Effect of oil shale semi-coke on deposit mineralogy and morphology in the flue path of a CFB burning Zhundong lignite

doi:10.1007/s11708-020-0668-1

Front. Energy

2021, Vol. 15

Issue (1) : 26-37 https://doi.org/10.1007/s11708-020-0668-1

RESEARCH ARTICLE

Effect of oil shale semi-coke on deposit mineralogy and morphology in the flue path of a CFB burning Zhundong lignite

Zhuo LIU¹, Jianbo LI¹(

), Mingming ZHU², Xiaofeng LU¹, Zhezi ZHANG², Dongke ZHANG²

¹. Key Laboratory of Low-grade Energy Utilization Technologies and Systems of the Ministry of Education, Chongqing University, Chongqing 400044, China
². Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

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Abstract

The effect of oil shale semi-coke (SC) on the mineralogy and morphology of the ash deposited on probes situated in the flue path of a circulating fluidized bed (CFB) which burns Zhundong lignite (ZD) was investigated. 10 wt% or 20 wt% SC was added to ZD, which were then combusted in the CFB furnace at 950°C. Two probes with vertical and horizontal orientations were installed in the flue duct to simulate ash deposition. Both windward and leeward ash deposits on probes (P₁W, P₁L, P₂W and P₂L) were analyzed by using a scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), an inductively coupled plasma optical emission spectrometry ICP-OES, and a particle size analyzer. When ZD was burned alone, the P₁W deposit was comprised of agglomerates (<30 mm) enriched in CaSO₄ and Na₂SiO₃, incurring significant sintering. The P₁L and P₂W deposits, however, were of both discrete and agglomerated particles in similar mineral phases but with coarser sizes. The P₂L deposit was mainly fine ash particles where Na₂SiO₃ and Na₂SO₄ were absent. As SC was added, the agglomerates in both P₁W and P₁L decreased. Moreover, SiO₂ and Ca/Na aluminosilicates dominated the mineral phases whereas Na₂SiO₃ and Na₂SO₄ disappeared, showing a decrease in deposit stickiness. Likewise, the P₂W deposit was found less spread on the probe, decreasing its deposition propensity. Na-bearing minerals turned into (Na, K)(Si₃Al)O₈ and (Ca, Na)(Si, Al)₄O₈ in the P₂W deposit. Moreover, Na in the deposits decreased from 32 mg/g to less than 15 mg/g as SC presented. The addition of SC would therefore help alleviate the propensity of ash deposition in the flue path in the CFB combustion of ZD.

Keywords ash deposition circulating fluidized bed (CFB) mineral transformation oil shale semi-coke (SC) Zhundong lignite (ZD)

Corresponding Author(s): Jianbo LI

Online First Date: 04 June 2020 Issue Date: 19 March 2021

Cite this article:

Zhuo LIU,Jianbo LI,Mingming ZHU, et al. Effect of oil shale semi-coke on deposit mineralogy and morphology in the flue path of a CFB burning Zhundong lignite[J]. Front. Energy, 2021, 15(1): 26-37.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-020-0668-1
https://academic.hep.com.cn/fie/EN/Y2021/V15/I1/26

Fig.1 Aschematic of experimental CFB system and ash sampling probes P₁ and P₂^.

Tab.1 Flue gas composition during experimentation

Fig.2 Temperature profiles of flue gas in CFB system at ZD100, ZD90SC10, and ZD80SC20.

Fig.3 Morphological features and EDX elemental analysis of P₁W deposits.

Fig.4 Morphological features and EDX elemental analysis of P₁L deposits.

Fig.5 Morphological features and EDX elemental analysis of P₂W deposits.

Fig.6 Morphological features and EDX elemental analysis of P₂L deposits of (a–c) ZD100; (d–f) ZD90SC10; (g–i) ZD80SC20.

Fig.7 XRD patterns of the P₁W deposit of ZD100, ZD90SC10, and ZD80SC20.

Fig.8 XRD patterns of P₁L deposit of ZD100, ZD90SC10, and ZD80SC20.

Fig.9 XRD patterns of P₂W deposit of ZD100, ZD90SC10, and ZD80SC20.

Fig.10 XRD patterns of P₂L deposit of ZD100, ZD90SC10, and ZD80SC20.

Fig.11 Variation of ash chemistry of Ca, Na, Mg contents.

Fig.12 Particle size distribution of ZD100, ZD90SC10, and ZD80SC20 deposits.

Fig.13 Schematic diagram of effect of probe layouts on ash deposition in flue path in co-firing of ZD and SC (ZD90SC10).

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