Chemical kinetic study on coal volatiles combustion for various oxygen concentrations

doi:10.11949/0438-1157.20220619

Abstract

Abstract:

Coal-burning organic pollutants have serious harm to human health and ecological environment, and O₂ has a significant regulatory effect on the formation of organic products in flames. In view of the fact that coal volatiles combustion is a crucial part of coal combustion, the effect of O₂ concentration on hydrocarbon formation characteristics and mechanisms in counterflow diffusion flame was studied by numerical simulation using coal pyrolysis gas as fuel. The results showed that the increase of O₂ concentration promoted the formation of O and OH, which in turn increased H concentration, highlighting the importance of reactions involving H and OH. In addition, concentrations of acetylene (C₂H₂), propyne (PC₃H₄), propargyl (C₃H₃), vinylacetylene (C₄H₄), benzene (C₆H₆) and naphthalene (C₁₀H₈) all increased. Increasing O₂ concentration promoted the conversion from C₂H₂ to PC₃H₄, and made C₃H₃ more inclined to convert to butadiene (C₄H₆), while fulvene was more inclined to generate C₆H₆ through phenyl (C₆H₅). Therefore, the status of C₆H₅ as a precursor of C₆H₆ was strengthened.

Key words: pyrolysis, oxygen concentration, counterflow diffusion flames, organic hydrocarbon pollutants, reaction kinetics, chemical analysis

摘要：

燃煤有机污染物对人类健康和生态环境存在严重危害，而O₂对火焰中有机产物的形成具有明显的调控作用。鉴于煤挥发分燃烧是燃煤过程中至关重要的一环，本文以煤热解气为燃料，通过数值模拟研究了氧化剂侧O₂浓度对对冲扩散火焰中碳氢产物生成特性和机制的影响。结果表明，O₂浓度升高促进了O和OH的生成，进而提高H浓度，突显了含H和OH参与的反应的重要性。此外，乙炔(C₂H₂)、丙炔(PC₃H₄)、炔丙基(C₃H₃)、乙烯基乙炔(C₄H₄)、苯(C₆H₆)和萘(C₁₀H₈)的浓度均增大。增加O₂浓度促进了C₂H₂向PC₃H₄的转化，并使得C₃H₃更倾向于转化为丁二烯(C₄H₆)，而富烯更倾向于通过苯基(C₆H₅)生成C₆H₆，因此C₆H₅作为C₆H₆前体的地位被加强。

关键词: 热解, 氧气浓度, 对冲扩散火焰, 有机烃类污染物, 反应动力学, 化学分析

CLC Number:

TK 11

Chen CHEN, Qian YANG, Yun CHEN, Rui ZHANG, Dong LIU. Chemical kinetic study on coal volatiles combustion for various oxygen concentrations[J]. CIESC Journal, 2022, 73(9): 4133-4146.

陈晨, 杨倩, 陈云, 张睿, 刘冬. 不同氧浓度下煤挥发分燃烧的化学动力学研究[J]. 化工学报, 2022, 73(9): 4133-4146.

Figures/Tables 18

Fig.1 Coal pyrolysis experimental device

Table 1 Proximate analysis and ultimate analysis of Jiaxing coal

煤样	工业分析/%（质量）					元素分析/%（质量）
煤样	M_ar	V_ar	FC_ar	A_ar		C_daf	H_daf	O_daf	N_daf	S_daf
嘉兴煤种	5.02	25.31	58.60	11.07		76.12	4.18	18.20	0.97	0.53

Table 2 Composition of coal pyrolysis gas at 600℃

热解温度	成分/%
热解温度	H₂	CO	CO₂	CH₄	C₂H₆	C₂H₄	C₃H₈	C₃H₆
600℃	18.74	19.55	24.21	29.49	3.46	2.45	0.79	1.31

Table 3 Flame conditions

燃料、氧化剂流量/(ml/min)	燃料浓度/%	氧化剂侧O₂浓度/%	氧化剂侧N₂浓度/%	火焰拉伸率/s^-1	化学计量混合分数
400	100	21	79	69.54	0.139
400	100	25	75	69.62	0.161
400	100	30	70	69.73	0.186

Fig.2 Mole fraction profiles of reactants

Fig.3 Mole fraction profile and production rate of H radical

Fig.4 Mole fraction profile and production rate of O radical

Fig.5 Mole fraction profile and production rate of OH radical

Fig.6 Mole fraction profile and production rate of C3H3

Fig.7 Mole fraction profile and production rate of C2H2

Fig.8 Mole fraction profile and production rate of PC3H4

Fig.9 Mole fraction profile and production rate of C4H4

Fig.10 Mole fraction profile and production rate of C6H6

Fig.11 Mole fraction profile and production rate of C10H8

Fig.12 Reaction paths of fuel consumption for various XO

Fig.13 Formation paths of C2H2 for various XO

Fig.14 Formation paths of C3H3 for various XO

Fig.15 Formation paths of C6H6 and C10H8 for various XO

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