Chemical looping combustion of high-sodium coal and gasification kinetics of coal char

doi:10.11949/j.issn.0438-1157.20181394

Abstract

Abstract:

The continuous extraction method was used to extract the Zhundong high-sodium coal from Xinjiang, and the Zhundong coal samples containing different forms of sodium were prepared. The water-soluble sodium, ammonium acetate-soluble sodium and dilute hydrochloric acid-soluble sodium were investigated on a small fluidized bed. The results showed that the concentrations of carbonaceous gases and carbon conversion efficiency were significantly improved for water-washed ZD (WW-ZD) compared with untreated ZD. However, poor reaction properties of ammonium acetate washed ZD (AAW-ZD) and hydrochloric acid washed ZD (HAW-ZD) were obtained during a CLC process. The kinetics analysis on the isothermal gasification of ZD char with different extraction level was also investigated. The results showed that the activation energy of WW-ZD-H₂O was minimal while the activation energy of HAW-ZD-H₂O was maximum. It indicated that the H₂O-soluble sodium plays a prohibitive role during the CLC of ZD, while the CH₃COONH₄-soluble sodium and HCl-soluble sodium have a distinct promotion effect on CLC combustion performance of ZD.

Key words: high-sodium coal, chemical looping combustion, sequential extraction method, reaction kinetics

摘要：

采用连续提取法对新疆准东高钠煤进行萃取处理，制备含有不同存在形式钠元素的准东煤样品，在小型流化床上考察了水溶性钠、醋酸铵溶性钠和稀盐酸溶性钠对于准东煤化学链燃烧特性的影响。结果表明，去除水溶性钠后准东煤化学链燃烧产物中含碳气体相对浓度显著提高，相同时刻碳转化率明显提高。而经过醋酸铵和稀盐酸处理后的准东煤相比未处理的准东煤，其化学链燃烧反应性能显著降低。对四种不同处理程度准东煤焦的等温气化反应进行动力学分析表明，WW-ZDJ与水蒸气的气化反应的活化能最小，HAW-ZDJ的气化反应活化能最大。水溶性钠对于准东煤化学链燃烧过程具有抑制作用，而醋酸铵和稀盐酸溶性的钠在准东煤的化学链燃烧过程中促进作用显著。

关键词: 高钠煤, 化学链燃烧, 连续提取法, 反应动力学

CLC Number:

TQ 541

Jingchun YAN, Laihong SHEN, Shouxi JIANG, Huijun GE. Chemical looping combustion of high-sodium coal and gasification kinetics of coal char[J]. CIESC Journal, 2019, 70(5): 1913-1922.

闫景春, 沈来宏, 蒋守席, 葛晖骏. 高钠煤化学链燃烧特性及煤焦气化反应动力学研究[J]. 化工学报, 2019, 70(5): 1913-1922.

Figures/Tables 16

Fig.1 Schematic diagram for chemical looping combustion (CLC) of coal with natural hematite as oxygen carrier

Table 1 Elemental composition of fresh hematite oxygen carrier/%(mass)

Compositions	Contents
Fe₂O₃	83.25
SiO₂	7.06
Al₂O₃	5.33
CaO	0.23
P₂O₅	0.29
TiO₂	0.09
K₂O	0.03
SO₃	0.25
others	3.47

Table 2 Proximate and ultimate analysis of ZD raw coal

工业分析/%(mass, ad)				元素分析/%(mass, ad)
M	V	FC	A	C	H	O	N	S
14.58	28.05	53.03	6.34	64.18	4.302	9.751	0.50	0.347

Table 3 Elemental composition analysis of ZD ash/%(mass)

CaO	SiO₂	SO₃	Fe₂O₃	Al₂O₃	Na₂O	MgO	TiO₂	K₂O	Others
21.55	16.56	13.99	14.05	9.88	9.22	5.75	1.75	0.51	6.74

Fig.2 Flow diagram of sequential extraction procedure

Fig.3 Fixed bed reactor for coal char preparation

Table 4 Ultimate analysis of coal char samples

样品	元素分析 /%(mass, ad)
样品	C	H	N	S
ZDJ	81.06	3.147	0.76	1.613
WW-ZDJ	80.43	2.977	0.96	1.071
AAW-ZDJ	82.28	3.403	0.41	1.719
HAW-ZDJ	79.71	2.876	1.01	1.48

Fig.4 Schematic layout of batch fluidized bed reactor

Table 5 Analysis of sodium in ZD sample/(μg/g)

1350

(58.70)

359

(15.61)

168

(7.30)

423

(18.39)

2300

(100)

Fig.5 Concentrations of gaseous products during CLC process of ZD (a), WW-ZD (b), AAW-ZD (c), HAW-ZD (d) with steam as gasification agent at 900℃

Fig.6 Carbon conversion efficiency during typical reduction process of CLC for ZD, WW-ZD, AAW-ZD and HAW-ZD

Table 6 Reaction kinetics models and correlation coefficients

反应模型	积分形式 $G α$	微分形式 $f α$	相关系数R
反应模型	积分形式 $G α$	微分形式 $f α$	ZDJ	WW-ZDJ	AAW-ZDJ	HAW-ZDJ
一维扩散	$α 2$	$1 2 α$	0.9473	0.9670	0.9940	0.9599
二维扩散（柱对称）	$α + 1 + α l n 1 - α$	$- 1 l n 1 - α$	0.9644	0.9721	0.9930	0.9564
三维扩散（球对称）	$1 - 1 - α 13 2$	$3 1 - α 13 2 1 - α 13 - 1$	0.9764	0.9720	0.9883	0.9427
随机核化（n=1）	$- l n 1 - α$	$1 - α$	0.9752	0.9682	0.9940	0.9689
随机核化（n=2）	$- l n 1 - α 12$	$2 1 - α - l n 1 - α 12$	0.9739	0.9606	0.9826	0.9726
随机核化（n=3）	$- l n 1 - α 13$	$3 1 - α - l n 1 - α 23$	0.9722	0.9568	0.9720	0.9673
收缩核模型（柱对称）	$1 - 1 - α 12$	$2 1 - α 12$	0.9701	0.9703	0.9894	0.9713
收缩核模型（球对称）	$1 - 1 - α 13$	$3 1 - α 23$	0.9820	0.9876	0.9994	0.9990

Table 6 Reaction kinetics models and correlation coefficients

反应模型	积分形式 $G α$	微分形式 $f α$	相关系数R
反应模型	积分形式 $G α$	微分形式 $f α$	ZDJ	WW-ZDJ	AAW-ZDJ	HAW-ZDJ
一维扩散	$α 2$	$1 2 α$	0.9473	0.9670	0.9940	0.9599
二维扩散（柱对称）	$α + 1 + α l n 1 - α$	$- 1 l n 1 - α$	0.9644	0.9721	0.9930	0.9564
三维扩散（球对称）	$1 - 1 - α 13 2$	$3 1 - α 13 2 1 - α 13 - 1$	0.9764	0.9720	0.9883	0.9427
随机核化（n=1）	$- l n 1 - α$	$1 - α$	0.9752	0.9682	0.9940	0.9689
随机核化（n=2）	$- l n 1 - α 12$	$2 1 - α - l n 1 - α 12$	0.9739	0.9606	0.9826	0.9726
随机核化（n=3）	$- l n 1 - α 13$	$3 1 - α - l n 1 - α 23$	0.9722	0.9568	0.9720	0.9673
收缩核模型（柱对称）	$1 - 1 - α 12$	$2 1 - α 12$	0.9701	0.9703	0.9894	0.9713
收缩核模型（球对称）	$1 - 1 - α 13$	$3 1 - α 23$	0.9820	0.9876	0.9994	0.9990

Fig.7 Carbon conversion with time for ZDJ, WW-ZDJ, AAW-ZDJ and HAW-ZDJ under different temperature

Fig.8 Fitting results of shrinking core model

Fig.9 Fitting relationship between gasification rate of coal char and temperature

Table 7 Kinetic parameters for coal char gasification

Sample	E/(kJ/mol)	A×10^-4/min	R ²
ZDJ	146.98	11.30	0.982
WW-ZDJ	104.68	0.11	0.988
AAW-ZDJ	156.45	27.32	0.999
HAW-ZDJ	204.66	1266.05	0.999

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