghai 200237, China
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Abstract

Co-gasification of industrial sludge (IS) and coal was an effective approach to achieve harmless and sustainable utilization of IS. The long-term and stable operation of a co-gasification largely depends on fluidity of coal-ash slag. Herein, the effects of IS addition on the crystallization and viscosity of Shuangmazao (SMZ) coal were investigated by means of high temperature stage coupled with an optical microscope (HTSOM), a scanning electron microscopy coupled with an energy dispersive X-ray spectrometry (SEM-EDS), X-ray diffraction (XRD), a Fourier transform infrared spectrometer (FTIR), and FactSage software. The results showed that when the proportion of IS was less than 60%, with the addition of IS, the slag existed in an amorphous form. This was due to the high content of SiO2 and Al2O3 in SMZ ash and blended ash, which had a high glass-forming ability (GFA). The slag formed at a high temperature had a higher polymerization degree and viscosity, which led to a decrease in the migration ability between ions, and ultimately made the slag difficult to crystallize during the cooling. When the proportion of IS was higher than 60%, the addition of IS increased the CaO and FeO content in the system. As network modifiers, CaO and FeO could provide O2− at a high temperature, which reacted with silicate network structure and continuously destroyed the complexity of network structure, thus reducing the polymerization degree and viscosity of slag. At this time, the migration ability between ions was enhanced, and needle-shaped/rod-shaped crystals were precipitated during the cooling process. Finally, the viscosity calculated by simulation and Einstein-Roscoe empirical formula demonstrated that the addition of IS could significantly improve the fluidity of coal ash and meet the requirements of the liquid slag-tapping gasifier. The purpose of this work was to provide theoretical support for slag flow mechanisms during the gasifier slagging-tapping process and the resource treatment of industrial solid waste.
Keywords co-gasification      industrial sludge      crystallization      viscosity      mineral matter evolution     
Corresponding Author(s): Xudong SONG,Guangsuo YU   
Online First Date: 22 March 2022    Issue Date: 17 January 2023
 Cite this article:   
Linmin ZHANG,Bin LIU,Juntao WEI, et al. Crystallization and viscosity-temperature characteristics during co-gasification of industrial sludge and coal[J]. Front. Energy, 2022, 16(6): 1037-1047.
 URL:  
https://academic.hep.com.cn/fie/EN/10.1007/s11708-022-0824-x
https://academic.hep.com.cn/fie/EN/Y2022/V16/I6/1037
Sample Proximate analysis (d)/% (mass percentage)
VM FC A
SMZ 27.14 54.52 18.34
IS 41.71 20.46 37.83
Tab.1  Proximate analysis of SMZ and IS
Sample Ultimate analysis (d)/% (mass percentage)
A C H N S O*
SMZ 18.34 63.01 4.10 0.74 1.86 11.95
IS 37.83 14.28 7.91 1.80 1.72 36.46
Tab.2  Ultimate analysis of SMZ and IS
Sample Compositions/% (mass percentage)
SiO2 Al2O3 Fe2O3 CaO Na2O K2O MgO SO3 Others B/A
SMZ 50.84 21.05 6.70 8.90 1.95 1.67 3.54 2.61 2.74 0.32
IS 33.12 13.82 12.51 21.08 6.17 1.05 4.94 4.89 2.42 0.97
Tab.3  Ash chemical compositions of SMZ and IS
Sample Ash fusion temperatures/°C
DT ST HT FT
SMZ 1190 1214 1219 1230
IS 1182 1220 1223 1228
Tab.4  Ash fusion temperatures of SMZ and IS
Fig.1  Temperature program of HTSOM test.
Fig.2  Crystal morphological variations of different samples during cooling.
Fig.3  Crystal morphology at room temperature.
Fig.4  SEM-EDS results of quenched slag.
Fig.5  XRD patterns of raw ashes (1—Quartz (SiO2), 2—Hematite (Fe2O3), 3—Anhydrite (CaSO4), 4—Lime (CaO)).
Fig.6  XRD patterns of samples with different IS proportion quenched at 1350°C.
Fig.7  FTIR spectra of quenched slag with different IS proportions.
Fig.8  A typical deconvolution of FTIR spectra.
Fig.9  Qn unit contents based on deconvolution results.
Fig.10  Viscosity-temperature curves of mixed samples with different IS proportions. (a) Calculated by simulation; (b) comparison of calculation and experimental.
AFTs Ash fusion temperatures
B/A Ratio of basic to acid
S/A Ratio of silicon to aluminum
DT Deformation temperature
  
ST Softening temperature
HT Hemispherical temperature
FT Flow temperature
GFA Glass-forming ability
Tliq Liquid temperature
HTSOM High temperature stage coupled with optical microscope system
SEM-EDS Scanning electron microscopy coupled with energy dispersive X-ray spectrometry
XRD X-ray diffraction
FTIR Fourier transform infrared spectrometer
SMZ Shuangmazao coal
IS Industrial sludge
IS0 0 wt% IS addition to SMZ coal
IS2 20 wt% IS addition to SMZ coal
IS4 40 wt% IS addition to SMZ coal
IS6 60 wt% IS addition to SMZ coal
IS8 80 wt% IS addition to SMZ coal
Q0 [SiO4]4− monomer structure
Q1 [Si2O7]6 dimer structure
Q2 [SiO3]2− chain structure
Q3 [Si2O5]2− planar layered structure
Q4 SiO2 three-dimensional network structure
  
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